JP2008277232A - Negative electrode material for lithium secondary battery, its manufacturing method, negative electrode for lithium secondary battery using the negative electrode material, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode material for a lithium secondary battery having a larger initial charge discharge capacity and more excellent charge discharge cycle characteristics compared with a conventional lithium secondary battery; to provide a negative electrode for the lithium secondary battery using the material, and the lithium secondary battery. <P>SOLUTION: The negative electrode material for the lithium ion secondary battery is formed by arranging carbonaceous material particles which are substances of at least one kind selected from graphite and carbon black on surfaces of composite particles including graphite particles, Si fine particles, and amorphous carbon (A), and covering the carbonaceous material particles with amorphous carbon (B). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a negative electrode material for a lithium secondary battery, a negative electrode for a lithium secondary battery using the material, and a lithium secondary battery using the negative electrode.

  Lithium secondary batteries that can be charged with high energy density and discharged with high energy density as power source batteries for electronic devices and as backup batteries for electronic devices as electronic devices become smaller, thinner, and lighter Has attracted attention. In addition, since lithium secondary batteries use lithium that has little impact on the environment and high safety, they are being developed as power sources for electric vehicles and further as distributed power storage batteries.

A conventional typical lithium secondary battery uses a carbon material as a negative electrode active material, lithium is inserted into the carbon material in an ionic state (intercalation) when the battery is charged, and lithium is released as an ion during discharge. "Rocking chair type" that intercalates) is adopted. However, in this battery configuration, it is difficult to increase the amount of lithium ions inserted into the carbon material, and the charge / discharge capacity as a secondary battery cannot be increased. For example, when graphite is used, the composition by charging is LiC ₆ and the theoretical charge / discharge capacity is 372 Ah / kg. This is as low as 1/10 or less of the lithium metal theoretical charge / discharge capacity of 3860 Ah / kg (lithium base).

  On the other hand, a negative electrode material for a lithium secondary battery having a further improved charge / discharge capacity is required from the electronic device side to which the battery is mounted. Examples of conventional high-capacity negative electrode materials include elements capable of forming an intermetallic compound with lithium, such as aluminum and lead. However, when used as a negative electrode material alone or mixed with conductive particles, cycle deterioration is rapid and substantial. Cannot be applied as a negative electrode material.

  There are various proposals for using a negative electrode material composed of particles containing an element capable of forming a compound with lithium and a carbonaceous material for a lithium secondary battery (see, for example, Patent Documents 1 to 3), but Sn having a low melting point (melting point 232). ), Pb (melting point 327 ° C.), Zn (melting point 419 ° C.), Al (melting point 660 ° C.) and the like can be used as an element capable of forming a compound with lithium. When carbonized at 800 ° C. or higher, Aggregation and coarsening may occur due to melting, and the performance of the product may be unexpectedly reduced.

  Further, Sn (22.0 ppm / K, at 25 ° C.), Al (23.1 ppm / K, at 25 ° C.), Mg (24.8 ppm / K, at 25 ° C.), Pb (28.9 ppm / K) having a high thermal expansion coefficient. , At 25 ° C.) and the like can be used, so that the adhesion with carbon cannot be maintained in the process of carbonization heat treatment and cooling, and the particle shape may not be maintained, resulting in a decrease in product performance.

In addition, development of many intermetallic compounds based on Si has been energetically advanced (see, for example, Patent Documents 4 to 7). However, although these compounds have a large charge / discharge capacity, there are problems that the initial irreversible capacity is large and the charge / discharge cycle characteristics are poor, and they have not yet been put into practical use.
Japanese Patent Laid-Open No. 05-286863 Japanese Patent Laid-Open No. 06-279112 JP-A-10-003920 JP 2004-045986 A JP 2001-243946 A JP 2001-297757 A JP 2004-277371 A

  The present invention provides a negative electrode material for a lithium secondary battery, a method for producing the same, a negative electrode for a lithium secondary battery using the same, and a lithium secondary battery that can solve the problems of the conventional Si-based negative electrode materials described above. With the goal.

  The present invention is characterized by the following items (1) to (12).

  (1) Carbonaceous material particles containing at least one or more selected from graphite or carbon black are disposed on the surface of composite particles containing graphite particles, Si fine particles, and amorphous carbon (A), and the carbonaceous material A negative electrode material for a lithium secondary battery, wherein the particles are coated with amorphous carbon (B).

  (2) The negative electrode material for a lithium secondary battery as described in (1) above, wherein the carbonaceous material particles have an average particle diameter (D50) of 0.01 to 5 μm.

  (3) The average particle diameter (D50) of the graphite particles is 0.5 to 5 μm, and the average particle diameter (D50) of the Si fine particles is 0.05 to 1 μm, as described in (1) or (2) above. Negative electrode material for lithium secondary battery.

(4) The negative electrode material for a lithium secondary battery according to any one of (1) to (3), wherein the BET specific surface area is ² to 20 m ² / g.

  (5) The negative electrode material for a lithium secondary battery according to any one of (1) to (4), wherein the average particle size (D50) is 5 to 40 μm.

  (6) (I) a step of mixing Si fine particles, graphite particles, and a precursor that becomes amorphous carbon (A) by heat treatment; (II) heat-treating the mixture obtained in the step (I); A step of producing a composite material containing the Si fine particles, the graphite particles, and the amorphous carbon (A), and (III) a carbonaceous material containing at least one selected from the composite material, graphite, and carbon black. For lithium secondary battery, comprising: a step of mixing material particles and a precursor that becomes amorphous carbon (B) by heat treatment; and (IV) a step of heat-treating the mixture obtained in the step (III). Manufacturing method of negative electrode material.

  (7) The manufacturing method of the negative electrode material for lithium secondary batteries as described in said (6) whose temperature of the heat processing in the said process (II) is the range of 700-1500 degreeC.

(8) the temperature of the heat treatment in the step (IV) The production method of the negative electrode material for a lithium secondary battery according to SL above the range of 700-2000 ° C. (6) or (7).

  (9) The negative electrode material for a lithium secondary battery according to any one of (6) to (8), wherein an average particle diameter (D50) of the carbonaceous material particles is 0.01 to 5 μm. Production method.

  (10) Any of (6) to (9) above, wherein the graphite particles have an average particle diameter (D50) of 0.5 to 5 μm and the Si fine particles have an average particle diameter (D50) of 0.05 to 1 μm. A method for producing a negative electrode material for a lithium secondary battery according to claim 1.

  (11) By the method for producing a negative electrode material for a lithium secondary battery according to any one of (1) to (5) or a negative electrode material for a lithium secondary battery according to any one of (6) to (10) above A negative electrode for a lithium secondary battery obtained by integrating a mixture containing the obtained negative electrode material for a lithium secondary battery and a binder and a current collector.

  (12) A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to (11) above.

  According to the present invention, a negative electrode material for a lithium secondary battery capable of producing a lithium secondary battery having a large initial charge / discharge capacity and excellent charge / discharge cycle characteristics as compared with a conventional lithium secondary battery. Can be obtained.

  The best mode for carrying out the invention will be described below.

(Anode material for lithium secondary battery)
The negative electrode material for a lithium secondary battery of the present invention is used as an active material for a negative electrode of a lithium secondary battery, and has a carbonaceous material on the surface of composite particles containing graphite particles, Si fine particles, and amorphous carbon (A). The material particles are dispersed and arranged, and the carbonaceous material particles are covered with amorphous carbon (B). Thus, by disperse | distributing and arrange | positioning carbonaceous substance particle | grains on the surface of a composite particle, the surface structure of negative electrode active material (negative electrode material) particle | grains is form-controlled, and the surface can be uneven | corrugated.

  Further, since the Si fine particles and the negative electrode active material containing Si fine particles are accompanied by a volume change at the time of occlusion / release of lithium, the electrode expands, and the electrochemical contact of some of the active material particles is lost. This causes a decrease in “charge / discharge cycle characteristics” which is an important characteristic of the secondary battery. Since there are many irregularities on the surface of the active material particles, the number of contact points between the active material particles increases, and the utilization rate of the active material particles when the electrodes expand is improved, thereby extending the life of the battery. . In addition, since there are many irregularities on the surface of the active material particles, the electrode contains a lot of voids when used as a negative electrode for a lithium secondary battery, and the above volume change can be alleviated. Charge / discharge cycle characteristics can be improved. In addition, the negative electrode material for a lithium secondary battery of the present invention can reduce the current density per surface area of the negative electrode active material, and allows the electrochemical reaction on the negative electrode surface to proceed slowly and uniformly. Become.

  The carbonaceous material particles used in the present invention preferably contain one or more selected from carbonaceous materials having high electron conductivity such as graphite and carbon black. Furthermore, in addition to graphite and carbon black, carbon nanotubes and carbon fibers may be included. As the graphite, artificial graphite and natural graphite can be used including graphitized mesophase spherules, and they may be used alone or in combination of two or more. The crystal structure of the graphite is not particularly limited. For example, the interplanar spacing d (002) is preferably 0.3354 to 0.34 nm, and more preferably 0.3354 to 0.337 nm. . Moreover, the form of the graphite is not particularly limited, and examples thereof include an indefinite shape, a flat plate shape (or flat shape), a flake shape, and a powder particle shape. Examples of the carbon black include acetylene black, ketjen black, thermal black, and furnace black.

  Moreover, it is preferable that the average particle diameter (D50) of the said carbonaceous substance particle is 0.01-5 micrometers. When it is larger than 5 μm, it is difficult to uniformly disperse the negative electrode material. For example, the weight ratio between the Si fine particles and the carbonaceous material particles is preferably 10/90 to 90/10, and more preferably 30/70 to 80/20.

  As the graphite particles contained in the composite particles, artificial graphite and natural graphite similar to the graphite that can be disposed on the surface of the composite particles as the carbonaceous material particles can be used, either alone or in combination of two or more. Can also be used. Moreover, it is preferable that the average particle diameter (D) 50 of the said graphite particle is 0.5-5 micrometers.

  The Si fine particles are preferably fine particles having a small particle diameter, and the average particle diameter (D50) is more preferably 0.05 to 1 μm. By using small-sized Si fine particles, it is difficult for the active material particles to fall off the negative electrode, and the life of the negative electrode can be extended. Specifically, by using fine Si fine particles having a small particle diameter for the negative electrode from the beginning, further fine pulverization of the Si fine particles during charge / discharge is suppressed, and charge / discharge cycle characteristics are improved. The method for preparing the Si fine particles used in the present invention is not particularly limited, but from the viewpoint of production cost, it is preferable to pulverize and prepare large Si particles that are available at a relatively low cost. As the pulverization method, for example, a dry pulverization method and a wet pulverization method can be employed. In addition, when producing fine Si particles by pulverization, if impurities due to the pulverizer are mixed into the Si fine particles, the negative electrode material characteristics such as cycle and charge / discharge efficiency deteriorate, and therefore, such as pulverization containers, beads, balls, etc. As the material, it is necessary to select a material having little influence on the charge / discharge reaction, for example, alumina, partially stabilized zirconia and the like.

  The amorphous carbon (A) contained in the composite particles and the amorphous carbon (B) covering the carbonaceous material particles arranged on the surface of the composite particles may be the same or different. , For example, pitch-based materials such as coal-based pitch materials, petroleum-based pitch materials, synthetic pitch materials, tar-based materials, thermoplastic resins, thermosetting resins, vinyl-based resins, cellulose-based resins, phenol-based resins, etc. It can be obtained by heat-treating and carbonizing an amorphous carbon precursor such as a material at 700 to 2000 ° C. In particular, pitch-based materials and tar-based materials are dissolved in a solvent (toluene, xylene, mesitylene, methylnaphthalene, creosote oil, etc.) used when producing Si fine particles by a wet pulverization method. Uniform mixing with each component constituting the material is possible, which is preferable. Amorphous carbon is a carbonaceous material having lower crystallinity than the above-mentioned carbonaceous material having relatively high electron conductivity.

  The method for producing the negative electrode material of the present invention is not particularly limited. For example, (I) a step of mixing Si fine particles, graphite particles, and a precursor that becomes amorphous carbon (A) by heat treatment, (II) a step of heat-treating the mixture obtained in the step (I) to produce a composite material containing Si fine particles, graphite particles, and amorphous carbon (A), (III) the composite material, and a carbonaceous material And (IV) a step of heat-treating the mixture obtained by the step (III).

  More specifically, in step (I) above, the precursor of amorphous carbon (A) is dissolved in an appropriate solvent, and Si fine particles and graphite particles are added to this and mechanically mixed, and then the solvent is removed. Next, the amorphous carbon (A) precursor is carbonized by heat treatment as in the above step (II), and a composite material containing Si fine particles, graphite particles, and amorphous carbon (A) is obtained. Can be obtained. Thus, by producing composite particles from the precursor of amorphous carbon (A), the surface of the Si fine particles can be covered with the precursor of amorphous carbon (A), and the surface of the Si fine particles can be oxidized. In addition to the advantage that it can be suppressed, the precursor of amorphous carbon (A) can function as a binder that binds and combines Si fine particles and graphite particles.

  Moreover, the temperature at the time of heat-processing the mixture produced in the said process (II) should just be the temperature which can carbonize the precursor of amorphous carbon (A), Although it does not specifically limit, It is 700-1500 degreeC. It is preferably 800 to 1400 ° C, particularly preferably 900 to 1300 ° C. When the heat treatment temperature is less than 700 ° C., the carbonization of the precursor that generates amorphous carbon (A) becomes insufficient, and the charge / discharge efficiency and cycle characteristics of the obtained negative electrode material tend to deteriorate. On the other hand, when the heat treatment temperature is higher than 1500 ° C., electrochemically inactive silicon carbide (SiC) is generated by the reaction between the Si fine particles and the graphite particles, and the charge / discharge capacity tends to be greatly reduced. Moreover, it is preferable that the atmosphere at the time of performing the heat treatment is a vacuum atmosphere or an inert gas atmosphere from the viewpoint of preventing oxidation of Si fine particles and suppressing an increase in irreversible capacity.

  In the composite particles, the weight ratio between the Si fine particles and the amorphous carbon (A) is usually 99/1 to 10/90, and preferably can be selected from the range of about 90/10 to 20/80. As the proportion of fine particles increases, the charge / discharge capacity increases.

  In the composite particles, the weight ratio of the graphite particles to the amorphous carbon (A) is preferably 90/10 to 30/70, more preferably 80/20 to 40/60, 70 More preferably, it is / 30-40 / 60. As the number of graphite particles increases, the electronic conductivity of the composite particles improves and the charge / discharge cycle characteristics tend to improve. However, if the amount of amorphous carbon (A) is too small, the function of the composite particles as a binder is insufficient, and it is difficult to make composite.

  In the step (III), for example, a precursor of amorphous carbon (B) is dissolved in a suitable solvent, and composite particles containing Si fine particles, graphite particles, and amorphous carbon (A) are dissolved therein. Then, after adding the carbonaceous material particles and mixing mechanically, the solvent is removed, and further, the carbonaceous material particles are dispersed and arranged on the surface of the composite particles by performing a heat treatment as in step (IV), In addition, the negative electrode material of the present invention can be obtained in which the carbonaceous material particles are covered with amorphous carbon (B) and have irregularities on the surface.

  Moreover, the temperature at the time of heat-processing the mixture produced in the said process (III) should just be the temperature which can carbonize the precursor of amorphous carbon (B), Although it does not specifically limit, It is 700-2000 degreeC. It is preferably 900 to 1500 ° C, more preferably 1000 to 1300 ° C. When the heat treatment temperature is less than 700 ° C., the precursor for producing amorphous carbon (B) is insufficiently carbonized, and the resulting negative electrode material tends to deteriorate in charge / discharge efficiency and cycle characteristics. On the other hand, when the heat treatment temperature is higher than 2000 ° C., the charge / discharge capacity tends to decrease. Further, it is preferable to perform the heat treatment in a vacuum atmosphere or an inert gas atmosphere from the viewpoint of preventing the oxidation of the Si fine particles and the carbonaceous material particles and suppressing an increase in irreversible capacity.

  In the negative electrode material of the present invention, the weight ratio of Si fine particles to amorphous carbon (B) is preferably 10/90 to 90/10. The weight ratio between the Si fine particles and the carbonaceous material particles is preferably 1/99 to 90/10. If the amount of carbonaceous material particles is too small, unevenness on the surface of the negative electrode material is reduced, which is not preferable.

The negative electrode material of the present invention preferably has a BET specific surface area of ^{2 to 20} m ² / g. When the BET specific surface area exceeds 20 m ² / g, decomposition of the electrolytic solution increases during the first charge, which is not preferable. Moreover, it is preferable that the average particle diameter (D50) of the negative electrode material of this invention is 5-40 micrometers. When the average particle diameter is less than 5 μm or exceeds 40 μm, the handleability is deteriorated in the electrode production process, which is not preferable.

(Anode for lithium secondary battery)
The negative electrode for a lithium secondary battery according to the present invention includes, for example, a negative electrode material for a lithium secondary battery according to the present invention, a binder, and various additives added as necessary together with a solvent, a stirrer, a ball mill, a super sand mill, etc. Kneaded by a pressure kneader or the like to prepare a paste-like negative electrode material slurry, which is, for example, a metal mask printing method, electrostatic coating method, dip coating method, spray coating method, roll coating method, doctor blade method, gravure It can be formed by applying and drying on a current collector by a known method such as a coating method or a screen printing method, and if necessary, compression molding by a molding method such as a roll press. Alternatively, the paste-like negative electrode material slurry can be formed into a sheet shape, a pellet shape, or the like, and then integrated with the current collector by a forming method such as a roll press.

  Examples of the binder include thermoplastic resins such as polypropylene and polyethylene, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, hydroxyethyl (meth) acrylate, butyl ( Including ethylenically unsaturated carboxylic acid esters such as (meth) acrylate, ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid and maleic acid, polytetrafluoroethylene, polyvinylidene fluoride and fluororubber Fluorine resin, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile and the like can be used. In addition, an aqueous dispersion of a cellulose-based or styrene-butadiene rubber that is an aqueous binder can also be used.

  The amount of the binder used depends on the particle size of the negative electrode material of the present invention, but the amount used is preferably larger from the viewpoint of adhesive strength. Specifically, the amount of the binder is 100 parts by weight of the negative electrode material of the present invention. The amount is preferably 3 to 25 parts by weight, and more preferably 5 to 20 parts by weight.

  As the solvent, a solvent capable of dissolving or dispersing the binder is usually used, and examples thereof include organic solvents such as N-methyl-2-pyrrolidone and N, N-dimethylformamide. Moreover, the usage-amount of the said solvent is not restrict | limited especially as long as it becomes paste form, For example, normally about 60-150 weight part with respect to 100 weight part of negative electrode materials of this invention, Preferably it is about 60-100 weight part. It is.

  Moreover, in order to improve the electroconductivity as an electrode, you may mix a conductive support agent as said additive. Examples of the conductive auxiliary agent include natural graphite, artificial graphite, carbon black (for example, acetylene black, thermal black, furnace black), graphite, conductive oxide, nitride, and the like. Two or more types can be used in combination. About 1 to 10 weight% is preferable with respect to the total amount of the negative electrode material of this invention, and a conductive support agent, and, as for the usage-amount of a conductive support agent, about 1 to 5 weight% is more preferable.

  Furthermore, you may mix the thickener for adjusting a slurry viscosity as said additive. Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, and casein.

  The material of the current collector is not particularly limited, and known materials such as aluminum, copper, nickel, titanium, stainless steel, and the like can be used. A porous material such as porous metal (foamed metal) or carbon paper can also be used.

The coating amount of the current collector of the negative electrode material paste is not particularly limited, preferably about 5 to 15 mg / cm ^2, about 7~13mg / cm ² is more preferable.

(Lithium secondary battery)
The lithium secondary battery of the present invention is obtained, for example, by placing the negative electrode for a lithium secondary battery of the present invention and the positive electrode capable of occluding / releasing lithium through a separator and injecting an electrolyte. Can do. In addition, a gasket, a sealing plate, a case, and the like that are usually used in the field may be further provided.

  The positive electrode can be obtained by forming a positive electrode material layer containing a positive electrode active material, a conductive agent and the like on the current collector surface in the same manner as the negative electrode. As the current collector in this case, a metal or alloy such as aluminum, titanium, stainless steel or the like made into a foil shape, a perforated foil shape, a mesh shape, or the like can be used.

As the positive electrode active material is not particularly limited, for _{example, LiNiO 2, LiCoO 2, LiMn} 2 O 4, LiMnO 2, LiCo 0.33 Ni 0.33 Mn 0.33 O 2 and lithium composite oxides and Cr ₃ O ₈ , Cr ₂ O ₅ , V ₂ O ₅ , V ₆ O ₁₃ , VO ₂ , MnO ₂ , TiO ₂ , MoV ₂ O ₈ , TiS ₂ , V ₂ S ₅ , VS ₂ , MoS ₂ , MoS ₃ , Conductive polymers such as polyaniline and polypyrrole, porous carbon and the like can be used alone or in combination.

  Examples of the conductive agent include natural graphite, artificial graphite, carbon black, and acetylene black.

Examples of the electrolytic solution include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiClF ₄ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ). ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCl, LiI, LiSO ₃ CF _{3 and} other lithium salts (electrolytes) that produce anions that are difficult to solvate, such as carbonates, lactones, chain ethers, cyclic So-called organic electrolytes dissolved in non-aqueous solvents such as ethers, sulfolanes, sulfoxides, nitriles, amides, polyoxyalkylene glycols can be used. In this case, a non-aqueous lithium secondary battery is used. Can be manufactured. The electrolyte concentration is preferably 0.3 to 5 mol of electrolyte, more preferably 0.5 to 3 mol, and more preferably 0.8 to 1.5 mol with respect to 1 L of the electrolyte solution. Particularly preferred.

  Specific examples of the solvent used in the electrolytic solution include ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, vinylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, dimethyl sulfoxide, 3 -Methyl-1,3-oxazolidine-2-one, γ-butyrolactone, diethyl carbonate, dimethoxyethane, dimethyl carbonate, methylpropyl carbonate, methylethyl carbonate, butylethyl carbonate, diprovir carbonate, 1,2-dimethoxyethane, dimethyl ether , Diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 4-methyldioxolane, 1,3-dioxolane, acetonitrile, pro Onitrile, benzonitrile, N, N-dimethylformamide, N, N-dimethylacetamide, diethylene glycol, methyl acetate, ethyl acetate and the like can be used, and these solvents may be used alone or in combination of two or more. Good.

  As said separator, the nonwoven fabric, cloth, porous film which combined polyolefin, such as polyethylene and a polypropylene, a porous film, or those combined can be used, for example. In addition, when it is set as the structure where the positive electrode and negative electrode of a lithium secondary battery to produce do not contact directly during use, it is not necessary to use a separator.

  The structure of the lithium secondary battery of the present invention is not particularly limited. Usually, a positive electrode and a negative electrode, and a separator provided as necessary, are wound into a flat spiral shape to form a wound electrode plate group. Are generally laminated to form a laminated electrode plate group, and the electrode plate group is enclosed in an exterior body. Moreover, the lithium secondary battery of the present invention can be in any form such as a paper type, a button type, a coin type, a stacked type, a square type, and a cylindrical type.

  Since the lithium secondary battery of the present invention has a large charge / discharge capacity and excellent charge / discharge cycle characteristics, it is suitable as a power source and auxiliary power source for electronic devices, electrical devices, automobiles, power storage, etc. It is.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these Examples.

Example 1
<Production of negative electrode material and negative electrode>
(Production of raw coke)
The coal-based coal tar was heat-treated at 10 kg · G and 500 ° C. for 10 hours using an autoclave to produce raw coke.

(Preparation of graphite particles)
The raw coke was pulverized with a free crusher (“SJM-3” manufactured by Nara Machinery Co., Ltd.) and then baked at 900 ° C. for 1 hour in a nitrogen atmosphere. Then, it grind | pulverized using the jet mill (Nisshin Engineering Co., Ltd. "CJ-10"), and then it baked at 3000 degreeC in nitrogen atmosphere, and obtained the graphite particle whose average particle diameter (D50) is 1.4 micrometers. .

(Preparation of Si fine particles)
3 kg of Si material (Toyo Kinzoku Co., Ltd., high-purity metal silicon powder) having an average particle size of 20 μm, 1.5 kg of ethylene oxide-added aliphatic amine (“Homogenol L1820” manufactured by Kao Corporation) as a Si dispersing agent, and methylnaphthalene Methylnaphthalene containing 12 kg of zirconia beads having a diameter of 0.3 mm and bead mill substituted with nitrogen gas, wet milled for 3 hours, and containing 20 wt% Si fine particles having an average particle diameter (D50) of 0.2 μm Was made. The average particle size of the Si fine particles was measured by irradiating methyl naphthalene containing Si fine particles with ultrasonic waves for 1 minute to disperse the Si fine particles, and then using a particle size analyzer Microtrac (“HRA” manufactured by Nikkiso Co., Ltd.). Used.

(Preparation of negative electrode material)
2 kg of graphite particles having an average particle diameter of 1.4 μm prepared above, 1.4 kg of coal tar pitch (“pellet” manufactured by Osaka Kasei Co., Ltd.) (precursor to be amorphous carbon (A)) and the above were prepared. After mixing 2.4 kg of methylnaphthalene containing 20% by weight of Si fine particles at 100 ° C. for 1 hour using a biaxial heating kneader, methyl naphthalene was evaporated at 200 ° C. Subsequently, it baked at 900 degreeC in nitrogen atmosphere for 1 hour, and produced the composite particle which consists of Si microparticles, graphite, and amorphous carbon (amorphous carbon (A)). Next, 200 g of this composite particle was pulverized for 5 minutes with an alumina vibration mill, and then 60 g of coal tar pitch (“PKQL” manufactured by Kawasaki Steel Corporation, precursor of amorphous carbon (B)) was dissolved. 10 g of acetylene black particles (“DENKA BLACK” manufactured by Denki Kagaku Kogyo Co., Ltd., average particle diameter of 2.1 μm, carbonaceous material particles) were added, and then the tetrahydrofuran was evaporated by an evaporator. Composite particles surface-coated with black particles and pitch were obtained. Subsequently, the surface-coated composite particles were fired at 1150 ° C. for 1 hour in a nitrogen atmosphere, and then pulverized with a pulverizer, and sieved with a 390 mesh sieve to obtain negative electrode material particles of 390 mesh or less. The average particle diameter (D50) of the negative electrode material was 5.6 μm. The particle size of the negative electrode material was measured using SALD-3000J (manufactured by Shimadzu Corporation) under the conditions of a refractive index of 2.00 to 0.20i and an average number of 64 times. Using an aqueous solution in which oxyethylene (20) sorbitan monolaurate ") was dissolved, the measurement was performed after ultrasonically dispersing for 30 seconds. The BET specific surface area was 10.2 m ² / g. The BET specific surface area was analyzed by BET method by measuring the N ₂ adsorption isotherm using AUTOSORB-1 (manufactured by Quantachrome). Further, as a pretreatment for measuring the specific surface area, evacuation was performed at 120 ° C. for 2 hours.

(Preparation of negative electrode)
As the negative electrode material, acetylene black (“HS-100” manufactured by Showa Denko Co., Ltd.) as a conductive agent is 5% by weight of the negative electrode material weight, polyvinylidene fluoride is also 10% by weight as a binder, and N-methylpyrrolidone as a solvent. Was added in an amount of 30% by weight, and kneaded to obtain a uniform slurry. The slurry was applied to an electrolytic copper foil having a thickness of 40 μm, dried, roll-rolled, consolidated, and then punched with a punch having a diameter of 9 mm to obtain a negative electrode. The negative electrode active material layer on the copper foil had a thickness of about 30 μm.

(Example 2)
A negative electrode material and a negative electrode were produced in the same manner as in Example 1 except that 20 g of acetylene black particles were used as the carbonaceous material particles. Table 1 shows the BET specific surface area and average particle diameter of the negative electrode material.

(Example 3)
A negative electrode material and a negative electrode were produced in the same manner as in Example 1 except that 40 g of acetylene black particles were used as the carbonaceous material particles. Table 1 shows the BET specific surface area and average particle diameter of the negative electrode material.

Example 4
A negative electrode material and a negative electrode were prepared in the same manner as in Example 1 except that 40 g of graphite particles having an average particle diameter of 1.4 μm prepared above were used as carbonaceous material particles instead of acetylene black particles. Table 1 shows the BET specific surface area and average particle diameter of the negative electrode material.

(Comparative Example 1)
2 kg of graphite having an average particle diameter of 1.4 μm prepared above, 1.4 kg of coal tar pitch (“pellet” manufactured by Osaka Kasei Co., Ltd.) and 2.4 kg of methylnaphthalene containing 20% by weight of the Si fine particles prepared above, After mixing at 100 ° C. for 1 hour using a biaxial heating kneader, methyl naphthalene was evaporated at 200 ° C. Subsequently, it baked at 900 degreeC in nitrogen atmosphere for 1 hour, and produced the composite particle which consists of Si microparticles, graphite, and amorphous carbon. Next, 200 g of the composite particles were pulverized for 5 minutes with an alumina vibration mill, and then dispersed in a tetrahydrofuran solution in which 60 g of coal tar pitch (“PKQL” manufactured by Kawasaki Steel Corporation) was dissolved, and then the tetrahydrofuran was evaporated. To obtain composite particles surface-coated with pitch. Subsequently, the surface-coated composite particles were fired at 1150 ° C. for 1 hour in a nitrogen atmosphere, and then pulverized with a pulverizer, and sieved with a 390 mesh sieve to obtain negative electrode material particles of 390 mesh or less. Thereafter, a negative electrode was produced in the same manner as in Example 1 using the negative electrode material particles. Table 1 shows the BET specific surface area and average particle diameter of the negative electrode material.

<Production and evaluation of lithium secondary battery>
(Production of lithium secondary battery)
The negative electrode obtained in each Example and each Comparative Example was used as a working electrode, and 1 mm thick metal lithium was used as a counter electrode, and both electrodes were opposed to each other via a separator (“Celguard # 2400” manufactured by Hosen Co., Ltd.). It was. Further, a nonaqueous electrolytic solution in which 1% by weight of vinylene carbonate was added to a mixed solution of 1.5 M LiPF ₆ / ethylene carbonate, diethyl carbonate and dimethyl carbonate (1: 1: 1 volume ratio) was injected, and a secondary lithium secondary solution was injected by a normal method. A battery was produced.

(Evaluation of lithium secondary battery)
About the lithium secondary battery produced above, 1 cycle discharge capacity and 32 cycle capacity maintenance factor were measured according to the following. The results are summarized in Table 1.

  Discharge capacity: The counter electrode (lithium electrode) was charged to 0.02 V with a current corresponding to 0.1 C. Discharge was performed up to 1.5 V with a current corresponding to 0.1 C with respect to the lithium electrode, and the initial (initial) discharge capacity was measured. The discharge capacity was the capacity when the cut voltage was 1.5V.

  Capacity maintenance rate: The above charge / discharge cycle was repeated 32 times, and the ratio of the discharge capacity at the 32nd cycle to the first cycle discharge capacity was calculated as the capacity maintenance rate (%). In the third and subsequent cycles, the charge / discharge current value was set to a value corresponding to 1.0C.

  From Table 1, it can be seen that by using the negative electrode material of the example, it is possible to obtain a lithium secondary battery having a large initial charge / discharge capacity and excellent charge / discharge cycle characteristics.

It is a cross-sectional schematic diagram which shows one form of the negative electrode material of this invention.

Explanation of symbols

1 Negative electrode material particle 2 Graphite particle 3 Si fine particle 4 Amorphous carbon (A)
5 Carbonaceous material particles 6 Amorphous carbon (B)
7 Composite particles

Claims (12)

  Carbonaceous material particles containing at least one or more selected from graphite or carbon black are disposed on the surface of the composite particles containing graphite particles, Si fine particles, and amorphous carbon (A), and the carbonaceous material particles are non-coated. A negative electrode material for a lithium secondary battery, which is coated with crystalline carbon (B).   2. The negative electrode material for a lithium secondary battery according to claim 1, wherein an average particle size (D50) of the carbonaceous material particles is 0.01 to 5 μm.   3. The lithium secondary battery according to claim 1, wherein an average particle diameter (D50) of the graphite particles is 0.5 to 5 μm, and an average particle diameter (D50) of the Si fine particles is 0.05 to 1 μm. Negative electrode material. The negative electrode material for a lithium secondary battery according to claim 1, wherein the BET specific surface area is ² to 20 m ² / g.   The negative electrode material for a lithium secondary battery according to any one of claims 1 to 4, wherein the average particle size (D50) is 5 to 40 µm. (I) a step of mixing Si fine particles, graphite particles, and a precursor that becomes amorphous carbon (A) by heat treatment;
(II) heat treating the mixture obtained in the step (I) to produce a composite material including the Si fine particles, the graphite particles, and the amorphous carbon (A);
(III) A step of mixing the composite material, carbonaceous material particles containing at least one selected from graphite and carbon black, and a precursor that becomes amorphous carbon (B) by heat treatment, and (IV) Heat-treating the mixture obtained by the step (III),
The manufacturing method of the negative electrode material for lithium secondary batteries which has this.   The method for producing a negative electrode material for a lithium secondary battery according to claim 6, wherein a temperature of the heat treatment in the step (II) is in a range of 700 to 1500 ° C.   The method for producing a negative electrode material for a lithium secondary battery according to claim 6 or 7, wherein a temperature of the heat treatment in the step (IV) is in a range of 700 to 2000 ° C.   The method for producing a negative electrode material for a lithium secondary battery according to any one of claims 6 to 8, wherein an average particle size (D50) of the carbonaceous material particles is 0.01 to 5 µm.   10. The lithium secondary battery according to claim 6, wherein the graphite particles have an average particle diameter (D50) of 0.5 to 5 μm and the Si fine particles have an average particle diameter (D50) of 0.05 to 1 μm. A method for producing a negative electrode material for a secondary battery.   The negative electrode material for lithium secondary batteries according to any one of claims 1 to 5, or the negative electrode material for lithium secondary batteries obtained by the method for producing a negative electrode material for lithium secondary batteries according to any one of claims 6 to 10. And a negative electrode for a lithium secondary battery obtained by integrating a mixture containing a binder and a current collector.   A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to claim 11.

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