JP5953249B2 - Composite graphite particles and their use in lithium ion secondary batteries - Google Patents

Description

  The present invention relates to composite graphite particles, a conductive material for a lithium ion secondary battery, 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, as the demand for increasing the energy density of batteries increases with the miniaturization or performance of electronic devices, lithium ions that can achieve higher voltages and achieve higher energy densities than other secondary batteries. Secondary batteries are particularly attracting attention.
A lithium ion secondary battery mainly includes an electrolyte solution (nonaqueous electrolyte) containing a lithium salt, a positive electrode using a lithium compound as a positive electrode active material, and a negative electrode, and both electrodes each function as a lithium ion carrier. As the negative electrode material responsible for the negative electrode battery mechanism (lithium ion occlusion during charge / lithium release during discharge), a carbon material having a high lithium ion occlusion and a high capacity is usually used. Among these, graphite having excellent charge / discharge characteristics and high discharge capacity and potential flatness is widely used as a negative electrode active material (see, for example, Patent Document 1).

  As a specific example using the graphite as the negative electrode material, typically, graphite particles having pores in which a plurality of flat particles are aggregated or bonded so that the orientation planes are non-parallel (see Patent Document 2), Graphite of mesocarbon microspheres composed of Brooks-Taylor single crystals in which basal planes of graphite (planes parallel to the hexagonal network of graphite crystals) are arranged in layers in a direction perpendicular to the diameter direction (see Patent Document 3) Composite graphite particles obtained by coating a carbonaceous material on natural graphite processed into a spherical shape (see Patent Document 4), bulk graphite particles obtained by pulverizing, oxidizing, and graphitizing bulk mesophase (see Patent Document 5) It is done.

Japanese Examined Patent Publication No. 62-23433 JP-A-10-158005 JP 2000-323127 A JP 2004-63321 A JP-A-10-139410

In recent years, the negative electrode materials of lithium-ion secondary batteries, especially for portable electronic devices and electric vehicles, have high capacity, rapid chargeability, rapid discharge, and initial discharge capacity even after repeated charge / discharge. There is a need for cycle characteristics that do not deteriorate. However, the conventional graphite-based negative electrode material described above does not have rapid chargeability, rapid discharge property, and cycle characteristics that satisfy high demands. This is partly due to the contact between the graphite particles coming off due to the expansion and contraction of the graphite accompanying charging / discharging, resulting in isolated graphite particles not involved in charging / discharging.
For this reason, it is customary to use together a conductive material for maintaining contact between graphite particles. As the conductive material, carbonaceous fine particles such as carbon black, scaly graphite such as artificial graphite and natural graphite, vapor grown carbon fiber, carbonaceous or graphitic fiber such as carbon nanotube, etc. are generally known. ing.

However, various problems may be caused by the blending of the various conductive materials.
For example, in the case of the above carbonaceous fine particles, the particle size of carbon black is usually about 10 to 500 nm, which is too fine. Therefore, a large amount of compounding is required to form a conductive path of graphite particles as an active material. Due to its high reactivity, the initial charge / discharge efficiency and cycle characteristics are reduced.
In addition, carbonaceous or graphitic fibers are difficult to completely defibrate, and the amount of the carbonaceous or graphitic fiber that exceeds the amount necessary for obtaining an effect as a conductive material is necessary, and is expensive and industrial. Difficult to spread.

  Scale-like graphite is excellent in economic efficiency among known conductive materials and is widely used, but due to its shape, the electrode surface and the inside are likely to be blocked, impeding the permeability and retention of the electrolyte, Electrolyte depletion is caused and rapid discharge and cycle characteristics are deteriorated. In addition, there is a problem that charging expansion is increased. That is, scaly graphite has a role of holding graphite particles together when the graphite particles, which are the main constituent components of the negative electrode material, are partially isolated by expansion and contraction associated with charge and discharge. In addition to hindering the movement of the electrolyte, it has a large charge expansion. In addition, since scaly graphite has a large specific surface area, the viscosity of the negative electrode mixture slurry increases, and the productivity may decrease. As described above, the scale-like graphite cancels out the effect of imparting conductivity as the blending amount increases, and if it is excessive, adverse effects appear greatly.

  The objective of this invention is providing the negative electrode material as a electrically conductive material which can express the outstanding cycling characteristics, when it mix | blends with the known negative electrode active material of a lithium ion secondary battery. In particular, even when the negative electrode is pressed to a high density, the negative electrode has a high discharge capacity per volume, without impairing the permeability and retention of the electrolyte, exhibiting excellent rapid chargeability, rapid discharge properties and cycle characteristics Is to provide.

  The present inventor has paid attention to the conductive material of the negative electrode material in order to realize a lithium ion secondary battery that satisfies high demands for quick chargeability, rapid discharge performance, and cycle characteristics, and has intensively studied scaly graphite that is particularly economical. In the meantime, the idea was to form scale-like graphite into hollow composite graphite particles. And in fact, according to the negative electrode material using the composite graphite particles having the hollow structure as a conductive material, the problem as the conductive material of the above-mentioned flaky graphite can be solved, and a desired demand for a lithium ion secondary battery can be achieved. It was confirmed that an effect could be obtained. Therefore, the following present inventions (1) to (13) are provided.

(1) Spherical or substantially spherical hollow particles containing scaly graphite particles (A) and carbonaceous material (B), with an average particle diameter of 5 to 25 μm and an average aspect ratio of 5 Consisting of composite graphite particles ,
The electrically conductive material for lithium ion secondary batteries whose volume ratio of the space | gap of the said composite graphite particle | grain is 30-95 volume% .
Upper Symbol composite graphite particles is usually more than 30% of the average particle diameter of the composite graphite particles, it is desirable, particularly with a cavity of 50% or more in size.
( 2 ) The composite graphite particles according to (1) , further comprising carbonaceous or graphite fibers (C).
( 3 ) The composite graphite particles according to (1) or (2) , wherein the carbonaceous material (B) is 0.1 to 20 parts by mass with respect to 100 parts by mass of the composite graphite particles.

  In the composite graphite particles, the average particle diameter of the scaly graphite particles (A) is preferably 1 to 15 μm.

( 4 ) For a lithium ion secondary battery comprising the conductive material for a lithium ion secondary battery according to any one of (1) to ( 3 ) and a negative electrode active material in a mass ratio of 1 to 40:99 to 60. Negative electrode material.
( 5 ) The negative electrode material for a lithium ion secondary battery according to ( 4 ), wherein an average particle size of the negative electrode active material is larger than an average particle size of the composite graphite particles.

( 6 ) A lithium ion secondary battery negative electrode formed using the negative electrode material according to ( 4 ) or ( 5 ).
( 7 ) A lithium ion secondary battery using the negative electrode according to ( 6 ).

(8) A precursor of the carbonaceous material (B) that is spherical or substantially spherical and the scaly graphite particles (A) are mixed, and the scaly graphite particles (A) are adhered to the surface of the precursor. An attaching step to obtain a adhered body;
The adhering body obtained in the adhering step is baked to make the precursor a carbonaceous material (B),
Spherical or substantially spherical hollow particles containing flaky graphite particles (A) and carbonaceous material (B), with an average particle diameter of 5 to 25 μm and an average aspect ratio of 5 or less Ri has a firing step of the void volume fraction to obtain a 30 to 95 vol% der Ru composite graphite particles, method for producing a composite graphite particles used in the conductive material for lithium ion secondary battery.
( 9 ) A spherical or substantially spherical carbonaceous material (B) precursor, scaly graphite particles (A), and carbonaceous or graphitic fibers (C) are mixed, and the precursor is coated on the surface of the precursor. An attachment step of obtaining an adherend to which the scaly graphite particles (A) and the fibers (C) are attached;
The adhering body obtained in the adhering step is baked to make the precursor a carbonaceous material (B),
Spherical or substantially spherical hollow particles containing scaly graphite particles (A) and carbonaceous material (B), with an average particle diameter of 5 to 25 μm and an average aspect ratio of 5 or less The manufacturing method of the composite graphite particle | grains used for the electrically conductive material for lithium ion secondary batteries which has the baking process which the volume ratio of a space | gap is 30-95 volume% and further contains carbonaceous or a graphite fiber (C).

( 10 ) a dispersion step of dispersing a precursor of the scaly graphite particles (A) and the carbonaceous material (B) in a dispersion medium to obtain a dispersion;
Spraying and drying the dispersion obtained in the dispersion step to obtain a hollow structure composed of precursors of the scaly graphite particles (A) and the carbonaceous material (B); and
A mixing step of mixing the hollow structure obtained in the spray drying step and the precursor of the carbonaceous material (B);
The mixture obtained in the mixing step is baked to make the precursor a carbonaceous material (B),
Spherical or substantially spherical hollow particles containing flaky graphite particles (A) and carbonaceous material (B), with an average particle diameter of 5 to 25 μm and an average aspect ratio of 5 or less Ri has a firing step of the void volume fraction to obtain a 30 to 95 vol% der Ru composite graphite particles, method for producing a composite graphite particles used in the conductive material for lithium ion secondary battery.
( 11 ) a dispersion step of dispersing the precursors of the scaly graphite particles (A) and the carbonaceous material (B) in a dispersion medium to obtain a dispersion;
Spraying and drying the dispersion obtained in the dispersion step to obtain a hollow structure composed of precursors of the scaly graphite particles (A) and the carbonaceous material (B); and
A mixing step of mixing the hollow structure obtained in the spray drying step, the precursor of the carbonaceous material (B) and the carbonaceous or graphitic fiber (C);
The mixture obtained in the mixing step is baked to make the precursor a carbonaceous material (B),
Spherical or substantially spherical hollow particles containing scaly graphite particles (A) and carbonaceous material (B), with an average particle diameter of 5 to 25 μm and an average aspect ratio of 5 or less And a composite composite used for a conductive material for a lithium ion secondary battery having a firing step of obtaining composite graphite particles having a void volume ratio of 30 to 95% by volume and further containing carbonaceous or graphite fibers (C) A method for producing graphite particles.

  The composite graphite particles having the specific structure of the present invention are interspersed in the interparticle voids of the graphite particles by forming an active material layer by blending with graphite particles known as lithium ion secondary battery negative electrode materials at a specific ratio. In addition, the graphite particles are effectively brought into contact with each other to exhibit high conductivity, and the degree of orientation of the composite graphite particles themselves is low, the charge expansion is small, and the electrolyte permeability and retention are excellent. Even if the density of the negative electrode is increased, the characteristics can be maintained. Therefore, the lithium ion secondary battery using the negative electrode containing the composite graphite particles 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.

The scanning electron micrograph of the composite graphite particle | grains obtained in the Example is shown. The polarizing microscope photograph of the cross section of the composite graphite particle | grains obtained in the Example is shown. 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.
The composite graphite particles of the present invention are spherical or substantially spherical particles granulated (formed) from at least scaly graphite particles (A) and a carbonaceous material (B). In particular, the composite graphite particles have a skeleton formed of scaly graphite particles (A) bound with a carbonaceous material (B), and inside the scaly graphite particles (A) and carbon A hollow structure having voids in which neither of the quality materials (B) exists.
First, the granulated material will be described.

[(A) scale-like graphite particles]
The scaly graphite particles (A) used in the present invention are scaly, plate-like, or tablet-like artificial graphite or natural graphite, and a plurality of them may be laminated, but dispersed as a single particle. The state which is carrying out is preferable. It may be in a state where it is bent in the middle of the scale shape or in a state where the end of the particle is rounded.
The average particle size of the scale-like graphite particles (A) may be ½ or less of the average particle size of the composite graphite particles, and the volume-converted average particle size is 1 to 15 μm, particularly 2 to 8 μm. It is preferable. If it is 1 μm or more, the finally obtained composite graphite particles can impart conductivity to the negative electrode, improve quick chargeability and cycle characteristics, suppress the reactivity of the electrolyte, and obtain high initial charge / discharge efficiency. be able to. When the average particle diameter of the composite graphite particles is ½ or less, generally about 15 μm or less, the composite graphite particles finally obtained have improved quick chargeability, rapid discharge properties, and cycle characteristics.
Here, the average particle diameter in terms of volume in the present specification 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. The same applies to the average particle diameter of other graphite particles.

The average aspect ratio of the scaly graphite particles (A) is preferably 5 or more, more preferably 20 or more, and preferably 60 or less. The smaller the aspect ratio and the smaller the thickness, the more the composite graphite particles finally obtained are in contact with other negative electrode active materials, and the conductivity of the negative electrode can be sufficiently increased. Cycle characteristics are improved. When the average aspect ratio is less than 5, the finally obtained composite graphite particles require a high pressure in order to make the active material layer high density, and the deformation and elongation of the copper foil as the current collector, Problems such as breakage may occur.
The aspect ratio means the ratio of the major axis length to the minor axis length of one particle to be measured. 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 scaly graphite particles (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 same applies to the average aspect ratio of other graphite particles.

The scaly graphite particles (A) have 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 0.3360nm or 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 (1986) (Month) and Modern Editing Company).

If the specific surface area of the scaly graphite particles (A) is too large, the resulting composite graphite particles will eventually reduce the initial charge / discharge efficiency of the secondary battery. 20 m ² / g or less is preferable (hereinafter simply referred to as a specific surface area).
The amount of the scaly graphite particles (A) with respect to 100 parts by mass of the composite graphite particles is preferably 99.9 to 80 parts by mass, and more preferably 98 to 90 parts by mass. When the amount of the scaly graphite particles (A) is within this range, the resulting composite graphite particles have high crystallinity, become soft, and partly peel off the negative electrode mixture layer when the density of the negative electrode mixture layer is increased. And copper foil does not stretch.

[(B) Carbonaceous material]
The carbonaceous material (B) is used as a binder (binder) for the scaly graphite particles (A). The carbonaceous material (B) is only required to adhere to at least a part of the scaly graphite particles (A) and to connect the plurality of scaly graphite particles (A) to each other. The surface of the graphite particles may be uniformly coated.

  Examples of the carbonaceous material (B) include carbides obtained by finally heat-treating the precursor at 500 ° C. or more and less than 1500 ° C. Any precursor can be used as long as a carbide is formed after heat treatment, such as coal-based or petroleum-based heavy oil, tars, pitches, various thermoplastic resins, thermosetting resins, and the like. Used.

  The amount of the carbonaceous material (B) with respect to 100 parts by mass of the composite graphite particles is preferably 0.1 to 20 parts by mass, particularly 0.5 to 10 parts by mass. When the amount is less than 0.1 part by mass, it becomes difficult to maintain the hollow structure of the finally obtained composite graphite particles, and the scale-like graphite particles (A ) Become primary particles, which may cause problems such as a decrease in the permeability and retention of the electrolyte and an increase in charge expansion, which are observed when the scaly graphite particles (A) are used alone. On the other hand, in the case of more than 20 parts by mass, the finally obtained composite graphite particles become hard and require high pressure to make the active material layer high in density, deformation of the copper foil as a current collector, Problems such as elongation and breakage may occur.

[Composite Graphite Particles]
The composite graphite particles of the present invention (hereinafter sometimes referred to as composite graphite particles (I)) are spherical or substantially spherical containing the scaly graphite particles (A) and the carbonaceous material (B) as described above. Hollow particles. The average particle size of the composite graphite particles is preferably 5 to 25 μm, particularly preferably 8 to 15 μm. If it is 5 micrometers or more, high initial stage charge / discharge efficiency can be obtained, providing high electroconductivity to another negative electrode active material. If it is 25 μm or less, rapid chargeability and cycle characteristics are improved.

  The average aspect ratio of the composite graphite particles is preferably 5 or less, and more preferably 2 or less. The smaller the aspect ratio and the more nearly a spherical shape, the more uniformly the other negative electrode active materials can be contacted, and the conductivity of the negative electrode can be sufficiently increased, and the quick chargeability and cycle characteristics are improved. When the average aspect ratio is more than 5, the charge expansion of the composite graphite particles themselves may be increased, the electrolyte permeability and retention may be impaired, and rapid discharge properties and cycle characteristics may be deteriorated.

The voids inside the composite graphite particles are preferably one large void, but a plurality of voids may be dispersed. For example, in Examples (FIGS. 1-2) described later, hollow structure particles having a cavity in the center are shown. As for the size of such a cavity, the length of the longest portion is desirably 30% or more, particularly 50% or more of the average particle diameter of the composite graphite particles.
The porosity of the largest cavity at the center is preferably 3 or more, particularly 12 or more and 50 or less, when the total porosity in the composite graphite particles is 100.

The void volume ratio of the composite graphite particles is preferably 30 to 95% by volume on average, and particularly preferably 30 to 90% by volume on average. If it is less than 10% by volume, the composite graphite particles become dense and hard, and a high pressure is required to increase the density of the active material layer, resulting in problems such as deformation, elongation, and breakage of the copper foil as the current collector. Sometimes. If it exceeds 95% by volume, it becomes difficult to maintain the hollow structure of the composite graphite particles, and the flaky graphite particles (A) constituting the composite graphite particles become primary particles when the negative electrode mixture is prepared. When the scaly graphite particles (A) are used alone, problems such as a decrease in the permeability and retention of the electrolyte and an increase in charge expansion may occur.
It is preferable that the composite graphite particles have pores on the surface, and the pores are connected to the voids inside the composite graphite particles. That is, it is preferable to have a void structure in which the electrolyte solution penetrates into the voids inside the composite graphite particles when the electrolyte solution is injected into the lithium ion battery. By adopting this structure, the ion conductivity of lithium ions is increased on the surface and inside of the composite graphite particles, and rapid chargeability and rapid discharge properties are enhanced.

In the present invention, the void volume ratio was calculated by the following simple method.
About 100 composite graphite particles, the particles were cut and polished to form a cross-section, and microscopically photographed at a magnification at which the particle shape could be recognized. The ratio of the area of the void contour inside the particle to the area of the outer surface contour of one composite graphite particle was determined, and the simple average value of 100 particles was defined as the void volume ratio.

  In the composite graphite particles of the present invention, the scaly graphite particles (A) are main constituents, and a plurality of scaly graphite particles (A) are bound by the carbonaceous material (B) to form a skeleton of the particles. The scaly graphite particles (A) are unevenly distributed on the outer periphery of the composite graphite particles, and the outermost surface is the basal surface of the scaly graphite particles (A). A) are preferably arranged concentrically.

The composite graphite particles have high crystallinity because the scaly graphite particles (A) having high crystallinity are the main constituent components. A preferable range of the average lattice spacing d ₀₀₂ is the same as that of the scaly graphite particles (A). The composite graphite particles of the present invention are soft because they have high crystallinity and the inside of the particles are hollow, and contribute to increasing the density of the active material layer.

  The composite graphite particles can further contain other components as long as the effects of the present invention are not impaired. For example, non-flaky carbonaceous or graphite particles may be attached to or combined with the skeleton consisting of the above (A) and (B), and an organic compound such as a surfactant or a polymer may be attached or combined. It may be coated, or may be deposited or embedded with fine particles of metal oxide such as silica, alumina, titania, etc., silicon, tin, cobalt, nickel, copper, silicon oxide, tin oxide, titanium A metal or a metal compound such as lithium acid may be attached, embedded, combined, or encapsulated.

[(C) Fiber]
Among the above, it is preferable that carbonaceous or graphite fibers (C) intervene and adhere to the inside and / or the surface of the composite graphite particles. When interposing inside, it is preferable to arrange so that it may contact with several scale-like graphite particles (A), or to penetrate a hollow part. When making it adhere to the surface, it is preferable to arrange | position so that a fiber (C) may protrude in this surface. By interposing and adhering the fibers (C) in this way, the conductivity is further increased, and battery characteristics such as rapid chargeability, rapid discharge properties, and cycle characteristics are improved.

  As the fiber (C), any carbonized carbonized at 500 ° C. or more and less than 1500 ° C. or graphitized at 1500 ° C. or more and less than 3300 ° C. can be used, but graphitized one is more preferable. Generally, fibers called carbon nanofibers, carbon nanotubes, and vapor grown carbon fibers are exemplified.

  The average fiber diameter of the fibers (C) is preferably in the range of 1 nm to 2 μm. Especially preferably, it is 10 nm-500 nm. If it is less than 1 nm, uniform dispersion of the fibers (C) becomes difficult, and the initial charge / discharge efficiency of the finally obtained composite graphite particles may be lowered. In the case of more than 2 μm, the composite graphite particles (I) finally obtained are hard, and a high pressure is required to make the active material layer high in density, and the deformation and elongation of the copper foil as a current collector, Problems such as breakage may occur.

  The average fiber length of the fiber (C) is preferably 2 to 30 μm. Especially preferably, it is 3-15 micrometers. If it is 2 micrometers or more, the electrical conductivity improvement effect will appear notably, and if it is 30 micrometers or less, a fiber (C) can be interposed uniformly and is preferable.

  The adhesion amount of the fiber (C) is preferably more than 0, 10 parts by mass or less, particularly 5 parts by mass or less, with respect to 100 parts by mass of the finally obtained composite graphite particles. In the case of more than 10 parts by mass, the effect of improving the conductivity by the fiber (C) is saturated, the productivity of the negative electrode mixture slurry may be impaired, and the reactivity with the electrolyte becomes excessive, resulting in an initial charge. Discharge efficiency may decrease.

[Example of production method of composite graphite particles (I)]
As long as the composite graphite particles as described above have the structure defined in the present invention, the production method is not particularly limited, and any production method can be adopted. .
(1) A mechanochemical treatment in which spherical resin beads that have a slight residual carbon content by baking treatment and scaly graphite particles (A) are mixed to impart mechanical energy such as compression, shear, collision, and friction. Apply. By this treatment, the scaly graphite particles (A) are attached to the surface of the resin beads, and the scaly graphite particles (A) are concentrically laminated on the surface of the resin beads. Subsequently, this is baked at 500-1500 degreeC in inert atmosphere, and a resin bead is lose | disappeared. A small amount of residual carbon (B) of the resin beads adheres to the scaly graphite (A) and acts as a binder. The obtained composite graphite particles form a hollow structure that substantially maintains the concentric structure of the scaly graphite particles (A) before the firing treatment.
In order to complex the carbonaceous or graphite fiber (C) with the composite graphite particles by the above method, the fiber (C) is mixed with the scaly graphite particles (A) and the resin beads, or It is also effective to use a resin-fiber (C) melt-kneaded in advance.

(2) The scaly graphite particles (A), the precursor of the carbonaceous material (B), and, if necessary, the fibers (C) are dispersed in a solution (dispersion medium liquid), and this dispersion is sprayed together with an air current. The solvent is instantly dried with hot air. The particles after drying form a spherical shape by the surface tension of the dispersion, and by adjusting the air flow, bubbles are intentionally interposed in the droplets of the spray to form a hollow structure (hollow structure). be able to. As above, composite graphite particles can be obtained by firing this at 500 to 1500 ° C. in an inert atmosphere.

  In any of the above production examples (1) and (2), the fiber (C) is attached to the scaly graphite particles (A) in advance, and the attached material is used as a raw material. Composite graphite particles containing (C) are obtained.

  Further, the precursor of the carbonaceous material (B) is attached or coated on the outer surface of the composite graphite particles obtained in the production example (1) or (2) or the hollow structure obtained in (2). It is possible to prepare composite graphite particles having a carbonaceous material (B) on the surface by performing a firing treatment (inert atmosphere, 500 ° C. to 1500 ° C.) later. At that time, the fiber (C) can be adhered together with the precursor of the carbonaceous material (B).

  The composite graphite particles of the present invention are useful as a conductive material that can exhibit excellent cycle characteristics when blended with a known negative electrode active material of a lithium ion secondary battery. In particular, even when the negative electrode is pressed to a high density, the negative electrode has a high discharge capacity per volume, without impairing the permeability and retention of the electrolyte, exhibiting excellent rapid chargeability, rapid discharge properties and cycle characteristics Can be obtained.

Hereinafter, a lithium ion secondary battery using the composite graphite particles of the present invention will be 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, for example, in a secondary battery can. It is enclosed. 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 negative electrode is generally composed of a current collector made of copper foil and a negative electrode material (active material) bound by a binder.
In the present invention, there is no particular limitation except that the composite graphite particles of the present invention are used as the negative electrode material, and other battery components such as a non-aqueous electrolyte, a positive electrode, a separator and the like are general secondary battery elements. Follow.

[Negative electrode material]
In the present invention, the negative graphite material is prepared by mixing the composite graphite particles (I) of the present invention as described above and the known negative electrode active material (II).
Various known materials can be used for the negative electrode active material (II), and typical examples include the following.
Graphite particles obtained by assembling or bonding a plurality of flat particles so that their orientation planes are non-parallel.
Graphitized product of spherical mesocarbon spherules or pulverized product of mesocarbon spherules. Composite graphite particles in which a carbonaceous material is filled in the voids between graphite particles of a granulated product obtained by spheroidizing or ellipsoidizing natural graphite, or composite graphite in which the surface of the granulated material is coated with a carbonaceous material particle. Artificial graphite particles made by graphitizing coke.
Bulk graphite particles obtained by pulverizing, oxidizing, carbonizing, and graphitizing bulk mesophase pitch.

  The negative electrode active material (II) may be a heterogeneous graphite material, a carbonaceous or graphite fiber, a carbon material such as amorphous hard carbon, an organic material, an inorganic material, a mixture with a metal material, or a composite. . Specifically, a surfactant, a polymer or other organic compound may be attached or coated, or a metal oxide fine particle such as silica, alumina or titania may be attached or embedded. In addition, a metal or a metal compound such as silicon, tin, cobalt, nickel, copper, silicon oxide, tin oxide, or lithium titanate may be attached, embedded, combined, or encapsulated.

  The average particle size of the negative electrode active material (II) is preferably larger than the average particle size of the composite graphite particles (I). A preferable average particle diameter is 8-30 micrometers, Most preferably, it is 10-25 micrometers.

  Even when a high-density negative electrode is prepared by making the average particle diameter of the negative electrode active material (II) larger than the average particle diameter of the composite graphite particles (I), the composite graphite particles (I) are particles. The inner hollow structure is maintained, and is interposed in the space between the particles of the negative electrode active material (II) so as to be in uniform contact with the plurality of negative electrode active materials (II), thereby exhibiting high conductivity. In the high-density negative electrode, the composite graphite particles (I) may be compressed and the hollow structure in the particles may be crushed. However, the composite graphite particles (I) can be selectively interposed in the gaps between the particles of the negative electrode active material (II), and the electrolytic solution found when the scaly graphite particles (A) are used alone. This does not cause problems such as a decrease in permeability and retention of the battery and an increase in charge expansion.

In the present invention, the composite graphite particles (I) and these negative electrode active materials (II) have a mass ratio of (I) and (II) of (I) :( II) = 1-40: 99-60. A negative electrode material is prepared by mixing in a range.
When the composite graphite particle (I) is less than 1%, the effect of improving the conductivity of the negative electrode active material (II) is insufficient, and when it exceeds 40%, the active material layer is pressed at a high density In addition, the composite graphite particles (I) may be excessively crushed and flattened, resulting in deterioration of electrolyte permeability, retention, rapid discharge rate, and cycle characteristics.

[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, 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 the production of the negative electrode, N-methylpyrrolidone, dimethylformamide, water, alcohol, etc., which are ordinary solvents for producing the negative electrode, can be used.

The negative electrode is produced, for example, by dispersing a negative electrode mixture in a solvent to prepare a paste-like negative electrode mixture, applying the negative electrode mixture to one or both sides of a current collector, and drying. 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 composite 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 0.1 to 5 mol / L, and more preferably 0.5 to 3 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 a 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, tetrahydrothiophene, di 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 electrolyte salt concentration in the non-aqueous electrolyte as a plasticizer is preferably 0.1 to 5 mol / L, and more preferably 0.5 to 2 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. 3 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 scale-like graphite material (A)]
Natural graphite was pulverized and adjusted to an average particle size of 3 μm, an average aspect ratio of 35, a d ₀₀₂ of 0.3357 nm, and a specific surface area of 14.5 m ² / g.

[Preparation of precursor of carbonaceous material (B)]
Spherical resin beads made of a benzoguanamine formaldehyde condensate having an average particle size of 5 μm were prepared. It was 20 mass% as a result of calculating | requiring the residual carbon rate at the time of baking processing at 1000 degreeC previously.

[Preparation of Graphite Fiber (C)]
Vapor growth carbon fibers having an average fiber diameter of 150 nm and an average fiber length of 10 μm were prepared.

[Preparation of Composite Graphite Particles (I)]
The scaly graphite material (A), the carbonaceous material (B) precursor (spherical resin beads) and the graphite fiber (C) were mixed at a ratio of 93, 25, and 2 parts by mass, respectively. The mixture was subjected to mechanochemical treatment in an apparatus capable of repeatedly applying compressive force and shearing force.
The obtained composite was fired at 1000 ° C. in a nitrogen stream to prepare composite graphite particles (I). In the obtained composite graphite particles (I), the scaly graphite material (A) is concentrically laminated, and the calcined product of the precursor of the carbonaceous material (B) adheres to the scaly graphite material (A). The graphite fibers (C) were uniformly dispersed and adhered around the scaly graphite material (A). When the cross section of the composite graphite particle (I) was observed, the inside of the particle had a hollow structure. The average particle diameter was 8 μm, the average aspect ratio was 1.2, d ₀₀₂ was 0.3359 nm, the specific surface area was 4.2 m ² / g, and the porosity inside the particles was 62%. In addition, when the ratio of the carbonaceous material (B) in the composite graphite particles (I) is calculated from the residual carbon ratio of the precursor of the carbonaceous material (B), it is 100 parts by mass of the composite graphite particles (I). 5 parts by mass.
Inside the composite graphite particles (I), there was one large spherical cavity at the center and a fine void around it. The central cavity had an average diameter of 4.5 μm, and when the total porosity inside the particles was 100, the porosity occupied by this central cavity was 29.

[Preparation of negative electrode active material (II)]
100 parts by mass of natural graphite particles granulated into a spherical to ellipsoidal shape (average aspect ratio 1.4, average particle diameter 18 μm, average lattice spacing d ₀₀₂ 0.3356 nm, specific surface area 5.0 m ² / g) , 3 parts by weight of pitch powder (average particle diameter 2 μm) with a softening point of 120 ° C. and 2 parts by weight of the above vapor-grown carbon fiber (average fiber diameter 150 nm, average fiber length 10 μm) are mixed to repeatedly apply compressive force and shear force. The mechanochemical treatment was performed with the equipment that can be used. The obtained sample was filled in a graphite crucible and fired at 1000 ° C. for 3 hours in a non-oxidizing atmosphere. The obtained spheroidized or ellipsoidized natural graphite has carbides deposited on its surface in the form of a film, with an average aspect ratio of 1.4, an average particle diameter of 18 μm, an average lattice spacing of d ₀₀₂ 0.3357 nm, and a specific surface area. It was 2.7 m ² / g.

[Preparation of negative electrode material]
12 parts by mass of the composite graphite particles (I) and 88 parts by mass of the negative electrode active material (II) were mixed to prepare a negative electrode material.

[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 applied on the copper foil was pressed with a hand press at 12 kN / cm ² (120 MPa), and further punched into a circular shape with a diameter of 15.5 mm. 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 against 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 at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate 33 vol% -methyl ethyl carbonate 67 vol% 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. 3 was produced 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 constant current charging of 0.9 mA 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 carried out 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.
Initial charge / discharge efficiency (%) = (discharge capacity / charge capacity) × 100
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, the current value was set to 4.5 mA, which is five times the first cycle, constant current charging was performed, the constant current charging capacity was obtained, and the rapid charging rate was calculated from the following equation.

[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. Then, the current value is set to 18 mA, which is 20 times the first cycle, and constant current discharge is performed until the circuit voltage reaches 1.5V. went. The discharge capacity per mass was calculated | required from the amount of electricity supply in the meantime, and the rapid discharge rate was computed by following Formula.

[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 performing 4.0 mA constant current charging 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 formula.

  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.

(Comparative Example 1)
In Example 1, the density of the negative electrode mixture layer was 1.75 g / in the same manner as in Example 1 except that the composite graphite particles (I) were not used and the negative electrode active material (II) was used alone as the negative electrode material. 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.

(Comparative Example 2)
In Example 1, instead of the composite graphite particles (I), the density of the negative electrode mixture layer was 1.75 g / cm in the same manner as in Example 1 except that the scaly graphite material (A) was used as it was. ^A working electrode was prepared by adjusting to ³ , 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.

(Examples 2 to 6)
In Example 1, the average particle diameter of the scaly graphite material (A), the average particle diameter and shape of the precursor of the carbonaceous material (B), and the mixing of the composite graphite particles (I) and the negative electrode active material (II) 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 ratio and the presence or absence of the graphite fiber (C) were manipulated. 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.

(Comparative Examples 3-5, Reference Example 1)
In Example 1, the average particle diameter of the scaly graphite material (A), the average particle diameter of the precursor of the carbonaceous material (B), and the mixing ratio of the composite graphite particles (I) and the negative electrode active material (II) 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 battery was operated outside the scope of the present invention, and 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.

(Example 7)
[Preparation of scale-like graphite material (A)]
Natural graphite was pulverized and adjusted to an average particle size of 2 μm, an average aspect ratio of 25, a d ₀₀₂ of 0.3357 nm, and a specific surface area of 16.3 m ² / g.

[Preparation of precursor of carbonaceous material (B)]
An aqueous solution of polyacrylic acid having a solid content concentration of 10% was prepared. As a result of obtaining the residual carbon ratio in the case of firing at 1000 ° C. in advance, it was 1% by mass with respect to the solid content of polyacrylic acid.
A heavy oil solution of coal tar was also prepared. It was 20 mass% as a result of calculating | requiring the residual carbon rate at the time of baking processing at 1000 degreeC previously.

[Preparation of Graphite Fiber (C)]
Vapor growth carbon fibers having an average fiber diameter of 150 nm and an average fiber length of 10 μm were prepared.

[Preparation of Composite Graphite Particles (I)]
A polyacrylic acid aqueous solution was mixed as a precursor of the scaly graphite material (A) and the carbonaceous material (B) in proportions of 95 and 100 parts by mass, respectively, to prepare a dispersion. The dispersion was sprayed and the solvent was instantly dried at 200 ° C. in a nitrogen atmosphere. The pressure of nitrogen gas introduced into the spray was adjusted so that bubbles were interposed in the droplets. The obtained spherical composite, the coal tar heavy oil solution as the precursor of the carbonaceous material (B), and the graphite fiber (C) at a ratio of 96, 10, and 2 parts by mass, respectively, at room temperature. Mix evenly for hours.
Subsequently, it baked at 1000 degreeC in nitrogen stream, and prepared composite graphite particle | grains (I). In the obtained composite graphite particles (I), the scaly graphite material (A) is concentrically laminated, and the calcined product of the precursor of the carbonaceous material (B) adheres to the scaly graphite material (A). The graphite fibers (C) were uniformly dispersed and adhered around the scaly graphite material (A). When the cross section of the composite graphite particle (I) was observed, the inside of the particle had a hollow structure. The average particle size was 12 μm, the average aspect ratio was 1.1, d ₀₀₂ was 0.3359 nm, the specific surface area was 3.3 m ² / g, and the porosity inside the particles was 55%. In addition, when the ratio of the carbonaceous material (B) in the composite graphite particles (I) is calculated from the residual carbon ratio of the precursor of the carbonaceous material (B), it is 100 parts by mass of the composite graphite particles (I). 3 parts by mass.
FIG. 1 shows a scanning electron micrograph of the composite graphite particles (I) obtained.
FIG. 2 shows a polarizing microscope photograph of a cross section of the obtained composite graphite particle (I).
Inside the composite graphite particles (I), there was one large spherical cavity at the center and a fine void around it. The central cavity had an average diameter of 6.8 μm, and the porosity occupied by the central cavity was 33 when the total porosity inside the particles was 100.

[Preparation of negative electrode active material (II)]
Mesophase microsphere graphitized material (average aspect ratio 1.1, average particle diameter 28 μm, average lattice spacing d ₀₀₂ 0.3359 nm, specific surface area 0.6 m ² / g) was prepared.

[Preparation of negative electrode material]
20 parts by mass of the composite graphite particles (I) and 80 parts by mass of the negative electrode active material (II) were mixed to prepare a negative electrode material.

In the same manner as in Example 1, 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.

(Comparative Example 6)
In Example 7, the density of the negative electrode mixture layer was 1.75 g / cm in the same manner as in Example 7 except that the scaly graphite material (A) was used as it was instead of the composite graphite particles (I). ^A working electrode was prepared by adjusting to ³ , 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.

(Examples 8 to 10, Reference Example 2)
In Example 7, the negative electrode mixture layer was prepared in the same manner as in Example 7 except that the mixing ratio of the composite graphite particles (I) and the negative electrode active material (II) and the presence or absence of the graphite fibers (C) were manipulated. A working electrode was prepared by adjusting the density 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.

(Comparative Example 7)
50 parts by mass of scaly natural graphite having an average particle diameter of 2 μm and 50 parts by mass of coal tar pitch (remaining carbon ratio 20%) were put into a biaxial kneader and kneaded at 150 ° C. for 30 minutes. The kneaded product was subjected to primary baking treatment at 500 ° C. for 5 hours in a non-oxidizing atmosphere.
The primary fired product was pulverized and adjusted to an average particle size of 12 μm, and then subjected to secondary firing in a nitrogen stream at 1000 ° C. to prepare composite graphite particles (I). In the obtained composite graphite particles (I), a plurality of scaly graphite materials were laminated and aggregated via a carbonaceous material, and the inside of the particles had a dense structure. There was no hollow cavity inside. The average particle diameter was 12 μm, the average aspect ratio was 4.8, d ₀₀₂ was 0.3363 nm, the specific surface area was 4.2 m ² / g, and the porosity inside the particles was 5%.
In the same manner as in Example 7, the density of the negative electrode mixture layer was adjusted to 1.75 g / cm ³ to 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.

(Comparative Example 8)
A hollow cavity is seen inside as in Example 7 except that granular graphite (granular graphite obtained by graphitizing pulverized mesophase spheres, average particle diameter of 3 μm) is used instead of flaky graphite. No composite graphite particles were obtained. In the same manner as in Example 7, 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.
(Comparative Example 9)
In Example 7, the density of the negative electrode mixture layer was set to 1 in the same manner as in Example 7 except that carbon black (EC300J manufactured by Kao, average primary particle size 40 nm) was used instead of the composite graphite particles (I). 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.
(Comparative Example 10)
In Example 7, instead of the composite graphite particles (I), vapor-grown carbon fiber (VGCF manufactured by Showa Denko, average fiber diameter 150 nm, average fiber length 10 μm) was used in the same manner as in Example 7. A 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.

  When the working electrode is made of the negative electrode material defined in the present invention, the density of the negative electrode mixture layer can be increased, and any of discharge capacity, initial charge / discharge efficiency, rapid charge rate, rapid discharge rate, and cycle characteristics can be obtained. Was excellent. On the other hand, when the working electrode was made of a negative electrode material that does not fall within the scope of the present invention, any of discharge capacity, initial charge / discharge efficiency, rapid charge rate, rapid discharge rate, and cycle characteristics was insufficient.

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

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 (11)

Spherical or substantially spherical hollow particles containing scaly graphite particles (A) and carbonaceous material (B), having an average particle diameter of 5 to 25 μm and an average aspect ratio of 5 or less , Composed of composite graphite particles,
The electrically conductive material for lithium ion secondary batteries whose volume ratio of the space | gap of the said composite graphite particle | grain is 30-95 volume%.   The conductive material for a lithium ion secondary battery according to claim 1, further comprising a carbonaceous or graphitic fiber (C).   The conductive material for a lithium ion secondary battery according to claim 1 or 2, wherein the carbonaceous material (B) is 0.1 to 20 parts by mass with respect to 100 parts by mass of the composite graphite particles.   The negative electrode material for lithium ion secondary batteries containing the electrically conductive material for lithium ion secondary batteries of any one of Claims 1-3, and a negative electrode active material by mass ratio of 1-40: 99-60.   The negative electrode material for a lithium ion secondary battery according to claim 4, wherein an average particle size of the negative electrode active material is larger than an average particle size of the composite graphite particles.   A lithium ion secondary battery negative electrode using the negative electrode material according to claim 4.   A lithium ion secondary battery using the negative electrode according to claim 6. Adherent in which a precursor of carbonaceous material (B) having a spherical or substantially spherical shape and scaly graphite particles (A) are mixed and the scaly graphite particles (A) are adhered to the surface of the precursor. An adhesion step to obtain,
The adhering body obtained in the adhering step is baked to make the precursor a carbonaceous material (B),
Spherical or substantially spherical hollow particles containing flaky graphite particles (A) and carbonaceous material (B), with an average particle diameter of 5 to 25 μm and an average aspect ratio of 5 or less Ri has a firing step of the void volume fraction to obtain a 30 to 95 vol% der Ru composite graphite particles, method for producing a composite graphite particles used in the conductive material for lithium ion secondary battery. A precursor of carbonaceous material (B) that is spherical or substantially spherical, scaly graphite particles (A), and carbonaceous or graphite fibers (C) are mixed, and the scaly graphite is formed on the surface of the precursor. An attaching step for obtaining an adherent in which the fine particles (A) and the fibers (C) are attached;
The adhering body obtained in the adhering step is baked to make the precursor a carbonaceous material (B),
Spherical or substantially spherical hollow particles containing scaly graphite particles (A) and carbonaceous material (B), with an average particle diameter of 5 to 25 μm and an average aspect ratio of 5 or less Composite graphite used for a conductive material for a lithium ion secondary battery, having a firing step of obtaining composite graphite particles having a void volume ratio of 30 to 95% by volume and further containing carbonaceous or graphitic fibers (C) A method for producing fine particles. A dispersion step of dispersing the precursors of the scaly graphite particles (A) and the carbonaceous material (B) in a dispersion medium to obtain a dispersion;
Spraying and drying the dispersion obtained in the dispersion step to obtain a hollow structure composed of precursors of the scaly graphite particles (A) and the carbonaceous material (B); and
A mixing step of mixing the hollow structure obtained in the spray drying step and the precursor of the carbonaceous material (B);
The mixture obtained in the mixing step is calcined, and the precursor is made into a carbonaceous material (B), which is spherical or substantially spherical and contains flaky graphite particles (A) and carbonaceous material (B). Hollow particles having an average particle diameter of 5 to 25 μm, an average aspect ratio of 5 or less, and a firing step of obtaining composite graphite particles having a void volume ratio of 30 to 95% by volume, The manufacturing method of the composite graphite particle | grains used for the electrically conductive material for lithium ion secondary batteries . A dispersion step of dispersing the precursors of the scaly graphite particles (A) and the carbonaceous material (B) in a dispersion medium to obtain a dispersion;
Spraying and drying the dispersion obtained in the dispersion step to obtain a hollow structure composed of precursors of the scaly graphite particles (A) and the carbonaceous material (B); and
A mixing step of mixing the hollow structure obtained in the spray drying step, the precursor of the carbonaceous material (B) and the carbonaceous or graphitic fiber (C);
The mixture obtained in the mixing step is baked to make the precursor a carbonaceous material (B),
Spherical or substantially spherical hollow particles containing scaly graphite particles (A) and carbonaceous material (B), with an average particle diameter of 5 to 25 μm and an average aspect ratio of 5 or less Composite graphite used for a conductive material for a lithium ion secondary battery, having a firing step of obtaining composite graphite particles having a void volume ratio of 30 to 95% by volume and further containing carbonaceous or graphitic fibers (C) A method for producing fine particles .