JP2008112710A - Negative electrode material for lithium secondary battery, negative electrode for lithium secondary battery using this, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode material for a lithium secondary battery for realizing such lithium secondary battery as of large charge/discharge capacitance, small initial irreversible capacitance, and excellent charge/discharge characteristics, along with a negative electrode for the lithium secondary battery using the same and the lithium secondary battery. <P>SOLUTION: The negative electrode material for the lithium secondary battery contains Si particles whose average particle size (D50) is 0.05-5 μm and a plurality of kinds of carbonaceous material, with oxygen content being 5 wt.% or less. <P>COPYRIGHT: (C)2008,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 relates to a negative electrode material for a lithium secondary battery for obtaining a lithium secondary battery having a large charge / discharge capacity, a small initial irreversible capacity, and excellent charge / discharge cycle characteristics, and a negative electrode for a lithium secondary battery using the same. Is intended to provide.

  Another object of the present invention is to provide a lithium secondary battery having a large charge / discharge capacity, a small initial irreversible capacity, and excellent charge / discharge cycle characteristics.

  The present invention is characterized by the following items (1) to (17).

  (1) A negative electrode material for a lithium secondary battery comprising Si particles having an average particle diameter (D50) of 0.05 to 5 μm and a plurality of types of carbonaceous materials, and having an oxygen content of 5% by weight or less.

  (2) The lithium secondary battery according to (1), wherein the plural types of carbonaceous materials include a carbonaceous material (A) and a carbonaceous material (B) having lower crystallinity than the carbonaceous material (A). Negative electrode material.

  (3) The negative electrode material for a lithium secondary battery according to (2), wherein the carbonaceous material (A) includes at least one selected from graphite and carbon black.

  (4) The negative electrode material for a lithium secondary battery according to (3), wherein the graphite has an average particle diameter (D50) of 0.1 to 20 μm.

  (5) The negative electrode material for a lithium secondary battery according to any one of (2) to (4), wherein the carbonaceous material (B) is amorphous carbon.

  (6) The lithium secondary battery according to any one of (2) to (5), wherein a weight ratio of the Si particles to the carbonaceous material (A) is 99.5 / 0.5 to 0.5 / 99.5. Negative electrode material.

  (7) The negative electrode material for a lithium secondary battery according to the above (2) to (6), wherein the weight ratio of the carbonaceous material (A) to the carbonaceous material (B) is 90/10 to 30/70.

  (8) The negative electrode material for a lithium secondary battery according to any one of (1) to (7), wherein the surface is carbon-coated.

  (9) The negative electrode material for a lithium secondary battery according to (8), wherein the ratio of the carbon coating layer (coating carbon weight / negative electrode material weight before carbon coating) is 0.1 / 99.9 to 50/50. .

  (10) For a lithium secondary battery comprising a step of preparing Si particles having an average particle size (D50) of 0.05 to 5 μm by a wet pulverization method, and a step of mixing the Si particles and a plurality of types of carbonaceous materials. Manufacturing method of negative electrode material.

  (11) A step of preparing Si particles having an average particle size (D50) of 0.05 to 5 μm by a wet pulverization method, the Si particles, the carbonaceous material (A), and a crystal that is more crystalline than the carbonaceous material (A) by heating. The manufacturing method of the negative electrode material for lithium secondary batteries which has the process of mixing the precursor used as carbonaceous substance (B) with low property, and the process of heat-processing the mixture obtained by the said mixing.

  (12) The method for producing a negative electrode material for a lithium secondary battery according to the above (10) or (11), wherein the wet pulverization method is pulverization using a bead mill.

  (13) The method for producing a negative electrode material for a lithium secondary battery according to any one of (10) to (12), wherein the mixing is wet mixing.

  (14) The method for producing a negative electrode material for a lithium secondary battery according to any one of (11) to (13), wherein the temperature of the heat treatment is in a range of 700 to 2000 ° C.

  (15) The method for producing a negative electrode material for a lithium secondary battery according to any one of the above (10) to (14), further comprising a step of coating the surface with carbon.

  (16) The negative electrode material for a lithium secondary battery according to any one of (1) to (9) above or the negative electrode material for a lithium secondary battery obtained by the production method according to any one of (10) to (15) above A negative electrode for a lithium secondary battery, which is formed by integrating a mixture containing a binder and a current collector.

  (17) A lithium secondary battery comprising the lithium secondary battery negative electrode according to (16).

  According to the present invention, it is possible to provide a negative electrode material for a lithium secondary battery for obtaining a lithium secondary battery having a large charge / discharge capacity, a small initial irreversible capacity, and excellent charge / discharge cycle characteristics.

  Moreover, according to the present invention, it is possible to provide a negative electrode for a lithium secondary battery for obtaining a lithium secondary battery having a large charge / discharge capacity, a small initial irreversible capacity, and excellent charge / discharge cycle characteristics. .

  Furthermore, according to the present invention, it is possible to provide a lithium secondary battery having a large charge / discharge capacity, a small initial irreversible capacity, and excellent charge / discharge cycle characteristics.

  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 according to the present invention is used as an active material for a negative electrode of a lithium secondary battery, and includes Si particles and a plurality of types of carbonaceous materials. In addition, other metal elements may be included as necessary. Examples of such metal elements include one or more selected from the group consisting of Ni, Cu, Co, Cr, Fe, Ag, and Ti. Elements.

  The Si particles are small particles having a small particle diameter, and the average particle diameter (D50) is 0.05 to 5 μm, preferably 0.05 to 1 μm, and more preferably 0.1 to 0.5 μm. In addition, the average particle diameter of Si particle | grains can be measured by the laser diffraction scattering method and electron microscope observation (SEM observation).

  By using the fine Si particles having a small particle diameter as described above, it is difficult for the active material particles to fall off the negative electrode, and the life of the negative electrode can be extended. In other words, since the Si particles are accompanied by a significant volume change at the time of occlusion / release of lithium, they gradually become microcrystallized or pulverized, resulting in cracks in the negative electrode, and electrochemical contact of some active material particles. This is lost, and this becomes a factor of deterioration of “charge / discharge cycle characteristics” which is one of important characteristics of the secondary battery. Therefore, in the present invention, by using fine Si particles having a small particle diameter from the beginning, further pulverization of Si particles during charge / discharge is suppressed, and deterioration of charge / discharge cycle characteristics is suppressed.

  On the other hand, the fine Si particles having a small particle size as described above are easily oxidized compared to particles having a relatively large particle size (for example, particles of several tens of μm) because of their large surface area. It becomes a factor of increase in the “irreversible capacity” in the first cycle, which is one of the important characteristics of. Specifically, when Si particles are oxidized and contain a large amount of oxygen, electrochemically intercalated lithium ions form a strong bond with oxygen atoms, and lithium ions are discharged during discharge. Ions are no longer dissociated. Therefore, the fine Si particles having a small particle size used in the present invention preferably have an amount of oxygen bonded to the Si particles of less than 5% by weight with respect to the Si particles and not more than 2% by weight. Is more preferable, and it is particularly preferably 1% by weight or less. By using fine Si particles having a low oxygen content in this way, the oxygen content in the negative electrode material of the present invention can be reduced to 5% by weight or less, and as a result, an increase in irreversible capacity in the first cycle is suppressed. Thus, it is possible to provide a lithium secondary battery having high charge / discharge efficiency. The oxygen content in the negative electrode material is preferably as low as possible. Of course, it is most preferable that no oxygen is contained at all, but the lowest oxygen content that can be reached at present is about 0.005% by weight. it is conceivable that. In addition, the oxygen content in the negative electrode material is obtained by heating the material in an inert gas (helium) stream and measuring the oxygen with an infrared detector. It can be calculated by comparing with (yttrium oxide).

  The method for preparing Si particles used in the present invention is not particularly limited as long as the necessary particle size and oxygen content are achieved, but from the viewpoint of production cost, large particles that can be obtained relatively inexpensively. It is preferable to pulverize Si. As a pulverization method, for example, a dry pulverization method and a wet pulverization method can be employed. From the viewpoint of suppressing the oxygen content, it is preferable to employ a wet pulverization method.

  Examples of the dry pulverization method include a jet mill, a vibration mill, and a ball mill. In order to suppress oxidation of the Si particles during pulverization, the pulverization atmosphere in contact with the Si particles is preferably an inert atmosphere (nitrogen, argon, helium, etc.) that does not contain oxygen.

  Examples of the wet pulverization method include a bead mill and a ball mill. The solvent to be used is preferably inert to Si, and for example, toluene, xylene, mesitylene, methylnaphthalene, creosote oil and the like can be used. In addition, if moisture is contained in these solvents, there is a possibility that Si oxides may be generated by reacting with Si during pulverization. Therefore, a solvent having a reduced moisture content using a drying agent such as distillation or zeolite is used. It is preferable to use it.

  In addition, when pulverization, impurities resulting from the pulverizer are mixed into Si particles, the cycle characteristics and charge / discharge efficiency of the resulting lithium secondary battery tend to deteriorate. It is desirable to select a material that has little influence on the above characteristics. Examples of such materials include alumina and partially stabilized zirconia.

  The plural types of carbonaceous materials used in the present invention are not particularly limited, but a carbonaceous material (A) having a relatively high electron conductivity and a carbonaceous material (B) having a lower crystallinity than the carbonaceous material (A). ), And the carbonaceous material (B) is more preferably amorphous carbon.

  The carbonaceous material (A) is not particularly limited, but is preferably at least one selected from graphite and carbon black, and selected from the group consisting of carbon nanotubes and carbon fibers in addition to graphite and carbon black. One or more types of carbonaceous materials may be included. Moreover, metal elements, such as Ni, Cu, Co, Cr, Fe, Ag, Ti, may be included.

  As the graphite, artificial graphite and natural graphite can be used, including graphitized mesophase spherules. These graphites can be used alone or in combination of two or more. Although the crystal structure of 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. In addition, 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. Moreover, it is preferable that the average particle diameter (D50) of graphite is 0.1-20 micrometers, 0.5-10 micrometers is more preferable, 0.5-5 micrometers is further more preferable. By using graphite with a small particle size, it is possible to uniformly disperse graphite in the negative electrode material, thereby suppressing poor electrical contact of Si particles, and charge / discharge cycle characteristics of the resulting lithium secondary battery As a result, the life of the negative electrode can be extended.

  Although it does not specifically limit as said carbon black, For example, acetylene black, Ketjen black, thermal black, furnace black etc. are mentioned.

  The method for producing the negative electrode material of the present invention is not particularly limited. For example, there is a method in which the Si particles and the plurality of types of carbonaceous materials or precursors thereof are dry-mixed or wet-mixed and heat-treated as necessary. Can be mentioned. Preferably, the precursor that becomes the carbonaceous material (B) is dissolved in an appropriate solvent by heating, and the Si particles and the carbonaceous material (A) are added thereto and wet-mixed. Then, the solvent is removed, and the heat treatment is further performed. Thus, the precursor of the carbonaceous material (B) is carbonized to produce composite particles (negative electrode material) in which the Si particles, the carbonaceous material (A), and the carbonaceous material (B) are composited. Thus, by producing composite particles using the precursor of the carbonaceous material (B), the surface of the Si particles can be covered with the precursor, and the oxidation of the Si particle surface is suppressed. In addition, the precursor functions as a binder, and the Si particles and the carbonaceous material (A) can be bound and combined more firmly.

  Examples of the precursor of the carbonaceous substance (B) include pitch-based materials such as coal-based pitch materials, petroleum-based pitch materials, and synthetic pitch materials, tar-based materials, vinyl-based resins, cellulose-based resins, phenol-based resins, and the like. The resin-based material can be used. 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.

  Moreover, when mixing each component, in order to suppress the oxidation of Si particle | grains, it is preferable to carry out in a low oxygen concentration environment, for example, the inside of a mixing device is inert gas (nitrogen, argon, helium) or pressure reduction. This can be realized by setting the atmosphere.

  The temperature during the heat treatment is not particularly limited as long as the temperature is sufficient to carbonize the precursor of the carbonaceous material (B), but is preferably in the range of 700 to 2000 ° C. More preferably, it is in the range of ˜1500 ° C., and particularly preferably in the range of 1000-1300 ° C. When the heat treatment temperature is lower than 700 ° C., carbonization of the precursor that generates the carbonaceous material (B) tends to be insufficient, and the charge / discharge efficiency and cycle characteristics of the obtained lithium secondary battery are deteriorated. If the temperature exceeds 2000 ° C., electrochemically inactive silicon carbide (SiC) is generated by the reaction between the Si particles and the carbonaceous material, and the charge / discharge capacity of the resulting lithium secondary battery is greatly reduced. There is a fear.

  Moreover, the atmosphere at the time of performing the heat treatment is performed in a vacuum atmosphere or an inert gas atmosphere from the viewpoint of preventing the oxidation of the Si particles and the carbonaceous material and suppressing the increase in the irreversible capacity of the lithium secondary battery. preferable.

  The weight ratio of the Si particles to the carbonaceous material (A) in the negative electrode material of the present invention is not particularly limited, but can be selected from the range of 99.5 / 0.5 to 0.5 / 99.5, 99 It is preferable to select from the range of / 1 to 1/99. The charge / discharge capacity increases as the proportion of Si particles increases.

  Further, the weight ratio of the carbonaceous material (A) and the carbonaceous material (B) in the negative electrode material of the present invention is not particularly limited, but as the carbonaceous material (A) increases, the electronic conductivity of the composite particles improves. On the other hand, considering that the charge / discharge cycle characteristics are improved, if the amount of the carbonaceous material (B) is too small, the function of the composite particles as a binder is insufficient and the composite tends to be difficult. The range is preferably 10-30 / 70, more preferably 80 / 20-40 / 60, and particularly preferably 70 / 30-40 / 60.

  Moreover, it is preferable to further coat the surface of the composite material particle (negative electrode material) with carbon because the charge / discharge cycle of the obtained lithium secondary battery is improved. This improvement in charge / discharge cycleability is thought to be due to the fact that the coated carbon suppresses falling off during charge / discharge of the Si particles exposed on the surface of the composite particles or in the vicinity of the surface.

  The carbon coating can be performed, for example, by pulverizing the obtained composite particles, coating the surface of the composite particles with a coated carbon precursor that is carbonized by heating, and heating. The coating with the coated carbon precursor can be performed, for example, by mixing a coated carbon precursor dissolved in an appropriate solvent with composite particles, and then removing the solvent by a wet method or a known surface modification apparatus (Mechanofusion manufactured by Hosokawa Micron). Any dry method in which the surface of the composite particles is coated with a coated carbon precursor using a nobilta, a hybridizer manufactured by Nara Machinery Co., Ltd., etc. can be employed. Further, a known vapor phase method such as a CVD method can also be employed.

  The coated carbon precursor may be the same as the material (pitch-based material, tar-based material, resin-based material, etc.) that can be used as the precursor that becomes the carbonaceous substance (B) by heating. it can.

  The ratio of the surface carbon coating layer to the composite particles (negative electrode material before carbon coating) (coating carbon weight / composite particle weight) is preferably in the range of 0.1 / 99.9 to 50/50. The range of 0.5 / 99.5 to 50/50 is more preferable, and the range of 1/99 to 30/70 is particularly 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. By using the negative electrode for a lithium secondary battery composed of the negative electrode material of the present invention, a lithium secondary battery having a large discharge capacity, a small irreversible capacity, and excellent charge / discharge cycle characteristics can be produced.

  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 ( Ethylenically unsaturated carboxylic acid ester such as (meth) acrylate, ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, polytetrafluoroethylene, polyvinylidene fluoride, fluororubber, 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.

  The amount of the solvent used is not particularly limited as long as it becomes a paste, and is usually about 60 to 150 parts by weight, preferably about 60 to 100 parts by weight with respect to 100 parts by weight of the negative electrode material of the present invention. .

  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, a small initial irreversible capacity, and excellent charge / discharge cycle characteristics, it is a distributed type, portable battery, such as an electronic device, an electric device, an automobile, and an electric power storage. It is suitable as a power source or an auxiliary power source.

  Hereinafter, although an example and a comparative example explain the present invention in detail, the present invention is not limited to these examples.

<Production of negative electrode material and negative electrode>
(Example 1)
(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.

(Production of graphite)
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, Then, graphite (carbonaceous substance (A)) with an average particle diameter (D50) of 2 micrometers was obtained by baking at 3000 degreeC in nitrogen atmosphere.

(Preparation of Si fine particles)
3 kg of Si material having an average particle size of 20 μm (manufactured by Toyo Kinzoku Co., Ltd., high-purity metal silicon powder), 1.5 kg of ethylene oxide-added aliphatic amine (“Homogenol L1820” manufactured by Kao Co., Ltd.) Methyl containing 20% by weight of Si fine particles having an average particle size (D50) of 0.2 μm and 12 kg of naphthalene in a bead mill substituted with nitrogen gas together with zirconia beads having a diameter of 0.3 mm for 3 hours. Naphthalene was produced. 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 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 having an average particle diameter of 2 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 Si fine particles prepared as described above, After mixing at 100 ° C. for 1 hour using an axial 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 | fine-particles, graphite, and pitch (carbonaceous substance (B)).

  Next, 200 g of the composite particles obtained above were pulverized for 5 minutes with a vibrating mill made of alumina, and then dispersed in tetrahydrofuran in which 60 g of coal tar pitch (“PKQL” manufactured by Kawasaki Steel Corporation) was dissolved. The composite particle surface was coated with pitch by evaporating with an evaporator. Next, the pitch-coated composite particles were fired at 1150 ° C. for 1 hour in a nitrogen atmosphere, then pulverized with a pulverizer, and further sieved with a 390 mesh sieve to obtain a negative electrode material. The oxygen content in the negative electrode material was 0.9% by weight. This oxygen content was measured using an oxygen / nitrogen analyzer (TC436: manufactured by LECO). More specifically, the temperature in the furnace is set to 1600 ° C. by setting the impulse furnace of the apparatus to 5400 W, and 0.1 to 0.2 g of the negative electrode material is in an inert gas (helium) stream in the furnace. After heating, the amount of oxygen generated was measured with an infrared detector. The oxygen content of the negative electrode material was calculated by comparing the obtained spectrum with a reference material (yttrium oxide) whose oxygen content was known.

(Preparation of negative electrode)
To 5 g of the negative electrode material obtained above, polyvinylidene fluoride as a binder was added in an amount of 10 wt% of the negative electrode material weight, and N-methylpyrrolidone as a solvent was also added in an amount of 10 wt%, and kneaded to obtain a uniform slurry. . Next, the slurry was applied to an electrolytic copper foil having a thickness of 40 μm, dried, roll-rolled and consolidated, and then a disk member obtained by punching using a punch having a diameter of 9 mm was used as a negative electrode. The thickness of the negative electrode material layer on the copper foil was 40 μm.

(Example 2)
A negative electrode material and a negative electrode were produced in the same manner as in Example 1, except that polyvinylidene fluoride was used at 15% by weight 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 graphite having an average particle diameter of 4 μm was used instead of graphite having an average particle diameter of 2 μm.

Example 4
A negative electrode material and a negative electrode were produced in the same manner as in Example 1 except that acetylene black (“DENKA BLACK” manufactured by Denki Kagaku Kogyo Co., Ltd.) was used instead of graphite having an average particle size of 2 μm.

(Example 5)
A negative electrode material and a negative electrode were produced in the same manner as in Example 3 except that polyvinylidene fluoride was used at 20% by weight of the negative electrode material.

(Example 6)
A negative electrode material and a negative electrode were produced in the same manner as in Example 2 except that 1.0 kg of coal tar pitch (“pellet” manufactured by Osaka Kasei Co., Ltd.) was used.

(Comparative Example 1)
(Preparation of Si fine particles)
100 g of Si material having an average particle diameter of 20 μm (manufactured by Toyo Kinzoku Co., Ltd., high-purity metal silicon powder) was placed in a stainless steel ball mill container, and several tens of stainless steel balls having a diameter of 10 mm were placed therein. After the inside of the container was replaced with nitrogen gas, dry pulverization was performed for 10 hours to produce Si fine particles having an average particle diameter (D50) of 0.2 μm.

(Preparation of negative electrode material)
200 g of graphite having an average particle diameter of 2 μm prepared in Example 1, 140 g of coal tar pitch (“pellet” manufactured by Osaka Kasei Co., Ltd.) and 48 g of the Si fine particles prepared as described above at 100 ° C. using a biaxial heating kneader. Mix for 1 hour. Subsequently, it baked at 900 degreeC in nitrogen atmosphere for 1 hour, and produced the composite particle which consists of Si microparticles, graphite, and pitch (carbonaceous substance (B)).

  Next, 200 g of the composite particles obtained above were pulverized for 5 minutes with a vibrating mill made of alumina, and then dispersed in tetrahydrofuran in which 60 g of coal tar pitch (“PKQL” manufactured by Kawasaki Steel Corporation) was dissolved. The composite particle surface was coated with pitch by evaporating with an evaporator. Next, the pitch-coated composite particles were fired at 1150 ° C. for 1 hour in a nitrogen atmosphere, then pulverized with a pulverizer, and further sieved with a 390 mesh sieve to obtain a negative electrode material. The oxygen content in the negative electrode material was 9.2% by weight.

(Preparation of negative electrode)
A negative electrode was produced in the same manner as in Example 1 except that the negative electrode material obtained above was used.

(Comparative Example 2)
Example 1 except that a Si material (manufactured by Toyo Metal Co., Ltd., high-purity metal silicon powder) having an average particle diameter of about 20 μm was used as it was without pulverizing instead of the Si fine particles having an average particle diameter of 0.2 μm. In the same manner, a negative electrode material and a negative electrode were produced. The oxygen content in the negative electrode material was 0.9% by weight.

(Comparative Example 3)
(Preparation of SiO fine particles)
3 kg of SiO material with an average particle diameter of 20 μm, 900 g of dispersion material (“Homogenol L1820” manufactured by Kao Corporation) and 7 kg of methylnaphthalene are wet-ground for 3 hours in a bead mill containing zirconia beads having a diameter of 0.3 mm. Then, methylnaphthalene containing 30% by weight of SiO fine particles having an average particle diameter (D50) of 1 μm was prepared.

(Preparation of negative electrode material)
2 kg of graphite having an average particle diameter of 2 μm prepared in Example 1, 1.4 kg of coal tar pitch (“pellet”, Osaka Kasei Co., Ltd.) and 9 kg of methylnaphthalene containing 30% by weight of SiO fine particles prepared as described above, After mixing at 100 ° C. for 1 hour using an axial 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 | fine-particles, graphite, and pitch (carbonaceous substance (B)).

  Next, 200 g of the composite particles obtained above were pulverized for 5 minutes with a vibrating mill made of alumina, and then dispersed in tetrahydrofuran in which 60 g of coal tar pitch (“PKQL” manufactured by Kawasaki Steel Corporation) was dissolved. The composite particle surface was coated with pitch by evaporating with an evaporator. Next, the pitch-coated composite particles were fired at 1150 ° C. for 1 hour in a nitrogen atmosphere, then pulverized with a pulverizer, and further sieved with a 390 mesh sieve to obtain a negative electrode material. The oxygen content in the negative electrode material was 14% by weight.

(Preparation of negative electrode)
A negative electrode was produced in the same manner as in Example 1 except that the negative electrode material obtained above was used.

<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, 1 cycle irreversible capacity, and 30 cycle capacity maintenance rate 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.

  Irreversible capacity: The initial (first) irreversible capacity was calculated by the difference between the charge capacity at the first cycle and the discharge capacity at the first cycle.

Capacity maintenance rate: The above charge / discharge cycle was repeated 30 times, and the ratio of the discharge capacity at the 30th cycle to the charge / 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, a small initial irreversible capacity, and excellent charge / discharge cycle characteristics.

Claims (17)

  A negative electrode material for a lithium secondary battery, comprising Si particles having an average particle diameter (D50) of 0.05 to 5 μm and a plurality of types of carbonaceous materials, and having an oxygen content of 5% by weight or less.   2. The negative electrode material for a lithium secondary battery according to claim 1, wherein the plurality of types of carbonaceous materials include a carbonaceous material (A) and a carbonaceous material (B) having lower crystallinity than the carbonaceous material (A).   The negative electrode material for a lithium secondary battery according to claim 2, wherein the carbonaceous material (A) contains at least one selected from graphite and carbon black.   The negative electrode material for a lithium secondary battery according to claim 3, wherein the graphite has an average particle diameter (D50) of 0.1 to 20 μm.   The negative electrode material for a lithium secondary battery according to any one of claims 2 to 4, wherein the carbonaceous substance (B) is amorphous carbon.   The negative electrode material for a lithium secondary battery according to any one of claims 2 to 5, wherein a weight ratio of the Si particles to the carbonaceous material (A) is 99.5 / 0.5 to 0.5 / 99.5. .   The negative electrode material for a lithium secondary battery according to any one of claims 2 to 6, wherein a weight ratio of the carbonaceous material (A) to the carbonaceous material (B) is 90/10 to 30/70.   The negative electrode material for a lithium secondary battery according to claim 1, wherein the surface is carbon-coated.   The negative electrode material for a lithium secondary battery according to claim 8, wherein a ratio of the carbon coating layer (coating carbon weight / negative electrode material weight before carbon coating) is 0.1 / 99.9 to 50/50. A step of preparing Si particles having an average particle size (D50) of 0.05 to 5 μm by a wet pulverization method, and a step of mixing the Si particles and a plurality of types of carbonaceous materials,
The manufacturing method of the negative electrode material for lithium secondary batteries which has this. A step of preparing Si particles having an average particle diameter (D50) of 0.05 to 5 μm by a wet pulverization method;
A step of mixing the Si particles, the carbonaceous material (A), and a precursor that becomes a carbonaceous material (B) having lower crystallinity than the carbonaceous material (A) by heating, and a mixture obtained by the mixing. The manufacturing method of the negative electrode material for lithium secondary batteries which has the process to heat-process.   The method for producing a negative electrode material for a lithium secondary battery according to claim 10 or 11, wherein the wet pulverization method is pulverization using a bead mill.   The said mixing is wet mixing, The manufacturing method of the negative electrode material for lithium secondary batteries in any one of Claims 10-12.   The method for producing a negative electrode material for a lithium secondary battery according to any one of claims 11 to 13, wherein a temperature of the heat treatment 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 10 to 14, further comprising a step of coating the surface with carbon.   The negative electrode material for lithium secondary batteries according to any one of claims 1 to 9, or the negative electrode material for lithium secondary batteries obtained by the production method according to any one of claims 10 to 15 and a binder. A negative electrode for a lithium secondary battery obtained by integrating a mixture and a current collector.   A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to claim 16.