JP6448462B2 - Anode active material for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery, and method for producing anode active material for nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a negative electrode active material for a non-aqueous electrolyte secondary battery. Moreover, this invention relates also to the nonaqueous electrolyte secondary battery containing this negative electrode active material. Furthermore, this invention relates also to the manufacturing method of the negative electrode material for nonaqueous electrolyte secondary batteries.

  In recent years, small electronic devices typified by mobile terminals have been widely used, and further downsizing, weight reduction, and long life have been strongly demanded. In response to such market demands, development of secondary batteries capable of obtaining a high energy density, in particular, being small and light is underway. This secondary battery is not limited to a small electronic device, but is also considered to be applied to a large-sized electronic device represented by an automobile or the like, or an electric power storage system represented by a house.

  Among them, lithium ion secondary batteries are highly expected because they are small and easy to increase in capacity, and can obtain higher energy density than lead batteries and nickel cadmium batteries.

  Said lithium ion secondary battery is equipped with the electrolyte solution with the positive electrode, the negative electrode, and the separator, and the negative electrode contains the negative electrode active material in connection with charging / discharging reaction.

  As this negative electrode active material, a carbon material is widely used, but further improvement in battery capacity is required due to recent market demand. In order to improve battery capacity, use of silicon as a negative electrode active material has been studied. This is because the theoretical capacity of silicon (4199 mAh / g) is 10 times or more larger than the theoretical capacity of graphite (372 mAh / g), so that significant improvement in battery capacity can be expected. The development of a siliceous material as a negative electrode active material has been examined not only for silicon itself but also for compounds represented by alloys and oxides. In addition, the shape of the active material has been studied from a standard coating type for carbon materials to an integrated type directly deposited on a current collector.

  However, when silicon is used as the negative electrode active material as the main raw material, the negative electrode active material expands and contracts during charge and discharge, and therefore, it tends to break mainly near the surface of the negative electrode active material. Further, an ionic material is generated inside the active material, and the negative electrode active material is easily broken. When the negative electrode active material surface layer is cracked, a new surface is generated thereby increasing the reaction area of the active material. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a coating that is a decomposition product of the electrolytic solution is formed on the new surface, so that the electrolytic solution is consumed. For this reason, the cycle characteristics are likely to deteriorate.

  To date, various studies have been made on negative electrode materials and electrode configurations for lithium ion secondary batteries mainly composed of a siliceous material in order to improve battery initial efficiency and cycle characteristics.

  Specifically, for the purpose of obtaining good cycle characteristics and high safety, silicon and amorphous silicon dioxide are deposited simultaneously using a vapor phase method (see, for example, Patent Document 1). Further, in order to obtain a high battery capacity and safety, a carbon material (electron conductive material) is provided on the surface layer of the silicon oxide particles (see, for example, Patent Document 2). Furthermore, in order to improve cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is produced, and an active material layer having a high oxygen ratio in the vicinity of the current collector is formed ( For example, see Patent Document 3). Further, in order to improve the cycle characteristics, oxygen is contained in the silicon active material, the average oxygen content is 40 at% or less, and the oxygen content is increased at a location close to the current collector. (For example, refer to Patent Document 4).

Further, Si phase, (for example, see Patent Document 5) by using a nanocomposite containing SiO 2, _M y _O metal oxide in order to improve the initial charge and discharge efficiency. In order to improve cycle characteristics, SiO _x (0.8 ≦ x ≦ 1.5, particle size range = 1 μm to 50 μm) and a carbon material are mixed and fired at a high temperature (see, for example, Patent Document 6). Further, in order to improve cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is set to 0.1 to 1.2, and the difference between the maximum value and the minimum value of the molar ratio in the vicinity of the active material and current collector interface The active material is controlled within a range of 0.4 or less (see, for example, Patent Document 7). Further, in order to improve battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 8). Further, in order to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface layer of the siliceous material (see, for example, Patent Document 9).

Further, in order to improve cycle characteristics, conductivity is imparted by using silicon oxide and forming a graphite film on the surface layer (see, for example, Patent Document 10). In Patent Document 10, with respect to the shift value obtained from the Raman spectra for graphite coating, with broad peaks appearing at 1330 cm ^-1 and 1580 cm ^-1, their intensity ratio _I 1330 _{/ I 1580} is _{1.5 <I 1330} / _{I 1580} <3. In addition, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used in order to improve high battery capacity and cycle characteristics (see, for example, Patent Document 11). Further, in order to improve overcharge and overdischarge characteristics, silicon oxide in which the atomic ratio of silicon and oxygen is controlled to 1: y (0 <y <2) is used (see, for example, Patent Document 12). In addition, in order to improve high battery capacity and cycle characteristics, a mixed electrode of silicon and carbon is prepared and the silicon ratio is designed to be 5 wt% or more and 13 wt% or less (see, for example, Patent Document 13).

JP 2001-185127 A JP 2002-042806 A JP 2006-164955 A JP 2006-114454 A JP 2009-070825 A JP 2008-282819 A JP 2008-251369 A JP 2008-177346 A JP 2007-234255 A JP 2009-212074 A JP 2009-205950 A Japanese Patent No. 2,997,741 JP 2010-092830 A

  As described above, in recent years, small electronic devices typified by mobile terminals and the like have been improved in performance and multifunction, and the lithium ion secondary battery as the main power source is required to increase the battery capacity. ing. As one method for solving this problem, development of a lithium ion secondary battery composed of a negative electrode using a siliceous material as a main material is desired.

  Moreover, the lithium ion secondary battery using a siliceous material is desired to have a battery characteristic close to that of a lithium ion secondary battery using a carbon material. Thus, the use of silicon oxide modified by insertion and desorption of Li as the negative electrode active material has improved the cycle retention rate and initial efficiency of the battery. However, since the modified silicon oxide has been modified using Li, its water resistance is low. For this reason, the slurry containing the modified silicon oxide prepared at the time of manufacturing the negative electrode is not sufficiently stabilized, and an apparatus generally used for coating a carbon-based active material must be used. There was a problem that could not be used or was difficult to use. As described above, when using silicon oxide whose initial efficiency and cycle retention ratio are improved by modification with Li, the stability of the slurry containing water becomes insufficient. A negative electrode active material for a non-aqueous electrolyte secondary battery superior in production has not been proposed.

  The present invention has been made in view of the above problems, and provides a negative electrode active material for a non-aqueous electrolyte secondary battery that has high stability with respect to an aqueous slurry, high capacity, and excellent cycle characteristics and initial efficiency. The purpose is to provide.

In order to achieve the above object, the present invention has negative electrode active material particles, and the negative electrode active material particles contain a silicon compound containing a Li compound (SiO _x : 0.5 ≦ x ≦ 1.6). A negative electrode active material for a non-aqueous electrolyte secondary battery, wherein the negative electrode active material particles have a cyclic carbonate layer containing a cyclic carbonate on the surface, and the cyclic carbonate layer further contains a Li salt. A negative electrode active material for a non-aqueous electrolyte secondary battery is provided.

  In the negative electrode active material of the present invention, negative electrode active material particles containing a silicon compound (hereinafter also referred to as silicon-based active material particles) have a cyclic carbonate layer made of cyclic carbonate and containing a Li salt on the surface thereof. Therefore, the water resistance against the aqueous slurry is high. Conventionally, aqueous slurries containing silicon oxide modified by Li insertion and desorption have been liable to touch the alkali side in pH. For this reason, carboxymethyl cellulose or a sodium salt thereof, which is a thickener (binder) that is relatively weak against alkali, cannot be used stably, so that the slurry is easily destabilized. However, in the present invention, since the silicon-based active material particles have the cyclic carbonate layer containing the Li salt as described above, the pH of the slurry becomes difficult to touch the alkali side, and in particular, the thickener is difficult to change. Thus, a stable coating film can be obtained, and sufficient binding properties can be secured. Therefore, if the negative electrode active material of the present invention is used, a non-aqueous electrolyte secondary battery having a high battery capacity and a good cycle maintenance ratio utilizing the original characteristics of silicon oxide modified with Li can be industrially produced. Manufacturing in an advantageous production.

At this time, the Li salt contained in the cyclic carbonate layer is LiPF ₆ , LiBF ₄ , LiClO ₄ , LiBOB (lithium bisoxalate borate), LiFSA (lithium bis (fluorosulfonyl) amide), LiTFSA (lithium (trifluoromethane). (Sulfonyl) amide) and LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) are preferably included.

Specific examples of the Li salt contained in the cyclic carbonate layer include those described above. Among these, especially, as the Li salt, LiPF ₆ , LiBF ₄ , and LiClO ₄ are contained in the cyclic carbonate layer, so that the slurry becomes more stable.

  At this time, it is preferable that the cyclic carbonate contained in the cyclic carbonate layer contains one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate.

  Since the cyclic carbonates as described above are solid at normal temperature, a cyclic carbonate layer containing these will provide a more stable water-resistant layer. Among these, when ethylene carbonate or fluoroethylene carbonate is included, particularly stable battery characteristics can be obtained.

  At this time, the mass of the cyclic carbonate layer is preferably 15% by mass or less based on the mass of the silicon compound.

  If the cyclic carbonate layer is formed at the above ratio, the cyclic carbonate layer does not become too thick, so that the negative electrode active material has high conductivity. Moreover, since the ratio of the cyclic carbonate layer in the negative electrode active material is within an appropriate range, the negative electrode active material can contain a sufficient amount of a silicon compound and has a high battery capacity.

  At this time, it is preferable that the cyclic carbonate layer further contains a chain carbonate.

  When the chain carbonate is contained in the cyclic carbonate layer, the pH of the slurry becomes more difficult to touch the alkali side.

  At this time, it is preferable that the negative electrode active material particles include at least one of lithium carbonate and lithium fluoride between the silicon compound and the cyclic carbonate layer.

  Thus, by forming lithium carbonate or lithium fluoride in at least a part between the silicon compound and the cyclic carbonate layer, the amount of Li consumed when charging as a battery can be reduced.

At this time, it is preferable that at least one of Li ₂ SiO ₃ and Li ₄ SiO ₄ is present as the Li compound contained in the silicon compound.

Since Li silicates such as Li ₂ SiO ₃ and Li ₄ SiO ₄ are relatively stable as Li compounds, better battery characteristics can be obtained.

  At this time, the negative electrode active material particles preferably have a carbon film on the surface of the silicon compound.

  By having the carbon coating, the conductivity of the negative electrode active material particles is improved, so that better battery characteristics can be obtained.

  At this time, it is preferable that the silicon compound is modified by inserting and removing Li by an electrochemical method.

  If it is an electrochemical method, it becomes easy to control the potential of the silicon compound by using an external potential and a reference electrode, and Li inserted in an unnecessary region can be removed by using a discharge process. Therefore, the silicon compound modified by such a method has desired characteristics.

  At this time, the half width (2θ) of the diffraction peak attributed to the Si (111) crystal plane obtained by X-ray diffraction of the silicon compound is 1.2 ° or more, and the crystallite size attributed to the crystal plane Is preferably 7.5 nm or less.

  Since the silicon-based active material having such a half-value width and crystallite size has low crystallinity and a small amount of Si crystals, battery characteristics can be improved.

  At this time, the median diameter of the silicon compound is preferably 0.5 μm or more and 20 μm or less.

  When the median diameter is 0.5 μm or more, the area where the side reaction occurs on the surface of the silicon compound is small, so that Li is not consumed excessively and the cycle maintenance rate of the battery can be maintained high. Further, if the median diameter is 20 μm or less, the expansion at the time of inserting Li is small, it is difficult to crack, and cracks are hardly generated. Furthermore, since the expansion of the silicon compound is small, for example, a negative electrode active material layer in which a carbon active material is mixed with a commonly used silicon-based active material is not easily destroyed.

  Moreover, in order to achieve the said objective, this invention provides the nonaqueous electrolyte secondary battery characterized by including any one of said negative electrode active materials for nonaqueous electrolyte secondary batteries.

  Such a secondary battery has a high cycle maintenance ratio and initial efficiency, and can be manufactured industrially.

In order to achieve the above object, the present invention provides a method for producing a negative electrode material for a non-aqueous electrolyte secondary battery including negative electrode active material particles, which has a general formula SiO _x (0.5 ≦ x ≦ 1.6). ), A step of modifying the silicon oxide particles by inserting and removing Li from the silicon oxide particles, and a step of forming the modified silicon oxide particles. Forming a cyclic carbonate layer made of cyclic carbonate containing Li salt on the surface, and using the silicon oxide particles with the cyclic carbonate layer formed as the negative electrode active material particles, a non-aqueous electrolyte secondary battery The manufacturing method of the negative electrode material for nonaqueous electrolyte secondary batteries characterized by manufacturing the negative electrode material for batteries is provided.

  If it is a manufacturing method of such a negative electrode material for nonaqueous electrolyte secondary batteries, the nonaqueous negative electrode which has the high battery capacity and the favorable cycle maintenance factor which utilized the original characteristic of the silicon oxide modified using Li A material can be obtained. Furthermore, since the negative electrode material manufactured in this manner contains silicon-based active material particles having the cyclic carbonate layer as described above, the slurry produced at the time of manufacturing the negative electrode becomes stable. That is, a negative electrode material capable of industrially producing a secondary battery can be obtained.

  At this time, in the step of forming the cyclic carbonate layer, the modified silicon oxide particles are washed with a solution containing the cyclic carbonate and the Li salt, and the washed silicon oxide particles are dried, whereby the modified It is preferable to form a cyclic carbonate layer made of a cyclic carbonate containing the Li salt on the surface of the subsequent silicon oxide particles.

  Specifically, a cyclic carbonate layer containing a Li salt can be formed by such a method.

  The negative electrode active material of the present invention can improve the stability of the slurry produced during the production of the secondary battery, and if this slurry is used, an industrially usable coating film can be formed. Capacity, cycle characteristics, and initial charge / discharge characteristics can be improved. Moreover, the secondary battery of the present invention containing this negative electrode active material can be produced industrially superiorly, and the battery capacity, cycle characteristics, and initial charge / discharge characteristics are good. Moreover, the same effect can be acquired also in the electronic device, electric tool, electric vehicle, electric power storage system, etc. which used the secondary battery of this invention.

  Further, the method for producing a negative electrode material of the present invention provides a negative electrode material that can improve the stability of a slurry produced during the production of a secondary battery and can improve battery capacity, cycle characteristics, and initial charge / discharge characteristics. Can be manufactured.

It is sectional drawing which shows the structure of the negative electrode containing the negative electrode active material of this invention. It is the reformer in the bulk used when manufacturing the negative electrode active material of this invention. It is a figure showing the structural example (laminate film type) of the lithium secondary battery containing the negative electrode active material of this invention.

  Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.

  As described above, as one method for increasing the battery capacity of a lithium ion secondary battery, the use of a negative electrode using a silicon-based active material as a main material as a negative electrode of a lithium ion secondary battery has been studied. Lithium ion secondary batteries using silicon-based active materials as the main material are expected to have cycle characteristics and initial efficiency close to those of lithium ion secondary batteries using carbon materials. With a silicon-based active material modified with Li in order to obtain cycle characteristics and initial efficiency close to those of a secondary battery, it is difficult to produce a stable slurry, and it is difficult to produce a good quality negative electrode.

  Therefore, the present inventors have made extensive studies in order to obtain a negative electrode active material capable of easily producing a nonaqueous electrolyte secondary battery having a high battery capacity and good cycle characteristics and initial efficiency. The present invention has been reached.

The negative electrode active material of the present invention has negative electrode active material particles, and the negative electrode active material particles contain a silicon compound containing a Li compound (general formula SiO _x : 0.5 ≦ x ≦ 1.6). Active material particles. Moreover, the negative electrode active material particles have a cyclic carbonate layer containing cyclic carbonate on the surface. And this cyclic carbonate layer contains Li salt further.

  Since such a negative electrode active material includes silicon-based active material particles in which a cyclic carbonate layer containing a Li salt is formed on at least a part of the surface, when preparing an aqueous slurry during the production of the negative electrode, the pH of the slurry is Hard to touch the alkali side. Therefore, the adverse effect on the thickener (binder) that is weak against alkali can be reduced. Moreover, the cyclic carbonate layer is excellent in water resistance. Furthermore, since the Li salt is contained inside the cyclic carbonate layer, it becomes easier to smoothly transfer and receive Li ions during charging and discharging of the secondary battery. Because of these effects, even when using silicon-based active material particles modified with Li, it is possible to stably produce an aqueous slurry, high capacity, good cycleability and good initial efficiency. The negative electrode active material is easily mass-produced industrially for secondary batteries.

[Configuration of negative electrode]
Then, the structure of the negative electrode of the secondary battery containing such a negative electrode active material of this invention is demonstrated.

  FIG. 1 shows a cross-sectional view of a negative electrode containing the negative electrode active material of the present invention. As shown in FIG. 1, the negative electrode 10 is configured to have a negative electrode active material layer 12 on a negative electrode current collector 11. The negative electrode active material layer 12 may be provided on both surfaces or only one surface of the negative electrode current collector 11. Furthermore, the negative electrode current collector 11 may not be provided in the negative electrode of the nonaqueous electrolyte secondary battery of the present invention.

[Negative electrode current collector]
The negative electrode current collector 11 is an excellent conductive material and is made of a material that is excellent in mechanical strength. Examples of the conductive material that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). This conductive material is preferably a material that does not form an intermetallic compound with lithium (Li).

  The negative electrode current collector 11 preferably contains carbon (C) or sulfur (S) in addition to the main element. This is because the physical strength of the negative electrode current collector is improved. In particular, in the case of having an active material layer that expands during charging, if the current collector contains the above-described element, there is an effect of suppressing electrode deformation including the current collector. Although content of said content element is not specifically limited, Especially, it is preferable that it is 100 ppm or less. This is because a higher deformation suppressing effect can be obtained.

  The surface of the negative electrode current collector 11 may be roughened or may not be roughened. The roughened negative electrode current collector is, for example, a metal foil subjected to electrolytic treatment, embossing treatment, or chemical etching. The non-roughened negative electrode current collector is, for example, a rolled metal foil.

[Negative electrode active material layer]
The negative electrode active material layer 12 may contain a plurality of types of negative electrode active materials such as carbon-based active materials in addition to silicon-based active material particles. Furthermore, other materials such as a thickener (also referred to as “binder” or “binder”) or a conductive aid may be included in battery design. The shape of the negative electrode active material may be particulate.

As described above, the negative electrode of the secondary battery of the present invention includes silicon-based active material particles made of SiO _x (0.5 ≦ x ≦ 1.6) as the silicon-based active material. The silicon-based active material particles are a silicon oxide material (SiO _x : 0.5 ≦ x ≦ 1.6), and the composition is preferably such that x is close to 1. This is because high cycle characteristics can be obtained. The composition of the silicon oxide material in the present invention does not necessarily mean 100% purity, and may contain a trace amount of impurity elements.

  In the present invention, the lower the crystallinity of the silicon compound contained in the negative electrode, the better. Specifically, the full width at half maximum (2θ) of a diffraction peak attributed to a (111) crystal plane obtained by X-ray diffraction of a silicon-based active material is 1.2 ° or more, and a crystallite attributed to the crystal plane It is desirable that the size is 7.5 nm or less. As described above, since the crystallinity is low and the amount of Si crystals present is small, not only the battery characteristics are improved, but also a stable Li compound can be generated.

  In addition, the median diameter of the silicon compound is not particularly limited, but is preferably 0.5 μm or more and 20 μm or less. This is because, within this range, it is easy to occlude and release lithium ions during charging and discharging, and the silicon-based active material particles are difficult to break. If the median diameter is 0.5 μm or more, the surface area is not too large, so that side reactions are unlikely to occur during charging and discharging, and the battery irreversible capacity can be reduced. On the other hand, a median diameter of 20 μm or less is preferable because the silicon-based active material particles are difficult to break and a new surface is difficult to appear.

Furthermore, in the present invention, the silicon-based active material is preferably one in which one or more of Li ₂ SiO ₃ and Li ₄ SiO ₄ are present as the Li compound contained in the silicon compound. Since Li silicates such as Li ₂ SiO ₃ and Li ₄ SiO ₄ are relatively more stable than other Li compounds, silicon-based active materials containing these Li compounds can obtain more stable battery characteristics. Can do. These Li compounds can be obtained by selectively changing a part of the SiO ₂ component generated inside the silicon compound to a Li compound.

  In particular, it is preferable that such a silicon compound is modified by inserting and desorbing Li by an electrochemical method. In the electrochemical method, potential regulation or current regulation with respect to the lithium counter electrode is performed, and the Li compound can be selectively produced by changing the conditions. Furthermore, if it is an electrochemical method, it becomes easy to control the potential of the silicon compound by using an external potential and a reference electrode, and Li inserted in an unnecessary region can be removed by using a discharge process. . Therefore, the silicon compound modified by such a method has desired characteristics.

The Li compound inside the silicon active material can be quantified by NMR (nuclear magnetic resonance) and XPS (X-ray photoelectron spectroscopy). The XPS and NMR measurements can be performed, for example, under the following conditions.
XPS
・ Device: X-ray photoelectron spectrometer,
・ X-ray source: Monochromatic Al Kα ray,
・ X-ray spot diameter: 100 μm,
Ar ion gun sputtering conditions: 0.5 kV 2 mm × 2 mm.
²⁹ Si MAS NMR (magic angle rotating nuclear magnetic resonance)
Apparatus: 700 NMR spectrometer manufactured by Bruker,
Probe: 4 mm HR-MAS rotor 50 μL,
Sample rotation speed: 10 kHz,
-Measurement environment temperature: 25 ° C.

  By producing a negative electrode active material using such a modification (in-bulk modification) method, it is possible to reduce or avoid the formation of a Li compound in the Si region, and in the atmosphere or in an aqueous slurry, a solvent It becomes a stable substance in the slurry. Further, by performing the modification by an electrochemical method, it is possible to make a more stable substance with respect to the thermal modification (thermal doping method) in which the compound is randomly formed.

Although at least one kind of Li ₄ SiO ₄ and Li ₂ SiO ₃ produced in the bulk of the silicon-based active material improves the characteristics, it is the coexistence state of these two kinds that further improves the characteristics.

  Moreover, it is desirable that the silicon-based active material particles have a carbon film on the surface of the silicon compound. This is because conductivity is easily obtained.

  Further, when the silicon compound is modified by the electrochemical method as described above, it is preferable to form a carbon film on the surface of the silicon compound before the modification. This is because, in the reforming process in the bulk by the electrochemical method, the presence of the carbon film on the surface of the silicon compound enables the potential distribution to be reduced, and the generated Li compound can be more uniformly controlled. is there.

  In the present invention, the negative electrode active material particles preferably include one or more of lithium carbonate and lithium fluoride between the silicon compound and the cyclic carbonate layer. By forming lithium carbonate and lithium fluoride at least partially between the silicon compound and the cyclic carbonate layer, the amount of Li released from the positive electrode side when the battery is initially charged can be consumed by the negative electrode. Therefore, the initial efficiency of the battery is improved. The lithium carbonate and lithium fluoride can be formed as SEI (Solid-Electrolyte Interface) on the surface of the silicon compound when the negative electrode active material particles are electrochemically modified, and the above-described Li silicate. It can be generated at the same time.

  Further, as described above, when the carbon film is formed before the modification of the silicon compound, a layer containing at least one of lithium carbonate and lithium fluoride is formed on the surface of the carbon film.

  When the silicon-based active material particles have a carbon coating, a layer containing at least one of lithium carbonate and lithium fluoride, and a cyclic carbonate layer, the carbon coating and lithium carbonate and / or fluoride covering the top of the carbon coating Each layer is preferably laminated in the order of a lithium layer and a cyclic carbonate layer which is a water-resistant layer covering the outermost layer. Further, as described above, this cyclic carbonate layer contains a Li salt. If it is a negative electrode active material which has such a lamination | stacking, since a slurry can be kept stable and a good-quality coating film can be obtained, battery characteristics will improve.

  In the present invention, the cyclic carbonate contained in the cyclic carbonate layer preferably contains one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate. Since the cyclic carbonates as described above are solid at normal temperature, a cyclic carbonate layer containing these will provide a more stable water-resistant layer. Among these, when ethylene carbonate or fluoroethylene carbonate is included, particularly stable battery characteristics can be obtained.

Also, Li salt contained in the cyclic carbonate _{layer, LiPF 6, LiBF 4, LiClO} 4, LiBOB, LiFSA, it preferably contains LiTFSA, and one or more of LiTFSI. Specific examples of the Li salt contained in the cyclic carbonate layer include those described above. Among these, especially, as the Li salt, LiPF ₆ , LiBF ₄ , and LiClO ₄ are contained in the cyclic carbonate layer, so that the slurry becomes more stable. Moreover, Li salt which exists in the inside of a cyclic carbonate layer can be confirmed by XPS. The XPS conditions may be the same as those for measuring the Li compound in the silicon active material described above.

  Moreover, in this invention, it is preferable that the mass of a cyclic carbonate layer is 15 mass% or less with respect to the mass of a silicon compound. If the cyclic carbonate layer is formed with such a thickness that the ratio is 15% by mass or less, the decrease in conductivity can be prevented. Moreover, since a sufficient amount of silicon compound is present, a high battery capacity can be obtained. In order to make the cyclic carbonate layer as thin as possible, it is desirable that the cyclic carbonate layer be coated in a minimum amount, but it is desirable to coat the required amount according to the slurry holding method. Even when the cyclic carbonate layer is thinner, the above-described effects are exhibited.

  At this time, the cyclic carbonate layer preferably further contains a chain carbonate. When the chain carbonate is contained in the cyclic carbonate layer, the pH of the slurry becomes more difficult to touch the alkali during the production of the negative electrode, so that the slurry becomes more stable.

[Production method of negative electrode]
Then, an example of the manufacturing method of the negative electrode of the nonaqueous electrolyte secondary battery of this invention is demonstrated.

First, a method for producing a negative electrode material included in the negative electrode will be described. First, silicon oxide particles represented by SiO _x (0.5 ≦ x ≦ 1.6) are produced. Next, the silicon oxide particles are modified by inserting and removing Li from the silicon oxide particles. At the same time, a Li compound can be generated inside or on the surface of the silicon oxide particles. And the cyclic carbonate layer which consists of cyclic carbonate containing Li salt is formed in the surface of the silicon oxide particle after modification | reformation. A negative electrode material can be produced by mixing such silicon oxide particles as negative electrode active material particles with a conductive agent or a binder.

  More specifically, the negative electrode material is manufactured by the following procedure, for example.

  First, a raw material that generates silicon oxide gas is heated in a temperature range of 900 ° C. to 1600 ° C. in the presence of an inert gas or under reduced pressure to generate silicon oxide gas. In this case, the raw material is a mixture of metal silicon powder and silicon dioxide powder, and considering the surface oxygen of the metal silicon powder and the presence of trace amounts of oxygen in the reactor, the mixing molar ratio is 0.8 <metal silicon powder / It is desirable that the silicon dioxide powder is in the range of <1.3. The Si crystallites in the particles are controlled by changing the preparation range and vaporization temperature, and by heat treatment after generation. The generated gas is deposited on the adsorption plate. The deposit is taken out with the temperature in the reactor lowered to 100 ° C. or lower, and pulverized and powdered using a ball mill, a jet mill or the like.

  Next, a carbon film can be formed on the surface of the obtained powder material, but this step is not essential. However, it is effective for improving battery characteristics.

As a method for forming a carbon film on the surface layer of the obtained powder material, pyrolytic CVD is desirable. In pyrolysis CVD, silicon oxide powder is set in a furnace, the furnace is filled with hydrocarbon gas, and the temperature in the furnace is raised. The decomposition temperature is not particularly limited, but is particularly preferably 1200 ° C. or lower. More desirably, the temperature is 950 ° C. or lower, and unintended disproportionation of silicon oxide can be suppressed. Hydrocarbon gas is not particularly limited, 3 ≧ n of C _n H _m composition it is desirable. This is because the low production cost and the physical properties of the decomposition products are good.

  In-bulk reforming is desirably performed using an apparatus capable of electrochemically inserting and extracting Li. Although the apparatus structure is not particularly limited, for example, the bulk reforming can be performed using the bulk reforming apparatus 20 shown in FIG. The in-bulk reformer 20 includes a bathtub 27 filled with an organic solvent 23, a positive electrode (lithium source, reforming source) 21 disposed in the bathtub 27 and connected to one of the power sources 26, And a separator 24 provided between the positive electrode 21 and the powder storage container 25. The powder storage container 25 is connected to the other side of the power source 26. The powder storage container 25 stores silicon oxide powder 22. The powder storage container stores silicon oxide particles, and a voltage is applied to the powder storage container and the positive electrode (lithium source) storing the silicon oxide particles by a power source. Thereby, since lithium can be inserted into and desorbed from the silicon oxide particles, the silicon oxide powder 22 can be modified.

The modification produces Li silicate in the silicon oxide powder 22 and at least one of lithium carbonate (Li ₂ CO ₃ ) and lithium fluoride (LiF) on the surface of the silicon oxide powder 22. A layer containing can be formed at the same time. When the carbon film is formed on the surface of the silicon active material particles before the modification, as described above, the layer containing the lithium carbonate or the like is formed on the carbon film.

  Further, as described above, the formation of the carbon film is not essential. However, since the carbon coating is present on the surface of the silicon compound, the potential distribution can be reduced and the generated Li compound can be more uniformly controlled. It is desirable to form on the surface.

As the organic solvent 23 in the bathtub 27, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, or the like can be used. As the electrolyte salt contained in the organic solvent 23, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), or the like can be used.

  The positive electrode 21 may use a Li foil or a Li-containing compound. Examples of the Li-containing compound include lithium carbonate, lithium oxide, lithium cobaltate, lithium olivine, lithium nickelate, and lithium vanadium phosphate.

  Subsequently, a cyclic carbonate layer made of cyclic carbonate containing Li salt is formed on the surface of the modified silicon oxide particles. For example, the cyclic carbonate layer can be formed by the following procedure.

First, the modified silicon oxide particles are washed with a solution containing cyclic carbonate and Li salt. For example, ethylene carbonate (cyclic carbonate) and diethyl carbonate (chain carbonate) and LiBF 4 and washed for about 30 minutes with a solution of a mixture of _(lithium salt). At this time, the coating amount of the cyclic carbonate layer can be controlled by controlling the type and ratio of the cyclic carbonate and the chain carbonate. For example, when reducing the coating amount of the cyclic carbonate layer to ensure conductivity and battery capacity, if dimethyl carbonate is used as the chain carbonate, the amount of ethylene carbonate coated on the surface can be greatly reduced. . The concentration of the lithium salt in the solution can be set to, for example, about 1 mol / Kg. If propylene carbonate or ethylene carbonate is used as the cyclic carbonate, the coating efficiency can be further improved. And a cyclic carbonate layer can be formed by drying the silicon oxide particles after washing.

  Subsequently, while mixing a silicon-based active material containing silicon oxide particles having the above cyclic carbonate layer and a carbon-based active material as necessary, these negative electrode active material and other materials such as a binder and a conductive auxiliary agent are mixed. After mixing to form a negative electrode mixture, an organic solvent or water is added to form a slurry.

  Next, the negative electrode mixture slurry is applied to the surface of the negative electrode current collector 11 and dried to form the negative electrode active material layer 12 shown in FIG. At this time, a heating press or the like may be performed as necessary. As described above, the negative electrode of the nonaqueous electrolyte secondary battery of the present invention can be produced.

<Lithium ion secondary battery>
Next, a laminated film type lithium ion secondary battery will be described as a specific example of the nonaqueous electrolyte secondary battery of the present invention.

[Configuration of laminated film type secondary battery]
A laminated film type lithium ion secondary battery 30 shown in FIG. 3 is one in which a wound electrode body 31 is accommodated mainly in a sheet-like exterior member 35. The wound electrode body 31 has a separator between a positive electrode and a negative electrode, and is wound. There is also a case where a separator is provided between the positive electrode and the negative electrode and a laminate is accommodated. In both electrode bodies, the positive electrode lead 32 is attached to the positive electrode, and the negative electrode lead 33 is attached to the negative electrode. The outermost peripheral part of the electrode body is protected by a protective tape.

  The positive and negative leads 32 and 33 are led out in one direction from the inside of the exterior member 35 to the outside, for example. The positive electrode lead 32 is formed of a conductive material such as aluminum, and the negative electrode lead 33 is formed of a conductive material such as nickel or copper.

  The exterior member 35 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protective layer are laminated in this order. This laminate film is formed of two films so that the fusion layer faces the electrode body 31. The outer peripheral edges of the fusion layer are bonded together with an adhesive or an adhesive. The fused part is, for example, a film such as polyethylene or polypropylene, and the metal part is aluminum foil or the like. The protective layer is, for example, nylon.

  An adhesion film 34 is inserted between the exterior member 35 and the positive and negative electrode leads to prevent intrusion of outside air. This material is, for example, polyethylene, polypropylene, or polyolefin resin.

[Positive electrode]
The positive electrode has, for example, a positive electrode active material layer on both sides or one side of the positive electrode current collector, similarly to the negative electrode 10 of FIG.

  The positive electrode current collector is formed of, for example, a conductive material such as aluminum.

  The positive electrode active material layer includes any one or more of positive electrode materials capable of occluding and releasing lithium ions, and other materials such as a positive electrode binder, a positive electrode conductive additive, and a dispersant depending on the design. May be included. In this case, details regarding the positive electrode binder and the positive electrode conductive additive are the same as, for example, the negative electrode binder and negative electrode conductive additive already described.

As the positive electrode material, a lithium-containing compound is desirable. Examples of the lithium-containing compound include a composite oxide composed of lithium and a transition metal element, or a phosphate compound having lithium and a transition metal element. Among these described positive electrode materials, compounds having at least one of nickel, iron, manganese, and cobalt are preferable. These chemical formulas are represented by, for example, Li _x M ₁ O ₂ or Li _y M ₂ PO ₄ . In the formula, M ₁ and M ₂ represent at least one transition metal element. The values of x and y vary depending on the battery charge / discharge state, but are generally expressed as 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Examples of the composite oxide having lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), and lithium nickel cobalt composite oxide. . Examples of the lithium nickel cobalt composite oxide include lithium nickel cobalt aluminum composite oxide (NCA) and lithium nickel cobalt manganese composite oxide (NCM).

Examples of the phosphate compound having lithium and a transition metal element include a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (0 <u <1)). Is mentioned. If these positive electrode materials are used, a high battery capacity can be obtained, and excellent cycle characteristics can also be obtained.

[Negative electrode]
The negative electrode has the same configuration as the negative electrode 10 for lithium ion secondary battery in FIG. 1 described above, and has, for example, a negative electrode active material layer on both sides of the current collector. This negative electrode preferably has a negative electrode charge capacity larger than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material agent. Thereby, precipitation of lithium metal on the negative electrode can be suppressed.

  The positive electrode active material layer is provided on part of both surfaces of the positive electrode current collector, and similarly, the negative electrode active material layer is provided on part of both surfaces of the negative electrode current collector. In this case, for example, the negative electrode active material layer provided on the negative electrode current collector is provided with a region where there is no opposing positive electrode active material layer. This is to perform a stable battery design.

  In the region where the negative electrode active material layer and the positive electrode active material layer do not face each other, there is almost no influence of charge / discharge. Therefore, the state of the negative electrode active material layer is maintained as it is immediately after formation, whereby the composition of the negative electrode active material can be accurately examined with good reproducibility without depending on the presence or absence of charge / discharge.

[Separator]
The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass through while preventing a short circuit due to contact between the two electrodes. This separator is formed of, for example, a porous film made of synthetic resin or ceramic, and may have a laminated structure in which two or more kinds of porous films are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, and polyethylene.

[Electrolyte]
At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolytic solution). This electrolytic solution has an electrolyte salt dissolved in a solvent, and may contain other materials such as additives.

  For example, a non-aqueous solvent can be used as the solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, and tetrahydrofuran. Among these, it is desirable to use at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. This is because better characteristics can be obtained. In this case, more advantageous characteristics can be obtained by combining a high viscosity solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate. This is because the dissociation property and ion mobility of the electrolyte salt are improved.

  The solvent additive preferably contains an unsaturated carbon bond cyclic carbonate. This is because a stable film is formed on the surface of the negative electrode during charging and discharging, and the decomposition reaction of the electrolytic solution can be suppressed. Examples of the unsaturated carbon bond cyclic ester carbonate include vinylene carbonate and vinyl ethylene carbonate.

  The solvent additive preferably contains sultone (cyclic sulfonic acid ester). This is because the chemical stability of the battery is improved. Examples of sultone include propane sultone and propene sultone.

  Furthermore, it is preferable that the solvent contains an acid anhydride. This is because the chemical stability of the electrolytic solution is improved. Examples of the acid anhydride include propanedisulfonic acid anhydride.

  The electrolyte salt can contain, for example, any one or more of light metal salts such as lithium salts. Examples of the lithium salt include lithium hexafluorophosphate (LiPF6) and lithium tetrafluoroborate (LiBF4).

  The content of the electrolyte salt is preferably 0.5 mol / kg or more and 2.5 mol / kg or less with respect to the solvent. This is because high ion conductivity is obtained.

[Production method of laminated film type secondary battery]

  First, a positive electrode is manufactured using the positive electrode material described above. First, a positive electrode active material and, if necessary, a positive electrode binder and a positive electrode conductive additive are mixed to form a positive electrode mixture, which is then dispersed in an organic solvent to form a positive electrode mixture slurry. Subsequently, the mixture slurry is applied to the positive electrode current collector with a coating apparatus such as a die coater having a knife roll or a die head, and dried with hot air to obtain a positive electrode active material layer. Finally, the positive electrode active material layer is compression molded with a roll press or the like. At this time, heating may be performed or compression may be repeated a plurality of times.

  Next, a negative electrode is produced by forming a negative electrode active material layer on the negative electrode current collector, using the same operation procedure as the production of the negative electrode 10 for a lithium ion secondary battery described above.

  When producing the positive electrode and the negative electrode, respective active material layers are formed on both surfaces of the positive electrode and the negative electrode current collector. At this time, the active material application length of both surface portions may be shifted in either electrode (see FIG. 1).

  Subsequently, the electrolytic solution is adjusted. Subsequently, the positive electrode lead 32 is attached to the positive electrode current collector and the negative electrode lead 33 is attached to the negative electrode current collector by ultrasonic welding or the like. Subsequently, the positive electrode and the negative electrode are laminated or wound via a separator to produce a wound electrode body 31, and a protective tape is bonded to the outermost periphery. Next, the wound body is molded so as to have a flat shape. Subsequently, after sandwiching the wound electrode body between the folded film-shaped exterior member 35, the insulating portions of the exterior member are bonded to each other by a thermal fusion method, and the wound electrode body is released in only one direction. Enclose. Subsequently, an adhesion film is inserted between the positive electrode lead and the negative electrode lead and the exterior member. Subsequently, a predetermined amount of the adjusted electrolytic solution is introduced from the release portion, and vacuum impregnation is performed. After impregnation, the release part is bonded by a vacuum heat fusion method. The laminated film type secondary battery 30 can be manufactured as described above.

  In the non-aqueous electrolyte secondary battery of the present invention such as the laminated film type secondary battery 30 produced as described above, the negative electrode utilization rate during charge / discharge is preferably 93% or more and 99% or less. If the negative electrode utilization rate is in the range of 93% or more, the initial charge efficiency does not decrease, and the battery capacity can be greatly improved. Moreover, if the negative electrode utilization rate is in the range of 99% or less, Li is not precipitated and safety can be ensured.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples.

(Example 1-1)
The laminate film type secondary battery 30 shown in FIG. 3 was produced by the following procedure.

First, a positive electrode was produced. The positive electrode active material is 95 parts by mass of lithium nickel cobalt aluminum composite oxide (LiNi _0.7 Co _0.25 Al _0.05 O), 2.5 parts by mass of positive electrode conductive additive (acetylene black), and a positive electrode binder. (Polyvinylidene fluoride, PVDF) 2.5 parts by mass were mixed to obtain a positive electrode mixture. Subsequently, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone, NMP) to obtain a paste slurry. Subsequently, the slurry was applied to both surfaces of the positive electrode current collector with a coating apparatus having a die head, and dried with a hot air drying apparatus. At this time, a positive electrode current collector having a thickness of 15 μm was used. Finally, compression molding was performed with a roll press.

Next, a negative electrode was produced. First, a silicon-based active material was prepared as follows. A raw material mixed with metallic silicon and silicon dioxide was placed in a reaction furnace, and vaporized in a 10 Pa vacuum atmosphere was deposited on an adsorption plate, cooled sufficiently, and the deposit was taken out and pulverized with a ball mill. . After adjusting the particle size, the carbon film was coated by performing thermal CVD. The produced powder was subjected to bulk reforming using an electrochemical method in a mixed solvent having an ethylene carbonate and dimethyl carbonate volume ratio of 3: 7 (containing an electrolyte salt at a concentration of 1.3 mol / kg). Next, the modified silicon oxide particles were washed with a mixed solution of ethylene carbonate (EC), diethyl carbonate (DEC), and LiBF ₄ , filtered and dried to remove DEC. Thereby, the cyclic carbonate layer containing ethylene carbonate and LiBF ₄ was formed.

  The negative electrode active material was produced by blending the silicon-based active material prepared as described above and the carbon-based active material in a mass ratio of 1: 9. Here, as the carbon-based active material, a mixture of natural graphite and artificial graphite coated with a pitch layer at a mass ratio of 5: 5 was used. The median diameter of the carbon-based active material was 20 μm.

  Next, the produced negative electrode active material, conductive additive 1 (carbon nanotube, CNT), conductive additive 2 (carbon fine particles having a median diameter of about 50 nm), styrene butadiene rubber (styrene butadiene copolymer, hereinafter referred to as SBR), Carboxymethyl cellulose (hereinafter referred to as CMC) was mixed at a dry weight ratio of 92.5: 1: 1: 2.5: 3, and then diluted with pure water to obtain a negative electrode mixture slurry. In addition, said SBR and CMC are negative electrode binders (negative electrode binder). Here, the pH of the negative electrode mixture slurry was measured to evaluate the stability of the slurry. The pH of the negative electrode mixture slurry was measured after 1 hour had elapsed after the negative electrode mixture slurry was prepared.

Further, as the negative electrode current collector, an electrolytic copper foil (thickness 15 μm) was used. Finally, the negative electrode mixture slurry was applied to the negative electrode current collector and dried in a vacuum atmosphere at 100 ° C. for 1 hour. The amount of deposition (also referred to as area density) of the negative electrode active material layer per unit area on one side of the negative electrode after drying was 5 mg / cm ² .

Next, after mixing fluoroethylene carbonate (FEC), ethylene carbonate (EC) and diethyl carbonate (DEC) as a solvent, an electrolyte salt (lithium hexafluorophosphate: LiPF ₆ ) is dissolved to obtain an electrolyte solution. Prepared. In this case, the composition of the solvent was FEC: EC: DEC = 1: 2: 7 by volume, and the content of the electrolyte salt was 1.0 mol / kg with respect to the solvent. Furthermore, 1.5% by mass of vinylene carbonate (VC) was added to the obtained electrolytic solution.

  Next, a secondary battery was assembled as follows. First, an aluminum lead was ultrasonically welded to one end of the positive electrode current collector, and a nickel lead was welded to the negative electrode current collector. Subsequently, a positive electrode, a separator, a negative electrode, and a separator were laminated in this order and wound in the longitudinal direction to obtain a wound electrode body. The end portion was fixed with PET protective tape. As the separator, a laminated film of 12 μm sandwiched between a film mainly composed of porous polyethylene and a film mainly composed of porous polypropylene was used. Subsequently, after sandwiching the electrode body between the exterior members, the outer peripheral edges except for one side were heat-sealed, and the electrode body was housed inside. As the exterior member, a nylon film, an aluminum foil, and an aluminum laminate film in which a polypropylene film was laminated were used. Subsequently, the prepared electrolyte was injected from the opening, impregnated in a vacuum atmosphere, and then heat-sealed and sealed.

  The cycle characteristics and initial charge / discharge characteristics of the secondary batteries produced as described above were evaluated.

  The cycle characteristics were examined as follows. First, in order to stabilize the battery, charge and discharge was performed for 2 cycles at 0.2 C in an atmosphere at 25 ° C., and the discharge capacity at the second cycle was measured. Subsequently, charge and discharge were performed until the total number of cycles reached 499 cycles, and the discharge capacity was measured each time. Finally, the discharge capacity at the 500th cycle obtained by 0.2 C charge / discharge was divided by the discharge capacity at the second cycle to calculate a capacity retention rate (hereinafter also simply referred to as a maintenance rate). In the normal cycle, that is, from the 3rd cycle to the 499th cycle, charging and discharging were performed with a charge of 0.7 C and a discharge of 0.5 C.

  When examining the initial charge / discharge characteristics, the initial efficiency (hereinafter sometimes referred to as initial efficiency) was calculated. The initial efficiency was calculated from an equation represented by initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100. The ambient temperature was the same as when the cycle characteristics were examined.

  The stability (pH) of the negative electrode mixture slurry of Example 1-1 and Examples 1-2 to 1-9 and Comparative Examples 1-1 to 1-4 described later, and cycle characteristics of the secondary battery ( Maintenance rate%) and initial charge / discharge characteristics (initial efficiency%) were examined. The results shown in Table 1 were obtained.

(Example 1-2 to Example 1-9)
A secondary battery was fabricated basically in the same manner as in Example 1-1 except that the ratio of the mass of the cyclic carbonate layer to the mass of the silicon compound was changed as shown in Table 1. Adjustment of the coating amount of the cyclic carbonate layer can be adjusted by changing the ratio of EC and DEC. For example, when the cyclic carbonate layer is coated so that the mass ratio is 2 mass%, the ratio is adjusted to EC: DEC = 5: 95.

  Further, as in Example 1-1, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated.

(Comparative Example 1-1)
A secondary battery was fabricated basically in the same manner as in Example 1-1 except that no Li compound was produced in the silicon compound and no cyclic carbonate layer was formed. Further, as in Example 1-1, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated.

(Comparative Example 1-2 to Comparative Example 1-3)
A secondary battery was fabricated basically in the same manner as in Example 1-1 except that the cyclic carbonate layer was not formed. Further, as in Example 1-1, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated. In Comparative Example 1-3, the cyclic carbonate layer was not formed, but the layer containing LiBF ₄ was formed on the surface of the silicon compound so that the mass thereof was 0.1% by mass with respect to the mass of the silicon compound. did.

(Comparative Example 1-4)
A secondary battery was fabricated basically in the same manner as in Example 1-1 except that a cyclic carbonate layer was formed but no Li salt was included. Further, as in Example 1-1, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated.

  At this time, the silicon-based active material particles of Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-4 had the following properties. Table 1 shows the presence or absence of a cyclic carbonate layer, the amount of coating, the presence or absence of a cyclic carbonate species, the presence or absence of a Li salt, the presence or absence of a Li salt species, a Li compound contained in a silicon compound, lithium carbonate and lithium fluoride. It is as follows.

In the silicon-based active material particles, the value of x of the silicon compound represented by SiO _x was 1.0, and the median diameter D ₅₀ of the silicon compound was 4 μm. Further, the half width (2θ) of the diffraction peak attributed to the Si (111) crystal plane obtained by X-ray diffraction is 2.593 °, and the crystallite size attributed to the crystal plane Si (111) is 3.29 nm. Met. Moreover, the coating amount of the carbon coating was 5% by mass with respect to the total of the silicon compound and the carbon coating.

  When the pH of the slurry exceeds 10, the alkalinity is strong and adversely affects the binder, so that it is difficult to obtain a stable coating film at the time of electrode application. As shown in Table 1, in Examples 1-1 to 1-9, it was confirmed that the pH of the slurry was less than 10 and a stable coating film could be obtained. On the other hand, in Comparative Examples 1-2 and 1-3 in which the silicon compound contained a Li compound therein and no cyclic carbonate layer was formed, the pH of the slurry exceeded 10. Further, even in Comparative Example 1-4 in which the cyclic carbonate layer did not contain an Li salt, the pH exceeded 10 and the alkali side was greatly touched. Moreover, in Comparative Example 1-1 in which the Li compound was not generated in the silicon compound, the cycle retention rate and the initial efficiency were lowered. When the Li compound is not generated in the silicon compound as in Comparative Example 1-1, it is difficult to improve the battery capacity because the initial efficiency is particularly low and the irreversible capacity is large.

  In particular, in Examples 1-1 to 1-8 in which the mass of the cyclic carbonate layer was 15% by mass or less with respect to the mass of the silicon compound, a particularly good cycle retention rate was obtained. The ratio of the mass of the cyclic carbonate layer to the mass of the silicon compound was calculated from the change in mass before and after the heat treatment of the silicon compound powder coated with the cyclic carbonate layer at 200 ° C. under vacuum for 4 hours.

(Example 2-1 to Example 2-6)
A secondary battery was made basically in the same manner as in Example 1-4, except that the type of Li salt contained in the cyclic carbonate layer was changed as shown in Table 2. Further, in the same manner as in Example 1-4, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated. The results are shown in Table 2.

As shown in Table 2, in Examples 2-1 to 2-6, the pH was 10 or less, and good cycle retention and initial efficiency were obtained. In particular, when LiPF ₆ and LiClO ₄ were included in the cyclic carbonate layer, the pH could be further reduced as in the case where LiBF ₄ was included.

(Example 3-1 to Example 3-6)
A secondary battery was made basically in the same manner as in Example 1-4, except that the type of cyclic carbonate was changed as shown in Table 3. Further, in the same manner as in Example 1-4, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated. The results are shown in Table 3. In Table 3, FEC represents fluoroethylene carbonate, PC represents propylene carbonate, DFEC represents difluoroethylene carbonate, and VC represents vinylene carbonate. The mixing ratio of each cyclic carbonate in Examples 3-1 and 3-6 is 50:50 (volume ratio).

  As shown in Table 3, in Examples 3-1 to 3-6, the pH was 10 or less, and good cycle maintenance ratio and initial efficiency were obtained. When FEC was included as the cyclic carbonate, particularly good cycle retention and initial efficiency were obtained.

(Examples 4-1, 4-2, Comparative examples 4-1, 4-2)
A secondary battery was fabricated basically in the same manner as in Example 1-4 except that the amount of oxygen was adjusted in the silicon compound represented by SiOx. Further, in the same manner as in Example 1-4, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated. The results are shown in Table 4.

  When the amount of oxygen in the silicon compound was reduced, that is, when x <0.5, Si was rich, and the cycle retention rate was significantly reduced. Further, in the case of oxygen rich, that is, when x> 1.6, the resistance of the silicon oxide was increased, and the cycle maintenance ratio was greatly reduced.

(Example 5-1)
A secondary battery was produced basically in the same manner as in Example 1-4, except that no carbon film was formed on the surface of the silicon compound. Further, in the same manner as in Example 1-4, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated. The results are shown in Table 5.

  As shown in Table 5, when the silicon compound had a carbon film, the cycle characteristics were greatly improved.

(Example 6-1 to Example 6-9)
A secondary battery was produced basically in the same manner as in Example 1-4 except that the crystallinity of the silicon compound was changed. Further, in the same manner as in Example 1-4, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated. Note that the change in crystallinity can be controlled by heat treatment in a non-atmospheric atmosphere. Table 6 shows the half-value width 2θ (°) of the diffraction peak caused by the (111) crystal plane obtained by X-ray diffraction of the silicon-based active material. In Example 6-9, the half-value width is calculated to be 20 ° or more, but it is a result of fitting using analysis software, and a peak is not substantially obtained. Therefore, it can be said that the silicon compound of Example 6-9 is substantially amorphous.

  As shown in Table 6, a high capacity retention ratio is obtained with a low crystalline material having a half width (2θ) of 1.2 ° or more and a crystallite size due to the Si (111) plane of 7.5 nm or less. And stable slurry properties were obtained.

(Example 7-1 to Example 7-6)
A secondary battery was produced basically in the same manner as in Example 1-4, except that the median diameter of the silicon compound was changed as shown in Table 7. Further, in the same manner as in Example 1-4, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated. The results are shown in Table 7.

  As shown in Table 7, when the median diameter of the silicon compound was 0.5 μm or more, the maintenance ratio was improved, and the pH of the slurry was reduced. This is presumably because the surface area of the silicon compound was not too large and the area where the side reaction occurred could be reduced. On the other hand, if the median diameter is 20 μm or less, the particles are difficult to break during charging, and the water resistance effect on the surface does not deteriorate. Furthermore, if the median diameter is 20 μm or less, a new surface is hardly generated on the surface of the particles, and SEI due to the new surface is difficult to be generated during charging and discharging, and therefore loss of reversible Li can be suppressed.

(Example 8-1 to Example 8-3, Comparative Example 8-1)
A secondary battery was produced basically in the same manner as in Example 1-4, except that the mass ratio of the silicon-based active material and the carbon-based active material in the negative electrode active material was changed. In addition, when increasing the quantity of a silicon type active material, the quantity of the conductive support agent and the binder was made the same as that of Example 1-4, and only the ratio of the carbon type active material was changed. In the same manner as in Example 1-4, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated. The results are shown in Table 8.

  As the ratio of the silicon-based active material in the negative electrode active material is increased, a higher battery capacity is obtained. However, as shown in Table 8, the maintenance ratio and the initial efficiency are lowered. Moreover, even if the ratio of the silicon-based active material modified with Li was increased, the pH of the slurry was lower than 10. On the other hand, as can be seen from Table 8, the unmodified silicon compound has high slurry resistance, but the initial efficiency is extremely low, so it is difficult to increase the capacity.

(Example 9-1 to Example 9-3)
A secondary battery was produced basically in the same manner as in Example 1-4 except that the cyclic carbonate layer contained a chain carbonate as shown in Table 9. In the filtration after washing the silicon compound, the chain carbonate can be sealed in a part of the cyclic carbonate layer by abrupt filtration, that is, by shortening the time required for filtration. Moreover, what is necessary is just to change the kind of chain carbonate contained in the mixed solution used for washing | cleaning, in order to change the kind of chain carbonate to seal.

  In the same manner as in Example 1-4, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge / discharge characteristics were evaluated. The results are shown in Table 9. Note that. In Table 9, DMC represents dimethyl carbonate, and EMC represents ethyl methyl carbonate.

  As can be seen from Table 9, it was found that if the cyclic carbonate layer contains a chain carbonate, the pH becomes smaller and the stability of the slurry is further improved.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

10 ... negative electrode, 11 ... negative electrode current collector, 12 ... negative electrode active material layer,
20 ... Li doping reformer, 21 ... Positive electrode (lithium source, reforming source),
22 ... Silicon oxide powder, 23 ... Organic solvent, 24 ... Separator,
25 ... Powder container, 26 ... Power supply, 27 ... Bathtub,
30 ... Lithium ion secondary battery (laminate film type), 31 ... Electrode body,
32 ... Positive electrode lead (positive electrode aluminum lead),
33 ... negative electrode lead (negative electrode nickel lead), 34 ... adhesion film,
35 ... exterior member.

Claims (12)

Non-aqueous electrolyte secondary for aqueous slurry , having negative electrode active material particles, wherein the negative electrode active material particles contain a silicon compound containing Li compound (SiO _x : 0.5 ≦ x ≦ 1.6) A negative electrode active material for a battery,
The negative electrode active material particles have a carbon coating on the surface of the silicon compound;
The negative electrode active material particles have a cyclic carbonate layer containing cyclic carbonate on the surface,
The mass of the cyclic carbonate layer is 15% by mass or less based on the mass of the silicon compound,
The negative electrode active material for a non-aqueous electrolyte secondary battery for aqueous slurry , wherein the cyclic carbonate layer further contains a Li salt. 2. The aqueous slurry according to claim 1, wherein the Li salt contained in the cyclic carbonate layer contains one or more of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiBOB, LiFSA, LiTFSA, and LiTFSI . negative electrode active material for a non-aqueous electrolyte secondary battery of. The cyclic carbonate contained in the cyclic carbonate layer contains one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate. Negative electrode active material for non-aqueous electrolyte secondary battery for aqueous slurry . The negative electrode active material for a non-aqueous electrolyte secondary battery for an aqueous slurry according to any one of claims 1 to 3 , wherein the cyclic carbonate layer further contains a chain carbonate. The negative active material particles, between the cyclic carbonate layer and the silicon compound, any one of claims 1 to 4, characterized in that it is intended to include one or more of lithium carbonate and lithium fluoride The negative electrode active material for nonaqueous electrolyte secondary batteries for aqueous slurry as described in an item. The Li compound contained in the silicon compound includes one or more of Li ₂ SiO ₃ and Li ₄ SiO ₄ , according to any one of claims 1 to 5. Negative electrode active material for non-aqueous electrolyte secondary battery for aqueous slurry . The water-based slurry according to any one of claims 1 to 6 , wherein the silicon compound is modified by insertion and desorption of Li by an electrochemical method . negative electrode active material for a non-aqueous electrolyte secondary battery of. The silicon compound has a half-width (2θ) of a diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more and a crystallite size due to the crystal plane of 7. The negative electrode active material for a nonaqueous electrolyte secondary battery for an aqueous slurry according to any one of claims 1 to 7 , wherein the negative electrode active material is 5 nm or less. Negative active for a non-aqueous electrolyte secondary batteries for aqueous slurry as claimed in any one of claims 8, wherein the median diameter of the silicon compound is of 0.5μm or 20μm or less material. A nonaqueous electrolyte secondary battery comprising the negative electrode active material for a nonaqueous electrolyte secondary battery for an aqueous slurry according to any one of claims 1 to 9 . A method of manufacturing a negative electrode active material for a non-aqueous electrolyte secondary batteries for aqueous slurry containing the negative electrode active material particles,
Producing silicon oxide particles represented by the general formula SiO _x (0.5 ≦ x ≦ 1.6);
Coating the surface of the silicon oxide particles with a carbon coating;
Modifying the silicon oxide particles by inserting and desorbing Li from the silicon oxide particles;
Forming a cyclic carbonate layer made of cyclic carbonate containing Li salt on the surface of the modified silicon oxide particles,
In the step of forming the cyclic carbonate layer, the mass of the cyclic carbonate layer is 15% by mass or less based on the mass of the silicon oxide particles,
By using silicon oxide particles, wherein the cyclic carbonate layer was formed as the anode active material particles, a non-aqueous electrolyte for the aqueous slurry, which comprises a negative electrode active material for a non-aqueous electrolyte secondary batteries for aqueous slurry method of preparing a negative electrode active material for a secondary battery. In the step of forming the cyclic carbonate layer, the modified silicon oxide particles are washed with a solution containing the cyclic carbonate and the Li salt, and the washed silicon oxide particles are dried, whereby the oxidized oxide after the modification. on the surface of the silicon particles, the production method of the negative electrode active material for a non-aqueous electrolyte secondary batteries for aqueous slurry according to claim 11, characterized in that to form a cyclic carbonate layer consisting of a cyclic carbonate containing the Li salt.

Images