TW201345031A - Negative electrode material for lithium-ion secondary battery, negative electrode for lithium-ion secondary battery, lithium-ion secondary battery - Google Patents

Abstract

This invention is related to a negative electrode material for lithium-ion secondary battery, a negative electrode for lithium-ion secondary battery using the material, and a lithium-ion secondary battery. The negative electrode material for lithium-ion secondary battery contains, in a specific mass ratio, a sphericalized or ellipsoided natural graphite (A) in which average particle size is 5 to 35 μ m and average aspect ratio is less than 2.0, a bulk mesophase graphite compound (B) in which average particle size is 2 to 25 μ m and average aspect ratio is less than 2.0, and a squamous graphite (C) in which average particle size is 1 to 15 μ m and is less than the average particle size of the bulk mesophase graphite compound (B), and average aspect ratio is 5.0 or more.

Description

Anode material for lithium ion secondary battery, anode for lithium ion secondary battery, and lithium ion secondary battery

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

In recent years, with the miniaturization or high performance of electronic devices, the demand for increasing the energy density of batteries has been increasing. In particular, since lithium ion secondary batteries can be increased in voltage compared with other secondary batteries, high energy density can be achieved, and attention has been paid.

The lithium ion secondary battery is mainly composed of a negative electrode, a positive electrode, and an electrolytic solution (nonaqueous electrolyte). Lithium ions move between the negative electrode and the positive electrode through the electrolytic solution during the discharge process and during charging to become a secondary battery. The negative electrode is usually composed of a current collector containing a copper foil and a negative electrode material (active material: active material) bonded by a binder. Usually, the anode material is made of a carbon material. As such a carbon material, graphite which is excellent in general charge and discharge characteristics and exhibits high discharge capacity and potential flatness (see Patent Document 1).

In the lithium ion secondary battery mounted on the latest portable electronic equipment, the industry requires excellent rapid charging performance and rapid discharge performance, and it is required that the initial discharge capacity does not deteriorate even if the charge and discharge are reversed (high cycle characteristics: cycle) Performance).

Representative examples of the prior graphite-based negative electrode materials have the following examples.

A graphite particle obtained by collecting or combining a plurality of flat particles so that the orientation surfaces are non-parallel, and having fine pores in the particles (Patent Document 2).

A graphitized material of mesophase carbon small spheres comprising a Brooks-Taylor type single crystal in which a basal surface of graphite is layered in a direction perpendicular to a diameter direction (Patent Document 3) ).

A composite graphite particle obtained by filling a void between graphite particles of a granulated product obtained by spheroidizing or ellipsoidizing natural graphite particles with a carbonaceous substance or coating a carbonaceous material The surface of the granular material is formed (Patent Document 4).

A block-shaped graphite particle obtained by pulverizing, oxidizing, carbonizing, and graphitizing a bulk mesophase pitch (Patent Document 5).

However, in response to the recent demand for high capacitance of a lithium ion secondary battery, in order to increase the density of the active material layer and to set a discharge capacitance per unit volume, the anode material is coated. When it is placed on a current collector and pressed at a high pressure to increase the density of the active material layer, various problems occur in these prior negative electrode materials.

When the density of the active material layer exceeds 1.7 g/cm ³ in the negative electrode material of the aggregated graphite particles described in Patent Document 2, the aggregate collapses, and the flat graphite particles as a constituent unit are aligned as a natural graphite. In the direction. Therefore, the ion diffusibility of lithium ions is lowered, and the rapid chargeability, rapid discharge properties, and cycle characteristics are lowered. Further, the surface of the active material layer is easily clogged, the permeability of the electrolytic solution is lowered, and the productivity of the battery is lowered, and the electrolyte solution is depleted inside the active material layer to reduce the cycle characteristics.

In the negative electrode material using the graphitized material of the mesocarbon small spheres described in Patent Document 3, since the graphitized compounds are spherical, the alignment of the base surface of the graphite can be suppressed to some extent even if the density is increased. However, since the graphite compound is dense and hard, high pressure is required for high density, and problems such as deformation, elongation, and fracture of the copper foil of the current collector are caused. In addition, the contact area with the electrolytic solution is small. Therefore, the rapid charging property is extremely low. The decrease in chargeability causes electrodeposition of lithium on the surface of the negative electrode during charging, resulting in a decrease in cycle characteristics.

In the negative electrode material using the bulk graphite particles described in Patent Document 4, the high reactivity (lower initial charge and discharge efficiency), which is a disadvantage of natural graphite having a high discharge capacity, can be improved by coating of carbonaceous materials, but When the density is high, the granules of the natural graphite particles collapse and become flat, and the rapid chargeability, the rapid discharge property, and the cycle characteristics are lowered. Further, since the carbonaceous material is peeled off and the natural graphite particles are exposed, the initial charge is performed. The discharge efficiency is lowered.

In the negative electrode material using the bulk graphite particles described in Patent Document 5, the alignment of the base surface of the graphite can be suppressed to some extent even if the density is increased. However, since the graphite compound is dense and hard, high pressure is required for high density, and problems such as deformation, elongation, and fracture of the copper foil of the current collector are caused. Further, since the crystallinity of the surface of the graphite particles is lowered by oxidation, there is a problem that the discharge capacity is low.

In this way, the industry is expected to maintain a high-density rapid chargeability, rapid discharge property, and cycle characteristics, and it is soft and can be easily densified at a low pressure. Therefore, it is proposed to mix a plurality of graphite materials. Representative examples are described below.

A lithium secondary battery using a graphite-based carbonaceous material in which a spherical graphite-formed natural graphite powder is coated with a scaly carbonaceous material, and a mesophase carbon having an average particle diameter of 2/3 or less of the scaly carbonaceous material. A negative electrode material of microspheres (Patent Document 6).

A negative electrode for a lithium ion secondary battery using a negative electrode material in which a mesophase small spherical graphite compound and a non-flaky graphite particle having a mean particle diameter smaller than the graphitized material (graphite of a mesophase small spherical pulverized material) are used ( Patent Document 7).

A negative electrode material for a lithium secondary battery in which a hydrophilized product of graphitized particles of mesophase small spheres and a composite graphite carbon material coated with a carbon material having low crystallinity are mixed (Patent Document 8).

A negative electrode for a lithium secondary battery, which is obtained by mixing spherical or ellipsoidal graphite having an average particle diameter of 10 μm to 30 μm coated with non-graphitic carbon, and having an average particle diameter of 1 μm to 10 μm. A negative electrode material of graphite (flat sheet) graphite (Patent Document 9).

A nonaqueous secondary battery using a mixture of pitch graphite and graphitized mesocarbon microbeads for a negative electrode material (Patent Document 10).

A nonaqueous electrolyte secondary battery using a graphite material in which a non-graphititic carbon material is coated and a negative electrode material of a natural graphite material (Patent Document 11).

A lithium secondary battery using mesophase spheroidal graphite having an average particle diameter of 8 μm or more and an intermediate phase fine spherical graphite having an average particle diameter of 3 μm or less and containing 7.5 wt% or less so as to fill a gap therebetween Anode material (patent literature) 12).

A nonaqueous electrolyte secondary battery using a mixture of graphite, a first non-graphitic carbon material, and acetylene black having a particle diameter smaller than these materials for a negative electrode material (Patent Document 13).

A nonaqueous electrolyte secondary battery using a graphite compound in which mesocarbon microbeads are mixed, and a negative electrode material in which an average graphite particle is less than the artificial graphite powder of the graphitized material (Patent Document 14).

Further, the applicant of the present application has previously proposed Patent Document 15.

Prior technical literature

Patent literature

Patent Document 1: Japanese Patent Publication No. Sho 62-23433

Patent Document 2: Japanese Patent Laid-Open No. Hei 10-158005

Patent Document 3: Japanese Patent Laid-Open Publication No. 2000-323127

Patent Document 4: Japanese Patent Laid-Open Publication No. 2004-63321

Patent Document 5: Japanese Patent Laid-Open No. Hei 10-139410

Patent Document 6: Japanese Patent Laid-Open Publication No. 2008-171809

Patent Document 7: Japanese Patent Laid-Open Publication No. 2007-134276

Patent Document 8: Japanese Patent Laid-Open Publication No. 2004-253379

Patent Document 9: Japanese Patent Laid-Open Publication No. 2005-44775

Patent Document 10: Japanese Patent Laid-Open Publication No. 2005-19096

Patent Document 11: Japanese Patent Laid-Open Publication No. 2001-185147

Patent Document 12: Japanese Patent Laid-Open No. Hei 11-3706

Patent Document 13: Japanese Patent Laid-Open No. Hei 10-270019

Patent Document 14: Japanese Patent Laid-Open No. Hei 7-37618

Patent Document 15: Japanese Patent Laid-Open No. 2011-9051

However, even when these mixed-type negative electrode materials are used, deterioration of battery performance such as rapid chargeability, rapid discharge performance, and cycle characteristics of the lithium ion secondary battery when the active material layer is increased in density is not eliminated. In other words, in the case of Patent Documents 6, 7, 10, 12, and 14, since the mesophase small spherical graphite is hard, in order to increase the density of the active material layer, a high pressing pressure is required, and copper of the current collector is generated. Problems such as deformation, elongation, and breakage of the foil. In the case of the high density of the active material layer, the ion diffusibility of lithium ions is lowered, and the rapid chargeability, rapid discharge performance, and cycle characteristics of the lithium ion secondary battery are lowered. . Further, the surface of the active material layer is liable to be clogged, the permeability of the electrolytic solution is lowered, and the productivity of the battery is lowered, and the electrolyte solution is depleted inside the active material layer, and the cycle characteristics are lowered. In the case of Patent Document 13, when a hard non-graphite carbon material is used, in order to increase the density of the active material layer, a high pressing pressure is required, and problems such as deformation, elongation, and breakage of the copper foil of the current collector are caused. In the case of Patent Document 15, there is still room for improvement in rapid chargeability and long-term cycle characteristics as battery characteristics in which conductivity is involved.

An object of the present invention is to provide a negative electrode material which, when used as a negative electrode material for a lithium ion secondary battery, can achieve a high density with a low pressing pressure, a high discharge capacity per unit volume, and although high density, It suppresses the collapse or alignment of graphite, does not impair the permeability or retention of the electrolyte, and has excellent rapid chargeability, rapid discharge properties, and cycle characteristics. In addition, it is an object of the present invention to provide a A lithium ion secondary battery negative electrode using the negative electrode material, and a lithium ion secondary battery including the negative electrode.

The inventors of the present invention conducted intensive studies to solve the above problems, and as a result, found that (A) spheroidized or ellipsoidal having an average particle diameter of 5 μm to 35 μm and an average aspect ratio of less than 2.0 is contained at a specific mass ratio. Natural graphite, (B) bulk mesophase graphitized material having an average particle diameter of 2 μm to 25 μm and an average aspect ratio of less than 2.0, and (C) an average particle diameter of 1 μm to 15 μm and smaller than the above-mentioned bulk mesophase graphite When the composition of the flaky graphite having an average particle diameter of the compound (B) and an average aspect ratio of 5.0 or more is used as a negative electrode material of a lithium ion secondary battery, the following is a negative electrode material for a lithium ion secondary battery: The low pressing pressure reaches a high density, the discharge capacity per unit volume is high, and although it is high in density, it can suppress the collapse or alignment of graphite, does not impair the permeability or retention of the electrolyte, and has excellent rapid charging property. Rapid discharge and cycle characteristics; thus completing the invention of the present application.

That is, the present invention provides the following 1 to 9.

A negative electrode material for a lithium ion secondary battery comprising: (A) an average particle diameter of 5 μm to 35 μm and an average aspect ratio smaller than a mass ratio satisfying the following formula (1) and the following formula (2): (A) 2.0 spheroidized or ellipsoidal natural graphite, (B) bulk mesophase graphitized material having an average particle diameter of 2 μm to 25 μm and an average aspect ratio of less than 2.0, and (C) an average particle diameter of 1 μm~ Flake graphite having an average particle diameter of 15 μm and smaller than the above-mentioned bulk mesophase graphitized product (B) and having an average aspect ratio of 5.0 or more; a: b = (60 to 95): (40 to 5) (1)

(a+b): c=(85 or more ~ less than 100): (15 or less ~ more than 0) (2)

Here, a, b, and c represent the masses of the components (A), (B), and (C) above.

2. The negative electrode material for a lithium ion secondary battery according to the above 1, wherein the spheroidized or ellipsoidal natural graphite (A) comprises a carbonaceous material or a graphite material adhered to at least a part of a surface thereof. Spheroidized or ellipsoidal natural graphite.

3. The negative electrode material for a lithium ion secondary battery according to the above 1 or 2, wherein the bulk mesophase graphitized material (B) comprises a tar oil and/or a pitch, heat treatment, pulverization, oxidation, carbonization, Graphitized blocky mesophase graphitized material.

4. The negative electrode material for a lithium ion secondary battery according to any one of the above 1 to 3, wherein the block-shaped mesophase graphitized material (B) has an average particle diameter smaller than the spheroidized or ellipsoidal natural graphite. (A) Average particle size.

5. The negative electrode material for a lithium ion secondary battery according to any one of the above 1 to 4, wherein the flaky graphite (C) comprises flaky graphite having a carbonaceous material adhered to at least a part of a surface thereof.

The negative electrode material for a lithium ion secondary battery according to any one of the above 1 to 5, wherein the spheroidized or ellipsoidal natural graphite (A), the bulk intermediate phase graphite (B), and At least one or all of the flaky graphite (C) is contained in graphite having a metal oxide embedded on the surface thereof.

A negative electrode material for a lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery according to any one of the above 1 to 6 as a main constituent material of the active material, and the density of the active material layer is 1.7 g. /cm ³ or more.

8. The lithium ion secondary battery negative electrode according to the above 7, wherein the diffraction peak intensity I004 of the (004) plane of the lithium ion secondary battery negative electrode under X-ray diffraction is The ratio of the diffraction peak intensity I110 of the (110) plane I110/I110 is 20 or less.

A lithium ion secondary battery comprising the lithium ion secondary battery negative electrode according to the above 7 or 8.

The lithium ion secondary battery negative electrode of the present invention is formed by the negative electrode material of the present invention containing the three types of graphite specified by (A) to (C) in the above specific ratio, thereby improving the active material layer. In the case of density, deformation or breakage of the current collector does not occur, and collapse or alignment of each graphite can be suppressed, and the permeability of the electrolytic solution is excellent. Further, since the electrolyte solution is likely to be present around the graphite, the diffusibility of lithium ions is good. Therefore, the lithium ion secondary battery (the lithium ion secondary battery of the present invention) using the negative electrode of the present invention has a high discharge capacity per unit volume, and has excellent battery performance such as rapid chargeability, rapid discharge performance, and cycle characteristics. Therefore, the lithium ion secondary battery of the present invention satisfies the demand for high energy density of the battery in recent years, and can be used for downsizing and high performance of the equipment to be mounted.

1‧‧‧Outer cover

2‧‧‧Working electrode (negative electrode)

3‧‧‧Outer cans

4‧‧‧ opposite pole (positive)

5‧‧‧Separator

6‧‧‧Insulation pad

7a, 7b‧‧‧ collector

Fig. 1 is a cross-sectional view showing the structure of a button type evaluation battery for a charge and discharge test in an embodiment.

Hereinafter, the present invention will be specifically described.

A lithium ion secondary battery (hereinafter also referred to simply as a secondary battery) generally uses an electrolytic solution (nonaqueous electrolyte), a negative electrode, and a positive electrode as main battery constituent elements. For example, it is enclosed in a secondary battery can. The negative electrode and the positive electrode each function as a carrier of lithium ions. This secondary battery utilizes a battery mechanism in which lithium ions are occluded by the negative electrode during charging, and lithium ions are detached from the negative electrode during discharge.

The secondary battery of the present invention is not particularly limited as long as the negative electrode material of the present invention is used as the negative electrode material, and other battery constituent elements such as a nonaqueous electrolyte, a positive electrode, and a separator are in accordance with elements of a general secondary battery.

The negative electrode material for a lithium ion secondary battery of the present invention (the negative electrode material of the present invention) satisfies the mass ratio of the following formula (1) and the following formula (2) and contains the following components: (A) the average particle diameter is 5 μm. Spheroidized or ellipsoidal natural graphite having a 35 μm average aspect ratio of less than 2.0, (B) bulk mesophase graphitized materials having an average particle diameter of 2 μm to 25 μm and an average aspect ratio of less than 2.0, and (C) The flaky graphite having an average particle diameter of 1 μm to 15 μm and less than the average particle diameter of the bulk intermediate phase graphitized product (B) and an average aspect ratio of 5.0 or more.

a:b=(60~95):(40~5) (1)

(a+b): c=(85 or more ~ less than 100): (15 or less ~ more than 0) (2)

Here, a, b, and c represent the masses of the components (A), (B), and (C) above.

The negative electrode material of the present invention contains specific spheroidized or ellipsoidal natural graphite (A) and two types of graphite (B), (C) in a specific amount ratio.

In the present invention, the spheroidized or ellipsoidal natural graphite (A), the bulky mesophase graphitized material (B), and the flaky graphite (C) are excellent in terms of rapid chargeability and excellent cycle characteristics. At least one or all of the particles preferably include graphite having a metal oxide embedded on the surface thereof.

Examples of the embodiment in which the metal oxide is buried include a spheroidized or ellipsoidal natural graphite (A), a bulk intermediate phase graphitized material (B), and scaly graphite (C) itself. In the case of a metal oxide; a carbonaceous material or a graphite material is adhered to the graphite, and a metal oxide is embedded in the interior or surface of the carbonaceous material or the graphite material; and a combination of these cases.

Examples of the metal oxide include cerium oxide, aluminum oxide, titanium oxide, zirconium oxide, and iron oxide.

As one of preferred embodiments, a metal oxide is exemplified as fine particles. The size of the metal oxide can be set to be smaller than graphite (A) (B) (C), and a carbonaceous material or a graphite material which can adhere to these graphites.

Examples of the method of embedding the metal oxide include a method in which a mixture of a raw material and a metal oxide is repeatedly subjected to a compressive force and a shearing force to perform mechanochemical treatment.

Hereinafter, graphite (A) to (C) will be described in detail.

[(A) Spheroidized or ellipsoidal natural graphite]

The spheroidized or ellipsoidal natural graphite (hereinafter also referred to as "substantially spherical natural graphite") (A) used in the present invention has an average particle diameter of 5 μm to 35 μm and an average aspect ratio of less than 2.0. Spheroidized or ellipsoidal natural graphite.

The shape of the substantially spherical natural graphite (A) is not particularly limited as long as it is spherical or ellipsoidal.

In addition, the substantially spherical natural graphite (A) is not particularly limited as long as it is a natural graphite obtained by spheroidizing or ellipsoidal natural graphite. It is preferably a natural graphite in which flat or scaly natural graphite is bent or folded to be substantially spherical, or a plurality of scaly natural graphite is granulated into a concentric shape or a cabbage shape to be spheroidized. Natural graphite.

The average particle diameter (average particle diameter in terms of volume) of the substantially spherical natural graphite (A) is 5 μm to 35 μm, and particularly preferably 10 μm to 30 μm. When it is 5 μm or more, the density of the active material layer can be increased, and the discharge capacity per unit volume can be improved. Further, when it is 35 μm or less, the rapid charging property or the cycle characteristics are improved.

The average aspect ratio of the substantially spherical natural graphite (A) is less than 2.0, preferably less than 1.5, more preferably 1.3 or less. The closer to the true spherical shape, the more the crystal structure of the substantially spherical natural graphite (A) is not aligned in one direction in the particles or on the negative electrode, and the higher the diffusibility of lithium ions in the electrolyte, the rapid chargeability, The rapid discharge performance and the cycle characteristics become better.

The substantially spherical natural graphite (A) has high crystallinity. Since it is high in crystallinity, it is soft and contributes to an increase in the density of the active material layer. The average lattice plane spacing d ₀₀₂ as an index of crystallinity is less than 0.3360 nm, and particularly preferably 0.3358 mm or less.

Further, since the substantially spherical natural graphite (A) has high crystallinity, it can exhibit a high discharge capacity in the case of a negative electrode active material used for a secondary battery. The discharge capacity when the substantially spherical natural graphite (A) is used as the negative electrode material alone varies depending on the production conditions of the negative electrode or the evaluation battery, but is about 350 mAh/g or more, preferably 360 mAh/g or more.

When the specific surface area of the substantially spherical natural graphite (A) is too large, the initial charge and discharge efficiency of the secondary battery is lowered. Therefore, the specific surface area is preferably 20 m ² /g or less, more preferably 10 m ² /g or less.

The production of the substantially spherical natural graphite (A) contained in the negative electrode material of the present invention is not particularly limited. For example, it can be produced by applying a mechanical external force to flat, scaly natural graphite. Specifically, natural graphite can be bent or granulated into concentric shapes by imparting high shear force or applying a rotating operation. Spheroidize it. It is also possible to mix the binder before and after the spheroidization treatment to promote granulation. For the spheroidizing treatment, "Counter-jet mill", "ACM Pulverizer" (manufactured by Hosokawa Micron Co., Ltd.), "Current Jet" (manufactured by Nissin Engineering Co., Ltd.), etc., "SARARA" (manufactured by Kawasaki Heavy Industries Co., Ltd.), "GRANUREX" (manufactured by Fulun Industrial Co., Ltd.), "New-Gra Machine" (manufactured by Shinsei Co., Ltd.), and "Agglomaster" (manufactured by Hosokawa Micron Co., Ltd.) Mixer such as granulator, pressure kneader, and twin roll mill, "Mechano-Micro System" (manufactured by Nara Machinery Co., Ltd.), extruder, ball mill, planetary grinder, "Mechano Fusion System" (manufactured by Hosokawa Micron Co., Ltd.), "Nobilta" (manufactured by Hosokawa Micron Co., Ltd.), "Hybridization" (manufactured by Nara Machinery Co., Ltd.), and a compression shear type processing device such as a rotary ball mill.

A part or all of the substantially spherical natural graphite (A) is more preferably a natural graphite (A1) having a carbonaceous material adhered to at least a part of the surface thereof or a natural graphite (A2) to which a graphite material is attached. The collapse of the natural graphite (A) can be prevented by the adhesion of the carbonaceous material or the graphite material.

Examples of the carbonaceous material adhering to the substantially spherical natural graphite (A1) include a final temperature of 500 ° C or more and less than 1500 ° C, and a heavy oil, tar, pitch, or phenol resin for coal or petroleum. A carbide obtained by heat treatment of a resin. The amount of adhesion of the carbonaceous material is preferably 0.1 parts by mass to 10 parts by mass, particularly preferably 0.5 parts by mass to 5 parts by mass, per 100 parts by mass of the substantially spherical natural graphite (A).

The graphite material adhered to the substantially spherical natural graphite (A2) may, for example, be a heavy oil or coke of coal or petroleum type at a temperature of 1500 ° C or more and less than 3300 ° C. A graphitized product obtained by heat-treating a resin such as oil, pitch, or phenol resin. The amount of adhesion of the graphite material is preferably from 1 part by mass to 30 parts by mass, particularly preferably from 5 parts by mass to 20 parts by mass, per 100 parts by mass of the substantially spherical natural graphite (A).

As a method of attaching a carbonaceous material or a graphite material to a part or all of the substantially spherical natural graphite (A), it can be produced by any of a gas phase method, a liquid phase method, and a solid phase method. In one method, a precursor of a carbonaceous material or a graphite material (for example, a petroleum-based or petroleum-based heavy oil, a tar, a pitch, or a phenol resin) is attached or coated to a substantially spherical natural graphite (A). Heat treatment is performed afterwards.

Specific examples of the gas phase method include a method of vapor-depositing a vapor of a precursor of a carbonaceous material represented by a hydrocarbon such as benzene or toluene on the surface of a substantially spherical natural graphite (A) at 900 ° C to 1200 ° C. At the time of vapor deposition, the hydrocarbon precursor is carbonized to obtain substantially spherical natural graphite (A1) to which a carbonaceous material adheres.

Specific examples of the liquid phase method include the following methods, namely, coal tar, tar light oil, tar oil, tar heavy oil, naphthalene oil, eucalyptus oil, coal tar pitch, asphalt oil, mesophase pitch, oxygen crosslinked petroleum pitch, and the like. A tar or a coal-based tar pitch, a thermoplastic resin such as polyvinyl alcohol, a thermosetting resin such as a phenol resin or a furan resin, or a solution of a saccharide or a cellulose (hereinafter also referred to as a carbonaceous material precursor). After the spherical natural graphite (A), the solvent is removed, or the carbonaceous material precursor or a solution of these precursors is attached to the substantially spherical natural graphite (A), and finally, the temperature is 500 ° C or more and less than 1500 ° C. The heat treatment is performed to produce substantially spherical natural graphite (A1) to which a carbonaceous material adheres. Similarly, by raising the heat treatment temperature to a temperature of 1500 ° C or more and less than 3300 ° C, substantially spherical natural graphite (A2) to which a graphite material adheres can be produced.

Further, when the carbonaceous material precursor or the solution of these precursors is brought into contact with the substantially spherical natural graphite (A), stirring, heating, and pressure reduction may be performed.

Specific examples of the solid phase method include a method in which a powder of a carbonaceous material precursor exemplified in the description of the liquid phase method is mixed with substantially spherical natural graphite (A) to impart compression and shear. A method of pressure-bonding a powder of a carbonaceous material precursor to a surface of substantially spherical natural graphite (A) by mechanochemical treatment of mechanical energy such as collision or friction. The carbonaceous material precursor is melted or softened by mechanochemical treatment to frictionally adhere to the substantially spherical natural graphite (A), thereby adhering. Examples of the apparatus that can be subjected to mechanochemical treatment include various compression shear processing apparatuses described above. By substantially heat-treating the substantially spherical natural graphite (A) to which the powder of the carbonaceous material precursor is attached at a temperature of 500 ° C or more and less than 1500 ° C, substantially spherical natural graphite (A1) to which a carbonaceous material adheres can be produced. ). Similarly, by raising the heat treatment temperature to a temperature of 1500 ° C or more and less than 3300 ° C, substantially spherical natural graphite (A2) to which a graphite material adheres can be produced.

In addition, a conductive material such as carbon fiber or carbon black may be used together with the carbonaceous material precursor. Further, in the case of producing substantially spherical natural graphite (A2) to which a graphite material adheres, an alkali metal such as Na or K, an alkaline earth metal such as Mg or Ca, Ti, V, Cr, Mn, Fe, Co, or the like can be used. Transition metals such as Ni, Zr, Nb, Mn, Mo, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, Pt, metals such as Al and Ge, and semimetals such as B and Si. A metal compound, for example, a hydroxide, an oxide, a nitride, a chloride, a sulfide, or the like, may be used alone or in combination of two or more kinds thereof together with a carbonaceous material precursor.

The substantially spherical natural graphite (A) contains natural graphite (A1) having a carbonaceous material attached to at least a part of its surface or a natural graphite-attached material. In the case of graphite (A2), even if the density of the negative electrode is increased, the shape of the substantially spherical natural graphite (A) is maintained, that is, the initial charge and discharge efficiency is excellent, (A1) of the total amount of (A) And/or the amount of (A2) is preferably from 30% by mass to 100% by mass.

In the present invention, the substantially spherical natural graphite (A1) to which the carbonaceous material is attached or the substantially spherical natural graphite (A2) to which the graphite material is attached may be contained inside or on the surface of the carbonaceous material or the graphite material. Natural graphite of a conductive material such as carbon fiber or carbon black, or natural graphite (for example, in the form of fine particles) may be attached or embedded with a metal oxide such as cerium oxide, alumina or titania. It is a natural graphite in which a metal or a metal compound such as bismuth, tin, cobalt, nickel, copper, cerium oxide, tin oxide or lithium titanate is adhered or buried.

Particularly preferably, the carbonaceous material or the graphite material adhered to the substantially spherical natural graphite (A) contains the above-mentioned metal oxide (for example, fine particles which are made into a metal oxide) in the interior or surface thereof, and is preferably buried. There are the above metal oxides.

The embedding method can be exemplified by the method of applying a mechanical external force to the substantially spherical natural graphite (A1) or (A2) in the coexistence of the fine particles of the metal oxide, and the method of using the above-described spheroidizing treatment can be used. Manufactured by a compression shear processing device.

The amount of the metal oxide is preferably 0.01 parts by mass to 10 parts by mass, more preferably 0.05 parts by mass to 2 parts by mass, per 100 parts by mass of the substantially spherical natural graphite (A1) or (A2).

The substantially spherical natural graphite (A) comprises natural graphite (A1) having a carbonaceous material attached to at least a part of its surface or natural graphite (A2) to which a graphite material is attached, and the carbonaceous material or the graphite material is In the case where the inside or the surface contains a metal oxide (this graphite material is referred to as natural graphite (A3)), it is rapidly charged. From the viewpoint of excellent electrical properties, the amount of natural graphite (A3) is preferably from 30% by mass to 100% by mass based on the total amount of (A).

Average spherical natural graphite (A1) to which a carbonaceous material adheres, approximate spherical natural graphite (A2) to which a graphite material adheres, and average grain size, average aspect ratio, and average crystal of natural graphite in which a metal oxide is embedded The lattice spacing d ₀₀₂ and the preferred range of the specific surface area are the same as those of the substantially spherical natural graphite (A) to which the carbonaceous material or the graphite material is not attached.

The substantially spherical natural graphite (A) may be used alone or in combination of two or more.

[(B) bulk mesophase graphitization]

The bulk mesophase graphitized material (B) used in the present invention is an artificial graphite particle dense inside the particles.

The average particle diameter (in terms of volume) of the bulk mesophase graphitized product (B) is 2 μm to 25 μm, particularly preferably 3 μm to 20 μm. When the average particle diameter is less than 2 μm, there is a case where the initial charge and discharge efficiency is lowered. When the average particle diameter exceeds 25 μm, in order to make the active material layer high in density, high pressure is required, and problems such as deformation, elongation, and fracture of the copper foil as a current collector are caused. In particular, in the case where the average particle diameter of the bulk mesophase graphitized product (B) is smaller than the average particle diameter of the spheroidized or ellipsoidal natural graphite (A), the active material layer can be made into a high density at a low pressure. Therefore, it is ideal.

The bulky mesophase graphitized material (B) has an average aspect ratio of less than 2.0, preferably less than 1.5, more preferably less than 1.3. The closer to the true spherical shape, the less the crystal structure of the bulk mesophase graphitized material (B) is aligned in one direction in the particle or on the negative electrode, and the higher the diffusivity of lithium ions in the electrolyte, the rapid charging Sexual, haste The discharge or cycle characteristics become good.

The bulk mesophase graphitized material (B) preferably has high crystallinity, and the average lattice spacing d _{002 is} less than 0.3370 nm, particularly preferably 0.3365 nm or less.

The discharge capacity when the bulk mesophase graphitized material (B) is used alone in the negative electrode active material of the secondary battery varies depending on the conditions of the negative electrode or the evaluation battery, but is 320 mAh/g or more, preferably 330 mAh/ g or more.

When the specific surface area of the bulk mesophase graphitized product (B) is too large, the initial charge and discharge efficiency of the secondary battery is lowered. Therefore, the specific surface area is preferably 20 m ² /g or less, more preferably 10 m ² /g or less. .

The bulk mesophase graphitized product (B) is preferably a bulk mesophase graphitized product obtained by heat-treating a tar oil and/or a pitch, and pulverizing, oxidizing, carbonizing, and graphitizing.

In order to make the aspect ratio of the bulk mesophase graphitized material (B) as close as possible to 1.0, that is, to approximate the shape of the true sphere, it is particularly preferable to use the mesophase calcined carbon obtained by heating the coal-based tar and/or pitch (block) A bulk intermediate phase graphitized product obtained by pulverizing, oxidizing, carbonizing, and graphitizing the raw phase. When the production method is exemplified, the coal tar and the pitch are heat-treated at 250 to 400 ° C to be polymerized, pulverized, and then heated in the air at 300 ° C to 500 ° C to oxidize the surface of the particles. Do not melt. Thereafter, carbonization is carried out at 500 ° C to 1300 ° C in an inert atmosphere, and then graphitization is carried out at 2500 ° C to 3300 ° C.

The crystal structure of the heat-treated bulk intermediate phase at a relatively low temperature is random, and is effective for reducing the aspect ratio after pulverization. In this state, since the meltability remains, the infusation treatment by oxidation is performed, and the heat treatment is performed in a stepwise manner to maintain the pulverized shape.

The amount of bulk mesophase graphitized by heat treatment of tar and asphalt, and pulverization, oxidation, carbonization, and graphitization can be set to 50% by mass to 100% of the total amount of bulk intermediate phase graphitized product (B). quality%.

In addition, it may be mixed, adhered, embedded, coated with metals, metal compounds, metal oxides, inorganic compounds, and resins in the raw material of the bulk mesophase graphitized product (B) or in the intermediate before the final heat treatment or after the final heat treatment. , carbon materials, fiber, graphite materials and other dissimilar components. Further, the intermediate treatment before the final heat treatment or the classification treatment for removing the fine particles after the final heat treatment or the granulation treatment for the purpose of the chamfering of the particle-pulverized surface or the low crystallization of the surface may be performed. In the sizing treatment, a mechanochemical treatment device capable of producing spheroidal or ellipsoidal natural graphite (A) imparting mechanical energy such as compression, shearing, collision, and friction can be used.

As one of preferred embodiments, a part or all of the bulk mesophase graphitized product (B) is a bulk intermediate phase graphitized material (B1) having a carbonaceous material attached to at least a part of its surface or attached thereto. Blocky mesophase graphitized (B2) of graphite material. The collapse of the bulk mesophase graphitized material (B) can be prevented by the adhesion of the carbonaceous material or the graphite material.

The carbonaceous materials that can be used are the same as described above. The amount of adhesion of the carbonaceous material is preferably from 0.1 part by mass to 10 parts by mass, particularly preferably from 0.5 part by mass to 5 parts by mass, per 100 parts by mass of the bulk mesophase graphitized product (B).

The graphite material that can be used is the same as described above. The amount of adhesion of the graphite material is preferably from 1 part by mass to 30 parts by mass, particularly preferably from 5 parts by mass to 20 parts by mass, per 100 parts by mass of the bulk mesophase graphitized product (B).

The method of attaching a carbonaceous material or a graphite material to a part or all of the bulk intermediate phase graphitized material (B) is the same as described above.

The bulk intermediate phase graphitized material (B) comprises a bulk intermediate phase graphitized material (B1) having a carbonaceous material attached to at least a part of its surface or a bulk intermediate phase graphitized material (B2) to which a graphite material is attached. In the case of increasing the density of the negative electrode, the shape of the bulk intermediate phase graphitized material (B) is maintained, that is, the initial charge and discharge efficiency is excellent, and (B) the total amount of (B1) and/or ( The amount of B2) is preferably from 30% by mass to 100% by mass.

The bulk mesophase graphitized material (B1) to which the carbonaceous material is attached or the bulky mesophase graphitized material (B2) to which the graphite material is attached may be carbon fiber or carbon in the interior or surface of the carbonaceous material or the graphite material. A bulk mesophase graphitized material of a conductive material such as black may also be a bulk intermediate phase in which metal oxides such as cerium oxide, alumina, and titania are attached or embedded (for example, in the form of fine particles). The graphitized material may also be a bulk intermediate phase graphitized metal or a metal compound such as ruthenium, tin, cobalt, nickel, copper, ruthenium oxide, tin oxide or lithium titanate.

It is particularly preferable that the carbonaceous material or the graphite material adhered to the bulk mesophase graphitized material (B) contains the above metal oxide (for example, fine particles which are made into a metal oxide) in the interior or surface thereof, more preferably The above metal oxide is buried. The embedding method is the same as described above.

The amount of the metal oxide is preferably 0.01 parts by mass to 10 parts by mass, more preferably 0.05 parts by mass to 2 parts by mass, per 100 parts by mass of the substantially spherical natural graphite (B1) or (B2).

The bulk intermediate phase graphitized material (B) comprises a bulk intermediate phase graphitized material (B1) having a carbonaceous material attached to at least a part of its surface or a bulk intermediate phase graphitized material (B2) to which a graphite material is attached, And carbonaceous or graphite materials When the inside or the surface contains a metal oxide (this graphite material is referred to as a bulk intermediate phase graphitized product (B3)), the bulky mesophase graphitized product (B3) is excellent in terms of rapid chargeability. The amount is preferably from 30% by mass to 100% by mass based on the total amount of (B).

The average grain size, average aspect ratio, and average crystal size of bulk intermediate phase graphitized (for example, (B1), (B2), (B3)) after adhering or embedding a carbonaceous material, a graphite material, a metal oxide, or the like The lattice spacing d ₀₀₂ and the preferred range of the specific surface area are the same as those of the bulk intermediate phase graphitized material (B) which is not attached or buried.

The bulk mesophase graphitized compounds (B) may be used alone or in combination of two or more.

[(C) scaly graphite]

The flaky graphite (C) used in the present invention is scaly artificial graphite or natural graphite. The flaky graphite (C) may be in a state in which a plurality of layers are laminated, but it is preferably in a state in which a single particle is dispersed. It may be in a state of being bent in the middle of the scale shape or a state in which the ends of the particles are rounded. The average particle diameter of the flaky graphite (C) must be smaller than the average particle diameter of the bulk intermediate phase graphitized product (B), and the volume-converted average particle diameter is 1 μm to 15 μm, particularly preferably 3 μm to 10 μm. When it is 1 μm or more, the reactivity of the electrolytic solution can be suppressed, and high initial charge and discharge efficiency can be obtained. Further, when it is 15 μm or less, the rapid discharge property or the cycle characteristics are improved. When the average particle diameter of the flaky graphite (C) is larger than the average particle diameter of the bulk intermediate phase graphitized product (B), when the active material layer is made higher in density, sufficient voids cannot be secured in the negative electrode, and lithium ions are not provided. The diffusibility is lowered to cause a rapid chargeability, a rapid discharge property, and a decrease in cycle characteristics.

The average aspect ratio of the flaky graphite (C) is 5.0 or more, preferably 20 the above. The more the flaky graphite having a large aspect ratio and a small thickness, the more the contact between the other graphites (A) and (B) is not hindered, the conductivity of the negative electrode including the respective graphites can be improved, and the rapid chargeability and cycle characteristics can be improved. . When the average aspect ratio is less than 5, in order to set the active material layer to a high density, high pressure is required, and problems such as deformation, elongation, and breakage of the copper foil as the current collector are caused.

The flaky graphite (C) has high crystallinity. Since it is high in crystallinity, it is soft and contributes to an increase in the density of the active material layer. The average lattice spacing d _{002 is} less than 0.3360 nm, and particularly preferably 0.3358 nm or less.

Further, since the flaky graphite (C) has high crystallinity, it exhibits a high discharge capacity in the case of a negative electrode active material used in a secondary battery. The discharge capacity when the scaly graphite (C) is used as the negative electrode material alone varies depending on the conditions of production of the negative electrode or the evaluation battery, but is about 350 mAh/g or more, preferably 360 mAh/g or more.

When the specific surface area of the flaky graphite (C) is too large, the initial charge and discharge efficiency of the secondary battery is lowered. Therefore, the specific surface area is preferably 20 m ² /g or less, more preferably 10 m ² /g or less.

The flaky graphite (C) is more preferably a part or all of flaky graphite (C1) having a carbonaceous material adhered to at least a part of its surface. The initial charge and discharge efficiency of the flaky graphite (C) can be improved by the adhesion of the carbonaceous material.

The carbonaceous material adhering to the flaky graphite (C1) is exemplified by the same carbonaceous material as the above-mentioned substantially spherical natural graphite (A1), and the amount of the carbonaceous material adhered to 100 parts by mass of the flaky graphite (C) is 0.1 parts by mass to 10 parts by mass, particularly preferably 0.5 parts by mass to 5 parts by mass.

As a part or all of the carbonaceous material attached to the flaky graphite (C) The method of the above part can be applied in the same manner as the method of heat-treating or coating the precursor of the carbonaceous material on the natural graphite (A) by any one of a gas phase method, a liquid phase method, and a solid phase method. Methods.

When the flaky graphite (C) contains scaly graphite (C1) having at least a part of the surface of the carbonaceous material adhered thereto, even if the density of the negative electrode is increased, the shape of the flaky graphite (C) is maintained, that is, From the viewpoint of excellent initial charge and discharge efficiency, the amount of (C1) in the total amount of (C) is preferably from 30% by mass to 100% by mass.

The flaky graphite (C) or the flaky graphite (C1) to which the carbonaceous material is attached may be scaly graphite containing a conductive material such as carbon fiber or carbon black on the surface or the carbonaceous material, or may be attached or embedded. Flaky graphite of fine particles of metal oxides such as cerium oxide, alumina, and titania, or may be attached or embedded with bismuth, tin, cobalt, nickel, copper, cerium oxide, tin oxide, or titanium. A flaky graphite of a metal or a metal compound such as lithium acid.

It is particularly preferable to embed the fine particles of the above metal oxide.

It is preferable that the carbonaceous material adhering to the flaky graphite (C) contains the above-mentioned metal oxide (for example, fine particles which are made into a metal oxide) in the inside or the surface thereof, and a more preferred embodiment is exemplified. The above metal oxide.

The embedding method can be exemplified by a method in which a mechanical external force is applied to the flaky graphite (C) or the flaky graphite (C1) to which the carbonaceous material is adhered in the coexistence of the fine particles of the metal oxide, and the ball can be used by using the following. It is manufactured by a compression shear type processing apparatus in the apparatus.

The amount of the metal oxide in this case is preferably 0.01 parts by mass to 10 parts by mass, more preferably 0.01 parts by mass to 10 parts by mass, per 100 parts by mass of the flaky graphite (C) or the flaky graphite (C1) to which the carbonaceous material is adhered. 0.05 parts by mass to 2 parts by mass.

The flaky graphite (C) contains scaly graphite (C1) having a carbonaceous material attached to at least a part of its surface, and the carbonaceous material contains a metal oxide in its interior or surface (this graphite material is called a scale) In the case of the graphite (C3), the amount of the flaky graphite (C3) is preferably 30% by mass to 100% by mass based on the total amount of (C).

An average particle diameter, an average aspect ratio, an average lattice spacing d ₀₀₂ of scaly graphite (for example, (C1), (C3)) after adhering or embedding a carbonaceous material, a graphite material, a metal oxide, or the like, and The preferred range of the specific surface area is the same as that of the flaky graphite (C) which is not attached or buried.

The flaky graphite (C) may be used alone or in combination of two or more.

[Anode material for lithium ion secondary battery]

The negative electrode material for a lithium ion secondary battery of the present invention (hereinafter, only referred to as a negative electrode material) substantially satisfies the specific ratios of the following formulas (1) and (2), and includes the above (A), (B), and (C). 3 components: a: b = (60 ~ 95): (40 ~ 5) (1)

(a+b): c=(85 or more ~ less than 100): (15 or less ~ more than 0) (2)

Here, a, b, and c represent the masses of the respective components (A), (B), and (C). The value exceeding 0 is expressed as a value exceeding 0.

When a:b is less than 60: more than 40, since the relatively hard bulk intermediate phase graphitized material (B) is excessive, high pressure is required in order to set the active material layer to a high density, and it may occur as a set. Problems such as deformation, elongation, and breakage of the copper foil of the electric body.

On the other hand, when a:b is more than 95: less than 5, the effect of preventing the alignment of the graphite using the bulk mesophase graphitized product (B) is small, and it is occupied by the active material. The spheroidized or ellipsoidal natural graphite (A) becomes excessive, and the graphite collapses with high density, and the graphite is aligned in one direction. Therefore, the ion diffusibility of lithium ions is lowered, resulting in a decrease in rapid chargeability, rapid discharge performance, and cycle characteristics. Further, the surface of the active material layer is easily clogged, the permeability of the electrolytic solution is lowered, and the productivity of the secondary battery is lowered, and the electrolyte solution is depleted inside the active material layer, or the charge expansion is increased to prevent the graphite particles from being retained. The contact is therefore reduced in cycle characteristics.

The value of a:b is preferably a:b=(70~92): (30~8), and further preferably a:b=(75~91): (25~9), and the best is a:b = (80~90): (20~10).

When (a+b):c is less than 85: more than 15, the flaky graphite (C) is excessive, the voids between the graphite particles in the negative electrode layer become small, or the flaky graphite (C) is aligned in one direction. Thereby, the ion diffusibility of lithium ions is lowered, resulting in a decrease in rapid discharge properties and cycle characteristics.

(a+b): The value of c is preferably (a+b): c=(87~99): (13~1), and further preferably (a+b): c=(93~98): (7~2).

In the negative electrode material of the present invention, a known active material or a conductive material other than the above (A), (B) and (C) may be mixed as long as the effects of the present invention are not impaired. For example, carbide particles such as soft carbon and hard carbon obtained by heat-treating the carbonaceous material precursor at 500 ° C to 1500 ° C, carbon blacks such as ketjenblack and acetylene black, and vapor phase growth Conductive materials such as carbon fibers, nano carbon fibers, and carbon nanotubes, and metal or semimetal particles such as antimony, tin, or oxides formed of lithium.

The negative electrode material of the present invention comprising the three components of the above (A), (B) and (C) The discharge capacity varies depending on the conditions of the negative electrode or the evaluation battery, but is about 355 mAh/g or more, preferably 360 mAh/g or more.

[Negative Electrode for Lithium Ion Secondary Battery]

The production of the negative electrode for a lithium ion secondary battery of the present invention (hereinafter, simply referred to as a negative electrode) can be carried out according to a method for producing a normal negative electrode, and a method for producing a negative electrode which is chemically and electrochemically stable can be used. There are no restrictions.

In the production of the negative electrode, a negative electrode mixture to which a binder is added to the above negative electrode material can be used. The binder is preferably a binder having chemical stability and electro-chemical stability to the electrolyte. For example, a fluorine-based resin such as polyvinylidene fluoride or polytetrafluoroethylene, polyethylene, polyvinyl alcohol or styrene may be used. Ene rubber, carboxymethyl cellulose, and the like. These binders can also be used in combination. The binder is usually preferably in a ratio of from 1% by mass to 20% by mass based on the total amount of the negative electrode mixture.

In the production of the negative electrode, N-methylpyrrolidone, dimethylformamide, water, alcohol, or the like which is a usual solvent for producing a negative electrode can be used.

The negative electrode can be prepared, for example, by dispersing a negative electrode mixture in a solvent to prepare a paste-form negative electrode mixture, and then applying the negative electrode mixture to one surface or both surfaces of the current collector and drying the mixture. Thereby, a negative electrode in which the negative electrode mixture layer (active material layer) is uniformly and firmly adhered to the current collector can be obtained.

More specifically, for example, a slurry of the above negative electrode material, a fluorine resin powder or a water dispersant of styrene butadiene rubber is mixed with a solvent to prepare a slurry, and a known mixer, mixer, or kneader is used. The kneading machine or the like is stirred and mixed to prepare a negative electrode mixture paste. When it is applied to a current collector and dried, the negative electrode mixture layer is uniformly and firmly adhered to the current collector. The film thickness of the negative electrode mixture layer is from 10 μm to 200 μm, preferably from 30 μm to 100 μm.

Further, the negative electrode mixture layer may be produced by dry-mixing particles of the above negative electrode material with a resin powder such as polyethylene or polyvinyl alcohol, and performing hot press forming in a mold. However, in dry mixing, a large amount of binder is required in order to obtain a sufficient strength of the negative electrode, and in the case where the binder is too large, the discharge capacity or the rapid charge and discharge efficiency may be lowered.

When the negative electrode mixture layer is formed and pressure-bonded by pressing or the like, the adhesion strength between the negative electrode mixture layer and the current collector can be further improved.

The density of the negative electrode mixture layer is preferably 1.70 g/cm ³ or more, particularly preferably 1.75 g/cm ³ or more, from the viewpoint of increasing the volume capacitance of the negative electrode.

The shape of the current collector used for the negative electrode is not particularly limited, and is preferably a mesh such as a foil, a mesh, or an expand metal. The material of the current collector is preferably copper, stainless steel, nickel or the like. In the case of a foil, the thickness of the current collector is preferably 5 μm to 20 μm.

[Orientation of the negative electrode]

Although the negative electrode material of the present invention has a high density, the collapse or alignment of graphite is suppressed. The degree of alignment of the negative electrode can be quantitatively evaluated by X-ray diffraction, and the measurement method will be described below.

The negative electrode whose density of the negative electrode mixture layer was adjusted to 1.70 g/cm ³ to 1.75 g/cm ³ was punched out into a disk shape of 2 cm ² , and was attached to the glass plate with the negative electrode mixture layer facing upward. When the sample is irradiated with X-rays to be diffracted, a diffraction peak corresponding to the crystal plane of the graphite appears. Among the plurality of diffraction peaks, the peak intensity I004 in the vicinity of 2θ=54.6° from the (004) plane and the ratio I004/I110 from the peak intensity I110 in the vicinity of 2θ=77.4° from the (110) plane can be set as the alignment. Indicator of degree. The lower the degree of alignment of the negative electrode, the smaller the expansion ratio of the negative electrode during charging, the better the permeability and fluidity of the electrolytic solution, and the rapid chargeability, rapid discharge performance, and cycle characteristics of the lithium ion secondary battery. good.

When the density of the negative electrode mixture layer is 1.70 g/cm ³ to 1.75 g/cm ³ , the refractive index (I004/I110) of the negative electrode of the present invention is 20 or less, preferably 15 or less, and more preferably 12 or less.

[Lithium ion secondary battery]

The lithium ion secondary battery of the present invention is formed using the above negative electrode.

The secondary battery of the present invention is not particularly limited, except for the use of the above-described negative electrode, and other battery constituent elements are in accordance with elements of a general secondary battery. That is, the electrolytic solution, the negative electrode, and the positive electrode are main battery constituent elements, and these elements are enclosed, for example, in a battery can. Further, the negative electrode and the positive electrode each function as a carrier of lithium ions, and lithium ions are detached from the negative electrode during charging.

[positive electrode]

The positive electrode used in the secondary battery of the present invention is formed, for example, by applying a positive electrode mixture containing a positive electrode material, a binder, and a conductive material to the surface of the current collector. As the material of the positive electrode (positive electrode active material), a lithium compound can be used, and a compound which can occlude/desorb a sufficient amount of lithium is preferably selected. For example, a lithium-containing transition metal oxide, a transition metal sulfur compound, a vanadium oxide, another lithium compound, or a chemical formula M _X Mo ₆ OS _8-Y (wherein X is a value in the range of 0≦X≦4, Y is a numerical value in the range of 0 ≦ Y ≦ 1, and M is a Chevrel phase compound represented by at least one transition metal element, activated carbon, activated carbon fiber, or the like. The vanadium oxide is V ₂ O ₅ , V ₆ O ₁₃ , V ₂ O ₄ , V ₃ O ₈ or the like.

The lithium-containing transition metal composite oxide is a composite oxide of lithium and a transition metal, and may be a composite oxide in which lithium and two or more transition metals are dissolved. The composite oxide may be used singly or in combination of two or more. Specifically, the lithium-containing transition metal oxide is LiM ¹ _1-X M ² _X O ₂ (wherein, X is a value in the range of 0≦X≦1, and M ¹ and M ² are at least one transition metal. Element) or LiM ¹ _1-Y M ² _Y O ₂ (wherein Y is a value in the range of 0≦Y≦1, and M ¹ and M ² are at least one transition metal element).

The transition metal elements represented by M ¹ and M ² are Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn, etc., preferably Co, Mn, Cr, Ti, V, Fe, Al, etc. Preferred specific examples are LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _0.9 Co _0.1 O ₂ , LiNi _0.5 Co _0.5 O ₂ and the like.

The lithium-containing transition metal oxide can be mixed, for example, by using lithium, a transition metal oxide, a hydroxide, a salt or the like as a starting material, and mixing the starting materials according to the composition of the desired metal oxide in an oxygen environment. It is obtained by calcination at a temperature of 600 ° C to 1000 ° C.

As the positive electrode active material, the above lithium compounds may be used singly or in combination of two or more kinds. Further, an alkali carbonate such as lithium carbonate may be added to the positive electrode.

For the positive electrode, for example, a positive electrode mixture containing the above-described lithium compound, a binder, and a conductive material for imparting conductivity to the positive electrode can be applied to one surface or both surfaces of the current collector to form a positive electrode mixture layer. As the binder, the same binder as that used in the production of the negative electrode can be used. As the conductive material, a carbon material such as graphite or carbon black can be used.

Similarly to the negative electrode, the positive electrode mixture may be dispersed in a solvent, and the positive electrode mixture formed into a paste may be applied onto a current collector and dried to form a positive electrode mixture layer, or after the positive electrode mixture layer is formed. Further, pressure bonding such as pressurization or the like is performed. Thereby, the positive electrode mixture layer can be uniformly and firmly attached to the current collector.

The shape of the current collector is not particularly limited, and is preferably a foil shape, a mesh shape, or an expansion gold. A network of genus. The material of the current collector is aluminum, stainless steel, nickel, and the like. In the case of a foil, the thickness is preferably from 10 μm to 40 μm.

[non-aqueous electrolyte]

The nonaqueous electrolyte (electrolyte) used in the secondary battery of the present invention is an electrolyte salt used in a usual nonaqueous electrolytic solution. As the electrolyte salt, for example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB(C ₆ H ₅ ) ₄ , LiCl, LiBr, LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiC can be used. (CF ₃ SO ₂ ) ₃ , LiN(CF ₃ CH ₂ OSO ₂ ) ₂ , LiN(CF ₃ CF ₂ OSO ₂ ) ₂ , LiN(HCF ₂ CF ₂ CH ₂ OSO ₂ ) ₂ , LiN[(CF ₃ ) ₂ a lithium salt such as CHOSO ₂ ] ₂ , LiB[C ₆ H ₃ (CF ₃ ) ₂ ] ₄ , LiAlCl ₄ or LiSiF ₅ . In terms of oxidative stability, LiPF ₆ and LiBF _{4 are} particularly preferred.

The electrolyte salt concentration of the electrolyte is preferably from 0.1 mol/L to 5 mol/L, more preferably from 0.5 mol/L to 3 mol/L.

The nonaqueous electrolyte may be in the form of a liquid, or may be a polymer electrolyte such as a solid or a gel. In the case of the former, the nonaqueous electrolyte battery is a so-called lithium ion secondary battery, and in the latter case, the nonaqueous electrolyte battery is configured as a polymer electrolyte battery such as a polymer solid electrolyte battery or a polymer gel electrolyte battery.

As the solvent constituting the nonaqueous electrolyte liquid, a carbonate such as ethylene carbonate, propylene carbonate, dimethyl carbonate or diethyl carbonate, 1,1- or 1,2-dimethoxyethane, 1, may be used. 2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3- An ether such as dioxolane, anisole or diethyl ether; a thioether such as cyclobutyl hydrazine or methylcyclobutyl hydrazine; a nitrile such as acetonitrile, chloronitrile or propionitrile; trimethyl borate or tetramethyl citrate; Nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene, benzamidine chloride, benzamidine bromide, tetrahydrothiophene, two Methyl hydrazine, 3-methyl-2-oxazolidinone, ethylene An aprotic organic solvent such as an alcohol or dimethyl sulfate.

In the case of using the above polymer electrolyte, it is preferred to use a polymer compound gelled by a plasticizer (nonaqueous electrolyte) as a matrix. The polymer compound constituting the matrix may be used singly or in combination with an ether polymer compound such as polyethylene oxide or a crosslinked product thereof, a polymethacrylate polymer compound, a polyacrylate polymer compound, or polyvinylidene fluoride. Or a fluorine-based polymer compound such as a vinylidene fluoride-hexafluoropropylene copolymer. It is particularly preferable to use a fluorine-based polymer compound such as polyvinylidene fluoride or a vinylidene fluoride-hexafluoropropylene copolymer.

A plasticizer is blended in the above polymer solid electrolyte or polymer gel electrolyte, and the above electrolyte salt or nonaqueous solvent can be used as the plasticizer. In the case of a polymer gel electrolyte, the electrolyte salt concentration in the nonaqueous electrolyte as a plasticizer is preferably from 0.1 mol/L to 5 mol/L, more preferably from 0.5 mol/L to 2 mol/L.

The method for producing the polymer solid electrolyte is not particularly limited, and examples thereof include a method in which a polymer compound constituting a matrix, a lithium salt, and a nonaqueous solvent (plasticizer) are mixed and heated to melt the polymer compound. a method in which a polymer compound, a lithium salt, and a nonaqueous solvent (plasticizer) are dissolved in an organic solvent for mixing, followed by evaporation of an organic solvent for mixing; a polymerizable monomer, a lithium salt, and a nonaqueous solvent (plastic) The compound is mixed, and the mixture is irradiated with an ultraviolet ray, an electron beam, a molecular beam or the like to polymerize the polymerizable monomer to obtain a polymer compound.

The ratio of the nonaqueous solvent (plasticizer) in the polymer solid electrolyte is preferably 10% by mass to 90% by mass, more preferably 30% by mass to 80% by mass. When it is less than 10% by mass, the electrical conductivity is lowered, and when it exceeds 90% by mass, the mechanical strength is weak, and it is difficult to form a film.

In the lithium ion secondary battery of the present invention, a separator can also be used.

The material of the separator is not particularly limited, and examples thereof include a woven fabric, a non-woven fabric, and a microporous film made of a synthetic resin. A microporous film made of a synthetic resin is preferable, and the polyolefin-based microporous film is preferable in terms of thickness, film strength, and film resistance. Specifically, it is a microporous film made of polyethylene or polypropylene, or a microporous film obtained by combining these films.

The secondary battery of the present invention can be produced by laminating the above-mentioned negative electrode, positive electrode, and nonaqueous electrolyte in the order of, for example, a negative electrode, a nonaqueous electrolyte, and a positive electrode, and accommodating them in an exterior material of a battery.

Further, a nonaqueous electrolyte may be disposed outside the negative electrode and the positive electrode.

The structure of the secondary battery of the present invention is not particularly limited, and the shape and shape thereof are not particularly limited, and may be from a cylindrical type, an angle type, a coin type, or a button depending on the application, the mounting equipment, and the required charge and discharge capacitance. Any type is selected. In order to obtain a sealed non-aqueous electrolyte battery having higher safety, it is preferable to include an element that senses an increase in internal pressure of the battery and blocks a current when an abnormality such as excessive charging occurs.

In the case of a polymer electrolyte battery, a structure in which a laminated film is sealed may be used.

[Examples]

Hereinafter, the present invention will be specifically described by way of examples, but the invention is not limited to the examples.

In the examples and the comparative examples, evaluation button-type secondary batteries having the configuration shown in FIG. 1 were produced and evaluated. The battery can be fabricated in accordance with the purpose of the present invention in accordance with known methods.

(Example 1)

[Modulation of spheroidized or ellipsoidal natural graphite (A)]

Natural graphite particles having a spherical shape to an ellipsoid shape (having an average aspect ratio of 1.4, an average particle diameter of 18 μm, an average lattice spacing d ₀₀₂ 0.3356 nm, and a specific surface area of 5.0 m ² /g) were prepared.

[Modulation of bulk mesophase graphitized material (B)]

In an inert environment, the coal tar pitch is heated to 400 ° C for 12 hours for heat treatment, and then naturally cooled to normal temperature in an inert environment. The obtained bulky mesophase was pulverized and shaped into a block having an average aspect ratio of 1.6 and an average particle diameter of 15 μm. Then, the surface was oxidized in air at 280 ° C for 15 minutes to oxidize the surface, and after infusibilization treatment, it was subjected to graphitization in a non-oxidizing atmosphere at 900 ° C for 6 hours and at 3000 ° C for 5 hours. A bulky mesophase graphitized product (B) is prepared.

The particle shape of the obtained bulk mesophase graphitized product (B) maintains the shape at the time of pulverization. The average lattice spacing d ₀₀₂ is 0.3362 nm and the specific surface area is 1.0 m ² /g.

[Modulation of flaky graphite (C)]

The natural graphite was pulverized and adjusted to have an average particle diameter of 5 μm, an average aspect ratio of 20, d ₀₀₂ of 0.3357 nm, and a specific surface area of 9.5 m ² /g.

[Modulation of Anode Material]

75 parts by mass of the spheroidized or ellipsoidal natural graphite (A), 20 parts by mass of the bulk intermediate phase graphitized product (B), and 5 parts by mass of the flaky graphite (C) were mixed to prepare a negative electrode material.

[Preparation of negative electrode mixture]

98 parts by mass of the above negative electrode material, 1 part by mass of the binder carboxymethylcellulose, and 1 part by mass of the styrene butadiene rubber were added to water, and the mixture was stirred to prepare a negative electrode mixture paste.

[Production of working electrode]

The negative electrode mixture paste was applied to a copper foil having a thickness of 16 μm in a uniform thickness, and the water in the dispersion medium was evaporated at 90 ° C in a vacuum to be dried. Then, the negative electrode mixture applied to the copper foil was pressed by hand pressure at 12 kN/cm ² (120 MPa), and then punched into a circular shape having a diameter of 15.5 mm, thereby producing a film containing the copper foil. A working electrode of a negative electrode mixture layer (thickness 60 μm). The density of the negative electrode mixture layer was 1.75 g/cm ³ . There is no extension or deformation in the working electrode, and there is no depression in the current collector observed from the cross section.

[production of the pole]

The lithium metal foil was pressed against a nickel mesh, and punched into a circular shape having a diameter of 15.5 mm to prepare a current collector including a nickel mesh, and a counter electrode including a lithium metal foil (thickness: 0.5 mm) in close contact with the current collector ( positive electrode).

[electrolyte. Diaphragm]

LiPF _{6 was} dissolved in a mixed solvent of 33 vol% of ethylene carbonate-methyl ethyl carbonate of 67 vol% at a concentration of 1 mol/L to prepare a nonaqueous electrolytic solution. The obtained nonaqueous electrolytic solution was impregnated into a porous polypropylene body (thickness: 20 μm) to prepare a separator impregnated with an electrolytic solution.

[Evaluation of battery production]

A coin-type secondary battery shown in Fig. 1 was produced as an evaluation battery.

The outer cover 1 and the outer can 3 are interposed with an insulating spacer 6 at a peripheral portion thereof, and the two peripheral portions are caulked and sealed. In the battery, a current collector 7a including a nickel mesh, a cylindrical counter electrode (positive electrode) 4 containing a lithium foil, and a separator 5 impregnated with an electrolyte are sequentially stacked from the inner surface of the outer can 3, including A disk-shaped working electrode (negative electrode) 2 of a negative electrode mixture and a current collector 7b containing a copper foil.

The evaluation battery was produced by sandwiching the separator 5 impregnated with the electrolytic solution between the working electrode 2 in close contact with the current collector 7b and the counter electrode 4 in close contact with the current collector 7a. After laminating, the working electrode 2 is housed in the exterior cover 1, the counter electrode 4 is housed in the outer can 3, and the outer cover 1 and the outer can 3 are joined, and the outer cover 1 and the outer cover are further The insulating pad 6 is interposed in the peripheral portion of the can 3, and the both peripheral portions are caulked and sealed.

In the solid battery, the evaluation battery is a battery including a working electrode 2 containing graphite particles which can be used as a negative electrode active material, and a counter electrode 4 including a lithium metal foil.

The evaluation battery fabricated as described above was subjected to a charge and discharge test as described below at a temperature of 25 ° C, and the discharge capacity per unit mass, the discharge capacity per unit volume, the initial charge and discharge efficiency, the rapid charge rate, the rapid discharge rate, and Cycle characteristics. The evaluation results are shown in Table 1.

[Discharge capacitance per unit mass, discharge capacitance per unit volume]

After constant current charging of 0.9 mA is reached until the circuit voltage reaches 0 mV, it is switched to constant voltage charging, and charging is continued until the current value becomes 20 μA. The charging capacitance per unit mass is obtained from the amount of energization therebetween. Thereafter, pause for 120 minutes. Then, constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 1.5 V, and a discharge capacitance per unit mass was obtained from the amount of energization therebetween. Set this to the first loop. The initial charge and discharge efficiency is calculated from the charge capacitance and the discharge capacitance in the first cycle by the following equation.

Initial charge and discharge efficiency (%) = (discharge capacitor / charge capacitor) × 100

Further, in this test, the process of occluding lithium ions on the negative electrode material was set as charging, and the process of detaching from the negative electrode material was set as discharge.

[rapid charge rate]

After the first cycle, rapid charging is performed in the second cycle.

The current value is set to 4.5 mA five times that of the first cycle, and constant current charging is performed until the circuit voltage reaches 0 mV, and a constant current charging capacitance is obtained. Calculate the rapid charging rate.

Rapid charging rate (%) = (constant current charging capacitor in the second cycle / discharge capacitance in the first cycle) × 100

[rapid discharge rate]

Another evaluation battery was used, and after the first cycle, rapid discharge was performed in the second cycle. Similarly to the above, after the first cycle, the battery was charged in the same manner as in the first cycle, and then the current value was set to 18 mA which was 20 times that of the first cycle, and constant current discharge was performed until the circuit voltage reached 1.5 V. The discharge capacity per unit mass was obtained from the amount of energization therebetween, and the rapid discharge rate was calculated by the following formula.

Rapid discharge rate (%) = (discharge capacitance in the second cycle / discharge capacitance in the first cycle) × 100

[Circulation characteristics]

An evaluation battery which is different from the battery for evaluating the discharge capacity, the rapid charge rate, and the rapid discharge rate of the unit mass was produced and evaluated as follows.

After constant current charging of 4.0 mA is reached until the circuit voltage reaches 0 mV, it is switched to constant voltage charging, and charging is continued until the current value becomes 20 μA, and then paused for 120 minutes. Then, constant current discharge is performed at a current value of 4.0 mA until the circuit voltage reaches 1.5 V. The charging and discharging were repeated 50 times, and the cycle characteristics were calculated from the obtained discharge capacitance per unit mass using the following formula.

Cycle characteristics (%) = (discharge capacitance in the 50th cycle / discharge capacitance in the 1st cycle) × 100

[Orientation]

X-ray diffraction analysis was performed on the same electrode as the working electrode supplied to the evaluation battery, and the peak intensity I004 from the (004) plane at 2θ=54.6° was derived from (110) The ratio I004/I110 of the peak intensity I110 in the vicinity of 2θ=77.4° of the surface was measured as the degree of alignment.

[Table 1]

[Production of working electrode]

As shown in Table 1, the evaluation battery obtained by using the negative electrode material of Example 1 in the working electrode can increase the density of the active material layer and exhibit a high discharge capacitance per unit mass. Therefore, the discharge capacity per unit volume can be greatly increased. That is, at this high density, the rapid charging rate, the rapid discharge rate, and the cycle characteristics are also excellent.

(Example 2)

[Preparation of spheroidized or ellipsoidal natural graphite (A1-1) with carbonaceous material attached]

To 100 parts by mass of the spheroidized or ellipsoidal natural graphite (A) used in Example 1, 3 parts by mass of pitch powder (average particle diameter 2 μm) having a softening point of 120 ° C and Ketjen black (average particle diameter) 30 nm) 0.1 mass part was placed in the "Mechano Fusion System", and the compressive force and the shearing force were repeatedly applied under the conditions of a peripheral speed of 20 m/s and a treatment time of 30 minutes, and mechanochemical treatment was performed. The obtained sample was filled in a graphite crucible, and calcined at 1000 ° C for 3 hours in a non-oxidizing atmosphere. The spheroidized or ellipsoidal natural graphite obtained has a carbide attached to a large portion of its surface.

[Preparation of scaly graphite (C1) with carbonaceous material attached]

With respect to the flaky graphite (C) used in Example 1, a carbonaceous material was also attached under the same conditions as described above. It was confirmed that most of the surface of the obtained flaky graphite adhered to the film in the form of carbide.

In the first embodiment, the spheroidized or ellipsoidal natural graphite (A) and the scaly graphite (C) are changed to these (A1-1) and (C1), and the examples and examples are given. In the same manner, the density of the negative electrode mixture layer was adjusted to 1.75 g/cm ^{3 in the} same manner to prepare a working electrode, thereby producing an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

(Examples 3 to 5)

In the second embodiment, as shown in Table 1, the spheroidized or ellipsoidal natural graphite (A1-1) to which the carbonaceous material adhered, the bulk mesophase graphitized material (B), and the carbonaceous material adhered thereto were changed. In addition, the density of the negative electrode mixture layer was adjusted to 1.75 g/cm ^{3 in the} same manner as in Example 2 except that the mass ratio of the flaky graphite (C1) was adjusted to prepare a working electrode, thereby producing an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

When the working electrode is formed by the negative electrode material having the mass ratio specified in the present invention, the density of the negative electrode mixture layer can be increased, and any of the discharge capacity, the initial charge and discharge efficiency, the rapid charge rate, the rapid discharge rate, and the cycle characteristics can be improved. Both are excellent.

(Comparative Example 1)

The density of the negative electrode mixture layer was adjusted to 1.75 g/cm in the same manner as in Example 1 except that the spheroidized or ellipsoidal natural graphite (A) used in Example 1 was separately prepared into a negative electrode material. ³ , a working electrode was fabricated to produce an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

(Comparative Example 2)

The negative electrode mixture layer was formed in the same manner as in Example 1 except that the spheroidized or ellipsoidal natural graphite (A1-1) to which the carbonaceous material was used in Example 2 was separately used as the negative electrode material. The working electrode was fabricated by adjusting the density to 1.75 g/cm ³ to prepare an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

As shown in Table 1, the spheroidized or ellipsoidal natural graphite is used alone. (A) When the spheroidized or ellipsoidal natural graphite (A1-1) having a carbonaceous material adhered thereto is used as a negative electrode material, the rapid charging rate, the rapid discharge rate, and the cycle characteristics are insufficient.

(Comparative Example 3)

The density of the negative electrode mixture layer was adjusted to 1.75 g/cm ^{3 in the} same manner as in Example 1 except that the bulk mesophase graphitized material (B) used in Example 1 was separately made into a negative electrode material. Electrodes, thereby making an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

As shown in Table 1, in the case where the bulk mesophase graphitized product (B) is used alone as the negative electrode material, a high pressing pressure is required when the density of the negative electrode mixture layer is adjusted to 1.75 g/cm ³ as a current collector. The copper foil extends and a part of the active material layer is peeled off. When the charge and discharge test was performed on the non-peeling portion, the discharge capacity, the initial charge and discharge efficiency, the rapid charge rate, and the cycle characteristics were insufficient.

(Comparative Example 4)

A working electrode was prepared by adjusting the density of the negative electrode mixture layer to 1.75 g/cm ^{3 in the} same manner as in Example 1 except that the flaky graphite (C) used in Example 1 was separately made into a negative electrode material. Make an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

(Comparative Example 5)

The density of the negative electrode mixture layer was adjusted to 1.75 g/cm ^{3 in the} same manner as in Example 1 except that the carbonaceous material-attached flaky graphite (C1) used in Example 2 was separately made into a negative electrode material. A working electrode was fabricated to produce an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

As shown in Table 1, when flaky graphite (C) or flaky graphite (C1) having a carbonaceous material adhered thereto, initial charge and discharge efficiency, rapid charge rate, rapid discharge rate, and cycle characteristics are insufficient. .

(Comparative Example 6 to Comparative Example 9)

In the second embodiment, as shown in Table 1, the spheroidized or ellipsoidal natural graphite (A1-1) to which the carbonaceous material adhered, the bulk mesophase graphitized material (B), and the carbonaceous material adhered thereto were changed. In addition, the density of the negative electrode mixture layer was adjusted to 1.75 g/cm ^{3 in the} same manner as in Example 2 except that the mass ratio of the flaky graphite (C1) was adjusted to prepare a working electrode, thereby producing an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

When the working electrode is formed by a negative electrode material which deviates from the mass ratio specified in the present invention, any of the discharge capacity, the initial charge and discharge efficiency, the rapid charge rate, the rapid discharge rate, and the cycle characteristics are insufficient.

(Example 6)

[Modulation of spheroidized or ellipsoidal natural graphite (A2-1) with graphite material attached]

In 100 parts by mass of the spheroidized or ellipsoidal natural graphite (A) used in Example 1, 25 parts by mass of pitch powder (average particle diameter: 2 μm) having a softening point of 120 ° C was mixed and put into "Mechano Fusion System". In the middle, the compression force and the shearing force were repeatedly applied under the conditions of a peripheral speed of 20 m/s and a treatment time of 30 minutes, and mechanochemical treatment was performed. The obtained sample was filled in a graphite crucible, and calcined at 1000 ° C for 3 hours in a non-oxidizing atmosphere. Then, in a non-oxidizing atmosphere, graphitization was carried out at 3000 ° C for 5 hours to prepare spheroidized or ellipsoidal natural graphite (A2-1) to which a graphite material adhered. Spheroidized or elliptical Most of the body-formed natural graphite has a graphitized film attached to the surface thereof.

The obtained spheroidized or ellipsoidal natural graphite (A2-1) to which the graphite material was attached had an average particle diameter of 19 μm, an average lattice spacing d ₀₀₂ of 0.3357 nm, and a specific surface area of 1.2 m ² / g.

In the same manner as in the second embodiment, the spheroidized or ellipsoidal natural graphite (A1-1) to which the carbonaceous material is adhered is changed to (A2-1) in the second embodiment. The density of the negative electrode mixture layer was adjusted to 1.75 g/cm ³ to prepare a working electrode, thereby producing an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

(Example 7)

[Modulation of spheroidized or ellipsoidal natural graphite (A3) in which metal oxide fine particles are embedded]

In 100 parts by mass of the carbonaceous spheroidized or ellipsoidal natural graphite (A1-1) to be used in Example 2, 0.5 parts by mass of cerium oxide powder (average particle diameter: 50 nm) was mixed and put into " In the Mechano Fusion System, the compression force and the shearing force were repeatedly applied under the conditions of a peripheral speed of 20 m/s and a treatment time of 30 minutes, and mechanochemical treatment was performed. The obtained spheroidized or ellipsoidal natural graphite (A3) is uniformly embedded with cerium oxide powder on the film of the carbide on the surface.

[Modulation of scaly graphite (C1') in which metal oxide fine particles are embedded]

The carbon dioxide-containing flaky graphite (C1) used in Example 2 was also embedded with cerium oxide powder under the same conditions as above. The obtained flaky graphite (C1') is uniformly embedded with cerium oxide powder on the film of the carbide on the surface.

In the second embodiment, the carbonaceous spheroidized or ellipsoidal natural graphite (A1-1) and the carbonaceous flaky graphite (C1) are changed to these (A3) and (C1). In the same manner as in Example 2, the density of the negative electrode mixture layer was adjusted to 1.75 g/cm ³ to prepare a working electrode, thereby producing an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

(Examples 8 to 9)

In the seventh embodiment, as shown in Table 1, the combination of (A1-1) or (A3), the bulk mesophase graphitized product (B), and (C1) or (C1') is changed, and In the same manner as in Example 7, the density of the negative electrode mixture layer was adjusted to 1.75 g/cm ³ to prepare a working electrode, thereby producing an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

(Examples 10 to 13)

In the seventh embodiment, as shown in Table 1, the spheroidized or ellipsoidal natural graphite (A3) in which the metal oxide fine particles are embedded, the bulk intermediate phase graphitized material (B), and/or the buried metal oxide are changed. A working electrode was produced by adjusting the density of the negative electrode mixture layer to 1.75 g/cm ^{3 in the} same manner as in Example 7 except that the average particle diameter of the flaky graphite (C1') of the fine particles was adjusted to prepare an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

When the working electrode is formed by the negative electrode material having the average particle size range specified by the present invention, the density of the negative electrode mixture layer can be increased, and the discharge capacity, initial charge and discharge efficiency, rapid charge rate, rapid discharge rate, and cycle characteristics can be improved. Any of them is excellent.

(Comparative Example 10 to Comparative Example 12)

In the same manner as in Example 7, except that the average particle diameter of (A3) and the bulk intermediate phase graphitized compounds (B) and (C1') was changed as shown in Table 1, the negative electrode was used in the same manner as in Example 7. The density of the mixture layer was adjusted to 1.75 g/cm ³ to prepare a working electrode, thereby producing an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

When the working electrode is formed by a negative electrode material deviating from the average particle diameter range defined by the present invention, any of the discharge capacity, the initial charge and discharge efficiency, the rapid charge rate, the rapid discharge rate, and the cycle characteristics are insufficient.

(Comparative Example 13)

In Example 2, the following non-granulated graphite having a small average aspect ratio was used in place of the flaky graphite (C1).

The coal tar pitch was heat-treated at 450 ° C for 90 minutes in an inert environment to form 35 mass % of mesophase small spheres in the asphalt matrix. Thereafter, oil in tar was used, and the mesophase microspheres were dissolved and extracted, separated by filtration, and dried at 120 ° C in a nitrogen atmosphere. This was subjected to heat treatment at 600 ° C for 3 hours in a nitrogen atmosphere to prepare a mesophase small sphere calcined product.

The calcined product was pulverized, filled in a graphite crucible, and graphitized at 3,150 ° C for 5 hours in a non-oxidizing atmosphere. Then, 0.5 parts by mass of cerium oxide powder (average particle diameter: 50 nm) was mixed with 100 parts by mass of the obtained graphitized product, and the mixture was placed in a "Mechano Fusion System" at a peripheral speed of 20 m/s in a rotary drum, and a treatment time. The compressive force and the shearing force were repeatedly applied under the conditions of 30 minutes, and mechanochemical treatment was performed. A cerium oxide powder was uniformly embedded on the surface of the obtained graphite.

The obtained non-granulated mesophase small-sphere graphitized material is a chamfered block having an average aspect ratio of 1.2, an average particle diameter of 5 μm, an average lattice spacing d ₀₀₂ of 0.3360 nm, and a specific surface area of 4.2 m ^{2 .} /g.

In the same manner as in Example 2, the density of the negative electrode mixture layer was adjusted to 1.75 g/cm ³ to prepare a working electrode, thereby producing an evaluation battery, except that the flaky graphite (C1) was changed to the non-granulated graphite. . The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

In the case where the working electrode is formed by a negative electrode material which deviates from the average aspect ratio range of the flaky graphite specified in the present invention, the rapid charging rate and the cycle characteristics are insufficient.

(Comparative Example 14)

In Example 2, the following granulated graphite having a small average aspect ratio was used in place of the flaky graphite (C1).

80 parts by mass of coke particles (average particle diameter: 5 μm) and 20 parts by mass of coal tar pitch were kneaded at 200 ° C for 1 hour using a biaxial kneader. The kneaded product was molded into a box shape at 200 ° C, and then graphitized at 3150 ° C for 5 hours in a non-oxidizing atmosphere. The obtained graphitized product was pulverized to prepare a granular graphite.

The obtained granulated graphite was a bulk aggregate having an average aspect ratio of 1.7, an average particle diameter of 15 μm, an average lattice spacing d ₀₀₂ of 0.3358 nm, and a specific surface area of 3.2 m ² /g.

In the same manner as in Example 2, the density of the negative electrode mixture layer was adjusted to 1.75 g/cm ³ to prepare a working electrode, and an evaluation battery was produced, except that the flaky graphite (C1) was changed to the granulated graphite. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

In the case where the working electrode is formed by a negative electrode material which deviates from the average aspect ratio range of the flaky graphite specified in the present invention, the rapid charging rate and the cycle characteristics are insufficient.

(Examples 14, 15)

In the second embodiment, the density of the negative electrode mixture layer was adjusted to 1.75 g/cm in the same manner as in Example 2 except that the combination of (A1-1) and (C1) was changed as shown in Table 1. ³ , a working electrode was fabricated to produce an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

(Embodiment 16)

[Modulation of bulk mesophase graphitized material (B1') in which metal oxide fine particles are buried]

The block-shaped mesophase graphitized product (B) used in Example 2 was also attached to the carbide in the same manner as A1-1 used in Example 2. Then, in the obtained bulky mesophase graphitized material (B1) to which the carbonaceous material was adhered, it was uniformly embedded in the same manner as the spheroidized or ellipsoidal natural graphite (A3) used in Example 7. The ceria powder is used to prepare a bulk intermediate phase graphitized material (B1') in which metal oxide fine particles are buried.

In the same manner as in Example 2, the density of the negative electrode mixture layer was adjusted to 1.75 g/cm ^{3 in the} same manner as in Example 2 except that the block-like mesophase graphitized product (B) was changed to the above (B1'). A working electrode was fabricated to produce an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

(Example 17)

In the second embodiment, in the case where the bulk intermediate phase graphitized product (B) is prepared, the pulverization method of the bulk intermediate phase is changed, and the average aspect ratio and the average particle diameter are changed, and otherwise, in the same manner as in the second embodiment. The working electrode was prepared by adjusting the density of the negative electrode mixture layer to 1.75 g/cm ³ to prepare an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

(Embodiment 18)

The spheroidized or ellipsoidal natural graphite (A3) in which the metal oxide fine particles are embedded and the bulk intermediate phase graphite (B1' embedded in the metal oxide fine particles prepared in Example 16 were used. And the flaky graphite (C1') in which the metal oxide fine particles are embedded in the seventh embodiment, and the density of the negative electrode mixture layer is adjusted to 1.75 g/cm ^{3 in the} same manner as in the first embodiment, thereby producing a working electrode. Make an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 2.

(Embodiment 19)

[Modulation of spheroidized or ellipsoidal natural graphite (A3') in which metal oxide fine particles are embedded]

A spheroidized or ellipsoidal natural graphite (A3') in which alumina was embedded was prepared in the same manner as in Example 7 except that alumina was used instead of cerium oxide as the metal oxide.

In the second embodiment, the negative electrode was changed to the above (A3') by changing the spheroidized or ellipsoidal natural graphite (A1-1) to which the carbonaceous material adhered, in the same manner as in the second embodiment. The density of the mixture layer was adjusted to 1.75 g/cm ³ to prepare a working electrode, thereby producing an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 2.

(Embodiment 20)

[Modulation of bulk mesophase graphitized material (B1") in which metal oxide fine particles are buried]

In the same manner as in Example 16, except that titanium oxide was used instead of cerium oxide as the metal oxide, in the same manner as in Example 16, a block in which titanium oxide was embedded was prepared. Interphase graphitized (B1").

In the second embodiment, the density of the negative electrode mixture layer was adjusted to 1.75 g/cm ^{3 in the} same manner as in Example 2 except that the bulk mesophase graphitized material (B) was changed to the above (B1"). The working electrode was produced to prepare an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 2.

(Example 21)

[Modulation of scaly graphite (C1") in which metal oxide fine particles are embedded]

Alumina-containing flaky graphite (C1") was prepared in the same manner as in Example 7 except that alumina was used instead of cerium oxide as the metal oxide.

In the same manner as in Example 2, the density of the negative electrode mixture layer was adjusted to 1.75 g/ in the same manner as in Example 2 except that the flaky graphite (C1) to which the carbonaceous material was adhered was changed to the above (C1"). The evaluation electrode was fabricated by producing a working electrode at cm ^3. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 2.

(Comparative Example 15)

(modulation of mesophase small sphere graphite)

The coal tar pitch was heat-treated at 450 ° C for 90 minutes in an inert atmosphere to form 35 mass % of mesophase small spheres in the asphalt matrix. Thereafter, oil in tar was used, and the mesophase microspheres were dissolved and extracted, separated by filtration, and dried at 120 ° C in a nitrogen atmosphere. This was subjected to heat treatment at 600 ° C for 3 hours in a nitrogen atmosphere to prepare a mesophase small sphere calcined product.

The calcined product was pulverized, filled in a graphite crucible, and graphitized at 3000 ° C for 5 hours in a non-oxidizing atmosphere to obtain mesophase small spherical graphite.

In the same manner as in Example 1, except that the bulk mesophase graphite compound (B) was changed to the mesophase small spherical graphite compound prepared as described above, the density of the negative electrode mixture layer was adjusted to A working electrode was fabricated at 1.75 g/cm ³ to prepare an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 2.

(Comparative Example 16)

In Example 2, the density of the negative electrode mixture layer was adjusted in the same manner as in Example 2 except that the bulk mesophase graphite compound (B) was changed to the mesophase small spherical graphite compound prepared in Comparative Example 15. A working electrode was fabricated at 1.75 g/cm ³ to prepare an evaluation battery. The same charge and discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 2.

[Industrial availability]

The negative electrode material of the present invention can be used for a negative electrode material of a lithium ion secondary battery that contributes to the miniaturization and high performance of the equipment to be mounted.

1‧‧‧Outer cover

2‧‧‧Working electrode (negative electrode)

3‧‧‧Outer cans

4‧‧‧ opposite pole (positive)

5‧‧‧Separator

6‧‧‧Insulation pad

7a, 7b‧‧‧ collector

Claims (9)

A negative electrode material for a lithium ion secondary battery comprising a mass ratio of the following formula (1) and the following formula (2): (A) a ball having an average particle diameter of 5 μm to 35 μm and an average aspect ratio of less than 2.0 Shaped or ellipsoidal natural graphite, (B) bulk mesophase graphitized material having an average particle diameter of 2 μm to 25 μm and an average aspect ratio of less than 2.0, and (C) an average particle diameter of 1 μm to 15 μm a flaky graphite having an average particle diameter smaller than the block-like mesophase graphitized product (B) and an average aspect ratio of 5.0 or more; a: b = (60 - 95): (40 - 5) (1) (a + b) c: (85 or more to less than 100): (15 or less to more than 0) (2) Here, a, b, and c represent the masses of the components (A), (B), and (C) above. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the spheroidized or ellipsoidal natural graphite (A) comprises a carbonaceous material or graphite attached to at least a part of a surface thereof. Spheroidized or ellipsoidal natural graphite of the material. The negative electrode material for a lithium ion secondary battery according to the first or second aspect of the invention, wherein the block-like mesophase graphitized material (B) comprises a tar oil and/or a pitch, and is pulverized, Blocky mesophase graphitized by oxidation, carbonization, and graphitization. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the block-shaped mesophase graphitized material (B) has an average particle diameter smaller than the spheroid or ellipsoid The average particle size of the natural graphite (A). The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the flaky graphite (C) comprises: a carbonaceous material adhered to at least a part of a surface thereof Flaky graphite. The negative electrode material for a lithium ion secondary battery according to any one of the items 1 to 5, wherein the spheroidized or ellipsoidal natural graphite (A), the bulk intermediate phase graphitized material At least one or all of (B) and the flaky graphite (C) include graphite in which a metal oxide is embedded on the surface. A lithium ion secondary battery negative electrode using the negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 6 as a main constituent material of the active material, and the density of the active material layer It is 1.7 g/cm ³ or more. The lithium ion secondary battery negative electrode according to claim 7, wherein the diffraction peak intensity I004 and the (110) plane of the (004) plane of the lithium ion secondary battery negative electrode under X-ray diffraction are wound. The ratio I004/I110 of the peak intensity I110 is 20 or less. A lithium ion secondary battery comprising the lithium ion secondary battery negative electrode according to claim 7 or 8.