JP4684581B2 - Negative electrode material for lithium ion secondary battery, method for producing the same, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery, in particular, a negative electrode material having a large capacity and excellent high rate charge / discharge characteristics, and a lithium ion secondary battery including the negative electrode material.

  Lithium ion secondary batteries, including lithium polymer batteries, are rapidly developing as power sources for portable electronic devices such as mobile phones and portable personal computers. In these power sources for portable devices, the most required characteristic is energy density, that is, energy storage amount per unit volume, and there is an interest in how long a portable device can be used.

  On the other hand, the size of lithium ion secondary batteries has been increased mainly for batteries for hybrid vehicles (HEV). The most required characteristic of a large battery is output. In other words, there is an interest in the high rate charge / discharge characteristics of how quickly can be charged or discharged in a unit time. That is, large batteries are interested in their power.

In addition, transition metal chalcogen compounds such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , TiS ₃ , TiS ₂ , and TiO ₂ used as the positive electrode of the lithium ion secondary battery release oxygen by overcharge, and the organic electrolyte solution There is a risk of burning and exploding.

In addition, graphite used as a negative electrode of a lithium ion secondary battery uses propylene carbonate (PC) as a solvent for an electrolytic solution, and an electrolyte such as LiPF ₆ or LiBF ₄ is added to and mixed with the solvent to obtain an organic electrolytic solution. In this case, the organic electrolyte solution is decomposed by overcharging and gas is released into the sealed battery. As a result, there is a risk that the internal pressure of the battery will rise and the battery will explode (see, for example, Patent Document 1). Therefore, the lithium ion secondary battery requires further safety measures as its size increases.

  Conventionally, amorphous carbon has been used as a negative electrode material for large batteries, particularly for HEV batteries that require high-rate charge / discharge characteristics. When amorphous carbon is used as a negative electrode material for a lithium ion secondary battery for HEV, the battery is said to have good acceleration performance at the time of discharging and to efficiently take in regenerative energy at the time of charging.

  Like amorphous carbon, graphite is also used as a negative electrode material for lithium ion secondary batteries as described above. Compared to graphite, amorphous carbon generally has a low catalytic reactivity with a solvent and is excellent in safety. Moreover, it is excellent in charging characteristics. These excellent physical properties contribute to the use of amorphous carbon as a negative electrode material for lithium ion secondary batteries over graphite.

However, amorphous carbon is expensive and unsuitable for a negative electrode material for a large lithium ion secondary battery. Therefore, a negative electrode material for large-sized lithium ion secondary batteries is required to have a negative electrode material that is low in price, excellent in high-rate charge / discharge characteristics, and high in safety.
JP 2002-141062 A (paragraph numbers [0005] to [0008])

  The present inventors have found that the high-rate charge / discharge characteristics depend on the size of the negative electrode material particles, and are greatly influenced by the contact state between the negative electrode material and the electrolyte solution that wets the negative electrode material. Furthermore, secondary particle formation reduces the specific surface area and improves initial coulomb efficiency, increases safety, and retains high electrical conductivity by using carbon as a binder for this secondary particle formation. Therefore, it has been found that further high rate charge / discharge characteristics can be obtained, and the present invention has been completed.

  Accordingly, an object of the present invention is to provide a negative electrode material for a large-sized lithium ion secondary battery, which has solved the above-described problems, is excellent in high rate characteristics, and is safe and inexpensive.

  The present invention for achieving the above object is described below.

  [1] A negative electrode for a lithium ion secondary battery having an average particle diameter of 2.5 to 40 μm, comprising crystalline carbon particles having an average particle diameter of 0.1 to 20 μm and bonded carbon bonding between the crystalline carbon particles. Wood.

  [2] The negative electrode material for a lithium ion secondary battery according to [1], wherein the ratio of bonded carbon to the entire negative electrode material is 0.2 to 30% by mass.

[3] The negative electrode material for a lithium ion secondary battery according to [1], wherein the ⁷ Li-NMR spectrum of the fully charged negative electrode material has one signal at 10 to 20 ppm based on the LiCl aqueous solution.

  [4] The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the crystalline carbon particles have a 002 lattice constant of 0.68 to 0.70 nm according to the XRD method.

  [5] The negative electrode material for a lithium ion secondary battery according to [1], wherein the carbon of the crystalline carbon particles is optically anisotropic.

  [6] A method for producing a negative electrode material for a lithium ion secondary battery, wherein the surface of crystalline carbon particles having an average particle size of 0.1 to 20 μm is subjected to chemical vapor deposition, A method for producing a negative electrode material for a lithium ion secondary battery, wherein the particles are bonded with bonded carbon by intermittently fluidizing.

  [7] The lithium according to [6], wherein the intermittent operation of fluidizing the crystalline carbon particles is an operation of repeating the fluidization operation for 1 to 10 minutes and the stationary operation for 1 to 5 minutes three times or more. The manufacturing method of the negative electrode material for ion secondary batteries.

  [8] The lithium ion according to [6], wherein the negative electrode material produced by the production method according to [6] is classified to remove fine particles, and the average particle size is 1.1 times or more that before classification. A method for producing a negative electrode material for a secondary battery.

  [9] A lithium ion secondary battery formed using the negative electrode material according to [1].

  The negative electrode material for a lithium ion secondary battery of the present invention uses an inexpensive crystalline carbon material as primary particles, and these primary particles are bonded with carbon to form secondary particles. Therefore, in a very high rate charge / discharge of 10C to 20C. A safe and inexpensive lithium ion secondary battery with high energy density, high initial coulomb efficiency, and low cost can be realized.

  Hereinafter, the present invention will be described in detail.

  The negative electrode material of the present invention is a carbon secondary particle in which a carbon coating layer is formed on the surface of crystalline carbon particles (primary particles) and primary particles are bonded via the carbon coating layer.

  The average diameter of the primary particles is 0.1 to 20 μm, preferably 1 to 5 μm. If the average primary particle diameter is less than 0.1 μm, the initial Coulomb efficiency is greatly reduced. On the other hand, when the average primary particle diameter exceeds 20 μm, the high-rate charge / discharge characteristics deteriorate.

  The particle size distribution of the primary particles is preferably sharp, and specifically, the particle size distribution region is preferably in the range of the average diameter ± 50%.

  The primary carbon particles used as the nucleus in the negative electrode material of the present invention may be crystalline carbon or amorphous carbon, but crystalline carbon is preferred in terms of cost and battery characteristics. This carbon primary particle uses a delayed coke made from coal-based pitch or tar, or a delayed coke made from petroleum heavy oil or a fluid coke as a raw material, and a coke obtained by firing this at 900 to 1400 ° C. be able to.

  The particle size adjustment of the primary particles may be performed at any stage before firing or after firing, but is more preferably performed before firing. That is, the particle size adjustment of the primary particles can be determined by the degree of pulverization of the carbon precursor such as raw material coke before firing.

  The primary particle carbon preferably has a 002 lattice constant of 0.68 nm to 0.70 nm according to the XRD method described later. When the 002 lattice constant by the XRD method is less than 0.68 nm, the discharge capacity decreases, and when the 002 lattice constant by the XRD method exceeds 0.70 nm, the high-rate charge / discharge characteristics decrease.

  The primary particles of carbon are preferably optically anisotropic. Optical anisotropy is a feature not found in amorphous carbon. Many optically anisotropic carbons are formed as mesophases when the precursor resin, tar, pitch, etc. are heat-treated at 350-500 ° C. in a liquid phase state, and further, by continuing the heat treatment, The entire phase is converted to carbon having an optically anisotropic structure.

  The ash content in the carbon of the primary particles is preferably 0.2% by mass or less, and more preferably 0.1% by mass or less. If the ash content exceeds 0.2% by mass, the risk of an abnormal electrode reaction increases.

  The high-rate charge / discharge characteristics are not uniquely determined only by the crystallinity of the negative electrode material carbon, but the spatial structure of the electrodes is important. In view of the high rate charge / discharge characteristics, the negative electrode material is preferably small particles, but it is essential that abundant electrolyte be present around the negative electrode material.

  For this purpose, the particle size of the negative electrode material is preferably small, and it is essential that sufficient voids exist between the particles. For this reason, it is preferable that the negative electrode material for a large-sized lithium ion secondary battery has a structure in which sufficient voids are maintained between primary particles in advance by forming secondary particles. The porosity in the electrode is preferably 20 to 50%, more preferably 25 to 35%.

  The secondary particles formed by combining the primary particles have an average diameter of 2.5 to 40 μm. When the secondary particle average diameter is less than 2.5 μm, the specific surface area becomes large, which causes a problem in safety. When the secondary particle average diameter exceeds 40, it is difficult to obtain high high-rate charge / discharge characteristics.

  Although the particle size of the secondary particles varies depending on the type and amount of the binder, it is most preferable to adjust the particle size by converting the primary particles into secondary particles by a chemical vapor deposition (CVD) method. The primary particles can be made into secondary particles by the CVD method by a method such as fluidized bed chemical vapor deposition or fixed bed chemical vapor deposition.

  FIG. 1 is a schematic cross-sectional view showing an example of the negative electrode material of the present invention obtained by converting primary particles into secondary particles by a CVD method. As shown in FIG. 1, in the CVD method, it becomes possible to uniformly coat the surfaces of the primary particles 2 with a small amount of vapor-deposited carbon 4 simultaneously with the formation of secondary particles. In particular, when performed in a fluidized bed, the surfaces of the primary particles 2 can be uniformly coated with a small amount of vapor-deposited carbon 4. Therefore, it is considered that the secondary particles obtained have a reduced surface area, resulting in a decrease in the non-conductive film formed on the surface and a decrease in electrode resistance. Moreover, the safety | security of the carbon-type negative electrode with respect to reaction with a solvent can be improved further according to the fall of a surface area.

Note that the bulk density of the fluidized bed during the fluidized bed chemical vapor deposition reaction is preferably 0.1 to 0.5 g / cm ³ . The obtained secondary particles have a structure in which sufficient voids 6 are maintained between the primary particles 2.

  The chemical vapor deposition temperature is preferably 650 to 1200 ° C., but the suitable temperature varies depending on the chemical species used for chemical vapor deposition. For example, when acetylene is used as the chemical species, chemical vapor deposition at 650 ° C. is possible.

  The higher the chemical vapor deposition temperature, the higher the rate of deposition of pyrolytic carbon and the higher the conversion rate of organic gas to carbon. At the same time, carbon grows in a fibrous or soot form rather than in a film form, It is not preferable for the treatment for surface coating. Moreover, the tendency for crystallinity to fall is recognized. Therefore, the chemical vapor deposition temperature is preferably 1200 ° C. or lower, more preferably 1150 ° C. or lower.

  Chemical species used as a carbon deposition source include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, diphenyl, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, etc. A tricyclic aromatic hydrocarbon, a derivative thereof, or a mixture thereof can be given.

  In addition to gas diesel oil, creosote oil, anthracene oil obtained from coal-based tar distillation process, petroleum-based fractionated oil and naphtha cracked tar oil, fats such as methane, ethane, propane, butane, pentane, and hexane An aromatic hydrocarbon or a dielectric alcohol thereof can be used alone or as a mixture.

  Furthermore, organic compounds having a double bond such as acetylene, ethylene, propylene, isopropylene, and butadiene can also be used. Among them, benzene having an aromatic ring number of 1 that does not generate tar during chemical vapor deposition, or a derivative such as toluene, xylene, styrene, or a mixture thereof is preferable.

  In the fluidized bed chemical vapor deposition treatment, the coating carbon to be formed is preferably 0.2 to 30% by mass, more preferably 3 to 20% by mass, and particularly preferably 10 to 18% by mass with respect to the entire negative electrode material. This is because the effect of reducing the surface area is manifested when the coated carbon amount is 0.2% by mass or more with respect to the entire negative electrode material. Further, when carbon having a coating amount of more than 30% by mass with respect to the whole negative electrode material is vapor-deposited, the effect of improving battery characteristics is almost saturated and adhesion between particles becomes remarkable, which tends to cause particle coarsening, which is not preferable. .

  The chemical vapor deposition process is performed in an inert gas atmosphere such as nitrogen. The inert gas is used to discharge oxygen and unreacted organic gas from the reaction system, but at the same time is important as a fluidizing medium for forming a fluidized bed. Therefore, the organic substance that becomes the chemical vapor deposition carbon source is diluted with an inert gas such as nitrogen and introduced into the fluidized bed.

  The concentration of the organic substance has a great influence on the crystallinity of the deposited carbon produced. When the molar concentration is low, the carbon deposition rate is lowered, but the crystallinity of the deposited carbon is improved. On the other hand, when the molar concentration is high, the carbon deposition rate increases, but at the same time, soot-like carbon is generated, and the crystallinity of the deposited carbon decreases. Therefore, in this invention, 2-50% is preferable and, as for the molar concentration with respect to the inert gas of organic substance, 5 to 33% is more preferable.

  Secondary particle formation can be performed not only by CVD, but also by carbonization after kneading with primary particles using a carbon precursor such as resin, tar, and pitch as a binder. FIG. 2 is a schematic cross-sectional view showing an example of the negative electrode material of the present invention obtained by making secondary particles into primary particles by kneading granulation using a binder such as coal tar. As shown in FIG. 2, the obtained secondary particles have a structure in which sufficient voids 26 are maintained between the primary particles 22 as in the case of the CVD method.

  In the case of secondary particle formation by kneading granulation using this binder, surface coating with a carbon precursor that becomes bonded carbon 24 after carbonization proceeds simultaneously with secondary particle formation. The carbonization temperature is preferably 850 to 1200 ° C. In addition, the amount of carbon precursor added is preferably 30% by mass or less, and more preferably 1 to 15% by mass with respect to the whole of the negative electrode material so that secondary particle formation does not proceed excessively when kneading with primary particles. Preferably, 3-8 mass% is especially preferable.

  On the other hand, the fluidized bed CVD method is often operated primarily for the purpose of suppressing secondary particle formation, but secondary particle formation can be promoted by intermittently stopping the flow. In this fluidization intermittent operation, a fluidization operation of 1 to 10 minutes and a stationary operation of 1 to 5 minutes are preferably repeated 3 times or more, more preferably 9 to 20 times.

  In addition, the secondary particle size adjustment is performed by classifying the carbon particles that have been converted into secondary particles into fine and coarse particles using a classifier to remove the fine particles, and only the coarse particles. It is good also as a negative electrode material. The average particle size of the coarse particles is preferably 1.1 times or more that before classification.

When a battery is composed of a negative electrode comprising the secondary particles of the present invention and metallic lithium, and a ⁷ Li-NMR spectrum is measured in a state where lithium ions are intercalated in the negative electrode, the chemical shift is almost equal to that of lithium chloride (0 ppm). One spectrum appears at a position of 0 to 20 ppm.

  This spectrum shows the state of lithium ions intercalated into crystalline carbon. That is, the carbon primary particles and the carbon that covers the primary particles and bonds the primary particles are both crystalline carbon, and the lithium ions inserted into these are detected separately from each other. Absent.

On the other hand, a battery is composed of a negative electrode having a secondary particle structure in which primary particles of amorphous carbon are bonded with crystalline carbon and metallic lithium, and a ⁷ Li-NMR spectrum is obtained with lithium ions intercalated in the negative electrode. When measured, one spectrum appears at a position of approximately 70 to 100 ppm of chemical shift and one spectrum at a position of 0 to 20 ppm on the basis of lithium chloride (0 ppm). These two spectra show the state of lithium ions intercalated separately into amorphous carbon and crystalline carbon.

  When a battery is composed of a negative electrode comprising the secondary particles of the present invention and metallic lithium, and lithium ions are intercalated into the negative electrode, a spectrum appears near 0 ppm when the amount of charge is small. As the amount of charge increases, the spectral position shifts. Further, in a fully charged state (a state where intercalation by Li ions is saturated), a spectrum appears at 10 to 20 ppm. Even in this case, the Li spectra intercalated in the primary particle carbon and the coated carbon are not separated.

  The method for preparing the negative electrode of the lithium ion secondary battery using the negative electrode material having the secondary particle structure of the present invention is not particularly limited. For example, a solvent in which a binder (for example, PVDF) is dissolved in this negative electrode material (for example, 1- (Methyl-2-pyrrolidone) is added and sufficiently kneaded to prepare a high-concentration slurry having a solid concentration of 40% by mass or more.

  The negative electrode material slurry is coated on a current collector of metal foil (for example, copper foil) to a thickness of 20 to 100 μm using a doctor blade or the like. The carbon fine particle slurry on the metal foil is in close contact with the metal foil current collector by drying. If necessary, pressurize to increase the adhesion to the metal foil current collector and increase the electrode density.

  Known materials such as various pitches, rubbers, and synthetic resins are used for the binder, and among them, polyvinylidene fluoride (PVDF) and carboxymethyl cellulose (CMC) are most suitable. Moreover, methylcellulose, polyvinyl alcohol, polyethylene oxide, starch, casein, etc. can also be used. The mixing ratio (mass ratio) between the carbon fine particles and the binder is preferably 100: 2 to 100: 20.

The positive electrode material is not particularly limited, but LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ or the like, or a mixture or metal substitution thereof is preferable. LiFePO ₄ or the like can also be used. If necessary, the powdered positive electrode material can be prepared by adding a conductive material, sufficiently kneading with a solvent in which a binder is dissolved, and then molding with a current collector. These are known techniques. The separator is not particularly limited, and a known material such as polypropylene or polyethylene can be used.

  As the non-aqueous solvent for the electrolyte of the lithium ion secondary battery, a known aprotic low dielectric constant solvent capable of dissolving a lithium salt is used. For example, ethylene carbonate, dimethyl carbonate, propylene carbonate, diethylene carbonate, acetonitrile, propionitrile, tetrahydrofuran, γ-butyrolactone, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2 -Solvents such as dimethoxyethane, 1,2-diethoxyethane, diethyl ether, sulfolane, methyl sulfolane, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide and the like may be used alone or in combination of two or more.

Lithium salts used as the electrolyte include LiClO ₄ , LiAsF ₅ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ), LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, etc., and these salts May be used alone or in admixture of two or more salts.

  Moreover, it can also be set as a lithium polymer secondary battery using the gel electrolyte which gelatinized the said electrolyte solution and electrolyte, polymer electrolytes, such as polyethylene oxide and a polyacrylonitrile. Furthermore, it can also be set as a lithium all-solid-state secondary battery using a solid electrolyte.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. Moreover, each physical property value of the negative electrode material in these Examples and Comparative Examples was measured by the following methods.

  Average particle size: Measured using a laser diffraction particle size distribution analyzer (SALD-200V) manufactured by Shimadzu Corporation and using water as a dispersant.

  Crystal lattice constant Co (002): Using a Philips X-ray diffractometer (Xpert-MPD PW3040), Cu-Kα rays were monochromated with Ni and a monochromator, and measured by the Gakushin method using high-purity silicon as a standard substance .

⁷ Li solid NMR: Measurement was performed using a solid nuclear magnetic resonance apparatus (DSX300wb) manufactured by Bruker, with a multi-nuclide broad probe head and an aqueous lithium chloride solution as a standard.

  Specific surface area: Using a high precision automatic gas adsorption device (BELSORB28) manufactured by Nippon Bell Co., Ltd., the nitrogen adsorption amount was measured by the multipoint method at the liquid nitrogen temperature, and the specific surface area was calculated by the BET method.

Electrical characteristics: A water slurry having a sample concentration of 53.3% by weight, CMC of 1% by weight as a binder and SBR latex of 2% by weight was prepared and coated on a copper foil using an applicator. After drying, uniaxial pressing was performed at 1 tonf / cm ² (98 MPa), a 2 cm ² electrode was punched out, and a 2032 coin battery was assembled in an argon atmosphere using metallic lithium as a counter electrode. Using this coin battery as a charge / discharge evaluation apparatus, battery characteristics were evaluated.

Examples 1-7
After pulverizing a delayed coke made by Nippon Oil Co., Ltd. with a rod mill, it was calcined at 950 ° C. for 30 minutes to prepare crystalline carbon having an average primary particle size of 0.8-20.5 μm shown in Table 1. This was subjected to chemical vapor deposition using toluene as a CVD chemical species in a fluidized bed reactor to obtain carbon secondary particles having a coating amount of 15% by mass.

  During this chemical vapor deposition process, fluidization was intermittently performed to promote secondary particle formation. This intermittent operation of fluidization was carried out by repeating the fluidization operation for 5 minutes and the stationary operation for 1 minute 10 times. The secondary carbon particles were classified into fine particles and coarse particles using a classifier [manufactured by Nippon Pneumatics Co., Ltd .: trade name MDS separator]. The average particle size of the coarse particles is 1.1 times, 1.1 times, 1.2 times, 1.2 times, 1.2 times, 1.2 times, 1.2 times before classification for Examples 1 to 7, respectively. Both 1.3 times and 1.1 times or more.

Coin batteries were prepared by the above method using the coarse carbon secondary particles as samples, and the charge / discharge rate characteristics were measured by changing the charge / discharge flow rate from 0.2C to 20C. Further, ⁷ Li solid NMR of the sample was measured in a fully charged coin battery. Table 1 shows the results of these physical property measurements.

Comparative Example 1
Various physical properties of the sample were measured in the same manner as in Example 1 except that the fine particles classified in Example 1 were used as samples for measuring various physical properties. The results are shown in Table 1. Although this carbon particle sample is made into secondary particles, the secondary particle average particle diameter is 2.1 μm and less than 2.5 μm, and the initial charge / discharge efficiency is low.

Comparative Example 2
Various physical properties of the sample were measured in the same manner as in Example 1 except that the primary particles of Example 1 were used as the primary particles, the primary particles were not subjected to chemical vapor deposition, and the primary particles were used as they were as samples. . The results are shown in Table 1. This carbon particle sample is not made into secondary particles, the average particle diameter is 0.5 μm and less than 2.5 μm, and the initial charge / discharge efficiency is low.

Comparative Example 3
Various physical properties of the sample were the same as in Example 1 except that primary particles having an average particle diameter of 25.4 μm were used as primary particles, the primary particles were not subjected to chemical vapor deposition, and the primary particles were used as they were as samples. Was measured. The results are shown in Table 1. This carbon particle sample is not made into secondary particles, and the average primary particle diameter exceeds 25.4 μm and 20 μm, the charge capacity is low, and the initial charge / discharge efficiency is also low.

Comparative Example 4
As primary particles, primary particles having an average particle diameter of 25.4 μm were used, and the primary particles were subjected to chemical vapor deposition in the same manner as in Example 1. A classifier [manufactured by Nippon Pneumatics Co., Ltd .: trade name MDS separator] Was used to classify into fine and coarse particles. Various physical properties of the sample were measured in the same manner as in Example 1 except that the classified fine particles were used as samples for measuring various physical properties. The results are shown in Table 1. This carbon particle sample is made into secondary particles and the initial charge / discharge efficiency is increased, but the charge capacity is low.

実施例８
新日本石油(株)製ディレードコークスをロッドミルで粉砕後、マツボー製エルボージェット分級機で分級して平均粒径３．３μｍのコークス粒子(炭素一次粒子)を調製した。該コークス粒子９５質量部と三井鉱山(株)製コールタール５質量部(炭素分)とを三井鉱山(株)製ヘンシェルミキサーを用いて混合し、コークス粒子上にコールタールを塗布した。

Example 8
New Japan Oil Co., Ltd. delayed coke was pulverized with a rod mill and then classified with a Matsubo elbow jet classifier to prepare coke particles (carbon primary particles) having an average particle size of 3.3 μm. 95 parts by mass of the coke particles and 5 parts by mass (carbon content) of coal tar manufactured by Mitsui Mining Co., Ltd. were mixed using a Henschel mixer manufactured by Mitsui Mining Co., Ltd., and coal tar was applied onto the coke particles.

  This mixture was inserted into a vertical reactor having a height of 50 cm and a diameter of 25 cm, heated to 1100 ° C. while flowing nitrogen gas, and held for 1 hour to obtain carbon secondary particles having an average particle size of 5.5 μm. The carbon secondary particles were again classified into fine and coarse fractions using a Matsubo elbow jet classifier. The average particle size of the coarse particles was 6.2 μm, which was 1.1 times that before classification. The coarse particles formed secondary particles in which primary particles were aggregated, and the primary particle size was 3.2 μm.

  Using the coarse carbon secondary particles as a sample, various physical properties of the sample were measured in the same manner as in Example 1. The results are shown in Table 2.

  The carbon particle sample had a primary particle size, a secondary particle size, and the like within the constitutional range of the present invention, and various physical properties such as a charge capacity and charge / discharge initial efficiency of the sample were good.

It is a schematic sectional drawing which shows an example of the negative electrode material of this invention obtained by making secondary particles into the primary particle by CVD method. It is a schematic sectional drawing which shows an example of the negative electrode material of this invention obtained by making secondary particles into primary particles by kneading granulation using binders, such as coal tar.

Explanation of symbols

2 Primary particles 4 Vapor deposited carbon 6 Voids 22 Primary particles 24 Bonded carbon 26 Voids

Claims (8)

The average particle diameter is composed of crystalline carbon particles having an average particle diameter of 0.1 to 20 μm and a 002 lattice constant of 0.68 to 0.70 nm according to the XRD method, and bonded carbon bonding between the crystalline carbon particles. A negative electrode material for lithium ion secondary batteries of 2.5 to 40 μm. 2. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the ratio of bonded carbon to the whole negative electrode material is 0.2 to 30 mass%. 2. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the ⁷ Li-NMR spectrum of the fully charged negative electrode material has one signal at 10 to 20 ppm based on the LiCl aqueous solution. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the carbon of the crystalline carbon particles is optically anisotropic. A method for producing a negative electrode material for a lithium ion secondary battery, in which the surface of crystalline carbon particles having an average particle diameter of 0.1 to 20 μm and a 002 lattice constant of 0.68 to 0.70 nm by XRD is subjected to chemical vapor deposition. A negative electrode for a lithium ion secondary battery having an average particle size of 2.5 to 40 μm , wherein the crystalline carbon particles are fluidized intermittently during chemical vapor deposition to bond the particles with bonded carbon. A method of manufacturing the material. 6. The lithium ion secondary according to claim 5 , wherein the intermittent operation of fluidizing the crystalline carbon particles is an operation of repeating the fluidization operation for 1 to 10 minutes and the stationary operation for 1 to 5 minutes three times or more. A method for producing a negative electrode material for a battery. 6. The lithium ion secondary battery according to claim 5 , wherein the negative electrode material produced by the production method according to claim 5 is classified to remove fine particles, and the average particle size is 1.1 times or more of that before classification. Manufacturing method for negative electrode material. A lithium ion secondary battery formed using the negative electrode material according to claim 1.

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