TW201931648A - Negative electrode material for lithium ion secondary battery - Google Patents

Abstract

The present invention relates to a negative electrode material for a lithium ion secondary battery, the negative electrode material comprising: a composite (A) including Si particles (A1) having an average particle diameter dAV of primary particles of 5-95 nm; an amorphous carbon coating layer (A1C) having a thickness of 1 nm to 20 nm and covering the particles (A1); particles (A2) made of a material including graphite; and a carbonaceous material (A3), wherein the half-value width of the (111) plane diffraction peak of the Si particle (A1) in the composite (A) is 0.40 degrees or more as determined by powder X-ray diffraction measurement. The present invention also relates to a negative electrode sheet and a lithium ion secondary battery. In the negative electrode agent of the present invention, the crystallite size is decreased while reducing the size of the Si particles, thereby making it possible to obtain a lithium ion secondary battery having a small electrode expansion coefficient and a long battery life.

Description

Anode material for lithium ion secondary battery

The present invention relates to a negative electrode material for a lithium ion secondary battery.

The multifunctionalization of mobile electronic devices is progressing at a faster rate than the power saving of electronic components, so the power consumption of mobile electronic devices is increased. Therefore, higher-capacity and miniaturization of lithium-ion secondary batteries, which are the main power sources for mobile electronic devices, are being sought more than ever. In addition, the demand for electric vehicles has increased, so lithium-ion secondary batteries used in electric vehicles are also strongly seeking to increase the capacity.

In response to such demands, a negative electrode material of composite silicon (Si) particles and a carbon material has been proposed. However, a lithium ion secondary battery using a composite material of Si particles and a carbon material has a high capacity, but its volume change during charge and discharge due to Si is significantly deteriorated. In order to cope with this, various correspondences such as nano-particle granulation of Si, application of a coating material for Si, and doping of dissimilar metals to Si are adopted, thereby maintaining a high capacity and continuously improving cycle life.

However, even when the Si nano particles are reduced, if the crystallite size is large, the expansion of the Si nano particles becomes anisotropic, so the expansion rate of the entire negative electrode containing Si increases. Further, from the viewpoint of suppressing the expansion rate, even if Si particles having an appropriate Si crystal particle size can be proposed, it cannot be achieved without sufficient coating conductivity and a coating material that suppresses side reactions with the electrolytic solution. Long-life battery.

Therefore, many attempts have been made to reduce the crystal size of Si particles. For example, Patent Document 1 discloses a negative electrode material composed of a Si-based alloy for a power storage device, which is a negative electrode material composed of a Si-based alloy for a power storage device that is accompanied by lithium ion movement during discharge, and is characterized by the aforementioned Si A negative electrode material composed of a series alloy has a main phase of Si composed of Si and a compound phase composed of Si and one or more elements other than Si. The aforementioned compound phase includes a phase composed of Si and Cu. Phase, the Si crystal grain size of the Si main phase is 30 nm or less, and the crystal grain size of the compound phase composed of Si and Cu is 40 nm or less.

In addition, Patent Document 2 discloses a silicon fine particle, which is mainly used as a negative electrode active material for a lithium ion secondary battery. The crystallite size measured by powder X-ray diffraction is 1 to 200 nm. The average particle diameter measured by the laser method is 0.1 to 5 μm, and the specific surface area measured by the BET method is 10 m ² / g or more.
[Prior technical literature]
[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2014-160554
[Patent Document 2] Japanese Patent Laid-Open No. 2016-15299

[Questions to be Solved by the Invention]

Although the invention of Patent Document 1 seeks to reduce the crystallinity size, it is unknown which crystal face is on which side, and the Si particle size is not described.
When the invention of Patent Document 2 is compared with Patent Document 1, the allowable Si crystal particle size is too large, and there is a possibility that it cannot be related to swelling suppression. In addition, even if the crystal size of Si is 30 nm or less as in Patent Document 1, from the point of forming a negative electrode material with Si simple substance or a point of Si particle diameter of 0.1 μm or more, it is a method for suppressing expansion of the negative electrode and improving battery life For the disadvantages.
An object of the present invention is to provide a negative electrode material for a lithium ion secondary battery that has a small swelling of the electrode accompanying use and a long battery life.

[Means to solve the problem]

The present invention includes the following aspects.
[1] A negative electrode material for a lithium ion secondary battery, which is a negative electrode material for a lithium ion secondary battery including a composite (A), the composite (A) includes: an average particle diameter d _AV of primary particles of 5 nm The Si particles (A1) above 95 nm, the amorphous carbon coating layer (A1C) with a thickness of 1 nm to 20 nm of the coated particles (A1), the particles (A2) made of a substance containing graphite, and (A3), characterized in that the full width at half maximum of the diffraction peak of the (111) plane of the Si particle (A1) measured by powder X-ray diffraction measurement of the composite (A) is 0.40 degrees or more.
[2] The negative electrode material for a lithium ion secondary battery according to the above item 1, wherein the particle (A2) has a 50% cumulative particle size distribution on a volume basis, and the particle diameter D _V50 is 2.0 μm or more and 20.0 μm or less, and the BET specific surface area ( S _BET ) is 1.0 m ² / g or more and 10.0 m ² / g or less.
[3] The negative electrode material for a lithium ion secondary battery according to the above item 1 or 2, wherein the particle (A2) is a peak intensity of a (110) plane of a graphite crystal measured by a powder X-ray diffraction method. The ratio of the peak intensity of I ₁₁₀ to the (004) plane I ₀₀₄ I ₁₁₀ / I ₀₀₄ is 0.10 to 0.35, and the average plane interval d ₀₀₂ of the (002) plane measured by the powder X-ray diffraction method is 0.3360 nm. Hereinafter, the total pore volume of pores having a diameter of 0.4 μm or less measured by a nitrogen gas adsorption method is 5.0 μL / g or more and 40.0 μL / g or less.
[4] The negative electrode material for a lithium ion secondary battery according to any one of the above items 1 to 3, wherein the content of the Si particles (A1) in the composite (A) is 10% by mass or more and 70% by mass or less .
[5] A negative electrode sheet, which is a negative electrode layer having a sheet-shaped current collector and a covered current collector. The negative electrode layer includes a binder, a conductive auxiliary agent, and the lithium ion secondary battery according to any one of the preceding paragraphs 1 to 4. Use negative material.
[6] A lithium ion secondary battery having the negative electrode sheet according to the item 5 above.

[Inventive effect]

According to the present invention, it is possible to provide a negative electrode material for a lithium ion secondary battery having a small electrode expansion rate accompanying use and a long battery life.

A negative electrode material for a lithium ion secondary battery according to an embodiment of the present invention includes a composite (A), and the composite (A) includes particles (A1) and an amorphous carbon coating layer (A1C) and particles (A2). With carbonaceous material (A3).

(1) Particle (A1)
The particles (A1) used in one embodiment of the present invention include Si as a main component capable of storing and releasing lithium ions. The Si content is preferably 90% by mass or more, and more preferably 95% by mass or more. The particles (A1) may be composed of a simple substance of Si or a compound containing a Si element, a mixture, a eutectic, or a solid solution. In addition, the particles (A1) before being composited with the particles (A2) and the carbonaceous material (A3) may be those agglomerated with a plurality of fine particles, or may be those obtained by secondary granulation. Examples of the shape of the particles (A1) include a block shape, a scale shape, a spherical shape, and a fibrous shape. Among these, a spherical shape or a block shape is preferable.

Examples of the substance containing the Si element include a simple substance of Si or a general formula including an element M other than Si and Li: M (= M ^a + M ^b + M ^c + M ^d ･ ･ ･) _m Si. The substance is a compound, a mixture, a eutectic, or a solid solution containing the element M in a ratio of m mole to Si1 mole.
Specific examples of the element M other than Li are B, C, N, O, S, P, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Pt, Be, Nb, Nd, Ce, W, Ta, Ag, Au, Cd, Ga, In, Sb, Ba, etc. In the formula, m is preferably 0.01 or more, more preferably 0.10 or more, and still more preferably 0.30 or more.

Specific examples of the substance containing the Si element include Si simple substance, alloys of Si and alkaline earth metals; alloys of Si and transition metals; alloys of Si and semi-metals; Si, and 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, V ₃ Si, VSi ₂ , PdSi, RuSi, RhSi and other silicides; SiO ₂ , SiC, Si ₃ N ₄ and so on.

The lower limit of the average particle diameter d _AV of the particles (A1) is 5 nm, preferably 10 nm, and more preferably 35 nm. The d _AV upper limit of the primary particles is 95 nm, and preferably 70 nm. If the d _AV of the primary particle of the particle (A1) is larger than 95 nm, the volume expansion and contraction of the particle (A1) will increase the influence given to the structure of the composite (A) containing the particle (A1) through charge and discharge. Reduce capacity maintenance. When the d _{AV of the} primary particles is smaller than 5 nm, the specific surface area of the particles (A1) is increased, and the amount of side reactions increases.
The average particle diameter d _AV [nm] is determined by
d _AV [nm] = 6 × 10 ³ / (ρ × S _BET )
definition. Here, ρ [g / cm ³ ] is the true density of Si particles, and a theoretical value of 2.3 [g / cm ³ ] is used. S _BET [m ² / g] is a specific surface area measured by a BET method using N ₂ gas as an adsorption gas.

The particles (A1) are preferably those whose surfaces are covered with a thin amorphous carbon coating layer (A1C). The upper limit of the thickness of the amorphous carbon coating layer (A1C) is 20 nm, preferably 10 nm, and more preferably 5 nm. This is because the side reaction between the electrolytic solution and the amorphous carbon coating layer (A1C) is suppressed. The lower limit value of the thickness of the amorphous carbon coating layer (A1C) is 1 nm, preferably 2 nm, and more preferably 3 nm. This is because the oxidation of the particles (A1) and the aggregation of the particles (A1) with each other are suppressed. In addition, compared with the amorphous carbon coating layer (A1C), the particles (A1) that undergo a large number of side reactions with the electrolytic solution are coated with the amorphous carbon coating layer (A1C), which greatly improves the initial Coulomb efficiency.

The thickness of the amorphous carbon coating layer (A1C) can be determined by measuring the film thickness in an image taken by observation with a transmission electron microscope (TEM). An example of specific observation by TEM is shown below.
Installation: H9500 by Hitachi,
Acceleration voltage: 300kV.
Sample preparation: After taking a small amount of sample in ethanol and dispersing it by ultrasonic irradiation, it is loaded with a microgrid observation mesh (without a support film) to become an observation sample.
Observation magnification: 50,000 times (when the particle shape is observed) and 400,000 times (when the thickness of the amorphous carbon layer is observed)

The core-shell structure (hereinafter referred to as a structure (α)) composed of particles (A1) and an amorphous carbon coating layer (A1C) covering the particles has a BET specific surface area of preferably 25 m ² / g or more and 70 m ² / g or less, more preferably 52 m ² / g or more and 67 m ² / g or less. The density of the primary particles was 2.2 g / cm ³ or more. If the BET specific surface area (S _BET ) of the structure (α) is 25 m ² / g or more, the particle size of the structure (α) will not be excessively increased, and the electron movement route and Li ions in the solid of the structure (α) will not be excessively increased. The proliferation route will not grow. That is, the resistance during charge and discharge is kept low. Furthermore, the absolute value of the expansion amount per particle of the structural body (α) does not increase, and the possibility of destroying the structure of the composite body (A) around the structural body (α) is low. In addition, if the density of the structure (α) is 2.2 g / cm ³ or more, it is also advantageous from the viewpoint of volume energy density.

The content of the particles (A1) in the composite (A) is preferably 2% by mass to 95% by mass, more preferably 5% by mass to 80% by mass, and even more preferably 10% by mass to 70% by mass. the following. When the content of the particles (A1) is 95% by mass or less, no problem in battery performance due to an increase in electrical resistance occurs. When the content rate of the particles (A1) is 2% by mass or more, the superiority is maintained in terms of volume or mass energy density.

Although the structure (α) composed of the particles (A1) and the amorphous carbon coating layer (A1C) can be produced by any of a solid phase method, a liquid phase method, and a gas phase method, the gas phase method is preferred. . Especially, it is preferable to use a CVD method to prepare Si particles from a gas-phase Si raw material such as monosilane, and then use a carbon raw material such as acetylene or ethylene to prepare a uniform amorphous carbon coating layer (A1C) by CVD. .

(2) Particle (A2)
In the preferred embodiment of the present invention, the graphite particles included in the particles (A2) are preferably artificial graphite particles. The size and shape of the optical structure are in a specific range. With artificial graphite particles having an appropriate degree of graphitization, an electrode material having excellent collapse characteristics and battery characteristics can be obtained.

In this specification, D _V50 means the particle diameter of 50% of the volume-based particle size distribution measured by a laser diffraction particle size distribution meter, and the apparent diameter of particles.

In the preferred embodiment of the present invention, the graphite particles included in the particles (A2) contain 50% of the cumulative particle size distribution on the basis of volume, and the particle diameter D _{V50 is} preferably 2.0 μm or more and 20.0 μm or less, and more preferably 5.0 μm or more and 18.0 μm or less. the following. If D _V50 is 2.0 μm or more, it is not necessary to use a special machine for pulverization during pulverization, and energy can be saved. In addition, since it is difficult to cause aggregation, the workability at the time of coating is also good. Furthermore, since the specific surface area is not excessively large, it does not cause a decrease in initial charge and discharge efficiency. On the other hand, if D _V50 is 20.0 μm or less, the lithium diffusion in the negative electrode material does not take time, and the input / output characteristics are good. In addition, the silicon-containing particles are uniformly compounded on the surface of the graphite particles to obtain good cycle characteristics.

In the preferred embodiment of the present invention, the graphite particles included in the particles (A2) have a BET specific surface area measured by an N ₂ gas adsorption method of 1.0 m ² / g or more and 10.0 m ² / g or less. more preferably 3.0m ² / g or more 7.5m ² / g or less. If the BET specific surface area of the graphite particles is within the above range, as a negative electrode material, irreversible side reactions can be suppressed, and the area in contact with the electrolytic solution can be largely ensured to improve the input / output characteristics.

In the preferred embodiment of the present invention, the artificial graphite particles included in the particle (A2) have a diffraction peak file obtained by the powder X-ray diffraction method, and the peak intensity of the (110) plane of the graphite crystal I ₁₁₀ and ( The ratio of the peak intensity I ₀₀₄ of the surface 004) I ₁₁₀ / I _{004 is} preferably 0.10 or more and 0.35 or less. The aforementioned ratio is more preferably 0.18 to 0.30, and still more preferably 0.21 to 0.30. If the aforementioned ratio is 0.10 or more, the alignment will not be too high, and the expansion and contraction accompanying the insertion and detachment (storage and release) of Si or graphite lithium ions in the negative electrode material will not cause the collection of electrodes. The electric body expands in the direction of the electrode facing the vertical direction, and obtains a good cycle life. In addition, since the carbon mesh surface of graphite is not parallel to the electrode surface, it is easy to cause the insertion of Li and obtain good rapid charge and discharge characteristics. If the aforementioned ratio is 0.35 or less, the alignment will not be too low, and it is easy to increase the electrode density when punching during the production of an electrode using the negative electrode material.

In the preferred embodiment of the present invention, the artificial graphite particles included in the particles (A2) preferably have an average interplanar interval d ₀₀₂ of the (002) plane measured by a powder X-ray diffraction method of 0.3360 nm or less. Thereby, the amount of lithium insertion and removal per mass of the artificial graphite particles in the negative electrode material itself is also large, that is, as a negative electrode material, the mass energy density is also improved. In addition, it is easy to ease expansion and contraction due to insertion and removal of lithium, which is Si as a negative electrode material, and the cycle life is improved.
The thickness Lc in the C-axis direction of the crystals of the artificial graphite particles is preferably 50 nm or more and 1000 nm or less, and is preferably from the viewpoint of mass energy density or collapse property.

In this specification, d ₀₀₂ and Lc can be determined by a known method using powder X-ray diffraction (XRD) method (Doragaki Ino, "Carbon", 1963, No. 36, pages 25-34; Iwashita et al., Carbon vol. 42 (2004), p. 701-714).

In the preferred embodiment of the present invention, the artificial graphite particles included in the particles (A2) have a total pore volume of pores with a diameter of 0.4 μm or less as measured by the BET method of nitrogen gas absorption under liquid nitrogen cooling. It is preferably 5.0 μL / g or more and 40.0 μL / g or less. More preferably, it is 25.0 μL / g or more and 40.0 μL / g or less. For artificial graphite particles having a total pore volume of 5.0 μL / g or more, the composite of the particles (A1) and the carbonaceous material (A3) is easy to proceed, and it is preferable from the viewpoint of improving the cycle capacity maintenance rate. In a carbon material having an Lc of 100 nm or more measured by X-ray diffraction method, if the aforementioned total pore volume is 40.0 μL / g or less, it is difficult to cause an anisotropic expansion and contraction structure of the graphite layer during charge and discharge. The irreversible change of the electrode also further improves the cycle characteristics of the anode material. In addition, when the total pore volume of the artificial graphite particles is within this range, the negative electrode material is easily penetrated when the negative electrode material is used as an active material, which is also excellent in terms of rapid charge and discharge characteristics.

Artificial graphite particles in a particle-like state (A2) of the preferred embodiment of the present invention comprises, from 1300 Raman spectroscopic measurement spectrum of a peak intensity of 1400cm ~ range amorphous component I _D ^-1 and from 1580 ~ 1620cm The ratio I _D / I _G (R value) of the peak intensity I _G of the graphite component in the range of ^-1 is preferably 0.04 or more and 0.18 or less, and more preferably 0.08 or more and 0.16 or less. If the R value is 0.04 or more, the crystallinity of graphite will not be too high, and good rapid charge and discharge characteristics will be obtained. If the R value is 0.18 or less, since a defect exists during charging and discharging, a side reaction does not occur, and good cycle characteristics are obtained.
The Raman spectrum can be measured, for example, by using a laser Raman spectrophotometer (manufactured by JASCO Corporation, NRS-5100) and observing a microscope.

(3) Method for producing particles (A2) The graphite particles included in the particles (A2) according to one embodiment of the present invention can be produced by heating and pulverizing particles of coke having a thermal resistance of 1000 ° C or lower.
As a raw material for coke, for example, petroleum pitch, coal pitch, coal pitch coke, petroleum coke, and mixtures thereof can be used. That is, as the graphite particles included in the particles (A2), those derived from petroleum-based coke and / or coal-based coke are preferably used. Among them, those who desire to perform delayed coking under specific conditions.

Examples of the raw materials passing through the delayed coking device include heavy residues during purification of crude oil, fluidized bed contact decomposition to remove catalyst residues, or coal tar extracted from bituminous coal and the like at a temperature of 200 ° C or higher. Distilling and heating the obtained tar to 100 ° C or more to make it sufficiently fluid. In the delayed coking process, such liquids are heated at least to 450 ° C, and then to 500 ° C, and further to 510 ° C, so as to increase the residual carbon during the heat treatment of the subsequent steps. Rate to increase yield. In addition, the pressure in the reel is preferably maintained above normal pressure, more preferably maintained above 300 kPa, and even more preferably maintained above 400 kPa. This further increases the capacity as a negative electrode. As described above, by performing coking under more severe conditions than usual to make the liquid more reactive, coke with a higher degree of polymerization can be obtained.

The obtained coke was cut out from the drum by a jet of water, and the obtained block was coarsely pulverized with a hammer or the like to about 5 cm. Although a biaxial roller crusher or a jaw crusher may be used for the coarse crushing, it is preferred that the crushing is performed such that the mass becomes 90% by mass or more on a 1 mm sieve. By performing the pulverization as described above, and subsequent heating steps, etc., after drying, it is possible to prevent the coke powder from flying up or increase the trouble of burning.

The coke is then crushed.
When pulverizing in a dry manner, if water is included in the coke during pulverization, the pulverizability is significantly reduced, and therefore it is preferable to dry it in advance at about 100 to 1000 ° C. It is more preferably 100 to 500 ° C. If the coke has a high thermal resistance, the crushing strength will be deteriorated due to the increased crushing strength, and the anisotropy of the crystal will be developed, so the cleaving property will be enhanced, and it will easily become a scaly powder. The pulverization method is not particularly limited, and it can be performed using a known jet mill, hammer mill, roll mill, pin mill, vibration mill, or the like.
The pulverization is preferably performed such that D _{V50 is} 2.0 μm or more and 20.0 μm or less, and more preferably 5.0 μm or more and 18.0 μm or less.

Graphitization is performed in an inert environment (such as a nitrogen gas or argon gas environment), preferably at a temperature of 2400 ° C or higher, more preferably 2800 ° C or higher, still more preferably 3050 ° C or higher, and still more preferably 3150 ° C or higher. get on. If it is processed at a higher temperature, an electrode can be obtained in which graphite crystals grow more and lithium ions can be stored at a higher capacity. On the other hand, if the temperature is too high, it is difficult to prevent the sublimation of graphite powder and the necessary energy is also increased. Therefore, the graphitization temperature is preferably 3600 ° C or lower.

To achieve these temperatures, electrical energy is preferably used. The ratio of electrical energy to other heat sources is high, especially in order to achieve temperatures above 2000 ° C, which consumes a large amount of electricity. Therefore, those who do not consume electrical energy other than graphitization are preferred. The carbon raw material is fired before graphitization to remove the organic volatile matter, that is, the fixed carbon content becomes 95% or more, more preferably 98% or more, and still more preferably 99% or more. This firing can be performed, for example, by heating at 700 to 1500 ° C. Since the mass reduction during graphitization is reduced by firing, it is possible to increase the amount of one-time processing with a graphitization processing apparatus.

After graphitization, it is preferred not to perform pulverization. However, after graphitization, it can be disintegrated to the extent that the particles are not crushed.
If graphite particles are used as an active material to make an electrode, the active material is easily uniformly distributed inside the electrode when the electrode is compressed, and the contact with adjacent particles is stable, so it can be more excellent in repeated charge and discharge. battery.

(4) Carbonaceous material (A3)
In a preferred embodiment of the present invention, the carbonaceous material (A3) is different from the particles (A2) and is a low-developed carbon material which is a crystal formed by carbon atoms. It is obtained by Raman scattering spectrometry. The Raman spectrum has a peak near 1360 cm ^-1 . The carbonaceous material (A3) may be the same as the amorphous carbon coating layer (A1C).
The carbonaceous material (A3) can be produced, for example, from a carbonized carbon precursor. Although the aforementioned carbon precursor is not particularly limited, it is preferably a petroleum-derived substance such as thermal heavy oil, thermal decomposition oil, straight run bitumen, blown bitumen, tar or petroleum bitumen produced as by-products during ethylene production, Coal tar produced during coal distillation, heavy components with low boiling point components removed from coal tar by distillation, and coal-derived materials such as coal tar pitch (coal pitch) are particularly preferably petroleum-based or coal-based pitch. Asphalt is a mixture of multiple polycyclic aromatic compounds. When pitch is used, a carbonaceous material (A3) having a high carbonization rate and few impurities can be produced. As the pitch contains a small amount of oxygen, the particles (A1) are hardly oxidized when the particles (A1) are coated with a carbonaceous material.

As the pitch of the precursor of the carbonaceous material (A3), the softening point is preferably 80 ° C or higher and 300 ° C or lower. If the softening point of the asphalt is 80 ° C or higher, the average molecular weight of the polycyclic aromatic compounds constituting it will not be too small, and the volatile content will be relatively small. Therefore, it will not cause a reduction in carbonation rate, an increase in manufacturing cost, and it is easy to obtain a large amount There is a problem with a carbonaceous material (A3) having a large specific surface area including pores. If the softening point of the asphalt is 300 ° C or lower, the viscosity will not be too high, so it can be uniformly mixed with the particles (A1). The softening point of asphalt can be measured by the METTLER method described in ASTM-D3104-77.

As the pitch of the precursor of the carbonaceous material (A3), the residual carbon ratio is preferably from 20% by mass to 70% by mass, and more preferably from 25% by mass to 60% by mass. When the residual carbon ratio of the pitch is 20% by mass or more, there is no problem that the manufacturing cost increases or a carbonaceous material with a large specific surface area is obtained. If the residual carbon content of the pitch is 70% by mass or less, the viscosity will not be too high, and therefore it can be uniformly mixed with the particles (A1).
The residual carbon ratio is determined by the following method. The solid pitch is pulverized with a mortar or the like, and the pulverized material is subjected to mass thermal analysis under a flow of nitrogen gas. The ratio of the insertion mass to the mass at 1100 ° C is defined as the residual carbon ratio.

The content of the pitch-based QI (quinoline insoluble) used in the present invention is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. The QI content of the pitch is a value corresponding to the amount of free carbon. If a large amount of asphalt containing free carbon is heat-treated, in the process of the appearance of mesophase spheres, since the free carbon adheres to the surface of the spheres, forming a three-dimensional network, which hinders the growth of the spheres, it is easy to become a mosaic structure. On the other hand, if the bitumen with little free carbon is heat-treated, the mesophase spheres grow significantly and needle coke is easily formed. When the QI content is within the above range, the electrode characteristics are changed to be good.

The pitch-based TI (toluene insoluble) content used in the present invention is preferably from 10% by mass to 70% by mass. Asphalt with low TI content, because the polycyclic aromatic compounds constituting it have a small average molecular weight and high volatile content, the carbonization rate becomes low, the manufacturing cost increases, and a large amount of carbonaceous material with a large specific surface area including pores is easily obtained. Bitumen with a high TI content has a large average molecular weight of the polycyclic aromatic compounds constituting it, and although the carbonization rate is increased, the bitumen with a high TI content tends to be difficult to uniformly mix with the particles (A1) due to its high viscosity. When the TI content is within the above range, the asphalt and other components can be uniformly mixed, and a negative electrode material exhibiting suitable characteristics as an active material for a battery can be obtained.

The QI content and the TI content of the pitch used in the present invention can be measured by a method described in JIS K2425 or a method based thereon.

The mass ratio of the carbonaceous material (A3) to the total mass of the aforementioned particles (A1), particles (A2), and carbonaceous material (A3) is preferably 2% by mass or more and 40% by mass, more preferably 4% by mass Above 30% by mass.
When the proportion of the carbonaceous material (A3) is 2% by mass or more, sufficient bonding between the particles (A1) and the particles (A2) is obtained, and since the surface of the particles (A1) can be changed to the carbonaceous material (A3) The coating becomes easy to impart conductivity to the particles (A1), obtains the effect of suppressing the surface reactivity of the particles (A1), or mitigates the effects of expansion and contraction, and obtains good cycle characteristics. On the other hand, if the proportion of the carbonaceous material (A3) is 40% by mass or less, the initial efficiency will not decrease even if the proportion of the carbonaceous material (A3) is increased.

(5) Complex (A)
The composite (A) according to an embodiment of the present invention preferably includes a structure (α) composed of particles (A1) and an amorphous carbon coating layer (A1C), particles (A2), and carbon. Material (A3), the aforementioned structure (α), particles (A2), and at least a part of the carbonaceous material (A3) are composited with each other. The compounding includes, for example, a state in which the structure (α) and the particles (A2) are fixed and bonded by the carbonaceous material (A3), or the structure (α) and / or the particles (A2) are made of the carbonaceous material. (A3) Covered state. In the present invention, it is preferable that the structure (α) is completely covered with the carbonaceous material (A3) and the surface of the structure (α) is not exposed. Among them, the structure (α) and the particles (A2) are preferred. ) Is connected by a carbonaceous material (A3), and the entire state is covered with the carbonaceous material (A3), and the structure is directly contacted with the structure (α) and the particles (A2), and the whole is covered by the carbonaceous material (A3). status.
As a negative electrode material, when used in a battery, the surface of the structure (α) is not exposed, the decomposition reaction of the electrolyte is suppressed, and the coulomb efficiency can be maintained at a high level. The carbon material (A3) is used to connect the particles (A2) and the structure. The body (α) can increase the conductivity between individuals, and the structure (α) is covered with the carbonaceous material (A3), which can buffer the volume change accompanying its expansion and contraction.

The composite body (A) according to an embodiment of the present invention may include uncomplexed particles (A2), carbonaceous materials (A3), or structures (α) alone. The amount of particles (A2), carbonaceous material (A3), or structure (α) that is not composited and contained separately is preferably smaller, and specifically, relative to the mass of the composite (A), it is preferably 10% by mass or less.

The D _V50 of the composite (A) according to an embodiment of the present invention is preferably 2.0 μm or more and 20.0 μm or less. More preferably, it is 2.0 μm or more and 18.0 μm or less. When D _V50 is 2.0 μm or more, economical production is possible. In addition, there is no difficulty in increasing the electrode density. Furthermore, since the specific surface area is not excessively large, it does not cause a decrease in initial charge and discharge efficiency due to side reactions with the electrolytic solution. When D _V50 is 20.0 μm or less, good I / O characteristics and cycle characteristics are obtained.

The BET specific surface area (S _BET ) of the composite (A) according to an embodiment of the present invention is preferably 1.0 m ² / g or more and 10.0 m ² / g or less. It is more preferably 1.0 m ² / g or more and 5.0 m ² / g or less. When the BET specific surface area (S _BET ) is 1.0 m ² / g or more, the input / output characteristics are not reduced, but uniform distribution in the electrode is maintained, and good cycle characteristics are obtained. When the BET specific surface area (S _BET ) is 10.0 m ² / g or less, the coating properties are not reduced and the handleability is good. In addition, a binder is not required for electrode production, electrode density is easily increased, and a decrease in initial charge and discharge efficiency due to a side reaction with the electrolytic solution can be suppressed.

The composite (A) according to one embodiment of the present invention is a half-width of the (111) plane diffraction peak of the Si particle (A1) measured by the X-ray diffraction method, preferably from 0.40 ° to 0.71 °. The temperature is 0.40 ° or more and 0.65 ° or less, and more preferably 0.40 ° or more and 0.65 ° or less. If the (111) plane diffraction peak half-width of the Si particle (A1) is less than 0.40 degrees, the crystal size of the Si particle (A1) increases, and the expansion of the Si particle (A1) becomes anisotropic. As a result, the electrode The expansion rate increases, reducing the cycle capacity maintenance rate.
The half-width of the diffraction peak of the particle (A1) can be measured using the aforementioned powder X-ray diffraction (XRD) method (Inagaki, "Carbon", 1963, No. 36, pages 25-34; Iwashita et al., Carbon vol. 42 (2004), p. 701-714). In this measurement, the half-width of the diffraction peak of the (111) plane of the Si particles (A1) is higher than 0.71 degrees, and the crystal size is less than 0 nm, which is impossible.

Regarding the composite (A) according to one embodiment of the present invention, the peak intensity I _D and the peak intensity of the peak in the range of 1300 to 1400 cm ^-1 when the Raman spectroscopic spectrum of the particle end face is measured with a micro Raman spectrometer are 1580 to The ratio I _D / I _G (R value) of the peak intensity I _G of the peak in the range of 1620 cm ^-1 is preferably 0.15 or more and 1.0 or less. It is more preferably 0.2 or more and 1.0 or less, and even more preferably 0.4 or more and 1.0 or less. If the R value is too small, a certain amount of the surface of the particle (A2) is exposed. Therefore, if the R value is 0.15 or more, the particles (A2) and (A1) are coated with the carbonaceous material (A3), and the effect is obtained by improving the effect of suppressing the surface reactivity of the particles (A1) or reducing the effects of expansion and contraction. Good cycling characteristics. On the other hand, an excessively large R value indicates that a large amount of carbonaceous material (A3) covering the surface of particles (A2) containing amorphous carbon with a large initial irreversible capacity was used. Therefore, if the R value is 1.0 or less, a decrease in the initial discharge efficiency is suppressed.

(6) Method for producing composite (A) The composite (A) according to one embodiment of the present invention can be produced according to a known method.
For example, a mixture obtained by heat-treating a structure (α) composed of particles (A1) and an amorphous carbon coating layer (A1C) and a precursor of particles (A2) and a carbonaceous material (A3) may be used. A method of using the foregoing precursor as a carbonaceous material (A3) to obtain a composite (A).
The mixture of the structure (α) and the particles (A2) and the precursor of the carbonaceous material (A3), for example, the molten asphalt and the structure (α ) Mix in an inert environment, solidify the mixture, and pulverize, and mix the pulverized material with the particles (A2); it can be obtained by mixing the structure (α) and the particles (A2), and then mixing the structure (α) and The mixture of the particles (A2) and the carbonaceous material (A3) precursor is obtained by mechanochemical treatment; or it can be obtained by dissolving the carbonaceous material (A3) precursor in a solvent and adding a mixed structure to the precursor solution ( α) and particles (A2), the solvent was removed, and the obtained solid was pulverized. For the mechanochemical treatment, for example, a known device such as a Hybridizer (registered trademark, manufactured by Nara Machinery Co., Ltd.) can be used.

For pulverization or mixing, although known devices and appliances such as ball mills, jet mills, rod mills, pin mills, rotary cutting mills, hammer mills, sprayers, and mortars can be used, it is preferable to use particles (A1) And the structure (α) does not increase the degree of oxidation. In general, since it is considered that small-sized particles having a large specific surface area of the oxidation system are more likely to progress, it is preferable to pulverize the large-sized particles preferentially, and to pulverize the small-sized particles to a lesser extent. For example, rod mills, hammer mills, etc., mainly by punching and pulverizing, tend to transfer the punching force preferentially to particles with large particle sizes, and not to particles with small particle sizes. Like pin mills, rotary cutting mills, etc., mainly by means of punching and shearing and pulverization, the shearing force tends to be transmitted preferentially to particles with large particle sizes and not to particles with small particle sizes. With such a device, the particles (A1) and the structure (α) can be pulverized or mixed without being oxidized.

In order to suppress the oxidation of the particles (A1) and the structure (α), the pulverization and mixing are preferably performed in a non-oxidizing environment. Examples of the non-oxidizing environment include an environment filled with an inert gas such as an argon gas and a nitrogen gas.

The heat treatment for using the carbonaceous material (A3) precursor as the carbonaceous material (A3) is preferably 200 ° C or more and 2000 ° C or less, more preferably 500 ° C or more and 1500 ° C or less, and particularly preferably 600 ° C or more The temperature is below 1200 ° C. By this heat treatment, the carbonaceous material (A3) covers the structures (α) and / or the particles (A2), and the carbonaceous material (A3) can be placed between the structures (α) and the particles (A2) between each other. The intermediate structure (α) and the particles (A2) are connected to each other. If the heat treatment temperature is too low, the carbonization of the carbonaceous material (A3) precursor may not be completed sufficiently, and hydrogen or oxygen may remain in the negative electrode material, which may adversely affect battery characteristics. Conversely, if the heat treatment temperature is too high, crystallization may progress excessively, charging characteristics may be reduced, or the constituent elements and carbon of the bonded particles (A1) may be inert to Li ions. The heat treatment is preferably performed in a non-oxidizing environment. Examples of the non-oxidizing environment include an environment filled with an inert gas such as an argon gas and a nitrogen gas. In addition, since the particles may be lumped by heat treatment, in order to use the heat-treated product as an electrode active material, it is preferable to perform disintegration. As the method of disintegration, a pulverizer using the impact force of a hammer or the like, a jet mill using the collision of the objects to be pulverized, and the like are preferred.

(7) Capacity adjustment As a negative electrode material for lithium ion secondary batteries, for the purpose of improving battery performance or for adjusting the capacity of negative electrode materials for lithium ion secondary batteries, a material containing a composite (A) and carbon may be mixed . A plurality of types of materials including mixed carbon may be used. As the material containing carbon, graphite having a high capacity is preferable. As graphite, natural graphite or artificial graphite can be selected and used. At this time, it is preferable that the composite (A) uses a composite having a relatively high capacity (700 mAh / g or more) because the cost of the negative electrode material for a lithium ion secondary battery can be reduced. The material containing the carbon for capacity adjustment can be mixed with the composite (A) in advance, and additives such as a binder, a solvent, and a conductive auxiliary agent are added to prepare a slurry for the negative electrode. Further, additives such as the composite (A), a material containing carbon, a binder, a solvent, and a conductive auxiliary agent may be mixed at the same time to prepare a slurry for a negative electrode. The order or method of mixing may be appropriately determined in consideration of powder handling and the like.

(8) Slurry for a negative electrode The slurry for a negative electrode according to one embodiment of the present invention includes additives such as the foregoing negative electrode material, a binder, a solvent, and a conductive auxiliary agent, if necessary. This negative electrode slurry can be obtained, for example, by kneading the foregoing negative electrode material, a binder, a solvent, and a conductive auxiliary agent if necessary. The slurry for the negative electrode may be formed into a shape such as a sheet shape, a round pellet shape, or the like.

Examples of the material used as a binder include polyethylene, polypropylene, ethylene-propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, acrylic rubber, and a polymer having a large ion conductivity. Compounds etc. Examples of the polymer compound having a large ionic conductivity include polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, and polyacrylonitrile. The amount of the binder is preferably 0.5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the negative electrode material.

The conductive auxiliary agent is not particularly limited as long as it functions to impart conductivity and electrode stability to the electrode (a buffering effect with respect to a volume change with insertion and detachment of lithium ions). For example, carbon nanotubes, carbon nanofibers, vapor-phase carbon fibers (e.g., "VGCF (registered trademark)" manufactured by Showa Denko Corporation), conductive carbon (e.g., "DENKA BLACK (registered trademark)", electro-chemical industry Co., Ltd., "Super C65" TIMCAL company, "Super C45" TIMCAL company, "KS6L" TIMCAL company) and so on. The amount of the conductive auxiliary agent is preferably 10 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the negative electrode material.

The solvent is not particularly limited, and N-methyl-2-pyrrolidone, dimethylformamide, isopropyl alcohol, water, and the like can be used. When water is used as a solvent, a thickener is preferably used in combination. The amount of the solvent may be adjusted so as to have a viscosity such that the slurry can be easily applied to a current collector.

(9) Negative electrode sheet A negative electrode sheet according to an embodiment of the present invention includes an electrode layer of a current collector and a covered current collector.
Examples of the current collector include a sheet shape such as a nickel foil, a copper foil, a nickel mesh, or a copper mesh.
The electrode layer contains a binder and the foregoing negative electrode material. The electrode layer can be obtained, for example, by applying the aforementioned slurry to a current collector and drying it. The coating method of the slurry is not particularly limited. The thickness of the electrode layer is preferably 50 to 200 μm. If the electrode layer is excessively thickened, the normalized battery container may not be able to accommodate the negative electrode sheet. The thickness of the electrode layer can be adjusted by the application amount of the slurry. Moreover, after drying a slurry, it can also adjust by press molding. Examples of the press forming method include a forming method such as roll pressing and press pressing. The pressure at the time of press forming is preferably about 100 to 500 MPa.
The electrode density of the negative electrode sheet can be calculated as follows. That is, the negative electrode sheet after punching was punched into a circular shape with a diameter of 16 mm, and its mass and thickness were measured. This subtracts the mass and thickness of the current collector foil (those punched into a circular shape with a diameter of 16 mm), which are measured separately, to determine the mass and thickness of the electrode layer, and calculates the electrode density based on this value.

(10) Lithium-ion secondary battery A lithium-ion secondary battery according to an embodiment of the present invention includes a positive electrode sheet having at least one selected from the group consisting of a non-aqueous electrolyte and a non-aqueous polymer electrolyte, and the foregoing. Negative plate.
As the positive electrode sheet, those conventionally used in lithium ion secondary batteries can be used. Specifically, a sheet including 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 solution and non-aqueous polymer electrolyte used in the lithium ion secondary 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, and the like are dissolved in ethylene carbonate, diethyl carbonate, and dicarbonate. Organic non-aqueous solvents such as methyl carbonate, ethyl methyl carbonate, propylene carbonate, butyl carbonate, acetonitrile, propionitrile, dimethoxyethane, tetrahydrofuran, γ-butyrolactone, etc. Electrolyte; gel polymer electrolyte containing polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, etc .; solid polymer electrolyte containing polymers with ethylene oxide bonds.

In addition, a small amount of an electrolyte may be added to a substance that causes a decomposition reaction during charging of a lithium ion secondary battery. Examples of the substance include ethylene carbonate (VC), biphenyl, propane sultone (PS), fluoroethylene carbonate (FEC), and ethylene sultone (ES). The added amount is preferably 0.01% by mass or more and 50% by mass or less.

A separator may be provided between the positive electrode sheet and the negative electrode sheet in the lithium ion secondary battery. Examples of the separator include a nonwoven fabric, a cloth, a microporous film, or a combination of polyolefins such as polyethylene and polypropylene as a main component.

Lithium-ion secondary batteries can be used as power sources for electronic devices such as mobile phones, laptops, and mobile information terminals; power sources for electric motors such as electric drills, vacuum cleaners, and electric cars; power generated by fuel cells, solar power, and wind power Storage, etc.

[Example]

Hereinafter, examples and comparative examples of the present invention will be described, and further specifically described. However, these are merely exemplifications for illustration, and the present invention is not limited to them in any way. In the examples and comparative examples, the average particle diameter d _AV of the primary particles of the particles (A1), the thickness of the amorphous carbon coating layer (A1C), and the values measured by the X-ray diffraction method of artificial graphite particles The average plane interval d _{002 of the} (002) plane, the thickness L _{C of the} crystal in the C-axis direction, the half width of the diffraction peak of the (111) plane of the Si particle (A1), and the R value in the Raman spectroscopic spectrum are based on this. Measured by the method described in "Embodiment" of the specification. Measurements of other physical properties and battery evaluation were performed as follows.

[Determination of I ₁₁₀ / I ₀₀₄ by powder X-ray diffraction method]
The carbon powder sample was filled in a glass sample plate (sample plate window 18 × 20 mm, depth 0.2 mm), and the measurement was performed under the following conditions.
X-ray diffraction device: Rigaku SmartLab (registered trademark)
X-ray type: Cu-Kα line
Kβ line removal method: Ni filter
X-ray output: 45kV, 200mA
Measurement range: 5.0 ～ 10.0deg.
Scanning speed: 10.0deg./min.
The obtained waveforms were smoothed, background removed, and Kα2 removed to perform file matching. From the (004) peak intensity of the plane of the results obtained with the I ₀₀₄ (110) plane peak intensity I _110, and calculates the feature isotropic strength index ratio I ₁₁₀ / I _004. It should be noted that the peaks on each side are selected as the individual peaks with the highest intensity among the following ranges.
(004) surface: 54.0 ～ 55.0deg
(110) surface: 76.5 ～ 78.0deg

[Particle diameter D _V50 ]
Two cups of a powdery mini spatula and two drops of a nonionic surfactant (TRITON (registered trademark) -X; manufactured by Roche Applied Science) were added to 50 ml of water, and ultrasonic dispersion was performed for 3 minutes. This dispersion was put into a laser diffraction particle size distribution measuring device (LMS-2000e, manufactured by SEISHIN Enterprise Co., Ltd.), and the volume-based cumulative particle size distribution was measured to obtain a 50% particle diameter D _v50 (μm).

[Specific surface area]
Using a specific surface area / pore distribution measurement device (manufactured by Quantachrome Instruments, NOVA 4200e) using a nitrogen gas as a detector, the BET specific surface area S _BET (m ^{2) was} measured by a BET multi-point method with relative pressures of 0.1, 0.2, and 0.3. / g).

[Pore volume]
About 5 g of the carbon material was weighed in a glass tank, and dried at 300 ° C. for about 3 hours under a reduced pressure of 1 kPa or less. After removing absorbing components such as moisture, the mass of the carbon material was measured. Then, the adsorption isotherm of the nitrogen gas of the carbon material after drying under liquid nitrogen cooling was measured with Autosorb-1 manufactured by Quantachrome. The total pore volume (μL / g) with a diameter of 0.4 μm or less was obtained from the nitrogen adsorption amount at the measurement point of the obtained adsorption isotherm P / P ₀ = 0.992 to 0.995 and the mass of the carbon material after drying. ).

[Determination of powder X-ray diffraction of complex (A)]
A glass sample plate (sample plate window 18 × 20 mm, depth 0.2 mm) was filled with the composite (A) powder, and the measurement was performed under the following conditions.
X-ray diffraction device: Rigaku SmartLab (registered trademark),
X-ray species: Cu-Kα line,
Kβ line removal method: Ni filter,
X-ray output: 45kV, 200mA,
Measurement range: 10.0 ～ 80.0deg,
Scanning speed: 10.0deg./min,
The obtained waveforms were smoothed, background removed, and Kα2 removed to perform file matching. From this, the half-width of the diffraction peak of the Si (111) plane was calculated.
Si (111): 27.5 to 29.0 deg.

[Manufacture of positive electrode sheet]
N-methylpyrrolidone was added and mixed while adding 192g of LiNi _0.6 Mn _0.2 Co _0.2 O ₂ , 4g of carbon black as a conductive auxiliary agent, and 4g of polyvinylidene fluoride (PVdF) as a binding material, and then stirring and mixing to obtain Slurry for positive electrode.
The slurry for a positive electrode was applied to an aluminum foil having a thickness of 20 μm by a roll coater, and dried to obtain a sheet for a positive electrode. The dried electrode was set to a density of 3.6 g / cm ³ by roll stamping to obtain a positive electrode sheet for battery evaluation.

[Manufacture of negative electrode sheet]
As a binding agent, carboxymethyl cellulose (CMC; Daimler, CMC1300) was used. Specifically, an aqueous solution of CMC powder with a solid content ratio of 2% was obtained.
As the conductive auxiliary, carbon black, carbon nanotube (CNT), and vapor-grown carbon fiber (VGCF (registered trademark) -H, manufactured by Showa Denko Co., Ltd.) will be prepared in a ratio of 3: 1: 1 (mass ratio) ) Mixer as a mixed conductive auxiliary.
90 mass parts of the mixture (A) produced in the examples and comparative examples described below, and graphite as a carbon-containing material for the purpose of capacity adjustment, and 2 mass parts of a conductive auxiliary agent are mixed to form a solid component of CMC 8 The mass CMC aqueous solution was kneaded in a rotation and revolution mixer to obtain a slurry for a negative electrode.
Or mixed with 90 parts by mass of the composite (A) produced in the examples and comparative examples, 2 parts by mass of the conductive auxiliary agent, and 8 parts by mass of the CMC aqueous solution in a CMC solid content, and kneaded in a rotation and revolution mixer. A negative electrode slurry was obtained.
The aforementioned slurry for a negative electrode was uniformly coated on a copper foil having a thickness of 20 μm using a doctor blade at 300 μm intervals, and after being dried on a hot plate, it was vacuum dried to obtain a negative electrode sheet. The dried electrode was pressed at a pressure of 300 MPa by a one-axis punch to obtain a negative electrode sheet for battery evaluation.

[Fine adjustment of positive and negative electrode capacity ratio]
When the positive electrode sheet and the negative electrode sheet are opposed to each other to make a lithium ion battery, it is necessary to consider the capacity balance between the two. That is, if the capacity of the negative electrode on the lithium-ion-receiving side is too small, excess Li is precipitated on the negative side to cause cycle degradation. On the other hand, if the capacity of the negative electrode is too large, the cycle characteristics are improved but the battery is charged in a low-load state Discharge, so energy density decreases. In order to prevent this, the same positive electrode sheet is used, and the negative electrode sheet is first evaluated in advance for the discharge amount of each mass of the active material in the opposite Li half cell, in order to the capacity of the negative electrode sheet (Q _C ). The ratio of Q _A ) is 1.2 and becomes a constant value, and the capacity of the negative electrode sheet is finely adjusted.

[Production of evaluation batteries]
The following operation was performed in a glove box maintained in a dry argon gas environment at a dew point of -80 ° C or lower.

[Two-pole laminated full battery]
The above-mentioned negative electrode sheet and positive electrode sheet were punched to obtain a negative electrode sheet and a positive electrode sheet having an area of 20 cm ² . The Al label was attached to the Al foil of the positive electrode sheet, and the Ni label was attached to the Cu foil of the negative electrode sheet. A polypropylene thin film microporous membrane was sandwiched between the negative electrode sheet and the positive electrode sheet, and in this state, it was packed with an aluminum laminate packaging material, and 700 μL of an electrolytic solution was poured. Then, the opening was sealed by thermal fusion to produce a battery for evaluation. The electrolyte solution is a solvent in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate are mixed in a volume ratio of 3: 5: 2, and 1% by mass of ethylene carbonate (VC) and fluoroethylene are mixed. Carbonate (FEC) was 10% by mass, and then the electrolyte LiPF ₆ was dissolved so as to have a concentration of 1 mol / L.

[Definition of charging and discharging]
The so-called charging refers to the application of voltage to the battery, and the so-called discharge refers to the operation of the voltage of the consumer battery. In the case of a bipolar laminated full cell, the opposite electrode is not suitable for Li metal, but a material having a higher redox potential than the negative electrode sheet described above. Therefore, the negative electrode sheet is treated as a negative electrode. Accordingly, in a bipolar laminated full battery, the so-called charging means the operation of inserting Li into the negative electrode sheet, and the so-called discharge means the operation of releasing Li from the negative electrode operation.

[Charge-discharge cycle test using bipolar laminated full cell]
In a cycle test using a bipolar laminated full cell, aging was performed for 5 cycles. The first cycle within aging is to charge from the resting potential at a current value of 0.025C in CC mode for 6 hours and 45 minutes, and introduce a rest for 12 hours. Then, CC charging was performed at 0.05C to 4.2V. The discharge was performed at a current value of 0.05C in CC mode to 2.7V. The second cycle of aging is under the same conditions as the fifth cycle. The charging is based on the current value of 0.1C, and after CC is charged to 4.3V, it is converted into CV charging at 4.3V, and the cut-off current value is charged at 0.025C. The discharge was performed at a current value of 0.1C in CC mode to 2.7V. The third and fourth cycles of aging are under the same conditions, and the current values of the second and fifth cycles of aging are replaced from 0.1C to 0.2C.
After the aging is performed, a charge-discharge cycle test is performed by the following method.
Charging is performed in CC mode with a current value of 1C until 4.3V, and then the discharge is switched to CV mode, and the cut-off current value is set to 0.05C.
Discharge was performed in CC mode with a current value of 1C until 3.0V.
This charge-discharge operation is set to 1 cycle for 20 cycles, and a low-speed test in which the above charge-discharge 1C is replaced with 0.1C is performed on the 21st cycle. This 21-cycle test was repeated to make a total of 500 cycles.
The discharge capacity maintenance rate of the Nth cycle is calculated by the following formula.
(Discharge capacity maintenance rate after N cycles (%)) =
((Discharge capacity at N cycles) / (initial discharge capacity)) × 100
The first discharge capacity in this formula means the first cycle after the aging is completed.

[Measurement of electrode swelling ratio]
After recovering the discharged bipolar laminated full battery after the above 504 cycle test, it was disassembled in a glove box maintained in a dry argon gas environment with a dew point of -80 ° C or lower, and the negative electrode was taken out. After the negative electrode was washed with ethyl methyl carbonate (EMC), a dial indicator (manufactured by Mitutoyo Corporation; Code. No547-401 ratio 0.001 mm) was used to measure the thickness of the electrode. The measurement locations were determined as 9 locations along the short side of the side electrode with the label attached, and the average value of the measurement values was determined as the electrode thickness. As an electrode to be used as a reference when determining the electrode expansion rate, an electrode immediately after punching was used. The electrode thickness herein means a value obtained by subtracting the thickness of the entire copper foil current collector.

The materials used in the following examples and comparative examples are as follows.

(1) Silicon-containing particles (Si fine particles)
The physical properties of Si particles and Si (1) to Si (3) used in the examples and comparative examples are shown in Table 1.
The average particle diameter d _AV of the primary particles is as described above, and is d _AV [nm] = 6 × 10 ³ / (ρ × S _BET ). Here, ρ is the true density of Si particles (2.3 [g / cm ³ ] as a theoretical value), and S _BET is a specific surface area [m ² / g] measured by the BET method.
[Table 1]

(2) Fabrication of Structure (α) After the Si fine particles Si (1) were produced by the CVD method, an acetylene gas was continuously used as a raw material, and a carbon coating layer having a thickness of 2 nm was formed by the CVD method to obtain a structure ( α) -1 (Table 1). Regarding Si fine particles Si (2) and Si (3), the structure (α) has not been produced.

(3) Asphalt is used petroleum asphalt (softening point 220 ° C). For this petroleum pitch, the residual carbon ratio at 1100 ° C was measured by thermal analysis under a nitrogen gas flow, and was 52% by mass.
In addition, the QI content of petroleum pitch measured by the method described in JIS K2425 or in accordance therewith was 0.62% by mass, and the TI content was 48.9% by mass.

(4) Graphite particles In the examples and comparative examples, the physical properties of graphite particles used as a material containing carbon for the purpose of capacity adjustment together with the particles (A2) are shown in Table 2.

[Table 2]

Example 1:
The petroleum-based coke was pulverized by a pulverizer (manufactured by Hosokawa Micron Co., Ltd.), and further pulverized by a jet mill (manufactured by SEISHIN Enterprise Co., Ltd.). This was heat-treated at 3000 ° C in an Aichson furnace to obtain D The artificial graphite particles (A2) -a having a _V50 of 7.5 μm and a BET specific surface area of 4.9 m ² / g.
Next, 16.4 parts by mass of the structure (α) -1 and the precursor of the carbonaceous material (A3), that is, 15.4 parts by mass of the aforementioned petroleum pitch (as mass after carbonized petroleum pitch) were put into a separable flask. A nitrogen gas was circulated and an inert environment was maintained, and the temperature was raised to 250 ° C. The mixer was rotated at 500 rpm and stirred to uniformly mix the pitch and the silicon-containing particles. This was cooled to solidify, and a mixture was obtained.
This mixture was added with 68.2 parts by mass of particles (A2) -a, that is, the aforementioned artificial graphite particles, and put into a rotary cutting mill to maintain a nitrogen gas in an inert environment, and stirred at a high speed of 25000 rpm to mix them.
This was placed in a firing furnace, and the temperature was raised to 1100 ° C at 150 ° C / h under a nitrogen gas flow, and the temperature was maintained at 1100 ° C for 1 hour to convert the (A3) precursor into (A3). After cooling to room temperature, the product was taken out from the sintering furnace, pulverized by a rotary cutting mill, and obtained under the sieve of a sieve with a sieve of 45 μm to obtain a composite (A) -a.
Different from the above, the petroleum-based coke was separately pulverized with a pulverizer (manufactured by Hosokawa Micron Co., Ltd.), and this was heat-treated at 3000 ° C in an Aichson furnace to obtain D _V50 of 12.1 μm and a BET specific surface area of 2.5 m ^2. / g of graphite (1). The petroleum-based coke was pulverized by a pulverizer (manufactured by Hosokawa Micron Co., Ltd.), and further pulverized by a jet mill (manufactured by Seishin Enterprise Co., Ltd.), and this was heat-treated at 3000 ° C in an Aichson furnace to obtain Graphite (2) having a D _V50 of 6.7 μm and a BET specific surface area of 6.1 m ² / g.

A negative electrode sheet was produced using a mixture of 67.0 parts by mass of the composite (A) -a with 16.5 parts by mass of graphite (1) and 16.5 parts by mass of graphite (2), and battery characteristics were measured. The results are shown in Table 3.

Comparative Example 1:
A composite (A) -b was obtained in the same manner as in Example 1 except that the structure (α) -1 was replaced with Si (2) in Table 1.

A negative electrode sheet was produced using a mixture of 67.0 parts by mass of the composite (A) -b with 16.5 parts by mass of graphite (1) and 16.5 parts by mass of graphite (2), and battery characteristics were measured. The results are shown in Table 3.

Comparative Example 2:
A composite (A) -c was obtained in the same manner as in Example 1 except that the structure (α) -1 was replaced with Si (3) in Table 1.

A negative electrode sheet was produced using a mixture of the composite (A) -c67.0 parts by mass with 16.5 parts by mass of graphite (1) and 16.5 parts by mass of graphite (2), and battery characteristics were measured. The results are shown in Table 3.

[table 3]

Regarding the results shown in Table 3, if Example 1 and Comparative Example 1 are compared, the average particle diameter of the Si particles is almost the same, but the half-width of the diffraction peak of the Si (111) plane in Comparative Example 1 is very small. That is, it means that the size of Si (111) crystals included in the composite of Comparative Example 1 is large, and the number of crystal particles included in Si particles is small. As a result, the Si particles in the composite of Comparative Example 1 expanded to an anisotropy, and the electrode mixture layer expansion rate at the end of the 500-cycle discharge increased. As a result, the capacity maintenance rate is also reduced.

Regarding the results shown in Table 3, if Example 1 and Comparative Example 1 and Comparative Example 2 are compared, the composite of Comparative Example 2 not only has a large Si (111) crystal size, but also has a very large average particle diameter of Si particles. . If the average particle diameter of the Si particles is large, the expansion space is localized while the expansion amount of each Si1 particle is increased. As a result, the electrode mixture layer is significantly damaged. On the other hand, if the average particle diameter of the Si particles is small, the amount of expansion of each Si1 particle is reduced and the super-expanded space is not localized. As a result, the destruction of the electrode mixture layer is small. Accordingly, the expansion rate and capacity retention rate of the electrode mixture layer of Comparative Example 2 were worse than those of Example 1 and Comparative Example 1.

Claims (6)

A negative electrode material for a lithium ion secondary battery, which is a negative electrode material for a lithium ion secondary battery including a composite (A). The composite (A) includes: an average particle diameter d _AV of primary particles of 5 nm or more and 95 nm or less. The Si particles (A1), the amorphous carbon coating layer (A1C) with a thickness of 1 nm to 20 nm of the coating particles (A1), the particles (A2) composed of a substance containing graphite, and the carbonaceous material (A3) It is characterized in that the half width of the diffraction peak of the (111) plane of the Si particle (A1) measured by powder X-ray diffraction measurement of the composite (A) is 0.40 degrees or more. For example, the negative electrode material for a lithium ion secondary battery of claim 1, wherein the particle (A2) has a 50% cumulative particle size distribution on a volume basis and the particle diameter D _V50 is 2.0 μm or more and 20.0 μm or less, and the BET specific surface area (S _BET ) is 1.0 m ² / g or more and 10.0 m ² / g or less. The negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the aforementioned particle (A2) is a peak intensity I ₁₁₀ and (110) of a graphite crystal measured by a powder X-ray diffraction method. The ratio of peak intensity I ₀₀₄ of the surface 004) I ₁₁₀ / I ₀₀₄ is 0.10 to 0.35, and the average surface spacing d ₀₀₂ of the (002) surface measured by powder X-ray diffraction method is 0.3360 nm or less. The total pore volume of pores having a diameter of 0.4 μm or less measured by a nitrogen gas absorption method is 5.0 μL / g or more and 40.0 μL / g or less. The negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the content of the Si particles (A1) in the composite (A) is 10% by mass or more and 70% by mass or less. A negative electrode sheet is provided with a sheet-shaped current collector and a negative electrode layer covering the current collector. The negative electrode layer includes a binder, a conductive auxiliary agent, and the negative electrode for a lithium ion secondary battery according to any one of claims 1 to 4. material. A lithium ion secondary battery having a negative electrode sheet as claimed in claim 5.