JP2002042786A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the active material density of an electrode using surface amorphous graphite in which a low-crystalline carbon material is attached to the surface of high-crystalline graphite, and to increase the energy density of a secondary battery. To achieve. SOLUTION: The positive electrode, a non-aqueous electrolyte, and a negative electrode, wherein the negative electrode has surface amorphous graphite in which low crystalline carbon is adhered to the surface of high crystalline graphite, and the negative electrode has a filling aid. Non-aqueous electrolyte secondary battery containing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a non-aqueous electrolyte, and a negative electrode. In particular, as a negative electrode material, a low-crystalline carbon material is formed on the surface of highly crystalline graphite. The present invention relates to a nonaqueous electrolyte secondary battery using adhered surface amorphous graphite.

[0002]

2. Description of the Related Art In recent years, high-capacity secondary batteries have been required as electronic devices have become smaller. Metal materials, carbon materials, and the like are being studied as the negative electrode material. However, when a metal material is used, there is a problem that if charge and discharge are repeated, metal ions in the solvent precipitate in a dendrite shape, and eventually both electrodes are short-circuited. On the other hand, when a carbon material is used, there is no problem of short-circuiting because of the electrochemical insertion / desorption reaction of metal ions between layers of the carbon material. Carbon materials have a wide range of horizontal structures or shapes from graphite to amorphous carbon, and their physical properties or the microstructure formed by the hexagonal mesh of carbon greatly affect the performance of the electrode. Various specified carbon materials have been proposed.

[0003] Carbon materials used for non-aqueous electrolyte secondary batteries, particularly for negative electrodes of lithium secondary batteries, are mainly classified into carbon-based materials fired at about 1000 ° C and graphite-based materials fired at about 2800 ° C. Separated.

When a carbon-based material fired at about 1000 ° C. is used, there is an advantage that the reaction with the electrolytic solution is small and decomposition of the electrolytic solution does not easily occur, but the change in potential due to release of lithium ions is large. There is a disadvantage that.

On the other hand, when a graphite-based material fired at about 2800 ° C. is used, there is an advantage that a change in potential due to release of lithium ions is small, but the electrolyte reacts with the electrolyte to cause decomposition of the electrolyte. Further, it is known that there is a disadvantage that the graphite material is destroyed (J. Electr.
ochem. Soc. , 117, 222 (197).
0)). As a result, graphite-based materials fired at around 2800 ° C. may cause problems such as a decrease in charge / discharge efficiency, a decrease in cycle characteristics, and a decrease in battery safety. It is known that when a specific electrolyte is used, a graphite-based material can be used without causing such a problem (J. Electrochem. Soc., 13).
7, 2009 (1990)), and there is a problem that the improvement in the temperature characteristics and cycle characteristics of the battery is considerably limited by the type of the electrolytic solution because the electrolytic solution is limited.

Therefore, it is an important task of the present battery system to develop a combination of an electrolyte and a carbon electrode which does not cause decomposition of the electrolyte or breakage of the graphite-based material.

To solve these problems, Japanese Patent Laid-Open Publication No.
68778, JP-A-4-370662, JP-A-5-94838, JP-A-5-121066 and the like disclose surface amorphous graphite in which a low-crystalline carbon material adheres to the surface of highly crystalline graphite. Has been proposed. Since this surface-modified carbon material suppresses decomposition of the electrolytic solution, it is effective for increasing the battery capacity, improving the cycle characteristics, and the like.

On the other hand, in designing an electrode of a non-aqueous electrolyte secondary battery, it is important that more active material is filled in a unit volume of the electrode. When producing an electrode, the active material powder and the binder are mixed, a paste-like electrode mixture is prepared by adding a dispersion solvent, and this is applied to a metal foil as a current collector. Thereafter, a method of drying the dispersion solvent is generally used. At this time, it is general to provide a compression molding step for performing compression molding for the purpose of pressing the electrode mixture onto the current collector, making the electrode thickness uniform, and improving the electrode capacity. This compression molding step increases the bulk density of the electrode and increases the energy density per unit volume of the battery.

[0009] Graphite-based materials are more crystalline than carbon-based materials,
True density is high. Therefore, if the electrode is formed using a graphite-based material, an electrode having a relatively high filling property can be obtained, and the energy density per unit volume of the battery can be increased. Further, it is required that the active material does not deteriorate the electrode characteristics even when the bulk density is increased.

[0010]

However, the energy density per unit volume of a secondary battery using surface amorphous graphite in which a low crystalline carbon material is adhered to the surface of high crystalline graphite can still be satisfied. It was not as big.

It is considered that this is partly due to the fact that the bulk density (apparent density or packing density) of the electrode containing surface amorphous graphite is hardly increased by the press or compression molding process. This is because the surface amorphous graphite has a low crystalline carbon coated on the surface of a highly crystalline graphite material, and the true density of the low crystalline carbon is higher than the true density of the highly crystalline graphite material. One of the causes is considered to be low.

In order to increase the bulk density of the negative electrode, it is necessary to increase the pressing pressure. However, if the pressing pressure is increased, the low-crystalline carbon covered on the surface of the graphite material may be cracked or even cracked, which may cause a problem that the effect of the coating is weakened.
In addition, when the pressing pressure is increased, the negative electrode is likely to be peeled off from the current collector, such as a metal foil, during the pressing, and may adhere to the press side. further,
The non-uniform pressing may cause the negative electrode to peel off or fall off from the current collector during charging and discharging, thereby impairing the cycle characteristics.

The present invention relates to a graphite material in which the surface of a highly crystalline graphite as an active material is coated with a low crystalline carbon material, that is, a carbon material having a high surface amorphous graphite filling property and exhibiting good electrode characteristics. An object is to obtain a nonaqueous electrolyte secondary battery having a negative electrode.

[0014]

Means for Solving the Problems A positive electrode, a non-aqueous electrolyte,
A negative electrode material, the negative electrode material being a material of the negative electrode, and having a surface amorphous graphite in which a low crystalline carbon material is adhered to the surface of highly crystalline graphite, and the negative electrode material having the surface amorphous It has been found that the problem can be solved by including a filling aid for improving the filling property of graphite.

Specifically, in the step of pressing or compression molding, by adding a filler, cracks in the low-crystalline carbon material covered on the surface of the highly crystalline graphite,
It is characterized in that cracks and the like are easily prevented, and a negative electrode having a high bulk density or an active material density is easily produced. Conventionally, an active material density of about 1.4 g / cm ³ could be produced without using a filling aid, but the active material density was 1.4 with the aim of further increasing the energy density.
Even if an electrode having a g / cm ³ or more, particularly 1.5 g / cm ³ or more is produced, it is effective in that the number of presses can be reduced.

The filling aid contained in the negative electrode material of the non-aqueous electrolyte secondary battery according to the present invention means that a low-crystalline carbon material covered on the surface of high-crystalline graphite causes cracks, cracks, and the like. Without filling, it means a material that is filled in order to increase the active material density by filling more active material in the electrode.

In general, it is generally considered that when a material other than the active material is contained, the material other than the active material enters the electrode, so that the active material density hardly increases.
However, the present inventor, by adding a filling aid to the material having low filling property and fluidity, despite the fact that the material other than the active material is contained, the active material density of the electrode is high. The present inventors have found new findings and completed the present invention based on such facts.

Bulk density (apparent density or packing density)
The term is obtained by dividing the total mass of the active material and the binder other than the active material by the volume occupied by the electrode mixture. That is, it can be expressed by an equation of bulk density = total mass of electrode mixture / volume occupied by electrode mixture. The packing structure of the powder particles depends on the size and shape of the particles, the interaction between the particles, and the like. As one of the indexes for quantitatively discussing the packing structure, the bulk density and the packing ratio are used.

On the other hand, the active material density is the weight of the active material in a unit volume of the electrode. The active material density does not become higher than the true density of the active material, and the difference from the true density is due to a change in volume of a material other than the active material such as a binder and a void in an electrode.

The content of the filling assistant is 0.1 to 0.1% of the negative electrode material.
Preferably it is 30 parts by weight. If the content of the filler is less than 0.1 parts by weight, the effect of the filler is less likely to be obtained. On the other hand, when the content of the filling assistant is more than 30 parts by weight, the density of the active material is hardly increased, and the actual charge / discharge capacity is reduced, which is not practical. Alternatively, if the filling aid itself electrochemically inserts / desorbs Li ions, it will be reflected in the electrode characteristics, resulting in a drawback such that the electrode characteristics of surface amorphous graphite cannot be utilized. The weight ratio here indicates the ratio to the surface amorphous graphite, and it is possible to include a binder as an electrode material.

Examples of the binder include, but are not limited to, fluoropolymers such as polytetrafluoroethylene and polyvinylidene fluoride, polyolefin polymers such as polyethylene and polypropylene, and synthetic rubbers. If the amount of the binder is less than 1 part by weight, the binding ability is lost, and if the amount is more than 30 parts by weight (parts by weight differ depending on the added binder), the ratio of the active material contained in the electrode decreases, and Is not practical because polarization and the like increase and the charge / discharge capacity decreases. Note that it is preferable to perform heat treatment at a temperature around the melting point (T _m ) of each binder in order to improve the binding property in the production of the negative electrode.

The surface amorphous graphite in the present invention means a gas phase method, a liquid phase method,
It can be obtained by attaching low crystallinity carbon to the surface of the graphite material by a technique such as a solid phase method.
The highly crystalline graphite used for the core material may be natural graphite, artificial graphite, or mesocarbon microbeads, mesophase pitch powder, etc. in the form of particles (scales or lumps, fibers, whiskers, spheres, crushed shapes, etc.). One or two or more types of graphitized products such as conductive pitch powder can be used.

Here, as the graphite material to be the core material, preferably, the average spacing (d ₀₀₂ ) of the (002) plane by the X-ray wide-angle diffraction method is 0.335 to 0.340 nm and (00)
2) The crystallite thickness (Lc) in the plane direction is 10 nm or more (more preferably 40 nm or more), and the crystallite thickness (La) in the (110) plane direction is 10 nm or more (more preferably 50 n).
m or more). Average surface spacing is 0.34
0 nm or when Lc and La are 10n
If it is smaller than m, the crystallinity of the carbon material is not sufficient, and a low potential portion (0 to 300 mV based on the potential of Li) close to the dissolution precipitation of lithium when the coated carbon material is produced.
This is not preferable because the capacity of the battery becomes insufficient.

As a method for determining the crystallite size (Lc, La) by the X-ray wide-angle diffraction method, a known method, for example, “Carbon Materials Experimental Techniques 1 p55-63, edited by The Society of Carbon Materials (Science and Technology Corporation) ) "Can be applied. In addition, the crystallite size (Lc, La) can be measured by the X-ray wide-angle diffraction method by the method described below. That is, if the sample is a powder, as it is, if the sample is in the form of small flakes, pulverize in an agate mortar, add about 15% by weight of the sample to the X-ray standard high-purity silicon powder as an internal standard substance, and mix. A sample is packed in a cell, and a wide angle X-ray diffraction curve is measured by a reflection type diffractometer method using a CuKα ray monochromatized by a graphite monochromator as a radiation source. For the correction of the curve, the following simple method is used without correcting so-called Lorentz, deflection factor, absorption factor, atomic scattering factor and the like. That is, a base line of a curve corresponding to the (002) diffraction is drawn, and the intensity from the base line is changed to (0
A corrected diffraction curve of the plane of 02) is obtained. Then, in the corrected diffraction curve, the crystallite size Lc in the C-axis direction is calculated by using a so-called half width β at a half position of the peak height as Lc =
It is calculated by (K · λ) / (β · cos θ). Here, λ is 1.5416 angstroms, and θ is a diffraction angle. Similarly, La can be measured.

Examples of the graphite material as the core, the peak intensity ratio in the vicinity of 1360 cm ^-1 to the peak intensity ratio in the vicinity of 1580 cm ^-1 by argon laser Raman (hereinafter referred to as R value), 0.5 or less (more preferably 0.4 or less)
It is preferred that When the R value exceeds 0.5, the crystallinity of the carbon material is not sufficient, and the low potential portion (L
It is not preferable because the capacity of 0 to 300 mV) based on the potential of i becomes insufficient.

The particle size distribution of the graphite material as the core material is 0.1%.
It is preferably about 150 μm. Since the particle size of the surface amorphous graphite substantially depends on the particle size of the graphite material as the core material, the particle size of the core material also substantially determines the particle size of the final product. If the particle size of the core material is smaller than 0.1 μm, there is a possibility that the risk of causing an internal short circuit through the pores of the battery separator may be increased. Also,
When the particle size of the core material is larger than 150 μm, the uniformity of the electrode and the handling property in the process of producing an electrode having a high filling density of the active material are deteriorated, which is not preferable.

As a method for forming a low-crystalline carbon material on the surface of highly crystalline graphite, a gas phase method, a liquid phase method, and a solid phase method can be applied.

In the gas phase method, a gaseous raw material or a liquid raw material is transported into a reaction system by a method such as spraying or bubbling, and the raw material is thermally decomposed to form a vapor phase on the surface of a highly crystalline graphite material. This is a method of forming carbon from. Although the pyrolysis temperature varies depending on the raw material, it is 450 to 15
It can be performed in a temperature range of about 00 ° C. Examples of the raw materials include aliphatic saturated hydrocarbons such as methane, ethane, and propane; aliphatic unsaturated hydrocarbons such as propylene; and aromatic hydrocarbons such as benzene, toluene, xylene, naphthalene, and perylene. Further, carboxylic acids, carboxylic anhydrides, carboxylic acid imidized compounds and the like derived from these aromatic hydrocarbons can also be used. The feed rate of the raw material can be appropriately set depending on the material, but the raw material concentration is 2 × 10 ^{21 to} 2.6 × 20 ²³ molecules / L, the feed rate is 0.05 to 20 mol / hour, and the flow rate is 0.5 to 70 c.
It is preferable to set within the range of m / min. In addition, an inert gas such as argon or nitrogen can be used as a carrier gas as appropriate, or a method of adding hydrogen to suppress generation of soot in a gas phase can be considered.

The liquid phase method is a method in which a raw material in which a carbon precursor is carbonized via a liquid phase is attached to the surface of graphite, and the carbon precursor is calcined to form carbon on the surface. As raw materials, aromatic hydrocarbons such as naphthalene, phenanthrene, acenaphthylene, anthracene, triphenylene, pyrene, chrysene, and perylene, tars or pitches obtained by polycondensation of these under heating and pressure, or of these aromatic hydrocarbons Examples of the mixture include tar, pitch, asphalt, oils, and the like having a mixture as a main component. These starting materials may be petroleum or coal.
In the present invention, the carbon material serving as the core material and heavy oil are mixed and stirred. The stirring method is not particularly limited, and includes, for example, a mechanical stirring method using a ribbon mixer, a screw-type kneader, a universal mixer, or the like. The stirring conditions (temperature and time) are appropriately selected according to the components of the raw materials (core material and heavy oil for coating), the viscosity of the mixture, and the like. The atmosphere at the time of stirring may be any of atmospheric pressure, pressurized pressure, and reduced pressure, and stirring under reduced pressure is preferable because the affinity between the core material and heavy oil is improved. In the present invention, in order to improve the conformity between the core material and the coating layer, make the thickness of the coating layer uniform, increase the thickness of the coating layer, and the like, if necessary, a plurality of the mixing and stirring steps described above are performed. It can be repeated several times. Further, prior to the subsequent washing step, the coated core material may be once separated and then subjected to the washing step.

The solid phase method is a method in which a raw material in which a carbon precursor is carbonized via a solid phase is attached to the surface of graphite, and the carbon is formed by firing them to form carbon on the surface. Some of the resin undergoes thermal decomposition and carbonization proceeds without an apparent melting state.However, in order to attach such a resin to the surface of highly crystalline graphite, the resin must be heated to a temperature above the melting point at which it dissolves in the solvent. For example, a method of forming a solid solution state by a method of mixing, mixing by the method described in the above description of the liquid phase method, and attaching the mixture to the surface. Further, it is also possible to mix the resin and the graphite material by mixing and holding the resin near the melting point of the resin during firing. Specific raw materials include polyimide resin;
Polyamide resin; conjugated resin such as polyacetylene, poly (p-phenylene), poly (p-phenylenevinylene), phenolic resin; furfuryl alcohol resin; cellulose; polyacrylonitrile, poly (α-halogenated acrylonitrile), polymethyl methacrylate It is possible to use acrylic resins or methacrylic resins such as, for example, vinyl halide resins such as polyvinyl chloride and polyvinylidene chloride, and copolymer resins thereof. As the firing conditions, the firing method and firing atmosphere described in the above-described liquid phase method can be applied.

The crystallinity of the low-crystalline carbon material is not particularly limited, but basically, a material having a low crystallinity as compared with the core material, that is, a material having a large d ₀₀₂ , a large R value, or the like, should be used. Thereby, the effect as surface amorphous graphite is obtained. In X-ray diffraction, the bulk properties of the material are specified, so when the surface layer is thin, it may not appear as a large difference. For example, in this case, Raman measurement that can measure the physical properties of the surface is performed. The measured R value can be used effectively. More preferably, the low crystalline carbon material has d ₀₀₂ greater than 0.34 nm and an R value of 0.5.
These are larger (preferably larger than 0.4), and these are prepared by simulating only the surface carbon material by setting the same conditions for the CVD of the carbon material to be deposited on the surface and the firing conditions for various raw materials. It can be defined indirectly by measuring physical properties.

The carbon material obtained in this way was
By firing at a temperature of about 2500 ° C.,
Surface amorphous graphite in which low crystalline carbon adheres to the surface of highly crystalline graphite can be obtained. The crystallinity of the surface carbon material can be controlled by the firing temperature. Examples of the atmosphere during firing include a non-oxidizing atmosphere such as a reducing atmosphere, an inert gas stream, a closed state of an inert gas, and a vacuum state. Regardless of the firing temperature, the heating rate is 1 to 300
It is appropriately selected from the range of about ° C / hour. Prior to firing, the highly crystalline graphite coated with the carbon precursor may be subjected to a washing step. By adding a washing step, it is possible to remove low molecular components of the carbon precursor, to improve the carbonization rate from the carbon precursor, and to suppress fusion or aggregation of the particles during firing. The effect is obtained. Here, as the organic solvent used for washing, toluene, quinoline, acetone, hexane, benzene, xylene, methylnaphthalene, alcohols,
Coal-based oil, petroleum-based oil, and the like. Among them, toluene, quinoline, acetone, benzene, xylene, methanol, coal-based light oil / medium oil, petroleum-based light oil / medium oil, and the like are more preferable.

In the washing step, the thickness of the coating layer, the remaining heavy oil component, and the like can be adjusted by selecting the type of solvent, washing time, washing temperature, and the like. Then, the separation step of the coated carbon material and the organic solvent,
It is performed by a method such as centrifugal separation, squeezing filtration, and gravity sedimentation. Drying of the separated coated carbon material is usually 100 to 4
It is performed in the range of 00 ° C. The dry-coated carbon material obtained in this way, even if it is subjected to carbonization and further graphitization, the pitch component around the core material particles is maintained, and the particles hardly fuse or aggregate. .

As the positive electrode of the present invention, for example, an oxide containing lithium can be used as the positive electrode active material. LiCoO ₂ , LiNiO ₂ , L
iMnO _2, LiFeO ₂ and of this series LiM _lX N _X O ₂
(Where M is any of Fe, Co, Ni, and Mn, and N represents a transition metal, a 4B group, or a 5B group metal; 0 ≦ X ≦ 1), LiMn ₂ O ₄ , and LiMn _{2−. X}
N _X O ₄ (where N represents a transition metal, a 4B group metal, or a 5B group metal; 0 ≦ X ≦ 2), LiVO _{2, and the} like, including a conductive agent, a binder, and, in some cases, It is formed by mixing a solid electrolyte and the like. The mixing ratio is preferably 1 to 50 parts by weight of the conductive agent and 1 to 30 parts by weight of the binder with respect to 100 parts by weight of the active material.

As the conductive agent, carbons such as carbon black (acetylene black, ketchen black, thermal black, channel black, etc.), graphite powder, metal powder and the like can be used, but are not limited thereto. is not. As the binder, a fluorine-based polymer such as polytetrafluoroethylene or polyvinylidene fluoride, a polyolefin-based polymer such as polyethylene or polypropylene, or a synthetic rubber can be used, but is not limited thereto.
When the amount of the conductive agent is less than 1 part by weight, the resistance and the polarization of the electrode are increased, and the charge / discharge capacity is reduced, which is not practical. When the amount of the conductive agent is more than 50 parts by weight (parts by weight vary depending on the type of the conductive agent to be mixed), the ratio of the active material contained in the electrode decreases, so that the discharge capacity as the positive electrode decreases. When the amount of the binder is less than 1 part by weight, the binding ability is lost. When the amount of the binder is more than 30 parts by weight, the amount of the active material contained in the electrode is reduced as in the case of the conductive agent, and the resistance of the electrode is reduced. Or, it is not practical because the polarization and the like increase and the discharge capacity decreases. It is preferable to perform heat treatment at a temperature around the melting point (T _m ) of each binder in order to improve the binding property in producing the positive electrode.

As the non-aqueous electrolyte (ionic conductor) of the present invention, an organic solvent-based electrolyte can be suitably used.
As a solvent of the organic solvent-based electrolyte, propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, esters such as γ-butyrolactone, tetrahydrofuran, substituted tetrahydrofuran such as 2-methyltetrahydrofuran, dioxolane, It is possible to use ethers such as diethyl ether, dimethoxyethane, diethoxyethane, and methoxyethoxyethane, dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl formate, methyl acetate, and the like. A mixture of two or more of these can be used. It is also possible to use solvents. Further, as a supporting electrolyte salt, lithium salts such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium arsenide hexafluoride, lithium trifluoromethanesulfonate, lithium halide, lithium chloride aluminate, etc. And these may be used alone or in combination of two or more. An organic solvent-based electrolyte is prepared by dissolving the supporting electrolyte salt in the organic solvent selected above. Note that the organic solvent and the supporting electrolyte salt used when preparing the organic solvent-based electrolyte are not limited to those described above.

Further, a typical form of the ionic conductor is a solid electrolyte. As a method for forming a solid electrolyte containing an organic solvent, a monomer or the like can be mixed with the above organic solvent, and a solidification can be performed by a polymerization reaction including a crosslinking reaction. Examples of the monomer include ethylene oxide, propylene oxide, glycidyl methacrylate and the like. These monomers may be used alone or in combination of two or more. The amount of the monomer relative to the solvent is
If the amount is too small, solidification is difficult, and if the amount is too large, lithium ion conductivity is impaired. Therefore, the volume fraction is preferably 1 to 50%. Further, an initiator for accelerating a crosslinking reaction or a polymerization reaction may be added. Examples of the polymerization initiator include azoisobutyronitrile and benzoyl peroxide. These initiators may be used alone or in combination of two or more. Alternatively, a polymer such as polyvinylidene fluoride, hexafluoropropylene, polymethyl methacrylate, polyvinyl chloride,
Or more, and mixed with tetrahydrofuran, N-methyl-2
-It can also be produced by dissolving in a solvent such as pyrrolidone, casting, and removing the solvent by drying or the like, and impregnating the solvent with the solvent. Alternatively, acrylonitrile, methyl acrylate, vinyl acetate, or the like as a vinyl monomer may be mixed with the organic solvent and polymerized by heating to be solidified. As the third electrolyte layer disposed between the positive electrode side and the negative electrode side, if necessary, a material impregnated in a support such as porous polyethylene, porous polypropylene, or nonwoven fabric may be used. In this case, it can be produced by impregnating the support with a liquid electrolyte and then polymerizing the vinyl monomer in the electrolyte with light or heat, or removing the solvent. Other ionic conductors include inorganic solid electrolytes, such as lithium nitride, halide,
It is possible to use oxyacid salts and the like, and more specifically, Li ₃ N, LiI, LiSiO ₄ —LiI—LiO
H, Li ₃ PO ₄ —Li ₄ SiO ₄ and the like. Further, a molten salt or the like can be applied instead of the organic solvent-based electrolyte.

As the separator for holding the electrolytic solution, it is possible to use a non-woven fabric or a woven fabric such as synthetic resin fibers, glass fibers, or natural fibers having electrical insulation properties, or a molded product of a powder such as alumina. . In particular, nonwoven fabrics such as polyvinylidene chloride, polyethylene, and polypropylene are preferable from the viewpoint of quality stability and the like. In the case of these synthetic resin non-woven fabrics, when the battery abnormally generates heat, the separator is melted by heat, and there is also added a function of shutting off between the positive and negative electrodes, and these can be suitably used from the viewpoint of safety. is there. Although the thickness of the separator is not particularly limited, it is sufficient that the separator has a thickness that can hold a required amount of the electrolytic solution and that prevents a short circuit between the positive electrode and the negative electrode.
Those having a thickness of about 1 to 1 mm can be used, and those having a thickness of about 0.02 to 0.05 mm can be used.

It is preferable that the filler is a powder. It is necessary that the filling auxiliary agent does not adversely affect the electrode characteristics. For example, a known lubricant or the like can be used. Specifically, oil,
It is possible to use lubricating oils such as animal and vegetable oils, synthetic lubricating oils such as dibasic acid esters and silicones, liquid lubricants such as liquid paraffin, and semi-solid grease. However, if a liquid or semi-solid material is used as a filling aid, the graphite material particles will be coated and must be removed by washing after forming the electrode. In addition, when the filling aid is liquid or semi-solid, there is a high possibility that the filling aid will penetrate into the pores of the graphite material particles. It is difficult to remove it, and if the filling aid remains in the pores, it becomes difficult for the electrolyte solution to penetrate into the battery when it is formed, which tends to have an adverse effect on battery characteristics. Therefore, a powder material that acts as a filling aid is particularly preferable in terms of the electrode manufacturing process and electrode characteristics.

The electron conductivity of the powder filling aid is preferably higher than the electron conductivity of the surface amorphous graphite, which is the negative electrode active material, in consideration of the mobility of electrons in the electrode.

It is preferable that the filler is a secondary particle in which primary particles are aggregated. That is, it is desirable that the primary particles of the filling aid be aggregated to form secondary particles. When secondary particles that are easily dispersed are selected, the particles are dispersed and enter the voids while assisting the filling of the graphite material particles with a relatively weak pressing force, so that the particles are less likely to remain between the graphite particles. Therefore, the filling aid is less likely to exist between the particles of the active material, and the active material density is likely to increase. On the other hand, artificial graphite and molybdenum disulfide are also known as solid lubricants. Such a layered material is slippery because it is strong against load and weak against shear. Therefore, when filling, the fact that it is weak against shearing is used. However, compared to the secondary particles being dispersed and entering the voids between the graphite material particles, there is a limit to the dispersion, the secondary particles are likely to remain between the graphite material particles, and the active material density is not easily increased. Furthermore, when artificial graphite is used as an active material, the smaller the particle size, the lower the initial charge / discharge efficiency tends to be. Therefore, it is not preferable that artificial graphite reduced by shearing exists in the electrode.

The structure of the secondary particles in the present invention means a structure in which several primary particles (unit particles) which are considered to be crystalline single are aggregated to form secondary particles (composite particles). Further, the “aggregation” in the present invention means that the force of the particles is based on the chemical bonding force or the physical Van der W
It is broadly divided into cases based on aals force and magnetic attraction. The former is called agglomerated particles or aggregates, and the latter is called collective particles or aggregates. The former is difficult to separate, and the latter is relatively easily dispersed into primary particles, but the latter used in the present invention is preferred but not limited. It is also possible to use secondary particles generated by sintering or solid-phase reaction.

It is possible to use carbon black as the filling aid. The carbon black particles forming the carbon black form aggregates called structures. The structure of the carbon black particles is defined as the permanently fused primary aggregates and Van
der Waals force and secondary aggregates aggregated by the interaction of der Waals forces. The carbon black used in the present invention is not particularly limited by the production history and the formation mechanism, but preferably has as high an electron conductivity as possible.

The smaller the particle diameter, the larger the abundance on the active material surface but the lower the electronic conductivity. Therefore, the primary particle diameter is preferably 5 to 75 nm, more preferably 10 to 40 nm. Therefore, acetylene black is preferred, but thermal black, furnace black, channel black and the like can also be used. Ketjen black having a graphitized surface can also be used. The mixing ratio of the surface amorphous graphite to the carbon black is 0.1 to 30 parts by weight, but it can be used as an electrode outside this range. When the content of the carbon black particles is more than 30 parts by weight, the active material density is hardly increased, and the charge / discharge capacity is reduced, which is not practical. Alternatively, if the carbon black particles themselves are capable of electrochemically inserting / desorbing Li ions, they will be reflected in the electrode characteristics, resulting in a drawback such that the electrode characteristics of surface amorphous graphite cannot be utilized.
If the content of the carbon black particles is less than 0.1 part by weight, the effect of the carbon black particles hardly appears.

It is possible to use zinc oxide as the filling aid. The zinc oxide particles forming zinc oxide are not particularly limited by the production history and the formation mechanism. The mixing ratio of the surface amorphous graphite and zinc oxide is 0.1 to 30 parts by weight, but it can be used as an electrode outside this range. If the zinc oxide content is more than 30 parts by weight, the resistance in the electrode increases, which is reflected in the electrode characteristics, and disadvantages such as the inability to utilize the electrode characteristics of the surface amorphous graphite occur. If the content of the zinc oxide particles is less than 0.1 part by weight, the effect of the content is difficult to appear. It is also possible to use secondary particles generated by sintering or solid-phase reaction.

Assuming that the average primary particle diameter of the negative electrode material particles forming the negative electrode material is R, the average secondary particle diameter in the particle size distribution of the filler aid particles forming the filler aid is (√2-
1) It is preferable that the average primary particle diameter of the filler auxiliary particles is larger than R and (√2-1) R or less.
When a material other than the active material exists between the graphite particles, the active material density of the electrode is unlikely to increase. Therefore, in order to increase the active material density of the electrode after the compression molding, it is desirable that the filling auxiliary agent enters the voids of the active material particles. For example, if a filler with low electronic conductivity is present between particles of graphite material, the electron conduction network will be partially broken, and the broken particles will become electrically isolated and no longer react. Will no longer be involved. As a result, the active material utilization of the negative electrode decreases, and the capacity decreases. Therefore, it is desirable that the filling aid in the electrode is dispersed after the electrode is subjected to compression molding or filling, enters the voids of the graphite material particles, and forms a network of electron conduction due to the connection between the graphite material particles.

From the above points, the present inventors have found the relationship between the particle diameter ratios of the surface amorphous graphite and the filler. That is, if the average secondary particle diameter in the particle size distribution of the filling aid is smaller than (√2-1) R, it becomes easy to enter the gaps between the surface amorphous graphite particles before compression molding or filling of the electrode, The function as a filling aid decreases. Also,
If the average primary particle diameter of the filler is larger than (√2-1) R, the active material density is increased because it is difficult to enter the voids between the surface amorphous graphite particles even when the filler is filled, and it is easy to remain between the particles. It is not preferable because it becomes difficult.

The average primary particle diameter R of the surface amorphous graphite as the negative electrode material is preferably in the range of 0.1 to 150 μm. When R is less than 0.1 μm, the risk of causing an internal short circuit through the pores of the battery separator increases. On the other hand, when R exceeds 150 μm, the uniformity of the electrode and the packing density of the active material are reduced. Any of these is not preferable because the handling property in the process of manufacturing a high electrode is reduced.

The average particle size is the average value of the primary particles visually observed from an electron micrograph, and the secondary particles in which the primary particles are aggregated are measured by a laser diffraction type particle size distribution analyzer. Is the mode diameter indicating the most frequent point.

[0050]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A negative electrode for a lithium secondary battery is characterized by a charging reaction in which lithium ions are inserted into the negative electrode via an electrolyte and a discharging reaction in which lithium ions in the negative electrode are desorbed into the electrolyte. It uses an electrochemical reaction.

The method for producing the negative electrode is described below. The binder is dissolved in a solvent in a mortar to disperse the negative electrode active material and the filling assistant. For the dispersion treatment, a kneader or a ball mill, a paint shaker, a dynamill, or the like is used.
The paste is adjusted so that the negative electrode active material, the binder, and the filling assistant are uniformly dispersed. This paste is applied to a metal foil of a current collector, which is temporarily dried at 40 to 100 ° C. and compression-molded. Roller presses are usually used for compression molding, and when these presses are applied, the material of the press surface, the rotation method, the temperature, the atmosphere, and the like are not particularly limited. After that, the excess filler is washed in an organic solvent. As the organic solvent, acetone, ethyl acetate and the like can be suitably used. Further, the lead is welded to the uncoated portion of the electrode. After that, one dried in vacuum at about 150 ° C. to remove moisture is used as a test negative electrode.

The method for producing the positive electrode is described below. The binder was dissolved in a solvent in a mortar to disperse the positive electrode active material and the conductive agent. For the dispersion treatment, a kneader, a ball mill, a paint shaker, a dynamill, or the like is used, and the paste is adjusted so that the positive electrode active material, the conductive agent, and the binder are uniformly dispersed. This paste is applied to the metal foil of the current collector,
This is preliminarily dried at 40 to 100 ° C., heat-treated at 150 ° C., and compression molded. Roller presses are usually used for compression molding, and when these presses are applied, the material of the press surface, the rotation method, the temperature, the atmosphere, and the like are not particularly limited. Weld the lead to the uncoated part of the electrode. Furthermore, what was dried under reduced pressure at about 150 ° C. to remove water is used as a positive electrode. The current collector is not limited to the above, and a conductor that is chemically and electrochemically stable with respect to the positive electrode / negative electrode active material and the electrolytic solution can be used.

For the evaluation of the electrochemical characteristics of the negative electrode, a three-electrode cell is applied, and the negative electrode is used as a test electrode, and metallic lithium is used as a counter electrode and a reference electrode. The cell configuration is such that the surface area of the counter electrode is sufficiently larger than that of the test electrode, and is set so as to be regulated by the potential of the test electrode. As the electrolyte, a mixed solvent mainly composed of ethylene carbonate (hereinafter abbreviated as EC) can be used, but there is no particular limitation. A solution in which 0.5 to 3.0 mol / dm ³ of a lithium salt is dissolved in this mixed solvent is used. The charge / discharge operation test was performed by constant current charge / discharge, and the charge termination potential was set to 0 to 0.01 V vs. 0 V. L
i / Li ⁺ , the discharge end potential is 2.0 to 3.0 V vs.
Li / Li ⁺ .

The characteristics of a non-aqueous secondary battery using the negative electrode of the present invention can be applied to various shapes such as a cylinder, a square, a coin, a button, a sheet, a paper, and a card. For example, in a cylindrical or prismatic battery, a sheet electrode is mainly inserted into a can, and the can and the sheet electrode are electrically connected. An electrolyte is injected and the sealing plate is sealed via an insulating packing, or the sealing plate and the can are insulated and hermetically sealed by hermetic sealing to produce a battery. At this time, a safety valve provided with a safety element can be used as a sealing plate. The safety element includes, for example, a fuse, a bimetal, a PTC element and the like as an overcurrent prevention element. In addition to the safety valve, the gasket is cracked as a measure against internal pressure rise in the battery can. A method of making a crack in the sealing plate, a method of making a cut in the battery can, and the like are used. Further, an external circuit incorporating measures for overcharging and overdischarging may be used. In the case of coin-type or button-type batteries, it is common practice to form the positive electrode and the negative electrode in the form of a pellet, put this in a can, and crimp the lid via an insulating packing. As the electrolyte, a mixed solvent mainly composed of EC is used, but there is no particular limitation. A solution in which 0.5 to 3.0 mol / dm ³ of a lithium salt is dissolved in this mixed solvent is used. As the separator, a synthetic resin nonwoven fabric was used. The charge / discharge operation test was performed at a constant current, the charge end voltage was 2.7 to 2.9 V, and the discharge end voltage was 4.1.
To 4.3V. Next, cycle characteristics of the manufactured battery are examined.

The evaluation of the electrodes and the battery was all performed in a glove box under an inert gas atmosphere. In general, argon, nitrogen, and the like are preferably used as the inert gas.

[0056]

The present invention will be described in more detail with reference to the following examples.

Example 1 In order to examine the increase in capacity of a negative electrode containing a filling aid by improving the filling property, a negative electrode was prepared by regulating the number of presses. Evaluation of the negative electrode characteristics was performed by applying a three-electrode cell and comparing the initial discharge capacity.

Carbon black (trade name: Toka Black # 5500, manufactured by Tokai Carbon), zinc oxide (trade name, manufactured by Kishida Chemical), artificial graphite (trade name: trade name:
KS-6; manufactured by Lonza), molybdenum disulfide (manufactured by Kishida Chemical), liquid paraffin (manufactured by Kishida Chemical) as a liquid filling aid, lubricating oil (product name: Molyoil Spray F10)
0; manufactured by Sumiko Lubricants Co., Ltd.).

As the negative electrode active material, surface amorphous graphite (particle size: 12
μm, d ₀₀₂ = 0.336 nm, R value = 0.35), the binder PVdF was dissolved in a solvent N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) in a mortar, and the above negative electrode The active material and the filler were dispersed. For the dispersing process, a twin-screw planetary mixing and kneading machine is used, and the anode active material, the binder,
The paste was adjusted so that the filling aid was uniformly dispersed.
The composition of the negative electrode was 100 parts by weight of surface amorphous graphite, PVdF1
The weight of the active material was about 10 mg / cm ² (the weight of the active material per unit area of the current collector), with 0 part by weight and the filling aid being 0.1 to 11 parts by weight. This paste was applied to a copper foil of 20 μm, which was temporarily dried at 50 to 70 ° C. and compression-molded. For compression molding, a test piece cut into the same area was pressed five times in the air using a roller press. The electrode size is 3.5 × 3.0cm (coating area 3.0 × 3.0c)
m). Further, those to which a liquid filling aid was applied were washed in acetone. After that, a lead of nickel foil (50 μm) was welded to the uncoated part, and 1
What was vacuum-dried at 50 ° C. for 12 hours was used as a negative electrode.

The crystallite size (Lc,
La) was determined. Form factor K for determining crystallite size
(= Lc · β · cos θ / λ; β: half width, θ: d ₀₀₂
, And λ: wavelength of X-ray) was 0.9. The particle size was measured using a laser diffraction particle size distribution meter (Shimadzu SALD110).
The measurement was carried out using 0) to obtain a particle size having a peak in the particle size distribution.

For the evaluation of the electrochemical characteristics of the negative electrode, a three-electrode cell was applied, and the negative electrode was used as a test electrode, and metallic lithium was used as a counter electrode and a reference electrode. The cell configuration was such that the surface area of the counter electrode was sufficiently larger than that of the test electrode, and was set so as to be regulated by the potential of the test electrode. As the electrolytic solution, a solution prepared by dissolving 1.0 mol / dm ³ of lithium perchlorate LiClO ₄ in a mixed solvent of EC and diethyl carbonate (hereinafter abbreviated as DEC) at a volume ratio of 1: 1 was used.

The charge / discharge operation test was performed at a constant current charge / discharge of 30 mA · g ⁻¹ and a charge termination potential of 0 V vs. Li / Li ⁺ , discharge end potential 2.5V vs. This was performed at 20 ° C. in a glove box under an atmosphere of Li / Li ⁺ and argon.

FIG. 1 shows the measurement results of the initial discharge capacity of the negative electrode containing each of the filling assistants. The cc of the unit of mAh / cc of the discharge capacity in the present embodiment indicates the entire volume of the electrode mixture. It has been clarified that the addition of a filling aid for improving the filling property and fluidity is effective in increasing the capacity. When no filler is added, the active material density is 1.44 g.
/ Cm ³ . The active material density of the electrode containing the filling aid was 1.47 to 1.57 g / cm ³ , and most of the electrodes were 1.5 g / cm ³ or more. In other words, it is considered that the fact that the active material density of the electrode was increased despite the fact that materials other than the active material were contained was reflected in the increase in the discharge capacity.

Example 2 In order to investigate the improvement of the filling property of the negative electrode containing the filling assistant, the yield at the time of producing the negative electrode was examined. The yield in the present embodiment refers to the negative electrode 100.
The individual pieces were pressed, and those having the negative electrode peeled off from the steel foil as the current collector during the press or adhered to the press side were rejected. The method for manufacturing the negative electrode, the amount of PVdF added, the weight of the active material, and the like were the same as those applied to Example 1 described above. Carbon black (trade name: Toka Black # 5500; manufactured by Tokai Carbon), zinc oxide (trade name: Kishida Chemical), artificial graphite (trade name: KS-6; manufactured by Lonza), molybdenum disulfide (trade name) Liquid paraffin (manufactured by Kishida Chemical) and a lubricating oil (trade name: Molyoil Spray F100; manufactured by Sumiko Lubricants) were used as liquid filling aids. The compression molding was repeated using a roller press until a predetermined active material density of 1.4 to 1.7 g / cm ³ was reached. In the case of a liquid filling assistant, a washing step was provided, and acetone was used as an organic solvent. Table 1 shows the number of acceptable negative electrodes containing the filling aid. Here, 0.1 part by weight of the filling aid is contained.

[0065]

[Table 1]

Example 3 The yield at the time of producing the negative electrode was examined in the same manner as in Example 2 except that 5 parts by weight of the filling aid was contained. Table 2 shows the acceptable number of negative electrodes containing the filling aid.

[0067]

[Table 2]

Example 4 The yield at the time of producing the negative electrode was examined in the same manner as in Example 2 except that 15 parts by weight of the filling aid was contained. Table 3 shows the acceptable number of negative electrodes containing the filling aid.

[0069]

[Table 3]

Use of filling aids described in Tables 1 to 3
The active material density is 1.5 g / cm ^ThreeIn the above,
It was revealed that the yield improved. this thing
Is to add a filling aid to improve the filling and fluidity.
With this, the surface amorphous graphite particles are easily filled
And the collection of electrode mixture observed when no filler was added.
Yield improved due to resolution of peeling from conductor
It is thought that it was done.

Example 5 In order to examine the cycle characteristics of a negative electrode containing a filling aid, a three-electrode cell was used to evaluate the negative electrode characteristics. Carbon black (trade name: # 3050; manufactured by Mitsubishi Chemical), zinc oxide (trade name; manufactured by Kishida Chemical), and artificial graphite (trade name: KS-6; manufactured by Lonza) were used as filling assistants. Negative electrode manufacturing method, PVdF addition amount,
The evaluation of the active material weight, the electrochemical characteristics, and the like were the same as those applied to Example 1 described above. The content of the filler was 1 part by weight, and the density of the active material was about 1.5 g / cm ^3, including those without the filler.

FIG. 2 shows the cycle characteristics of the negative electrode containing each of the fillers. The discharge capacity retention rate in this example was (discharge capacity in each cycle / discharge capacity in the first cycle) × 100 = discharge capacity retention rate (%). The cycle characteristics of the negative electrode containing the filler were better than those of the electrode without the filler. In the case where no filling assistant was added, the discharge capacity rapidly decreased around 60 cycles.
After the completion of the cycle test, when the electrode without the filling aid was observed, the electrode mixture was almost peeled off from the current collector and was barely adhered.

Therefore, since the negative electrode contains a filling aid, it is possible to perform compression molding uniformly and reasonably. Therefore, unlike the case where no filling aid is added, the amorphous carbon on the surface of the amorphous graphite may be broken. It is considered that the cycle characteristics were improved because the surface amorphous graphite did not peel off from the current collector.

Example 6 In order to examine a material that can be suitably used as a filling aid, a three-electrode cell was applied to the evaluation of negative electrode characteristics, and the initial charge / discharge efficiency was compared. As a powder filling aid, artificial graphite (trade name: KS-6; manufactured by Lonza), carbon black (trade name: Asahi HS-500; manufactured by Asahi Carbon), and liquid paraffin (Kishida) as a liquid filling aid. Chemical Co., Ltd.) and a lubricating oil (trade name: Ultra Road Spray; manufactured by Sumiko Lubricants). The surface active graphite (particle diameter 18 μm, d
₀₀₂ = 0.336 nm, R value = 0.5), and the method of manufacturing the negative electrode, the amount of PVdF added, the weight of the active material, the evaluation of the electrochemical characteristics, and the like were the same as those applied to Example 1 described above. . The content of the filling aid is 0.7 to 1.0 parts by weight, the active material density is about 1.6 g / cm ³ , a washing step is provided for a liquid filling aid, and acetone is used as the organic solvent. Was used.

FIG. 3 shows the initial charge / discharge efficiency of the negative electrode containing each of the fillers. The initial charge / discharge efficiency in this embodiment means initial discharge capacity / initial charge capacity. It was clarified that the initial charge / discharge efficiency was almost the same in the case of the liquid filling aid as in the case of no addition, but increased in the case of the powder filling aid. This is thought to be due to the fact that although the washing step was provided, the liquid filling auxiliary agent was attached to the pores and the binder of the graphite material and could not be completely washed. Therefore, it is considered that the battery easily reacts with the electrolytic solution at the time of charging, and the apparent charge capacity becomes large because the amount of cathode electricity is used for reductive decomposition, so that the charging / discharging efficiency does not become large.
In addition, when the filling aid was not added, the active material density was 1.6 g /
At a high density of ³ cm ³ , the surface of the surface amorphous graphite is peeled off during compression molding, and highly crystalline graphite material particles are exposed, so it is considered that the initial charge / discharge efficiency is unlikely to increase.

From the above, from the viewpoint of designing a battery, it is necessary to secure an initial charge / discharge efficiency of 80% or more of the negative electrode, and it is possible to omit a complicated step called a washing step.
It has been found that it is preferable to include a powder filling aid.

Example 7 The active material density was evaluated with respect to the number of times of pressing in order to examine conditions that can be suitably used as a powder filling auxiliary agent, in particular, the state of particles. Carbon black (trade name: Asahi HS-50) is used as a powder filling aid.
0; manufactured by Asahi Carbon), acetylene black (brand name: Denka Black; manufactured by Denki Kagaku Kogyo), ketchen black (brand name: Ketchen Black EC; manufactured by Ketchen Black International), zinc oxide (manufactured by Kishida Chemical), Artificial graphite (trade name: KS-10; manufactured by Lonza),
Molybdenum disulfide (Kishida Chemical) was used. The content of the filling assistant was 5 parts by weight, and the surface amorphous graphite (particle size: 25 μm) was used.
m, d ₀₀₂ = 0.336 nm, R value = 0.25), and the production method, composition, active material weight, etc. of the negative electrode were as in Example 1.
It was the same as that applied to

FIG. 4 shows the density of the active material of the negative electrode containing each filling aid with respect to the number of presses. The tendency of artificial graphite and molybdenum disulfide, which do not form secondary particles, tend to hardly increase to an active material density of 1.5 g / cm ³ or more even after repeated pressing. On the other hand, a material in which the powder filling aid forms secondary particles, that is, carbon black in which primary particles aggregate to form secondary particles as a result of SEM observation,
In the case of acetylene black, ketchen black, and zinc oxide, it was found that the active material density easily increased even at a density of 1.5 g / cm ³ or more. This means that artificial graphite particles and molybdenum disulfide particles do not become small enough to enter the voids of amorphous graphite particles on the surface as they are pressed as they are repeatedly pressed, and the density hardly increases because they remain between the graphite particles. it is conceivable that. Meanwhile, carbon black particles,
The zinc oxide particles function as a filling aid between the particles without entering the voids at the beginning of filling. It is considered that as the number of presses increases, the fillability of the graphite particles increases, and the secondary particles formed by weak physical bonding force enter the voids while being dispersed. From the above, it was found that a material forming secondary particles is preferable as a powder filling aid.

Thus, an electrode containing 5 parts by weight of carbon black, zinc oxide, artificial graphite, and molybdenum disulfide each as a powder filling aid was prepared, and negative electrode characteristics were evaluated using a three-electrode cell. 1.6g / c of active material density
m ^3, and the method of manufacturing the negative electrode, the amount of PVdF added, the weight of the active material, the evaluation of the electrochemical characteristics, and the like are described in Example 1 described above.
It was the same as that applied to

FIG. 5 shows the discharge capacity retention ratio of the negative electrode containing each of the filling assistants. The discharge capacity retention rate in this example was (discharge capacity at 100th cycle / discharge capacity at 1st cycle) × 100 = discharge capacity retention rate (%). Carbon black that forms secondary particles, the negative electrode containing zinc oxide maintains a relatively high discharge capacity retention rate,
The discharge capacity retention ratio of artificial graphite and molybdenum disulfide was relatively low. As described above, when the artificial graphite particles and molybdenum disulfide particles are repeatedly pressed, the particles themselves are sheared and made finer, and the reactivity with the electrolyte during charging and discharging increases. Furthermore, it is considered that the capacity retention rate was lowered because the surface of the surface amorphous graphite was peeled off due to weak dispersing power and the highly crystalline graphite particles were exposed. On the other hand, carbon black particles and zinc oxide particles
Since the secondary particles formed by weak physical bonding force enter into the voids while dispersing, it is unlikely to damage the surface of the surface amorphous graphite at the time of pressing, and it did not adversely affect the capacity retention ratio Conceivable.

From the above, as a powder filling aid, a material having a high lubricating property is not suitable for the present invention and is not suitable for the present invention. It has been found that zinc particles are preferably used.

Example 8 In order to examine the particle diameter ratio between the surface amorphous graphite of the powder and the filling aid, the characteristics of the negative electrode were evaluated using a three-electrode cell. Carbon black (trade name: Toka Black # 380) is used as a powder filling aid.
0; Tokai Carbon) and zinc oxide (Kishida Chemical). The content of the filler was 5 parts by weight, and the surface amorphous graphite (particle size: 12 μm, d ₀₀₂ = 0.336 nm, R value =
0.35), the active material density was set to about 1.6 g / cm ^{3, the} method of manufacturing the negative electrode, the amount of PVdF added, the weight of the active material,
The number of presses, evaluation of electrochemical characteristics, and the like were the same as those applied to Example 1 described above. Table 4 shows the initial discharge capacity of the negative electrode containing the filling aid of each powder.

[0083]

[Table 4]

The carbon black particles were formed by aggregating 70 nm primary particles to form secondary particles of about 7 μm. The zinc oxide particles had primary particles of about 0.5 μm aggregated to form secondary particles of about 3 μm, 5 μm, and 12 μm.

As shown in Table 4, if the average secondary diameter of the filling aid is smaller than (√2-1) R, and in this embodiment, smaller than 4.97 μm, the effect cannot be sufficiently obtained even if it is contained. It is understood that there is a tendency. Regarding the particle size ratio between the surface amorphous graphite and the filling auxiliary, if the average secondary particle size in the particle size distribution of the filling auxiliary is smaller than 4.97 μm, the particle diameter ratio between the surface amorphous graphite particles before compression molding or filling is reduced. It is considered that it enters the voids and does not easily function as a filling aid at the time of filling.

From the above, assuming that the average primary particle diameter of the negative electrode material particles forming the negative electrode material is R, the average secondary particle diameter in the particle size distribution of the filling aid particles forming the filling aid is (√2 -1) It was found that a relationship larger than R was suitably used.

(Example 9) In order to examine the average primary particle diameter of the filling aid, the characteristics of the negative electrode were evaluated using a three-electrode cell. Carbon black (trade name: Toka Black # 3800; manufactured by Tokai Carbon) and zinc oxide (manufactured by Kishida Chemical) were used as powder filling aids. The content of the filling auxiliary was 5 parts by weight, and the surface amorphous graphite (particle size: 12 μm) was used.
m, d ₀₀₂ = 0.336 nm, R value = 0.35), and the method of manufacturing the negative electrode, the amount of PVdF added, the weight of the active material, the number of presses, the evaluation of the electrochemical characteristics, and the like are applied to Example 1 described above. The same as what was done. Table 5 shows the initial discharge capacity of the negative electrode containing the filling aid of each powder.

[0088]

[Table 5]

As shown in Table 5, no effect was obtained even when the content of the filling auxiliary agent was larger than (# 2-1) R, and in this embodiment, larger than 4.97 μm. This is difficult to enter into the gap between the surface amorphous graphite particles even if filled,
Since the particles easily remain between the particles, the filling property is not increased, and the resistance in the electrode due to the partial disconnection of the electron conduction network, which increases the polarization, has affected the capacity reduction. It is considered something.

From the above, when the average primary particle diameter of the negative electrode material is R, the average primary particle diameter of the filler aid particles forming the filler aid has a relationship of (√2-1) R or less. It has been found that it is preferably used.

(Example 10) A battery was produced using a filling aid that had been obtained so far and a surface amorphous graphite produced by a different production method was evaluated. Carbon black (trade name: Asahi HS-500; manufactured by Asahi Carbon) and zinc oxide (manufactured by Kishida Chemical) were used as powder filling aids. 5 parts by weight of the filling aid and 1.5 g / cm of the active material density
And about ^3, a method of manufacturing a negative electrode, PVdF amount, the active material weight, etc. were the same as those applied in Example 1. The electrode size was 3.5 × 3.5 cm (coating area 3.0 × 3.5 cm).
3.0 cm).

First, in the case of the vapor phase method, artificial graphite (trade name: KS-25; manufactured by Lonza) was used as a core material, and low-crystalline carbon was attached to the graphite surface. Using propane as a source gas and argon as a carrier gas, a gas flow rate of 2 L / m
in. At this time, the raw material gas concentration was 20% by volume. The thermal decomposition temperature was 800 ° C., and the processing time was 5 hours. The obtained surface amorphous graphite was coated with the low-crystalline carbon at a ratio of 1 to the graphite material 9.

In the case of the liquid phase method, the core material is also KS-25.
Was used to attach low crystalline carbon to the graphite surface. Coal tar pitch was used as a raw material of low crystalline carbon. The carbon material as the core material and the coal tar pitch were mixed and stirred. The stirring conditions were 100 ° C. and atmospheric pressure.
The carbon material thus obtained was washed once with toluene, filtered and dried at 60 ° C. The thus obtained product was fired at 1000 ° C. to obtain surface amorphous graphite in which a low crystalline carbon material was adhered to the surface of high crystalline graphite. The atmosphere during firing was a vacuum state. The heating rate was 100 ° C./hour, and the firing time was 12 hours. The amount of low crystalline carbon in the obtained surface amorphous graphite was 2 in the ratio of the low crystalline carbon to the graphite material 8.

In the case of the solid phase method, cellulose was used as a raw material of low crystalline carbon. In this example, cellulose was once dissolved in a solvent, mixed with KS-25 as a core material, and stirred. The stirring conditions were room temperature and atmospheric pressure. The material thus obtained was once dried, lightly pulverized, and then calcined at 1000 ° C. to obtain a carbon material having a low crystalline carbon material adhered to the surface of highly crystalline graphite. . The atmosphere during firing was an N ₂ atmosphere. The heating rate was 100 ° C./hour, and the firing time was 12 hours. The coating amount of the low-crystalline carbon of the obtained surface amorphous graphite is 3
Was the percentage.

Lithium cobaltate LiC was used as the positive electrode active material.
oO ₂ was used. Binder polyvinylidene fluoride PVd
F was dissolved in a solvent NMP in a mortar to disperse the positive electrode active material and the conductive agent acetylene black. 2 for distributed processing
The paste was adjusted to a state in which the positive electrode active material, the conductive agent, and the binder were uniformly dispersed using an axial planetary mixing and kneading machine.
The composition of the positive electrode was 100 parts by weight of LiCoO ₂ , 5 parts by weight of acetylene black, and 10 parts by weight of PVdF10, and the weight of the active material was about 20 mg / cm ² (weight of the active material per unit area of the current collector). This paste was applied on an aluminum foil having a thickness of 50 μm, and was temporarily dried at 50 to 70 ° C., heat-treated at 150 ° C., and then compression-molded. For the compression molding, the active material density was 2.8 using a roller press machine in the atmosphere.
It was compression-molded to 9 to 2.91 g / cm ³ . Furthermore, what was dried under reduced pressure at about 150 ° C. for removing water was used as a positive electrode. The electrode size is 3.5 × 3.5 cm
(Coating part 3.0 × 3.0 cm).

In the battery, the negative electrode and the positive electrode prepared as described above were each separated by a separator (porous polyethylene body, 25 μm thick).
m), covered with a laminate film containing aluminum foil, and heat sealed on three sides.
1 mol / d to a mixed solution of C and DEC at a volume ratio of 1: 1
A solution prepared by dissolving m ³ of LiClO ₄ was injected, and the other was sealed with heat to produce the product.

In the charging / discharging operation test, the charging current was set to a constant current of 1.0 mA, and after reaching the charging end voltage of 4.2 V, the charging current was changed to 4.2 V.
, And the charging time was set to 24 hours. The discharge current is 0.2 mA, with the discharge end voltage being 2.75 V.
And All battery evaluations were performed at 20 ° C. in a glove box under an argon atmosphere. Table 6 shows the initial discharge capacity of the battery containing the filling aid of each powder.

[0098]

[Table 6]

As shown in Table 6, it was found that the effect can be obtained even when the filling aid is used for the surface amorphous graphite obtained by different production methods.

It should be understood that the embodiments and examples disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0101]

The non-aqueous electrolyte secondary battery of the present invention contains a filling aid in a negative electrode having surface amorphous graphite in which a low-crystalline carbon material is adhered to the surface of highly crystalline graphite. for that reason,
The filling property of the surface amorphous graphite as an active material is high and good electrode characteristics are exhibited without impairing the coating effect of the low-crystalline carbon material due to cracks and cracks. Therefore, a secondary battery with a high energy density can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a measurement result of an initial discharge capacity of a negative electrode.

FIG. 2 is a diagram illustrating measurement results of cycle characteristics of a negative electrode.

FIG. 3 is a diagram illustrating a measurement result of initial charge / discharge efficiency of a negative electrode.

FIG. 4 is a diagram illustrating a measurement result of an active material density of a negative electrode.

FIG. 5 is a diagram illustrating a measurement result of a discharge capacity retention ratio of a negative electrode.

Continued on the front page (72) Inventor Kazuo Yamada 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term (reference) 5H029 AJ03 AK03 AL07 AL08 AM03 AM05 AM07 DJ16 DJ17 DJ18 EJ04 EJ05 HJ05 5H050 AA08 CA08 CB08 CB30 DA09 EA10 EA12 FA17 FA18 FA19 FA20 HA05

Claims (6)

[Claims] 1. A non-aqueous electrolyte secondary battery having a positive electrode, a non-aqueous electrolyte, and a negative electrode, wherein the negative electrode has a low-crystalline carbon material attached to a surface of highly crystalline graphite as a negative electrode material. A non-aqueous electrolyte secondary battery having surface amorphous graphite and having, in the negative electrode material, a filling aid for improving the filling property of the surface amorphous graphite. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the filler is a powder. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the filling auxiliary agent is a secondary particle in which primary particles are aggregated. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the filler is carbon black. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein said filling auxiliary agent is zinc oxide. 6. When the average primary particle diameter of the negative electrode material particles forming the negative electrode material is R, the average secondary particle diameter in the particle size distribution of the filler aid particles forming the filler aid is (√2 -1) larger than R, and the average primary particle diameter of the filler auxiliary particles is (√2-1) R or less.
6. The non-aqueous electrolyte secondary battery according to any one of 5.