JP2015008125A - Method for manufacturing composite graphite particles for lithium ion secondary battery negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing composite graphite particles as a negative electrode material for a lithium ion secondary battery by which a high discharge capacity, high initial charge and discharge efficiencies, an excellent high-temperature resistance, and a low resistance can be achieved.SOLUTION: A method for manufacturing composite graphite particles comprises: a first mixing step in which graphite particles (b) are obtained by mixing graphite particles (a) having cavities inside, a carbonaceous precursor (x), and a solvent to fill the cavities inside the graphite particles (a) with the liquid solution of the carbonaceous precursor (x) and the solvent; a second mixing step in which graphite particles (c) are obtained by mixing the graphite particles (b) and a carbonaceous precursor (y) to cause the carbonaceous precursor (y) to deposit on the surface of the graphite particles (b) subsequently to the first mixing step; and a baking step in which composite graphite particles (d) that are the graphite particles (a) inside and surfaces of which are coated with carbonaceous material are obtained by baking the graphite particles (c) obtained by the second mixing step under an inactive atmosphere at a temperature of 700-1400°C to change the carbonaceous precursor (x) and the carbonaceous precursor (y) into the carbonaceous material.

Description

  The present invention relates to a method for producing composite graphite particles for a negative electrode for a lithium ion secondary battery.

In recent years, demand for higher performance of lithium ion secondary batteries has been increasing due to the spread of hybrid vehicles and electric vehicles as well as higher performance of electronic devices.
As a negative electrode material for a lithium ion secondary battery, it is common to use a carbon material that has the ability to occlude and release lithium ions and can prevent the precipitation of lithium metal. Carbon materials having a wide variety of structures, structures, or forms such as a graphite crystalline structure to a turbulent layer structure are known, and the electrode characteristics during charging and discharging are greatly different. Among them, it is known that graphite is particularly excellent in charge / discharge characteristics and exhibits high discharge capacity and potential flatness (Patent Document 1).

As the graphite structure develops, that is, the higher the crystal structure is, the more easily a stable lithium intercalation compound is formed, and lithium is more easily inserted between the carbon network surfaces, thereby obtaining a high discharge capacity. Has been reported. In general, the theoretical capacity of the carbon anode material is assumed to be a discharge capacity of 372 mAh / g, assuming that an ideal graphite intercalation compound LiC _{6 of} graphite and lithium is formed.

On the other hand, there is a problem with a lithium ion secondary battery using graphite as a negative electrode material. For example, as the crystallinity of graphite increases, side reactions that do not participate in battery reactions, such as decomposition of the electrolyte, are likely to occur on the graphite surface during the first charge, and the amount of electricity is taken out during the subsequent charge-discharge process. An increase in discharge capacity loss called irreversible capacity cannot be mentioned.
Side reactions such as the decomposition of the electrolytic solution mainly occur in the portion with high reaction activity. Therefore, it continues until the decomposition product accumulates on the surface and grows, and the part with high reaction activity decreases.
Such an increase in irreversible capacity, that is, a low initial charge / discharge efficiency can be compensated for by adding a positive electrode material to the secondary battery, but the addition of excess positive electrode material is a new energy density decrease. It is desirable to avoid it because it causes problems.

  As described above, in a lithium ion secondary battery using graphite as a negative electrode material, a high discharge capacity and a low irreversible capacity are contradictory requirements, but as a solution to this, a highly crystalline graphite material (nucleus) There has also been proposed a method in which the surface is coated with a low crystalline material to form a multilayer structure.

  Specifically, the surface of a highly crystalline graphite material that serves as a nucleus is coated with low crystalline carbon using a pyrolysis gas of an organic compound such as propane or benzene (Patent Document 2), A crystalline graphite material is coated or impregnated with a carbon material such as pitch in a liquid phase and then fired at a temperature of about 1000 ° C. to form a carbonaceous material on the surface layer (Patent Document 3), a graphite crystalline material or A graphite precursor such as raw coke is oxidized at a gas phase or a liquid phase in an oxidizing atmosphere at about 300 ° C. (Patent Document 4), or a combination thereof (Patent Document 5).

  However, the method described in Patent Document 2 and the method described in Patent Document 5 have a problem that the manufacturing process is complicated and expensive from the viewpoint of industrial production. Further, the method described in Patent Document 2 is a coating method. Since it is difficult to control the thickness, there is a problem that high electrode performance and powder performance cannot be exhibited stably.

Japanese Examined Patent Publication No. 62-23433 JP-A-4-368778 Japanese Patent Laid-Open No. 5-121066 JP-A-10-326611 JP-A-10-214615

As a subject of such conventional coating techniques, there is a compatibility between low resistance (excellent in high rate characteristics) and high temperature durability.
That is, if the coating thickness is reduced, the resistance due to the low crystal material is reduced, but the exposure of the high crystal graphite material serving as the base material is increased, and there is concern about high temperature durability. On the contrary, if the coating thickness is increased, the high-temperature durability is excellent, but the resistance may be increased. Thus, low resistance and high temperature durability often conflict.
Although there has been stated that high discharge capacity and low irreversible capacity can be achieved by coating (JP-A-9-213328), there is no mention of low resistance and high-temperature durability.

  In view of the situation as described above, the present invention can achieve high discharge capacity and high initial charge / discharge efficiency when used as a negative electrode material for a lithium ion secondary battery. It aims at providing the manufacturing method of the composite graphite particle | grains which can obtain low resistance together.

As a negative electrode material for a lithium ion secondary battery, the present inventor has intensively studied composite graphite particles capable of obtaining both high discharge capacity and initial charge / discharge efficiency, and excellent high-temperature durability and low resistance.
As a result, when using graphite particles having voids or pores inside as a raw material and coating the surface with a low crystalline material, the graphite particles, the carbonaceous precursor, and the solvent are first mixed, By impregnating, the inside of the graphite particles is coated, and further, a carbonaceous precursor is added to coat and sinter the outside of the graphite particles, and the carbonaceous precursor is changed to a carbonaceous material, so that a high discharge capacity, initial It has been found that composite graphite particles can be obtained which can obtain both charge / discharge efficiency, excellent high-temperature durability and low resistance.
This is the first step. By filling the internal voids of the graphite particles with a liquid phase in which the carbonaceous precursor and solvent are mixed, the low boiling point components and solvent in the carbonaceous precursor are volatilized in the subsequent firing step. In addition, a coating that ensures the pore structure of the graphite particles is performed, and low resistance can be secured. In addition, it is considered that high temperature durability can be secured because the orientation of graphite particles that are originally easily oriented can be suppressed by the coating of the graphite particles outside in the solid phase in the next step. In addition, the composite graphite particles are covered with the low crystalline carbonaceous precursor both inside and outside the graphite particles while maintaining the original graphite structure throughout the entire process, so that high discharge capacity and initial charge / discharge efficiency are achieved. It is thought to develop.
That is, this invention is the following (1)-(6).

(1) The graphite particles (a) having voids therein, the carbonaceous precursor (x), and the solvent are mixed, and the voids inside the graphite particles (a) are mixed with the carbonaceous precursor (x) and the solvent. And a first mixing step of obtaining graphite particles (b) in which the voids inside the graphite particles (a) are filled with the solution,
After the first mixing step, the graphite particles (b) and the carbonaceous precursor (y) are mixed, and the carbonaceous precursor (y) is attached to the surface of the graphite particles (b). A second mixing step of obtaining graphite particles (c) having the carbonaceous precursor (y) attached to the surfaces of the graphite particles (b);
The graphite particles (c) obtained in the second mixing step are fired at a temperature of 700 to 1400 ° C. in an inert atmosphere to convert the carbonaceous precursor (x) and the carbonaceous precursor (y) to carbon. And a firing step for obtaining composite graphite particles (d) in which the inside and surface of the graphite particles (a) are coated with a carbonaceous material. Manufacturing method.
(2) The composite graphite for a negative electrode of a lithium ion secondary battery according to (1), wherein the graphite particles (a) are granulated graphite particles formed by aggregating a plurality of graphite particles. Particle production method.
(3) The composite for a negative electrode of a lithium ion secondary battery according to (1) or (2), wherein the content of the carbonaceous material is 1 to 20% by mass of the composite graphite particles (d). A method for producing graphite particles.
(4) Said (1)-(3) whose content of carbonaceous material by said carbonaceous precursor (x) and said solvent is 5-40 mass% of content of all the carbonaceous materials in said 1st mixing process. ) For producing composite graphite particles for negative electrodes of lithium ion secondary batteries.
(5) In the second mixing step, any of the above (1) to (4), wherein the carbonaceous material content of the carbonaceous precursor (y) is 60 to 95% by mass of the total carbonaceous material content. The manufacturing method of the composite graphite particle for lithium ion secondary battery negative electrodes as described in any one.
(6) Furthermore,
The calcining step of calcining the graphite particles (c) at a temperature of 200 ° C. or higher and lower than 700 ° C. in an inert atmosphere, after the second mixing step and before the baking step, The manufacturing method of the composite graphite particle for lithium ion secondary battery negative electrodes as described in any one of 1)-(5).

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the negative electrode material for lithium ion secondary batteries which is excellent also in a high rate characteristic (small resistance value) can be provided with a capacity | capacitance, initial stage charge / discharge efficiency, and cycling characteristics.

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

The present invention is described in detail below.
First, features in contrast to the prior art of the present invention will be described.
A feature of the present invention is that after filling the voids inside the graphite particles having voids inside with a solution of a carbonaceous precursor and a solvent, the surface of the graphite particles filling the voids inside with the above solution is continuously provided. Further, the carbonaceous precursor is attached.
By firing the intermediate material thus obtained, composite graphite particles having pores on the surface can be obtained, and the surface of the composite graphite particles has pores. It is considered that the value becomes smaller and the high rate characteristic becomes excellent. When the voids inside the graphite particles are filled with a solution of a carbonaceous precursor and a solvent and then dried or fired, it is considered that no pores are formed on the surface, and this effect is obtained. I can't.
The pores on the surface of the composite graphite particles break through the coating of the carbonaceous precursor on the surface of the graphite particles when the intermediate substance is fired, and the volatile matter and solution of the carbonaceous precursor evaporate from the voids inside the graphite particles. Although the present inventor expects that it is formed by this, it is not limited to this.

  Japanese Patent Application Laid-Open No. 2004-63457 discloses a primary mixing step of mixing a graphitic carbonaceous material and a first organic compound, and heat-treating the obtained first mixture to obtain the first organic compound. A first firing step for carbonization; a second mixing step for mixing the obtained composite carbonaceous material and the second organic compound; and a second mixture obtained by heat-treating the second organic compound. A method for producing a carbon material for electrodes (prior invention 1), characterized in that it comprises a second firing step for carbonizing the carbon. In the present invention, the second mixing step is subsequently performed after the first mixing step, whereas in the first invention, the first firing step is performed after the first mixing step, and then the second mixing step is performed. The point to do is different. Due to this difference, it is considered that the carbon material of Cited Invention 1 does not form an appropriate amount of pores on the particle surface. As a result, the lithium ion secondary battery using the composite graphite particles of the present invention as a negative electrode material is superior in resistance value and high rate characteristics as compared with the lithium ion secondary battery using the carbon material of the prior invention 1 as a negative electrode material. Conceivable.

  Japanese Patent Application Laid-Open No. 2003-1000029 discloses an attachment step of attaching a composition containing a drying oil or a fatty acid thereof and a phenol resin to a carbonaceous powder, a curing step of curing the carbonaceous powder, and the carbonaceous material. And a baking step of heat-treating the powder in a non-oxidizing atmosphere, wherein the adhesion step and the curing step are repeated at least once and not more than 20 times, and then the baking step is performed. A method (prior invention 2) is described. In the present invention, after the first mixing step, the second mixing step is subsequently performed, and then the firing step is performed, whereas in the prior invention 2, the curing step is performed after the adhesion step, and further the adhesion step and the curing step. The point which performs a baking process after repeating a process is different. Due to this difference, it is considered that the carbon material of Cited Invention 2 does not form an appropriate amount of pores on the particle surface. As a result, the lithium ion secondary battery using the composite graphite particles of the present invention as a negative electrode material is superior in resistance value and high rate characteristics as compared with the lithium ion secondary battery using the carbon material of the prior invention 2 as a negative electrode material. Conceivable.

(1) Selection of raw material The graphite particles (raw material graphite particles) used for the raw material of the present invention are not particularly limited as long as they are graphite particles having voids inside (also referred to as “graphite particles (a)”). Those obtained by granulating flake-shaped natural graphite particles or artificial graphite particles have many voids inside the particles and are preferable.
These graphite particles have a low bulk density and are generally about 0.4 to 0.7 g / cm ³ .

  The average crystallinity of the graphite particles (a) can be determined from the interplanar spacing (d002) of the carbon network layer and the size of the crystallite in the C-axis direction (Lc) in the X-ray wide angle diffraction method. That is, using a CuKα ray as an X-ray source and high-purity silicon as a standard substance, a diffraction peak on the (002) plane was measured for the composite graphite particles, and d002 and Lc were determined from the peak position and its half width, respectively. Is calculated. The calculation method conforms to the Gakushin method, and a specific method is described in JIS R 7651: 2007 “Method for measuring the lattice constant and crystallite size of a carbon material”.

  D002 and Lc of the graphite particles (a) are preferably d002 ≦ 0.3365 nm and Lc ≧ 40 nm, and d002 ≦ 0.3362 nm, Lc ≧ 40 nm from the viewpoint of increasing the doping amount of lithium and expressing a higher discharge capacity. 50 nm is more preferable.

The average particle diameter of the graphite particles (a) is preferably 5 to 100 μm, more preferably 5 to 30 μm, although it depends on the thickness of the negative electrode for a lithium ion secondary battery.
The average particle size of the graphite particles (a) is a particle size (D50) at which the cumulative frequency of the laser diffraction particle size distribution meter is 50% by volume.

The specific surface area of the graphite particles (a) is not particularly limited, but is preferably 4 m ² / g or more so that the specific surface area of the obtained composite graphite particles is not too small. On the other hand, if the specific surface area is too large, the electrode density is lowered, the initial charge / discharge efficiency in battery characteristics and the high temperature durability are lowered, and the like is preferably 20 m ² / g or less, more preferably 15 to ⁵ m ² / g.
The specific surface area is a nitrogen adsorption BET specific surface area.

  The carbonaceous precursor (x) is not particularly limited as long as it contains fixed carbon, but heavy oils such as coal tar pitch, coal-based heavy oil, and heat-treated pitch are preferable.

  The solvent is not particularly limited as long as it dissolves at least a part of the carbonaceous precursor (x) to be used. By using a solvent, the carbonaceous precursor (x) can easily penetrate into the graphite particles (a) and can be applied uniformly.

  The solution of the carbonaceous precursor (x) and the solvent is a mixture of the carbonaceous precursor (x) and the solvent, and at least a part of the solvent-soluble component of the carbonaceous precursor (x) is dissolved in the solvent. It is a thing. The carbonaceous precursor (x) or all of its solvent-soluble components may not be dissolved in the solvent.

  The carbonaceous precursor (x) and the solvent may be mixed in advance to form a solution of the carbonaceous precursor (x) and the solvent, and then mixed with the graphite particles (a).

  The carbonaceous precursor (y) is not particularly limited as long as it contains fixed carbon, but heavy oils such as coal tar pitch, coal-based heavy oil, and heat-treated pitch are preferred, and the carbonaceous precursor (x) May be the same or different. In addition, the carbonaceous precursor (y) may be a solid phase, may not be a solid phase, and may be a melt. The carbonaceous precursor (y) does not contain a solvent.

(2) Mixing ratio In the present invention, usually, the graphite particles (a), the carbonaceous precursor (x), and the solvent are mixed, and after further adding the carbonaceous precursor (y), calcining or carbonization firing. As a result, composite graphite particles (d) in which the inside and outside of the graphite particles are coated with a carbonaceous material are finally obtained, but by reducing the coating film derived from the inside and outside carbonaceous precursors to the necessary minimum, lithium ion secondary particles can be obtained. Battery characteristics when used as a negative electrode material for a secondary battery can be optimized. That is, the content (content ratio, mass%) of the carbonaceous material in the composite graphite particles is preferably 1 to 20 mass%, more preferably 1 to 18 mass%, and further preferably 2 to 7 mass%.

  The content of the carbonaceous material can be calculated from the mass of the carbonaceous material precursor and the solvent to be used and the remaining carbon ratio, and the residual carbon ratio is determined by the type and mixing ratio of the organic material. The residual carbon ratio of the carbonaceous precursor and the solvent is measured in advance by a test method defined by JIS M 8812: 2004 “Coal and cokes—industrial analysis method”. Adjust to be within the preferred range.

In Formula 1, A, B, and C are respectively the following.
A = carbon residue of carbonaceous precursor used in the first mixing step × mass of carbonaceous precursor used in the first mixing step = residual carbon rate of solvent used in the first mixing step × first mixing step Mass of solvent used in C = carbon residue ratio of carbonaceous precursor used in the second mixing step × mass of carbonaceous precursor used in the second mixing step

Moreover, about the solvent amount to be used, it adds 6-80 mass parts with respect to 100 mass parts of graphite particles (a), More preferably, a solvent is added so that it may become 12-48 mass parts. Within this range, the internal voids of the graphite particles (a) can be sufficiently filled with the solution of the carbonaceous precursor (x) and the solvent, and the carbonaceous precursor (y) is converted into the graphite particles (b). A sufficient coating film can be formed on the outside.
In the present invention, if the amount of the solvent is too small, the voids inside the graphite particles (a) cannot be filled with the solution of the carbonaceous precursor (x) and the solvent in the first mixing step, Coating is not achieved. On the other hand, when the amount of the solvent is too large, in the second mixing step, the organic substance is dissolved in the remaining solvent, and the outside of the graphite particles cannot be coated.

  In the present invention, the content of the carbonaceous material by the carbonaceous precursor (x) and the solvent, that is, the content of the carbonaceous material by the solution of the carbonaceous precursor (x) and the solvent is not particularly limited. 5-40 mass% of content of the total carbonaceous material calculated by 1) is preferable, 10-40 mass% is more preferable, and 10-30 mass% is further more preferable. In the present invention, the content of the carbonaceous material by the carbonaceous precursor (y) is not particularly limited, but is preferably 60 to 95% by mass of the content of all carbonaceous materials calculated by the above formula (1). 60-90 mass% is more preferable, and 70-90 mass% is further more preferable. Within this range, the resistance value due to the full cell becomes lower.

(3) Manufacturing method The manufacturing method for obtaining the composite graphite particle concerning this invention is demonstrated below.
The method for producing composite graphite particles of the present invention mainly comprises the following steps.
(A) A step of mixing a graphite particle, a carbonaceous precursor (x), and a solvent to obtain a mixture (first mixing step).
(B) A step of adding the carbonaceous precursor (y) to the mixture and mixing to obtain an intermediate material (second mixing step).
(C) A step of heating the intermediate substance at 700 to 1400 ° C., preferably 900 to 1400 ° C. in an inert gas atmosphere to obtain a carbonized substance (firing step). If desired, a step of calcining at a temperature of 200 ° C. or higher and lower than 700 ° C., preferably 200 to 500 ° C. in an inert atmosphere (calcination step) may be performed before the firing step.
In the present invention, the calcination step and the firing step may be combined or the firing step may be referred to as a carbonization step.

(A) First mixing step In the first mixing step, graphite particles having voids therein (also referred to as “graphite particles (a)”), a carbonaceous precursor (x), and a solvent are mixed, and the graphite particles are mixed. The inside voids of (a) are filled with a solution of the carbonaceous precursor (x) and the solvent, and the inside of the graphite particles (a) is filled with the solution of graphite particles (“graphite particles ( b) "is also a step of obtaining.
In the first mixing step in the present invention, the graphite particles (a), the carbonaceous precursor (x), and the solvent are mixed. The carbonaceous precursor (x) and the solvent may be mixed in advance before mixing with the graphite particles (a) to form a solution of the carbonaceous precursor (x) and the solvent. In the first mixing step, the room temperature or the mixing tank may be heated. When the mixing tank is heated, the viscosity of the solvent can be reduced, and the impregnation efficiency of the solution of the carbonaceous precursor (x) and the solvent into the graphite particles (a) can be increased. Furthermore, the carbonaceous precursor (x) and the solvent into the graphite particles (a) can be obtained by reducing the pressure in the mixing tank when mixing the graphite particles (a), the carbonaceous precursor (x) and the solvent. The impregnation efficiency of the solution can be increased.
As a mixing device, a device that stirs with a single blade such as a butterfly mixer, a device that performs mixing by means of a shear force in the mixing tank and between two blades such as a kneader type, a Nauta mixer type An apparatus that vigorously mixes the entire interior of the tank can be used by stirring and mixing the raw materials while stirring the screw shaft attached obliquely as described above and rotating the screw shaft itself.

(B) Second mixing step The second mixing step is continued after the first mixing step, and the graphite particles (b) and the carbonaceous precursor (y) are mixed, and the graphite particles (b). The carbonaceous precursor (y) is adhered to the surface of the graphite particles, and the graphite particles (b) are adhered to the surface of the graphite particles (b) (also referred to as “graphite particles (c)”). It is the process of obtaining.
“Continue” in this step means that different steps such as heating, curing, and drying do not occur between the first mixing step and the second mixing step, and the first and second mixing steps are short. It does not prescribe that it must be done continuously in time. It is preferable that the second mixing step is performed while the organic solution in the voids in the graphite particles obtained by the first mixing step exists as it is and no significant change occurs.
The mixture (graphite particles (b)) obtained in the first mixing step holds a solution in which at least a part of the solvent-soluble component of the carbonaceous precursor (x) is dissolved in the solvent inside the graphite particles (a). ing. A solid carbonaceous precursor (y) is added to the mixture and mixed to adhere the carbonaceous precursor (y) to the outside of the graphite particles (b). The carbonaceous precursor (y) may be melted and attached. A powder mixing device such as a Nauta mixer type can be used as the mixing device. Preferably, a mixing device capable of applying a shearing force such as a kneader type or a mechano-fusion system is used.

(C) Carbonization step In the carbonization step, the graphite particles (c) are calcined at a temperature of 700 to 1400 ° C in an inert atmosphere to convert the carbonaceous precursor (x) and the carbonaceous precursor (y) to carbon. A firing step of obtaining composite graphite particles (also referred to as “composite graphite particles (d)”) in which the inside and surface of the graphite particles (a) are coated with a carbonaceous material, and a second mixing step if desired. And before the firing step, a calcining step of calcining the graphite particles (c) at a temperature of 200 ° C. or higher and lower than 700 ° C. in an inert atmosphere.
In this step, the intermediate substance (graphite particles (c)) obtained through the first mixing step and the second mixing step is heated in an inert gas atmosphere such as nitrogen gas or argon gas. By the heat treatment, the thermochemical reaction of the intermediate substance proceeds, and the remaining volatile components are removed.
In the firing step, the heat treatment temperature is important. That is, heat treatment at 700 ° C. or higher is performed in order to remove the volatile matter of the organic matter and form a film of fixed carbon. It is the temperature range of 700-1400 degreeC, Preferably it is the range of 900-1400 degreeC. In addition, the apparatus used for this process may be either a batch type or a continuous type.
In the calcination step, a heat treatment is performed at 200 ° C. or more and less than 700 ° C., preferably 200 to 500 ° C., so that a volatile component and a solvent are skipped to generate an appropriate amount of holes in the coating of the carbonaceous precursor. Shrinkage can be reduced and firing can be performed more uniformly, and the resulting composite graphite particles (d) can be more appropriately coated with a carbonaceous material inside and outside.

(4) Composite graphite particles The composite graphite particles obtained by the above process preferably have an average particle size of 1 to 100 µm, more preferably 5 to 30 µm. The average particle diameter of the composite graphite particles is a particle diameter (D50) at which the cumulative frequency of the laser diffraction particle size distribution meter is 50% by volume.

The specific surface area of the obtained composite graphite particles is not particularly limited, but the specific surface area is preferably not too small, and more preferably 3 m ² / g or more. The specific surface area of the composite graphite particles is a nitrogen adsorption BET specific surface area.

(5) Negative electrode for lithium ion secondary battery The above composite graphite particles can be used as a negative electrode for lithium ion secondary battery (hereinafter also referred to as “negative electrode of the present invention”) by a conventionally known method. As a method for producing a negative electrode using the present invention, specifically, for example, a negative electrode mixture is prepared by mixing the composite graphite particles of the present invention and a binder, and this negative electrode mixture is collected into a current collector. The method of forming a negative mix layer by apply | coating to the single side | surface or both surfaces of a body is mentioned. An active material other than the composite graphite particles of the present invention (composite graphite particles (d)), a conductive agent, a thickener and the like may be added to the negative electrode mixture.
The binder is not particularly limited, and a conventionally known binder for negative electrode mixture can be used, but one having chemical stability and electrochemical stability with respect to the electrolyte is preferably used. Specifically, as the binder, for example, polyethylene, polyvinyl alcohol, styrene butadiene rubber, carboxymethyl cellulose and the like can be used alone or in combination of two or more. The content of the binder in the negative electrode mixture is not particularly limited, but is preferably 1 to 20% by mass in the total amount of the negative electrode mixture. With this content, a stable electrode can be formed without hindering the performance of the negative electrode material.
In the method for producing a negative electrode of the present invention, the negative electrode mixture is dispersed in a conventionally known dispersion medium for producing a negative electrode to form a paste, and then applied to a current collector using a doctor blade and dried. Also good. It is preferable that the negative electrode mixture is pasted with the dispersion medium and used as the negative electrode mixture paste, because the negative electrode mixture layer is more uniformly and firmly adhered to the current collector. Specifically, for example, the above negative electrode mixture, a water dispersion binder such as styrene butadiene rubber, a water soluble binder such as carboxymethylcellulose, and a dispersion medium such as water and / or alcohol are mixed. After making into a slurry, it can knead | mix using a kneader, a mixer, etc., and a negative mix paste can be prepared. If this negative electrode mixture paste is applied to one or both sides of the current collector and dried, a negative electrode in which the negative electrode mixture layer is uniformly bonded to the current collector can be obtained.

(6) Lithium ion secondary battery As the configuration of the lithium ion secondary battery of the present invention, the negative electrode obtained as described above, any known positive electrode, and an electrolyte solution interposed between the negative electrode and the positive electrode are used. Any known separator to be held, such as polyethylene or polypropylene, can be used. As the electrolytic solution, any known electrolytic solution, for example, a non-aqueous electrolytic solution in which an electrolyte such as LiClO ₄ or LiBF _{4 is} dissolved at a predetermined concentration in a specific protic organic solvent such as ethylene carbonate or propylene carbonate can be used.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.

[Example 1]
1. Production of composite graphite particles (1) First mixing step Spherical natural graphite particles produced by granulating a plurality of flake-like natural graphite in a 1 L internal volume kneader device (with voids inside) (average particle size 12 μm, 500 g of a specific surface area of 7.0 m ² / g) is added, 5 g of coal-based pitch (softening point 105 ° C., residual carbon ratio 60% by mass) is added as a carbonaceous precursor, and a solvent (methylnaphthalene and quinoline are main components). 180 g of residual carbon ratio = 0 mass%) was added, and the mixture was stirred at normal pressure and room temperature for 60 minutes.
(2) Second mixing step After the first mixing step, 40 g of the same coal-based pitch (softening point 105 ° C., residual carbon ratio 60 mass%) is added in the same kneader apparatus as described above, and the mixture is stirred for 60 minutes. Obtained material.
(3) Carbonization process The obtained intermediate substance was calcined by holding at 500 ° C. for 3 hours under N ₂ atmosphere. After calcination, it was treated at 1100 ° C. for 3 hours in an N ₂ gas atmosphere, and baked to obtain composite graphite particles (527 g).
2. Analysis of Composite Graphite Particles (1) Average Particle Size The average particle size of the obtained composite graphite particles was measured with a laser diffraction particle size distribution meter (model LMS-300, manufactured by Seishin Enterprise). The results are shown in the “average particle size” column of Table 1.
(2) Specific surface area The specific surface area of the obtained composite graphite particles was measured with a high-precision gas / vapor adsorption amount measuring apparatus (model BELSORP-MAX, manufactured by Nippon Bell). The results are shown in the “specific surface area” column of Table 1.
(3) Content of carbonaceous material The content of carbonaceous material was calculated from the mass of the carbonaceous material and solvent used, the residual carbon ratio, and the mass of the obtained composite graphite particles according to the above equation 1. The results are shown in the column “Content of carbonaceous material” in Table 1.
3. Electrode performance evaluation (1) Preparation of negative electrode 1% by mass of carboxymethylcellulose ammonium and 1% by mass of carboxy-modified styrene butadiene rubber were mixed with the manufactured composite graphite particles and solid content, and water was used as a dispersion medium. The negative electrode mixture paste was manufactured by mixing and stirring with a hybrid mixer. This paste was applied onto a 15 μm thick copper foil and vacuum dried at a temperature of 110 ° C. to produce a negative electrode.
(2) Battery Evaluation by Half Cell 2.1) Manufacture of Button Type Lithium Ion Secondary Battery A button type lithium ion secondary battery (see FIG. 1) was manufactured. Hereinafter, a description will be given with reference to FIG. 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. Thereafter, the working electrode 2 is accommodated in the exterior cup 1, the counter electrode 4 is accommodated in the exterior can 3, the exterior cup 1 and the exterior can 3 are combined, and further, the peripheral portions of the exterior cup 1 and the exterior can 3 are insulated. Gasket 6 was interposed, and both peripheral portions were caulked and sealed. Thus, 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 electrolytic solution, and a disk-like made of a negative electrode mixture A button-type secondary battery in which a working electrode (negative electrode) 2 and a current collector 7b made of copper foil were laminated was manufactured. This button type secondary battery is a battery composed of a working electrode 2 made of a produced negative electrode and a counter electrode 4 made of a lithium metal foil.
2.2) Measurement of discharge capacity and initial charge / discharge efficiency Using the manufactured button-type secondary battery, the discharge capacity and the initial charge / discharge efficiency were measured as follows.
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, and the charging capacity was determined from the amount of current applied during that time. Then, it rested for 120 minutes. Next, constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 1.5 V, and the discharge capacity was obtained from the energization amount during this period.
The initial charge / discharge efficiency was calculated from (Equation 2).
Initial charge / discharge efficiency (%) = (discharge capacity / charge capacity) × 100 (Equation 2)
The discharge capacity by the half cell and the initial charge / discharge efficiency are shown in the corresponding columns of Table 1, respectively.
(3) Battery evaluation by full cell 3.1) Manufacture of button-type lithium ion secondary battery The above (2) except that a positive electrode made of LiCoO ₂ , a conductive material and a binder (93 wt%: 4 wt%: 3 wt%) was used. ) To produce a button-type lithium ion secondary battery.
3.2) Measurement of resistance value From the change in voltage when the manufactured button-type secondary battery was charged to 50% SOC and discharged at 0 ° C for 0.5 second at 0.5 C, the resistance value was calculated according to (Equation 3). Asked.
Resistance value = − (Voltage after discharge−Voltage before discharge) / Current value (Equation 3)
3.3) Measurement of capacity retention rate The discharge capacity was determined in the same manner as in (2) 2.2).
At 60 ° C., charging / discharging from 3V to 4.2V of 1C was repeated 50 cycles, and the discharge capacity at the 50th cycle was determined.
From the discharge capacity and the discharge capacity at the 50th cycle, the capacity retention rate was determined by (Equation 4).
Capacity retention ratio (50 cycles) = (discharge capacity / 50th cycle discharge capacity) × 100 (Equation 4)
The resistance value and capacity retention rate (50 cycles) by the full cell are shown in the corresponding columns of Table 1, respectively.

[Example 2]
1. Production of composite graphite particles (1) First mixing step Spherical natural graphite particles produced by granulating a plurality of flake graphite in a 1 L internal volume kneader (with internal voids) (average particle size 12 μm, ratio 500 g of surface area 7.0 m ² / g) is added, 5 g of coal-based pitch (softening point 105 ° C., residual carbon ratio 60% by mass) is added as an organic substance, and a solvent (methylnaphthalene and quinoline are main components, residual carbon ratio 180 g was added, and the mixture was stirred at 110 ° C. for 60 minutes under reduced pressure (≦ 9.93 Torr).
(2) Second mixing step After the first mixing step, 40 g of the same coal-based pitch (softening point 105 ° C., residual carbon ratio 60% by mass) is added in the same kneader apparatus as above, and the mixture is stirred at 110 ° C. for 60 minutes. Intermediate material was obtained.
(3) Carbonization process The obtained intermediate substance was processed like Example 1, and the composite graphite particle (527g) was obtained.
2. Analysis of Composite Graphite Particles As in Example 1, the average particle diameter and specific surface area of the obtained composite graphite particles were measured, and the content of carbonaceous material was calculated. The carbonaceous material content, average particle size, and specific surface area are shown in the corresponding columns of Table 1, respectively.
3. Electrode performance evaluation (1) Production of negative electrode A negative electrode was produced in the same manner as in Example 1.
(2) Battery evaluation by half cell In the same manner as in Example 1, the discharge capacity and the initial charge / discharge efficiency were measured. The results are shown in the corresponding column of Table 1.
(3) Battery evaluation by full cell In the same manner as in Example 1, the resistance value and the capacity retention ratio (50 cycles) were measured. The results are shown in the corresponding column of Table 1.

[Example 3]
1. Production of composite graphite particles (1) Spherical natural graphite particles produced by granulating a plurality of flake graphite in a 1 L kneader apparatus having an internal volume of 1 L (with internal voids) (average particle size 12 μm, ratio 500 g of surface area 7.0 m ² / g) is added, 5 g of coal-based pitch (softening point 105 ° C., residual carbon ratio 60% by mass) is added as an organic substance, and a solvent (methylnaphthalene and quinoline are main components, residual carbon ratio 180 g was added, and the mixture was stirred at 110 ° C. for 60 minutes under reduced pressure (≦ 9.93 Torr).
(2) Second mixing step After the first mixing step, 10 g of the same coal-based pitch (softening point 105 ° C., residual carbon ratio 60% by mass) is added in the same kneader apparatus as above, and the mixture is stirred at 110 ° C. for 60 minutes. Intermediate material was obtained.
(3) Carbonization process The obtained intermediate substance was processed like Example 1, and the composite graphite particle (509g) was obtained.
2. Analysis of Composite Graphite Particles As in Example 1, the average particle diameter and specific surface area of the obtained composite graphite particles were measured, and the content of carbonaceous material was calculated. The carbonaceous material content, average particle size, and specific surface area are shown in the corresponding columns of Table 1, respectively.
3. Electrode performance evaluation (1) Production of negative electrode A negative electrode was produced in the same manner as in Example 1.
(2) Battery evaluation by half cell In the same manner as in Example 1, the discharge capacity and the initial charge / discharge efficiency were measured. The results are shown in the corresponding column of Table 1.
(3) Battery evaluation by full cell In the same manner as in Example 1, the resistance value and the capacity retention ratio (50 cycles) were measured. The results are shown in the corresponding column of Table 1.

[Example 4]
1. Manufacture of composite graphite particles (1) First mixing step 500 g of natural graphite particles (average particle size 12 μm, specific surface area 7.0 m ² / g) are put into a 1 L internal volume kneader, and coal-based pitch (softening) is used as organic matter. 5 g of a point 105 ° C. and a residual carbon ratio of 60% by mass) are added, and 180 g of a solvent (methylnaphthalene and quinoline are main components, residual carbon ratio≈0% by mass) are added, and 110 ° C. under reduced pressure (≦ 9.93 Torr). For 60 minutes.
(2) Second mixing step After the first mixing step, 55 g of the same coal-based pitch (softening point 105 ° C., residual carbon ratio 60 mass%) is added in the same kneader apparatus as above, and the mixture is stirred at 110 ° C. for 60 minutes. Intermediate material was obtained.
(3) Carbonization process The obtained intermediate substance was processed like Example 1, and the composite graphite particle (536g) was obtained.
2. Analysis of Composite Graphite Particles As in Example 1, the average particle diameter and specific surface area of the obtained composite graphite particles were measured, and the content of carbonaceous material was calculated. The carbonaceous material content, average particle size, and specific surface area are shown in the corresponding columns of Table 1, respectively.
3. Electrode performance evaluation (1) Production of negative electrode A negative electrode was produced in the same manner as in Example 1.
(2) Battery evaluation by half cell In the same manner as in Example 1, the discharge capacity and the initial charge / discharge efficiency were measured. The results are shown in the corresponding column of Table 1.
(3) Battery evaluation by full cell In the same manner as in Example 1, the resistance value and the capacity retention ratio (50 cycles) were measured. The results are shown in the corresponding column of Table 1.

[Example 5]
1. Manufacture of composite graphite particles (1) First mixing step 500 g of natural graphite particles (average particle size 12 μm, specific surface area 4.3 m ² / g) are introduced into a 1 L internal volume kneader, and coal-based pitch (softening) is used as an organic substance. 10 g of a point 105 ° C. and a residual carbon ratio of 60% by mass) are added, and 180 g of a solvent (methylnaphthalene and quinoline are main components, residual carbon ratio≈0% by mass) are added, and 110 ° C. under reduced pressure (≦ 9.93 Torr). For 60 minutes.
(2) Second mixing step After the first mixing step, 5 g of the same coal-based pitch (softening point 105 ° C., residual carbon ratio 60 mass%) is added in the same kneader apparatus as described above, and the mixture is stirred at 110 ° C. for 60 minutes. Intermediate material was obtained.
(3) Carbonization process The obtained intermediate substance was processed like Example 1, and the composite graphite particle (536g) was obtained.
2. Analysis of Composite Graphite Particles As in Example 1, the average particle diameter and specific surface area of the obtained composite graphite particles were measured, and the content of carbonaceous material was calculated. The carbonaceous material content, average particle size, and specific surface area are shown in the corresponding columns of Table 1, respectively.
3. Electrode performance evaluation (1) Production of negative electrode A negative electrode was produced in the same manner as in Example 1.
(2) Battery evaluation by half cell In the same manner as in Example 1, the discharge capacity and the initial charge / discharge efficiency were measured. The results are shown in the corresponding column of Table 1.
(3) Battery evaluation by full cell In the same manner as in Example 1, the resistance value and the capacity retention ratio (50 cycles) were measured. The results are shown in the corresponding column of Table 1.

[Comparative Example 1]
1. Production of composite graphite particles (1) Mixing step Spherical natural graphite particles produced by granulating a plurality of flake graphite in a 1 L internal volume kneader (with voids inside) (average particle size 12 μm, specific surface area 7 0.0 g ² / g) is added, 45 g of coal-based pitch (softening point 105 ° C., residual carbon ratio 60% by mass) is added as an organic substance, and a solvent (methylnaphthalene and quinoline are main components, residual carbon ratio≈0 180 g (mass%) was added, and the mixture was stirred at 110 ° C. for 60 minutes under reduced pressure (≦ 9.93 Torr) to obtain an intermediate substance.
(2) Carbonization process The obtained intermediate substance was processed like Example 1, and the composite graphite particle (527g) was obtained.
2. Analysis of Composite Graphite Particles As in Example 1, the average particle diameter and specific surface area of the obtained composite graphite particles were measured, and the content of carbonaceous material was calculated. The carbonaceous material content, average particle size, and specific surface area are shown in the corresponding columns of Table 1, respectively.
3. Electrode performance evaluation (1) Production of negative electrode A negative electrode was produced in the same manner as in Example 1.
(2) Battery evaluation by half cell In the same manner as in Example 1, the discharge capacity and the initial charge / discharge efficiency were measured. The results are shown in the corresponding column of Table 1.
(3) Battery evaluation by full cell In the same manner as in Example 1, the resistance value and the capacity retention ratio (50 cycles) were measured. The results are shown in the corresponding column of Table 1.

[Comparative Example 2]
1. Production of Composite Graphite Particles (1) Mixing Step Spherical natural graphite particles produced by granulating a plurality of flake graphite using an AMS circulation type mechanofusion system (with internal voids) (average particle size 12 μm, 45 g of a coal-based pitch (softening point 105 ° C., residual carbon ratio 60 mass%) was added to a specific surface area of 7.0 m ² / g) to form a composite carbon material precursor.
(2) Carbonization step The obtained composite carbon material precursor was treated in the same manner as in Example 1 to obtain composite graphite particles (527 g).
2. Analysis of Composite Graphite Particles As in Example 1, the average particle diameter and specific surface area of the obtained composite graphite particles were measured, and the content of carbonaceous material was calculated. The carbonaceous material content, average particle size, and specific surface area are shown in the corresponding columns of Table 1, respectively.
3. Electrode performance evaluation (1) Production of negative electrode A negative electrode was produced in the same manner as in Example 1.
(2) Battery evaluation by half cell In the same manner as in Example 1, the discharge capacity and the initial charge / discharge efficiency were measured. The results are shown in the corresponding column of Table 1.
(3) Battery evaluation by full cell In the same manner as in Example 1, the resistance value and the capacity retention ratio (50 cycles) were measured. The results are shown in the corresponding column of Table 1.

[Comparative Example 3]
1. Production of composite graphite particles (1) Spherical natural graphite particles produced by granulating a plurality of flake graphite in a 1 L kneader apparatus having an internal volume of 1 L (with internal voids) (average particle size of 12 μm, 500 g of a specific surface area of 7 m ² / g) is added, 5 g of coal-based pitch (softening point 105 ° C., residual carbon ratio 60% by mass) is added as a carbonaceous precursor, and a solvent (methylnaphthalene and quinoline are the main components and the residual 180 g of charcoal ratio≈0% by mass) was added, and the mixture was stirred at 110 ° C. for 60 minutes under reduction (≦ 9.93 Torr).
(2) Drying process The processed material obtained at the 1st mixing process was dried at 200 degreeC.
(3) Second mixing step After the drying step, 40 g of the same coal-based pitch (softening point 105 ° C., residual carbon ratio 60% by mass) is added in the same kneader apparatus as described above, and the mixture is stirred at 110 ° C. for 60 minutes. An intermediate was obtained.
(4) Carbonization process The obtained intermediate substance was processed like Example 1, and the composite graphite particle (527g) was obtained.
2. Analysis of Composite Graphite Particles As in Example 1, the average particle diameter and specific surface area of the obtained composite graphite particles were measured, and the content of carbonaceous material was calculated. The carbonaceous material content, average particle size, and specific surface area are shown in the corresponding columns of Table 1, respectively.
3. Electrode performance evaluation (1) Production of negative electrode A negative electrode was produced in the same manner as in Example 1.
(2) Battery evaluation by half cell In the same manner as in Example 1, the discharge capacity and the initial charge / discharge efficiency were measured. The results are shown in the corresponding column of Table 1.
(3) Battery evaluation by full cell In the same manner as in Example 1, the resistance value and the capacity retention ratio (50 cycles) were measured. The results are shown in the corresponding column of Table 1.

[Comparative Example 4]
1. Preparation of Graphite Particles Spherical natural graphite particles produced by granulating a plurality of flake graphite (with voids inside) (average particle size 12 μm, specific surface area (7 m ² / g)) were prepared.
2. Electrode Performance Evaluation (1) Production of Negative Electrode A negative electrode was produced in the same manner as in Example 1 except that the prepared spherical natural graphite particles were used instead of the composite graphite particles.
(2) Battery evaluation by half cell In the same manner as in Example 1, the discharge capacity and the initial charge / discharge efficiency were measured. The results are shown in the corresponding column of Table 1.
(3) Battery evaluation by full cell In the same manner as in Example 1, the resistance value and the capacity retention ratio (50 cycles) were measured. The results are shown in the corresponding column of Table 1.

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

Claims (6)

The graphite particles (a) having voids therein, the carbonaceous precursor (x), and a solvent are mixed, and the voids inside the graphite particles (a) are mixed into a solution of the carbonaceous precursor (x) and the solvent. A first mixing step of obtaining graphite particles (b) filled with the solution, wherein the voids inside the graphite particles (a) are filled with the solution;
After the first mixing step, the graphite particles (b) and the carbonaceous precursor (y) are mixed, and the carbonaceous precursor (y) is attached to the surface of the graphite particles (b). A second mixing step of obtaining graphite particles (c) having the carbonaceous precursor (y) attached to the surfaces of the graphite particles (b);
The graphite particles (c) obtained in the second mixing step are fired at a temperature of 700 to 1400 ° C. in an inert atmosphere to convert the carbonaceous precursor (x) and the carbonaceous precursor (y) to carbon. And a firing step for obtaining composite graphite particles (d) in which the inside and surface of the graphite particles (a) are coated with a carbonaceous material. Manufacturing method.   The method for producing composite graphite particles for a lithium ion secondary battery negative electrode according to claim 1, wherein the graphite particles (a) are granulated graphite particles formed by aggregating a plurality of graphite particles. .   The method for producing composite graphite particles for a lithium ion secondary battery negative electrode according to claim 1 or 2, wherein the content of the carbonaceous material is 1 to 20% by mass of the composite graphite particles (d).   In said 1st mixing process, content of the carbonaceous material by the said carbonaceous precursor (x) and the said solvent is 5-40 mass% of content of all the carbonaceous materials, The any one of Claims 1-3 The manufacturing method of the composite graphite particle | grains for lithium ion secondary battery negative electrodes of description.   The said 2nd mixing process WHEREIN: Content of the carbonaceous material by the said carbonaceous precursor (y) is 60-95 mass% of content of all the carbonaceous materials, The any one of Claims 1-4. A method for producing composite graphite particles for a negative electrode of a lithium ion secondary battery. further,
The calcining step of calcining the graphite particles (c) at a temperature of 200 ° C or higher and lower than 700 ° C under an inert atmosphere is provided after the second mixing step and before the baking step. The manufacturing method of the composite graphite particle for lithium ion secondary battery negative electrodes of any one of 1-5.

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