JP5322804B2 - Negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

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

  In recent years, with the miniaturization or high performance of electronic devices, there is an increasing demand for increasing the energy density of batteries. In particular, lithium ion secondary batteries are attracting attention because they can achieve higher voltages than other secondary batteries, and can achieve high energy density.

  A lithium ion secondary battery includes a negative electrode, a positive electrode, and an electrolytic solution (nonaqueous electrolyte) as main components. Lithium ions move between the negative electrode and the positive electrode through the electrolytic solution during the discharging process and the charging process to form a secondary battery. The negative electrode is generally composed of a current collector made of copper foil and a negative electrode material (active material) bound by a binder. Usually, a carbon material is used for the negative electrode material. As such a carbon material, graphite having excellent charge / discharge characteristics and high discharge capacity and potential flatness is widely used (see Patent Document 1).

  Lithium ion secondary batteries installed in recent portable electronic devices are required to have excellent rapid chargeability and rapid discharge characteristics, and the initial discharge capacity does not deteriorate even after repeated charge and discharge (cycle characteristics) ) Is required.

Typical examples of conventional graphite negative electrode materials include the following.
Graphite particles obtained by collecting or combining a plurality of flat particles so that their orientation planes are non-parallel, and having fine pores in the particles (Patent Document 2).
Graphite of mesocarbon spherules made of Brooks-Taylor single crystals in which basal planes of graphite are arranged in layers in a direction perpendicular to the diameter direction (Patent Document 3).
Composite graphite particles in which the carbonaceous material is filled in the voids between the graphite particles of the granulated product obtained by spheroidizing or ellipsoidizing natural graphite particles, or the surface of the granulated material is coated with the carbonaceous material Composite graphite particles (Patent Document 4).
Bulk graphite particles obtained by pulverizing, oxidizing, carbonizing, and graphitizing bulk mesophase pitch (Patent Document 5).

  However, in order to meet the demand for higher capacity of lithium ion secondary batteries in recent years, when the density of the active material layer is increased and the discharge capacity per volume is set higher, that is, the negative electrode material is applied to the current collector. Thereafter, when the active material layer is densified by pressing at a high pressure, various problems arise with these conventional negative electrode materials.

In the negative electrode material using the aggregated graphite particles described in Patent Document 2, when the density of the active material layer exceeds 1.7 g / cm ³ , the aggregate is crushed, and the flat graphite particles as the structural unit are natural graphite. As shown in FIG. Therefore, the ion diffusibility of lithium ions is reduced, and the rapid chargeability, rapid discharge property, and cycle characteristics are deteriorated. In addition, the surface of the active material layer is likely to be clogged, the electrolyte permeability is lowered, the battery productivity is lowered, and the electrolyte solution is depleted inside the active material layer, thereby reducing the cycle characteristics.

  In the negative electrode material using the mesocarbon microsphere graphitized material described in Patent Document 3, since the graphitized material is spherical, the orientation of the basal plane of graphite can be suppressed to some extent even when the density is increased. However, since the graphitized material is dense and hard, high pressure is required to increase the density, and problems such as deformation, elongation, and breakage of the copper foil of the current collector occur. Further, the contact area with the electrolytic solution is small. Therefore, quick chargeability is particularly low. The decrease in chargeability causes the electrodeposition of lithium on the negative electrode surface during charging and causes a decrease in cycle characteristics.

  In the negative electrode material using the massive graphite particles described in Patent Document 4, the high reactivity (decrease in initial charge / discharge efficiency), which is a defect of natural graphite having a high discharge capacity, is improved by the coating of the carbonaceous material. When the density is increased, the granulated product of natural graphite particles is crushed and flattened, and the rapid chargeability, rapid discharge property, cycle characteristics are deteriorated, and the carbonaceous material is peeled off to expose the natural graphite particles. Initial charge / discharge efficiency decreases.

  The negative electrode material using the massive graphite particles described in Patent Document 5 can suppress the orientation of the basal plane of graphite to some extent even when the density is increased. However, since the graphitized material is dense and hard, high pressure is required to increase the density, and problems such as deformation, elongation, and breakage of the copper foil of the current collector occur. Further, due to the oxidation, the crystallinity of the graphite particle surface is lowered, so that there is a problem that the discharge capacity is low.

  Thus, a negative electrode material that maintains excellent rapid chargeability, rapid discharge performance and cycle characteristics even at high density, is soft, and can be easily densified even at a low press pressure is desired. For this purpose, it has been proposed to mix a plurality of types of graphite materials. Representative examples are as follows.

Lithium using a negative electrode material obtained by mixing a graphite-based carbonaceous material obtained by coating spheroidized natural graphite powder with a scaly carbonaceous material and mesocarbon microbeads having an average particle size of 2/3 or less of the scaly carbonaceous material. Secondary battery (Patent Document 6).
A negative electrode for a lithium ion secondary battery using a negative electrode material in which a mesophase small sphere graphitized product and non-flaky graphite particles having a smaller average particle diameter than the graphitized product (graphitized product of mesophase small spheres) are mixed. (Patent Document 7).
A negative electrode material for a lithium secondary battery in which a hydrophilized product of graphitized particles of mesophase microspheres and a composite graphitic carbon material coated with a low crystalline carbon material are mixed (Patent Document 8).
A negative electrode material obtained by mixing spherical or ellipsoidal graphite having an average particle diameter of 10 to 30 μm and graphite having an average particle diameter of 1 to 10 μm and coated with non-graphitic carbon. The negative electrode for lithium secondary batteries used (Patent Document 9).

A non-aqueous secondary battery using a mixture of pitch graphitized material and graphitized mesocarbon microbeads as a negative electrode material (Patent Document 10).
A non-aqueous electrolyte secondary battery using a negative electrode material obtained by mixing a graphite material coated with a non-graphitic carbon material and a natural graphite material (Patent Document 11).
Lithium secondary battery using negative electrode material comprising mesophase spherical graphite having an average particle size of 8 μm or more and mesophase microspherical graphite having an average particle size of 3 μm or less so as to fill the gap (7.5% by weight or less) Patent Document 12).
A non-aqueous electrolyte secondary battery using a mixture of graphite, a first non-graphite carbon material, and acetylene black having a smaller particle diameter as a negative electrode material (Patent Document 13).
A nonaqueous electrolyte secondary battery using a negative electrode material obtained by mixing graphitized mesocarbon microbeads and artificial graphite powder having an average particle size smaller than that of the graphitized material (Patent Document 14).

  However, even if these mixed 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 still not solved. . That is, in the case of Patent Documents 6, 7, 10, 12, and 14, since the mesophase small sphere graphitized material is hard, a high press pressure is required to increase the density of the active material layer. Problems such as deformation, elongation, and breakage of the copper foil occur. In the case of Patent Documents 8, 9, and 11, with the increase in the density of the active material layer, the ion diffusibility of lithium ions decreases, and the rapid chargeability, rapid discharge properties, and cycle characteristics of the lithium ion secondary battery decrease. Cause. In addition, the surface of the active material layer is easily clogged, the electrolyte permeability is lowered, the battery productivity is lowered, and the electrolyte solution is depleted inside the active material layer, resulting in a reduction in cycle characteristics. In the case of Patent Document 13, when a hard non-graphitic carbon material is used, a high press pressure is required to increase the density of the active material layer, and problems such as deformation, elongation, and breakage of the copper foil of the current collector arise. .

Japanese Examined Patent Publication No. 62-23433 JP-A-10-158005 JP 2000-323127 A JP 2004-63321 A JP-A-10-139410 JP 2008-171809 A JP 2007-134276 A JP 2004-253379 A JP-A-2005-44775 JP 2005-19096 A JP 2001-185147 A Japanese Patent Laid-Open No. 11-3706 JP-A-10-270019 JP-A-7-37618

  The object of the present invention is that when used as a negative electrode material of a lithium ion secondary battery, it reaches a high density at a low pressing pressure, has a high discharge capacity per volume and a high density, while the graphite is crushed. An object of the present invention is to provide a negative electrode material that has excellent rapid chargeability, rapid discharge property, and cycle characteristics without being impaired in the orientation and without impairing the permeability and retention of the electrolyte. Moreover, it is providing the lithium ion secondary battery negative electrode using this negative electrode material, and the lithium ion secondary battery which has this negative electrode.

  The present invention includes the following (1) to (6).

(1) Average particle diameter of 10 to 40 [mu] m, average aspect ratio Ri der less than 1.2, coal or heavy oil petroleum, to heat treatment at least one selected from the tars and pitches such obtained Mesophase microsphere graphitized product (A) obtained by graphitizing the obtained spherical polymer having optical anisotropy ,
Spherical or ellipsoidal natural graphite having an average particle size of 5 to 35 μm, smaller than the average particle size of the mesophase small sphere graphitized product (A) and having an average aspect ratio of less than 2.0 (B) As well as
Graphite (C) having an average particle diameter of 2 to 25 μm, smaller than the average particle diameter of the mesophase microsphere graphitized product (A), and having an average aspect ratio of less than 2.0
The mesophase microsphere graphitized product (A), the spheroidized or ellipsoidized natural graphite (B) and the graphite (C) in the mixture have a mass ratio of the following formulas (1) and ( 2) The negative electrode material for lithium ion secondary batteries characterized by satisfying | filling.
a: b = (10 to 70): (90 to 30) (1)
(A + b): c = ( 80 to 95): ( 20 to 5) (2)
Here, a represents the proportion of the mesophase small sphere graphitized product (A), b represents the proportion of the spheroidized or ellipsoidized natural graphite (B), and c represents the proportion of the graphite (C).

(2) The mesophase microsphere graphitized product (A) is spherical, and the graphite (C) is spherical, ellipsoidal or massive, for the lithium ion secondary battery according to (1) above Negative electrode material.

(3) In the above (1) or (2), a carbonaceous material or a graphite material is attached to at least a part of the surface of the spheroidized or ellipsoidized natural graphite (B). The negative electrode material for lithium ion secondary batteries as described.

(4) The negative electrode material for a lithium ion secondary battery according to any one of (1) to (3), wherein the graphite (C) is non-granulated graphite and / or granulated graphite. .

(5) A lithium ion secondary, wherein the negative electrode material according to any one of (1) to (4) is used as an active material, and the density of the active material layer is 1.7 g / cm ³ or more. Battery negative electrode.

(6) A lithium ion secondary battery using the lithium ion secondary battery negative electrode according to (5).

  The lithium ion secondary battery negative electrode containing the mesophase microsphere graphitized product (A), spheroidized or ellipsoidized natural graphite (B) and graphite (C) of the present invention can be used even when the density of the active material layer is increased. The current collector is not deformed or broken, and each graphite (A), (B), or (C) is prevented from being crushed and oriented, and the electrolyte has excellent permeability. And since electrolyte solution exists easily around each graphite (A) (B) (C), the diffusibility of lithium ion becomes good. Therefore, the lithium ion secondary battery using the negative electrode of the present invention has a high discharge capacity per volume and good battery performance such as rapid chargeability, rapid discharge performance, and cycle characteristics. Therefore, the lithium ion secondary battery of the present invention satisfies the recent demand for higher energy density of batteries, and is useful for downsizing and higher performance of equipment to be mounted.

It is a schematic cross section which shows the structure of the button type evaluation battery for using for a charging / discharging test in an Example.

Hereinafter, the present invention will be specifically described.
A lithium ion secondary battery (hereinafter also simply referred to as a secondary battery) usually has an electrolyte solution (non-aqueous electrolyte), a negative electrode, and a positive electrode as main battery components, and these elements are enclosed in, for example, a secondary battery can. Has been. The negative electrode and the positive electrode each act as a lithium ion carrier. The battery mechanism is such that lithium ions are occluded in the negative electrode during charging and lithium ions are released from the negative electrode during discharging.
The secondary battery of the present invention is not particularly limited except that the negative electrode material of the present invention is used as the negative electrode material, and other battery components such as a non-aqueous electrolyte, a positive electrode, and a separator are general secondary battery elements. According to

[Mesophase small sphere graphitized product (A)]
The mesophase small sphere graphitized product (A) of the present invention (hereinafter also simply referred to as small sphere graphitized product (A)) is non-granulated and non-crushed graphite particles. The average particle diameter of the small sphere graphitized product (A) of the present invention is preferably 10 to 40 μm, particularly preferably 15 to 35 μm in terms of volume average particle diameter. If it is 10 micrometers or more, the density of an active material layer can be raised and the discharge capacity per volume will improve. If it is 40 micrometers or less, quick charge property and cycling characteristics will improve. Here, the average particle diameter in terms of volume means a particle diameter at which the cumulative frequency of the particle size distribution measured by a laser diffraction particle size distribution meter is 50% by volume percentage.

The shape of the small sphere graphitized product (A) of the present invention is preferably spherical, particularly close to a true sphere, the average aspect ratio is preferably less than 1.3, more preferably less than 1.2, More preferably, it is less than 1.1. The closer to the true sphere, the more the crystal structure of the graphitized product (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 electrolytic solution, the quick chargeability, the rapid discharge property and the cycle. Good characteristics.
The aspect ratio means the ratio of the major axis length of one particle of the small sphere graphitized product (A) to the minor axis length. Here, the long axis length means the longest diameter of the particle to be measured, and the short axis length means a short diameter perpendicular to the long axis of the particle to be measured. The average aspect ratio is a simple average value of the aspect ratio of each particle measured by observing 100 small sphere graphitized products (A) with a scanning electron microscope. Here, the magnification at the time of observing with a scanning electron microscope is a magnification at which the shape of the particles to be measured can be confirmed.

The small sphere graphitized product (A) of the present invention has high crystallinity. Since it has high crystallinity, it is soft and contributes to increasing the density of the active material layer. It as an index of crystalline lattice plane in X-ray wide angle diffraction (002) average lattice spacing _{d 002} (hereinafter, simply referred to as an average lattice spacing _{d 002)} of less than 0.3363 nm, in particular 0.3360mm less Is preferred. Here, the average lattice spacing d ₀₀₂ is a diffraction peak on the (002) plane of the microsphere graphitized product (A) using CuKα rays as X-rays and using high-purity silicon as a standard material, Calculate from the peak position. The calculation method follows the Japan Science and Technology Act (measurement method defined by the 17th Committee of the Japan Society for the Promotion of Science). Specifically, “Carbon Fiber” (written by Suguro Otani, pages 733-742 (March 1986)). (Month) and Modern Editing Company).

  Since the microsphere graphitized material (A) of the present invention has high crystallinity, it exhibits a high discharge capacity when used as a negative electrode active material for a secondary battery. Although the discharge capacity varies depending on the production conditions of the negative electrode and the evaluation battery, it is about 330 mAh / g or more, preferably 340 mAh / g or more, more preferably 350 mAh / g or more.

If the specific surface area of the small spherical graphitized material (A) of the present invention is too large, the initial charge / discharge efficiency of the secondary battery is reduced. Therefore, the nitrogen gas adsorption BET specific surface area (hereinafter also simply referred to as the specific surface area) is 20 m ^2. / G or less is preferable, and 5 m ² / g or less is more preferable.

  The small sphere graphitized product (A) of the present invention is a mixture or composite of different types of graphite materials, carbon materials such as amorphous hard carbon, inorganic materials, metal materials, etc. within the range not impairing the object of the present invention. There may be. Specifically, the surface of the microsphere graphitized material (A) is coated with tar pitches or resins and baked, the conductive material such as carbon fiber or carbon black is attached or embedded, silica, alumina, titania Attached or embedded with metal oxide fine particles such as silicon, tin, cobalt, nickel, copper, silicon oxide, tin oxide, lithium titanate or other metals or metal compounds, or a combination of these Things can be mentioned. The small sphere graphitized product (A) may have a surface smoothed or roughened.

[Method for producing mesophase microsphere graphitized product (A)]
The microsphere graphitized product (A) of the present invention is an optically anisotropic spherical polymer produced by heat-treating coal-based, petroleum-based heavy oil, tars, and pitches at 350 to 500 ° C. It is a raw material. The spherical polymer is separated and purified from the pitch matrix by centrifugation or using an organic solvent (benzene, toluene, quinoline, tar medium oil, tar heavy oil, washing oil, etc.), and the separated spherical polymer is then removed in a non-oxidizing atmosphere. The small sphere graphitized product (A) can be obtained by performing primary firing at a temperature of not lower than ° C. and finally high-temperature heat treatment at a temperature exceeding 2500 ° C. in a non-oxidizing atmosphere. The final high-temperature heat treatment is preferably performed at 2800 ° C. or more, more preferably 3000 ° C. or more. However, in order to avoid sublimation and decomposition of the particles of the small sphere graphitized product (A), the upper limit temperature is usually about 3300 ° C. . The final high-temperature heat treatment can be performed using a known high-temperature furnace such as an Acheson furnace. Although the final high-temperature heat treatment time cannot be said, it is about 1 to 50 hours.

  The coal-based, petroleum-based heavy oil, tars, and pitches, which are raw materials for the microsphere graphitized product (A) of the present invention, can be used within the range not impairing the object of the present invention, metals, metal compounds, inorganic compounds, Different components such as carbon materials and resins can be blended. In addition, before primary firing of mesophase spherules (spherical polymer) separated from the pitch matrix, or before final high-temperature heat treatment or after final high-temperature heat treatment, metals, metal compounds, inorganic compounds, carbon It is also possible to attach, embed, and cover different components such as materials and resins.

[Spheroidized or Ellipsoidized Natural Graphite (B)]
The spheroidized or ellipsoidal natural graphite (B) of the present invention is obtained by bending or folding a flat or scaly natural graphite, or by concentrating a plurality of scaly natural graphites. And those which have been granulated into a cabbage shape and spheroidized are preferred.
The average particle size of the spheroidized or ellipsoidized natural graphite (B) of the present invention must be smaller than the average particle size of the small sphere graphitized product (A), and the average particle size in terms of volume is 5 to 5. It is preferable that it is 35 micrometers, especially 10-30 micrometers. If it is 5 micrometers or more, the density of an active material layer can be raised and the discharge capacity per volume will improve. And if it is 35 micrometers or less, quick charge property and cycling characteristics will improve. When the average particle size of the spheroidized or ellipsoidized natural graphite (B) is larger than the average particle size of the small sphere graphitized material (A), when the active material layer is densified, the spheroidized or ellipsoidal shape The natural graphite (B) is easily crushed, and the crystal structure of the spheroidized or ellipsoidal natural graphite (B) is oriented in one direction in the particle or on the negative electrode. For this reason, the diffusibility of lithium ions is lowered, causing rapid chargeability, rapid discharge properties, and cycle characteristics to be degraded.

  The average aspect ratio of the spheroidized or ellipsoidized natural graphite (B) of the present invention is preferably less than 2.0, more preferably less than 1.5, and less than 1.3. Further preferred. The closer the shape to a true sphere, the more the crystal structure of the spheroidized or ellipsoidized natural graphite (B) is not oriented in one direction in the particles or on the negative electrode, and the diffusibility of lithium ions in the electrolyte is higher. Rapid chargeability, rapid discharge, and cycle characteristics can be improved.

The spheroidized or ellipsoidized natural graphite (B) of the present invention has high crystallinity. Since it has high crystallinity, it is soft and contributes to increasing the density of the active material layer. It is preferable that the average lattice spacing d ₀₀₂ as an index of crystallinity is less than 0.3360 nm, particularly 0.3358 mm or less.
In addition, since the spheroidized or ellipsoidal natural graphite (B) of the present invention has high crystallinity, it exhibits a high discharge capacity when used as a negative electrode active material for a secondary battery. Although the discharge capacity varies depending on the production conditions of the negative electrode and the evaluation battery, it is about 350 mAh / g or more, preferably 360 mAh / g or more.
When the specific surface area of the spheroidized or ellipsoidized natural graphite (B) of the present invention is too large, the initial charge / discharge efficiency of the secondary battery is reduced. Therefore, the specific surface area is preferably 20 m ² / g or less, and preferably 10 m ^2. / G or less is more preferable.

Part or all of the spheroidized or ellipsoidized natural graphite (B) of the present invention has a carbonaceous material attached to at least a part of its surface (B1) or a graphite material attached ( More preferably, it is B2). The adhesion of the carbonaceous material or the graphite material can prevent the natural graphite (B) from being crushed.
As the carbonaceous material adhering to the spheroidized or ellipsoidal natural graphite (B1), coal-based or petroleum-based heavy oil, tars, pitches, and resins such as phenol resins are finally added at 500 ° C. The carbide formed by heat-processing above 1500 degreeC above is mentioned. The adhesion amount of the carbonaceous material is preferably 0.1 to 10 parts by mass, particularly 0.5 to 5 parts by mass with respect to 100 parts by mass of the spheroidized or ellipsoidal natural graphite (B).
Examples of the graphite material adhering to the spheroidized or ellipsoidal natural graphite (B2) include coal-based or petroleum-based heavy oil, tars, pitches, and resins such as phenol resins at 1500 ° C to 3300 ° C. A graphitized product obtained by heat treatment with less than the above may be mentioned. The adhesion amount of the graphite material is preferably 1 to 30 parts by mass, particularly 5 to 20 parts by mass with respect to 100 parts by mass of the spheroidized or ellipsoidal natural graphite (B).

The preferred range of the average particle diameter, average aspect ratio, average lattice spacing d ₀₀₂ , and specific surface area of the natural graphite (B1) or natural graphite (B2) to which the carbonaceous material or graphitic material is attached is the carbonaceous material or This is the same as in the case of natural graphite (B) without adhesion of the graphite material.

  Natural graphite (B1) or natural graphite (B2) to which a carbonaceous material or a graphite material is attached has a conductive material such as carbon fiber or carbon black inside or on the surface of the carbonaceous material or graphite material. It may be a metal oxide fine particle such as silica, alumina, titania attached or embedded, such as silicon, tin, cobalt, nickel, copper, silicon oxide, tin oxide, lithium titanate, etc. A metal or a metal compound may be attached or embedded.

[Method for Producing Spheroidized or Ellipsoidized Natural Graphite (B)]
The spheroidized or ellipsoidized natural graphite (B) of the present invention (hereinafter also simply referred to as natural graphite (B)) can be produced by applying mechanical external force to flat and scale-like natural graphite. . Specifically, it can be spheroidized by applying a high shearing force, bending by applying a rolling operation, or spheroidizing by concentric granulation. Before and after the spheronization treatment, a binder can be added to promote granulation. Spheroidizers that can be spheroidized include “counter jet mill” (manufactured by Hosokawa Micron Corporation), “current jet” (manufactured by Nissin Engineering Co., Ltd.), and “SARARA” (Kawasaki Heavy Industries, Ltd.). ), “GRANUREX” (manufactured by Freund Sangyo Co., Ltd.), “New Gramachine” (manufactured by Seishin Enterprise Co., Ltd.), “Agromaster” (manufactured by Hosokawa Micron Co., Ltd.), pressure kneader, Kneading machine such as this roll, “Mechano Micro System” (manufactured by Nara Machinery Co., Ltd.), Extruder, Ball Mill, Planetary Mill, “Mechano Fusion System” (manufactured by Hosokawa Micron Corporation), “Nobilta” (Hosokawa Micron Corporation) )), "Hybridization" (manufactured by Nara Machinery Co., Ltd.), compression shearing processing equipment such as a rotating ball mill, etc. Door can be.

  As a method for attaching a carbonaceous material or a graphite material to a part or all of the natural graphite (B) of the present invention, a gas phase method is used in which a carbonaceous material or a precursor of the graphite material is attached to the natural graphite (B). It can be manufactured by heat treatment after being attached or coated by either liquid phase method or solid phase method.

  A specific example of the vapor phase method is a method in which vapor of a precursor of a carbonaceous material typified by hydrocarbons such as benzene and toluene is deposited on the surface of natural graphite (B) at 900 to 1200 ° C. A hydrocarbon precursor is carbonized during vapor deposition, and natural graphite (B1) with a carbonaceous material attached is obtained.

  Specific examples of the liquid phase method include coal tar, tar light oil, tar middle oil, tar heavy oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, mesophase pitch, oxygen-crosslinked petroleum pitch, etc. Immerse natural graphite (B) in solutions such as pitches, thermoplastic resins such as polyvinyl alcohol, thermosetting resins such as phenolic resins and furan resins, sugars, and celluloses (hereinafter also referred to as carbonaceous material precursors). Then, after removing the solvent, a method of producing natural graphite (B1) to which the carbonaceous material is adhered can be exemplified by removing the solvent and finally performing heat treatment at 500 ° C. or more and less than 1500 ° C. Similarly, by increasing the heat treatment temperature to 1500 ° C. or higher and lower than 3300 ° C., natural graphite (B2) having a graphitic material attached thereto can be produced.

  As a specific example of the solid-phase method, a carbonaceous material precursor powder exemplified in the description of the liquid-phase method and natural graphite (B) are mixed to provide mechanical energy such as compression, shear, collision, friction and the like. There is a method in which the carbonaceous material precursor powder is pressure-bonded to the surface of natural graphite (B) by chemical treatment. By the mechanochemical treatment, the carbonaceous material precursor is melted or softened, and is adhered by being rubbed against natural graphite (B). Examples of the apparatus capable of mechanochemical treatment include the various compression shearing processing apparatuses described above. Natural graphite (B) to which the carbonaceous material precursor powder is adhered, and finally heat-treated at 500 ° C. or more and less than 1500 ° C., can produce natural graphite (B1) to which the carbonaceous material is adhered. Similarly, by increasing the heat treatment temperature to 1500 ° C. or higher and lower than 3300 ° C., natural graphite (B2) having a graphitic material attached thereto can be produced.

  A conductive material such as carbon fiber or carbon black may be used together with the carbonaceous material precursor. Furthermore, in the case of producing natural graphite (B2) to which a graphite material is adhered, together with a carbonaceous material precursor, an alkali metal such as Na and K, an alkaline earth metal such as Mg and Ca, Ti, V, and Cr Mn, Fe, Co, Ni, Zr, Nb, Mn, Mo, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, Pt and other transition metals, Al, Ge and other metals, Semimetals such as B and Si, and metal compounds thereof, for example, hydroxides, oxides, nitrides, chlorides, sulfides and the like may be used alone or in combination.

[Non-granulated graphite (C1) and granulated graphite (C2)]
The graphite (C) of the present invention may be either non-granulated graphite (C1) or granulated graphite (C2).
The non-granulated graphite (C1) is a fine spherical, ellipsoidal, or massive graphite particle inside the particle, and the granulated graphite (C2) is a spherical particle formed by granulating fine primary particles. Graphite particles such as ellipsoidal shape and lump shape.
The average particle diameter of the non-granulated graphite (C1) and the granulated graphite (C2) must be smaller than the average particle diameter of the small spherical graphitized product (A), and the average particle diameter is 2 to 25 μm. In particular, the thickness is preferably 3 to 20 μm. If it is less than 2 μm, the initial charge / discharge efficiency may be lowered. In the case of more than 25 μm, non-granulated graphite (C1) requires high pressure to make the active material layer high in density, and causes problems such as deformation, elongation and breakage of the copper foil as a current collector. In the case of granulated graphite (C2), when the active material layer is made dense, the granulated graphite (C2) particles are oriented in one direction, so that the diffusibility of lithium ions is reduced and rapid charging is performed. , Rapid discharge, and cycle characteristics may be deteriorated.

  When the average particle size of the non-granulated graphite (C1) and the granulated graphite (C2) is larger than the average particle size of the small spherical graphitized product (A), the non-granulated graphite (C1) High pressure is required to increase the density of the copper foil, and problems such as deformation, elongation, and breakage of the copper foil as the current collector become more apparent. Further, in the granulated graphite (C2), when the active material layer is densified, the granulated graphite (C2) is more easily crushed, and the crystal structure of the granulated graphite (C2) is in the particles or in the negative electrode. It will be oriented in one direction. For this reason, the diffusibility of lithium ions is lowered, causing rapid chargeability, rapid discharge properties, and cycle characteristics to be degraded.

  The average aspect ratio of the non-granulated graphite (C1) and the granulated graphite (C2) is preferably less than 2.0, more preferably less than 1.5, and less than 1.3. Further preferred. The closer to a spherical shape, the more the crystal structure of non-granulated graphite (C1) and granulated graphite (C2) is not oriented in one direction in the particles or on the negative electrode, and the diffusion of lithium ions in the electrolytic solution High chargeability, quick chargeability, rapid discharge properties and cycle characteristics are improved.

The non-granulated graphite (C1) and the granulated graphite (C2) preferably have high crystallinity, and the average lattice spacing d ₀₀₂ is preferably less than 0.3363 nm, particularly preferably 0.3360 nm or less.
The discharge capacity when non-granulated graphite (C1) and granulated graphite (C2) are used as the negative electrode active material of the secondary battery varies depending on the production conditions of the negative electrode and the evaluation battery, but is 340 mAh / g or more, Preferably it is 350 mAh / g or more.
If the specific surface area of the non-granulated graphite (C1) and the granulated graphite (C2) is too large, the initial charge / discharge efficiency of the secondary battery is reduced. Therefore, the specific surface area is preferably 20 m ² / g or less, preferably 10 m. ² / g or less is more preferable.
The granulated graphite (C2) is preferably used because it has more lithium ion insertion ports and is excellent in quick chargeability than the non-granulated graphite (C1).

The production of non-granulated graphite (C1) includes, for example, coal-based tar, mesophase calcined carbon obtained by heating pitch (bulk mesophase), pulverized mesophase spherules, coke (raw coke, green coke, Pitch coke, needle coke, petroleum coke, etc.) are preliminarily pulverized to a final non-granulated graphite (C1) particle shape and an average particle size of 2 to 25 μm, and then heat treated at 2500 ° C. or more and less than 3300 ° C. And graphitized, or petroleum-based tar and pitch graphitized by heat treatment in the same manner.
The pulverization method is not particularly limited, and various pulverization methods can be applied. However, it is preferable to take a corner of the pulverization surface simultaneously with pulverization or after pulverization, and use of a ball mill, a vortex pulverizer, an attrition pulverizer, etc. Is preferred.

  Different components such as metals, metal compounds, inorganic compounds, carbon materials, and resins can be attached, embedded, and coated on the raw material of non-granulated graphite (C1) and the intermediate product before final heat treatment. Furthermore, after the final heat treatment, it is preferable to perform a sizing treatment to bring the particle shape closer to a spherical shape. For the sizing treatment, a mechanochemical treatment apparatus that imparts mechanical energy such as compression, shearing, collision, and friction can be used.

  As a method for producing granulated graphite (C2), mesophase calcined carbon (bulk mesophase), pulverized mesophase spheroids, coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.), or A heat-treated petroleum tar, pitch, etc. are finely pulverized to an average particle size of 1 to 15 μm and heat-treated as it is or at a temperature of 500 ° C. or higher and lower than 3300 ° C. to bind the carbonaceous material precursor. Granulated as an agent, and finally heat-treated at 2500 ° C. or higher and lower than 3300 ° C. for graphitization, or artificial graphite having an average particle diameter of 1 to 15 μm and natural graphite as a binder for the carbonaceous material precursor The granulated product is finally heat-treated at 2500 ° C. or higher and lower than 3300 ° C. for graphitization, and the fine particles having an average particle size of 1 to 15 μm Crushed material or artificial graphite having an average particle diameter of 1 to 15 μm, or natural graphite granulated with the carbonaceous material precursor as an adhesive to an average particle diameter of more than 15 μm is finally heat treated at 2500 ° C. or more and less than 3300 ° C. Examples thereof include a method of pulverizing to an average particle diameter of 2 to 25 μm after graphitization.

[Method for producing non-granulated graphite (C1)]
The non-granulated graphite (C1) of the present invention includes coal-based tar, mesophase calcined carbon (bulk mesophase) obtained by heating pitch, pulverized mesophase spheroids, coke (raw coke, green coke, pitch). Coke, needle coke, petroleum coke, etc.) are preliminarily pulverized to a final product particle shape and an average particle diameter of 2 to 25 μm, and finally heat treated at 2500 ° C. or higher and lower than 3300 ° C. to graphitize Can be manufactured. The pulverization method is not particularly limited, and various pulverization methods can be applied. However, it is preferable to take a corner of the pulverization surface simultaneously with the pulverization, and use of a ball mill, a vortex pulverizer, an attrition pulverizer, or the like is preferable.

  Different components such as metals, metal compounds, inorganic compounds, carbon materials, and resins can be attached, embedded, and coated on the raw material of non-granulated graphite (C1) and the intermediate product before final heat treatment. Furthermore, after the final heat treatment, it is preferable to perform a sizing treatment to bring the particle shape closer to a spherical shape. The sizing treatment can use a mechanochemical processing apparatus that can produce spherical or ellipsoidal natural graphite and impart mechanical energy such as compression, shearing, collision, and friction.

[Production method of granulated graphite (C2)]
The granulated graphite (C2) of the present invention has an average particle size of mesophase calcined carbon (bulk mesophase), pulverized mesophase spheroids, coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.) What was finely pulverized to 1 to 15 μm, or was heat-treated at 500 ° C. or more and less than 3300 ° C., or after heat-treating petroleum tar and pitch and finely pulverized to an average particle size of 1 to 15 μm Heat treated at 500 ° C. or higher and lower than 3300 ° C., and granulate these primary particles using the carbonaceous material precursor as a binder and finally heat treated at 2500 ° C. or higher and lower than 3300 ° C., or Artificial graphite and natural graphite having an average particle diameter of 1 to 15 μm are used as primary particles, and the resultant is granulated using the carbonaceous material precursor as a binder. Those graphitized manner was heat-treated at lower than 2500 ° C. or higher 3300 ° C. is exemplified. Further, after forming the granulated body having an average particle diameter of more than 15 μm using the carbonaceous material precursor as an adhesive and finally heat-treating at 2500 ° C. to less than 3300 ° C., the primary particles are graphitized. The thing grind | pulverized to 2-25 micrometers is illustrated.
When the average particle diameter of the primary particles is less than 1 μm, the initial charge / discharge efficiency may be lowered. When the average particle diameter exceeds 15 μm, it is difficult to adjust the average particle diameter after granulation to 25 μm or less. .

As a granulation method, the mixture of the primary particles and the carbonaceous material precursor is uniformly mixed at a temperature equal to or higher than the melting temperature of the carbonaceous material precursor using an apparatus capable of kneading with high viscosity such as a twin screw extruder. It is preferable. The carbonaceous material precursor may be blended as a solution, in which case it is desirable to remove the solvent during kneading.
After kneading, it is preferable to perform a preliminary heat treatment at 500 to 1500 ° C. Although it can grind | pulverize either before and after preliminary heat processing, the grinding | pulverization method in the case of grind | pulverizing so that it may become 2-25 micrometers in an average particle diameter is not specifically limited, Although various grinding | pulverization systems can be used, it grind | pulverizes At the same time, since it is preferable to take a corner of the crushing surface, a vortex type or grinding type crusher is suitable. Moreover, it is preferable to perform a sizing treatment to make the particle shape close to spherical after pulverization. The said processing apparatus can be used for the sizing process method. Even when pulverizing to an average particle diameter of 2 to 25 μm after final heat treatment at 2500 ° C. or more and less than 3300 ° C. and then graphitizing without being pulverized after kneading, the above-mentioned pulverizer and processing device may be used. it can.

  Different components such as metals, metal compounds, inorganic compounds, carbon materials, and resins can be blended with the raw material of granulated graphite (C2) and the intermediate product before the final heat treatment. Furthermore, before the final heat treatment, an oxidation treatment can be performed in advance to make it infusible. After the final heat treatment, different components such as metals, metal compounds, inorganic compounds, carbon materials, and resins can be attached, embedded, and coated.

[Anode material for lithium ion secondary battery]
The negative electrode material for lithium ion secondary batteries of the present invention (hereinafter also simply referred to as negative electrode material) is a mixture containing the three components (A), (B) and (C). In the present invention, the mass ratio of these three components is defined as a: b = 10 to 70:90 to 30 and (a + b): c = 60 to 95:40 to 5. Here, a, b, and c represent the ratios of (A), (B), and (C), respectively.

When a: b is less than 10: more than 90, the effect of preventing orientation of graphite by the small sphere graphitized product (A) is small, and the spherical or ellipsoidal natural graphite (B) in the active material becomes excessive. As the density increases, the graphite collapses and the graphite is oriented in one direction. For this reason, the ion diffusibility of lithium ions is lowered, causing rapid chargeability, rapid discharge properties, and cycle characteristics to be degraded. In addition, the surface of the active material layer is likely to be clogged, the electrolyte permeability is reduced, the productivity of the secondary battery is reduced, and the electrolyte solution is depleted inside the active material layer, resulting in cycle characteristics. Also decreases.
On the other hand, when a: b is more than 70:30 and less, relatively hard microsphere graphitized material (A) is excessive, and thus a high pressure is required to increase the density of the active material layer. In some cases, problems such as deformation, elongation and breakage of the copper foil as the current collector may occur.

(A + b): When c is less than 60: more than 40, the average particle size is small, and relatively hard non-granulated graphite (C1) and / or granulated graphite (C2) is excessive. In addition to problems such as deformation, elongation and breakage of the copper foil as the current collector, initial charge / discharge efficiency and cycle characteristics may be reduced due to increased reactivity.
On the other hand, when (a + b): c is more than 95: less than 5, the effect of improving conductivity by the non-granulated graphite (C1) and / or the granulated graphite (C2) is reduced, and quick chargeability, Rapid discharge and cycle characteristics may be degraded. More preferably, a: b = 25-60: 75-40 and (a + b): c = 75-90: 25-10.

  A known active material or conductive material can be mixed with the negative electrode material of the present invention as long as the effects of the present invention are not impaired. For example, carbide particles obtained by heat-treating the carbonaceous material precursor at 500 to 1500 ° C., ketjen black, acetylene black, vapor-grown carbon fiber, carbon nanofiber, carbon nanotube and other conductive materials, lithium and alloys. Examples thereof include metal particles such as silicon, tin, and oxides thereof.

[Anode for lithium ion secondary battery]
The negative electrode for a lithium ion secondary battery of the present invention (hereinafter also simply referred to as a negative electrode) can be produced in accordance with a normal method for producing a negative electrode, but a chemically and electrochemically stable negative electrode is obtained. There is no limitation as long as it is a manufacturing method capable of satisfying the requirements.
For the production of the negative electrode of the present invention, a negative electrode mixture obtained by adding a binder to the negative electrode material can be used. As the binder, those having chemical stability and electrochemical stability with respect to the electrolyte are preferably used. For example, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene, polyvinyl alcohol, and styrene. Butadiene rubber, carboxymethyl cellulose and the like are used. These can also be used together. Usually, the binder is preferably in a proportion of 1 to 20% by mass in the total amount of the negative electrode mixture.
For production of the negative electrode of the present invention, N-methylpyrrolidone, dimethylformamide, water, alcohol, etc., which are ordinary solvents for producing a negative electrode, can be used.

The negative electrode of the present invention is produced, for example, by dispersing a negative electrode mixture in a solvent to prepare a paste-like negative electrode mixture, and then applying the negative electrode mixture to one or both sides of a current collector and drying it. . Thereby, a negative electrode in which the negative electrode mixture layer (active material layer) is uniformly and firmly bonded to the current collector is obtained.
More specifically, for example, after mixing the negative electrode material particles, fluorine resin powder or styrene butadiene rubber water dispersant and solvent into a slurry, a known stirrer, mixer, kneader, kneader or the like is used. The mixture is stirred and mixed to prepare a negative electrode mixture paste. When this is applied to the current collector and dried, the negative electrode mixture layer adheres uniformly and firmly to the current collector. The film thickness of the negative electrode mixture layer is 10 to 200 μm, preferably 30 to 100 μm.

The negative electrode mixture layer can also be produced by dry-mixing the particles of the negative electrode material and resin powder such as polyethylene and polyvinyl alcohol and hot pressing in a mold. However, dry mixing requires a large amount of binder to obtain sufficient negative electrode strength, and if the binder is excessive, the discharge capacity and rapid charge / discharge efficiency may be reduced.
When the negative electrode mixture layer is formed and then pressure bonding such as pressurization is performed, the adhesive strength between the negative electrode mixture layer and the current collector can be further increased.
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 in order to increase the volume capacity of the negative electrode.
The shape of the current collector used for the negative electrode is not particularly limited, but is preferably a foil, a mesh, a net-like material such as expanded metal, or the like. The material for the current collector is preferably copper, stainless steel, nickel or the like. When the current collector has a foil shape, the thickness is preferably 5 to 20 μm.

[Lithium ion secondary battery]
The lithium ion secondary battery of the present invention is formed using the negative electrode.
The secondary battery of the present invention is not particularly limited except that the negative electrode is used, and other battery components conform to the elements of a general secondary battery. That is, an electrolytic solution, a negative electrode, and a positive electrode are the main battery constituent elements, and these elements are enclosed in, for example, a battery can. The negative electrode and the positive electrode each act as a lithium ion carrier, and lithium ions are released 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 composed of a positive electrode material, a binder and a conductive material to the surface of the current collector. As the positive electrode material (positive electrode active material), a lithium compound is used, but it is preferable to select a material that can occlude / desorb a sufficient amount of lithium. For example, lithium-containing transition metal oxide, transition metal chalcogenide, vanadium oxide, other lithium compounds, chemical formula M _X Mo ₆ OS _8-Y (where X is 0 ≦ X ≦ 4, Y is 0 ≦ Y ≦ 1) And the like, and M is at least one kind of transition metal element), and the like can be used. 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 solid solution of lithium and two or more transition metals. Complex oxides may be used alone or in combination of two or more. Specifically, the lithium-containing transition metal compound oxide is LiM ¹ _1-X M ² _X O ₂ (wherein X is a numerical value in the range of 0 ≦ X ≦ 1, and M ¹ and M ² are at least one kind) Is a transition metal element) or LiM ¹ _1-Y M ² _Y O ₄ (where Y is a numerical value in the range of 0 ≦ Y ≦ 1, and M ¹ and M ² are at least one transition metal element). Indicated.
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 and the like. Preferred 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.
Examples of the lithium-containing transition metal oxide include lithium, transition metal oxides, hydroxides, salts, and the like as starting materials, and these starting materials are mixed in accordance with the composition of the desired metal oxide, and are mixed under an oxygen atmosphere. It can be obtained by firing at a temperature of ˜1000 ° C.

As the positive electrode active material, the lithium compound may be used alone or in combination of two or more. Moreover, alkali carbonates, such as lithium carbonate, can be added in a positive electrode.
The positive electrode is formed by, for example, applying a positive electrode mixture composed of the lithium compound, the binder, and a conductive material for imparting conductivity to the positive electrode on one or both sides of the current collector to form a positive electrode mixture layer. Produced. As the binder, the same one as that used for producing the negative electrode can be used. Carbon materials such as graphite and carbon black are used as the conductive material.

Similarly to the negative electrode, the positive electrode mixture may be formed by dispersing the positive electrode mixture in a solvent and applying the paste-like positive electrode mixture to a current collector and drying to form a positive electrode mixture layer. After that, pressure bonding such as press pressing may be further performed. As a result, the positive electrode mixture layer is uniformly and firmly bonded to the current collector.
The shape of the current collector is not particularly limited, but is preferably a foil shape, a mesh shape, a net shape such as expanded metal, or the like. The material of the current collector is aluminum, stainless steel, nickel or the like. In the case of a foil shape, the thickness is preferably 10 to 40 μm.

[Nonaqueous electrolyte]
The nonaqueous electrolyte (electrolytic solution) used for the secondary battery of the present invention is an electrolyte salt used for a normal nonaqueous electrolytic solution. Examples of the electrolyte salt include 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 (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 CHOSO ₂ ] ₂ , LiB [C ₆ H ₃ (CF ₃ ) ₂ ] ₄ , LiAlCl ₄ , LiSiF _{5 and} other lithium salts can be used. In particular, LiPF ₆ and LiBF ₄ are preferable from the viewpoint of oxidation stability.
The electrolyte salt concentration of the electrolytic solution is preferably from 0.1 to 5 mol / l, more preferably from 0.5 to 3.0 mol / l.

The non-aqueous electrolyte may be liquid, or may be a solid or gel polymer electrolyte. In the former case, the nonaqueous electrolyte battery is configured as 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 solution, carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, 1,1- or 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2- Methyltetrahydrofuran, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, ethers such as anisole and diethyl ether, thioethers such as sulfolane and methylsulfolane, nitriles such as acetonitrile, chloronitrile and propionitrile , Trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene, benzoyl chloride, benzoyl bromide, tetrahy Rochiofen, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, may be used an aprotic organic solvent such as dimethyl sulfite, and the like.

  When the polymer electrolyte is used, it is preferable to use a polymer compound gelled with a plasticizer (non-aqueous electrolyte) as a matrix. Examples of the polymer compound constituting the matrix include ether-based polymer compounds such as polyethylene oxide and its crosslinked products, polymethacrylate-based polymer compounds, polyacrylate-based polymer compounds, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene. Fluorine polymer compounds such as copolymers can be used alone or in combination. It is particularly preferable to use a fluorine-based polymer compound such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer.

  A plasticizer is blended in the polymer solid electrolyte or polymer gel electrolyte, and the electrolyte salt or non-aqueous solvent can be used as the plasticizer. In the case of a polymer gel electrolyte, the concentration of the electrolyte salt in the non-aqueous electrolyte as a plasticizer is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 2.0 mol / l.

The method for producing the polymer solid electrolyte is not particularly limited. For example, the polymer compound constituting the matrix, the lithium salt, and the nonaqueous solvent (plasticizer) are mixed and heated to melt the polymer compound. Method of evaporating organic solvent for mixing after dissolving polymer compound, lithium salt, and non-aqueous solvent (plasticizer) in organic solvent, mixing polymerizable monomer, lithium salt and non-aqueous solvent (plasticizer) In addition, a method of obtaining a polymer compound by irradiating the mixture with ultraviolet rays, an electron beam, a molecular beam or the like to polymerize a polymerizable monomer can be exemplified.
10-90 mass% is preferable, and, as for the ratio of the nonaqueous solvent (plasticizer) in a polymer solid electrolyte, 30-80 mass% is more preferable. If it is less than 10% by mass, the electrical conductivity will be low, and if it exceeds 90% by mass, the mechanical strength will be weak and film formation will be difficult.

In the lithium ion secondary battery of the present invention, a separator can also be used.
Although the material of a separator is not specifically limited, For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are mentioned. A synthetic resin microporous membrane is preferred, and among them, a polyolefin microporous membrane is preferred in terms of thickness, membrane strength, and membrane resistance. Specifically, it is a microporous membrane made of polyethylene and polypropylene, or a microporous membrane that combines these.

The secondary battery of the present invention is produced by laminating the negative electrode, the positive electrode, and the nonaqueous electrolyte in the order of, for example, the negative electrode, the nonaqueous electrolyte, and the positive electrode, and accommodating the laminate in the battery exterior material.
Further, a non-aqueous 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 form thereof are not particularly limited, and may be cylindrical, rectangular, depending on the application, mounted equipment, required charge / discharge capacity, and the like. A coin type, a button type, or the like can be arbitrarily selected. In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to include a means for detecting an increase in the internal pressure of the battery and shutting off the current when there is an abnormality such as overcharging.
In the case of a polymer electrolyte battery, a structure enclosed in a laminate film can also be used.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In Examples and Comparative Examples, button-type secondary batteries for evaluation having a configuration as shown in FIG. 1 were produced and evaluated. The battery can be produced according to a known method based on the object of the present invention.

[Example 1]
[Preparation of mesophase microsphere graphitized product (A)]
The coal tar pitch was heat-treated at 450 ° C. for 90 minutes in an inert atmosphere to generate 35% by mass of mesophase microspheres in the pitch matrix. Thereafter, mesophase spherules were dissolved and extracted using oil in tar, separated by filtration, and dried at 120 ° C. in a nitrogen atmosphere. This was heat-treated at 600 ° C. for 3 hours in a nitrogen atmosphere to prepare a mesophase microsphere fired product. Next, the fired product was immersed in an aqueous ferrous chloride solution, and then water was removed while stirring, followed by drying to adhere 5% by mass of ferrous chloride to the surface of the mesophase microsphere fired product.
The mesophase small sphere calcined product to which ferrous chloride was adhered was filled in a graphite crucible and heated at 3150 ° C. for 5 hours in a non-oxidizing atmosphere to conduct graphitization to prepare a mesophase small sphere graphitized product (A). . The graphitized product (A) contained no iron compound.
The shape of the graphitized product (A) was close to a sphere with fine irregularities on the surface, and the average aspect ratio was 1.1. The average particle diameter was 32 μm, the average lattice spacing d ₀₀₂ was 0.3357 nm, and the specific surface area was 2.9 m ² / g.

[Preparation of Spheroidized or Ellipsoidized Natural Graphite (B)]
Natural graphite particles (average aspect ratio 1.4, average particle diameter 20 μm, average lattice spacing d ₀₀₂ 0.3356 nm, specific surface area 5.0 m ² / g) granulated into spherical to ellipsoidal shapes were prepared.

[Preparation of non-granulated graphite (C1)]
The mesophase microsphere fired product (heat treatment at 600 ° C. for 3 hours) was pulverized by a vortex pulverizer. The pulverized product was filled in a graphite crucible and graphitized at 3150 ° C. for 5 hours in a non-oxidizing atmosphere. Next, 0.5 parts by mass of titanium oxide powder (average particle size 21 nm) was mixed with 100 parts by mass of the obtained graphitized material, and the mixture was put into a “Mechano-Fusion System” (manufactured by Hosokawa Micron Co., Ltd.). Under the conditions of a speed of 20 m / sec, a processing time of 60 minutes, and a distance of 5 mm between the rotating drum and the internal member, a compressive force and a shearing force were repeatedly applied to perform a mechanochemical treatment. The obtained non-granulated mesophase small spherical graphite (C1) was a lump with a rounded particle, and the titanium oxide powder was uniformly embedded on the surface. The non-granulated mesophase small spherical graphite (C1) had an average aspect ratio of 1.3, an average particle diameter of 13 μm, an average lattice spacing d ₀₀₂ of 0.3359 nm, and a specific surface area of 3.5 m ² / g.

[Preparation of negative electrode material]
40 parts by mass of the mesophase microsphere graphitized product (A), 40 parts by mass of spheroidized or ellipsoidal natural graphite particles (B) and 20 parts by mass of non-granulated mesophase microsphere graphite (C1) are mixed, and negative electrode material Was prepared.

[Preparation of negative electrode mixture]
98 parts by mass of the negative electrode material, 1 part by mass of the binder carboxymethyl cellulose and 1 part by mass of styrene butadiene rubber were put in water and stirred to prepare a negative electrode mixture paste.

[Production of working electrode]
The negative electrode mixture paste was applied on a copper foil having a thickness of 16 μm to a uniform thickness, and further, water in a dispersion medium was evaporated at 90 ° C. in a vacuum to dry the paste. Next, the negative electrode mixture coated on the copper foil was pressed with a hand press at 12 kN / cm ² (120 MPa) and punched into a circular shape having a diameter of 15.5 mm, thereby adhering to the negative electrode mixture adhered to the copper foil. A working electrode having an agent layer (thickness 60 μm) was prepared. The density of the negative electrode mixture layer was 1.75 g / cm ³ . The working electrode was stretched and not deformed, and the current collector viewed from the cross section had no dent.

[Production of counter electrode]
A lithium metal foil is pressed onto a nickel net and punched into a circular shape with a diameter of 15.5 mm, and consists of a current collector made of nickel net and a lithium metal foil (thickness 0.5 mm) in close contact with the current collector. A counter electrode (positive electrode) was produced.

[Electrolyte / Separator]
LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate 33 vol% -methyl ethyl carbonate 67 vol% at a concentration of 1 mol / l to prepare a non-aqueous electrolyte. The obtained nonaqueous electrolytic solution was impregnated into a polypropylene porous body (thickness: 20 μm) to produce a separator impregnated with the electrolytic solution.

[Production of evaluation battery]
A button-type secondary battery shown in FIG. 1 was prepared as an evaluation battery.
The exterior cup 1 and the exterior can 3 were sealed by interposing an insulating gasket 6 at the peripheral portion thereof and caulking both peripheral portions. Inside, in order from the inner surface of the outer can 3, a current collector 7 a made of nickel net, a cylindrical counter electrode (positive electrode) 4 made of lithium foil, a separator 5 impregnated with an electrolyte, and a disk-like action made of a negative electrode mixture A battery in which an electrode (negative electrode) 2 and a current collector 7b made of copper foil are laminated.
In the evaluation battery, the separator 5 impregnated with the electrolytic solution was sandwiched 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, and then the working electrode 2 was attached to the exterior cup 1. The counter electrode 4 is accommodated in the outer can 3, the outer cup 1 and the outer can 3 are combined, and an insulating gasket 6 is interposed between the outer cup 1 and the outer can 3, It was made by sealing and sealing.
The evaluation battery is a battery composed of a working electrode 2 containing graphite particles that can be used as a negative electrode active material and a counter electrode 4 made of a lithium metal foil in an actual battery.

  The evaluation battery produced as described above was subjected to the following charge / discharge test at a temperature of 25 ° C., discharge capacity per mass, discharge capacity per volume, initial charge / discharge efficiency, rapid charge rate, rapid discharge. Rate and cycle characteristics were evaluated. The evaluation results are shown in Table 1.

[Discharge capacity per mass, discharge capacity per volume]
After 0.9 mA constant current charging was performed until the circuit voltage reached 0 mV, switching to constant voltage charging was continued until the current value reached 20 μA. The charging capacity per mass was determined from the energization amount during that time. Then, it rested for 120 minutes. Next, constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 1.5 V, and the discharge capacity per mass was determined from the amount of electricity supplied during this period. This was the first cycle. From the charge capacity and discharge capacity in the first cycle, the initial charge / discharge efficiency was calculated by the following equation (1).
Initial charge / discharge efficiency (%) = (discharge capacity / charge capacity) × 100 (1)
In this test, the process of occluding lithium ions in the negative electrode material was charged, and the process of detaching from the negative electrode material was discharged.

[Quick charge rate]
Following the first cycle, rapid charging was performed in the second cycle.
Until the circuit voltage reached 0 mV, constant current charging was performed by setting the current value to 4.5 mA which is five times the first cycle, the constant current charging capacity was obtained, and the rapid charging rate was calculated from the following equation (2).
Rapid charge rate (%) = (constant current charge capacity in the second cycle / in the first cycle
Discharge capacity) x 100 (2)

[Rapid discharge rate]
Using another evaluation battery, rapid discharge was performed in the second cycle following the first cycle. As described above, after performing the first cycle, charging is performed in the same manner as in the first cycle, and then the constant current discharge is performed until the circuit voltage reaches 1.5 V with the current value set to 18 mA, which is 20 times the first cycle. went. The discharge capacity per mass was calculated | required from the amount of electricity supply in the meantime, and the rapid discharge rate was calculated by following Formula (3).
Rapid discharge rate (%) = (discharge capacity in the second cycle / discharge capacity in the first cycle)
Amount) x 100 (3)

[Cycle characteristics]
An evaluation battery different from the evaluation battery that evaluated the discharge capacity per mass, the rapid charge rate, and the rapid discharge rate was produced and evaluated as follows.
After 4.0 mA constant current charging was performed until the circuit voltage reached 0 mV, switching to constant voltage charging was continued until the current value reached 20 μA, and then rested for 120 minutes. Next, constant current discharge was performed at a current value of 4.0 mA until the circuit voltage reached 1.5V. The charge / discharge was repeated 20 times, and the cycle characteristics were calculated from the obtained discharge capacity per mass using the following equation (4).
Cycle characteristics (%) = (discharge capacity in the 20th cycle / in the first cycle)
Discharge capacity) x 100 (4)

  As shown in Table 1, the evaluation battery obtained by using the negative electrode material of Example 1 as the working electrode can increase the density of the active material layer and exhibits a high discharge capacity per mass. For this reason, the discharge capacity per volume can be improved significantly. Even at its high density, the rapid charge rate, rapid discharge rate, and cycle characteristics maintain excellent results.

[Examples 4 and 5 , Reference Examples 2 and 3 ]
In Example 1, except that the mass ratio of the mesophase microsphere graphitized product (A), the granulated natural graphite particles (B), and the non-granulated mesophase microsphere graphite (C1) was changed as shown in Table 1. Produced a working electrode by adjusting the density of the negative electrode mixture layer to 1.75 g / cm ³ in the same manner as in Example 1 to prepare an evaluation battery. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
When the working electrode is made of a negative electrode material that falls within the mass ratio specified by the present invention, the density of the negative electrode mixture layer can be increased, and the discharge capacity, initial charge / discharge efficiency, rapid charge rate, rapid discharge rate, cycle characteristics None of them were excellent.

[Comparative Example 1]
The 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 mesophase microsphere graphitized product (A) used in Example 1 was used alone as the negative electrode material. An evaluation battery was prepared. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when the mesophase microsphere graphitized material (A) was used alone as the negative electrode material, the rapid charge rate and cycle characteristics were insufficient.

[Comparative 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 1 except that the granulated natural graphite particles (B) used in Example 1 were used alone as the negative electrode material. Thus, a working electrode was produced, and an evaluation battery was produced. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when the natural graphite particles (B) granulated as the negative electrode material were used alone, the rapid charge rate, rapid discharge rate, and cycle characteristics were 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 non-granulated mesophase microsphere graphite (C1) used in Example 1 was used alone as the negative electrode material. Thus, a working electrode was produced, and an evaluation battery was produced. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when non-granulated mesophase small spherical graphite (C1) is used alone as the negative electrode material, a high press is required when adjusting the density of the negative electrode mixture layer to 1.75 g / cm ^3. Pressure was required, the copper foil as the current collector was stretched, and a part of the active material layer was peeled off. When a charge / discharge test was performed on the non-peeled portion, initial charge / discharge efficiency, rapid charge rate, and cycle characteristics were insufficient.

[Comparative Examples 4 to 7]
In Example 1, except that the mass ratio of the mesophase microsphere graphitized product (A), the granulated natural graphite particles (B), and the non-granulated mesophase microsphere graphite (C1) was changed as shown in Table 1. Produced a working electrode by adjusting the density of the negative electrode mixture layer to 1.75 g / cm ³ in the same manner as in Example 1 to prepare an evaluation battery. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when the working electrode is made of a negative electrode material that deviates from the mass ratio specified by the present invention, any one of discharge capacity, initial charge / discharge efficiency, rapid charge rate, rapid discharge rate, cycle characteristics Was insufficient.

[Example 6]
[Preparation of Spheroidized or Ellipsoidized Natural Graphite (B1)]
100 parts by mass of natural graphite particles granulated into spherical to ellipsoidal shapes (average particle size 20 μm, average lattice spacing d ₀₀₂ 0.3356 nm, average aspect ratio 1.4, specific surface area 5.0 m ² / g) , 3 parts by mass of mesophase pitch powder (average particle size 2 μm) with a softening point of 150 ° C. and 0.1 part by mass of ketjen black (average particle size 30 nm) were mixed into a “Mechanofusion System” (manufactured by Hosokawa Micron Corporation) The mechanochemical treatment was performed by repeatedly applying compressive force and shearing force under the conditions of a peripheral speed of the rotating drum of 20 m / sec, a processing time of 60 minutes, and a distance of 5 mm between the rotating drum and the internal member. The obtained mesophase pitch-coated natural graphite was filled in a graphite crucible and fired at 1200 ° C. for 3 hours in a non-oxidizing atmosphere. The obtained mesophase pitch carbide coated natural graphite (B1) had an average aspect ratio of 1.4, an average particle diameter of 20 μm, an average lattice spacing d ₀₀₂ of 0.3358 nm, and a specific surface area of 3.5 m ² / g. .

A negative electrode mixture in the same manner as in Example 1, except that the natural graphite particles (B) granulated into spherical to ellipsoidal shapes in Example 1 were changed to the mesophase pitch carbide-coated natural graphite (B1). A working electrode was prepared by adjusting the density of the layer to 1.75 g / cm ³ to prepare an evaluation battery. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when a negative electrode material is produced using mesophase pitch carbide-coated natural graphite (B1), the active material layer has a high density and a high discharge capacity per mass. For this reason, the discharge capacity per volume is significantly improved. Further, even at a high density, the rapid charge rate, rapid discharge rate, and cycle characteristics are excellent.

[Example 7]
Mesophase pitch carbide-coated natural graphite (B1) of Example 6 was filled in a graphite crucible and graphitized at 3000 ° C. for 5 hours in a non-oxidizing atmosphere to obtain mesophase pitch graphite-coated natural graphite (B2). Prepared. The obtained mesophase pitch graphitized natural graphite (B2) had an average aspect ratio of 1.4, an average particle diameter of 20 μm, an average lattice spacing d ₀₀₂ of 0.3356 nm, and a specific surface area of 2.7 m ² / g. It was.
A negative electrode mixture in the same manner as in Example 1 except that the natural graphite particles (B) granulated into spherical to ellipsoidal shapes in Example 1 were changed to the mesophase pitch graphitized natural graphite (B2). A working electrode was prepared by adjusting the density of the layer to 1.75 g / cm ³ to prepare an evaluation battery. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when a negative electrode material is prepared using mesophase pitch graphitized natural graphite (B2), the active material layer has a high density and a high discharge capacity per mass. For this reason, the discharge capacity per volume is significantly improved. Further, even at a high density, the rapid charge rate, rapid discharge rate, and cycle characteristics are excellent.

[Example 8]
[Preparation of granulated graphite (C2)]
Coke particles (average particle size 5 μm) 80 parts by mass and coal tar pitch 20 parts by mass 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 calcined at 600 ° C. for 3 hours in a non-oxidizing atmosphere. The fired product was filled into a graphite crucible and graphitized at 3150 ° C. for 5 hours in a non-oxidizing atmosphere. The obtained graphitized material was pulverized with a grinding pulverizer to prepare granulated graphite (C2). The average particle size was 15 μm, the average aspect ratio was 1.7, the average lattice spacing d ₀₀₂ was 0.3358 nm, and the specific surface area was 3.2 m ² / g.
The non-granulated mesophase microsphere graphite (C1) of Example 1 is changed to the granulated graphite (C2), and natural graphite particles (B) granulated into spherical to ellipsoidal shapes of Example 1 Was changed to mesophase pitch carbide-coated natural graphite (B1) prepared in Example 6, and the density of the negative electrode mixture layer was adjusted to 1.75 g / cm ³ in the same manner as in Example 1 to obtain a working electrode. An evaluation battery was prepared. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when a negative electrode material is produced using granulated graphite (C2), the density of the active material layer is high and the discharge capacity per mass is high. For this reason, the discharge capacity per volume is significantly improved. Further, even at a high density, the rapid charge rate, rapid discharge rate, and cycle characteristics are excellent.

[Comparative Examples 8 to 10]
Example 1 except that mesophase pitch carbide-coated natural graphite (B1), mesophase pitch graphitized-coated natural graphite (B2) and granulated graphite (C2) used in Examples 6 to 8 were used alone. Similarly, 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 / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when each of mesophase pitch carbide-coated natural graphite (B1), mesophase pitch graphitized-coated natural graphite (B2) and granulated graphite (C2) is used alone, the graphite has a high density. Oriented, in particular, rapid discharge rate and cycle characteristics were insufficient.

[Example 9]
In the preparation of the mesophase microsphere graphitized product (A) of Example 1, the microsphere graphitized product was prepared in the same manner as in Example 1 except that the heat treatment time at 450 ° C. in an inert atmosphere of coal tar pitch was shortened to 30 minutes. (A) was prepared. The shape of the obtained mesophase small sphere graphitized product (A) is close to a sphere although it has fine irregularities on the surface, the average aspect ratio is 1.1, the average particle diameter is 15 μm, the average lattice spacing d ₀₀₂ is 0.3360 nm, The specific surface area was 3.9 m ² / g.
In the preparation of the natural graphite particles (B) of Example 1, natural graphite particles granulated into spherical to ellipsoid shapes (average aspect ratio 1.3, average particle diameter 12 μm, average lattice spacing d ₀₀₂ 0.3356 nm The specific surface area was 6.5 m ² / g).

In the preparation of the non-granulated mesophase small sphere graphite (C1) of Example 1, the particle diameter was further reduced when the mesophase small sphere fired product was pulverized by a vortex pulverizer. Moreover, it replaced with the titanium oxide powder and used the silicon oxide powder (average particle diameter of 30 nm). The obtained non-granulated mesophase small spherical graphite (C1) had a lump shape with rounded corners, and silicon oxide powder was uniformly embedded on the surface. The average aspect ratio was 1.2, the average particle diameter was 5 μm, the average lattice spacing d ₀₀₂ was 0.3360 nm, and the specific surface area was 4.2 m ² / g.
In Example 1, except that these components were used, in the same manner as in Example 1, 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 / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when the working electrode is made of a negative electrode material having a mass ratio defined by the present invention, the density of the active material layer can be increased, and the discharge capacity, initial charge / discharge efficiency, rapid charge rate, Both rapid discharge rate and cycle characteristics are excellent.

[Example 10]
In the preparation of the mesophase microsphere graphitized product (A) of Example 1, the microsphere graphitized product was prepared in the same manner as in Example 1 except that the heat treatment time at 450 ° C. in an inert atmosphere of coal tar pitch was increased to 110 minutes. (A) was prepared. The shape of the obtained mesophase microsphere graphitized material (A) is close to a sphere although it has fine irregularities on the surface, the average aspect ratio is 1.1, the average particle diameter is 36 μm, the average lattice plane distance d ₀₀₂ is 0.3356 nm, The specific surface area was 2.3 m ² / g.
In the preparation of spheroidized or ellipsoidal natural graphite (B) of Example 1, natural graphite particles granulated into a spherical to ellipsoidal shape (average aspect ratio 1.8, average particle diameter 28 μm, average lattice plane) The distance d ₀₀₂ 0.3356 nm and the specific surface area 3.5 m ² / g) were prepared.

In the preparation of the non-granulated mesophase microsphere graphite (C1) of Example 1, when the mesophase microsphere fired product was pulverized using a vortex pulverizer, the particle size was set to be larger. Moreover, it replaced with the titanium oxide powder and used the silicon oxide powder (average particle diameter of 30 nm). The obtained non-granulated graphite (C1) was in a lump shape with corners of the particles, and silicon oxide powder was uniformly embedded on the surface. The average aspect ratio was 1.3, the average particle size was 18 μm, the average lattice spacing d ₀₀₂ was 0.3358 nm, and the specific surface area was 3.2 m ² / g.
In Example 1, except that these components were used, in the same manner as in Example 1, 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 / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when the working electrode is made of a negative electrode material having a mass ratio defined by the present invention, the density of the active material layer can be increased, and the discharge capacity, initial charge / discharge efficiency, rapid charge rate, Both rapid discharge rate and cycle characteristics are excellent.

[Comparative Examples 11-15]
In the preparation of the mesophase microsphere graphitized product (A) of Example 1, the heat treatment time at 450 ° C. in an inert atmosphere of coal tar pitch was adjusted, and the mesophase microsphere graphitized product having an average particle size as shown in Table 1 (A) was prepared in the same manner as Example 1.
As for the natural graphite particles (B) of Example 1, natural graphite particles granulated into spherical to ellipsoidal shapes as shown in Table 1 were prepared.
In the preparation of the non-granulated mesophase microsphere graphite (C1) of Example 1, the pulverized conditions of the mesophase microsphere calcined product were operated using a vortex crusher, and coal tar having an average particle diameter as shown in Table 1 was obtained. By adjusting the heat treatment time at 450 ° C. in an inert atmosphere of pitch, non-granulated mesophase microsphere graphite (C1) having an average particle size as shown in Table 1 was prepared.
In Example 1, except that these components were used, in the same manner as in Example 1, 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 / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when the working electrode is made of a negative electrode material deviating from the average particle diameter defined in the present invention, any one of discharge capacity, initial charge / discharge efficiency, rapid charge rate, rapid discharge rate, and cycle characteristics is It has deteriorated.

[Example 11]
[Preparation of Spheroidized or Ellipsoidized Natural Graphite (B2)]
100 parts by mass of natural graphite particles granulated into a spherical to ellipsoidal shape (average particle diameter 20 μm, average lattice spacing d ₀₀₂ 0.3356 nm, average aspect ratio 1.4, specific surface area 5.0 m ² / g) Then, 25 parts by mass of coal tar pitch having a volatile content of about 40% by mass is immersed in 100 parts by mass of a solution obtained by dissolving 75 parts by mass of tar oil, and stirring is continued at 150 ° C. and a pressure of 5 mmHg or less. Removed and dried. The obtained pitch-impregnated natural graphite particles were heat-treated at 450 ° C. for 30 hours in a non-oxidizing atmosphere to obtain a composite of carbonaceous material and natural graphite particles.
100 parts by mass of the composite and 2 parts by mass of vapor-grown carbon fiber graphitized material (diameter: 150 nm, average aspect ratio: about 50) are mixed and put into a “Mechano-Fusion System” (manufactured by Hosokawa Micron Corporation) for rotation. A mechanochemical treatment was performed by repeatedly applying a compressive force and a shearing force under the conditions of a peripheral speed of the drum of 20 m / second, a treatment time of 60 minutes, and a distance of 5 mm between the rotating drum and the internal member. The obtained carbon fiber graphitized substance-attached composite was filled in a graphite crucible and graphitized at 3000 ° C. for 5 hours in a non-oxidizing atmosphere. The obtained pitch-graphitized-coated natural graphite particles (B2) have carbon fiber graphitized particles attached to their surfaces, an average aspect ratio of 1.4, an average particle size of 20 μm, and an average lattice spacing d ₀₀₂ of 0.3357nm, the specific surface area was 1.7m ² / g.

In Example 1, the mesophase pitch carbide-coated natural graphite (B1) was changed to the vapor-grown carbon fiber graphitized material-attached pitch graphitized-coated natural graphite (B2), and the non-granulated graphite (C1) was carried out. 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 granulated graphite (C2) prepared in Example 8 was changed to an evaluation battery. Was made. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when a negative electrode material was produced using carbon fiber graphitized material-attached pitch graphitized coated natural graphite (B2), the density of the active material layer was high and the discharge capacity per mass was high. For this reason, the discharge capacity per volume is significantly improved. Further, even at a high density, the rapid charge rate, rapid discharge rate, and cycle characteristics are excellent.

[Example 12]
[Preparation of Spheroidized or Ellipsoidized Natural Graphite (B1)]
90 parts by mass of natural graphite particles granulated into spherical to ellipsoidal shapes (average particle diameter 20 μm, average lattice spacing d ₀₀₂ 0.3356 nm, average aspect ratio 1.4, specific surface area 5.0 m ² / g) Then, it was immersed in a mixed solution consisting of 25 parts by mass of a phenol resin having a residual carbon ratio of 40% by mass, 500 parts by mass of ethylene glycol and 2.5 parts by mass of hexamethylenetetramine, and stirred at 150 ° C. for 30 minutes. Subsequently, stirring was continued at 150 ° C. and 5 mmHg or less, and the solvent was ethylene glycol, which was then dried. The obtained resin-impregnated natural graphite particles were heated in air to 270 ° C. over 5 hours, further held at 270 ° C. for 2 hours, and heated. After crushing a few fused materials, carbonization was performed at 1250 ° C. in a nitrogen atmosphere. The obtained resin carbide-coated natural graphite particles (B1) had an average aspect ratio of 1.4, an average particle diameter of 20 μm, an average lattice spacing d ₀₀₂ of 0.3359 nm, and a specific surface area of 3.9 m ² / g. .

In Example 1, the mesophase pitch carbide-coated natural graphite (B1) is changed to the resin carbide-coated natural graphite particles (B1), and the non-granulated graphite (C1) is granulated graphite prepared in Example 8. Except for changing to (C2), the density of the negative electrode mixture layer was adjusted to 1.75 g / cm ³ in the same manner as in Example 1 to produce a working electrode, and an evaluation battery was produced. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when a negative electrode material is produced using resin carbide-coated natural graphite particles (B1), the active material layer has a high density and a high discharge capacity per mass. For this reason, the discharge capacity per volume is significantly improved. Further, even at a high density, the rapid charge rate, rapid discharge rate, and cycle characteristics are excellent.

[Example 13]
[Preparation of Spheroidized or Ellipsoidized Natural Graphite (B1)]
100 parts by mass of natural graphite particles granulated into spherical to ellipsoidal shapes (average particle size 20 μm, average lattice spacing d ₀₀₂ 0.3356 nm, average aspect ratio 1.4, specific surface area 5.0 m ² / g) , 1.5 parts by mass of mesophase pitch powder with a softening point of 150 ° C. (average particle size 2 μm) and 0.5 parts by mass of graphitized carbon vapor phase carbon fiber (diameter 150 nm, average aspect ratio about 50), Inserted into “Mechano-Fusion System” (manufactured by Hosokawa Micron Co., Ltd.), repeated compression force and shearing force under conditions of peripheral speed of rotating drum 20m / second, processing time 60 minutes, distance between rotating drum and internal member 5mm And subjected to mechanochemical treatment. The obtained carbon fiber graphitized substance-attached composite was filled in a graphite crucible and fired at 1200 ° C. for 3 hours in a non-oxidizing atmosphere. The obtained pitch carbide-coated natural graphite particles (B1) have carbon fiber graphitized particles adhering to the surface, the average aspect ratio is 1.4, the average particle diameter is 20 μm, and the average lattice spacing d ₀₀₂ is 0. The specific surface area was 4.4 m ² / g.

In Example 1, mesophase pitch carbide-coated natural graphite (B1) was changed to graphitized material-attached pitch carbide-coated natural graphite particles (B1) of the carbon fiber, and non-granulated graphite (C1) was obtained in Example 8. Except for changing to the prepared granulated graphite (C2), the density of the negative electrode mixture layer was adjusted to 1.75 g / cm ³ in the same manner as in Example 1 to produce a working electrode, and an evaluation battery was produced. . The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when a negative electrode material is produced using resin carbide-coated natural graphite particles (B1), the active material layer has a high density and a high discharge capacity per mass. For this reason, the discharge capacity per volume is significantly improved. Further, even at a high density, the rapid charge rate, rapid discharge rate, and cycle characteristics are excellent.

[Example 14]
[Preparation of non-granulated graphite (C1)]
A coal tar pitch having a volatile content of about 40% by mass was filled in a steel container and fired at 480 ° C. for 20 hours in a non-oxidizing atmosphere. The obtained bulk mesophase was taken out from the steel container and pulverized by a grinding pulverizer. The pulverized product was put into a “Mechano-Fusion System” (manufactured by Hosokawa Micron Co., Ltd.), and the compression force, Shear force was repeatedly applied to perform mechanochemical treatment. The obtained bulk mesophase particles were filled in a graphite crucible and graphitized at 3000 ° C. for 5 hours in a non-oxidizing atmosphere. The obtained non-granulated bulk mesophase graphite particles (C1) were agglomerated with the corners of the particles removed. The average aspect ratio was 1.5, the average particle diameter was 10 μm, the average lattice spacing d ₀₀₂ was 0.3360 nm, and the specific surface area was 2.0 m ² / g.

In Example 1, the density of the negative electrode mixture layer was changed to 1.75 g in the same manner as in Example 1 except that the graphitized product (C1) of the mesophase microsphere pulverized product was changed to the bulk mesophase graphite particles (C1). A working electrode was prepared by adjusting to / cm ³ to prepare an evaluation battery. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, even when a negative electrode material is produced using bulk mesophase graphite particles (C1), the density of the active material layer is high and the discharge capacity per mass is high. For this reason, the discharge capacity per volume is significantly improved. Further, even at a high density, the rapid charge rate, rapid discharge rate, and cycle characteristics are excellent.

[Example 15]
[Preparation of granulated graphite (C2)]
70 parts by mass of natural graphite particles (average particle size 5 μm) granulated into a substantially spherical shape and 30 parts by mass of coal tar pitch were kneaded at 200 ° C. for 1 hour using a biaxial kneader. The kneaded product was calcined at 500 ° C. for 3 hours in a non-oxidizing atmosphere. The calcined product was pulverized with a grinding pulverizer to obtain a lump granulated calcined product (average particle size 13 μm). The massive granulated fired product was filled in a graphite crucible and graphitized at 3150 ° C. for 5 hours in a non-oxidizing atmosphere. The obtained granulated graphite (C2) was a bowl-shaped lump. The average aspect ratio was 1.5, the average particle size was 17 μm, the average lattice spacing d ₀₀₂ was 0.3358 nm, and the specific surface area was 2.8 m ² / g.

The density of the negative electrode mixture layer was changed to 1. in the same manner as in Example 1 except that the coke granulated graphite (C2) of Example 8 was changed to natural graphite (C2) granulated into a substantially spherical shape. A working electrode was prepared by adjusting to 75 g / cm ³ to prepare an evaluation battery. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when a negative electrode material is produced using natural graphite (C2) granulated into a substantially spherical shape, the active material layer has a high density and a high discharge capacity per mass. For this reason, the discharge capacity per volume is significantly improved. Further, even at a high density, the rapid charge rate, rapid discharge rate, and cycle characteristics are excellent.

[Example 16]
[Preparation of mesophase microsphere graphitized product (A)]
In the preparation of the mesophase small sphere graphitized product (A) of Example 1, the mesophase small sphere graphitized product (A) was prepared in the same manner as in Example 1 except that ferrous chloride was not attached to the calcined mesophase small sphere. The obtained graphitized product (A) has a smooth and nearly spherical surface, an average aspect ratio of 1.1, an average particle diameter of 32 μm, an average lattice spacing d ₀₀₂ of 0.3359 nm, and a specific surface area of 0.5 m. ² / g.

[Preparation of Spheroidized or Ellipsoidized Natural Graphite (B)]
Natural graphite particles (average particle diameter 25 μm, average lattice spacing d ₀₀₂ 0.3356 nm, average aspect ratio 1.6, specific surface area 3.9 m ² / g) granulated into spherical to ellipsoidal shapes were prepared.

[Preparation of non-granulated graphite (C1)]
The mesophase microsphere graphitized product (pulverized product) of Example 1 was used as it was as non-granulated graphite (C1) without being subjected to the mechanochemical treatment in which the titanium oxide powder was mixed. The non-granulated graphite (C1) was agglomerated, the average aspect ratio was 1.5, the average particle diameter was 14 μm, the average lattice spacing d ₀₀₂ was 0.3359 nm, and the specific surface area was 0.9 m ² / g. .

[Preparation of negative electrode material]
The mesophase microsphere graphitized product (A) 40 parts by mass, spheroidized or ellipsoidized natural graphite (B1) 40 parts by mass and non-granulated graphite (C1) 20 parts by mass were mixed to prepare a negative electrode material.

[Preparation of negative electrode mixture]
95 parts by mass of the negative electrode material and 5 parts by mass of a binder polyvinylidene fluoride were placed in N-methylpyrrolidone and stirred to prepare a negative electrode mixture paste.

In Example 1, 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 / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, 40 parts by mass of mesophase microsphere graphitized material (A), 40 parts by mass of spheroidized or ellipsoidized natural graphite (B1) and 20 parts by mass of non-granulated graphite (C1) were mixed. When the negative electrode material is used, the density of the active material layer is high and the discharge capacity per mass is high. For this reason, the discharge capacity per volume is significantly improved. Further, even at a high density, the rapid charge rate, rapid discharge rate, and cycle characteristics are excellent.

[Comparative Example 16]
In Example 8, instead of granulated graphite (C2), scaly natural graphite (average particle diameter 8 μm, average lattice spacing d ₀₀₂ 0.3356 nm, average aspect ratio 5.2, specific surface area 7.6 m ² / g) was used. In the same manner as in Example 8, the density of the negative electrode mixture layer was adjusted to 1.75 g / cm ³ to produce a working electrode, and an evaluation battery was produced. The same charge / discharge test as in Example 1 was performed, and the evaluation results of the battery characteristics are shown in Table 1.
As shown in Table 1, when a negative electrode material is produced by blending granulated graphite (C2) and scale-like natural graphite, the rapid charge rate, rapid discharge rate, and cycle characteristics are reduced to a high density. To do.

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

1 exterior cup 2 working electrode (negative electrode)
3 Exterior can 4 Counter electrode (positive electrode)
5 Separator 6 Insulating gasket 7a, 7b Current collector

Claims (6)

Average particle diameter of 10 to 40 [mu] m, average aspect ratio Ri der less than 1.2, coal or heavy oil petroleum, optical obtained by heat treatment of at least one selected from the tars and pitches such Mesophase small sphere graphitized product (A) obtained by graphitizing spherical polymer having mechanical anisotropy ,
Spherical or ellipsoidal natural graphite having an average particle size of 5 to 35 μm, smaller than the average particle size of the mesophase small sphere graphitized product (A) and having an average aspect ratio of less than 2.0 (B) As well as
Graphite (C) having an average particle diameter of 2 to 25 μm, smaller than the average particle diameter of the mesophase microsphere graphitized product (A), and having an average aspect ratio of less than 2.0
The mesophase microsphere graphitized product (A), the spheroidized or ellipsoidized natural graphite (B) and the graphite (C) in the mixture have a mass ratio of the following formulas (1) and ( 2) The negative electrode material for lithium ion secondary batteries characterized by satisfying | filling.
a: b = (10 to 70): (90 to 30) (1)
(A + b): c = ( 80 to 95): ( 20 to 5) (2)
Here, a is the ratio of the mesophase microsphere graphitized product (A), b is the ratio of the spheroidized or ellipsoidized natural graphite (B), and c is the ratio of the graphite (C).   2. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the mesophase microsphere graphitized product (A) is spherical, and the graphite (C) is spherical, ellipsoidal or massive.   3. The lithium ion according to claim 1, wherein a carbonaceous material or a graphite material is attached to at least a part of the surface of the spherical or ellipsoidal natural graphite (B). Negative electrode material for secondary batteries.   The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the graphite (C) is granulated graphite and / or non-granulated graphite. A negative electrode material according to any one of claims 1 to 4, wherein the active material layer has a density of 1.7 g / cm ³ or more.   The lithium ion secondary battery which has a lithium ion secondary battery negative electrode of Claim 5.

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