WO2015080204A1

WO2015080204A1 - Carbon material for negative electrode of nonaqueous rechargeable battery, negative electrode for nonaqueous rechargeable battery and nonaqueous rechargeable battery using same

Info

Publication number: WO2015080204A1
Application number: PCT/JP2014/081388
Authority: WO
Inventors: 陽介齋藤; 布施　亨; 山田　俊介; 哲赤坂; 大悟長山
Original assignee: 三菱化学株式会社
Priority date: 2013-11-27
Filing date: 2014-11-27
Publication date: 2015-06-04
Also published as: JPWO2015080204A1; JP6432520B2

Abstract

　Provided is a carbon material for negative electrode of nonaqueous rechargeable battery that provides a nonaqueous rechargeable battery having low initial loss, high capacity and excellent cycle properties.　The present invention pertains to a carbon material for electrode of nonaqueous rechargeable battery, including: (1) composite carbon particles (A) containing elemental silicon; and (2) noncrystalline composite graphite particles (B) obtained by compounding graphite particles (C) with a polymer which has poor solubility in the nonaqueous electrolyte.

Description

Non-aqueous secondary battery negative electrode carbon material, non-aqueous secondary battery negative electrode and non-aqueous secondary battery using the same

The present invention relates to a carbon material for a non-aqueous secondary battery negative electrode used in a non-aqueous secondary battery, a negative electrode formed using the carbon material, and a non-aqueous secondary battery including the negative electrode.

A nonaqueous secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and a nonaqueous electrolyte solution in which lithium salts such as LiPF ₆ and LiBF ₄ are dissolved has been developed and put into practical use.

Various types of negative electrode materials have been proposed for this battery. From the viewpoint of high capacity and excellent discharge potential flatness, artificial graphite obtained by graphitization of natural graphite, coke, etc. Graphite carbon materials such as graphitized mesophase pitch and graphitized carbon fiber are used as the negative electrode material.

On the other hand, the application development of non-aqueous secondary batteries, especially lithium ion secondary batteries, has been attempted recently. In addition to conventional notebook PCs, mobile communication devices, portable cameras, portable game machines, etc., electric tools, Applications for electric vehicles are also being developed. As a result, there is a demand for a lithium ion secondary battery that has a rapid charge / discharge characteristic that has been increased as compared with the prior art, a high capacity, and a high cycle characteristic.

Therefore, in order to increase the filling rate of the carbon material in the electrode plate and improve the discharge capacity, a carbon material mixed with graphite particles having different properties is used.

However, while a high capacity is desired in this way, a carbon-centered negative electrode has a theoretical capacity of 372 mAh, so it is impossible to desire a capacity higher than this. Therefore, application of various high capacity materials, particularly metal particles to the negative electrode has been studied.

For example, Patent Document 1 proposes a method for producing Si composite carbon particles by firing a mixture of a fine powder of a Si compound, graphite, and a pitch of carbonaceous material precursor.

In Patent Document 2, it is proposed to use different materials (metal oxide and carbon material) having different equilibrium potentials by performing different electrochemical reduction reactions as active materials.

Further, Patent Documents 3 and 4 propose non-aqueous secondary batteries containing Si composite carbon particles made of Si compound and graphite powder and graphite particles. It has been reported in these documents that a non-aqueous secondary battery having a high capacity and excellent cycle characteristics can be provided thereby.

JP 2003-238992 A Japanese Patent Laid-Open No. 11-135106 JP 2012-124114 A International Publication No. 2012-018035

However, according to the study by the present inventors, the technique described in Patent Document 1 is Si composite carbon particles obtained by combining graphite and Si compound fine powder with a carbonaceous material composed of carbon. As the Si compound fine powder expands and contracts, the conductive path of the Si composite carbon particles is cut off, resulting in a problem that cycle characteristics are reduced. As a result, the Si composite carbon particles have not reached the practical level of non-aqueous secondary batteries.

On the other hand, according to the technique described in Patent Document 2, structural destruction of a metal oxide can be prevented beforehand by mixing a metal oxide capable of inserting and extracting lithium with a carbon material. It is described that a non-aqueous secondary battery having a high capacity and excellent cycle characteristics can be obtained. However, since the metal oxide is not a composite particle with carbon, it is not possible to suppress the destruction of the electrode due to the swelling of the metal oxide, and the carbon material is not specially specified. Therefore, it must be said that the technique of Patent Document 2 requires further improvement in order to obtain a battery having the high cycle characteristics required recently.

Patent Documents 3 and 4 describe that, according to the technique described in the document, mixing of Si composite carbon particles and graphite particles improves cycle characteristics and suppresses battery swelling. However, the carbon material used for mixing has a large amount of gas generation due to side reactions with the non-aqueous electrolyte solution, and therefore the increase in loss cannot be sufficiently suppressed.

Regarding the increase in loss, since voids are formed in the active material layer due to gas generation, the expansion of the Si compound is promoted, and as a result, a protective coating called SEI (Solid Electrolyte Interface) associated with the expansion and contraction of the Si compound is regenerated. One factor is considered to be a larger loss during formation.

The present invention solves the above-mentioned problems of the prior art and is obtained by using the carbon material for a non-aqueous secondary battery negative electrode that provides a non-aqueous secondary battery having high capacity, excellent cycle characteristics, and low initial loss. An object of the present invention is to provide a non-aqueous secondary battery negative electrode and a non-aqueous secondary battery including the negative electrode.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have developed a composite carbon particle (A) containing silicon element (hereinafter sometimes referred to as Si composite carbon particle (A)) and a non-aqueous electrolyte solution. Mixing a poorly soluble polymer (also referred to simply as a polymer in this specification) and a composite graphite particle (B) (hereinafter sometimes referred to as composite graphite particle (B)) in which graphite particles (C) are combined. Thus, it was found that a carbon material for a negative electrode of a non-aqueous secondary battery having a high capacity, excellent cycle characteristics, and low initial loss can be produced.

Although the mechanism by which the carbon material for a nonaqueous secondary battery negative electrode of the present invention (hereinafter sometimes referred to as the carbon material of the present invention) exhibits excellent battery characteristics has not been clarified, for example, the following mechanism can be considered. . By using the Si composite carbon particles (A), it is possible to have a high capacity derived from Si. Further, since the composite graphite particles (B) enter between the Si composite carbon particles (A), the expansion of the Si composite carbon particles (A) during charging is alleviated. It is considered that the resulting path cut is suppressed and the cycle characteristics are improved. In addition, the polymer that is hardly soluble in the non-aqueous electrolyte solution of the composite graphite particles (B) reduces gas generation by reducing the contact between the graphite particles and the non-aqueous electrolyte solution and suppressing side reactions. It is thought to reduce loss. Moreover, it is thought that the additive consumption in electrolyte solution is suppressed by suppressing a side reaction, As a result, it is thought that the cycling characteristics improvement effect of electrolyte solution additive is accelerated | stimulated.

That is, the gist of the present invention is as follows.
(1) Composite carbon particles containing silicon element (A), and (2) Composite graphite particles (B) in which a polymer that is hardly soluble in a non-aqueous electrolyte and graphite particles (C) are combined.
It exists in the carbon material for non-aqueous secondary battery negative electrodes containing.

Further, another gist of the present invention resides in a negative electrode for a non-aqueous secondary battery formed using the carbon material for a negative electrode for a non-aqueous secondary battery.

Further, another gist of the present invention resides in a non-aqueous secondary battery that includes a positive electrode, a negative electrode, and an electrolyte, and the negative electrode is the negative electrode for a non-aqueous secondary battery.

According to the present invention, it is possible to provide a non-aqueous secondary battery negative electrode carbon material having excellent stability, high capacity, small initial loss, and excellent cycle characteristics, and a non-aqueous secondary battery using the same. it can.

Hereinafter, the contents of the present invention will be described in detail. In addition, description of the structure of this invention described below is an example (representative example) of the embodiment of this invention, and this invention is not specified to these forms, unless the summary is exceeded.

The carbon material for a non-aqueous secondary battery negative electrode of the present invention contains Si composite carbon particles (A) and composite graphite particles (B). The Si composite carbon particles (A) contain silicon element, and the composite graphite particles (B). Is characterized in that a polymer that is hardly soluble in a non-aqueous electrolyte and graphite particles (C) are combined.

Hereinafter, the Si composite carbon particles (A) and the composite graphite particles (B) used in the present invention will be described.

[Si composite carbon particles (A)]
The Si composite carbon particles (A) in the present invention will be described below.
The Si composite carbon particle (A) of the present invention is not particularly limited as long as it is a carbon material containing at least a silicon element, and a known material may be used. For example, Si composite carbon particles disclosed in JP2012-043546A, JP2005-243508A, JP2008-027897A, JP2008-186732A, and the like can be used in the present invention. Below, it describes about Si composite carbon particle (A) from which the effect of this invention is improved further.

(Characteristics of Si composite carbon particles (A))
The Si composite carbon particles (A) preferably have the following characteristics.

(A) Volume-based average particle diameter (d50) of Si composite carbon particles (A)
The volume-based average particle diameter (d50) (hereinafter also referred to as average particle diameter d50) of the Si composite carbon particles (A) is usually 1 μm or more, preferably 4 μm or more, more preferably 7 μm or more, and usually 50 μm or less. The thickness is preferably 40 μm or less, more preferably 30 μm or less, and still more preferably 25 μm or less. If the average particle diameter d50 is too large, the total number of particles decreases and the proportion of the composite graphite particles (B) existing between the particles decreases, so that particle deformation cannot be sufficiently suppressed in the press at the time of preparing the negative electrode. As a result, the ability to secure the flow path of the electrolyte decreases, and the input / output characteristics of the non-aqueous secondary battery (hereinafter also referred to as “non-aqueous secondary battery” or “battery”) obtained using the carbon material of the present invention. There is a tendency to lead to a decline. On the other hand, if the average particle size d50 is too small, the specific surface area increases, so that the decomposition of the electrolyte increases and the initial efficiency tends to decrease.

In addition, the measuring method of average particle diameter d50 is as follows. 0.01 g of a sample is suspended in 10 mL of a 0.2% by mass aqueous solution of polyoxyethylene sorbitan monolaurate, which is a surfactant, and introduced into a commercially available laser diffraction / scattering particle size distribution analyzer, and ultrasonic waves of 28 kHz are used. Is measured as a volume-based median diameter in a measuring apparatus after being irradiated for 1 minute at an output of 60 W, and is defined as a volume-based average particle diameter d50 in the present invention.

(B) Aspect ratio of Si composite carbon particles (A) The aspect ratio of the Si composite carbon particles (A) is usually 1 or more, preferably 1.3 or more, more preferably 1.4 or more, and still more preferably 1.5. As described above, it is usually 4 or less, preferably 3 or less, more preferably 2.5 or less, and further preferably 2 or less.

If the aspect ratio is too large, the particles tend to be aligned in the direction parallel to the current collector when used as an electrode, so that there are not enough continuous voids in the thickness direction of the electrode, and lithium ion mobility in the thickness direction. However, the rapid charge / discharge characteristics of the non-aqueous secondary battery tend to be reduced. The aspect ratio is determined by grinding a resin embedding or electrode plate of particles perpendicularly to a flat plate, taking a cross-sectional photograph thereof, extracting 50 or more particles at random, and extracting the longest diameter of the particles (on the flat plate). It can be measured by measuring the parallel direction) and the shortest diameter (perpendicular to the flat plate) by image analysis and taking the average of the longest diameter / shortest diameter. Since particles embedded in a resin or made into an electrode plate usually tend to have the thickness direction of the particles aligned perpendicular to a flat plate, the above-mentioned method can obtain the longest and shortest diameters characteristic of the particles. I can do it.

(C) Circularity of Si composite carbon particles (A) The circularity of the Si composite carbon particles (A) is usually 0.85 or more, preferably 0.88 or more, more preferably 0.89 or more, and still more preferably 0. .90 or more. The circularity is usually 1 or less, preferably 0.99 or less, more preferably 0.98 or less, and still more preferably 0.97 or less. In addition, the spherical shape in this specification can also be expressed in the range of the circularity.

If the circularity is too small, particles tend to be aligned in parallel with the current collector when used as an electrode, so that there is not enough continuous void in the thickness direction of the electrode, and lithium ion mobility in the thickness direction However, the rapid charge / discharge characteristics of the non-aqueous secondary battery tend to be reduced. If the circularity is too large, there is a tendency that the effect of suppressing the conduction path breakage is reduced and the cycle characteristics are lowered.

The circularity is defined by the following formula (1). When the circularity is 1, a theoretical sphere is obtained.
Formula (1)
Circularity = (perimeter of equivalent circle having the same area as the particle projection shape) / (actual circumference of particle projection shape)

For the circularity value, a flow type particle image analyzer (for example, FPIA manufactured by Sysmex Industrial Co.) is used, polyoxyethylene (20) monolaurate is used as a surfactant, and ion-exchanged water is used as a dispersion medium. The degree of circularity is calculated by the equivalent circle diameter. The equivalent circle diameter is the diameter of a circle (equivalent circle) having the same projected area as the photographed particle image, and the circularity is the circumference of the equivalent particle as a molecule and the circumference of the photographed particle projection image. The ratio is the denominator. The circularity of particles having a measured equivalent diameter in the range of 10 to 40 μm is averaged to obtain the circularity in the present invention.

(D) Interplanar spacing (d ₀₀₂ ) and crystallite size (Lc) of Si composite carbon particles (A)
The interplanar spacing (d ₀₀₂ ) of the 002 plane by the X-ray wide angle diffraction method of the Si composite carbon particles (A) is usually 0.337 nm or less, preferably 0.336 nm or less. When the d value is too large, the crystallinity is lowered, and the discharge capacity of the nonaqueous secondary battery tends to be lowered. On the other hand, the lower limit is 0.3354 nm, which is the theoretical value of graphite.

The crystallite size (Lc) of the Si composite carbon particles (A) is usually in the range of 30 nm or more, preferably 50 nm or more, more preferably 100 nm or more. Below this range, the crystallinity decreases and the discharge capacity of the battery tends to decrease.

(E) Si Raman R value of the Raman R value Si composite carbon particles (A) of the composite carbon particles (A), in the Raman spectrum of Si composite carbon particles (A), the intensity of the maximum peak _{P A} around 1580 cm ^-1 I _A and the intensity I _B of the maximum peak P _B near 1360 cm ⁻¹ are measured, and the intensity ratio R (R = I _B / I _A ) is calculated and defined. The value is usually 1 or less, preferably 0.8 or less, more preferably 0.6 or less, still more preferably 0.5 or less, and usually 0.05 or more, preferably 0.1 or more, more preferably 0. 2 or more, more preferably 0.25 or more. If the Raman R value is less than this range, the crystallinity of the particle surface becomes too high, the number of Li insertion sites decreases, and the rapid charge / discharge characteristics of the nonaqueous secondary battery tend to be reduced. On the other hand, if it exceeds this range, the crystallinity of the particle surface will be disturbed, the reactivity with the electrolyte will increase, and the charge / discharge efficiency will tend to decrease and the gas generation will increase.

The Raman spectrum can be measured with a Raman spectrometer. Specifically, the sample particles are naturally dropped into the measurement cell to fill the sample, and the measurement cell is rotated in a plane perpendicular to the laser beam while irradiating the measurement cell with an argon ion laser beam. Measure.

(F) Surface functional group amount of Si composite carbon particle (A) The Si composite carbon particle (A) has a surface functional group amount O / C value represented by the following formula (2) of usually 0.1% or more. , Preferably 1% or more, more preferably 2% or more, while usually 30% or less, preferably 20% or less, more preferably 15% or less. If the surface functional group amount O / C value is too small, the desolvation reactivity of the Li ion and the electrolyte solvent on the negative electrode active material surface tends to decrease, and the large current charge / discharge characteristics of the nonaqueous secondary battery tend to decrease. When O / C is too large, the reactivity with the electrolytic solution increases, and the charge / discharge efficiency tends to decrease.

Formula (2)
O / C value (%)
= {(O atom concentration determined based on peak area of O1s spectrum in X-ray photoelectron spectroscopy (XPS) analysis) / (C atom concentration determined based on peak area of C1s spectrum in XPS analysis)} × 100

The surface functional group amount O / C value in the present invention can be measured using X-ray photoelectron spectroscopy (XPS) as follows.

Using an X-ray photoelectron spectrometer, the object to be measured is placed on a sample stage so that the surface is flat, and aluminum Kα rays are used as an X-ray source. ) Spectrum. The obtained C1s peak top is corrected to be 284.3 eV, the peak areas of the C1s and O1s spectra are obtained, and the device sensitivity coefficient is multiplied to calculate the surface atomic concentrations of C and O, respectively. The obtained ratio of the atomic concentration of O and C, O / C (O atomic concentration / C atomic concentration), expressed as a percentage, is defined as the surface functional group amount of the sample (Si composite carbon particles (A)). .

(G) BET specific surface area (SA) of Si composite carbon particles (A)
About the specific surface area measured by BET method of Si composite carbon particle (A), it is 0.1 m < ² > / g or more normally, Preferably it is 0.7 m < ² > / g or more, More preferably, it is 1 m < ² > / g or more. Moreover, it is 40 m < ² > / g or less normally, Preferably it is 30 m < ² > / g or less, More preferably, it is 20 m < ² > / g or less, More preferably, it is 18 m < ² > / g or less, Most preferably, it is 17 m < ² > / g or less.

If the specific surface area is too small, the number of sites where lithium ions enter and exit is small, and the high-speed charge / discharge characteristics and output characteristics are inferior. On the other hand, if the specific surface area is too large, the active material becomes excessively active with respect to the electrolyte solution, Therefore, there is a tendency that a high-capacity non-aqueous secondary battery cannot be manufactured.

The BET specific surface area is measured by a BET one-point method using a specific surface area measuring device by a nitrogen gas adsorption flow method.

(H) Tap density of Si composite carbon particles (A) The tap density of Si composite carbon particles (A) is usually 0.5 g / cm ³ or more, preferably 0.6 g / cm ³ or more, more preferably 0. .8g / cm ³ or more, more preferably 0.85 g / cm ³ or more, particularly preferably 0.9 g / cm ³ or more and usually less than 1.3 g / cm ^3, preferably 1.2 g / cm ³ or less Yes, more preferably 1.1 g / cm ³ or less. When the tap density is too low, the high-speed charge / discharge characteristics of the non-aqueous secondary battery are inferior. When the tap density is too high, the cycle characteristics may be deteriorated due to the disconnection of the conductive path due to the decrease in particle contactability.

In the present invention, the tap density is measured by dropping a sample (Si composite carbon particles (A)) through a sieve having a mesh size of 300 μm through a cylindrical tap cell having a diameter of 1.6 cm and a volume capacity of 20 cm ³ using a powder density measuring device. Then, after the cell is fully filled, a tap having a stroke length of 10 mm is performed 1000 times, and the density is defined as the density obtained from the volume at that time and the weight of the sample.

(I) DBP oil absorption of Si composite carbon particles (A) The DBP (dibutyl phthalate) oil absorption of Si composite carbon particles (A) is usually 65 ml / 100 g or less, preferably 62 ml / 100 g or less, more preferably 60 ml / 100 g or less, more preferably 57 ml / 100 g or less. Moreover, it is 30 ml / 100g or more normally, Preferably it is 40 ml / 100g or more, More preferably, it is 50 ml / 100g or more. If the DBP oil absorption is too large, it tends to cause streaking during the application of the slurry containing the carbon material of the present invention when forming the negative electrode, and if it is too small, there is almost no pore structure in the particles. There is a possibility that it has not, and there is a tendency for the reaction surface to decrease.

In addition, the DBP oil absorption amount in the present invention is defined by measured values when 40 g of a measurement material is added, the dropping speed is 4 ml / min, the rotation speed is 125 rpm, and the set torque is 500 N · m in accordance with JIS K6217. For the measurement, an absorption meter (S-500) from Asahi Research Institute can be used.

(J) Press load (Pa) of Si composite carbon particles (A)
In the present invention, the press load is a press load when an electrode plate is prepared using particles, and is used as an index of particle hardness. Negative electrodes made using hard particles tend to have a higher press load, while negative electrodes made using soft particles tend to have a lower press load.

The value of the press load (Pa) of the Si composite carbon particles (A) is usually 500 kg / 5 cm or more, preferably 800 kg / 5 cm or more, more preferably 1000 kg / 5 cm or more, still more preferably 1200 kg / 5 cm or more, particularly preferably 1400 kg. / 5 cm or more, most preferably 1500 kg / 5 cm or more, usually 4000 kg / 5 cm or less, preferably 3000 kg / 5 cm or less, more preferably 2500 kg / 5 cm or less, more preferably 2300 kg / 5 cm or less, particularly preferably 2200 kg / 5 cm or less, Most preferably, it is 2000 kg / 5 cm or less.

When the value of the press load (Pa) is too large, the effect of suppressing the conduction path breakage during charging / discharging of the non-aqueous secondary battery is low, and the cycle characteristics tend to be deteriorated. There is a tendency that the flow path of the electrolytic solution is crushed and the input / output characteristics are deteriorated.

In the present invention, the press load is a linear pressure (kg / 5 cm) required to form Si composite carbon particles (A) on a current collector by rolling so that the density is 1.35 g / cm ^3. ).

The measuring method of press load is as follows. With respect to 100% by mass of the Si composite carbon material (A), 1.5% by mass of styrene-butadiene rubber as a binder, 1% by mass of sodium carboxymethylcellulose as a thickener, and 102.5% by mass of a dispersion medium Water is added to form a slurry, which is applied onto a current collector and dried. This electrode is adjusted so that the width of the active material layer is 5 cm (the coating width may be adjusted at the time of application), and roll-pressed so that the density of the active material layer becomes the above value, It can be measured by measuring the stress at the time of pressing.

(K) Aspect of silicon element in Si composite carbon particle (A) As an aspect of silicon element contained in the Si composite carbon particle (A) in the present invention, Si, SiOx, SiNx, SiCx, SiZxOy (Z = C, N) and the like, and these are collectively referred to as Si compounds in the present invention. Of these, Si and SiOx are preferred. The general formula SiOx is obtained using Si dioxide (SiO ₂ ) and metal Si (Si) as raw materials, and the value of x is usually 0 <x <2, preferably 0.2 or more and 1.8 or less. More preferably, it is 0.4 or more and 1.6 or less, More preferably, it is 0.6 or more and 1.4 or less. Within this range, the non-aqueous secondary battery has a high capacity, and at the same time, the irreversible capacity due to the combination of Li and oxygen can be reduced.

As an aspect of the silicon element in the Si composite carbon particles (A) in the present invention, an aspect of Si compound particles in which an Si compound is formed into particles is preferable.

Further, the content of silicon element in the Si composite carbon particles (A) in the present invention is usually 0.5% by mass or more, preferably 1% by mass or more, more preferably 2% with respect to the Si composite carbon particles (A). It is at least 5% by mass, more preferably at least 5% by mass, particularly preferably at least 10% by mass. Moreover, it is 99 mass% or less normally, Preferably it is 50 mass% or less, More preferably, it is 30 mass% or less, More preferably, it is 25 mass% or less, Most preferably, it is 20 mass% or less. This range is preferable in that a non-aqueous secondary battery having a sufficient capacity can be obtained.

In addition, the measuring method of content of the silicon element in Si composite carbon particle (A) is as follows. After completely melting the sample with alkali, the sample is dissolved and fixed in water, measured with an inductively coupled plasma emission analyzer (Horiba, Ltd., ULTIMA2C), and the amount of silicon element is calculated from the calibration curve. Thereafter, the silicon element content in the Si composite carbon particles (A) can be calculated by dividing the silicon element amount by the weight of the Si composite carbon particles (A).

(L) Abundance ratio of silicon element in Si composite carbon particles (A) The abundance ratio of silicon element calculated by the following measurement method in the Si composite carbon particles (A) used in the present invention is usually 0.8. 2 or more, preferably 0.3 or more, more preferably 0.4 or more, further preferably 0.5 or more, particularly preferably 0.6 or more, and usually 1.5 or less, preferably 1.2. Below, more preferably 1.0 or less. The higher this value, the more silicon element present inside the Si composite carbon particles (A) compared to the silicon element present outside the Si composite carbon particles (A), and the negative electrode was formed. At this time, there is a tendency that a decrease in charge / discharge efficiency due to the disconnection of the conductive path between particles can be suppressed.

The abundance ratio of silicon element in the Si composite carbon particles (A) is calculated as follows. First, a coating film of Si composite carbon particles (A) or Si composite carbon particles (A) is embedded in a resin to produce a thin piece of resin, and a cross section of the particle is cut out by focused ion beam (FIB) or ion milling. Then, it observes by observation methods, such as particle | grain cross-section observation by SEM (scanning electron microscope).

The accelerating voltage when observing the cross section of one Si composite carbon particle (A) with an SEM (scanning electron microscope) is preferably 1 kV or more, more preferably 2 kV or more, and further preferably 3 kV or more. 10 kV or less, more preferably 8 kV or less, still more preferably 5 kV or less. Within this range, the graphite particles and the Si compound can be easily identified due to the difference in the reflected secondary electron image in the SEM image. The imaging magnification is usually 500 times or more, more preferably 1000 times or more, still more preferably 2000 times or more, and usually 10000 times or less. If it is said range, the whole image of 1 particle | grains of Si composite carbon particle (A) is acquirable. The resolution is 200 dpi (ppi) or more, preferably 256 dpi (ppi) or more. The number of pixels is preferably evaluated at 800 pixels or more. Next, while observing the image, the graphite and silicon elements are identified by the energy dispersion type (EDX) and the wavelength dispersion type (WDX).

In the acquired image, one Si composite carbon particle (A) particle is extracted, and the area (a) of the Si compound in the particle is calculated. Next, after binarizing the extracted 1 particle and the background other than the 1 particle, the shrinking process is repeated on the particle, and a figure with an area of 70% of the extracted 1 particle is extracted. The area (b) of the silicon element present is calculated. In addition, in the area when the reduction process is repeatedly performed, when the value of 70% cannot be accurately shown, the value closest to 70% in the value of 70% ± 3% is 70% in the present invention. A figure. The extraction of one particle, the calculation of the area, the binarization process, and the reduction process can be performed using general image processing software. Examples of such software include “Image J” and “Image-Pro plus”. Etc.

The value obtained by dividing the area (b) calculated above by the area (a) is measured with arbitrary three particles, and the value obtained by averaging the values of these three particles is the silicon element in the Si composite carbon particles (A). The abundance ratio.

(Aspect of Si composite carbon particles (A))
The aspect of the Si composite carbon particles (A) described above is not particularly limited as long as it is a carbon material containing a silicon element.
(I) Si compound particles dispersed in a granulated body made of a carbon material,
(B) Si compound particles are attached or coated on the outer periphery of the carbon material serving as a nucleus,
(C) Si compound particles dispersed inside a spheroidized carbon material,
(D) A carbonaceous material attached or coated on the outer periphery of the Si compound particles as the core,
(E) A combination of these may be used.

By encapsulating Si compound particles inside the Si composite carbon particles (A), by suppressing the stress due to volume expansion associated with charge and discharge of the Si compound, particle breakage and the accompanying conduction path interruption are suppressed, (C) Because non-aqueous secondary batteries tend to exhibit high capacity and high cycle characteristics, and tend to exhibit high initial efficiency by inhibiting side reactions by preventing contact with the electrolyte. A material in which Si compound particles are dispersed inside a spheroidized carbon material is preferable. At this time, it is preferable that at least one of the Si compound particles is in contact with the carbon material from the viewpoint of suppressing an increase in irreversible capacity.

In the present specification, the term “adhesion” refers to a state in which Si compound particles are attached to, adhered to, or combined with the surface of a carbon material, and these states are, for example, a field emission scanning electron microscope-energy dispersive type. This can be confirmed by observing the cross section of the particle using a technique such as X-ray (SEM-EDX) analysis or X-ray photoelectron spectroscopy (XPS) analysis.

<Method for producing Si composite carbon particles (A)>
(Raw material for Si composite carbon particles (A))
The Si composite carbon particles (A) described above are not particularly limited as long as they are Si composite carbon particles in which a silicon element and a carbon material are combined. For example, Si composite carbon particles (A) can be produced using a carbon material, Si compound particles, and an organic compound that becomes a carbonaceous material.

-Carbon material The carbon material used as a raw material is not particularly limited, but when producing the Si composite carbon particles (A) of (a) or (c) above, graphite particles such as natural graphite, artificial graphite, or the like Examples thereof include a fired material made of a material selected from the group consisting of coal-based coke, petroleum-based coke, furnace black, acetylene black, and pitch-based carbon fiber having slightly lower crystallinity. These may be used individually by 1 type and may be used in combination of 2 or more type.

Among these, natural graphite is classified into flake graphite (FlakeGraphite), scaly graphite (CrystalLine (Vein) Graphite), and soil graphite (Amorphous Graphite) (“Powder and Particle Process Technology Assembly” ) Graphite section of Industrial Technology Center, published in 1974, and "HANDBOOKOK CARBON, GRAPHITE, DIAMOND AND AND FULLLENES" (issued by Noyes PubLications)). Graphite crystallinity (degree of graphitization) is the highest at 100% for scaly graphite, followed by 99.9% for scaly graphite. Therefore, it is preferable to use these graphites.

The production areas of scaly graphite, which is natural graphite, are Madagascar, China, Brazil, Ukraine, Canada, etc., and the production area of scaly graphite is mainly Sri Lanka. The main producers of soil graphite are the Korean Peninsula, China and Mexico.

Among these natural graphites, scaly graphite and scaly graphite have advantages such as high graphite crystallinity and low impurity content, and therefore can be preferably used in the present invention. Visual methods for confirming that graphite is scaly include particle surface observation with a scanning electron microscope, embedding particles in a resin to produce a thin piece of resin, and cutting out the particle cross section, or coating consisting of particles Examples of the method include a method of observing a particle cross section with a scanning electron microscope after preparing a cross section of a coating film with a cross section polisher and cutting out the particle cross section.

Scaly graphite and scaly graphite have natural graphite that is highly purified so that the crystallinity of graphite is almost completely crystallized, and artificially formed graphite. Natural graphite is soft and folded. It is preferable in that it is easy to fabricate the structure.

In addition, when producing (B) Si composite carbon particles (A), from the viewpoint of maintaining the shape as the core of the particles, for example, graphite particles obtained by spheroidizing by applying mechanical stress to flaky graphite or the like and graphite and carbonaceous material It is preferable to use graphite particles obtained by mixing and granulating an organic compound.

The carbon material used as a raw material in the present invention preferably has the following physical properties.

The volume-based average particle diameter (d50) of the carbon material used as a raw material is not particularly limited, but is usually 1 μm or more and 120 μm or less, preferably 3 μm or more and 100 μm or less, more preferably 5 μm or more and 90 μm or less. If the average particle diameter d50 of the carbon material used as a raw material is too large, the particle diameter of the Si composite carbon particles (A) becomes large, and the negative electrode active material mixed with the Si composite carbon particles (A) is applied in a slurry form. In this process, streaks or irregularities due to large particles may occur. If the flat body particle size d50 is too small, it is difficult to form a composite, and it may be difficult to produce the Si composite carbon particles (A).

The tap density of the carbon material used as a raw material is usually less than 0.1 g / cm ³ or more 1.0 g / cm ^3, preferably 0.13 g / cm ³ or more 0.8 g / cm ³ or less, more preferably 0 .15 g / cm ³ or more and 0.6 g / cm ³ or less. When the tap density is within the above range, minute voids are easily formed in the Si composite carbon particles (A), and thus the destruction of the Si composite carbon particles (A) due to the expansion and contraction of the Si compound particles can be suppressed.

BET specific surface area of the carbon material used as a raw material is usually ^{1 m} 2 / g or more ^{40 m} 2 / g or less, preferably less ^2m 2 / g or more ^{^{35m 2 / g, 3m 2 /}} g or more ^{30 m} 2 / g The following is more preferable. The specific surface area of the carbon material used as a raw material is reflected in the specific surface area of the Si composite carbon particles (A), and the battery capacity due to an increase in the irreversible capacity of the Si composite carbon particles (A) by being 40 m ² / g or less. Can be prevented.

The interplanar spacing (d ₀₀₂ ) of the 002 plane according to the X-ray wide angle diffraction method of the carbon material used as a raw material is usually 0.337 nm or less. Meanwhile _{d 002} is usually 0.334nm more. The carbon material used as a raw material has an Lc of 90 nm or more, preferably 95 nm or more by X-ray wide angle diffraction. When the interplanar spacing (d ₀₀₂ ) of the 002 plane is 0.337 nm or less, it indicates that the carbon material used as a raw material has high crystallinity, and provides a high capacity non-aqueous secondary battery (A) Can be obtained. In addition, when Lc is 90 nm or more, Si composite carbon particles (A) exhibiting high crystallinity and having a high capacity for the nonaqueous secondary battery can be obtained.

-Si compound particle | grains As a Si compound particle | grain used as a raw material of Si composite carbon particle (A) in this invention, what shows the following physical properties is preferable.

The volume average particle diameter (d50) of the Si compound particles used as a raw material is usually 0.005 μm or more, preferably 0.01 μm or more, more preferably 0.02 μm or more, and further preferably 0.03 μm, from the viewpoint of cycle life. These are usually 10 μm or less, preferably 9 μm or less, more preferably 8 μm or less. When the average particle diameter (d50) is within the above range, volume expansion associated with charge / discharge of the nonaqueous secondary battery is reduced, and good cycle characteristics can be obtained while maintaining the charge / discharge capacity.

The specific surface area by the BET method of the Si compound particles used as a raw material is usually 0.5 m ² / g or more and 120 m ² / g or less, and preferably 1 m ² / g or more and 100 m ² / g or less. It is preferable that the specific surface area is within the above range because the charge / discharge efficiency and discharge capacity of the non-aqueous secondary battery are high, lithium is taken in and out quickly during high-speed charge / discharge, and the rate characteristics are excellent.

Although there is no restriction | limiting in particular in the oxygen content of Si compound particle | grains used as a raw material, Usually, it is 0.01 mass% or more and 12 mass% or less, and it is preferable that it is 0.05 mass% or more and 10 mass% or less.

The oxygen distribution state in the Si compound particles may be present in the vicinity of the surface, in the particle, or uniformly in the particle, but is preferably present in the vicinity of the surface. It is preferable for the oxygen content of the particles to be in the above-mentioned range because the volume expansion associated with charge / discharge is suppressed due to strong bonding between Si and O, and the cycle characteristics of the nonaqueous secondary battery are excellent.

The crystallite size of the Si compound particles used as a raw material is not particularly limited, but is usually 0.05 nm or more, preferably 1 nm or more in the (111) plane crystallite size calculated from XRD. It is 100 nm or less, and preferably 50 nm or less. It is preferable that the crystallite size of the particles is in the above range because the reaction between Si and Li ions proceeds rapidly and is excellent in battery input / output.

Note that the Si compound particles in the Si composite carbon particles (A) preferably have the same properties as the physical properties of the Si compound particles used as a raw material.

-Organic compound used as carbonaceous material As an organic compound used as a carbonaceous material used as a raw material of Si composite carbon particles (A) in the present invention, a carbon material described in the following (a) or (b) is preferable.

(A) Coal heavy oil, DC heavy oil, cracked heavy oil, aromatic hydrocarbon, N ring compound, S ring compound, polyphenylene, organic synthetic polymer, natural polymer, thermoplastic resin and Carbonizable organic substance selected from the group consisting of thermosetting resins (b) Carbonized organic substance dissolved in low molecular organic solvent

As the coal-based heavy oil, coal tar pitch from soft pitch to hard pitch, dry distillation liquefied oil and the like are preferable,
As the DC heavy oil, atmospheric residual oil, vacuum residual oil, etc. are preferable,
The cracked petroleum heavy oil is preferably ethylene tar produced as a by-product during thermal decomposition of crude oil, naphtha, etc.
As the aromatic hydrocarbon, acenaphthylene, decacyclene, anthracene, phenanthrene and the like are preferable,
As the N-ring compound, phenazine, acridine and the like are preferable,
As the S ring compound, thiophene, bithiophene and the like are preferable,
As the polyphenylene, biphenyl, terphenyl and the like are preferable,
As the organic synthetic polymer, nitrogen-containing polymers such as polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insolubilized products of these, polyacrylonitrile, polypyrrole, polyallylamine, polyvinylamine, polyethyleneimine, urethane resin, urea resin, etc. , Polythiophene, polystyrene, polymethacrylic acid and the like are preferable,
As the natural polymer, polysaccharides such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, saccharose and the like are preferable,
As the thermoplastic resin, polyphenylene sulfide, polyphenylene oxide and the like are preferable,
As the thermosetting resin, furfuryl alcohol resin, phenol-formaldehyde resin, imide resin and the like are preferable.

Further, the carbonizable organic substance may be a carbide such as a solution dissolved in a low molecular organic solvent such as benzene, toluene, xylene, quinoline, n-hexane or the like.

Moreover, these may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations.

In addition, as a carbonaceous material in Si composite carbon particle (A), a thing (amorphous thing) whose graphite crystallinity is lower than a graphite particle is preferable. Specifically, what shows the following physical properties is preferable.

The interplanar spacing (d ₀₀₂ ) of the (002) plane of the carbonaceous material powder by X-ray wide angle diffraction method is usually 0.340 nm or more, preferably 0.342 nm or more. Moreover, it is less than 0.380 nm normally, Preferably it is 0.370 nm or less, More preferably, it is 0.360 nm or less. If the d ₀₀₂ value is too large, it indicates that the crystallinity is low, and the cycle characteristics of the non-aqueous secondary battery tend to deteriorate. If the d ₀₀₂ value is too small, the effect of combining carbonaceous materials is obtained. hard.

The crystallite size (Lc (002)) of the carbonaceous material obtained by X-ray diffraction based on the Gakushin method of the carbonaceous material powder is usually 5 nm or more, preferably 10 nm or more, more preferably 20 nm or more. Moreover, it is 300 nm or less normally, Preferably it is 200 nm or less, More preferably, it is 100 nm or less. If the crystallite size is too large, the cycle characteristics of the non-aqueous secondary battery tend to decrease.If the crystallite size is too small, the charge / discharge reactivity decreases, resulting in increased gas generation and high current during high-temperature storage. There is a risk of deterioration of charge / discharge characteristics.

<Type of manufacturing method>
The Si composite carbon particles (A) described above are not particularly limited as long as they are Si composite carbon particles in which a silicon element and a carbon material are combined. For example, the following methods (i) to (iii) are used. Can be manufactured by.

(Method (i))
(B) Si compound carbon particles (A) in which Si compound particles are dispersed in the granulated body made of carbon material (A) and (b) Si compound particles are attached or coated on the outer periphery of the carbon material that becomes the nucleus. In order to manufacture Si composite carbon particle (A), the method of mixing and granulating the carbon compound, Si compound particle | grains, and the organic compound used as a carbonaceous material is mentioned, for example.

As a concrete process in the method,
(1) A step of mixing Si compound particles, a carbon material, and an organic compound to be a carbonaceous material, and (2) a step of firing the mixture obtained in (1). Si composite carbon particles (A) can be produced by a method including at least these steps (1) to (2). Hereinafter, the steps (1) and (2) will be described.

(1) Step of mixing Si compound particles, carbon material, and organic compound that becomes carbonaceous material Mixing Si compound particles, carbon material, and organic compound that becomes carbonaceous material, and if a mixture can be obtained, in order to prepare the raw materials in particular There is no limit, but for example
A method of mixing an organic compound that becomes a carbonaceous material after mixing a carbon material with Si compound particles,
A method of mixing Si compound particles after mixing an organic compound that becomes a carbonaceous material with a carbon material,
A method of mixing a carbon material after mixing an organic compound that becomes a carbonaceous material into Si compound particles,
Examples thereof include a method of mixing Si compound particles, a carbon material, and an organic compound to be a carbonaceous material at a time.

In the method of mixing an organic compound that becomes a carbonaceous material after mixing a carbon material with Si compound particles, the carbonaceous material is adhered to the surface and / or inside of the carbon material by mechanical treatment. You may mix the organic compound which becomes. The mechanical treatment here is not particularly limited. For example, a dry ball mill, a wet bead mill, a planetary ball mill, a vibrating ball mill, a mechano-fusion system, an agromaster (Hosokawa Micron Corporation), a hybridization system, a micros, a mirror ( (Nara Machinery Co., Ltd.) and the like.

Among the mixing methods described above, the method of mixing an organic compound that becomes a carbonaceous material after mixing a carbon material with Si compound particles mixes the Si compound particles and the carbon material in a powder state, so that the dispersibility is good. It is preferable in that it is.

Specific examples of the mixing method in the method of mixing the Si compound particles, the carbon material, and the organic compound that becomes the carbonaceous material include a powder mixing method, a melt mixing method, and a solution mixing method.

The mixing temperature in these methods is usually from room temperature to 300 ° C., and can be appropriately determined depending on the type of organic compound that becomes a carbonaceous material. The mixing time is usually 10 minutes or more and 1 hour or less. In addition, the solvent used in the solution mixing method with the Si compound particles, the carbon material, and the organic compound that becomes the carbonaceous material can be appropriately selected from water or an organic solvent in which the organic compound is dissolved or dispersed. Two or more different solvents may be mixed and used.

When using a solution mixing method of Si compound particles, a carbon material, and an organic compound that becomes a carbonaceous material, it is usually dried in the range of 40 ° C. to 300 ° C. Although drying time can be suitably determined according to the kind of solvent used, it is normally 1 hour or more and 24 hours or less. Vacuum drying can be selected as appropriate.

When mixing the Si compound particles, the carbon material, and the organic compound that becomes the carbonaceous material, it is usually performed under normal pressure, but may be performed under reduced pressure or under pressure if desired. Mixing can be carried out either batchwise or continuously. In any case, mixing efficiency can be improved by using a combination of an apparatus suitable for rough mixing and an apparatus suitable for fine mixing.

Batch-type mixing devices include high-speed mixers, homogenizers, ultrasonic homogenizers, mixers with a structure in which two frame types rotate and revolve, dissolvers that are high-speed, high-shear mixers, and butterfly mixers for high viscosity. An apparatus having a structure in which one blade stirs and disperses in a tank, a so-called kneader type apparatus having a structure in which a stirring blade such as a sigma type rotates along the side surface of a semi-cylindrical mixing tank, and a stirring blade A trimix type apparatus having a three axis, a so-called bead mill type apparatus having a rotating disk and a dispersion medium in a container, and the like are used.

It also has a container with a paddle that is rotated by a shaft, and the inner wall surface of the container is formed substantially along the outermost line of rotation of the paddle, preferably in a long twin cylinder shape, and the paddle has side surfaces facing each other. A device having a structure in which many pairs are arranged in the axial direction of the shaft so as to be slidably engaged (for example, KRC reactor manufactured by Kurimoto Iron Works, SC processor, TEM manufactured by Toshiba Machine Celmac, TEX-K manufactured by Nippon Steel Works) Etc.), and a container having a plurality of pavement or sawtooth paddles fixed to the shaft and arranged in multiple phases, the inner wall surface of which is the outermost line of rotation of the paddle (External heating type) apparatus having a structure preferably formed in a cylindrical shape substantially (for example, a Redige mixer manufactured by Redige Co., Ltd., a flow share mixer manufactured by Taiyo Koki Co., Ltd., and Tsukishima Kikai Co., Ltd.) DT dryers, etc.) can also be used.

In order to perform mixing in a continuous mode, a pipeline mixer or a continuous bead mill may be used.

The mixing ratio of the Si compound particles with respect to the total of the Si compound particles, the carbon material, and the organic compound as the carbonaceous material is usually 1% by mass or more, preferably 1.5% by mass or more, more preferably 2% by mass or more, and still more preferably. Is 2.5% by mass or more. Moreover, it is 50 mass% or less normally, Preferably it is 40 mass% or less, More preferably, it is 30 mass% or less, More preferably, it is 20 mass% or less. When there are too many Si compound particles, the volume expansion accompanying charging / discharging will become large in a non-aqueous secondary battery, and there exists a tendency for capacity deterioration to become remarkable. Moreover, when there are too few Si compound particles, there exists a tendency for sufficient capacity | capacitance not to be obtained.

The mixing ratio of the carbon material to the total of the Si compound particles, the carbon material, and the organic compound as the carbonaceous material is usually 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass. That's it. Moreover, it is 95 mass% or less normally, Preferably it is 90 mass% or less, More preferably, it is 85 mass% or less, More preferably, it is 80 mass% or less. If the carbon material is too much, the amount of voids formed by the carbon material increases, and it tends to be difficult to increase the electrode density. Moreover, when there are too few carbon materials, the space | gap which suppresses volume expansion cannot be formed, it becomes difficult to take a conductive path, and there exists a tendency for the effect which improves cycling characteristics not to be fully acquired.

The mixing ratio of the organic compound that becomes the carbonaceous material to the total of the organic compound that becomes the Si compound particles, the carbon material and the carbonaceous material is usually 1% by mass or more, preferably 1.5% with respect to the total mass of the carbon material and the Si compound particles. It is at least 2 mass%, more preferably at least 2.5 mass%. Moreover, it is 60 mass% or less normally, Preferably it is 50 mass% or less, More preferably, it is 40 mass% or less, More preferably, it is 30 mass% or less. When there are too many organic compounds used as a carbonaceous material, there exists a tendency for active material to aggregate easily in a baking process. Moreover, when there are too few organic compounds used as a carbonaceous material, there exists a tendency for sufficient effect not to be acquired in progress of a reductive reaction, or aggregation suppression of an active material.

(2) Step of firing the mixture obtained in (1) In this step, the mixture containing the Si compound particles, the carbon material, and the organic compound that becomes the carbonaceous material obtained in the step (1) is fired.

The atmosphere at the time of firing is a non-oxidizing atmosphere, and preferably, firing is performed in a non-oxidizing atmosphere by circulating nitrogen, argon, carbon dioxide, ammonia, hydrogen, or the like.

The reason for firing in a non-oxidizing atmosphere is that it is necessary to prevent oxidation of Si compound particles, carbon materials, and organic compounds that become carbonaceous materials.

The firing temperature varies depending on the firing atmosphere and the organic compound that becomes the carbonaceous material, but as an example, the firing temperature is usually 500 ° C. or higher, preferably 800 ° C. or higher, more preferably 850 ° C. or higher, under a nitrogen circulation atmosphere. Further, it is usually at most 3000 ° C., preferably 2000 ° C. or less, more preferably 1500 ° C. or less, even if it is high. If the firing temperature is too low, carbonization does not proceed sufficiently, and the irreversible capacity at the beginning of charge / discharge of the non-aqueous secondary battery may increase, and the reduction rate of the Si compound decreases, so the firing time is increased. Need arises. However, the reduction rate can be increased even at a low temperature by setting the firing atmosphere to a stronger reducing atmosphere such as a hydrogen atmosphere.

On the other hand, if the firing temperature is too high, the carbonized organic compound carbide will reach a crystal structure equivalent to the crystal structure of the raw material carbon material in the mixture, making it difficult to obtain the coating effect, and vaporizing the silicon element. This tends to reduce the yield and increase the manufacturing cost.

In the firing treatment conditions, the heat history temperature condition, the temperature rise rate, the cooling rate, the heat treatment time, etc. are set as appropriate. Further, after heat treatment in a relatively low temperature region, the temperature can be raised to a predetermined temperature.

In addition, the reactor used for this process may be a batch type or a continuous type, and may be one or more. The furnace used for firing is not particularly limited as long as the above requirements are satisfied. For example, a reactor such as a shuttle furnace, a tunnel furnace, a lead hammer furnace, a rotary kiln, an autoclave, a coker (heat treatment tank for coke production), a Tamman furnace, The Atchison furnace can be mentioned. As the heating method, high-frequency induction heating, direct resistance heating, indirect resistance heating, direct combustion heating, radiant heat heating, or the like can be used. During the treatment, stirring may be performed as necessary.

Other Steps The composite carbon material that has undergone the above steps is subjected to powder processing such as pulverization, crushing, and classification to obtain Si composite carbon particles (A).

There are no particular restrictions on the apparatus used for pulverization and pulverization, for example, the coarse pulverizer includes a shearing mill, jaw crusher, impact crusher, cone crusher, etc., and the intermediate pulverizer includes roll crusher, hammer mill, etc. Examples of the pulverizer include a ball mill, a vibration mill, a pin mill, a stirring mill, and a jet mill.

There is no particular limitation on the apparatus used for classification, but for example, in the case of dry sieving, a rotary sieving, a swaying sieving, a rotating sieving, a vibrating sieving, etc. can be used. In this case, gravity classifier, inertial classifier, centrifugal classifier (classifier, cyclone, etc.) can be used, wet sieving, mechanical wet classifier, hydraulic classifier, sedimentation classifier A centrifugal wet classifier or the like can be used.

Si composite carbon particles (A) can be produced by the production method as described above. However, Si composite carbon particle (A) is not limited to what was manufactured with the said manufacturing method.

(Method (ii))
Examples of the method for producing the Si composite carbon particles (A) in which the Si compound particles are dispersed inside the spheroidized carbon material described above are, for example, mixing the carbon material and the Si compound particles, and then spherical An example is a method of encapsulating Si compound particles inside Si composite carbon particles by performing a chemical treatment. In addition, the carbon material as a raw material in the method (ii), the Si compound particles, and the organic compound that becomes the carbonaceous material used in the step (3) described later are not particularly limited, and the method (i) and The same can be used.

A preferable production method includes the following steps.
(1) Step of mixing and fixing carbon material and Si compound particles (2) Step of applying spheroidizing treatment to those obtained in (1) These steps will be described below.

(1) Step of mixing and fixing carbon material and Si compound particles The mixing ratio of Si compound particles to the total of Si compound particles and carbon material is usually 1% by mass or more, preferably 3% by mass or more, more preferably 5%. It is at least 7% by mass, more preferably at least 7% by mass, particularly preferably at least 10% by mass. Moreover, it is 95 mass% or less normally, Preferably it is 70 mass% or less, More preferably, it is 60 mass% or less, More preferably, it is 50 mass% or less, Most preferably, it is 40 mass% or less, Most preferably, it is 35 mass% or less. This range is preferable in that a sufficient capacity can be obtained in the non-aqueous secondary battery.

There is no particular limitation on the method of mixing and fixing the carbon material and the Si compound particles. For example, there is a method in which a Si slurry in which Si compound particles are dispersed in a solvent is used and mixed with a carbon material so that the wet Si compound particles are not dried. Since such Si slurry suppresses aggregation of Si compound particles, it is preferable because the Si compound particles are easily fixed on the surface of the carbon material.

Examples of the dispersion solvent for the Si compound particles include a nonpolar compound having an aromatic ring and an aprotic polar solvent. The type of the nonpolar compound having an aromatic ring is not particularly limited, but reacts with the Si compound. It is more preferable if it does not have the property. For example, aromatic compounds such as benzene, toluene, xylene, cumene, and methylnaphthalene that are liquid at room temperature, alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, methylcyclohexene, and bicyclohexyl, petrochemicals such as light oil and heavy oil Residual oil in coal chemistry. Among these, xylene is preferred, methylnaphthalene is more preferred, and heavy oil is more preferred because of its high boiling point. In wet pulverization, heat generation tends to occur when the pulverization efficiency is increased. A solvent having a low boiling point may volatilize and become a high concentration. On the other hand, as the aprotic polar solvent, NMP (N-methyl-2-pyrrolidone), GBL (γ-butyrolactone), DMF (NN dimethylformamide) and the like which dissolve not only water but also organic solvents are preferable. NMP (N-methyl-2-pyrrolidone) is preferred because it is difficult to resist and has a high boiling point.

The mixing ratio of the Si compound particles and the dispersion solvent is a ratio of usually 10% by mass or more, preferably 20% by mass or more, usually 50% by mass or less, preferably 40% by mass or less as the ratio of the Si compound particles in the resulting mixture. It is.

If the mixing ratio of the dispersion solvent is too high, the cost tends to increase, and if the mixing ratio of the dispersion solvent is too low, uniform dispersion of the Si compound particles tends to be difficult.

It is preferable that the Si compound particles are uniformly dispersed on the surface of the carbon material. For this purpose, the dispersion solvent used in wet pulverizing the Si compound particles may be added excessively during mixing. In the present specification, when mixing the Si compound particles into the carbon material as a slurry, the solid content of the Si compound particles is usually 10% or more, preferably 15% or more, more preferably 20% or more. Usually, it is 90% or less, preferably 85% or less, more preferably 80% or less. If the ratio of the solid content is too large, the fluidity of the slurry is lost, and the Si compound particles tend to be difficult to disperse in the carbon material. If the ratio is too small, the process tends to be difficult to handle.

Then, after mixing, the Si compound particles can be immobilized on the carbon material by evaporating and removing the dispersion solvent using an evaporator, a dryer, or the like.

Alternatively, the mixture may be mixed and fixed while evaporating the dispersion solvent while heating in a high-speed stirrer without adding an excessive dispersion solvent. At this time, in order to immobilize the Si compound particles on the carbon material, a buffer material such as resin or pitch can be used, and it is preferable to use the resin among them. This resin is considered not only to play a role of immobilizing the Si compound particles to the carbon material but also to prevent the Si compound particles from being detached from the carbon material during the spheronization process. In addition, when adding a buffering material, you may add at this stage and may add at the time of the wet grinding | pulverization of Si compound particle | grains.

In addition, the resin that can be used as the buffer material in the step (1) is not particularly limited, but may be a resin corresponding to the above-described organic compound that becomes a carbonaceous material, preferably polystyrene, polymethacrylic acid, Polyacrylonitrile is mentioned. Polyacrylonitrile can be particularly preferably used because it has a large amount of residual carbon during firing and a relatively high decomposition temperature. The decomposition temperature of the resin can be measured in an inert gas atmosphere by differential scanning calorimetry (DSC). The decomposition temperature of the resin is preferably 50 ° C. or higher, more preferably 75 ° C. or higher, and still more preferably 100 ° C. or higher. When the decomposition temperature is too high, there is no particular problem. However, when the decomposition temperature is too low, there is a possibility of decomposition in the drying step described below.

The buffer material may be used in a state where it is dispersed in a solvent or in a dry state, but when a solvent is used, the same solvent as the dispersion solvent of the Si compound particles can be used.

Mixing is usually performed under normal pressure, but if desired, it can also be performed under reduced pressure or under pressure. Mixing can be carried out either batchwise or continuously. In any case, mixing efficiency can be improved by using a combination of an apparatus suitable for rough mixing and an apparatus suitable for fine mixing. Moreover, you may utilize the apparatus which performs mixing and fixation (drying) simultaneously. Drying can usually be carried out under reduced pressure or under pressure, and preferably dried under reduced pressure.

The drying time is usually 5 minutes or longer, preferably 10 minutes or longer, more preferably 20 minutes or longer, more preferably 30 minutes or longer, and usually 5 hours or shorter, preferably 3 hours or shorter, more preferably 1 hour or shorter. . If the time is too long, the cost increases. If the time is too short, uniform drying tends to be difficult.

The drying temperature is preferably a time that can realize the above time although it varies depending on the solvent. Moreover, it is preferable that it is below the temperature which resin does not modify | denature.

As a batch-type mixing device, a mixer with a structure in which two frame molds rotate and revolve; a blade such as a dissolver that is a high-speed high-shear mixer and a butterfly mixer for high viscosity is placed in the tank. A device having a structure for stirring and dispersing; a so-called kneader-type device having a structure in which a stirring blade such as a sigma type rotates along the side surface of a semi-cylindrical mixing tank; a trimix type device having three stirring blades A so-called bead mill type apparatus having a rotating disk and a dispersion solvent body in a container is used.

It also has a container with a paddle that is rotated by a shaft, and the inner wall surface of the container is formed substantially along the outermost line of rotation of the paddle, preferably in a long twin cylinder shape, and the paddle has side surfaces facing each other. A device having a structure in which many pairs are arranged in the axial direction of the shaft so as to be slidably engaged (for example, KRC reactor manufactured by Kurimoto Iron Works, SC processor, TEM manufactured by Toshiba Machine Celmac, TEX-K manufactured by Nippon Steel Works) Furthermore, it has a container in which a single inner shaft and a plurality of pavement or sawtooth paddles fixed to the shaft are arranged in different phases, and the inner wall surface is the outermost line of rotation of the paddle (External heat type) apparatus having a structure preferably formed in a cylindrical shape (e.g., Redige mixer manufactured by Redige Co., Ltd., flow share mixer manufactured by Taiyo Kiko Co., Ltd., Tsukishima Machine Co., Ltd.) Of DT dryers, etc.) can also be used. In order to perform mixing in a continuous manner, a pipeline mixer, a continuous bead mill, or the like may be used. It is also possible to homogenize by means such as ultrasonic dispersion.

(2) A step of spheroidizing the product obtained in (1) Through this step (2), a structure in which a carbon material is folded is observed, and a gap in the folded structure is observed. Si composite carbon particles (A) in which Si compound particles are present can be produced. Note that the above structure is obtained by using, for example, a Si composite carbon particle (A) using a technique such as field emission scanning electron microscope-energy dispersive X-ray (SEM-EDX) analysis, X-ray photoelectron spectroscopy (XPS) analysis, or the like. This can be confirmed by observing the cross section of the particles.

That is, in the production method for obtaining the Si composite carbon particles (A), a composite in which Si compound particles are immobilized on the surface of the carbon material before being folded obtained in the step (1) (hereinafter referred to as the composite material) In the present invention, the spheroidizing treatment is performed. In particular, in the present invention, the Si compound particles within a predetermined range are present in the gaps in the folded structure as described later. It is preferable to set conditions appropriately.

The spheronization process is basically a process using mechanical energy (mechanical action such as impact compression, friction and shear force), and specifically, a process using a hybridization system is preferable. The system has a rotor having a large number of blades that apply mechanical actions such as impact compression, friction and shearing force, and a large air flow is generated by the rotation of the rotor, and thus obtained in step (1) above. A large centrifugal force is applied to the carbon material in the composite, the carbon materials in the composite obtained in the step (1), and the carbon material, the wall and the blade in the composite obtained in the (1) step. The carbon material in the composite obtained in the step (1) can be neatly folded.

As an apparatus used for the spheroidization treatment, for example, a rotor having a large number of blades installed in a casing, and the rotor is rotated at a high speed, whereby the composite obtained in the step (1) introduced into the interior is used. A device for applying a mechanical action such as impact compression, friction, shearing force, etc. to the carbon material and performing a surface treatment can be used. For example, dry ball mill, wet bead mill, planetary ball mill, vibrating ball mill, mechano-fusion system, Agromaster (Hosokawa Micron Corporation), hybridization system, Micros, Miraro (manufactured by Nara Machinery Co., Ltd.), CF mill (Ube) And theta composer (manufactured by Deoksugaku Kogyo Co., Ltd.). Preferred examples of the apparatus include a dry ball mill, a wet bead mill, a planetary ball mill, a vibration ball mill, a mechano-fusion system, an agromaster (Hosokawa Micron ( Co., Ltd.), hybridization system, Micros, Miraro (manufactured by Nara Machinery Co., Ltd.), CF mill (manufactured by Ube Industries, Ltd.), theta composer (manufactured by Tokuju Kosakusho Co., Ltd.), pulperizer and the like. Among these, a hybridization system manufactured by Nara Machinery Co., Ltd. is particularly preferable.

Note that the carbon material in the composite obtained in the step (1) to be subjected to the spheronization treatment may have already been subjected to a certain spheronization treatment under the conditions of the conventional method. Moreover, you may give a mechanical action repeatedly by circulating the composite_body | complex obtained at the said (1) process, or passing through this process in multiple times.

A spheronization process is performed using such an apparatus. In this process, the rotation speed of the rotor is usually 2000 rpm or more and 8000 rpm or less, preferably 4000 rpm or more and 7000 rpm or less, and usually in a range of 1 minute or more and 60 minutes or less. Then, the spheronization process is performed.

In addition, if the number of rotations of the rotor is too small, the process of forming a sphere is weak, and the tapping density of the resulting Si composite carbon particles (A) may not be sufficiently increased. This may increase the effect, and the particles may collapse to reduce the tapping density. Further, if the spheroidizing time is too short, the particle size is sufficiently reduced and a high tapping density cannot be achieved. On the other hand, if it is too long, the carbon material in the composite obtained in the step (1) is used. May be shattered.

The obtained Si composite carbon particles (A) may be subjected to classification treatment. When the obtained Si composite carbon particles (A) are not within the specified physical property range of the present invention, the desired physical properties are obtained by repeated (usually 2 to 10 times, preferably 2 to 5 times) classification treatment. Can range. Examples of the classification include dry (aerodynamic classification, sieving), wet classification, and the like, but dry classification, particularly aerodynamic classification is preferable from the viewpoint of cost and productivity.

(3) The step of coating the Si composite carbon particles (A) obtained in (2) with a carbonaceous material The Si composite carbon particles (A) are obtained as in the above step (2). (A) preferably contains a carbonaceous material, and as a more specific embodiment, it is more preferable that at least a part of the surface thereof is coated with the carbonaceous material (hereinafter, such Si composite carbon particles ( A) is also referred to as a carbonaceous material-coated Si composite carbon particle). In the present specification, the carbonaceous material-coated Si composite carbon particles are described separately from the Si composite carbon particles (A) for convenience, but in this specification, the carbonaceous material-coated Si composite carbon particles are also referred to as Si composite carbon particles (A). ) To be interpreted.

In the coating treatment, an organic compound that becomes a carbonaceous material is used as a coating raw material for the above-described Si composite carbon particles (A), and these are mixed and fired to obtain carbonaceous material-coated Si composite carbon particles.

When the firing temperature is usually 600 ° C. or higher, preferably 700 ° C. or higher, more preferably 900 ° C. or higher, usually 2000 ° C. or lower, preferably 1500 ° C. or lower, more preferably 1200 ° C. or lower, an amorphous material is obtained as a carbonaceous material. When a heat treatment is usually performed at 2000 ° C. or higher, preferably 2500 ° C. or higher and usually 3200 ° C. or lower, a graphite material is obtained as a carbonaceous material. The amorphous material is carbon with low crystallinity, and the graphite material is carbon with high crystallinity.

In the coating treatment, the above-described Si composite carbon particles (A) are used as a core material, an organic compound that becomes a carbonaceous material is used as a coating material, and these are mixed and fired to obtain carbonaceous material-coated Si composite carbon particles. The coating layer may contain Si compound particles and carbon fine particles. The shape of the carbon fine particles is not particularly limited, and may be any of granular, spherical, chain-like, needle-like, fibrous, plate-like, and scale-like shapes.

Specifically, the carbon fine particles are not particularly limited, but examples thereof include coal fine powder, vapor phase carbon powder, carbon black, ketjen black, and carbon nanofiber. Among these, carbon black is particularly preferable. Carbon black has the advantage that non-aqueous secondary batteries have high input / output characteristics even at low temperatures, and at the same time are inexpensive and easily available.

The average particle diameter d50 of the carbon fine particles is usually 0.01 μm or more and 10 μm or less, preferably 0.05 μm or more, more preferably 0.07 μm or more, further preferably 0.1 μm or more, preferably 8 μm or less. More preferably, it is 5 micrometers or less, More preferably, it is 1 micrometer or less.

When the carbon fine particles have a secondary structure in which primary particles are aggregated and aggregated, other physical properties and types are not particularly limited as long as the primary particle size is 3 nm or more and 500 nm or less, but the primary particle size is preferably 3 nm or more, more preferably 15 nm or more, further preferably 30 nm or more, particularly preferably 40 nm or more, preferably 500 nm or less, more preferably 200 nm or less, still more preferably 100 nm or less, particularly preferably 70 nm or less. is there. The primary particle size of the carbon fine particles can be measured by observation with an electron microscope such as SEM or a laser diffraction particle size distribution analyzer.

(Physical properties of carbonaceous material-coated Si composite carbon particles)
The carbonaceous material-covered Si composite carbon particles exhibit the same physical properties as the Si composite carbon particles (A) described above, but the preferred physical properties of the carbonaceous material-coated Si composite carbon particles that vary depending on the coating treatment are described below.

-(002) plane spacing (d ₀₀₂ )
The interplanar spacing (d ₀₀₂ ) of the (002) plane of the carbonaceous material-coated Si composite carbon particles by X-ray wide angle diffraction method is usually 0.336 nm or more, preferably 0.337 nm or more, more preferably 0.340 nm or more, and still more preferably. 0.342 nm or more. Moreover, it is less than 0.380 nm normally, Preferably it is 0.370 nm or less, More preferably, it is 0.360 nm or less. If the d ₀₀₂ value is too large, it indicates that the crystallinity is low, and the cycle characteristics of the non-aqueous secondary battery tend to deteriorate. If the d ₀₀₂ value is too small, the effect of combining carbonaceous materials is obtained. hard.

-Content The carbonaceous material-coated Si composite carbon particles contain an amorphous material or a graphite material, and among them, the amorphous carbonaceous material is contained from the point of acceptability of lithium ions. preferable. The content of the amorphous carbonaceous material is usually 0.5% by mass or more and 30% by mass or less, preferably 1% by mass or more and 25% by mass or less, more preferably 2% by mass or more and 20% by mass or less. When this content is too large, the amorphous material portion of the negative electrode material increases, and the reversible capacity when the battery is assembled tends to be small. On the other hand, if the content is too small, the amorphous Si compound carbon particles (A) that are the core are not uniformly coated and strong granulation is not performed, and the particle size becomes too small when pulverized after firing. Tend.

In addition, the content (coverage) of the amorphous substance derived from the organic compound finally obtained is based on the amount of the Si composite carbon particles (A) to be used, the amount of the organic compound that becomes the carbonaceous material, and JIS K 2270. It can be calculated by the following formula (4) based on the residual carbon ratio measured by the micro method.

Formula (4)
Carbonaceous material content (% by mass)
= (Mass of organic compound to be carbonaceous material × residual carbon ratio × 100) / {total mass of graphite particles and Si compound particles contained in sample (Si composite carbon particles (A)) + (organic to be carbonaceous material) Compound mass x residual carbon ratio)}

Method (ii) may include a pulverization process, a particle size classification process, and a mixing process with another negative electrode active material, in addition to the carbonaceous material coating process described above.

(Method (iii))
Examples of the method for producing the Si composite carbon particles (A) in which the carbon compound is attached to or coated on the outer periphery of the Si compound particles as the nucleus described above (solid phase reaction, liquid phase reaction, sputtering, chemical vapor deposition, etc.) The method using is mentioned.

Here, a synthesis method using a solid phase reaction will be described. The solid phase reaction is a method of synthesizing composite particles by weighing and mixing solid raw materials such as powders so as to have a predetermined composition and then performing a heat treatment. With respect to the Si composite carbon particles (A) in the present invention, for example, a method in which an Si compound particle and an organic compound that becomes a carbonaceous material are brought into contact with each other at a high temperature to cause a reaction is applicable.

The contact between the Si compound particles and the carbonaceous organic compound in the solid phase reaction step is performed under an oxygen-free (low oxygen) environment at a high temperature of 1000 ° C. or higher, and thus an apparatus capable of setting such an environment. For example, the process can be performed using a high-frequency induction heating furnace, a graphite furnace, an electric furnace, or the like. The temperature conditions in the solid phase reaction step are not particularly limited, but are usually higher than the melting temperature of the Si compound particles, preferably 10 ° C. or higher, more preferably 30 ° C. higher than the melting temperature of the Si compound particles. It is. The specific temperature is usually 1420 ° C. or higher, preferably 1430 ° C. or higher, more preferably 1450 ° C. or higher, and usually 2000 ° C. or lower, preferably 1900 ° C. or lower, more preferably 1800 ° C. or lower. The oxygen-free (low oxygen) environment is preferably performed under an inert atmosphere such as argon and under reduced pressure (vacuum). When performed under reduced pressure (vacuum), the pressure is usually 2000 Pa or less, preferably 1000 Pa or less. More preferably, it is 500 Pa or less. Further, the treatment time is usually 0.1 hour or longer, preferably 0.5 hour or longer, more preferably 1 hour or longer, and usually 3 hours or shorter, preferably 2.5 hours or shorter, more preferably 2 hours or shorter.

Method (iii) may include a pulverization process, a particle size classification process, and a mixing process with another negative electrode active material, in addition to the above-described solid phase reaction process.

Examples of the coarse pulverizer used in the pulverization process include a jaw crusher, an impact crusher, and a cone crusher. Examples of the intermediate pulverizer include a roll crusher and a hammer mill. Examples of the fine pulverizer include a ball mill, A vibration mill, a pin mill, a stirring mill, a jet mill, etc. are mentioned.

Among these, a ball mill, a vibration mill, and the like are preferable from the viewpoint of processing speed because of a short grinding time.

The pulverization speed is appropriately set depending on the type and size of the apparatus. For example, in the case of a ball mill, it is usually 50 rpm or more, preferably 100 rpm or more, more preferably 150 rpm or more, and further preferably 200 rpm or more. Moreover, it is 2500 rpm or less normally, Preferably it is 2300 rpm or less, More preferably, it is 2000 rpm or less. If the speed is too high, control of the particle size tends to be difficult, and if the speed is too low, the processing speed tends to be slow.

The pulverization time is usually 30 seconds or longer, preferably 1 minute or longer, more preferably 1 minute 30 seconds or longer, and further preferably 2 minutes or longer. Moreover, it is usually 3 hours or less, preferably 2.5 hours or less, more preferably 2 hours or less. If the pulverization time is too short, particle size control tends to be difficult, and if the pulverization time is too long, the productivity of the Si composite carbon particles (A) tends to decrease.

In the case of a vibration mill, the grinding speed is usually 50 rpm or more, preferably 100 rpm or more, more preferably 150 rpm or more, and further preferably 200 rpm or more. Moreover, it is 2500 rpm or less normally, Preferably it is 2300 rpm or less, More preferably, it is 2000 rpm or less. If the speed is too high, control of the particle size tends to be difficult, and if the speed is too low, the processing speed tends to be slow.

The pulverization time is usually 30 seconds or longer, preferably 1 minute or longer, more preferably 1 minute 30 seconds or longer, and further preferably 2 minutes or longer. Moreover, it is usually 3 hours or less, preferably 2.5 hours or less, more preferably 2 hours or less. If the pulverization time is too short, the particle size control tends to be difficult, and if the pulverization time is too long, the productivity tends to decrease.

As the classification treatment condition of the classification treatment step, the opening is usually 53 μm or less, preferably 45 μm or less, more preferably 38 μm or less so as to have the above particle diameter.

There is no particular limitation on the apparatus used for the classification treatment, for example, in the case of dry sieving: a rotary sieving, a shaking sieving, a rotating sieving, a vibrating sieving, etc. can be used,
For dry airflow classification: Gravity classifier, inertial force classifier, centrifugal classifier (classifier, cyclone, etc.) can be used,
In the case of wet sieving: a mechanical wet classifier, a hydraulic classifier, a sedimentation classifier, a centrifugal wet classifier or the like can be used.

Among the above-described methods (i) to (iii), by encapsulating silicon element in the spheroidized graphite, electrode plate swelling and particle destruction can be suppressed, and the reaction between the electrolyte and silicon element can be suppressed. The method (ii) is more preferable from the viewpoint of suppressing the property.

[Composite graphite particles (B)]
The composite graphite particles (B) in the present invention will be described below.
The composite graphite particles (B) are composite particles in which a polymer that is hardly soluble in a non-aqueous electrolyte and graphite particles (C) are combined.

In the present specification, poorly soluble in a non-aqueous electrolyte means that the polymer is immersed in a solvent in which ethyl carbonate and ethyl methyl carbonate are mixed at a volume ratio of 3: 7 for 24 hours and then dried before and after immersion. The reduction rate (rate dissolved in the solvent) is 10% by mass or less.

Further, “composite of a polymer and graphite particles (C)” means that the polymer is attached to, adhered to, and combined with the surface of the graphite particles (C), and the pores of the graphite particles (C). A state in which a polymer is attached inside is shown. In order to observe such a state, for example, the cross section of a particle is analyzed by using a technique such as a field emission scanning electron microscope-energy dispersive X-ray (SEM-EDX) analysis or X-ray photoelectron spectroscopy (XPS) analysis. This can be confirmed by observation.

(Characteristics of composite graphite particles (B))
The composite graphite particles (B) of the present invention are not particularly limited as long as a polymer that is hardly soluble in the non-aqueous electrolyte described below is combined with the graphite particles (C), but the composite graphite particles (B) are as follows. It is preferable to have the following characteristics.

(A) Volume-based average particle diameter (d50) of composite graphite particles (B)
The volume-based average particle diameter (d50) (hereinafter also referred to as average particle diameter d50) of the composite graphite particles (B) is usually 1 μm or more, preferably 4 μm or more, more preferably 7 μm or more, and usually 50 μm or less. Preferably it is 40 micrometers or less, More preferably, it is 30 micrometers or less, More preferably, it is 25 micrometers or less. If the average particle size d50 is too large, the total number of particles decreases and the proportion of Si composite carbon particles (A) existing between the particles decreases. Therefore, the effect of suppressing the conduction path breakage in the non-aqueous secondary battery is reduced, and the cycle characteristics are reduced. It tends to cause a decline. On the other hand, if the average particle size d50 is too small, the specific surface area increases, so that the decomposition of the electrolyte increases and the initial efficiency tends to decrease.

(B) Aspect ratio of composite graphite particles (B) The aspect ratio of the composite graphite particles (B) is usually 1 or more, preferably 1.5 or more, more preferably 1.6 or more, still more preferably 1.7 or more, Usually, it is 4 or less, preferably 3 or less, more preferably 2.5 or less, and still more preferably 2 or less.

If the aspect ratio is too large, the particles tend to be aligned in the direction parallel to the current collector when used as an electrode, so that there are not enough continuous voids in the thickness direction of the electrode, and lithium ion mobility in the thickness direction. However, the rapid charge / discharge characteristics of the non-aqueous secondary battery tend to be reduced.

(C) Circularity of the composite graphite particles (B) The circularity of the composite graphite particles (B) is usually 0.88 or more, preferably 0.89 or more, more preferably 0.90 or more, and still more preferably 0.92. That's it. The circularity is usually 1 or less, preferably 0.99 or less, more preferably 0.98 or less, and still more preferably 0.97 or less. In addition, the spherical shape in this specification can also be expressed in the range of the circularity.

(D) Interplanar spacing of composite graphite particles (B) (d ₀₀₂ )
The interplanar spacing (d ₀₀₂ ) of the composite graphite particles (B) by the X-ray wide angle diffraction method is usually 0.337 nm or less, preferably 0.336 nm or less. When the d value is too large, the crystallinity is lowered, and the discharge capacity of the nonaqueous secondary battery tends to be lowered. On the other hand, the lower limit value of 0.3354 nm is a theoretical value of graphite.

The crystallite size (Lc) of the composite graphite particles (B) is usually 30 nm or more, preferably 50 nm or more, more preferably 100 nm or more. Below this range, the crystallinity decreases and the discharge capacity of the battery tends to decrease.

(E) Surface functional group amount of composite graphite particles (B) The composite graphite particles (B) have a surface functional group amount O / C value represented by the above formula (2) of usually 2% or more, preferably 3 %, More preferably 4%, while usually 30% or less, preferably 20% or less, more preferably 15% or less.

If this surface functional group amount O / C value is too small, it indicates that the polymer is unevenly distributed and the coating is insufficient, the effect of preventing contact with the electrolyte is poor, and the initial efficiency and cycle characteristics of the non-aqueous secondary battery are reduced. There is a tendency for the amount of gas to increase. On the other hand, if the surface functional group amount O / C value is too large, it indicates an excessive coating state of the polymer, which causes an increase in resistance and tends to deteriorate the input / output characteristics.

(F) BET specific surface area (SA) of composite graphite particles (B)
The specific surface area of the composite graphite particles (B) measured by the BET method is usually 0.1 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1 m ² / g or more, and further preferably 2 m ^2. / G or more, particularly preferably 3 m ² / g or more. Moreover, it is 20 m < ² > / g or less normally, Preferably it is 15 m < ² > / g or less, More preferably, it is 12 m < ² > / g or less, More preferably, it is 11 m < ² > / g or less, Most preferably, it is 8 m < ² > / g or less. Further, the specific surface area of the composite graphite particles (B) usually tends to be smaller than the specific surface area of the graphite particles before being combined with the polymer.

If the specific surface area is too small, the number of sites where lithium ions enter and exit is small, and the high-speed charge / discharge characteristics and output characteristics are inferior. On the other hand, if the specific surface area is too large, the active material becomes excessively active with respect to the electrolyte solution Therefore, there is a tendency that a high capacity battery cannot be manufactured.

(G) Tap density of composite graphite particles (B) The tap density of the composite graphite particles (B) is usually preferably 0.5 g / cm ³ or more, preferably 0.6 g / cm ³ or more, and more preferably 0.7 g / cm ³ or more. More preferred. Further, usually 1.5 g / cm ³ or less and 1.2 g / cm ³ or less are preferable, and 1.1 g / cm ³ or less is more preferable. If the tap density is too low, the non-aqueous secondary battery is inferior in high-speed charge / discharge characteristics, and if the tap density is too high, the cycle characteristics may be deteriorated due to a reduction in the effect of suppressing the conduction path breakage.

Also, the tap density of the composite graphite particles (B) usually tends to be the same as or smaller than the tap density of the graphite particles before being combined with the polymer.

In the present invention, for the tap density, a sample (composite graphite particle (B)) is dropped through a sieve having a mesh size of 300 μm through a cylindrical tap cell having a diameter of 1.6 cm and a volume capacity of 20 cm ³ using a powder density measuring device. After the cell is fully filled, a tap with a stroke length of 10 mm is performed 1000 times, and the density obtained from the volume at that time and the weight of the sample is defined as the tap density.

(H) DBP oil absorption of composite graphite particles (B) The DBP (dibutyl phthalate) oil absorption of composite graphite particles (B) is usually 65 ml / 100 g or less, preferably 60 ml / 100 g or less, more preferably 55 ml / 100 g or less. More preferably, it is 53 ml / 100 g or less. Moreover, it is 30 ml / 100g or more normally, Preferably it is 40 ml / 100g or more. If the DBP oil absorption is too large, it tends to cause streaking during the application of the slurry containing the carbon material of the present invention when forming the negative electrode, and if it is too small, there is almost no pore structure in the particles. The reaction area with the electrolytic solution tends to be short.

(I) Press load (Pb) of composite graphite particles (B)
The press load (Pb) of the composite graphite particles (B) is usually 10 kg / 5 cm or more, preferably 100 kg / 5 cm or more, more preferably 150 kg / 5 cm or more, still more preferably 200 kg / 5 cm or more, and usually 800 kg / 5 cm or less. Preferably it is 600 kg / 5 cm or less, More preferably, it is 500 kg / 5 cm or less, More preferably, it is 400 kg / 5 cm or less, Most preferably, it is 350 kg / 5 cm or less.

When the press load (Pb) of the composite graphite particles (B) is too large, the effect of relaxing the expansion of the Si composite carbon particles (A) is reduced. If the cycle characteristics tend to be reduced, and if the cycle characteristics are too small, the flow path of the electrolyte solution is crushed due to excessive particle deformation, and the input / output characteristics tend to be reduced.

[Production method of composite graphite particles (B)]
The composite graphite particles (B) in the present invention are not particularly limited as long as they are composite particles in which at least the graphite particles (C) and a polymer that is hardly soluble in a non-aqueous electrolyte solution are combined, but preferably graphite particles (C ) In the form of spherical composite particles in which a polymer that is hardly soluble in a non-aqueous electrolyte is attached or attached. Although the manufacturing method is not specifically limited, For example, the following three methods are mentioned.

<Method (i)>
In the method (i), a polymer that is hardly soluble in a non-aqueous electrolyte is dissolved in an organic solvent or water, or a mixed solvent of organic solvent / water, and the solution is mixed with graphite particles (C), and then heated and / or It is a method having a step of drying by reduced pressure.

The solvent to be used is not particularly limited as long as a poorly soluble polymer dissolves in the non-aqueous electrolyte, but preferable examples include water, ethyl methyl ketone, toluene, acetone, methyl isobutyl ketone, ethanol, methanol, and the like. It is done. Among these, water, ethyl methyl ketone, acetone, methyl isobutyl ketone, ethanol, and methanol are more preferable because of cost and ease of drying.

The concentration of the polymer in a solution obtained by dissolving a polymer that is hardly soluble in a non-aqueous electrolyte solution in a solvent is usually 70% by mass or less, preferably 60% by mass or less, and preferably 50% by mass or less. It is more preferable. When it deviates from this range, the polymer solution does not sufficiently permeate into the pores of the graphite particles (C), and the contained polymer is present non-uniformly, and the effect tends to be difficult to be obtained. About the said drying (heating) temperature, it is 300 degrees C or less normally, and 250 degrees C or less is preferable. Moreover, it is 50 degreeC or more normally, and 100 degreeC or more is preferable. Above this temperature, there is a tendency that the polymer is partially decomposed or the interaction between the graphite particles (C) and the polymer becomes weak, and the effects such as reduction of specific surface area, improvement of cycle characteristics, shortening of charging speed, etc. are reduced. is there. On the other hand, the battery performance due to residual solvent tends to decrease because the solvent does not dry at a sufficient rate below this temperature.

Further, when the graphite particle (C) and polymer solution is dried under reduced pressure, the pressure is usually 0 MPa or less and −0.2 MPa or more in gauge pressure notation. If it is this range, it can dry comparatively efficiently. The pressure is preferably −0.03 MPa or less, and preferably −0.15 MPa or more.

<Method (ii)>
In addition, the method (ii) for producing the composite graphite particles (B) is based on the fact that a polymer that is hardly soluble in the non-aqueous electrolyte has an adsorptivity to the surface of the graphite particles (C). The graphite particles (C) are placed in a solution of a poorly soluble polymer and stirred, and after removing the poorly soluble polymer solution from the excess nonaqueous electrolyte by filtration, the graphite particles and the nonaqueous electrolyte are dried. This is a method having a step of combining a hardly soluble polymer with a polymer. Furthermore, it is preferable to heat-treat after drying.

As a method for measuring the solution concentration of a polymer that is sparingly soluble in the non-aqueous electrolyte solution, for example, in the case of an aqueous solution, a method of measuring with a moisture meter such as Sartorius moisture meter MA45, and in the case of an organic solvent solution, the solution is made of an aluminum cup. For example, a method of calculating the original concentration based on a weight difference before and after the operation in which the solvent is blown off in a vacuum dryer in a container such as the like.

<Method (iii)>
Method (iii) is a mechanochemical treatment of a powder obtained by mixing graphite particles (C) and a polymer powder that is sparingly soluble in a non-aqueous electrolyte solution, whereby polymer particles that are sparingly soluble in a non-aqueous electrolyte solution are formed on the graphite particle surface. It is a method of compounding. Preferable apparatuses used for mechanochemical treatment include, for example, a hybridization system (manufactured by Nara Machinery Co., Ltd.), a mechanofusion system (manufactured by Hosokawa Micron Corporation), and the like. Of these, the mechanofusion system is preferred.

Among the methods (i) to (iii), the method (i) is more preferable in terms of simplicity.

(Content of polymer hardly soluble in non-aqueous electrolyte solution in composite graphite particles (B))
The content of the polymer hardly soluble in the non-aqueous electrolyte solution in the composite graphite particles (B) is usually 0.01% by mass or more, preferably 0.05% by mass or more, as a blending ratio with respect to the graphite particles (C). More preferably, it is 0.1 mass% or more, More preferably, it is 0.2 mass% or more, Most preferably, it is 0.3 mass% or more. Moreover, it is 10 mass% or less normally, 5 mass% or less is preferable, 2 mass% or less is more preferable, 1.5 mass% or less is further more preferable, 1 mass% or less is especially preferable, and 0.6 mass% or less is the most. preferable. If the content of the polymer that is hardly soluble in the non-aqueous electrolyte is too large, the charge / discharge capacity of the non-aqueous secondary battery tends to decrease, and the input / output characteristics tend to decrease due to the increase in charge transfer resistance. When the content of the hardly soluble polymer is too small, the side reaction reaction suppressing effect of the electrolyte solution is poor, and the initial charge / discharge efficiency and the cycle characteristics tend to be lowered.

The content of the polymer that is hardly soluble in the non-aqueous electrolyte solution in the composite graphite particles (B) is, as a general rule, when the solution containing the polymer that is hardly soluble in the non-aqueous electrolyte solution is dried at the time of manufacture. The amount of the slightly soluble polymer added to the liquid is, for example, filtered, and when the poorly soluble polymer is removed from the non-aqueous electrolyte not attached to the composite graphite particles (B), It can be calculated from the weight loss in the TG-DTA analysis or the amount of the polymer hardly soluble in the non-aqueous electrolyte contained in the filtrate.

The above confirmation may be performed when the composite graphite particles (B) are manufactured, or may be detected from a product manufactured as a negative electrode or a battery.

-Slightly soluble polymer in non-aqueous electrolyte Next, the poorly soluble polymer in the non-aqueous electrolyte that is a component of the composite graphite particles (B) in the present invention will be described.

The polymer that is sparingly soluble in the non-aqueous electrolyte may be any polymer that is sparingly soluble in the non-aqueous electrolyte and can be combined with the graphite particles, but is a polymer having an ionic group. It is preferable. The definition of “slightly soluble” is as described above.

In the present invention, the ionic group is a group capable of generating an anion or cation in water.

Specific examples include carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, phosphonic acid groups, and salts thereof. Examples of the salt include lithium salt, sodium salt, potassium salt and the like. Among these, a sulfonic acid group and a lithium salt or a sodium salt thereof are preferable from the viewpoint of the initial irreversible capacity in the case of a non-aqueous secondary battery.

The polymer having the ionic group hardly swells in the non-aqueous electrolyte and has high adsorptivity to the graphite particles.

The weight average molecular weight of the polymer that is hardly soluble in the non-aqueous electrolyte is not particularly limited, but is usually 500 or more, preferably 1000 or more, more preferably 2000 or more, and further preferably 2500 or more. On the other hand, the weight average molecular weight is usually 1,000,000 or less, preferably 500,000 or less, more preferably 300,000 or less, and still more preferably 200,000 or less.

In this specification, the weight average molecular weight is a weight average molecular weight in terms of standard polystyrene measured by gel permeation chromatography (GPC) using a solvent as tetrahydrofuran (THF), or the solvent is aqueous or N, N-dimethylformamide. It is a weight average molecular weight in terms of standard polyethylene glycol measured by GPC of (DMF) or dimethyl sulfoxide (DMSO).

The polymer that is hardly soluble in the non-aqueous electrolyte used in the present invention preferably has a functional group that acts and adsorbs on a functional group present on the basal surface or surface of the graphite particles. Examples of the functional group that acts and adsorbs on the basal surface of the graphite particle include an aromatic ring group, and the functional group that acts and adsorbs on the functional group present on the surface of the graphite particle includes an amino group.

Hereinafter, a polymer having an aromatic ring group and a polymer having an amino group will be described as preferred embodiments of the polymer that is hardly soluble in the non-aqueous electrolyte solution used in the present invention.

(1. Polymer having an aromatic ring group)
In the polymer having an aromatic ring group, which is one of the preferred embodiments of the polymer that is hardly soluble in the non-aqueous electrolyte, the π-conjugated structure of the aromatic ring is adsorbed by π-π interaction with the basal surface of the graphite particles (C). Therefore, it is considered that the basal surface of the graphite particles (C) is effectively covered. Therefore, it is considered that the polymer can effectively suppress the reaction between the basal surface of the graphite particles (C) and the non-aqueous electrolyte and the generation of gas, and suppress the increase in negative electrode resistance.

In the present specification, the π-conjugated structure is an unsaturated cyclic structure having a structure in which atoms having π electrons are arranged in a ring, satisfying the Hückel rule, and π electrons are delocalized on the ring. The ring has a planar structure.

Examples of the monomer compound constituting the polymer having an aromatic ring group include furan, pyrrole, imidazole, thiophene, phosphole, pyrazole, oxazole, isoxazole, thiazole, and monocyclic six-membered benzene. , Pyridine, pyrazine, pyrimidine, pyridazine, triazine, bicyclic 5-membered ring + 6-membered ring benzofuran, isobenzofuran, indole, isoindole, benzothiophene, benzophosphole, benzimidazole, purine, indazole, benzoxazole, benzo Examples thereof include cyclic compounds having a skeleton such as isoxazole, benzothiazole, bicyclic 6-membered ring + 6-membered ring naphthalene, quinoline, isoquinoline, quinoxaline, quinazoline, cinnoline, polycyclic anthracene and pyrene.

Among these, a compound having a benzene ring and a compound having a naphthalene ring are preferable from the viewpoint of suppressing the generation of gas when a non-aqueous secondary battery is used.

Examples of the monomer serving as the structural unit constituting the polymer having an aromatic ring group include a monomer having an ionic group and a monomer having an aromatic ring. Moreover, the monomer which has both an ionic group and an aromatic ring may be sufficient.

In this case, the polymer having an aromatic ring group may be a copolymer of a monomer having an ionic group and no aromatic ring and a monomer having an aromatic ring and no ionic group. A polymer of a monomer having both an ionic group and an aromatic ring may be used. Further, it may be a mixture of a monomer polymer having an ionic group and a monomer polymer having an aromatic ring.

Examples of the monomer having an ionic group and an aromatic ring include styrene sulfonic acid, naphthalene carboxylic acid, naphthalene sulfonic acid, vinyl naphthalene carboxylic acid, vinyl naphthalene sulfonic acid, vinyl aminonaphthalene, anthracene carboxylic acid, vinyl anthracene carboxylic acid. , Anthracene sulfonic acid, vinyl anthracene sulfonic acid, vinyl aminoanthracene, aniline, aniline sulfonic acid, vinyl benzoate and salts thereof.

Among these, sodium styrenesulfonate, lithium styrenesulfonate, sodium naphthalenesulfonate, and lithium naphthalenesulfonate are preferable.

Furthermore, examples of the monomer having an ionic group and not having an aromatic ring include vinyl sulfonic acid, lithium vinyl sulfonate, sodium vinyl sulfonate, acrylic acid, sodium acrylate, lithium acrylate, etc., methacrylic acid Examples of the monomer having an aromatic ring and not having an ionic group include styrene, benzyl acrylate, and benzyl methacrylate.

Specific examples of polymers containing structural units derived from such monomers include styrene-vinyl sulfonic acid copolymers, styrene-vinyl sulfonic acid copolymers, styrene-vinyl sulfonic acid copolymers, polystyrene sulfonic acid. Styrene-styrene sulfonic acid copolymer, polyvinyl benzoic acid, styrene-vinyl benzoic acid copolymer, polyvinyl benzocyclobutene, vinyl benzocyclobutene-styrene sulfonic acid copolymer, vinyl benzocyclobutene-vinyl sulfonic acid copolymer Polymer, vinyl benzocyclobutene-acrylic acid copolymer, vinyl benzocyclobutene-methacrylic acid copolymer, polyvinyl naphthalene carboxylic acid, polyvinyl naphthalene sulfonic acid, polyvinyl amino naphthalene, polyvinyl naphthalene sulfonic acid, vinyl naphthalene -Acrylic acid copolymer, vinyl naphthalene-methacrylic acid copolymer, vinyl naphthalene-vinyl sulfonic acid copolymer, vinyl naphthalene-styrene sulfonic acid copolymer, vinyl naphthalene sulfonic acid-styrene sulfonic acid copolymer, vinyl naphthalene Carboxylic acid-styrenesulfonic acid copolymer, vinylnaphthalenesulfonic acid-styrenesulfonic acid copolymer, naphthalenesulfonic acid formalin condensate, polyvinylanthracene-carboxylic acid, polyvinylanthracenesulfonic acid, polyvinylaminoanthracene, polyvinylanthracenecarboxylic acid, polyvinyl Anthracenesulfonic acid, polyvinylaminoanthracene, vinylanthracene-acrylic acid copolymer, vinylnaphthalene-methacrylic acid copolymer, vinylanthracene-vinyls Phosphonic acid copolymer, vinylanthracene-styrenesulfonic acid copolymer, vinylanthracenesulfonic acid-styrenesulfonic acid copolymer, vinylanthracenecarboxylic acid-styrenesulfonic acid copolymer, vinylanthracenesulfonic acid-styrenesulfonic acid copolymer Examples include coalesces, anthracene sulfonic acid formalin condensates, and salts thereof.

From the viewpoint of effectively suppressing gas generation, polystyrene sulfonic acid, polyvinyl benzocyclobutene, polyvinyl naphthalene carboxylic acid, polyvinyl naphthalene sulfonic acid, polyvinyl amino naphthalene, polyvinyl naphthalene sulfonic acid, naphthalene sulfonic acid formalin condensate, polyvinyl anthracene sulfone Acid, polyvinylaminoanthracene, polyvinylanthracenecarboxylic acid, polyvinylanthracenesulfonic acid, anthracenesulfonic acid formalin condensate, and salts thereof are more preferable, among which polystyrenesulfonic acid, polyvinylbenzocyclobutene, naphthalenesulfonic acid formalin condensate, and these Lithium salt and sodium salt are highly adsorbable on the active material surface, especially the graphite basal surface, and there is little elution into the electrolyte. Preferred.

As the polymer having an aromatic ring group described above, a commercially available polymer may be used, or the polymer may be synthesized by a known method. In addition, in this invention, it can be used individually by 1 type or in combination of 2 or more types.

(2. Polymer having amino group)
The polymer having an amino group which is one of the preferred embodiments of the polymer that is hardly soluble in the non-aqueous electrolyte used in the present invention, the amino group acts on the functional group on the surface of the graphite particles (C), and the graphite particles ( The surface activity of C) is suppressed. In addition, the amino group improves the adsorptivity between the surface of the graphite particles (C) and the polymer, so that the decomposition of the electrolytic solution is suppressed and further excellent battery cycle characteristics are exhibited. The

The amino group in the polymer having an amino group is not particularly limited, and examples thereof include a primary amino group, a secondary amino group, a tertiary amino group, and a quaternary ammonium group.

Among these, a primary amino group, a secondary amino group, and a tertiary amino group are preferable, and a primary amino group and a secondary amino group are particularly preferable in terms of high adhesiveness or reactivity with the active material surface functional group.

Hereinafter, the polymer having an amino group will be described.
The polymer having an amino group is preferably at least one of an amine homopolymer and a copolymer containing an ethylenically unsaturated group. Specifically, it is preferably at least one of homopolymers and copolymers of vinylamine, allylamine or derivatives thereof.

As a polymer having an amino group, a homopolymer of vinylamine, allylamine or a derivative thereof, a copolymer of any two or more of the above vinylamine, allylamine or a derivative thereof, or the above vinylamine, allylamine or a derivative thereof Any one or more of them and one or more copolymers of other components can be used.

Furthermore, maleic acid, acrylamide, sulfur dioxide, phosphorus oxide, sulfur oxide, organic acid, boron compound, etc. may be used as other components. Examples of the copolymer containing other components include diallylamine-maleic acid copolymer, diallylamine-sulfur dioxide copolymer, and the like.

The polymer having an amino group is preferably vinylamine, allylamine, N-alkyl-substituted allylamine (such as N-methylallylamine), N, N-dialkyl-substituted allylamine (N) from the viewpoint of initial charge / discharge efficiency of the non-aqueous secondary battery. , N-dimethylallylamine, etc.) or diallylamine homopolymers or copolymers, more preferably polyvinylamine, polyallylamine, poly-N-methylallylamine, poly-N, N-dimethylallylamine, polydiallylamine, poly-N-methyl Diallylamine, polydiallylamine-sulfur dioxide copolymer, most preferably polyvinylamine, polyallylamine or polydiallylamine-sulfonyl copolymer.

The polymer having an amino group may be in the form of a salt such as acetate, hydrochloride, sulfate, amidosulfate or ammonium salt. The amine moiety may be modified such as partially ureated or partially carbonylated.

In the present invention, the polymer that is hardly soluble in the non-aqueous electrolyte may be a mixture of two or more kinds of polymers, and the mixture of the polymer having an aromatic ring group and the polymer having an amino group described above is a graphite particle. (C) It is preferable because of its high adsorptivity to the surface, lithium ion conductivity, and productivity.

Since the polymer that is hardly soluble in the non-aqueous electrolyte described above can efficiently and selectively coat the surface of the graphite particles with a small amount, polyvinylamine, polyallylamine, poly-N-methylallylamine, poly- N, N-dimethylallylamine, polydiallylamine, polyN-methyldiallylamine, diallylamine-sulfur dioxide copolymer, polystyrene sulfonic acid, styrene sulfonic acid-maleic acid copolymer, naphthalene sulfonic acid formalin condensate, benzyl methacrylate-styrene sulfone It is preferably an acid copolymer, an ethylene glycol monophenyl ether acrylate-styrene sulfonic acid copolymer, a propyl phenyl ether methacrylate-styrene sulfonic acid copolymer, or a salt thereof.

(3. Other polymers)
The composite graphite particles (B) used in the present invention may further contain other polymers in addition to the above-mentioned polymer that is hardly soluble in the non-aqueous electrolyte solution, and particularly have a lithium ion coordinating group. It preferably contains a polymer. The lithium ion coordinating group is defined as a group having a non-conjugated electron pair, and is not particularly limited as long as it is such a group, but an oxyalkylene group, a sulfonyl group, a sulfo group And at least one selected from the group consisting of a boron-containing functional group, a carbonyl group, a carbonate group, a phosphorus-containing functional group, an amide group, and an ester group. In addition, the polymer having a lithium ion coordinating group preferably has a structure of an oxyalkylene group or a sulfonyl group from the viewpoint of high coordination and conductivity of lithium ions.

These lithium ion coordinating groups can be expected to promote desolvation from the solvent with respect to lithium ions solvated with the electrolyte. Thereby, reductive decomposition of the electrolytic solution is suppressed, and the initial charge / discharge efficiency of the non-aqueous secondary battery can be improved. Further, the lithium ion coordinating group promotes the diffusion of lithium ions in the film of the graphite particles on which a film made of an organic compound is formed, and thus it is possible to suppress an increase in negative electrode resistance.

In the present invention, a polymer that is hardly soluble in the above non-aqueous electrolyte may have a lithium ion coordinating group. That is, a polymer that is hardly soluble in a non-aqueous electrolyte (a polymer having an aromatic ring group or a polymer having an amino group) has a monomer unit used for a polymer having a lithium ion coordination group, which will be described below. May be.

Hereinafter, a polymer having a lithium ion coordination group will be described.
In the composite graphite particles (B) used in the present invention, the composition ratio of the polymer having a lithium ion coordinating group to the polymer that is hardly soluble in the non-aqueous electrolyte is a polymer that is hardly soluble in a sufficient amount of the non-aqueous electrolyte. Is 1 mass% to 300 mass%, preferably 2 mass% to 150 mass%, and more preferably 3 mass% or more, because it acts on the graphite particles (C) and can suppress an increase in negative electrode resistance. It is 100 mass% or less, More preferably, it is 4 to 50 mass%, Most preferably, it is 5 to 40 mass%.

A preferred embodiment of the polymer having a lithium ion coordinating group is represented by the following structural formula (1).

Wherein R ¹ and R ² are each independently a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, a glycidyl group or an epoxy group. AO is an oxyalkylene group having 2 to 5 carbon atoms. And n is an integer from 1 to 50.)

The glycidyl group is a functional group represented by the following structural formula (2), and the epoxy group is a functional group represented by the following structural formula (3).

The alkyl group in the structural formula (1) may be linear or branched, and examples thereof include alkyl groups having 1 to 20 carbon atoms. From the viewpoint of suppressing an increase in negative electrode resistance, an alkyl group having 1 to 15 carbon atoms is preferable, and an alkyl group having 1 to 10 carbon atoms is particularly preferable.

Examples of the aryl group in the structural formula (1) include an unsubstituted or alkyl group-substituted phenyl group. From the viewpoint of availability of materials, a phenyl group which is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms is preferable, and an unsubstituted phenyl group is particularly preferable.

Examples of the aralkyl group in the structural formula (1) include an unsubstituted or alkyl group-substituted benzyl group. From the viewpoint of easy availability of the material, a benzyl group which is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms is preferable, and an unsubstituted benzyl group is particularly preferable.

In the structural formula (1), R ¹ and R ² are preferably a hydrogen atom, an alkyl group, an epoxy group, or a glycidyl group, more preferably an alkyl group, from the viewpoint of the initial charge / discharge efficiency of the nonaqueous secondary battery. Group, an epoxy group and a glycidyl group, more preferably a glycidyl group.

AO in the structural formula (1) is an oxyalkylene group having 2 to 5 carbon atoms, and is preferably an oxyethylene group or an oxypropylene group from the viewpoint of suppressing an increase in negative electrode resistance.

As a preferable combination of R ¹ and R ² and AO, R ¹ and R ² are each independently a hydrogen atom, an alkyl group, an epoxy group, or a glycidyl group, and AO is an oxyalkylene group having 2 to 5 carbon atoms. Preferably there is. More preferably, R ¹ and R ² are each independently an alkyl group, an epoxy group, or a glycidyl group, and AO is an oxyalkylene group having 2 to 5 carbon atoms. More preferably, R ¹ and R ² are each independently an alkyl group, an epoxy group, or a glycidyl group, and AO is an oxyethylene group or an oxypropylene group. Most preferably, R ¹ and R ² are both glycidyl groups, and AO is a combination of oxyethylene groups or oxypropylene groups.

In the structural formula (1), n represents the number of oxyalkylene groups, and is preferably an integer of 1 to 25 from the viewpoint of suppressing increase in negative electrode resistance. When n is 2 or more, a plurality of AOs may be the same as or different from each other.

Specific examples of the polymer having a lithium ion coordinating group include polyoxyethylene glycol diglycidyl ether, polyoxypropylene glycol diglycidyl ether, butoxypolyethylene glycol glycidyl ether and the like.

The weight average molecular weight of the polymer having a lithium ion coordinating group is not particularly limited, but is usually 50 or more, preferably 150 or more, more preferably 300 or more, and further preferably 350 or more. On the other hand, the weight average molecular weight is usually 1 million or less, preferably 500,000 or less, more preferably 10,000 or less, and still more preferably 5000 or less.

In addition, the polymer which has a lithium ion coordination group can be used individually or in combination of 2 or more types.

・ Graphite particles (C)
As the graphite particles (C) contained in the composite graphite particles (B) used in the present invention, either natural graphite or artificial graphite may be used. As graphite, those with few impurities are preferable, and they are used after being subjected to various purification treatments as necessary.

The shape of the graphite particles (C) is not particularly limited, and may be appropriately selected from spherical, flaky, fibrous, amorphous particles, particles obtained by collecting or bonding a plurality of particles non-parallelly, and the like. One preferred embodiment of the present invention is spherical.

Examples of the natural graphite include scaly graphite, scaly graphite, and soil graphite. The production area of the scaly graphite is mainly Sri Lanka, the production area of the scaly graphite is Madagascar, China, Brazil, Ukraine, Canada, etc., and the main production area of the soil graphite is the Korean Peninsula, China, Mexico, etc. It is.

Among these natural graphites, soil graphite generally has a small particle size and low purity. On the other hand, scaly graphite and scaly graphite have advantages such as a high degree of graphitization and a low amount of impurities, and therefore can be preferably used in the present invention.

The artificial graphite includes graphite particles such as coke, needle coke, and high-density carbon material produced by heat-treating pitch raw materials.

Specific examples of artificial graphite include coal tar pitch, coal heavy oil, atmospheric residue, petroleum heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenylene, polyvinyl chloride, Organic substances such as polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, imide resin are usually baked at a temperature in the range of 2500 ° C to 3200 ° C. And graphitized ones.

As the graphite particles (C) used in the present invention, natural graphite, artificial graphite, coke powder, needle coke powder, and powders of graphitized materials such as resin can be used as described above. Of these, natural graphite is preferable from the viewpoints of the high discharge capacity of the non-aqueous secondary battery and the ease of production.

(Sphericalized graphite particles (C))
The composite graphite particles (B) are preferably spherical from the viewpoint of suppressing swelling when the electrode is used as an electrode and improving the packing density. In order to obtain such composite graphite particles (B), for example, spheroidized graphite particles (C) can be used. Hereinafter, a method of performing the spheroidization process will be described, but the method is not limited to this method.

As an apparatus used for the spheroidizing treatment, for example, an apparatus that repeatedly gives mechanical action such as compression, friction, shearing force, etc. including interaction between graphite particles, mainly to impact force, to particles can be used. .

Specifically, it has a rotor with a large number of blades installed inside the casing, and the rotor rotates at a high speed, so that the graphite particles (C) introduced into the casing have impact compression, friction, shearing force, etc. An apparatus that provides a mechanical action and performs surface treatment is preferred. Moreover, it is preferable to have a mechanism that repeatedly gives mechanical action by circulating graphite.

Preferable apparatuses that give mechanical action to graphite particles include, for example, a hybridization system (manufactured by Nara Machinery Co., Ltd.), a kryptron (manufactured by Earth Technica), a CF mill (manufactured by Ube Industries), and a mechanofusion system (Hosokawa Micron) And theta composer (manufactured by Deoksugaku Kosakusha). Among these, a hybridization system manufactured by Nara Machinery Co., Ltd. is preferable.

When processing using the apparatus, for example, the peripheral speed of the rotating rotor is usually 30 m / second or more and 100 m / second or less, preferably 40 m / second or more and 100 m / second or less, and 50 m / second or more and 100 m / second or less. It is more preferable to set it to 2 seconds or less. Further, the treatment that gives mechanical action to the graphite particles can be performed simply by passing the graphite, but it is preferable to circulate or stay the graphite in the apparatus for 30 seconds or more, and to treat the inside of the apparatus for 1 minute or more. More preferably, the treatment is performed by circulation or retention.

(Graphite particles coated with carbonaceous material (C))
As the graphite particles (C) contained in the composite graphite particles (B) used in the present invention, those appropriately selected from the graphite particles described in the section of the Si composite carbon particles (A) described above are preferably used. Moreover, as graphite particle | grains (C), you may use what coat | covered at least one part of the surface with the carbonaceous material.

In the coating treatment, although not particularly limited, for example, using the above-described graphite particles as a core material, using the organic compound that becomes the carbonaceous material described above as a coating raw material, after mixing or coating these, by firing these, Graphite particles (C) coated with a carbonaceous material can be obtained.

When the firing temperature is usually 600 ° C. or higher, preferably 700 ° C. or higher, more preferably 900 ° C. or higher, usually 2000 ° C. or lower, preferably 1500 ° C. or lower, more preferably 1200 ° C. or lower, amorphous carbon is obtained as a carbonaceous material. When a heat treatment is usually performed at 2000 ° C. or higher, preferably 2500 ° C. or higher, and usually 3200 ° C. or lower, a graphitized product is obtained as a carbonaceous material.

(Amorphous content)
The content of the carbonaceous material in the graphite particles (C) coated with the carbonaceous material is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% or more as a ratio to the core material. In particular, the content is 0.7% by mass or more, and the content is usually 20% by mass or less, preferably 15% by mass or less, more preferably 10% by mass or less, particularly preferably 7% by mass or less, and most preferably. Is 5% by mass or less.

If the content is too high, the carbon material will be damaged and material destruction will occur when rolling at a sufficient pressure to achieve high capacity in non-aqueous secondary batteries, and charge and discharge during the initial cycle will occur. There is a tendency to increase the irreversible capacity and decrease the initial efficiency.

On the other hand, if the content is too small, the effect of coating tends to be difficult to obtain. That is, the side reaction with the electrolyte in the battery cannot be sufficiently suppressed, and the charge / discharge irreversible capacity during the initial cycle tends to increase and the initial efficiency tends to decrease.

The content of the carbonaceous material can be calculated by the following formula (4) from the mass of the graphite particles, the amount of the organic compound that becomes the carbonaceous material, and the residual carbon ratio measured by a micro method based on JIS K 2270. it can.

Formula (4)
Carbonaceous material content (% by mass)
= (Mass of organic compound to be carbonaceous material x residual carbon ratio x 100) / {mass of graphite particles + (mass of organic compound to be carbonaceous material x residual carbon ratio)}

[Carbon material for negative electrode of non-aqueous secondary battery]
The carbon material for a non-aqueous secondary battery negative electrode according to the present invention contains the Si composite carbon particles (A) and the composite graphite particles (B) described above, thereby ensuring the flow path of the electrolyte when the electrode plate is formed. It is possible to achieve a negative electrode structure in which particles are in contact with each other, and a non-aqueous secondary battery with high capacity and low loss and excellent cycle characteristics can be obtained.

Hereinafter, preferred characteristics of the carbon material for a non-aqueous secondary battery negative electrode of the present invention will be described. In addition, various characteristics of the carbon material of the present invention are weighted by values of corresponding characteristics of the Si composite carbon particles (A) and composite graphite particles (B) constituting the carbon material, and other materials described later when present. By averaging, it is roughly predictable.

(A) Ratio (Pa / Pb) of press load (Pa) of Si composite carbon particles (A) and press load (Pb) of composite graphite particles (B)
Ratio of the press load (Pa) value of the Si composite carbon particles (A) and the press load (Pb) of the composite graphite particles (B) in the carbon material for a nonaqueous secondary battery negative electrode of the present invention (Pa / Pb) The value of is usually greater than 1, preferably 3 or more, more preferably 5 or more, more preferably 5.5 or more, particularly preferably 5.8 or more, most preferably 6 or more, usually 30 or less, preferably 25 or less. More preferably, it is 20 or less, More preferably, it is 15 or less, Especially preferably, it is 10 or less, Most preferably, it is 8 or less.

When the value of (Pa / Pb) is too large, a large force is required at the time of producing the negative electrode. As a result, the active material is destroyed, and the irreversible capacity and cycle characteristics of the nonaqueous secondary battery may be deteriorated.

(B) Press load of carbon material for non-aqueous secondary battery negative electrode The value of the press load of the carbon material for non-aqueous secondary battery negative electrode of the present invention is usually 200 kg / 5 cm or more, preferably 300 kg / 5 cm or more, more preferably 400 kg / 5 cm or more, more preferably 500 kg / 5 cm or more, particularly preferably 550 kg / 5 cm or more, most preferably 600 kg / 5 cm or more, and usually 3000 kg / 5 cm or less, preferably 2000 kg / 5 cm or less, more preferably 1700 kg / 5 cm or less. More preferably, it is 1500 kg / 5 cm or less, particularly preferably 1000 kg / 5 cm, most preferably 900 kg / 5 cm or less.

If the value of the press load is too large, it will be difficult to press the electrode to the desired density, and it will not be possible to press to the target density. In addition, since a large residual stress is generated in the electrode during pressing, the electrode tends to expand during electrode thermal drying or charge / discharge. On the other hand, if it is too small, the particle deformation cannot be sufficiently suppressed in the press at the time of producing the negative electrode, so that the ability to secure the flow path of the electrolytic solution is lowered, and the input / output characteristics tend to be lowered.

(C) X-ray parameter of carbon material for non-aqueous secondary battery negative electrode The surface spacing (d ₀₀₂ ) of the 002 plane by the X-ray wide angle diffraction method of the carbon material for a non-aqueous secondary battery negative electrode of the present invention is usually 0. It is 337 nm or less, preferably 0.336 nm or less. If the d002 value is too large, it indicates that the graphite crystallinity is low, and the initial irreversible capacity may increase when a non-aqueous secondary battery is used. On the other hand, since the theoretical value of the interplanar spacing of the 002 plane of graphite is 0.3354 nm, the d value is usually 0.3354 nm or more.

In addition, the crystallite size (Lc) of the carbon material for a nonaqueous secondary battery negative electrode of the present invention is usually 30 nm or more, preferably 50 nm or more, more preferably 100 nm or more. Below this range, the crystallinity decreases and the discharge capacity of the battery tends to decrease. The lower limit of Lc is the theoretical value of graphite.

(D) Volume-based average particle diameter of carbon material for negative electrode of non-aqueous secondary battery (d50)
The average particle diameter d50 of the carbon material for a non-aqueous secondary battery negative electrode of the present invention is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, still more preferably 25 μm or less, and particularly preferably 22 μm or less. It is 1 μm or more, preferably 3 μm or more, more preferably 4 μm or more, further preferably 5 μm, and particularly preferably 7 μm or more. If the average particle diameter d50 is too small, the specific surface area becomes large, so that the decomposition of the electrolytic solution increases and the initial efficiency of the non-aqueous secondary battery tends to decrease. If the average particle diameter d50 is too large, the rapid charge / discharge characteristics are reduced. It tends to cause a decline.

(E) Aspect ratio of carbon material for nonaqueous secondary battery negative electrode The aspect ratio of the carbon material for nonaqueous secondary battery negative electrode of the present invention is usually 1 or more, preferably 1.3 or more, more preferably 1.4 or more. More preferably, it is 1.5 or more, usually 4 or less, preferably 3 or less, more preferably 2.5 or less, and still more preferably 2 or less.

(F) BET specific surface area (SA) of carbon material for negative electrode of non-aqueous secondary battery
The specific surface area according to the BET method of the carbon material for a non-aqueous secondary battery negative electrode of the present invention is usually 0.5 m ² / g or more, preferably 1 m ² / g or more, more preferably 3 m ² / g or more, still more preferably 5 m ^2. / G or more, particularly preferably 8 m ² / g or more. Moreover, it is 30 m < ² > / g or less normally, Preferably it is 20 m < ² > / g or less, More preferably, it is 18 m < ² > / g or less, More preferably, it is 16 m < ² > / g or less, Most preferably, it is 14 m < ² > / g or less. If the specific surface area is too large, the reactivity between the portion exposed to the electrolyte and the electrolyte when used as the negative electrode active material is increased, which tends to cause a decrease in initial efficiency and an increase in the amount of gas generated, making it difficult to obtain a preferable battery. Tend. When the specific surface area is too small, there are few sites where lithium ions enter and exit, and the high-speed charge / discharge characteristics and output characteristics tend to be inferior.

(G) Circularity of carbon material for non-aqueous secondary battery negative electrode The circularity of the carbon material for non-aqueous secondary battery negative electrode of the present invention is usually 0.85 or more, preferably 0.88 or more, more preferably 0.8. 89 or more, more preferably 0.90 or more. The circularity is usually 1 or less, preferably 0.99 or less, more preferably 0.98 or less, and still more preferably 0.97 or less. If the circularity is too small, particles tend to be aligned in parallel with the current collector when used as an electrode, so that there is not enough continuous void in the thickness direction of the electrode, and lithium ion mobility in the thickness direction However, the rapid charge / discharge characteristics of the non-aqueous secondary battery tend to be reduced. If the circularity is too large, there is a tendency that the effect of suppressing the conduction path breakage is reduced and the cycle characteristics are lowered.

(H) Raman R value of carbon material for nonaqueous secondary battery negative electrode The Raman R value (as defined above) of the carbon material for nonaqueous secondary battery negative electrode of the present invention is usually 1 or less, preferably 0. 8 or less, more preferably 0.6 or less, still more preferably 0.5 or less, usually 0.05 or more, preferably 0.1 or more, more preferably 0.2 or more, still more preferably 0.25 or more. is there. If the Raman R value is less than this range, the crystallinity of the particle surface becomes too high, the number of Li insertion sites decreases, and the rapid charge / discharge characteristics of the nonaqueous secondary battery tend to be reduced. On the other hand, if it exceeds this range, the crystallinity of the particle surface will be disturbed, the reactivity with the electrolyte will increase, and the charge / discharge efficiency will tend to decrease and the gas generation will increase.

(I) a tap density of nonaqueous secondary battery negative electrode carbon material of the tap density the invention of a nonaqueous secondary battery negative electrode carbon material is usually 0.6 g / cm ³ or higher, preferably 0.7 g / cm ³ or more, More preferably, it is 0.8 g / cm ³ or more, and further preferably 0.9 g / cm ³ or more. On the other hand, it is usually 1.8 g / cm ³ or less, preferably 1.5 g / cm ³ or less, more preferably 1. 3 g / cm ³ or less, more preferably 1.2 g / cm ³ or less.

If the tap density is smaller than the above range, sufficient continuous voids are not secured in the electrode, and the mobility of lithium ions in the electrolyte held in the voids is reduced, so that the rapid charge / discharge characteristics of the non-aqueous secondary battery Tends to decrease.

(Mass ratio of Si composite carbon particles (A) and composite graphite particles (B))
In the nonaqueous secondary battery negative electrode carbon material of the present invention, the mass ratio of the composite graphite particles (B) to the total amount of the Si composite carbon particles (A) and the composite graphite particles (B) is not particularly limited, but is 0 mass. %, Preferably 1% by mass or more, more preferably 10% by mass or more, further preferably 20% by mass or more, particularly preferably 30% by mass or more, and usually 90% by mass or less, preferably 80% by mass or less, More preferably, it is 70 mass% or less.

When the ratio of the Si composite carbon particles (A) to the total amount of the Si composite carbon particles (A) and the composite graphite particles (B) is too large, the initial efficiency of the non-aqueous secondary battery is decreased and the strength of the electrode plate is decreased. There is. Moreover, when there is too little ratio of composite carbon particle (A), there exists a tendency which causes the fall of a capacity | capacitance.

In obtaining the carbon material of the present invention, the mixing method is not particularly limited as long as the Si composite carbon particles (A) and the composite graphite particles (B) are uniformly mixed. As a mixer with a structure in which two frame molds rotate and revolve; a single blade, such as a dissolver that is a high-speed high-shear mixer or a butterfly mixer for high viscosity, stirs and disperses in a tank Structured device; so-called kneader-type device having a structure in which a stirring blade such as a sigma type rotates along the side surface of a semi-cylindrical mixing tank; a trimix type device with three stirring blades; rotating in a container A so-called bead mill type apparatus having a disk and a dispersion medium is used.

It also has a container with a paddle that is rotated by a shaft, and the inner wall surface of the container is formed substantially along the outermost line of rotation of the paddle, preferably in a long twin cylinder shape, and the paddle has side surfaces facing each other. A device having a structure in which many pairs are arranged in the axial direction of the shaft so as to be slidably engaged (for example, KRC reactor manufactured by Kurimoto Iron Works, SC processor, TEM manufactured by Toshiba Machine Celmac, TEX-K manufactured by Nippon Steel Works) Furthermore, it has a container in which a single inner shaft and a plurality of pavement or sawtooth paddles fixed to the shaft are arranged in different phases, and the inner wall surface is the outermost line of rotation of the paddle (External heat type) apparatus having a structure preferably formed in a cylindrical shape (e.g., Redige mixer manufactured by Redige Co., Ltd., flow share mixer manufactured by Taiyo Kiko Co., Ltd., Tsukishima Machine Co., Ltd.) Of DT dryers, etc.) can also be used. In order to perform mixing in a continuous manner, a pipeline mixer, a continuous bead mill, or the like may be used.

<Mixing with other materials>
The carbon material for a non-aqueous secondary battery negative electrode of the present invention is suitably used as a negative electrode material for a non-aqueous secondary battery by using Si composite carbon particles (A) and composite graphite particles (B) in any composition and combination. Although it can be used, it may be used as a negative electrode material for a non-aqueous secondary battery, preferably a non-aqueous secondary battery, by mixing with one or two or more other materials not corresponding to these.

When mixing other materials, the mixing amount of the other materials with respect to the total amount of the carbon material for the nonaqueous secondary battery negative electrode is usually 10% by mass or more, preferably 30% by mass or more, more preferably 50% by mass or more, Preferably it is 60 mass% or more, Most preferably, it is 70 mass% or more. Moreover, it is 90 mass% or less normally, Preferably it is the range of 80 mass% or less.

When the mixing ratio of other materials is less than the above range, the added effect tends to hardly appear. On the other hand, when the above range is exceeded, the characteristics of the carbon material for a non-aqueous secondary battery negative electrode of the present invention tend to hardly appear.

As other materials, for example, materials selected from natural graphite, artificial graphite, amorphous carbon-coated graphite, amorphous carbon, metal particles, and metal compounds can be used. Any of these materials may be used alone, or two or more of these materials may be used in any combination and composition.

As the natural graphite, for example, highly purified scaly graphite particles or scaly graphite can be used. The volume-based average particle diameter of natural graphite is usually 8 μm or more, preferably 12 μm or more, and usually 60 μm or less, preferably 40 μm or less. The natural graphite has a BET specific surface area of generally 3.5 m ² / g or more, preferably 4.5 m ² / g or more, and usually 8 m ² / g or less, preferably 6 m ² / g or less.

Examples of the artificial graphite include particles obtained by graphitizing a carbon material. For example, particles obtained by firing and graphitizing single graphite precursor particles while being powdered can be used.

As the amorphous carbon-coated graphite, for example, natural graphite or artificial graphite coated with an amorphous carbon precursor and fired particles, or natural graphite or artificial graphite coated with amorphous carbon by CVD are used. be able to.

As the amorphous carbon, for example, particles obtained by firing a bulk mesophase, or particles obtained by firing an infusible carbonizable pitch or the like can be used.

As an apparatus used for mixing the essential component of the carbon material for a non-aqueous secondary battery negative electrode and other materials, there is no particular limitation, for example,
For rotary mixers: cylindrical mixers, twin cylindrical mixers, double cone mixers, regular cubic mixers, vertical mixers,
In the case of a fixed mixer: a spiral mixer, a ribbon mixer, a Muller mixer, a Helical Flyt mixer, a Pugmill mixer, a fluidized mixer, or the like can be used.

Examples of the metal particles include Fe, Co, Sb, Bi, Pb, Ni, Ag, Si, Sn, As, Al, Zr, Cr, P, S, V, Mn, Nb, Mo, Cu, Zn, A metal selected from the group consisting of Ge, In, Ti and the like or a compound thereof is preferable. Further, an alloy composed of two or more kinds of metals may be used, and the metal particles may be alloy particles formed of two or more kinds of metal elements. Among these, a metal selected from the group consisting of Si, Sn, As, Sb, Al, Zn, and W or a compound thereof is preferable.

Examples of the metal compound include metal oxides, metal nitrides, and metal carbides. Moreover, you may use the alloy which consists of 2 or more types of metals.

Of these, Si compounds are preferred. As the Si compound, the same compound as the Si compound in the Si composite carbon particles (A) can be used.

[Negative electrode for non-aqueous secondary battery]
The present invention also relates to a negative electrode for a non-aqueous secondary battery formed using the carbon material for a non-aqueous secondary battery negative electrode of the present invention, and a specific example thereof includes a negative electrode for a lithium ion secondary battery. .

There are no particular limitations on the method for producing the negative electrode for a non-aqueous secondary battery and the selection of materials other than the carbon material for a non-aqueous secondary battery negative electrode of the present invention constituting the negative electrode for a non-aqueous secondary battery.

The negative electrode for a non-aqueous secondary battery of the present invention includes a current collector and an active material layer formed on the current collector, and the active material layer is a carbon material for a non-aqueous secondary battery negative electrode of the present invention. It contains. The active material layer preferably further contains a binder.

The binder is not particularly limited, but a binder having an olefinically unsaturated bond in the molecule is preferable. Specific examples include styrene-butadiene rubber, styrene / isoprene / styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene / propylene / diene copolymer.

By using such a binder having an olefinically unsaturated bond in the molecule, the swellability of the active material layer with respect to the electrolytic solution can be reduced. Of these, styrene-butadiene rubber is preferred because of its availability.

The mechanical strength of the negative electrode plate can be increased by using a binder having an olefinically unsaturated bond in the molecule and the carbon material for a nonaqueous secondary battery negative electrode of the present invention in combination. When the mechanical strength of the negative electrode plate is high, deterioration of the negative electrode due to charging / discharging of the nonaqueous secondary battery is suppressed, and the cycle life can be extended.

The binder having an olefinically unsaturated bond in the molecule preferably has a large molecular weight and / or a large proportion of unsaturated bonds.

As the molecular weight of the binder, the weight average molecular weight can usually be 10,000 or more, and can usually be 1,000,000 or less. If it is this range, both mechanical strength and flexibility can be controlled to a favorable range. The weight average molecular weight is preferably 50,000 or more, and preferably 300,000 or less.

As the ratio of olefinically unsaturated bonds in the binder molecule, the number of moles of olefinically unsaturated bonds per gram of the total binder can be usually 2.5 × 10 ⁻⁷ mol or more, and usually 5 × It can be 10 ⁻⁶ mol or less. If it is this range, the intensity | strength improvement effect will be acquired sufficiently and flexibility will also be favorable. The number of moles is preferably 8 × 10 ⁻⁷ moles or more, and preferably 1 × 10 ⁻⁶ moles or less.

Further, for a binder having an olefinically unsaturated bond in the molecule, the degree of unsaturation can usually be 15% or more and 90% or less. The degree of unsaturation is preferably 20% or more, more preferably 40% or more, and preferably 80% or less. In the present specification, the degree of unsaturation represents the ratio (%) of the double bond to the repeating unit of the polymer.

As the binder, a binder having no olefinically unsaturated bond can also be used. By using a binder having an olefinically unsaturated bond in the molecule and a binder having no olefinically unsaturated bond in the molecule, improvement in coating property can be expected.

When the binder having an olefinically unsaturated bond in the molecule is 100% by mass, the mixing ratio of the binder having no olefinically unsaturated bond in the molecule is to suppress the strength of the active material layer from being lowered. Usually, it can be 150 mass% or less, Preferably it is 120 mass% or less.

Examples of the binder having no olefinically unsaturated bond in the molecule include thickening polysaccharides such as methylcellulose, carboxymethylcellulose, starch, carrageenan, pullulan, guar gum, xanthan gum (xanthan gum);
Polyethers such as polyethylene oxide and polypropylene oxide;
Vinyl alcohols such as polyvinyl alcohol and polyvinyl butyral;
Polyacids such as polyacrylic acid and polymethacrylic acid or metal salts thereof;
Fluorine-containing polymers such as polyvinylidene fluoride;
Examples thereof include alkane polymers such as polyethylene and polypropylene, and copolymers thereof.

In the active material layer in the negative electrode for a non-aqueous secondary battery of the present invention, a conductive additive may be contained in order to improve the conductivity of the negative electrode. The conductive aid is not particularly limited, and examples thereof include carbon black such as acetylene black, ketjen black, and furnace black, fine powder made of Cu, Ni having an average particle size of 1 μm or less, or an alloy thereof.

It is preferable that the addition amount of the conductive additive is 10 parts by mass or less with respect to 100 parts by mass of the carbon material for a nonaqueous secondary battery negative electrode of the present invention.

The negative electrode for a non-aqueous secondary battery of the present invention is a slurry obtained by dispersing the carbon material for a non-aqueous secondary battery negative electrode of the present invention and optionally a binder and / or a conductive additive in a dispersion medium. It can be formed by coating and drying. As the dispersion medium, an organic solvent such as alcohol or water can be used.

The current collector to which the slurry is applied is not particularly limited, and a known current collector can be used. Specific examples include metal thin films such as rolled copper foil, electrolytic copper foil, and stainless steel foil.

The thickness of the current collector can be usually 4 μm or more, and can usually be 30 μm or less. The thickness is preferably 6 μm or more, and preferably 20 μm or less.

The thickness of the active material layer obtained by applying and drying the slurry is usually 5 μm or more from the viewpoint of practicality as a negative electrode and sufficient lithium ion occlusion / release function for high-density current values. In addition, it can usually be 200 μm or less. Preferably it is 20 micrometers or more, More preferably, it is 30 micrometers or more, Preferably it is 100 micrometers or less, More preferably, it is 75 micrometers or less.

The thickness of the active material layer may be adjusted to a thickness in the above range by pressing after applying the slurry and drying.

The density of the carbon material for the non-aqueous secondary battery negative electrode in the active material layer varies depending on the application. However, in applications in which input / output characteristics such as in-vehicle applications and power tool applications are emphasized, the density is usually 1.1 g / cm ³ or more 1 .65 g / cm ³ or less.

Within this range, an increase in contact resistance between particles due to the density being too low can be avoided, while a decrease in rate characteristics due to the density being too high can also be suppressed.

The density is preferably 1.2 g / cm ³ or more, more preferably 1.25 g / cm ³ or more.

In applications in which capacity is important, such as portable device applications such as mobile phones and personal computers, it is usually 1.45 g / cm ³ or more, and usually 1.9 g / cm ³ or less.

Within this range, it is possible to avoid a decrease in battery capacity per unit volume due to the density being too low, and it is also possible to suppress a decrease in rate characteristics due to the density being too high.

Density is preferably 1.55 g / cm ³ or more, more preferably 1.65 g / cm ³ or more, and particularly preferably 1.7 g / cm ³ or more.

[Non-aqueous secondary battery]
The basic configuration of the nonaqueous secondary battery according to the present invention can be the same as, for example, a known lithium ion secondary battery, and usually includes a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte. The negative electrode is a negative electrode for a non-aqueous secondary battery according to the present invention described above.

<Positive electrode>
The positive electrode can include a current collector and an active material layer formed on the current collector. The active material layer preferably contains a binder in addition to the positive electrode active material.

Examples of the positive electrode active material include metal chalcogen compounds that can occlude and release alkali metal cations such as lithium ions during charge and discharge. Of these, metal chalcogen compounds capable of inserting and extracting lithium ions are preferred.

Examples of metal chalcogen compounds include transition metal oxides such as vanadium oxide, molybdenum oxide, manganese oxide, chromium oxide, titanium oxide, and tungsten oxide;
Transition metal sulfides such as vanadium sulfide, molybdenum sulfide, titanium sulfide, CuS;
Phosphorus-sulfur compounds of transition metals such as NiPS ₃ and FePS ₃ ;
Selenium compounds of transition metals such as VSe ₂ and NbSe ₃ ;
Complex oxides of transition metals such as Fe _0.25 V _0.75 S ₂ , Na _0.1 CrS ₂ ;
Examples thereof include composite sulfides of transition metals such as LiCoS ₂ and LiNiS ₂ .

Among them, from the viewpoint of occlusion / release of lithium ions, V ₂ O ₅ , V ₅ O ₁₃ , VO ₂ , Cr ₂ O ₅ , MnO ₂ , TiO ₂ , MoV ₂ O ₈ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , TiS ₂ , V ₂ S ₅ , Cr _0.25 V _0.75 S ₂ , Cr _0.5 V _0.5 S _{2 and the} like are preferable, and LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _4, and their transitions A lithium transition metal composite oxide in which a part of the metal is substituted with another metal is particularly preferable.

These positive electrode active materials may be used alone or in combination.

The binder for the positive electrode is not particularly limited, and a known binder can be arbitrarily selected and used. Examples include inorganic compounds such as silicate and water glass, and resins having no unsaturated bond such as Teflon (registered trademark) and polyvinylidene fluoride. Among them, a resin having no unsaturated bond is preferable because it is difficult to decompose during the oxidation reaction.

The weight average molecular weight of the binder can usually be 10,000 or more, and can usually be 3 million or less. The weight average molecular weight is preferably 100,000 or more, and preferably 1,000,000 or less.

In the positive electrode active material layer, a conductive additive may be contained in order to improve the conductivity of the positive electrode. The conductive auxiliary agent is not particularly limited, and examples thereof include carbon powders such as acetylene black, carbon black, and graphite, and various metal fibers, powders, and foils.

In the present invention, in the same manner as the above-described negative electrode manufacturing method, the positive electrode is dispersed in a dispersion medium with an active material and, optionally, a binder and / or a conductive auxiliary agent, and this is applied to the surface of the current collector. Can be formed. The current collector of the positive electrode is not particularly limited, and examples thereof include aluminum, nickel, stainless steel (SUS), and the like.

<Electrolyte>
The electrolyte (sometimes referred to as “electrolyte”) is not particularly limited, and a non-aqueous electrolyte obtained by dissolving a lithium salt as an electrolyte in a non-aqueous solvent, or an organic polymer compound or the like is added to the non-aqueous electrolyte. By doing so, a gel-like, rubber-like, or solid sheet-like shape can be mentioned.

The non-aqueous solvent used in the non-aqueous electrolyte is not particularly limited, and a known non-aqueous solvent can be used.

For example, chain carbonates such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate;
Cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate;
Chain ethers such as 1,2-dimethoxyethane;
Cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, 1,3-dioxolane;
Chain esters such as methyl formate, methyl acetate and methyl propionate;
and cyclic esters such as γ-butyrolactone and γ-valerolactone.

The non-aqueous solvent may be used alone or in combination of two or more. In the case of a mixed solvent, a combination of a mixed solvent containing a cyclic carbonate and a chain carbonate is preferable from the balance of conductivity and viscosity, and the cyclic carbonate is preferably ethylene carbonate.

The lithium salt used in the non-aqueous electrolyte is not particularly limited, and a known lithium salt can be used. For example, halides such as LiCl and LiBr;
Perhalogenates such as LiClO ₄ , LiBrO ₄ , LiClO ₄ ;
Inorganic lithium salts such as inorganic fluoride salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ ;
Perfluoroalkanesulfonates such as LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ ;
Fluorine-containing organic lithium salts such as perfluoroalkanesulfonic acid imide salts such as Li trifluoromethanesulfonylimide ((CF ₃ SO ₂ ) ₂ NLi) can be used. Among these, LiClO ₄ , LiPF ₆ , and LiBF ₄ are preferable.

Lithium salts may be used alone or in combination of two or more. The concentration of the lithium salt in the nonaqueous electrolytic solution can be in the range of 0.5 mol / L to 2.0 mol / L.

When the organic polymer compound is included in the non-aqueous electrolyte solution described above and used in the form of a gel, rubber, or solid sheet, specific examples of the organic polymer compound include polyethylene oxide, polypropylene oxide, and the like. Polyether polymer compounds;
A crosslinked polymer of a polyether polymer compound;
Vinyl alcohol polymer compounds such as polyvinyl alcohol and polyvinyl butyral;
Insolubilized vinyl alcohol polymer compound;
Polyepichlorohydrin;
Polyphosphazene;
Polysiloxane;
Vinyl polymer compounds such as polyvinylpyrrolidone, polyvinylidene carbonate, and polyacrylonitrile;
Examples thereof include polymer copolymers such as poly (ω-methoxyoligooxyethylene methacrylate), poly (ω-methoxyoligooxyethylene methacrylate-co-methyl methacrylate), and poly (hexafluoropropylene-vinylidene fluoride).

The non-aqueous electrolyte solution described above may further contain a film forming agent.
Specific examples of the film forming agent include carbonate compounds such as vinylene carbonate, vinyl ethyl carbonate, and methyl phenyl carbonate;
Alkene sulfides such as ethylene sulfide and propylene sulfide;
Sultone compounds such as 1,3-propane sultone, 1,4-butane sultone;
Examples of the acid anhydride include maleic acid anhydride and succinic acid anhydride.

Further, an overcharge inhibitor such as diphenyl ether or cyclohexylbenzene may be added to the non-aqueous electrolyte.

When using the above-mentioned various additives, the total content of the additives is the total amount of the non-aqueous electrolyte so as not to adversely affect other battery characteristics such as an increase in initial irreversible capacity, low temperature characteristics, and deterioration in rate characteristics. In general, it can be 10% by mass or less, in particular, 8% by mass or less, more preferably 5% by mass or less, and particularly preferably 2% by mass or less.

Further, as the electrolyte, a polymer solid electrolyte that is a conductor of an alkali metal cation such as lithium ion can also be used.

Examples of the polymer solid electrolyte include those obtained by dissolving a Li salt in the above-described polyether polymer compound, and polymers in which the terminal hydroxyl group of the polyether is substituted with an alkoxide.

<Others>
In order to prevent a short circuit between the electrodes, a porous separator such as a porous membrane or a nonwoven fabric can usually be interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte is impregnated into the porous separator. It is convenient to use it. As a material for the separator, polyolefin such as polyethylene and polypropylene, polyethersulfone, and the like are used, and polyolefin is preferable.

The form of the non-aqueous secondary battery is not particularly limited, for example, a cylinder type in which a sheet electrode and a separator are spiraled;
Inside-out cylinder type that combines pellet electrode and separator;
The coin type etc. which laminated | stacked the pellet electrode and the separator are mentioned.

In addition, by storing batteries of these forms in an optional outer case, the battery can be used in an arbitrary shape and size such as a coin shape, a cylindrical shape, and a square shape.

The procedure for assembling the non-aqueous secondary battery is not particularly limited, and can be assembled by an appropriate procedure according to the structure of the battery. For example, a negative electrode can be placed on an outer case, an electrolyte and a separator can be provided thereon, and a positive electrode can be placed so as to face the negative electrode, and can be caulked together with a gasket and a sealing plate to form a battery.

Next, specific embodiments of the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. In addition, the measuring method of each physical property is as follows.

<Measuring method of average particle diameter d50>
The measuring method of the average particle diameter d50 is as follows. A commercially available laser diffraction / scattering particle size is prepared by suspending 0.01 g of a sample in 10 mL of a 0.2 mass% aqueous solution of polyoxyethylene sorbitan monolaurate (for example, Tween 20 (registered trademark)) as a surfactant. The sample was introduced into the distribution measuring apparatus “LA-920 manufactured by HORIBA” and irradiated with ultrasonic waves of 28 kHz at an output of 60 W for 1 minute, and then the volume-based median diameter in the measuring apparatus was measured. Defined.

<Measurement method of BET specific surface area (SA)>
The BET specific surface area (SA) was measured by a BET 1-point method by a nitrogen gas adsorption flow method using a specific surface area measuring device “AMS8000” manufactured by Okura Riken. Specifically, 0.4 g of a sample is filled in a cell, heated to 350 ° C., pretreated, cooled to liquid nitrogen temperature, and saturated adsorption of 30% nitrogen and 70% He gas is performed. The amount of gas desorbed by heating to room temperature was measured. From the obtained results, the specific surface area was calculated by a normal BET method.

<Raman R value>
The sample to be measured was filled by naturally dropping into the measurement cell, and measurement was performed while rotating the measurement cell in a plane perpendicular to the laser beam while irradiating the measurement cell with an argon ion laser beam. The measurement conditions of the Raman spectrum are shown below.

The obtained Raman spectrum, the intensity _{I A} of the peak _{P A} in the vicinity of 1580 cm ^-1, and measuring the intensity _{I B} of a peak _{P B} in the vicinity of 1360 cm ^-1, the intensity ratio R _{(R =} I B / _{I A} ) And calculated as the Raman R value.

<Tap density>
The method for measuring the tap density is as follows. Using a powder density measuring device, a sample was dropped into a cylindrical tap cell having a diameter of 1.6 cm and a volume capacity of 20 cm ³ through a sieve having an opening of 300 μm, and the cell was fully filled. The density obtained from the volume and the mass of the sample was defined as the tap density.

<DBP oil absorption>
The DBP oil absorption amount is defined by measured values when 40 g of measurement material is added, the dropping speed is 4 ml / min, the rotation speed is 125 rpm, and the set torque is 500 N · m, in accordance with JIS K6217. For the measurement, an absorption meter (S-500) from Asahi Research Institute was used.

<Si content of composite carbon particles>
The Si content of the composite carbon particles was determined as follows. The composite carbon particles were completely melted with an alkali, then dissolved and fixed in water, measured with an inductively coupled plasma emission spectrometer (HORIBA, Ltd. ULTIMA2C), and the amount of Si was calculated from a calibration curve. Thereafter, the Si content of the composite carbon particles was calculated by dividing the Si amount by the weight of the composite carbon particles.

<Observation of cross-sectional structure of composite carbon particles>
The cross-sectional structure of the composite carbon particles was measured as follows. The electrode plate prepared in <Preparation of Electrode Sheet> described later was processed with a cross section polisher (JEOL IB-09020CP) to obtain an electrode plate cross section. While observing the obtained electrode plate cross section with SEM (Hitachi High-Tech SU-70), mapping of graphite and Si was performed using EDX. The SEM acquisition conditions were an acceleration voltage of 3 kV and a magnification of 2000 times, and an image in a range where one particle could be acquired at a resolution of 256 dpi was obtained.

<Initial discharge capacity, initial efficiency>
Using a non-aqueous secondary battery (2016 coin type battery) produced by the method described later, the capacity during battery charging / discharging was measured by the following measurement method.

Charge to 5 mV with respect to the lithium counter electrode at a current density of 0.05 C (the current value for discharging the rated capacity with a 1 hour rate discharge capacity in 1 hour is assumed to be 1 C), and the current at a constant voltage of 5 mV. The battery was charged until the density reached 0.005 C, lithium was doped into the negative electrode, and then discharged to 1.5 V with respect to the lithium counter electrode at a current density of 0.1 C. The discharge capacity (mAh / g) at this time is taken as the discharge capacity (mAh / g) of the tested carbon material, and the difference between the charge capacity (mAh / g) and the discharge capacity (mAh / g) is the irreversible capacity (mAh / g). It was. Moreover, the discharge capacity (mAh / g) of the first cycle obtained here was divided by the charge capacity (mAh / g), and the value obtained by multiplying by 100 was defined as the initial efficiency (%).

<Discharge capacity maintenance rate>
Cycle durability was measured by the following measuring method using a laminate type non-aqueous secondary battery manufactured by the following non-aqueous secondary battery manufacturing method.

For non-aqueous secondary batteries that have not undergone charge / discharge cycles, voltage range 4.1V to 3.0V at 25 ° C, current cycle 0.2C, 3 cycles, voltage range 4.2V to 3.0V, current value Initial charge / discharge was performed for 2 cycles at 0.2 C (constant voltage charging was further performed for 2.5 hours at 4.2 V during charging).

Furthermore, after charging and discharging for 100 cycles at 60 ° C. in a voltage range of 4.2 V to 3.0 V and a current value of 2.0 C, a value obtained by dividing the discharge capacity at the 100th cycle by the discharge capacity at the first cycle is discharged. Calculated as the capacity maintenance rate.

<Production of electrode sheet>
Using the carbon material (negative electrode material) of the example or the comparative example, an electrode plate having an active material layer with an active material layer density of 1.6 ± 0.03 g / cm ³ was produced. Specifically, 20.00 ± 0.02 g of a negative electrode material, 20.00 ± 0.02 g of a 1% by mass aqueous solution of carboxymethylcellulose sodium salt (0.200 g in terms of solid content), and styrene having a weight average molecular weight of 270,000 -Aqueous dispersion of butadiene rubber 0.75 ± 0.05 g (0.3 g in terms of solid content) was added, stirred for 5 minutes with a hybrid mixer manufactured by Keyence, and defoamed for 30 seconds to obtain a slurry.

This slurry was applied to a width of 5 cm using a doctor blade so that the negative electrode material was 12.0 ± 0.3 mg / cm ² on a 18 μm-thick copper foil as a current collector, and air-dried at room temperature. Went. Further, after drying at 110 ° C. for 30 minutes, roll pressing was performed using a roller having a diameter of 20 cm to adjust the density of the active material layer to be 1.60 ± 0.03 g / cm ³ to obtain an electrode sheet.

<Preparation of non-aqueous secondary battery (2016 coin type battery)>
The electrode sheet produced by the above method was punched into a disk shape with a diameter of 12.5 mm, and a lithium metal foil was punched into a disk shape with a diameter of 14 mm as a counter electrode. Between the two electrodes, a separator (porous polyethylene film) impregnated with an electrolytic solution in which LiPF ₆ was dissolved at 1 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio = 3: 7). 2016 coin type batteries were prepared.

<Creation of non-aqueous secondary battery (laminate cell)>
Lithium nickel manganese cobaltate (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ) is used as the positive electrode active material, and this is mixed with a conductive agent and polyvinylidene fluoride (PVdF) as a binder to form a slurry. did. The obtained slurry was applied to an aluminum foil having a thickness of 15 μm, dried, and rolled with a press, and the positive electrode active material layer had a width of 30 mm, a length of 40 mm, and an uncoated portion for current collection. A positive electrode was cut out into a shape. The density of the positive electrode active material layer was 2.6 g / cm ³ .

As the negative electrode, an electrode sheet produced by the above-described method was cut out into a shape having a width of 32 mm as a size of the negative electrode active material layer, a length of 42 mm, and an uncoated portion as a current collector tab welded portion. . At this time, the density of the negative electrode active material layer was 1.35 g / cm ³ .

The positive electrode and the negative electrode were arranged so that the active material surfaces face each other, and a porous polyethylene sheet separator was sandwiched between the electrodes. At this time, the positive electrode active material surface was faced so as not to deviate from the negative electrode active material surface.

A laminate sheet (total thickness) obtained by laminating a polypropylene film, an aluminum foil having a thickness of 0.04 mm, and a nylon film in this order by welding current collecting tabs to uncoated portions of each of the positive electrode and the negative electrode. 0.1 mm) was used to sandwich the polypropylene film on the inner surface side, and the region without electrodes was heat sealed except for one side for injecting the electrolyte solution.

Then, the non-aqueous electrolyte solution (ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) = 3/3/4 (volume ratio)) was added to the active material layer at a concentration of 1.2 mol / L. 200 μL of lithium phosphate (LiPF ₆ ) dissolved therein was injected, sufficiently infiltrated into the electrode, and sealed to prepare a laminate cell. The rated capacity of this battery is 20 mAh.

Initial conditioning was performed under the following conditions in a 25 ° C. environment.
1 cycle: Charged for 1 hour at 0.2C, then discharged to 3V at 0.2C. 2 cycles: Charged to 4.1V at 0.2C, then discharged to 3V at 0.2C. 3 cycles: 4.2V cccv at 0.5C. After charging (current amount 0.05C cut condition), discharge to 3V at 0.2C 4 cycles: 4.2Vcccv charge at 0.5C (current amount 0.05C cut condition)
(“Ccvv charge” represents charging after a certain amount of charge at a constant current until a termination condition is reached at a constant voltage.)

(Preparation of carbon material)
Table 1 below shows the physical properties of the carbon materials used in the examples and comparative examples.
Si composite carbon particles (A), composite graphite particles (B-1) and composite graphite particles (B-2) were prepared as follows.

・ Si composite carbon particles (A)
Si slurry (I) was prepared by crushing polycrystalline Si (manufactured by Wako) having a d50 of 30 μm together with NMP (N-methyl-2-pyrrolidone) with a bead mill (Ashizawa Finetech) to d50: 0.2 μm. . 500 g (solid content 40%) of this Si slurry (I) was charged into 750 g of NMP in which 60 g of polyacrylonitrile was uniformly dissolved, and mixed with a mixing stirrer. Next, 1000 g of scaly natural graphite (d50: 45 μm) was added and mixed to obtain slurry (II) in which polyacrylonitrile, Si, and graphite were uniformly dispersed.

The slurry (II) was appropriately dried under reduced pressure for 3 hours at 150 ° C., which is lower than the thermal decomposition temperature of polyacrylonitrile, so that the polyacrylonitrile is not denatured. In addition, the decomposition temperature of polyacrylonitrile was 270 degree | times from DSC analysis. The obtained lump was crushed with a hammer mill (MF10 manufactured by IKA) at a rotation speed of 6000 rpm, and then charged into a hybridization system (manufactured by Nara Machinery Co., Ltd.). Circulation or retention was performed to spheroidize, Si particles were encapsulated in scaly natural graphite, and heat treatment was performed at 1000 ° C. for 1 hour in a nitrogen atmosphere to obtain Si composite carbon particles (E).

Coal tar pitch was mixed with Si composite carbon particles (E) so that the coverage after firing was 7.5%, and kneaded and dispersed by a biaxial kneader.

The obtained dispersion was introduced into a firing furnace and fired at 1000 ° C. for 1 hour in a nitrogen atmosphere. The fired lump is crushed using the mill described above under the condition of 3000 rpm, and then classified with a vibrating screen having an opening of 45 μm to obtain Si composite carbon particles (A) coated with amorphous carbon. (Si content is 8.2% by mass).

In addition, when the cross-sectional structure was observed by the above measurement method, the Si composite carbon particles (A) had a structure in which flaky graphite was folded, and Si compound particles were present in the gaps in the folded structure. It was. Moreover, it was observed that there is a portion where the Si compound particles and the scaly graphite are in contact.

・ Composite graphite particles (B-1)
The scaly natural graphite having a d50 of 100 μm was spheroidized by a mechanical action for 3 minutes at a rotor peripheral speed of 85 m / sec using a hybridization system NHS-1 manufactured by Nara Machinery Co., Ltd. This sample was treated by classification to obtain spherical graphite particles (C-1) having a d50 of 15.7 μm. An aqueous solution of sodium salt of naphthalene sulfonic acid formalin condensate (Labelin manufactured by Daiichi Kogyo Seiyaku Co., Ltd .: weight average molecular weight 3200) as a polymer hardly soluble in the non-aqueous electrolyte solution in the resulting spheroidized graphite particles (C-1). And water was distilled off by heating to obtain composite graphite particles (B-1). In the composite graphite particles (B-1) obtained from the weight change, it was confirmed that the mass ratio of the spheroidized graphite particles to the hardly soluble polymer (spherical graphite particles: poorly soluble polymer) was 1: 0.005. It was.

・ Composite graphite particles (B-2)
The scaly natural graphite having a d50 of 100 μm was spheroidized by a mechanical action for 3 minutes at a rotor peripheral speed of 85 m / sec using a hybridization system NHS-1 manufactured by Nara Machinery Co., Ltd. This sample was treated by classification to obtain spherical graphite particles (C-1) having a d50 of 15.7 μm. The obtained spheroidized graphite particles (C-1) and coal tar pitch as an amorphous carbon precursor are mixed, subjected to heat treatment at 1300 ° C. in an inert gas, and then the fired product is crushed and classified. As a result, a multi-layer structure carbon material (C-2) in which spheroidized graphite particles and amorphous carbon were combined was obtained. From the residual carbon ratio, it was confirmed that the mass ratio of spheroidized graphite particles to amorphous carbon (spheroidized graphite particles: amorphous carbon) was 1: 0.03 in the obtained multilayer carbon material. It was done. An aqueous solution of naphthalene sulfonic acid formalin condensate sodium salt (Labelin manufactured by Daiichi Kogyo Seiyaku Co., Ltd .: weight average molecular weight 3200) is added to this multi-layered carbon material as a polymer that is sparingly soluble in a non-aqueous electrolyte, and heated. Water was distilled off to obtain composite graphite particles (B-2). In the composite graphite particles (B-2) obtained from the change in weight, the mass ratio of the multilayer structure carbon material to the hardly soluble polymer (multilayer structure carbon material: sparingly soluble polymer) is 1: 0.0025. confirmed.

・ MCMB
MCMB6-28 manufactured by Osaka Gas Chemical Co., Ltd. was used as mesocarbon microbeads (MCMB).

The various characteristics of the above various materials are summarized in Table 1 below.

[Example 1]
Si composite carbon particles (A) and composite graphite particles (B-1) are mixed at Si composite carbon particles (A) / composite graphite particles (B-1) = 70/30 (mass ratio), and non-aqueous secondary It was set as the carbon material for battery negative electrodes.

[Comparative Example 1]
A carbon material for a non-aqueous secondary battery negative electrode was obtained in the same manner as in Example 1 except that the composite graphite particles (B-1) were changed to MCMB.

[Example 2]
Si composite carbon particles (A) and composite graphite particles (B-1) are mixed at Si composite carbon particles (A) / composite graphite particles (B-1) = 50/50 (mass ratio), and non-aqueous secondary It was set as the carbon material for battery negative electrodes.

[Example 3]
A carbon material for a nonaqueous secondary battery negative electrode was obtained in the same manner as in Example 2 except that the composite graphite particles (B-1) were changed to composite graphite particles (B-2).

[Comparative Example 2]
A carbon material for a non-aqueous secondary battery negative electrode was obtained in the same manner as in Example 2 except that the composite graphite particles (B-1) were changed to MCMB.

[Example 4]
Si composite carbon particles (A) and composite graphite particles (B-1) are mixed at Si composite carbon particles (A) / composite graphite particles (B-1) = 30/70 (mass ratio) to obtain a non-aqueous secondary battery. A carbon material for a negative electrode was obtained.

[Example 5]
A carbon material for a non-aqueous secondary battery negative electrode was obtained in the same manner as in Example 4 except that the composite graphite particles (B-1) were changed to composite graphite particles (B-2).

[Comparative Example 3]
A carbon material for a non-aqueous secondary battery negative electrode was obtained in the same manner as in Example 4 except that the composite graphite particles (B-1) were changed to MCMB.

[Comparative Example 4]
The composite graphite particles (B-1) were used as a carbon material for a nonaqueous secondary battery negative electrode.

[Comparative Example 5]
The composite graphite particles (B-2) were used as a carbon material for a non-aqueous secondary battery negative electrode.

[Comparative Example 6]
MCMB was used as a carbon material for a non-aqueous secondary battery negative electrode.

[Comparative Example 7]
Si composite graphite particles (A) were used as a carbon material for a non-aqueous secondary battery negative electrode.

The initial discharge capacity, initial efficiency, and cycle durability of the carbon materials for non-aqueous secondary battery negative electrodes of Examples 1 to 5 and Comparative Examples 1 to 7 were measured by the measurement methods described above. The results are shown in Table 2 below.

The cycle durability values of Examples 1 to 5 and Comparative Examples 4 to 5 were calculated as follows.

Cycle durability (%) of Example 1 = Discharge capacity maintenance rate at 100th cycle of Example 1 / Discharge capacity maintenance rate at 100th cycle of Comparative Example 1 × 100
Cycle durability (%) of Example 2 = Discharge capacity maintenance rate at 100th cycle of Example 2 / Discharge capacity maintenance rate at 100th cycle of Comparative Example 2 × 100
Cycle durability (%) of Example 3 = discharge capacity maintenance rate at 100th cycle of Example 3 / discharge capacity maintenance rate at 100th cycle of Comparative Example 2 × 100
Cycle durability (%) of Example 4 = discharge capacity maintenance rate at 100th cycle of Example 4 / discharge capacity maintenance rate at 100th cycle of Comparative Example 3 × 100
Cycle durability (%) of Example 5 = discharge capacity maintenance rate at 100th cycle of Example 5 / discharge capacity maintenance rate at 100th cycle of Comparative Example 3 × 100
Cycle durability (%) of Comparative Example 4 = Discharge capacity maintenance rate at 100th cycle of Comparative Example 4 / Discharge capacity maintenance rate at 100th cycle of Comparative Example 6 × 100
Cycle durability (%) of Comparative Example 5 = Discharge capacity maintenance rate at 100th cycle of Comparative Example 5 / Discharge capacity maintenance rate at 100th cycle of Comparative Example 6 × 100
Cycle durability (%) of Comparative Example 7 = Discharge capacity maintenance rate at 100th cycle of Comparative Example 7 / Discharge capacity maintenance rate at 100th cycle of Example 1 × 100

As can be seen from Table 2, the non-aqueous secondary battery negative electrode carbon materials (Examples 1 to 5) containing the Si composite carbon particles (A) and the composite graphite particles (B) are non-aqueous secondary materials made of a single material. Compared with the carbon material for battery negative electrodes (Comparative Examples 4 to 7), the balance between the initial discharge capacity and the initial efficiency is excellent.

Regarding cycle durability, the carbon for non-aqueous secondary battery negative electrode made of composite graphite particles (B) alone compared to the carbon material for non-aqueous secondary battery negative electrode made of MCMB single material (Comparative Example 6). Despite the lower material (Comparative Examples 4 and 5), compared with the carbon material for non-aqueous secondary battery negative electrode (Comparative Examples 1 to 3) containing Si composite carbon particles (A) and MCMB, It can be seen that the carbon materials for non-aqueous secondary battery negative electrodes (Examples 1 to 5) containing Si composite carbon particles (A) and composite graphite particles (B) are higher.

This is considered to be because a polymer that is hardly soluble in the non-aqueous electrolyte solution of the composite graphite particles (B) suppresses side reactions between the graphite particles and the non-aqueous electrolyte solution.

Thus, by using the non-aqueous secondary battery negative electrode carbon material of the present invention, it is possible to provide a non-aqueous secondary battery that is balanced at a high initial discharge capacity, initial efficiency, and discharge capacity retention rate. .

Claims

(1) Composite carbon particles containing silicon element (A), and (2) Composite graphite particles (B) in which a polymer that is hardly soluble in a non-aqueous electrolyte and graphite particles (C) are combined.
A carbon material for a negative electrode of a non-aqueous secondary battery.
2. The non-aqueous secondary battery according to claim 1, wherein the composite carbon particles (A) have a structure in which scaly graphite is folded, and Si compound particles are present in a gap in the folded structure. Carbon material for negative electrode.
The carbon material for a non-aqueous secondary battery negative electrode according to claim 1 or 2, wherein the graphite particles (C) are spheroidized natural graphite.
With respect to a polymer that is hardly soluble in the non-aqueous electrolyte, when the polymer is immersed in a solvent in which ethyl carbonate and ethyl methyl carbonate are mixed at a volume ratio of 3: 7 for 24 hours, the dry weight loss rate before and after immersion is 10 The carbon material for a nonaqueous secondary battery negative electrode according to any one of claims 1 to 3, wherein the carbon material is not more than mass%.
The non-aqueous secondary according to any one of claims 1 to 4, wherein the composite carbon particles (A) contain at least one Si compound selected from the group consisting of Si and SiOx (0 <x <2). Carbon material for battery negative electrode.
A non-aqueous secondary battery negative electrode comprising a current collector and an active material layer formed on the current collector, wherein the active material layer is according to any one of claims 1 to 5. A negative electrode for a nonaqueous secondary battery, comprising a carbon material for a nonaqueous secondary battery negative electrode.
A non-aqueous secondary battery comprising a positive electrode and a negative electrode, and an electrolyte, wherein the negative electrode is a negative electrode for a non-aqueous secondary battery according to claim 6.