JP2017063040A - Negative electrode material for lithium ion battery and use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode material for a lithium ion battery, which is large in charge/discharge capacity, less in the resistance in charge/discharge, and superior in charge/discharge cycle characteristic and rapid charge/discharge characteristic.SOLUTION: A negative electrode material for a lithium ion battery comprises: a mixture of particles (A) including an element capable of occluding and releasing lithium, and carbon particles (B). In the negative electrode material, the particles (A) are 500 nm or less in 90%-particle diameter in a volume-based cumulative particle-size distribution; the carbon particles (B) include graphite particles; and the peak intensity ratio I(110)/I(004) of the carbon particle (B) is 0.2 or larger. A method for manufacturing a negative electrode material for a lithium ion battery comprises a step of mixing particles (A) including an element capable of occluding and releasing lithium, and carbon particles (B) so as to bury the particles (A) in the carbon particles (B) while loosening the agglomeration of the particles (A) by application of a mechanical energy thereto.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a negative electrode material for a lithium ion battery and use thereof. More specifically, the present invention relates to a negative electrode material capable of obtaining a lithium ion battery having a large charge / discharge capacity and good charge / discharge cycle characteristics, a paste containing the negative electrode material, a negative electrode sheet formed by applying the paste, and The present invention relates to a lithium ion battery having the negative electrode sheet.

The power consumption of portable electronic devices is increasing because the functionality of portable electronic devices is increasing at a speed exceeding the power saving of electronic components. Therefore, higher capacity and smaller size of the lithium ion battery, which is the main power source for portable electronic devices, are more strongly demanded than ever. In addition, the demand for electric vehicles is increasing, and the lithium-ion batteries used there are also strongly required to have a high capacity.
Conventional lithium-ion batteries mainly use graphite as a negative electrode material. Since graphite can only occlude Li up to a stoichiometric ratio of LiC ₆ , the theoretical capacity of a lithium ion battery using graphite as a negative electrode is 372 mAh / g.

  In order to increase the capacity of a lithium ion battery, it has been studied to use particles containing a metal element such as Si or Sn having a large theoretical capacity as a negative electrode material. For example, the theoretical capacity of a lithium ion battery when Si-containing particles are used as the negative electrode material is 4200 mAh / g. Since the theoretical capacity of a lithium battery using metal lithium is 3900 mAh / g, if Si or the like can be used as a negative electrode material, it is expected that a lithium ion battery having a smaller size and higher capacity than a lithium battery can be obtained. . However, negative electrode materials such as Si have a large expansion rate and contraction rate due to insertion / desorption (occlusion / release) of lithium ions. For this reason, gaps are generated between the particles, and the expected capacity cannot be obtained. Further, since the particles are crushed and pulverized by repeated large expansion and contraction, the electrical contact is interrupted and the internal resistance is increased, so that the obtained lithium ion battery has a short charge / discharge cycle life.

Therefore, a negative electrode material (Patent Document 1) containing particles containing Si and / or Sn and fibrous carbon, and a carbonaceous material containing particles containing Si and fibrous carbon are attached to the surface of the graphite particles. and the negative electrode material (Patent Document 2) comprising, Si, Sn, area ratio of G peak and D peak metal-based particles and d _002, such as Ge is by and Raman spectroscopy below 0.338nm than 0.3354nm is G / A negative electrode material composed of a mixture of graphite particles with D ≧ 9 (Patent Document 3), an element capable of occluding and releasing lithium ions such as Si and Ge, and an element not capable of occluding and releasing lithium ions such as copper. A negative electrode material (Patent Document 4) made of a solid solution is proposed.

JP 2004-178922 A JP 2004-182512 A JP 2004-362789 A Japanese Patent Laid-Open No. 2002-0775350

  The objective of this invention is providing the negative electrode material which can obtain the lithium ion battery which was large in charging / discharging capacity | capacitance, there was little resistance increase in charging / discharging, and was excellent in charging / discharging cycling characteristics and rapid charging / discharging characteristics.

As a result of intensive studies to achieve the above object, the present inventors have completed the invention including the following aspects.
[1] A negative electrode material comprising a mixture of particles (A) containing an element capable of inserting and extracting lithium and carbon particles (B) containing a graphite material,
The carbon particles have an aspect ratio of 1 or more and 5 or less calculated from an optical microscope image, and a 50% particle diameter in a volume-based cumulative particle size distribution measured by a laser diffraction particle size distribution analyzer is 2 to 40 μm, and The bulk density when tapping 400 times is 1.0 g / cm ³ or more and 1.35 g / cm ³ or less;
Graphite material, the ratio I _D / I _G of the peak intensity in the vicinity of the peak intensity (I _D) and 1580 cm ^-1 in the vicinity of 1360 cm ^-1 as measured by Raman spectroscopy spectra (I _G) ( R value) is 0.01 or more and 0.2 or less, and a coefficient of thermal expansion (CTE) of 30 ° C. to 100 ° C. is 4.0 × 10 ⁻⁶ / ° C. or more and 5.0 × 10 ⁻⁶ / ° C. or less. Lithium ions, which are obtained by heat-treating petroleum coke and / or coal coke at 2500 ° C. or higher, with an interplanar distance d ₀₀₂ determined from 002 diffraction lines in X-ray diffraction of 0.3340 nm to 0.3380 nm Negative electrode material for batteries.

[2] The negative electrode material for a lithium ion battery according to [1], wherein the particles (A) have a 90% particle diameter in a volume-based cumulative particle size distribution of 500 nm or less.
[3] The negative electrode material for a lithium ion battery according to [1] or [2], further including carbon fibers having a fiber diameter of 2 to 1000 nm and an aspect ratio of 10 to 15000.
[4] the carbon fiber is less than the surface spacing d ₀₀₂ obtained from 002 diffraction line in has been heat treated and powder X-ray diffraction at 2000 ° C. or more 0.344 nm, a lithium ion battery according to [3] Negative electrode material.
[5] The negative electrode material for a lithium ion battery according to [3] or [4], wherein the carbon fiber has a hollow structure therein and includes a branched carbon fiber.
[6] The negative electrode material for a lithium ion battery according to any one of [3] to [5], wherein the amount of the carbon fiber is 1 to 20 parts by mass with respect to 100 parts by mass of the carbon particles (B).
[7] The negative electrode material for a lithium ion battery according to any one of [1] to [6], wherein the amount of the particles (A) is 5 to 40 parts by mass with respect to 100 parts by mass of the carbon particles (B).
[8] The lithium ion battery according to any one of [1] to [7], wherein the element capable of inserting and extracting lithium ions is at least one selected from the group consisting of Si, Sn, Ge, and In. Negative electrode material.

[9] Carbon particles (B) are carbon-coated graphite particles containing particles composed of the above graphite material and a carbonaceous layer present on the surface thereof.
Carbonaceous layer, the ratio I of the intensity of a peak in the range of the peak intensity (I _D) and 1580～1620Cm ^-1 in the range of 1300～1400Cm ^-1 as measured by Raman spectroscopy spectra (I _{G) The} negative electrode material for a lithium ion battery according to any one of [1] to [8], wherein _D / I _G (R value) is 0.1 or more.
[10] The negative electrode material for a lithium ion battery according to [9], wherein the carbonaceous layer is obtained by adhering an organic compound to particles made of a graphite material and then heat-treating at a temperature of 500 ° C. or higher.

[11] The organic compound is at least one selected from the group consisting of petroleum pitch, coal pitch, phenol resin, polyvinyl alcohol resin, furan resin, cellulose resin, polystyrene resin, polyimide resin, and epoxy resin. ] The negative electrode material for lithium ion batteries of description.
[12] The negative electrode material for a lithium ion battery according to any one of [9] to [11], wherein the adhesion amount of the organic compound is 0.05 to 10 parts by mass with respect to 100 parts by mass of particles made of graphite material.
[13] The negative electrode material for a lithium ion battery according to any one of [1] to [12], including one in which the particles (A) are dispersed so as to fill the gaps between the carbon particles (B).
[14] The negative electrode material for a lithium ion battery according to any one of [1] to [12], including a carbon particle (B) in which the particle (A) is embedded.

[15] Particles (A) containing an element capable of inserting and extracting lithium;
Carbon particles (B) containing a graphite material,
A method for producing a negative electrode material for a lithium ion battery, comprising a step of applying mechanical energy to dissolve the particles (A) and mixing the carbon particles (B) so as to embed the particles (A).

[16] A negative electrode sheet comprising the negative electrode material according to any one of [1] to [14] and a binder.

[17] A lithium ion battery having at least one selected from the group consisting of a non-aqueous electrolyte and a non-aqueous polymer electrolyte, a positive electrode sheet, and the negative electrode sheet according to [16].
[18] The lithium ion according to [17], further containing at least one selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, and vinylene carbonate. battery.

  By using the negative electrode material of the present invention, a lithium ion battery having a large charge / discharge capacity, a small increase in resistance during charge / discharge, and excellent charge / discharge cycle characteristics and rapid charge / discharge characteristics can be produced.

It is a figure which shows the volume reference | standard accumulation particle size distribution of the Si particle used in Examples 1-4. 3 is a diagram showing an SEM image of the negative electrode material of Example 1. FIG. 6 is a view showing an SEM image of a negative electrode material of Example 2. FIG. It is a figure which shows the volume reference particle size distribution of the negative electrode material of Example 1 and 2, and the Si particle used in Examples 1-4. 6 is a diagram showing an SEM image of a negative electrode material of Example 3. FIG. 6 is a view showing an SEM image of a negative electrode material of Example 4. FIG.

  A negative electrode material for a lithium ion battery according to an embodiment of the present invention comprises a mixture of particles (A) containing an element capable of occluding and releasing lithium ions and carbon particles (B) containing a graphite material. Is.

(Particles containing elements that can occlude and release lithium ions (A))
The particles (A), which is one of the constituent materials of the negative electrode material according to one embodiment of the present invention, are made of a material containing an element capable of inserting and extracting lithium ions. Of course, the particles (A) mean other than the carbon particles (B) described later. The element contained in the particles (A) is not particularly limited as long as it can occlude / release lithium ions. Preferable elements include Si, Sn, Ge, or In. The particles (A) may be composed of a simple substance of the element or a compound containing the element, or a compound, a mixture, a eutectic or a solid solution containing at least two of the elements. May be. The particles (A) may be agglomerates of a plurality of fine particles. Examples of the shape of the particles (A) include lumps, scales, spheres, and fibers. Of these, spherical or lump shape is preferable. The particles (A) may be secondary particles.

Examples of the substance containing Si element include a substance represented by the general formula: M ^a _m Si. The substance is ^a compound, mixture, eutectic or solid solution containing the element Ma in ^a ratio of mmol to 1 mol of Si.
M ^a is an element excluding Li. Specifically, as ^{M a, Si, B, C} , N, O, S, P, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Examples thereof include Mo, Ru, Rh, Pd, Pt, Be, Nb, Nd, Ce, W, Ta, Ag, Au, Cd, Ga, In, Sb, and Ba. In addition, when ^Ma is Si, it means Si alone. In the formula, m is preferably 0.01 or more, more preferably 0.1 or more, and further preferably 0.3 or more.
Specific examples of the substance containing Si element include an alloy of Si element and alkaline earth metal; an alloy of Si and transition metal; an alloy of Si and metalloid; Si, Be, Ag, Al, Au, Cd. , Ga, In, Sb or Zn solid solution alloy or eutectic alloy; CaSi, CaSi ₂ , Mg ₂ Si, BaSi ₂ , Cu ₅ Si, FeSi, FeSi ₂ , CoSi ₂ , Ni ₂ Si, NiSi ₂ , _{MnSi, MnSi 2, MoSi 2,} CrSi 2, Cr 3 Si, TiSi 2, Ti 5 Si 3, NbSi 2, NdSi 2, CeSi 2, WSi 2, W 5 Si 3, TaSi 2, Ta 5 Si 3, PtSi, Silicides such as V ₃ Si, VSi ₂ , PdSi, RuSi, RhSi; SiO ₂ , SiC, Si ₃ N _{4 and the} like can be mentioned.

Examples of the substance containing Sn element include tin alone, tin alloy, tin oxide, tin sulfide, tin halide, and stannate. Specific examples of the substance containing the Sn element include an alloy of Sn and Zn, an alloy of Sn and Cd, an alloy of Sn and In, an alloy of Sn and Pb; SnO, SnO ₂ , M ^b ₄ SnO ₄ ( M ^b represents a metal element other than Sn) tin oxide such as;. SnS, tin sulfide such as ^{_{SnS 2, M b 2 SnS 3}} ; SnX 2, SnX 4, M b SnX 4 (M b is a metal other than Sn Tin is a tin halide such as MgSn, Mg ₂ Sn, FeSn, FeSn ₂ , MoSn, and MoSn ₂ .

The particle (A) has a 90% particle diameter (D ₉₀ ) in a volume-based cumulative particle size distribution measured by a laser diffraction particle size distribution analyzer, preferably 500 nm or less, more preferably 450 nm or less. In the measurement of the particle size distribution, the particle size of secondary particles is also included. The particles (A) preferably have a particle size distribution substantially free of particles having a size of 1 μm or more. As the particle diameter (A) increases, the particles (A) tend to be crushed by contraction and expansion during charge / discharge, and increase in internal resistance and decrease in charge / discharge cycle characteristics.
The particle (A) has a 10% particle diameter (D ₁₀ ) in a volume-based cumulative particle size distribution measured by a laser diffraction particle size distribution analyzer, preferably 80 nm or more, more preferably 100 nm or more. Further, the particle (A) has a 50% particle size (D ₅₀ ) in a volume-based cumulative particle size distribution measured by a laser diffraction particle size distribution analyzer, preferably 100 to 400 nm, more preferably 200 to 300 nm.

  In order to adjust the particle size distribution, a known pulverization method and / or classification method can be used. Examples of the pulverizer include a hammer mill, a jaw crusher, and a collision pulverizer. Moreover, classification can be performed by airflow classification and / or sieving. Examples of the airflow classifier include a turbo cryfire and a turboplex.

(Carbon particles (B))
The carbon particles (B), which is one of the constituent materials of the negative electrode material according to an embodiment of the present invention, generally have an aspect ratio of particles calculated from an optical microscope image of 1 to 5, preferably 1 to 2. It is. When the aspect ratio is within this range, a high-density electrode that satisfies the energy density required for a large battery can be produced.

The carbon particles (B) have a 50% particle diameter (D ₅₀ ) in a volume-based cumulative particle size distribution of preferably 2 to 40 μm, more preferably 2 to 15 μm. In the measurement of the particle size distribution, the particle size of secondary particles is also included.
If there are many fine particles, it is difficult to increase the electrode density. Conversely, if there are many large particles, the negative electrode sheet may be spotted to deteriorate the battery characteristics. Accordingly, the carbon particles (B) preferably have a particle size distribution in which 90% or more of particles having a particle diameter in the range of 1 to 50 μm are present on a number basis, and the number of particles having a particle diameter in the range of 5 to 50 μm The particle size distribution is preferably 90% or more on the basis. The carbon particles (B) have a 10% particle diameter (D ₁₀ ) in a volume-based cumulative particle size distribution measured by a laser diffraction particle size distribution analyzer, preferably 1 μm or more, more preferably 2 μm or more. Further, the carbon particles (B) have a 50% particle size (D ₅₀ ) in a volume-based cumulative particle size distribution measured by a laser diffraction particle size distribution analyzer, preferably 3 to 10 μm, more preferably 4 to 8 μm. .
In addition, the particle diameters of carbon particles made of only graphite materials described later, carbon particles containing graphite particles and a carbonaceous layer, and carbon particles made of graphite particles bound with carbon fibers or carbon-coated graphite particles are also used. The particle diameter is preferably as described above.

The carbon particles (B) have a bulk density of 400 g / cm ^{3 to} 1.35 g / cm ³ , preferably 1.1 g / cm ^{3 to} 1.3 g / cm when tapped 400 times. ³ or less. When the tapping density of the carbon particles (B) is within this range, the electrode density before pressing when applied to the electrode can be further increased. Further, it can be predicted from the value of the tapping density whether it is possible to obtain an electrode having a sufficient density by a single roll press. Furthermore, when the tapping density is within the above range, the electrode density reached during pressing can be sufficiently increased.

  The carbon particles (B) contain a graphite material. The carbon particles (B) may be particles composed only of graphite material (ie, graphite particles), or particles composed of graphite particles and a carbonaceous layer existing on the surface thereof (ie, carbon-coated graphite particles). It may be carbon-coated graphite particles or particles obtained by attaching carbon fibers to graphite particles.

[Particles made of graphite material]
Examples of the graphite material include artificial graphite, pyrolytic graphite, expanded graphite, natural graphite, scaly graphite, and scaly graphite. Of these, artificial graphite is preferred.
(1) R value graphite material, the ratio I _D between the intensity of a peak in the vicinity of the peak intensity (I _D) and 1580 cm ^-1 in the vicinity of 1360 cm ^-1 as measured by Raman spectroscopy spectra (I _G) / I _G (R value) is usually 0.01 or more and 0.2 or less, preferably 0.03 or more and 0.15 or less. The R value is considered as an index indicating the crystal growth state on the surface of the graphite material. In general, the larger the R value, the less developed the crystal.

(2) CTE
The graphite material has a coefficient of thermal expansion (CTE) of 30 ° C. to 100 ° C. of 4.0 × 10 ⁻⁶ / ° C. to 5.0 × 10 ⁻⁶ / ° C., preferably 4.1 × 10 ⁻⁶ / ° C. The above is 4.6 × 10 ⁻⁶ / ° C. or less.
The coefficient of thermal expansion (CTE) is determined as follows. First, 500 g of graphite material is pulverized to a size of 28 mesh or less and classified. Oil of 125 ° C. is prepared by mixing 60 g of grains having a size of 28 to 60 mesh, 32 g of grains having a size of 60 to 200 mesh, and 8 g of grains having a size of 200 mesh or less, and adding 25 g of a pitch serving as a binder thereto. Heat in bath for 20 minutes and mix evenly. The mixture is cooled and crushed to a size below 28 mesh again. 30 g of the obtained pulverized product is put into a pressure molding machine at 125 ° C. and molded by pressurizing at a gauge pressure of 450 kg / cm ² for 5 minutes. This molded body is put in a magnetic crucible, placed in a firing furnace, and heated from room temperature to 1000 ° C. in 5 hours, and then fired under the condition of holding at 1000 ° C. for 1 hour. Then, it cools to room temperature, takes out from a baking furnace, cuts a baked product into 4.3x4.3x20.0mm with a precision cutter, and obtains the test piece for a coefficient of thermal expansion measurement. The test piece is measured for the thermal expansion coefficient in the length direction of the test piece at 30 to 100 ° C. using a TMA (thermomechanical analyzer; for example, TMA / SS350 manufactured by Seiko Electronics).

(3) d ₀₀₂
The graphite material has d ₀₀₂ of 0.3340 nm to 0.3380 nm, preferably 0.3362 to 0.3370 nm. Further, the graphite material preferably has L _C of 50 nm or more, more preferably 50 nm to 100 nm. Incidentally, d ₀₀₂ is spacing calculated from 002 diffraction line in the powder X-ray diffraction, L _C is a c-axis direction of the crystallite size determined from 002 diffraction line in the powder X-ray diffraction. d ₀₀₂ is considered to be an index indicating the crystal growth state of the entire graphite material. In general, the smaller d ₀₀₂ represents the more developed crystal.

(4) Coal coke and / or petroleum coke The graphite material uses coal coke and / or petroleum coke as a raw material. The raw material coke preferably has a coefficient of thermal expansion from 30 ° C. to 100 ° C. of 2.0 × 10 ⁻⁶ / ° C. or less. This coefficient of thermal expansion can be measured by the following method. 500 g of raw material coke is pulverized to a size of 28 mesh or less and classified. Oil of 125 ° C. is prepared by mixing 60 g of grains having a size of 28 to 60 mesh, 32 g of grains having a size of 60 to 200 mesh, and 8 g of grains having a size of 200 mesh or less, and adding 25 g of a pitch serving as a binder thereto. Heat in bath for 20 minutes and mix evenly. The mixture is cooled and crushed to a size below 28 mesh again. 30 g of the obtained pulverized product is put into a pressure molding machine at 125 ° C. and molded by pressurizing at a gauge pressure of 450 kg / cm ² for 5 minutes. This compact was put in a magnetic crucible, placed in a firing furnace, and heated from room temperature to 1000 ° C. in 5 hours and then fired under the condition of holding at 1000 ° C. for 1 hour. Then, it cools to room temperature, takes out from a baking furnace, cuts a baked product into 4.3x4.3x20.0mm with a precision cutter, and obtains the test piece for a coefficient of thermal expansion measurement. The test piece is measured for the thermal expansion coefficient in the length direction of the test piece at 30 to 100 ° C. using a TMA (thermomechanical analyzer; for example, TMA / SS350 manufactured by Seiko Electronics).

  The graphite material is obtained by heat-treating the above raw material coke usually at a temperature of 2500 ° C. or higher. Although the upper limit of heat processing temperature is not specifically limited, 3200 degreeC is preferable. This heat treatment is preferably performed in an inert atmosphere. In the heat treatment, a conventional Atchison-type graphitization furnace or the like can be used.

The particles made of a suitable graphite material preferably have a BET specific surface area of 1 to 10 m ² / g, more preferably 1 to 7 m ² / g.

(Carbon-coated graphite particles)
The carbon particles (B) may be those containing particles made of the above graphite material and a carbonaceous layer existing on the surface thereof (hereinafter sometimes referred to as carbon-coated graphite particles). Good.
The carbonaceous layer present on the surface, the graphite component in the range 1300~1400cm amorphous component derived from the intensity of the peak in the range of ^-1 (I _D) and 1580～1620Cm ^-1 measured by Raman spectroscopy The ratio I _D / I _G (R value) to the intensity (I _G ) of the peak derived from is preferably 0.1 or more, more preferably 0.2 or more, still more preferably 0.4 or more, particularly preferably 0. 6 or more. By providing a carbonaceous layer having a large R value, that is, a layer made of an amorphous carbon material, on the surface of the graphite particles, lithium ion insertion / extraction is facilitated, and rapid charge / discharge characteristics of the lithium ion battery are improved. The

  The carbon-coated graphite particles can be produced according to a known method. For example, graphite powder is first pulverized to obtain graphite particles finely pulverized to a predetermined size. Next, the graphite particles are stirred while spraying the organic compound. Alternatively, graphite particles and an organic compound such as pitch or phenol resin are mixed with an apparatus such as a hybridizer manufactured by Nara Machinery to perform mechanochemical treatment.

  The organic compound is not particularly limited, but isotropic pitch, anisotropic pitch, resin, resin precursor or monomer is preferable. When a resin precursor or monomer is used, it is preferable to polymerize the resin precursor or monomer to make a resin. Suitable organic compounds include at least one compound selected from the group consisting of phenol resins, polyvinyl alcohol resins, furan resins, cellulose resins, polystyrene resins, polyimide resins, and epoxy resins. Among these, the organic compound is preferably at least one selected from the group consisting of petroleum pitch, coal pitch, phenol resin, polyvinyl alcohol resin, furan resin, cellulose resin, polystyrene resin, polyimide resin, and epoxy resin. The amount of the carbonaceous layer present on the surface of the graphite particles can be adjusted by the amount of the organic compound attached. The adhesion amount of the organic compound is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the graphite particles. If the amount of the carbonaceous layer is too large, the battery capacity may be reduced.

Next, the graphite particles to which the organic compound is attached are preferably heat-treated at 200 ° C. or higher and 2000 ° C. or lower, more preferably 500 ° C. or higher and 1500 ° C. or lower, and further preferably 900 ° C. or higher and 1200 ° C. or lower. Carbon-coated graphite particles are obtained by this heat treatment. If the heat treatment temperature is too low, carbonization of the organic compound is not sufficiently completed, and hydrogen and oxygen remain in the carbon particles (B), which may adversely affect battery characteristics. On the other hand, if the heat treatment temperature is too high, crystallization proceeds excessively and the charging characteristics may be deteriorated. The heat treatment is preferably performed in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include an atmosphere filled with an inert gas such as argon gas or nitrogen gas. Since the carbon-coated graphite particles may be fused and formed by heat treatment, the carbon-coated graphite particles are preferably crushed so as to have the above-described particle diameter in order to use the carbon-coated graphite particles as an electrode active material. The BET specific surface area of the carbon-coated graphite particles is preferably 0.5 to 30 m ² / g, more preferably 0.5 to 10 m ² / g, still more preferably 0.5 to ⁵ m ² / g.

  Furthermore, the negative electrode active material according to the present invention forms a mixture layer by applying a mixture comprising the negative electrode active material and a binder onto a copper foil, drying, and then press molding, The peak intensity ratio I (110) / I (004) when the mixture layer is measured by the X-ray diffraction method is preferably 0.2 or more, more preferably 0.35 or more and 0.9 or less. The peak intensity ratio I (110) / I (004) obtained by this measurement method indicates the orientation of the graphite powder. The larger this value, the lower the orientation.

(Graphite particles with carbon fibers bound)
The carbon particles (B) may be formed by binding carbon fibers to the surface of the above-described graphite particles or carbon-coated graphite particles. Examples of the carbon fiber include vapor grown carbon fiber, petroleum pitch-based carbon fiber, coal pitch-based carbon fiber, and PAN-based carbon fiber. Of these, vapor grown carbon fiber is preferred.
The carbon fiber used has an average fiber diameter of preferably 2 to 1000 nm, more preferably 10 to 500 nm, still more preferably 50 to 300 nm, still more preferably 70 to 200 nm, and particularly preferably 100 to 180 nm. When the average fiber diameter is too small, the handling property tends to decrease.
The aspect ratio of the carbon fiber is not particularly limited, but is preferably 5 to 1000, more preferably 5 to 500, still more preferably 5 to 300, and particularly preferably 5 to 200. When the aspect ratio is 5 or more, the function as the fibrous conductive material is exhibited, and when the aspect ratio is 1000 or less, the handling property is good.

Further, the carbon fibers preferably have a surface spacing d ₀₀₂ obtained from 002 diffraction line in the powder X-ray diffraction 0.344nm, more preferably at most 0.339 nm.
Furthermore, it is preferable that carbon fiber has a hollow structure inside and contains branched carbon fiber.

  Vapor-grown carbon fiber is produced by introducing organic compounds such as benzene, which is a raw material, into a high-temperature reactor using a carrier gas together with a catalyst composed of an organic transition metal compound such as ferrocene, followed by gas-phase pyrolysis. be able to. As a production method, for example, a method of generating pyrolytic carbon fibers on a substrate (Japanese Patent Laid-Open No. 60-27700), a method of generating pyrolytic carbon fibers in a floating state (Japanese Patent Laid-Open No. 60-54998), There are methods for growing pyrolytic carbon fibers on the reactor wall (Japanese Patent No. 2778434), and vapor grown carbon fibers used in the present invention can be produced by these methods.

The vapor-grown carbon fiber produced in this way can be used as a raw material for the carbon particles (B) as it is, but in the state as it is after vapor-phase growth, thermal decomposition of the organic compound as a raw material on the surface is performed. There are cases in which objects are attached or the crystal structure of the carbon fiber is not yet developed. Therefore, heat treatment can be performed in an inert gas atmosphere in order to remove impurities such as thermal decomposition products and develop a crystal structure. In order to treat impurities such as pyrolysates, it is preferable to perform a heat treatment at about 800 to 1500 ° C. in an inert gas such as argon. In order to develop the crystal structure, it is preferable to perform heat treatment at 2000 ° C. or higher, more preferably about 2000 to 3000 ° C. in an inert gas such as argon. At this time, vapor phase carbon using boron compounds such as boron carbide (B ₄ C), boron oxide (B ₂ O ₃ ), elemental boron, boric acid (H ₃ BO ₃ ), and borate as graphitization catalyst. Can be mixed into the fiber. The amount of boron compound added depends on the chemical or physical properties of the boron compound used, and therefore cannot be specified unconditionally. For example, when boron carbide (B ₄ C) is used, the amount is preferably 0.05 to 10% by mass, more preferably 0.1 to 5% by mass with respect to the vapor grown carbon fiber. Examples of the vapor grown carbon fiber treated in this way include commercial products such as “VGCF” (registered trademark; manufactured by Showa Denko KK).

  There is no particular limitation on the method for binding (adhering) the carbon fibers to the surface of the graphite particles or carbon-coated graphite particles. For example, by mixing carbon fiber with an organic compound, attaching it to graphite particles or carbon-coated graphite particles, and then performing a heat treatment, the carbon fiber can be bound to the carbonaceous layer in the process of forming the carbonaceous layer. it can. The amount of the carbon fiber is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 15 parts by mass with respect to 100 parts by mass of the graphite particles. By using 0.1 mass part or more, the graphite particle surface can be covered widely. Since the carbonaceous layer having conductivity is connected between the graphite particles and the carbon fibers, the contact resistance is small. When carbon particles (B) made of graphite particles with carbon fibers bound thereto are used, the effect of improving battery characteristics is greater than when carbon fibers are simply added to an electrode.

[Mixture of particles (A) and carbon particles (B)]
The mixture in the present invention is a mixture of particles (A) and carbon particles (B). In the mixture of the present invention, the aggregation of the particles (A) is unraveled and dispersed almost uniformly on the surface of the carbon particles (B), and the particles (A) are mixed so as to fill the gaps between the carbon particles (B). It is preferable to include. Moreover, it is more preferable that the mixture in the present invention includes a mixture in which the particles (A) are embedded on the surfaces of the carbon particles (B). As a method for including the particles (A) embedded in the surface of the carbon particles (B) in the mixture, mixing while applying high mechanical energy can be mentioned.
The amount of the particles (A) is preferably 5 to 40 parts by mass, more preferably 20 to 40 parts by mass, and further preferably 30 to 40 parts by mass with respect to 100 parts by mass of the carbon particles (B).

  Carbon fiber may be mixed in the mixture in the present invention. The carbon fiber used for mixing has a fiber diameter of preferably 2 to 1000 nm, more preferably 10 to 500 nm, still more preferably 50 to 300 nm, still more preferably 70 to 200 nm, and particularly preferably 100 to 180 nm. Other characteristics of the carbon fiber used for mixing may be the same as those of the carbon fiber bound to the graphite particles. The amount of the carbon fiber is preferably 1 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, and further preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the carbon particles (B).

  Mixing with the particles (A), the carbon particles (B) and the carbon fibers added as necessary can be performed by a known method. For example, they can be mixed while being crushed or ground in a mortar. They can be mixed by a pulverizer such as a bead mill or a ball mill. Or it can mix by mechanochemical processing with apparatuses, such as a hybridizer made from Nara machine.

(Paste for negative electrode)
The negative electrode paste according to an embodiment of the present invention includes a negative electrode material, a binder, a solvent, and a conductive additive as necessary. In the present invention, the above mixture is used as the negative electrode material. This negative electrode paste can be obtained, for example, by kneading the negative electrode material, a binder, a solvent, and a conductive additive as necessary. The negative electrode paste can be formed into a sheet shape or a pellet shape.

  Examples of the binder include polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, acrylic rubber, and a polymer compound having high ionic conductivity. Examples of the polymer compound having a large ionic conductivity include polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphasphazene, polyacrylonitrile and the like. The amount of the binder is preferably 0.5 to 100 parts by mass with respect to 100 parts by mass of the negative electrode material.

  The conductive auxiliary agent is not particularly limited as long as it has a function of imparting conductivity and electrode stability (a buffering action against volume change in insertion / extraction of lithium ions) to the electrode. For example, vapor grown carbon fiber (for example, “VGCF” manufactured by Showa Denko KK), conductive carbon (for example, “Denka Black” manufactured by Denki Kagaku Kogyo, “Super C65” manufactured by TIMCAL, “Super C45” manufactured by TIMCAL "KS6L" manufactured by TIMCAL, Inc.). The amount of the conductive auxiliary is preferably 10 to 100 parts by mass with respect to 100 parts by mass of the negative electrode material.

  The solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone, dimethylformamide, isopropanol, and water. In the case of a binder using water as a solvent, it is preferable to use a thickener together. The amount of the solvent is adjusted so that the viscosity of the paste can be easily applied to the current collector.

(Negative electrode sheet)
The negative electrode sheet which concerns on one Embodiment of this invention contains a binder and said negative electrode material. The negative electrode sheet usually has a current collector.
Examples of the current collector include nickel foil, copper foil, nickel mesh, or copper mesh.
The negative electrode sheet can be obtained, for example, by applying the paste to a current collector and drying it. The method for applying the paste is not particularly limited. The thickness of the negative electrode sheet is usually 50 to 200 μm. If the thickness of the negative electrode sheet becomes too large, the negative electrode sheet may not be accommodated in a standardized battery container. The thickness of the negative electrode sheet can be adjusted by the amount of paste applied. It can also be adjusted by drying the paste and then press molding. Examples of the pressure molding method include molding methods such as roll pressing and press pressing. The pressure at the time of pressure molding is preferably about 100 MPa to about 300 MPa (about 1 ton / cm ² ).

(Lithium ion battery)
A lithium ion battery according to an embodiment of the present invention includes at least one selected from the group consisting of a non-aqueous electrolyte and a non-aqueous polymer electrolyte, a positive electrode sheet, and the negative electrode sheet.
As the positive electrode sheet used in the present invention, those conventionally used for lithium ion batteries, specifically, a sheet containing a positive electrode active material can be used. Examples of the positive electrode active material include LiNiO ₂ , LiCoO ₂ , LiMn ₂ O ₄ , LiNi _0.34 Mn _0.33 Co _0.33 O ₂ , and LiFePO ₄ .

The non-aqueous electrolyte and non-aqueous polymer electrolyte used for the lithium ion battery are not particularly limited. For example, lithium salts such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li can be converted into ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene. Organic electrolytes dissolved in non-aqueous solvents such as carbonate, butylene carbonate, acetonitrile, propyronitrile, dimethoxyethane, tetrahydrofuran, and γ-butyrolactone; polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, and polymethyl methacrylate Examples thereof include a gel polymer electrolyte and a solid polymer electrolyte containing a polymer having an ethylene oxide bond.

  In addition, a small amount of a substance that causes a decomposition reaction when the lithium ion battery is initially charged may be added to the electrolytic solution. Examples of the substance include vinylene carbonate, biphenyl, propane sultone, and the like. As addition amount, 0.01-5 mass% is preferable.

  The lithium ion battery of the present invention can be provided with a separator between the positive electrode sheet and the negative electrode sheet. Examples of the separator include non-woven fabrics, cloths, microporous films, or a combination thereof, mainly composed of polyolefins such as polyethylene and polypropylene.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

In this example, various physical properties were measured by the following methods.
(Raman R value)
Using a laser Raman spectrometer (NRS-3100) manufactured by JASCO Corporation, measurement was performed under the conditions of an excitation wavelength of 532 nm, an incident slit width of 200 μm, an exposure time of 15 seconds, an integration count of 2 times, and a diffraction grating of 600 lines / mm. It was. From the measured spectrum, the ratio (I _D / I _G ) between the peak intensity I _D (derived from the amorphous component) near 1360 cm ⁻¹ and the peak intensity I _G (derived from the graphite component) near 1580 cm ⁻¹ was calculated. . This was used as an index of the degree of graphitization as the R value.

(Coefficient of thermal expansion (CTE))
First, 500 g of the carbon raw material was pulverized to 28 mesh or less with a vibration mill. This sample was sieved and mixed at a ratio of 28 to 60 mesh 60 g, 60 to 200 mesh 32 g, 200 mesh or less 8 g to make the total amount 100 g. 100 g of this blended sample was put in a stainless steel container, 25 g of binder pitch was added, and the mixture was heated and uniformly mixed in an oil bath at 125 ° C. for 20 minutes. The mixture was cooled and pulverized with a vibration mill to reduce the total amount to 28 mesh or less. 30 g of the sample was placed in a pressure molding machine at 125 ° C., and pressed at a gauge pressure of 450 kg / cm 2 for 5 minutes to be molded. The molded product was put in a magnetic crucible, heated from room temperature to 1000 ° C. in a baking furnace in 5 hours, and held at 1000 ° C. for 1 hour to cool. This fired product was cut into 4.3 × 4.3 × 20.0 mm with a precision cutting machine to obtain a test piece. The test piece was subjected to thermal expansion measurement at 30 to 100 ° C. by TMA (Thermomechanical Analyzer) / SS 350 manufactured by Seiko Electronics Co., Ltd., and CTE was calculated.

(Tapping density)
A certain amount of carbon material (6.0 g) was put in a 15 mmφ measuring cell and set in a tapping device. The drop height was 46 mm, the tapping speed was 2 seconds / time, and after dropping freely 400 times, the volume was measured. The bulk density was calculated from the relationship between mass and volume.

(D ₀₀₂ , L _C )
From 002 diffraction line in the powder X-ray diffraction, in the c-axis direction of the surface spacing d ₀₀₂ and crystallite was determined thickness L _C.

(Aspect ratio of particles (length of major axis / length of minor axis))
The aspect ratio of the particles can be determined from an optical microscope, but may be measured by image analysis using a FPIA 3000 manufactured by Sysmex. The maximum length D _max / maximum length vertical length DN _max (D _max: maximum length in two points on the particle image contour; DN _max: When sandwiching the image with a maximum length of 2 straight lines parallel to, two straight lines The aspect ratio was defined as the shortest length connecting the two vertically. The number of measurement points was 3000 or more, and the average value was calculated.

(Particle size)
Two cups of ultra-small spatula and 2 drops of nonionic surfactant (Triton-X; manufactured by Roche Applied Science) were added to 50 ml of water and ultrasonically dispersed for 3 minutes. This dispersion was put into a laser diffraction particle size distribution analyzer (LMS-2000e) manufactured by Seishin Enterprise Co., Ltd., and a volume-based cumulative particle size distribution was measured.

(I (110) / I (004))
A 1% by mass carboxymethylcellulose (CMC) aqueous solution was kneaded while being added little by little to graphite so as to have a solid content of 1.5% by mass. Next, 1.5% by mass of styrene butadiene rubber (SBR) manufactured by Nippon Zeon Co., Ltd. is added as a binder, and further kneaded. Further, pure water is added so as to have sufficient fluidity, and a defoaming kneader manufactured by Nippon Seiki Seisakusho ( NBK-1) was kneaded at 500 rpm for 5 minutes to obtain a paste. The paste was applied onto the current collector using an automatic coating machine and a doctor blade having a clearance of 250 μm. The current collector on which the paste was applied was placed on a hot plate at about 80 ° C. to remove moisture. Then, it was dried at 120 ° C. for 6 hours with a vacuum dryer. After drying, it was pressure-molded by uniaxial pressing so that the electrode density determined from the total mass and volume of graphite and binder was 1.45 ± 0.05 g / cm ³ to obtain a negative electrode. The obtained negative electrode was cut out to an appropriate size, attached to a glass cell for XRD measurement, measured for the XRD spectrum attributed to the (004) plane and the (110) plane, and the peak intensity ratio was calculated from each peak intensity. Calculated. The peak intensity ratio I (110) / I (004) obtained by this measurement method indicates the orientation of the graphite powder. The larger this value, the lower the orientation.

(Fiber diameter and aspect ratio of carbon fiber)
The average fiber diameter and average fiber length were determined from SEM image analysis. Further, (average fiber diameter) / (average fiber length) was defined as the aspect ratio of the carbon fiber.

Example 1
(Preparation of carbon particles (B))
Petroleum coke was pulverized to an average particle size of 5 μm. This was heat-treated at 3000 ° C. in an Atchison furnace to obtain graphite particles. Next, petroleum pitch was mixed with the graphite particles at a mass ratio of 1%, and the petroleum pitch was adhered to the surface of the graphite particles. Then, it carbonized at 1100 degreeC by inert atmosphere. BET specific surface area is 2.6 m ² / g, I _D / I _G (R value) is 0.77, and coefficient of thermal expansion (CTE) from 30 ° C. to 100 ° C. is 4.2 × 10 ⁻⁶ / ° C. , 400 times tapping, bulk density 1.20 g / cm ³ , d ₀₀₂ 0.3361 nm, L _C 59 nm, particle aspect ratio 1.3, 10% particle size (D ₁₀ ) is 2.3 μm, 50% particle size (D ₅₀ ) is 5.7 μm, 90% particle size (D ₉₀ ) is 11.8 μm, and I (110) / I (004) is 0.40. Some carbon-coated graphite particles were obtained.

(Preparation of negative electrode material)
Si particles (Alfa Aesar, CAS7440-21-3, product number 44384, primary particle diameter of 50 nm or less) were prepared. The volume-based cumulative particle size distribution of the Si particles is shown in FIG. The 10% particle size (D ₁₀ ) is 140 nm, the 50% particle size (D ₅₀ ) is 210 nm, and the 90% particle size (D ₉₀ ) is about 390 nm. The proportion of particles having a particle size of 500 nm or less is 98% of the total.
3 g of carbon-coated graphite particles and 1 g of Si particles were placed in an agate mortar and mixed for 30 minutes while taking care not to apply force to obtain a negative electrode material according to the present invention.
In the obtained negative electrode material, as shown in FIG. 2, the Si particles were dispersed so as to separate from the carbon-coated graphite particles and fill the gaps. Moreover, the obtained negative electrode material had the particle size distribution shown in the line 1 in FIG. It was a double peak in which the peak derived from the Si particles and the peak derived from the carbon-coated graphite particles overlapped. Note that a line A-1 in FIG. 4 indicates the particle size distribution of the particles (A-1).

(Manufacture of negative electrode sheet)
Ethylene / vinyl acetate / acrylic acid copolymer aqueous emulsion (“Polysol [registered trademark]” manufactured by Showa Denko KK) and carboxymethylcellulose (manufactured by Daicel, product number: 1380) are mixed so that the solid content mass ratio is 1: 1. A binder was prepared.
TIMCAL carbon black (SUPER C65) was prepared as a conductive aid.
100 parts by mass of the negative electrode material, 100 parts by mass of the binder, and 85.7 parts by mass of the conductive additive are mixed, and an appropriate amount of water for viscosity adjustment is added thereto, followed by kneading with a rotation / revolution mixer (Sinky Corporation). A negative electrode paste was obtained.
The negative electrode paste was applied onto a copper foil so that the negative electrode layer had a thickness of 120 μm. This was dried at 90 ° C. for 3 hours. A sheet piece having a diameter of 15 mm was punched from the obtained sheet. The sheet piece was vacuum-dried at 50 ° C. for 12 hours to obtain a negative electrode sheet.

(Production of evaluation battery)
The following operation was carried out in a glove box kept in a dry argon gas atmosphere having a dew point of -80 ° C or lower.
A 2032 type coin cell (diameter 20 mm, thickness 3.2 mm) was prepared.
A foil piece having a diameter of 15 mm was punched from a lithium foil having a thickness of 0.1 mm. This was used as a positive electrode sheet. The positive electrode sheet was lightly pressure-bonded to a SUS spacer with a punch. This was put in a coin cell cap. Next, an electrolytic solution was injected into the coin cell. Thereafter, a separator (manufactured by Celgard, product number: 2500) and a negative electrode sheet were placed in this order, and the coin cell case was crimped and sealed with a coin cell cap to obtain an evaluation lithium ion battery.
The electrolytic solution was prepared by mixing 1% by mass of vinylene carbonate in a solvent in which ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed at a volume ratio of 3: 5: 2, and further adding 1 mol of electrolyte LiPF ₆ thereto. It is a liquid obtained by dissolving at a concentration of / L.

(Charge / discharge test)
The lithium ion battery for evaluation was charged at a constant current of 40 mA / g from rest potential to 25 mV. Subsequently, constant current discharge was performed at 40 mA / g and cut off at 2.0 V. This charge / discharge operation was performed as 20 cycles for 20 cycles. The charge capacity at the first cycle (initial charge capacity), the discharge capacity at the first cycle (initial discharge capacity), and the discharge capacity at the 20th cycle were measured. The results are shown in Table 1.
In Table 1, the initial efficiency is the ratio of the initial discharge capacity to the initial charge capacity, and the discharge amount maintenance ratio is the ratio of the discharge capacity at the 20th cycle to the initial discharge capacity.

Example 2
Petroleum coke was pulverized to an average particle size of 5 μm. This was heat-treated at 3000 ° C. in an Atchison furnace, and had a BET specific surface area of 3.2 m ² / g, I _D / I _G (R value) of 0.06, and a thermal expansion coefficient of 30 ° C. to 100 ° C. ( CTE) is 4.2 × 10 ⁻⁶ / ° C., the bulk density after tapping 400 times is 1.20 g / cm ³ , d ₀₀₂ is 0.3361 nm, L _C is 61 nm, The ratio is 1.3, the 10% particle size (D ₁₀ ) is 2.5 μm, the 50% particle size (D ₅₀ ) is 5.1 μm and the 90% particle size (D ₉₀ ) is 12.3 μm. Graphite particles having (110) / I (004) of 0.75 were obtained.
A negative electrode material was obtained in the same manner as in Example 1 except that the carbon-coated graphite particles used in Example 1 were changed to the graphite particles.
In the obtained negative electrode material, Si particles were dispersed so as to fill the gaps between the graphite particles as shown in FIG. Moreover, the obtained negative electrode material had the particle size distribution shown in the line 2 in FIG. It was a double peak in which a peak derived from Si particles and a peak derived from graphite particles overlapped. Note that a line A-1 in FIG. 4 indicates the particle size distribution of the particles (A-1).
A lithium ion battery for evaluation was prepared in the same manner as in Example 1 except that the negative electrode material in Example 1 was changed to the negative electrode material obtained here, and a charge / discharge test was performed. The results are shown in Table 1.

Comparative Example 1
A negative electrode material was obtained in the same manner as in Example 1 except that the carbon-coated graphite particles used in Example 1 were replaced with commercially available natural graphite particles.
A lithium ion battery for evaluation was prepared in the same manner as in Example 1 except that the negative electrode material in Example 1 was changed to the negative electrode material obtained here, and a charge / discharge test was performed. The results are shown in Table 1.
Natural graphite particles have a BET specific surface area of 1.8 m ² / g, an I _D / I _G (R value) of 0.23, and a thermal expansion coefficient (CTE) of 30 ° C. to 100 ° C. of 0.95. The bulk density when tapping 400 times at × 10 ⁻⁶ / ° C. is 1.10 g / cm ³ , d ₀₀₂ is 0.3355 nm, L _C is 109 nm, and the 10% particle diameter (D ₁₀ ) is At 9.6 μm, the 50% particle size (D ₅₀ ) was 16.8 μm, the 90% particle size (D ₉₀ ) was 28.1 μm, and I (110) / I (004) was 0.02.

  As shown in Table 1, it can be seen that the negative electrode materials (Examples 1 and 2) of the present invention have high initial efficiency and the discharge capacity maintenance rate at the 20th time is 93% or more. On the other hand, it can be seen that the negative electrode material (Comparative Example 1) obtained by the conventional manufacturing method has a high initial efficiency, but has a low discharge capacity maintenance ratio at the 20th time.

Example 3
3 g of the carbon-coated graphite particles obtained in Example 1 and 1 g of Si particles were put in an agate mortar and mixed for 3 minutes while being crushed by applying mechanical energy to obtain a negative electrode material according to the present invention.
As shown in FIG. 5, the obtained negative electrode material was divided into a portion where Si particles were aggregated and a portion where Si particles were agglomerated and dispersed so as to be embedded in the surface of the carbon-coated graphite particles. A lithium ion battery for evaluation was prepared in the same manner as in Example 1 except that the negative electrode material in Example 1 was changed to the negative electrode material obtained here, and a charge / discharge test was performed. The results are shown in Table 2.

Example 4
3 g of the carbon-coated graphite particles and 1 g of Si particles obtained in Example 1 are put in a rotating / revolving mixer (made by Sinky), and further 80 g of zirconia balls having a diameter of 3 mm are put into a mechanochemical mixture at 2000 rpm for 3 minutes. The negative electrode material which concerns on was obtained.
As shown in FIG. 6, the obtained negative electrode material was dispersed so that the Si particles were agglomerated and embedded in the surface of the carbon-coated graphite particles. A lithium ion battery for evaluation was prepared in the same manner as in Example 1 except that the negative electrode material in Example 1 was changed to the negative electrode material obtained here, and a charge / discharge test was performed. The results are shown in Table 2.

  As shown in Table 2, the negative electrode material of the present invention (Examples 3 and 4) has a higher initial efficiency than that of Examples 1 and 2, and the 20th discharge capacity retention rate is 93% or more. Recognize. This is considered to be because the effect of relaxing the expansion and contraction of the Si particles is greater in the case where mixing is performed so that the Si particles are embedded in the graphite particles by applying mechanical energy than in the case of simple mixing.

Claims (10)

A negative electrode material for a lithium ion battery comprising a mixture of particles (A) containing an element capable of inserting and extracting lithium and carbon particles (B),
The particle (A) has a 90% particle size in a volume-based cumulative particle size distribution of 500 nm or less,
The carbon particle (B) is a negative electrode material for a lithium ion battery, containing particles made of a graphite material, and having a peak intensity ratio I (110) / I (004) indicating the orientation of graphite of 0.2 or more.   2. The negative electrode material for a lithium ion battery according to claim 1, wherein the peak intensity ratio I (110) / I (004) indicating the orientation of graphite is 0.35 or more and 0.9 or less. 3. The lithium according to claim 1, wherein the graphite material has a coefficient of thermal expansion (CTE) of 30 ° C. to 100 ° C. of 4.0 × 10 ⁻⁶ / ° C. to 5.0 × 10 ⁻⁶ / ° C. Negative electrode material for ion batteries.   The negative electrode material for a lithium ion battery according to any one of claims 1 to 3, further comprising carbon fibers having a fiber diameter of 2 to 1000 nm and an aspect ratio of 10 to 15000.   5. The negative electrode material for a lithium ion battery according to claim 1, wherein the amount of the particles (A) is 5 to 40 parts by mass with respect to 100 parts by mass of the carbon particles (B).   The negative electrode material for a lithium ion battery according to any one of claims 1 to 5, wherein the element capable of inserting and extracting lithium is at least one selected from the group consisting of Si, Sn, Ge, and In. The carbon particles (B) are carbon-coated graphite particles containing particles made of the graphite material and a carbonaceous layer present on the surface thereof,
Carbonaceous layer, the ratio I of the intensity of a peak in the range of the peak intensity (I _D) and 1580～1620Cm ^-1 in the range of 1300～1400Cm ^-1 as measured by Raman spectroscopy spectra (I _{G) The} negative electrode material for a lithium ion battery according to any one of claims 1 to 6, wherein _D / I _G (R value) is 0.1 or more.   The negative electrode sheet containing the negative electrode material for lithium ion batteries as described in any one of Claims 1 thru | or 7, and a binder. At least one selected from the group consisting of a non-aqueous electrolyte and a non-aqueous polymer electrolyte;
A lithium ion battery comprising a positive electrode sheet and the negative electrode sheet according to claim 8.   The particles (A) and the carbon particles (B) are mixed so as to embed the particles (A) in the carbon particles (B) while applying mechanical energy to dissolve the particles (A). The manufacturing method of the negative electrode material for lithium ion batteries as described in any one of Claims 1 thru | or 7 which has a process to do.

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