KR20170057427A - Graphite particles for lithium ion secondary battery negative electrode materials, lithium ion secondary battery negative electrode and lithium ion secondary battery - Google Patents

Abstract

Disclosed is a negative electrode material having at least one of excellent initial charging / discharging efficiency, rapid charging property, rapid discharging property, and long-term cycle characteristic, a negative electrode using the negative electrode material, and a lithium secondary battery. A composite graphite particle (C1) having a carbonaceous material (B1) in the inside of the particle and / or at least a part of the particle surface of the spheroidized graphite particle (A) formed into a spherical or substantially spherical shape, (C2) having a graphite material (B2) in its particle and / or on at least part of its particle surface of the spheroidized graphitized particles (A) (5). ≪ / RTI > (1) surface of the hexagonal carbon plane layer spacing (d ₀₀₂₎ is 0.3360㎚ or less, (2) a tap density 1.0g / ㎤ or more, (3) the average particle size of 5 to 25㎛, (4) the average aspect ratio is 1.2 or more 4.0 And (5) a pore volume of not more than 0.5 μm in pore diameter by mercury porosimeter of not more than 0.08 ml / g.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphite particle for lithium ion secondary battery negative material, a lithium ion secondary battery negative electrode, and a lithium ion secondary battery. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode active material,

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

2. Description of the Related Art In recent years, there has been a growing demand for increasing the energy density of a battery accompanied with miniaturization or high performance of electronic devices. In particular, a lithium ion secondary battery can attain higher voltage than other secondary batteries, and thus has attracted attention because a high energy density is achieved. The lithium ion secondary battery has a negative electrode, a positive electrode, and an electrolytic solution (non-aqueous electrolyte) as main components.

The negative electrode is generally composed of a current collector made of copper foil and a working material for the anode bonded by a binder. Normally, a carbon material is used for the negative electrode material. As such a carbon material, graphite which has excellent charge-discharge characteristics and exhibits a high discharge capacity and potential flatness has been widely used.

Lithium ion secondary batteries mounted on portable electronic devices in recent years are required to have high energy density, excellent quick-chargeability, and rapid discharge performance, and that initial discharge capacity will not deteriorate even after repeated charging and discharging ) Is required.

Patent Document 1 discloses a graphite of a mesocarbon small spherical body made of a Brooks-Taylor type single crystal in which basal planes of graphite are arranged in layers in a direction perpendicular to the radial direction Lt; / RTI > Patent Document 2 proposed so far by the applicant discloses composite graphite particles in which graphite granules are filled with and / or coated with a carbonaceous layer having a lower crystallinity than the graphite granules and containing carbon fine particles. Patent Document 3 discloses a composite graphite material in which spherical graphite granules are epibolized with a graphite covering material and a graphite surface layer having a low crystallinity on the outer surface. Patent Document 4 discloses a graphite composite powder mixture of a graphite composite powder and an artificial graphite powder composed of a constituent material of the graphite composite powder.

Patent Document 5 discloses an invention in which a mixture of three types of graphite particles A, B and C having different hardnesses and shapes is used for the negative electrode to improve the infiltration rate of the electrolytic solution. Graphite particle A uses an artificial graphite block composed of coke and binder pitch, and graphite powder whose outermost surface is lower in crystal than the inside is used.

Patent Document 6 discloses that a mixture of graphite particles (A) and (B) having different physical properties is used for a negative electrode material. In the examples, graphite particles (A) obtained by firing at 1000 占 폚 are further used as graphite particles (B) after further calcination at 3000 占 폚. In this case, since the carbonization yield of the carbonaceous material in the graphite particles (B) calcined at a higher temperature is smaller, the amount of the graphitized carbonaceous material in the graphite particles (B) It is thought to be less than the vaginal material.

When a mixture of graphite particles having different physical properties is used for the negative electrode, the battery characteristics of the lithium secondary battery depend on the physical properties of the graphite particles constituting the mixture. Therefore, in order to obtain a mixture having excellent characteristics of the lithium secondary battery It is desired to examine a more suitable combination of graphite particles.

However, the above-mentioned conventional graphite-based negative electrode material has not obtained sufficient performance for the higher requirements of recent energy density, rapid charging property, rapid discharge property and cycle characteristics. In particular, in order to attain a high energy density, it is necessary to increase the discharge capacity per mass of the graphite-based negative electrode material and increase the density of the active material layer to set the discharge capacity per unit volume. In the conventional negative electrode material, other characteristics of the battery such as peeling of the active material layer from the negative electrode, breakage or elongation of the copper foil as the current collector, poor permeability and retention of the electrolyte, and cell expansion due to decomposition reaction of the electrolyte occur , Which causes various problems such as rapid chargeability, rapid discharge property, deterioration of battery characteristics such as cycle characteristics, and the like.

The negative electrode material using the graphite of the mesocarbon microspheres described in Patent Document 1 can suppress the orientation of the basal plane of the graphite to some extent even if the density of the graphite is increased because the graphite is spherical. However, since the graphite is dense and hard, it requires high pressure for high density, and problems such as deformation, elongation, and breakage of the copper foil of the current collector occur. And the contact area with the electrolytic solution is small. Therefore, the rapid filling property is particularly low. The lowering of the filling property causes all the lithium ions to be generated on the surface of the negative electrode at the time of charging, thereby causing a decrease in the cycle characteristics.

In the negative electrode material using the composite graphite particles described in Patent Document 2, when the density of the active material layer is increased, the coating of the carbonaceous substance or a part of the graphite-based graphite substrate is broken, and the decomposition reaction of the electrolyte proceeds Resulting in insufficient long-term cycle characteristics.

The negative electrode material using the composite graphite material described in Patent Document 3 has an excellent initial charging / discharging efficiency, but has insufficient rapid charging ability. The long-term cycle characteristics in the case of increasing the density of the active material layer are higher than those in the other patent documents, but also require a further improvement.

The negative electrode material using the graphite composite mixture powder described in Patent Document 4 had insufficient discharge capacity per mass. In addition, the initial charging / discharging efficiency was low, and the rapid charging property was also insufficient.

Japanese Patent Application Laid-Open No. 2000-323127 Japanese Patent Application Laid-Open No. 2004-63321 Japanese Patent Application Laid-Open No. 2003-173778 Japanese Patent Application Laid-Open No. 2005-259689 Japanese Patent Application Laid-Open No. 2007-324067 Japanese Patent Application Laid-Open No. 2008-27664

SUMMARY OF THE INVENTION An object of the present invention is to solve the problem of a conventional negative electrode material.

Namely, the present invention is to provide a negative electrode material having the following characteristics and having at least one of excellent initial charge / discharge efficiency, rapid chargeability, rapid discharge property and long-term cycle characteristics.

1) High discharge capacity per mass with high crystallinity

2) High active material density is obtained at low press pressure

3) A graphite particle having a high density but suppressing collapse, breakage, and orientation of graphite so as not to impair the permeability and retention of the electrolyte

4) It is excellent in lithium ion water solubility on the graphite surface and does not have a reaction active surface, whereby the decomposition reaction of the electrolytic solution can be suppressed even if charge / discharge is repeated

A lithium ion secondary battery negative electrode using the negative electrode material, and a lithium ion secondary battery having the negative electrode.

[1] Composite graphite particles (C1) having a carbonaceous material (B1) in its particle and at least a part of the particle surface of an amorphous spherical graphite particle (A) putting in a shape of spherical or rough spheres , A mixture of composite graphite particles (C2) having a graphite material (B2) in the inside of the particle and at least a part of the particle surface of the spheroidized graphite particle (A)

And the mixture satisfies the following (1) to (5).

(1) the surface interval (d ₀₀₂ ) of the carbon nanotube surface layer is 0.3360 nm or less,

(2) a tap density of 1.0 g / cm < 3 &

(3) an average particle diameter of 5 to 25 mu m,

(4) an average aspect ratio of 1.2 to less than 4.0, and

(5) Pore volume of not more than 0.5 占 퐉 and not more than 0.08 ml / g by mercury porosimeter.

The content of the carbonaceous material (B1) is 0.1 to 10 parts by mass based on 100 parts by mass of the spheroidized graphite particles (A) in the composite graphite particles (C1)

The lithium ion secondary battery negative electrode material according to [1], wherein the content of the carbonaceous material (B2) is 5 to 30 parts by mass relative to 100 parts by mass of the spheroidized graphite particles (A) in the composite graphite particles (C2) Graphite particles.

[3] The lithium ion secondary battery negative electrode material described in [1] or [2], wherein the ratio of the composite graphite particles (C1) to the composite graphite particles (C2) is 1:99 to 90:10 in mass ratio Graphite particles.

[4] A lithium ion secondary battery negative electrode containing graphite particles for lithium ion secondary battery negative electrode material according to any one of [1] to [3] above.

[5] A lithium ion secondary battery having the lithium ion secondary battery negative electrode described in [4] above.

According to the present invention, it is possible to provide a negative electrode material having the following characteristics and having at least one of excellent initial charge / discharge efficiency, rapid chargeability, rapid discharge property and long-term cycle characteristics.

1) High discharge capacity per mass with high crystallinity

2) High active material density is obtained at low press pressure

3) A graphite particle having a high density but suppressing collapse, breakage, and orientation of graphite so as not to impair the permeability and retention of the electrolyte

4) It is excellent in lithium ion water solubility on the graphite surface and does not have a reaction active surface, whereby the decomposition reaction of the electrolytic solution can be suppressed even if charge / discharge is repeated

1 is a cross-sectional view schematically showing the structure of a button-type evaluation cell for use in a charge-discharge test in the embodiment.
Figure 2 is an embodiment of a peak intensity near 1360cm ^-1 in the Raman spectrum of a mixture of 1 (I ₁₃₆₀₎ and the intensity ratio of the peak intensity (I ₁₅₈₀₎ of around 1580cm ^-1 (I ₁₃₆₀ / I ₁₅₈₀₎ The measurement results of the distribution FIG.
3 is a graph showing the rapid filling rate for mixing ratio (C2) / [(C1) + (C2)].
FIG. 4 is a graph showing the rapid discharge rate versus mixing ratio (C2) / ((C1) + (C2)).
5 is a graph showing the cycle characteristics for the mixing ratio (C2) / ((C1) + (C2)).

[Conventionalized graphite particles (A)]

The flaky graphite particles constituting the spheroidized graphite particles (A) used in the present invention are artificial graphite, plate graphite or tablet graphite or natural graphite. Particularly, natural graphite having high crystallinity is preferable, and the average lattice plane spacing (d ₀₀₂ ) is preferably less than 0.3360 nm, particularly preferably 0.3358 nm or less. When it is less than 0.3360 nm, the discharge capacity per mass can be increased.

The scaly graphite particles are spherical or roughly spherical. Roughly refers to an elliptical shape, a mass, and the like, which means that there is no large concave or acute projections on the surface.

The spheroidized graphite particles (A) may be formed by aggregating, laminating, assembling or bonding plural pieces of scaly graphite particles, and the single scaly graphite particles may be curved, bent, folded or chamfered. In particular, concentric circular or cabbage-like structures in which planar portions (bases) of platelet-shaped graphite are arranged on the surface of the spheroidized graphite particles are preferable.

The average particle size (average particle size in terms of volume) of the spheroidized graphite particles (A) is preferably from 5 to 25 mu m, more preferably from 10 to 20 mu m. If it is 5 mu m or more, the density of the active material layer can be increased, and the discharge capacity per volume can be improved. If it is 25 m or less, the rapid filling property and the cycle characteristics are improved.

Here, the mean particle size in terms of volume means a particle size at which the cumulative frequency of the particle size distribution measured by the laser diffraction type particle size distribution is 50% by volume.

The average aspect ratio of the spheroidized graphite particles (A) is preferably 1.2 or more and less than 4.0. In the case of a shape close to the true spherical shape of less than 1.2, deformation of the graphite particles becomes large in the case where the active material layer is pressed to cause cracking of the graphite particles in some cases. And when it is 4.0 or more, the diffusion property of the lithium ion is lowered, and the rapid discharge property and the cycle characteristic may be lowered.

Average aspect ratio means the ratio of the short axis length to the long axis length of one particle. Here, the long axis length means the longest diameter of the particles to be measured, and the short axis length means a short diameter perpendicular to the long axis of the particles to be measured. The average aspect ratio is a simple average value of the aspect ratios of the respective particles measured by observing 100 particles by a scanning electron microscope. Here, the magnification at the time of observation with a scanning electron microscope is a magnification at which the shape of the particle to be measured can be confirmed.

The method for producing the spheroidized graphite particles (A) is not particularly limited. For example, it can be produced by adding a mechanical external force to a flat or scaly natural graphite. Specifically, a high shear force may be imparted or an electric manipulation may be applied to perform the sphericalization by curving, or the sphericalization may be assembled into a concentric circle. Before and after the spheroidizing treatment, a binder may be blended to promote the assembly. Examples of devices capable of performing the spheroidization treatment include grinding machines such as "Counter Jet Mill", "ACM Pulverizer" (manufactured by Hosokawa Micron Corporation) and "Current Jet" (manufactured by Nisshin Engineering Co., Ltd.), "SARARA" A granulator such as "GRANUREX" (manufactured by PROTON SANGYO KABUSHIKI KAISHA), "NEW GRA MACHINE" (manufactured by Seishin Kagyo Co., Ltd.) and "Agulo Master" (manufactured by Hosokawa Micron Corporation) A kneader such as a press kneader and a biaxial roll, a kneader such as a " Mechano Micro System " (manufactured by Nara Kai Seisakusho), an extruder, a ball mill, a planetary mill, a " MechanoFusion System " (manufactured by Hosokawa Micron Corporation) (Manufactured by Hosokawa Micron Corporation), " Hybridization " (manufactured by Nara Kikai Seisakusho Co., Ltd.), a rotating ball A compression shearing machine such as a mill, and the like.

After the spheroidizing treatment, pressing treatment may be performed to densify the inside of the spheroidized graphite particles.

After the spheroidizing treatment is performed, the surface of the spheroidized graphite particles (A) may be oxidized, crystallized or a functional group may be imparted by heat treatment in an oxidizing atmosphere, immersion in an acidic liquid, fluorination treatment or the like.

[Composite graphite particles (C1)]

The composite graphite particles (C1) used in the present invention have a carbonaceous material (B1) in at least a part of the inside and the particle surface of the spheroidized graphite particles (A). The adhesion of the carbonaceous material (B1) prevents the spheroidized graphite particles (A) from collapsing, and improves the water solubility of lithium ions to exhibit excellent quick-filling properties.

Examples of the carbonaceous material (B1) attached to the spheroidized graphite particle (A) include resins such as coal or petroleum heavy oils, tar oils, pitch oils and phenol resins, And a carbide formed by heat treatment. The amount of the carbonaceous material (B1) to be adhered is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, and most preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the spheroidized graphite particles (A). When the amount is less than 0.1 part by mass, the spheroidized graphite particles (A) are liable to collapse and the initial charge-discharge efficiency and rapid discharge property are lowered. In addition, there are cases where the cycle characteristics in a long term are lowered. When the amount is more than 10 parts by mass, the composite graphite particles (C1) are hardened and require a high pressure when pressing the active material layer. Therefore, in addition to causing breakage and elongation of the copper foil as a current collector, the irreversible capacity of the carbonaceous material (B1) is increased, leading to a decrease in initial charge / discharge efficiency.

[Composite graphite particles (C2)]

The composite graphite particles (C2) used in the present invention have a graphite material (B2) in at least part of the inside and / or the particle surface of the spheroidized graphite particles (A). It is possible to prevent collapse of the spheroidized graphite particles (A) by adhesion of the graphite material (B2), to densify the active material layer with a low pressing pressure, and to exhibit excellent initial charge / discharge efficiency and rapid discharge .

As the graphite material (B2) attached to the spheroidized graphite particles (A), for example, resins such as coal-based or petroleum-derived heavy oils, tar oils, pitch oils, Lt; 0 > C or less. The amount of the graphite material (B2) to be adhered is preferably 5 to 30 parts by mass, more preferably 10 to 25 parts by mass, per 100 parts by mass of the spheroidized graphite particles (A). When the amount is less than 5 parts by mass, the spheroidized graphite particles (A) are liable to be crushed, resulting in a decrease in initial charge / discharge efficiency and rapid discharge. In addition, there are cases where the cycle characteristics in a long term are lowered. When the amount is more than 30 parts by mass, the composite graphite particles (C2) are hardened and require a high pressure when pressing the active material layer, resulting in breakage or elongation of copper foil as a current collector. Further, the composite graphite particles (C2) are easily fused during the heat treatment, resulting in generation of fractured surfaces in the graphite material (B2), leading to a decrease in initial charge / discharge efficiency.

[It is preferable that the adhesion amount of the carbonaceous material B1 with respect to 100 parts by mass of A in the composite graphite particles C1 and the adhesion amount of the graphite material B2 with respect to 100 parts by mass of A in the composite graphite particles C2). This is because the collapse and breakage of the composite graphite particles C1 and C2 at a high active material density can be suppressed to a minimum, and particularly, the rapid charging performance of the composite graphite particles C1, the excellent initial charging / Efficiency, and rapid discharge characteristics.

That is, since the carbonaceous material (B1) is harder than the graphite material (B2) and the initial efficiency is lowered, it is preferable that the carbonaceous material (B1) is coated thinly by reducing the adherence to the spheroidized graphite particles (A) relatively. The rapid filling property of the composite graphite particles (C1) is derived from the interfacial reaction between the carbonaceous material (B1) coated with the film and the electrolyte. However, since the composite graphite particles (C1) alone cause crushing or fracture at high active material densities, by using the composite graphite particles (C2) reinforced by the graphite material (B2) It is to solve the problem.

As a method for attaching the carbonaceous material (B1) or the graphite material (B2) to at least a part of the inside of the spheroidized graphite particle (A) and / or the surface of the particle, B1 or a precursor of the graphite material B2, for example, a petroleum or coal-based heavy oil, a tar, a pitcher or a phenol resin is adhered or coated by any one of a liquid phase method and a solid phase method, .

As concrete examples of the liquid phase method, there may be mentioned, for example, coal tar, diesel oil, tar heavy oil, tar heavy oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, mesophase pitch, oxygen bridge petroleum pitch, Petroleum-based or coal-based tar pitch such as ethylene residues, thermoplastic resins such as polyvinyl alcohol and polyacrylic acid, thermosetting resins such as phenol resin and furan resin, saccharides, cellulose (hereinafter also referred to as a carbonaceous material precursor) Or the solution thereof is sprayed, mixed, or impregnated with the spheroidized graphite particles (A), and if necessary, the hard material such as a solvent is removed, and finally heated at a temperature of 500 ° C to 1500 ° C , To thereby produce a composite graphite particle (C1) having the carbonaceous material (B1) adhered thereto. Similarly, the composite graphite particles (C2) to which the graphite material (B2) is adhered can be produced by finally subjecting the graphite material (B2) to heat treatment at a temperature of 1500 ° C or more and less than 3300 ° C in a non-oxidizing atmosphere.

Further, when the carbonaceous material precursor or a solution thereof is brought into contact with the spheroidized graphite particles (A), stirring, heating, or depressurization can be carried out. A plurality of carbonaceous material precursors may be used which differ in kind. The carbonaceous material precursor may include an oxidizing agent or a crosslinking agent.

Specific examples of the solid phase method include a method in which the powder of the carbonaceous material precursor exemplified in the description of the liquid phase method is mixed with the spheroidized graphite particle (A), or the mechanical energy of mechanical energy such as compression, shearing, And a method of pressing the powder of the carbonaceous material precursor on the surface of the spheroidized graphite particle (A) by chemical treatment. The carbonaceous material precursor is melted or softened by mechanochemical treatment to be applied to the spheroidized graphite particles (A) and adhered thereto. Examples of the mechanochemical processable apparatus include the above-mentioned various compression and shearing type processing apparatuses. The spheroidized graphite particles (A) to which the powder of the carbonaceous material precursor is adhered is finally subjected to a heat treatment in a non-oxidizing or oxidizing atmosphere at a temperature of 500 ° C or more and less than 1,500 ° C to form composite graphite particles ( C1). ≪ / RTI > Similarly, the composite graphite particles (C2) to which the graphite material (B2) is adhered can be produced by finally subjecting the graphite material (B2) to heat treatment at a temperature of 1500 ° C or more and less than 3300 ° C in a non-oxidizing atmosphere.

The heat treatment may be performed stepwise. It is preferable that the composite graphite particles (C1) and (C2) of the present invention have substantially no crushing surface derived from crushing. As means for preventing fusion during the heat treatment process, a rotary kiln system It is preferable to employ it. The composite graphite particles (C1) and (C2) having smooth surfaces and no fusion can be obtained by stirring the spheroidized graphite particles (A) in a temperature region where the carbonaceous material precursor migrates from the molten state to carbonization.

Further, the fact that substantially no fracture surface derived from pulverization means that the composite graphite particles (C1) and (C2) after completion of the final heat treatment show a powder phase and the whole is not fusion bonded. It is not applicable that a part of the carbonaceous material (B1) and the graphite material (B2) adhered to the composite graphite particles (C1) and (C2) are peeled off and observed as individual powders. Even in the case of a powder phase, it does not exclude a case where a little of the fusion is included.

In the case of pulverizing the fused particles in the heat treatment (corresponding to Patent Document 4), the fracture surface derived from the pulverization serves as a starting point of the decomposition reaction of the electrolyte solution, resulting in a decrease in the initial charge / discharge efficiency.

In addition to the carbonaceous material precursor, a conductive material such as carbon fiber or carbon black, carbonaceous or graphite fine particles, flat artificial graphite or natural graphite may be used. In addition, in the case of producing the composite graphite particles (C2) having the graphite material (B2) attached thereto, it is also possible to use metals such as Fe, Co, Ni, Al and Ti, which act to increase the degree of graphitization, Semi-metals such as Si and B, and compounds thereof may be used.

In the present invention, the composite graphite particles (C1) to which the carbonaceous material (B1) is attached or the composite graphite particles (C2) to which the graphite material (B2) It is also possible to use a conductive material such as carbon fiber or carbon black, other carbonaceous material, fine particles of graphite material, flat artificial graphite or natural graphite on the inside or on the surface of the material B2. Further, metal oxides such as silica, aluminum oxide (alumina), and titanium oxide (titania) may be attached or embedded in (for example, as fine particles). Or a metal or a metal compound which can be an active material such as Si, Sn, Co, Ni, SiO, SnO, or lithium titanate may be adhered or embedded.

[Graphite particles for secondary battery negative electrode material]

The graphite particles for secondary battery negative electrode material of the present invention (hereinafter sometimes referred to as mixed graphite particles) are a mixture of the composite graphite particles (C1) and the composite graphite particles (C2). The mixture is, at a peak intensity of 1360cm ^-1 of Raman spectrum around (I ₁₃₆₀₎ and the intensity ratio (I ₁₃₆₀ / I ₁₅₈₀₎ of the peak intensity (I ₁₅₈₀₎ of the distribution around 1580cm ^-1, and 0.01 to 0.08 and 0.12 to 0.30 in the range of the maximum value. The composite graphite particles (C1) exhibit a maximum peak in the range of the intensity ratio (I ₁₃₆₀ / I ₁₅₈₀ ) of 0.12 to 0.30 and the composite graphite particles (C2) exhibit the intensity ratio (I ₁₃₆₀ / I ₁₅₈₀ ) of 0.01 to 0.08 Of the peak.

In order to obtain the intensity ratio (I ₁₃₆₀ / I ₁₅₈₀ ) distribution, the intensity ratio (I ₁₃₆₀ / I ₁₅₈₀₎ is measured for any 200 points of the mixture, and the corresponding points are counted at 0.004 intervals.

The mass ratio of the composite graphite particles (C1) to the composite graphite particles (C2) is about 20 to 80: 80 to 20 as the compounding ratio representing the maximum peaks of the bivalent peaks. Particularly preferably 30 to 70: 70 to 30. 20 to 80:80 to 20, the active material layer can be densified at a low pressing pressure, and the balance between rapid charging property and rapid discharge property is improved, and excellent cycle characteristics can be obtained.

In the mixed graphite particles of the present invention, the plane interval (d ₀₀₂ ) of the carbon nanotubes is 0.3360 nm or less. Particularly preferably 0.3358 nm or less. The discharge capacity when the mixed graphite particles are used as the negative electrode material varies depending on the manufacturing conditions and the evaluation conditions of the negative electrode and the evaluation cell, and is about 355 mAh / g or more, preferably 360 MAh / g or more.

The mixed graphite particles of the present invention have a 300 tap density of 1.00 g / cm 3 or more. Particularly preferably not less than 1.10 g / cm 3. The tap density is an index of the spherical shape or surface smoothness of the graphite particles, and the mixed graphite particles do not substantially have the fracture surface derived from the pulverization, so that the tap density is increased. The higher the tap density, the higher the density before pressurizing the active material layer, the smaller the deformation of the graphite particles due to the press, and the deformation and breakage of the graphite particles in the case of high density can be suppressed. Here, the tap density is an increased bulk density obtained after mechanically tapping the vessel containing the powder sample.

The mixed graphite particles of the present invention have an average particle size of 5 to 25 mu m. Particularly preferably 10 to 20 mu m. If it is 5 mu m or more, the density of the active material layer can be increased, and the discharge capacity per volume can be improved. When the thickness is 25 mu m or less, rapid chargeability and cycle characteristics are improved.

The mixed graphitized particles of the present invention have an average aspect ratio of 1.2 or more and less than 4.0. In the case of a shape close to a true spherical shape of less than 1.2, deformation of the graphite particles becomes large when the active material layer is pressed to cause cracking in the graphitic particles, or expansion due to rebound after pressing may become large. And if it is 4.0 or more, the diffusion property of lithium ions is lowered, and the rapid discharge property and cycle characteristics are lowered.

The mixed graphite particles of the present invention have a pore volume of not more than 0.08 ml / g with a pore diameter of not more than 0.5 탆 measured by a mercury porosimeter. Particularly preferably 0.05 ml / g or less. When the pore volume is 0.08 ml / g or less, long-term cycle characteristics become good. It is not clear why the cycle characteristics are lowered when the pore volume exceeds 0.08 ml / g. However, when the pore volume is excessive, the decomposition reaction of the electrolyte proceeds inside the graphite particles, The spheroid structure of the spheroidized graphitized particles (A) is repeated, and it is considered that the spheroid structure of the spheroidized graphitized particles (A) is easily broken in the course of charging and discharging.

In addition, the pore volume determined by the mercury porosimeter is set to 0.5 μm or less in order to exclude voids between the particles when the graphite particles are filled in the measuring cell to measure the pore volume. If the pore diameter of the object to be measured is 0.5 mu m or less, voids between particles are not included, and only pores of the graphite particles can be detected.

Examples of the method for adjusting the pore volume include controlling the density within the particles according to the operating conditions of the spheroidizing device (for example, electric time, pressure addition conditions at the same time as spheroidization) when the spheroidized graphite particles (A) , A method of subjecting the produced spherical graphite particles (A) to compression treatment, a method of subjecting the graphite particles (A) to a compression treatment, a carbonaceous material (B1) as a covering material of the composite graphite particles (C1) A method of controlling the degree of impregnation into the vaginal particles A (for example, by impregnating the inside of the spheroidized graphite particles A by lowering the viscosity of the precursor of the carbonaceous material (B1) or the graphite material (B2) , And furthermore, the impregnation is promoted by heating, decompression, etc.).

[Negative electrode material for lithium ion secondary battery]

The negative electrode material for a lithium ion secondary battery of the present invention (hereinafter simply referred to as a negative electrode material) uses the above-mentioned mixed graphite particles as an active material alone or as a main material. As the member, various known conductive materials, carbonaceous particles, graphitic particles, metallic particles, or composite particles thereof can be mixed so long as the effect of the present invention is not impaired. However, the mixing ratio of the members is preferably 30% Or less.

Examples of the member include carbonaceous or graphite fibers, carbon black, conductive materials such as artificial graphite and natural graphite, carbonaceous particles such as soft carbon and hard carbon, graphite of spherical mesocarbon small sphere, Or graphite of pulverized mesoporous carbonaceous material, graphite of coke or bulk mesophase, bulk graphite material obtained by pulverizing, oxidizing, carbonizing or graphitizing the bulk mesophase pitch, a pore composed of a plurality of flat graphite particles And graphite particles such as natural graphite which is spheroidized.

These members may be a carbon material, an organic material, an inorganic material, a mixture with a metal material, a coating, or a composite. A metal oxide such as silica, alumina, titania, or the like may be adhered or embedded, and silicon, tin, cobalt, nickel, copper, silicon oxide, Tin oxide, lithium titanate, or the like, or a metal compound.

[Negative electrode for lithium ion secondary battery]

The negative electrode for a lithium ion secondary battery of the present invention (hereinafter, simply referred to as a negative electrode) can be produced in accordance with a conventional negative electrode manufacturing method, but is not limited at all in the case of a production method capable of obtaining a chemically and electrochemically stable negative electrode Do not.

For the production of the negative electrode, a composite anode material in which a binder is added to the negative electrode material may be used. As the binder, it is preferable to use those having chemical stability and electrochemical stability with respect to the electrolyte, and examples thereof include fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene, polyvinyl alcohol, styrene butadiene rubber, Carboxymethylcellulose and the like are used. These may be used in combination. The binder is usually preferably in a proportion of 1 to 20 mass% of the total amount of the negative electrode mixture.

For the production of the negative electrode, N-methylpyrrolidone, dimethylformamide, water, alcohol and the like which are common 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 negative electrode mixture, applying the negative electrode mixture to one side or both sides of the current collector, and drying the paste. Thereby, a negative electrode having a negative electrode mixture layer (active material layer) uniformly and firmly adhered to the current collector is obtained.

More specifically, for example, the negative electrode material particles, the fluorine resin powder or the styrene butadiene rubber water dispersant and the solvent are mixed to prepare a slurry, followed by stirring and mixing using a known stirrer, a mixer, a kneader, To prepare a negative electrode material mixture paste. When this is applied to the current collector and dried, the negative electrode material mixture layer is uniformly and strongly adhered to the current collector. The thickness of the negative electrode material mixture layer is 10 to 200 占 퐉, preferably 30 to 100 占 퐉.

The negative electrode material mixture layer can also be produced by hot-mixing the particles of the negative electrode material with resin powders such as polyethylene and polyvinyl alcohol and hot-pressing them in a mold. However, in the case of dry mixing, a large amount of binder is required to obtain sufficient strength of the negative electrode, and when the binder is excessive, the discharge capacity and the rapid charge / discharge efficiency may be lowered.

When the negative electrode mixture layer is formed and compression is performed by pressing or the like, the bonding strength between the negative electrode mixture layer and the collector can be further increased.

The density of the negative electrode mixture layer is preferably 1.70 to 1.85 g / cm3, particularly 1.75 to 1.85 g / cm3 from the viewpoint of increasing the volume capacity of the negative electrode.

The shape of the current collector used for the negative electrode is not particularly limited, but it is preferable that the current collector is made of a foil, a mesh, an expanded metal or the like. The material of the current collector is preferably copper, stainless steel, nickel or the like. The thickness of the current collector is preferably 5 to 20 占 퐉 in the case of a thin shape.

[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 are based on elements of a general secondary battery. That is, an electrolyte, a negative electrode, and a positive electrode are used as main battery components, and these elements are enclosed in a battery can, for example. The negative electrode and the positive electrode each function as a carrier of lithium ions, and lithium ions are separated from the negative electrode during charging.

[Positive]

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 material (positive electrode active material) of the positive electrode, a lithium compound is used, and it is preferable to select a material capable of absorbing / desorbing a sufficient amount of lithium. For example, a lithium-containing transition metal oxide, a transition metal chalcogenide, a vanadium oxide, other lithium compounds, a compound represented by the formula M _X Mo ₆ OS _{8 -Y wherein} X is 0? X? 4, Y is 0? 1, and M is at least one kind of transition metal element), activated charcoal, activated carbon fiber 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, and the like.

The lithium-containing transition metal alloy 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. The composite oxides may be used alone or in combination of two or more. Specifically, the lithium-containing transition metal alloy oxide is LiM1 _{1 - X} M2 _X O ₂ (wherein X is a range value of 0? X? 1, and M1 and M2 are at least one transition metal element), or LiM1 _{1 - Y} M2 _Y O _{4 wherein} Y is a range value of 0 _{? Y} ? ₁ , and M1 and M2 are at least one transition metal element.

Mn, Cr, Ti, V, Fe, Al and the like are preferably used as the transition metal element represented by M1, M2, Mn, Cr, Ti, V, Fe, Zn, to be. 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.

The lithium-containing transition metal oxide may be prepared by mixing, as starting materials, lithium, transition metal oxides, hydroxides, salts, and the like, according to the composition of the desired metal oxide and mixing the starting materials in an oxygen atmosphere at a temperature of 600 to 1000 占 폚 Followed by calcination at a temperature.

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

The positive electrode is produced, for example, by applying the positive electrode mixture containing the lithium compound, the binder and the conductive material for imparting conductivity to the positive electrode to one surface or both surfaces of the current collector to form a positive electrode mixture layer. As the binder, the same materials as those used for producing the negative electrode can be used. As the conductive material, carbon materials such as graphite and carbon black are used.

As in the case of the positive electrode negative electrode, a positive electrode mixture may be formed by dispersing a composite cathode material in a solvent and applying the positive electrode mixture in paste form to the current collector, followed by drying to form a positive electrode mixture layer. And press-bonding such as press-pressing may be performed. As a result, the positive electrode material mixture layer is uniformly and strongly adhered to the current collector.

The shape of the current collector is not particularly limited, but it is preferable that the current collector is thin, mesh, expanded metal or the like. The material of the current collector is aluminum, stainless steel, nickel and the like. The thickness is preferably 10 to 40 占 퐉 in the case of a thin shape.

[Non-aqueous electrolyte]

The nonaqueous electrolyte (electrolytic solution) used in the secondary battery of the present invention is an electrolytic salt used in ordinary nonaqueous electrolytic solution. As the electrolyte salt, such as _{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 , and LiSiF ₅ . Particularly, 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, more preferably 0.5 to 3 mol / L.

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

Examples of the solvent constituting the nonaqueous electrolyte solution include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, 1,1- or 1,2-dimethoxyethane, 1,2 Ether such as diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran,? -Butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, anisole, diethyl ether, A nitrile such as acetonitrile, chloronitrile or propionitrile, a nitrile such as trimethyl borate, tetramethyl silicate, nitromethane, dimethyl formamide, N-methyl pyrrolidone, ethyl acetate, trimethyl ortho Propionic organic solvents such as formate, nitrobenzene, benzoyl chloride, benzoyl bromide, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, dimethyl sulfide and the like can be used.

When the above 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 product, polymethacrylate-based polymer compounds, polyacrylate-based polymer compounds, polyvinylidene fluoride, vinylidene fluoride-hexafluoro Propylene copolymer and the like may be used alone or in combination. It is particularly preferable to use a fluorinated polymer compound such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer.

The polymer solid electrolyte or the polymer gel electrolyte is mixed with a plasticizer. As the plasticizer, the electrolyte salt or non-aqueous solvent may be used. In the case of the polymer gel electrolyte, the electrolyte salt concentration in the non-aqueous electrolyte as the plasticizer is preferably 0.1 to 5 mol / L, more preferably 0.5 to 2 mol / L.

The method of producing the polymer solid electrolyte is not particularly limited. For example, a method in which a polymer compound constituting the matrix, a lithium salt and a nonaqueous solvent (plasticizer) are mixed and heated to melt the polymer compound, a method in which a polymer compound, a lithium salt and a nonaqueous solvent (plasticizer) are dissolved in an organic solvent for mixing A method of mixing a polymerizable monomer, a lithium salt and a nonaqueous solvent (plasticizer), and a method of polymerizing a polymerizable monomer by irradiating ultraviolet rays, electron beams, molecular beams or the like to the mixture to obtain a polymer compound .

The ratio of the nonaqueous solvent (plasticizer) in the polymer solid electrolyte is preferably from 10 to 90 mass%, more preferably from 30 to 80 mass%. When the content is less than 10% by mass, the electrical conductivity is lowered. When the content exceeds 90% by mass, the mechanical strength is weakened, and film formation becomes difficult.

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

The material of the separator is not particularly limited, and examples thereof include a woven fabric, a nonwoven fabric, and a synthetic resin microporous membrane. A synthetic resin microporous membrane is suitable, and in particular, a polyolefin microporous membrane is preferable in terms of thickness, membrane strength and membrane resistance. Specifically, it is a polyethylene or polypropylene microporous membrane, or a microporous membrane composed of these membranes.

The secondary battery of the present invention is produced by stacking the negative electrode, the positive electrode and the nonaqueous electrolyte in the order of, for example, a negative electrode, a nonaqueous electrolyte and a positive electrode, and accommodating the negative electrode, the positive electrode and the non-

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 the shape of the secondary battery of the present invention are not particularly limited and may be selected arbitrarily from a cylindrical shape, a square shape, a coin shape, a button shape, have. In order to obtain a more stable sealed nonaqueous electrolyte battery, it is preferable that the battery includes a means for detecting an increase in the internal pressure of the battery when the battery is overcharged, thereby blocking the current.

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

Example

Hereinafter, the present invention will be described concretely with reference to Examples, but the present invention is not limited to these Examples.

In the Examples and Comparative Examples, a button-type secondary battery for evaluation having the structure shown in Fig. 1 was produced and evaluated. The battery can be manufactured in accordance with a known method based on the object of the present invention.

(Example 1)

[Preparation of spheroidized graphite particles (A)]

And while milling the flake-shaped natural graphite having an average particle size 55㎛, while electric conducting folding process and ended in spherical shape, average particle size 12㎛, the average aspect ratio is 1.4, (d ₀₀₂₎ is 0.3357㎚, the specific surface area 7.0㎡ / g and a pore volume of 0.5 탆 or less in diameter by a mercury porosimeter was adjusted to 0.12 ml / g.

The spherical graphite particles were subjected to compression treatment at a pressure of 0.5 ton / cm 2 by a mold press to obtain an average particle size of 12 μm, an average aspect ratio of 1.8, (d ₀₀₂ ) of 0.3357 nm, a specific surface area of 6.5 m 2 / The pore volume was adjusted to 0.08 ml / g by a porosimeter with a pore diameter of 0.5 m or less.

[Preparation of composite graphite particles (C1)]

, 100 parts by mass of the spheroidized graphite particles (A), 8 parts by mass of a pulverized product (average particle size: 4 탆) of a coal tar pitch having a softening point of 80 캜 and a balance ratio of 50% as a precursor of the carbonaceous material (B1) And 2 parts by mass of scaly natural graphite were mixed and subjected to a first firing at 500 DEG C under a nitrogen atmosphere in a rotary kiln for one hour, followed by a firing treatment at 1100 DEG C for 3 hours under a nitrogen atmosphere to obtain a carbonaceous material (B1) And the spheroidized graphite particles (A) were obtained.

The composite graphite particles (C1) obtained had a high sieve yield of 99.8% by sieving with an eye size of 53 탆 and were practically unfused. (D ₀₀₂ ) of 0.3357 nm, a specific surface area of 3.6 m < 2 > / g, a pore diameter of 0.5 m or less by mercury porosimetry, The volume was 0.06 ml / g.

Observation of the composite graphite particles (C1) in a scanning electron microscope revealed that the coated graphite particles had smooth ellipsoidal shape with natural scale graphite attached to the surface. No particles of calcined carbon originating from the coal tar pitch were observed and no crushing fracture profile derived from the crushing of the fused portion was observed.

[Preparation of composite graphite particles (C2)]

100 parts by mass of the above-mentioned spheroidized graphite particles (A) and 25 parts by mass of a pulverized product (average particle size 5 μm) of a calcareous pitch heat treatment product having a softening point of 270 ° C and a residual carbon percentage of 80% were mixed as a precursor of the graphite material (B2) The graphite was subjected to a first calcination in a kiln under a nitrogen atmosphere at 500 DEG C for 1 hour and then subjected to a graphitization treatment at 2800 DEG C for 5 hours in a non-oxidizing atmosphere to obtain a composite of graphitic material (B2) and spheroidized graphite particles To obtain graphitized particles (C2).

The composite graphite particles (C2) obtained had a sieve yield of 99.5% by sieving with an eye size of 53 탆 and were substantially unfused. (D ₀₀₂ ) of 0.3358 nm, a specific surface area of 0.6 m 2 / g, a pore diameter of 0.5 μm or less by mercury porosimetry, and the like. The volume was 0.04 ml / g.

Composite graphite particles (C2) were observed with a scanning electron microscope and it was an elliptical coated graphite particle having a smooth surface. No particles of graphite alone derived from the coal tar pitch heat treatment were observed, and no crushing fracture profile derived from the crushing of the fused portion was observed.

[Preparation of mixed graphite particles]

50 parts by mass of the composite graphite particles (C1) and 50 parts by mass of the composite graphite particles (C2) were mixed. This mixture is the average particle diameter 14㎛, the average aspect ratio is 1.8, (d ₀₀₂₎ is 0.3358㎚, a specific surface area of 2.1㎡ / g, is 0.05ml / g pore volume of pore diameters less than 0.5㎛ by mercury captive meter, 300 tap density was 1.21 g / cm < 3 >.

Relative to the mixture, the Raman spectrum of the intensity ratio (I ₁₃₆₀ / I ₁₅₈₀₎ of the distribution of the peak intensity near 1360cm ^-1 (I ₁₃₆₀₎ and the peak intensity (I ₁₅₈₀₎ of around 1580cm ^-1 of an arbitrary point 200 The measurement results are shown in Fig. Intensity ratio (I ₁₃₆₀ / I ₁₅₈₀ ) showed a maximum peak near 0.04 and 0.172.

[Preparation of negative electrode mixture]

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

[Production of working electrode]

The negative electrode material mixture paste was applied on a copper foil having a thickness of 16 mu m to a uniform thickness, and further the water of the dispersion medium was evaporated in a vacuum at 90 deg. Subsequently, the negative electrode material mixture applied on the copper foil was pressed by a hand press at 12 kN / cm 2 (120 MPa) and further punched into a circular shape with a diameter of 15.5 mm to form a negative electrode mixture layer Mu m) was prepared. The density of the negative electrode mixture layer was 1.75 g / cm 3. There was no elongation or deformation of the working electrode, and there was no recess in the current collector viewed from the cross section.

[Production of the main pole]

A lithium metal foil was pressed against a nickel net and punched into a circular shape having a diameter of 15.5 mm to prepare a collector composed of a nickel net and a lithium metal foil (thickness: 0.5 mm) adhered to the collector.

[Electrolyte / Separator]

Aqueous electrolyte was prepared by dissolving LiPF ₆ in a mixed solvent of 33 vol% of methylene carbonate and 67 vol% of methylene carbonate at a concentration of 1 mol / L. The resultant nonaqueous electrolyte solution was impregnated with a polypropylene porous body (thickness: 20 mu m) to prepare a separator impregnated with an electrolytic solution.

[Production of Evaluation Battery]

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

The external cup (1) and the external can (3) were caulked at their periphery with insulating gasket (6) sandwiched between both peripheral edges. A separator 5 impregnated with an electrolytic solution and a separator 5 impregnated with an electrolytic solution and a separator 5 made of a negative electrode mixture in this order from the inner surface of the outer can 3 in this order, A working electrode 2, and a current collector 7b made of copper foil.

The evaluation cell is obtained by laminating the separator 5 impregnated with the electrolytic solution between the working electrode 2 adhered to the current collector 7b and the counter electrode 4 adhered to the current collector 7a, The outer can 1 and the outer can 3 are accommodated by accommodating the outer can 1 and the outer can 3 in the outer cup 1 and the outer can 3, With an insulating gasket 6 interposed therebetween, and both peripheral edges were caulked and sealed.

The evaluation battery is a battery composed of a working electrode 2 containing graphite particles usable as a negative electrode active material and a counter electrode 4 made of a lithium metal foil in an actual battery.

The evaluation battery thus prepared was subjected to the following charge / discharge test at a temperature of 25 캜 to evaluate the discharge capacity per mass, the discharge capacity per volume, the initial charge / discharge efficiency, the rapid charge rate, the rapid discharge rate and the cycle characteristics . The evaluation results are shown in Table 1 (refer to Table 1-1 and Table 1-2, the same applies hereinafter).

[Discharge capacity per mass, discharge capacity per volume]

The constant current charging was performed at 0.9 mA until the circuit voltage reached 0 V, then the charging was switched to the constant voltage charging and the charging was continued until the current value became 20 A. And the charge capacity per mass was obtained from the amount of electricity flowing therebetween. Thereafter, it was stopped for 120 minutes. Next, constant-current discharge was performed until the circuit voltage reached 1.5 V at a current value of 0.9 mA, and the discharge capacity per mass was obtained from the amount of electricity flowing therebetween. This was the first cycle. From the charging capacity and the discharge capacity in the first cycle, the initial charge-discharge efficiency was calculated by the following formula.

Initial charge / discharge efficiency (%) = (discharge capacity / charge capacity) × 100

Further, in this test, the process of charging lithium ions into the negative electrode material and discharging the lithium ions from the negative electrode material was regarded as discharging.

[Rapid charge rate]

Fast charging was performed in the second cycle following the first cycle.

The constant current charging was carried out at 7.2 mA, which is eight times the first cycle, until the circuit voltage reached 0., And the constant current charging capacity was determined. The rapid charging rate was calculated from the following equation.

Fast charge rate (%) = (constant current charge capacity in the second cycle / discharge capacity in the first cycle) × 100

[Rapid discharge rate]

Using another evaluation cell, rapid discharging was performed in the second cycle following the first cycle. After performing the first cycle as described above, the battery was charged in the same manner as in the first cycle, and then the constant current discharge was performed until the circuit voltage reached 1.5 V at 18 mA which was 20 times the first cycle. The discharge capacity per mass was obtained from the amount of electricity flowing therebetween, and the rapid discharge rate was calculated by the following equation.

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

[Cycle characteristics]

An evaluation cell different from the evaluation cell in which the discharge capacity per mass, initial charge / discharge efficiency, rapid charge rate, and rapid discharge rate were evaluated was prepared as follows.

As the four counter electrodes of the button-type battery of Fig. 1, a mixture of lithium cobalt oxide and carbon black was used instead of lithium foil, and a positive electrode coated on aluminum foil with polyvinylidene fluoride as a binder was used. The amount of the positive electrode active material was adjusted so as to exhibit a discharge capacity equivalent to 95% of the charging capacity of the negative electrode.

The battery was charged at a constant current of 7.2 mA until the circuit voltage reached 4.2 V, then switched to constant-voltage charging, continued to charge until the current value became 120 μA, and then stopped for 10 minutes. Next, constant current discharge was performed until the circuit voltage reached 3V at a current value of 7.2 mA. The cycle characteristics were calculated from the discharge capacity obtained by repeating charge and discharge 100 times by using the following formula.

Cycle characteristic (%) = (discharge capacity in the 100th cycle / discharge capacity in the first cycle) × 100

As shown in Table 1, the evaluation cell obtained by using the negative electrode material of Working Example 1 for the working electrode can increase the density of the active material to 1.75 g / cm 3, and also has a high discharge capacity per mass and a high initial charge- . Therefore, the discharge capacity per volume can be remarkably improved. Even at such a high density, rapid charging rate, rapid discharge rate and cycle characteristics maintain excellent results.

(Examples 2 to 5)

The density of the negative electrode mixture layer was changed to 1.75 g / cm < 3 > by changing the press pressure in the same manner as in Example 1 except that the mixing ratio of the composite graphite particles (C1) and the composite graphite particles (C2) To prepare a working electrode, and an evaluation battery was produced. The same charge / discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

(Comparative Examples 1 and 2)

The procedure of Example 1 was repeated except that the composite graphite particles (C1) and the composite graphite particles (C2) were not mixed and the negative electrode material was used alone, and the density of the negative electrode mixture layer was adjusted to 1.75 g / Cm < 3 > to prepare a working electrode. The same charge / discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1. 3 to 5 show the relationship between the mixing ratio of the composite graphite particles (C1) and the composite graphite particles (C2) and the battery characteristics together with Examples 1 to 5.

The mixed graphitized particles of the present invention combine the rapid charging rate shown in Fig. 3, the rapid discharge rate shown in Fig. 4, and the cycle characteristics shown in Fig. 5 at high levels. On the other hand, in the case where the composite graphite particles (C1) and the composite graphite particles (C2) are not mixed with each other but used as a negative electrode material, the characteristics of either the rapid filling rate or the rapid discharge rate are insufficient, The cycle characteristics are deteriorated.

(Example 6)

A working electrode was fabricated in the same manner as in Example 1 except that the density of the negative electrode material mixture layer was changed to 1.80 g / cm 3 (Example 6). The same charge / discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1.

As the density of the negative electrode mixture layer is increased, the characteristics of each battery tend to decrease. However, the density is maintained at a sufficiently high level at a density of 1.80 g / cm 3. On the other hand, if the density is too high, the deformation of the copper foil as the current collector and the deterioration of the battery characteristics become remarkable.

(Examples 7 to 9 and Comparative Examples 3 to 7)

The ratio of the carbonaceous material (B1) and the graphite material (B2) to the composite graphite particles (C1), the average particle size of the spheroidized graphite particles (A) Type graphite, and 2 parts by mass of graphitized carbon fibers having a length of 120 nm and a length of 5 mu m are added together with the precursor of the graphite material (B2) when the composite graphite particles (C2) are produced A working electrode was prepared in the same manner as in Example 1 except for the above, and an evaluation battery was produced. The same charge / discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1. Table 1 shows various physical properties of the mixed graphite particles.

When the surface interval (d ₀₀₂ ) of the carbon net surface layer, which is a requirement of the mixed graphite particles, exceeds 0.3360 nm, the discharge capacity is low. When the tap density is less than 1.0 g / cm < 3 > or when the average aspect ratio is 4 or more, rapid discharge rate and cycle characteristics are insufficient. When the average particle size is less than 5 탆, the initial charge / discharge efficiency is low, and when the average particle size exceeds 25 탆, the rapid charge rate and cycle characteristics are insufficient. When the pore volume of the pore diameter of 0.5 탆 or less by the mercury porosimeter exceeds 0.08 ml / g, the cycle characteristics are relatively lowered.

(Example 10)

A working electrode was prepared in the same manner as in Example 1 except that 85 mass parts of the mixed graphite particles of Example 9 were mixed with 15 mass parts of bulk mesophase graphite as the following negative electrode material, Respectively. The same charge / discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1. Table 1 shows various physical properties of the mixed graphite particles.

[Adjustment of bulk mesophase graphite material]

The coal tar pitch was heated to 400 DEG C over 12 hours in an inert atmosphere and heat-treated, and then naturally cooled to room temperature in an inert atmosphere. The obtained bulk mesophase was pulverized, and was formed into a mass having an average aspect ratio of 1.6 and an average particle size of 10 mu m. Subsequently, the graphite was subjected to a heat treatment at 280 ° C for 15 minutes in air to oxidize the graphite, followed by graphitization treatment at 900 ° C for 6 hours and at 3000 ° C for 5 hours in a non-oxidizing atmosphere to prepare bulk mesophase graphite .

The particle shape of the obtained bulk mesophase graphitized product maintained the shape at the time of pulverization. (d ₀₀₂ ) of 0.3362 nm and a specific surface area of 1.2 m 2 / g.

(Example 11)

10 parts by mass of bulk mesophase graphite as shown in Example 10 as another negative electrode material, and 5 parts by mass of scaly graphite coated with a carbonaceous material shown below were added to 80 parts by mass of the mixed graphite particles of Example 9 A working electrode was prepared in the same manner as in Example 1 to prepare an evaluation cell. The same charge / discharge test as in Example 1 was carried out, and the evaluation results of the battery characteristics are shown in Table 1. Table 1 shows various physical properties of the mixed graphite particles.

[Table 1-1]

[Table 1-2]

[Preparation of flaky graphite coated with carbonaceous material]

To 100 parts by mass of scaly natural graphite having an average particle size of 5 占 퐉, 3 parts by mass of a pulverized product (average particle size 3 占 퐉) of a coal tar pitch having a softening point of 80 占 폚 and a residual carbon percentage of 50% was mixed as a precursor of a carbonaceous material. And then subjected to a first firing at 500 ° C for 1 hour in an atmosphere, followed by a firing treatment at 1100 ° C for 3 hours under a nitrogen atmosphere to obtain scaly natural graphite coated with a carbonaceous material.

The scale-type coating by the carbonaceous material obtained had a natural graphite having an average particle size 5㎛, the average aspect ratio is 34, (d ₀₀₂₎ is 0.3357㎚, the specific surface area 7.0㎡ / g.

As shown in Table 1, even when other negative electrode materials are mixed and used in a range that does not impair the high discharge capacity of the mixed graphite particles of the present invention, the excellent initial charge / discharge efficiency, rapid charge rate, And cycle characteristics were obtained.

As described above, in the embodiment in which the working electrode is fabricated by the negative electrode material specified by the present invention, the density of the negative electrode mixture layer can be increased, and the discharge capacity, the initial charge / discharge efficiency, the rapid charge rate, the rapid discharge rate, Both were excellent. On the other hand, in the comparative example in which the working electrode was fabricated by the negative electrode material deviating from the present invention, either the discharge capacity, the initial charge / discharge efficiency, the rapid charge rate, the rapid discharge rate or the cycle characteristics were insufficient.

The negative electrode material of the present invention can be used as a negative electrode material of a lithium ion secondary battery which effectively contributes to miniaturization and high performance of a device to be mounted.

1: External Cup
2: working electrode
3: External can
4: antipode
5: Separator
6: Insulation gasket
7a and 7b:

Claims (5)

Composite graphite particles (C1) having a carbonaceous material (B1) in the inside of the particle and at least a part of the surface of the particle of the spheroidizing graphite particle (A) formed into a spherical or substantially spherical shape, ) And a composite graphite particle (C2) having a graphite material (B2) in at least part of its particle surface,
And the mixture satisfies the following conditions (1) to (5).
(1) the surface interval (d ₀₀₂ ) of the carbon nanotube surface layer is 0.3360 nm or less,
(2) a tap density of 1.0 g / cm < 3 &
(3) an average particle diameter of 5 to 25 mu m,
(4) an average aspect ratio of 1.2 to less than 4.0, and
(5) Pore volume of not more than 0.5 占 퐉 and not more than 0.08 ml / g by mercury porosimeter. The method according to claim 1,
Wherein the content of the carbonaceous material (B1) is 0.1 to 10 parts by mass based on 100 parts by mass of the spheroidized graphite particles (A) in the composite graphite particles (C1)
Wherein the content of the carbonaceous material (B2) is 5 to 30 parts by mass relative to 100 parts by mass of the spheroidized graphite particles (A) in the composite graphite particles (C2). 3. The method according to claim 1 or 2,
Wherein the ratio of the composite graphite particles (C1) to the composite graphite particles (C2) is 1:99 to 90:10 in mass ratio. A lithium ion secondary battery negative electrode comprising the graphite particles for lithium ion secondary battery negative electrode material according to any one of claims 1 to 3. A lithium ion secondary battery having the lithium ion secondary battery negative electrode according to claim 4.

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