JP2017071524A - Composite graphite particle and method producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an electrode-forming material capable of enhancing high-temperature storage characteristics without deteriorating the charge-discharge cycle property of an electrode in the electrode formation of a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery; and a method for producing the same.SOLUTION: There is provided composite graphite particles 100 comprising graphite-containing particles 110 and a polymer film 120. The graphite-containing particles comprise at least a graphite part 111 and have projections PJ on the surface. The polymer coating film is mainly composed of a polyether-based polymer and partially or wholly coats the graphite-containing particles. Then, the mass ratio of the polymer coating film to the graphite-containing particles is in the range of 0.0001 or more and 0.02 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to composite graphite particles and a method for producing the same.

  In the past, in order to improve the high temperature storage characteristics of a graphite negative electrode of a lithium ion secondary battery, “covering graphite particles with a polyethylene oxide coating” has been proposed (see, for example, JP-A-09-045328).

JP 09-045328 A

  However, if the graphite particles are covered with the polyethylene oxide film in this way, there is a problem that the charge / discharge cycle characteristics of the graphite negative electrode are deteriorated.

  An object of the present invention is to provide an electrode forming material capable of improving high-temperature storage characteristics without deteriorating charge / discharge cycle characteristics of electrodes in electrode formation of non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, and a method for producing the same Is to provide.

  The composite graphite particle (electrode forming material) according to one aspect of the present invention includes graphite-containing particles and a polymer coating. The graphite-containing particles include at least a graphite part and have protrusions on the surface. The polymer coating is composed mainly of a polyether polymer and covers the graphite-containing particles. The polymer coating may partially or entirely cover the graphite-containing particles. The mass ratio of the polymer coating to the graphite-containing particles is in the range of 0.0001 to 0.02.

  As a result of intensive studies by the inventor of the present application, in the case of the above-mentioned graphite-containing particles, even if the graphite-containing particles are covered with a polymer film, the electrode is used in forming an electrode for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. It was revealed that the high-temperature storage characteristics can be improved without degrading the charge / discharge cycle characteristics.

  In the composite graphite particles described above, the graphite-containing particles preferably have graphite particles and conductive carbonaceous fine particles. The graphite-containing particles may be formed only from graphite particles and conductive carbonaceous fine particles, or may contain particles other than graphite particles and conductive carbonaceous fine particles. The conductive carbonaceous fine particles are attached to the surface of the graphite particles. The conductive carbonaceous fine particles may be indirectly attached to the graphite particles or may be directly attached. The conductive carbonaceous fine particles are preferably bonded to the surface of the graphite particles with a carbon material. The mass ratio of the conductive carbonaceous fine particles to the graphite particles is preferably in the range of 0.003 to 0.1. The average particle size ratio of the primary particles of the conductive carbonaceous fine particles to the graphite particles is preferably in the range of 0.0003 or more and 0.1 or less. The mass ratio of the carbon material to the sum of the graphite particles and the conductive carbonaceous fine particles is preferably in the range of 0.01 to 0.15.

  In the composite graphite particles described above, the polyether polymer preferably has an average molecular weight in the range of 10,000 to 10,000,000. This average molecular weight is determined based on the label display value of polyethylene glycol manufactured by Wako Pure Chemical Industries.

  Composite graphite particles according to another aspect of the present invention include graphite-containing particles and a polymer coating. The graphite-containing particles include at least a graphite part and have protrusions on the surface. The polymer coating is composed mainly of a polyether polymer and covers the entire surface of the graphite-containing particles so as not to bury the protrusions.

  As a result of intensive studies by the inventor of the present application, in the case of the above-mentioned graphite-containing particles, even if the graphite-containing particles are covered with a polymer film, the electrode is used in forming an electrode for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. It was revealed that the high-temperature storage characteristics can be improved without degrading the charge / discharge cycle characteristics.

  The method for producing composite graphite particles according to another aspect of the present invention includes a contact step and a drying step. In the contacting step, the graphite-containing particles are polymer solutions mainly composed of a polyether polymer so that the mass ratio of the polymer coating to the graphite-containing particles is within the range of 0.0001 to 0.02. To be contacted. The graphite-containing particles include at least a graphite part and have protrusions on the surface. In the drying step, the graphite-containing particles brought into contact with the polymer solution are dried.

  The composite graphite particles described above are obtained by this method for producing composite graphite particles. Therefore, the composite graphite particles obtained by this method for producing composite graphite particles can exhibit the same effects as described above.

  The composite graphite particles described above can be used as an active material constituting an electrode, particularly an electrode of a nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery is represented by a lithium ion secondary battery.

It is a schematic diagram of the composite graphite particle which concerns on embodiment of this invention. 2 is a scanning electron micrograph of composite graphite particles according to Example 1. FIG.

<Structure of composite graphite particles>
As shown in FIG. 1, composite graphite particle 100 according to the embodiment of the present invention is a particle having protrusions PJ, and is mainly composed of graphite-containing particles 110 and polymer coating 120. Such composite graphite particles 100 can be used as an active material constituting an electrode, particularly a negative electrode of a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery or the like. Hereinafter, these components will be described in detail.

(1) Graphite-containing particles As shown in FIG. 1, the graphite-containing particles 110 are particles having protrusions, and are mainly composed of graphite particles 111 and conductive carbonaceous fine particles 112. In order to immobilize the conductive carbonaceous fine particles 112 on the surface of the graphite particles 111, the conductive carbonaceous fine particles 112 may be bonded to the graphite particles 111 with a carbon material (not shown). These graphite-containing particles 110 may be partially or wholly graphitized at a temperature of 3000 ° C. or higher as graphite-containing particles.

(1-1) Graphite particles The graphite particles may be either natural graphite particles or artificial graphite particles, but are preferably natural graphite particles. As the graphite particles, a mixture of natural graphite particles and artificial graphite particles may be used. The graphite particles are preferably spherical graphite granules formed by aggregating a plurality of scaly graphite particles. Examples of the scale-like graphite particles include natural graphite particles, artificial graphite particles, graphitized mesophase calcined carbon (bulk mesophase carbon such as mesophase carbon microbeads, needle coke, etc.) using tar pitch as a raw material, etc. In particular, those granulated using a plurality of highly crystalline natural graphite particles are preferable. One graphite granule is usually formed by agglomerating 2 to 100, preferably 3 to 20, scaly graphite particles, but the graphite particles are folded to be spheroidized. You can also.

  The average particle diameter of the graphite particles is preferably in the range of 1 μm to 30 μm, and more preferably in the range of 5 μm to 20 μm. This is because if the average particle diameter of the graphite particles is within this range, the high-temperature storage characteristics and the output characteristics are well balanced.

  The distance between carbon layer surfaces (d002) of the graphite particles is preferably 0.337 nm or less from the viewpoint of realizing high capacity.

(1-2) Conductive Carbonaceous Fine Particles The conductive carbonaceous fine particles 112 are attached to the surface of the graphite particles 111 and function not only as a conductive aid but also as a protrusion forming material (see FIG. 1). ). The conductive carbonaceous fine particles 112 may be indirectly attached to the surface of the graphite particles or may be directly attached. As described above, in order to immobilize the conductive carbonaceous fine particles 112 on the surface of the graphite particles 111, the conductive carbonaceous fine particles 112 may be bonded to the graphite particles 111 with a carbon material (not shown). The conductive carbonaceous fine particles are, for example, carbon black such as ketjen black, furnace black, acetylene black, thermal black, lamp black, and channel black (usually having a primary particle diameter in the range of 10 nm to 200 nm). Examples thereof include carbon nanotubes, carbon nanofibers, carbon nanocoils, graphite, coke, and pulverized particles of resin carbide. Of these conductive carbonaceous fine particles, acetylene black is particularly preferred. The conductive carbonaceous fine particles may be a mixture of different types of carbon black or the like. The mass ratio of the conductive carbonaceous fine particles to the graphite particles is preferably in the range of 0.003 to 0.1, more preferably in the range of 0.005 to 0.05, 0.005 More preferably, it is in the range of 0.02 or less. The average primary particle diameter of the conductive carbonaceous fine particles is preferably in the range of 0.01 μm to 1 μm, and more preferably in the range of 0.05 μm to 0.5 μm. The average particle size ratio of the primary particles of the conductive carbonaceous fine particles to the graphite particles is preferably in the range of 0.0003 or more and 0.1 or less. Here, the average particle diameter of the graphite particles is a volume-based median diameter. The average particle diameter of the primary particles of the conductive carbonaceous fine particles is an arithmetic average particle diameter obtained by observing 100 primary particles of the conductive carbonaceous fine particles with an electron microscope.

(1-3) Carbon Material The carbon material can be used for bonding conductive carbonaceous fine particles to graphite particles. The carbon material is composed of at least one of non-graphitic carbon and graphitic carbon. That is, the carbon material may be composed only of non-graphitic carbon, may be composed only of graphitic carbon, or may be composed of non-graphitic carbon and graphitic carbon.

  Non-graphitic carbon is at least one of amorphous carbon and turbostratic carbon. Here, “amorphous carbon” has short-range order (several atoms to tens of atoms order), but does not have long-range order (several hundreds to thousands of atoms order). Refers to carbon. Here, “turbulent structure carbon” refers to carbon composed of carbon atoms having a turbulent structure parallel to the hexagonal network plane direction but having no crystallographic regularity in the three-dimensional direction. In the X-ray diffraction pattern, hkl diffraction lines corresponding to the 101 plane and the 103 plane do not appear. However, the composite graphite particles 100 according to the embodiment of the present invention are difficult to confirm by X-ray diffraction because the diffraction lines of the substrate are strong. For this reason, it is preferable that the turbostratic structure carbon is confirmed with a transmission electron microscope (TEM) or the like.

  By the way, this carbon material is obtained by firing a carbon material raw material (hereinafter referred to as “carbon raw material”). Examples of the carbon raw material include tar, petroleum-based pitch powder, coal-based pitch powder, and resin powder. The carbon raw material may be a mixture of different types of pitches. Among these, coal-based pitch powder is particularly preferable. As an example of the heat treatment conditions for firing, the heat treatment temperature is set to a temperature in the range of 800 ° C. to 3000 ° C. This heat treatment time is appropriately determined in consideration of the heat treatment temperature and the characteristics of the carbon raw material, and is typically about 1 hour. Although depending on the type of carbon raw material, graphitic carbon is easily obtained when the heat treatment temperature is high, and amorphous carbon is easily obtained when the heat treatment temperature is low. Depending on the type of carbon raw material, amorphous carbon may be obtained even when the heat treatment temperature is 3000 ° C. The atmosphere during the heat treatment is preferably a non-oxidizing atmosphere (inert gas atmosphere, vacuum atmosphere), and a nitrogen atmosphere is preferred from an economic viewpoint. The mass ratio of the carbon material to the sum of the graphite particles and the conductive carbonaceous fine particles is preferably in the range of 0.01 to 0.15.

(1-4) Method for Producing Graphite-Containing Particles The graphite-containing particles 110 can be produced by various production methods including the following examples (1-4-1) to (1-4-6). In addition, the manufacturing method should just be a manufacturing method which can form protrusion on the graphite containing particle 110, and the manufacturing method is not limited to the following examples.

(1-4-1)
The graphite-containing particles can be produced through a mechanical treatment process. In the mechanical treatment process, the graphite particles and the conductive carbonaceous fine particles are mechanically treated such as a mechanochemical (registered trademark) treatment and a mechanofusion (registered trademark) treatment to embed the conductive carbonaceous fine particles in the surface layer of the graphite particles. As a result, target graphite-containing particles are obtained. If necessary, the graphite-containing particles may be heat-treated at a temperature in the range of 800 ° C. to 3000 ° C.

(1-4-2)
The graphite-containing particles can also be produced through a mechanical treatment process, a carbon raw material mixing process, and a carbonization process. In the mechanical treatment step, primary composite particles are prepared by mechanically treating the graphite particles and the conductive carbonaceous fine particles with a mechanochemical (registered trademark) treatment, a mechanofusion (registered trademark) treatment or the like. In the carbon raw material mixing step, the primary composite particles and the carbon raw material powder are mixed to prepare a mixed powder. In the carbonization step, the mixed powder is heated at a temperature in the range of 800 ° C. to 3000 ° C. to convert the carbon raw material powder into a carbon material. As a result, the carbon material adheres partially or entirely to the primary composite particles, and the conductive carbonaceous fine particles are fixed to the graphite particles by the carbon material. As a result, target graphite-containing particles are obtained.

(1-4-3)
The graphite-containing particles can also be produced through a mechanical treatment process and a carbonization process. In the mechanical processing process, the carbon raw material powder is softened into a mixture of graphite particles, conductive carbonaceous fine particles and solid carbon raw material powder by mechanical processing such as mechanochemical (registered trademark) processing and mechanofusion (registered trademark) processing. An intermediate composite particle is prepared by applying a compressive force and a shearing force at a temperature equal to or higher than the point. At this time, the conductive carbonaceous fine particles are bonded to the graphite particles by the molten carbon raw material powder serving as an adhesive under the condition where the compressive force acts. At this time, a mixture of graphite particles, conductive carbonaceous fine particles, and solid carbon raw material powder may be charged into a mechanochemical system or mechanofusion system, or graphite particles, conductive carbonaceous fine particles, and solid carbon raw material. After each powder is put into a mechanochemical system and a mechanofusion system in order, mechanical processing such as mechanochemical (registered trademark) processing and mechanofusion (registered trademark) processing may be performed while mixing the particles. In the carbonization step, the intermediate composite particles are heat-treated at a temperature in the range of 800 ° C. or higher and 3000 ° C. or lower in a non-oxidizing atmosphere (inert gas atmosphere, vacuum atmosphere, etc.). As a result, the carbon raw material powder is converted into a carbon material, and target graphite-containing particles are obtained.

(1-4-4)
The graphite-containing particles can also be produced through a heating and kneading step and a carbonization step. In the heating and kneading step, the graphite particles, the conductive carbonaceous fine particles, and the carbon raw material are kneaded while being heated to a temperature equal to or higher than the softening point of the carbon raw material to prepare a graphite-containing particle precursor. Here, the carbon raw material may be a solid carbon raw material powder or a carbon raw material heated and melted at a softening point temperature or higher. When heating and kneading, the molten carbon raw material serves as an adhesive, and the conductive carbonaceous fine particles are bonded to the graphite particles. In this heating and kneading step, for example, a normal kneader can be used. In the carbonization step, the precursor of the graphite-containing particles is heated at a temperature in the range of 800 ° C. to 3000 ° C. to convert the carbon raw material into a carbon material. As a result, target graphite-containing particles are obtained.

(1-4-5)
The graphite-containing particles can also be produced through a mixing process, a drying process, and a carbonization process. In the mixing step, graphite particles and conductive carbonaceous fine particles are added to and mixed with a solution in which tar pitches or resins as carbon raw materials are dissolved in a solvent or the like to prepare a mixed solution. In the drying step, the solvent is removed from the mixed solution to dry the residue. In the carbonization step, the obtained dried product is heat-treated to carbonize the carbon raw material. The heat treatment may be performed in one step, or may be performed stepwise by changing the temperature. The final heat treatment temperature is preferably in the range of 800 ° C. or higher and 3000 ° C. or lower. As a result, target graphite-containing particles are obtained.

  It is preferable to adjust the particle size such as pulverization, sieving, and fine powder removal by classification at any stage before and after the heat treatment.

(1-4-6)
The graphite-containing particles can also be produced through a mechanical treatment process and a carbon coating process. In the mechanical treatment step, primary composite particles are prepared by mechanically treating the graphite particles and the conductive carbonaceous fine particles with a mechanochemical (registered trademark) treatment, a mechanofusion (registered trademark) treatment or the like. In the carbon coating process, for example, primary using vacuum deposition, sputtering, ion plating, laser ablation, thermal chemical vapor deposition, chemical vapor deposition (CVD), and plasma chemical vapor deposition. The composite particles are covered with a carbon material. As a result, target graphite-containing particles are obtained. If necessary, the graphite-containing particles may be heat-treated at a temperature in the range of 800 ° C. to 3000 ° C.

(1-5) Characteristics of Graphite-Containing Particles The average particle size of the graphite-containing particles 110 is preferably in the range of 1 μm to 30 μm, and more preferably in the range of 5 μm to 20 μm. Here, the average particle diameter of the graphite-containing particles is a volume-based median diameter. The specific surface area of the graphite-containing particles 110 is preferably in the range of ^{1 m} 2 / g or more ^{10 m} 2 / g, and more preferably in a range of ^2m 2 / g or more ^{6 m} 2 / g. This is because if the specific surface area of the graphite-containing particles 110 is within this range, the durability can be effectively improved while maintaining a high output density.

(2) Polymer Film The polymer film 120 covers the graphite-containing particles 110 so as not to bury the protrusions of the graphite-containing particles 110 as shown in FIG.

  The polymer film 120 is formed of a polymer mainly composed of a polyether polymer. Examples of the polyether polymer include polyethylene glycol (polyethylene oxide), polypropylene glycol (polypropylene oxide), and a copolymer of ethylene glycol and propylene glycol. The average molecular weight of the polyether polymer is preferably in the range of 10,000 to 10,000,000 and more preferably in the range of 100,000 to 2,000,000. When the average molecular weight of the polyether polymer is within this range, the polyether polymer can be easily applied uniformly to the graphite-containing particles, and a high effect of improving high-temperature storage characteristics can be obtained. . This average molecular weight is determined based on the label display value of polyethylene glycol manufactured by Wako Pure Chemical Industries. The mass ratio of the polymer coating to the graphite-containing particles is preferably in the range of 0.0001 or more and 0.02 or less, and more preferably in the range of 0.001 or more and 0.01 or less. When the mass ratio is within this range, sufficient high-temperature storage characteristics can be imparted to the electrode, and the resistance of lithium ion conduction can be kept low, and the output characteristics can be maintained well. Because it can. A plasticizer such as polyethylene glycol dimethyl ether or other polymer may be added to the polymer film 120 without departing from the gist of the present invention.

<Manufacture of composite graphite particles>
The composite graphite particles according to the embodiment of the present invention are manufactured through a mixing process and a drying process. In the mixing step, the graphite-containing particles 110 are mixed into a polymer solution containing a polyether polymer as a main component (hereinafter referred to as “polymer solution”). In the drying step, the polymer solution containing the graphite-containing particles is dried. The polymer solvent is preferably water from the viewpoint of environment and cost. In the drying step, the polymer solution containing the graphite-containing particles may be dried using a spray drying method.

<Characteristics of composite graphite particles>
The composite graphite particles according to the embodiment of the present invention can improve the high-temperature storage characteristics without deteriorating the charge / discharge cycle characteristics of the electrodes in forming electrodes of non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. It is very useful as a material for forming electrodes.

<Examples and Comparative Examples>
Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples.

<Manufacture of composite graphite particles>
(1) spherical natural graphite powder and composite spherical natural graphite powder (average particle size 8 [mu] m, a specific surface area of 9.9 m ² / g) of acetylene black and acetylene black (primary particle diameter 35 nm, specific surface area ^68m 2 / g) and The spherical natural graphite powder and acetylene black were mixed so that the mass ratio thereof was 100: 1 to prepare 600 g of mixed powder. The 600 g of the mixed powder was put into a mechanofusion system (AMS-Lab manufactured by Hosokawa Micron) with a gap between the rotor and the inner piece of 5 mm, and then the mixed powder was processed at a rotational speed of 2600 rpm for 5 minutes to form a spherical shape. Natural graphite powder and acetylene black were combined. Hereinafter, this composite is referred to as “primary composite powder”. Here, the mass ratio of acetylene black to spherical natural graphite powder was 0.01, and the average particle diameter ratio of primary particles of acetylene black to spherical natural graphite powder was 0.004375.

(2) Composite of primary composite powder and non-graphitic carbon Primary composite so that the mass ratio of primary composite powder and coal-based pitch powder (softening point 86 ° C., average particle size 20 μm) is 100: 8. After mixing the activated powder and the coal-based pitch powder, the mixed powder was heat-treated at 1300 ° C. for 1 hour in a nitrogen stream to obtain graphite-containing particles. During this heat treatment, the coal-based pitch powder changed to non-graphitic carbon. From the mass change before and after the heat treatment, it was confirmed that the pitch residual carbon ratio was 50%.

(3) Polyethylene glycol coating After adding 100 g of the graphite-containing particles described above to 100 g of a 0.1% by mass polyethylene glycol aqueous solution, the mixed solution is heated to 100 ° C. and dried to obtain the desired composite graphite particles. (See the photograph in FIG. 2). The polyethylene glycol in the polyethylene glycol aqueous solution was manufactured by Wako Pure Chemical Industries, Ltd., and the average molecular weight displayed on the label was 500,000. Here, the mass ratio of polyethylene glycol to graphite-containing particles was 0.001.

<Evaluation of battery characteristics of composite graphite particles>
(1) Preparation of negative electrode CMC (Carboxymethylcellulose sodium) powder was mixed with the composite graphite particles described above, an aqueous dispersion of SBR (styrene-butadiene rubber) was added to the mixed powder, and the mixture was stirred to form an electrode. A mixture slurry was obtained. Here, CMC and SBR are binders. The compounding ratio of the composite graphite particles, CMC and SBR was 98: 1: 1 by mass ratio. And this negative mix slurry was apply | coated by the doctor blade method on the 17-micrometer-thick copper foil (current collector) (coating amount was 7.5 mg / cm < ² >). After drying the coating solution to obtain a coating film, a negative electrode was produced by pressurizing with a press molding machine so that the density of the coating film was 1.5 g / cm ³ .

(2) Battery Preparation The above-described negative electrode and positive electrode LiCoO ₂ coated aluminum foil were disposed on both sides of a polyolefin separator to prepare an electrode assembly. And the electrolyte solution was inject | poured into the inside of the electrode assembly, and the laminate type non-aqueous test cell was produced. The electrolytic solution was a 1M LiPF ₆ solution. The solvent of this electrolytic solution was a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC), and the mass ratio thereof was ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 3. It was.

(3-1) Evaluation of charge / discharge cycle characteristics In a non-aqueous test cell at an ambient temperature of 23 ° C., first, constant current charging was performed until the battery voltage reached 4.2 V at a current value of 1.4 mA. Further, while maintaining the battery voltage at 4.2 V, the battery was charged at a constant voltage until the current value reached 0.14 mA. Next, the battery was discharged at a constant current of 1.4 mA until the battery voltage reached 3.0V. And charging / discharging was repeated 50 times on the said conditions. The charge / discharge cycle characteristics were evaluated based on the ratio (capacity maintenance ratio) of the “discharge capacity at the 50th cycle” to the “discharge capacity at the 1st cycle”. The capacity retention rate of the non-aqueous test cell of this example was 91% (see Table 1).

(3-2) Evaluation of high-temperature storage characteristics In a non-aqueous test cell at an ambient temperature of 23 ° C., first, constant current charging was performed until the battery voltage reached 4.2 V at a current value of 1.4 mA. Further, constant voltage charging was performed until the current value reached 0.14 mA while maintaining the battery voltage at 4.2V. Next, the battery was discharged at a constant current of 1.4 mA until the battery voltage reached 3.0V. Charging / discharging was repeated twice under the above conditions, and the second discharge capacity was measured. And after charging again on the said conditions, after storing the non-aqueous test cell at 60 degreeC for 1 week, it discharged at the environmental temperature of 23 degreeC, and measured the discharge capacity at that time. The high-temperature storage characteristics were evaluated by the ratio (capacity retention rate) of “discharge capacity after storage at 60 ° C.” to “discharge capacity at the second cycle”. In addition, the capacity | capacitance maintenance factor at the time of high temperature preservation | save of the non-aqueous test cell of a present Example was 71% (refer Table 1).

(3-3) Evaluation of output resistance In a non-aqueous test cell at an ambient temperature of 23 ° C., first, constant current charging was performed until the battery voltage reached 4.2 V at a current value of 1.4 mA, and then further While maintaining the battery voltage at 4.2 V, charging was continued at a constant voltage until the current value reached 0.14 mA. Next, discharging was performed at a constant current of 1.4 mA until the battery voltage reached 3.0V. After repeating charging and discharging twice under the above conditions, the battery was charged with a current value of 1.4 mA for 5 hours. Then, the nonaqueous test cell was pulse-discharged at 14 mA for 10 seconds, and the voltage change at that time was measured. This voltage change was divided by 14 mA to obtain the output resistance of the non-aqueous test cell. The output resistance of the non-aqueous test cell of this example was 4.5Ω (see Table 1).

  Example 1 except that the 0.1 mass% polyethylene glycol aqueous solution in “(3) Polyethylene glycol coating” was replaced with a 0.5 mass% polyethylene glycol aqueous solution (the same polyethylene glycol used in Example 1). Similarly, the target composite graphite particles were obtained, and the battery characteristics of the composite graphite particles were evaluated in the same manner as in Example 1. Here, the mass ratio of polyethylene glycol to graphite-containing particles was 0.005.

  As a result, the capacity retention rate of the non-aqueous test cell was 95% (see Table 1), the capacity retention rate during high-temperature storage was 79% (see Table 1), and the output resistance was 4.3Ω ( (See Table 1).

  Except that the 0.1 mass% polyethylene glycol aqueous solution was replaced with a 1 mass% polyethylene glycol aqueous solution (the same polyethylene glycol used in Example 1) in “(3) Polyethylene glycol coating”, the same as in Example 1. The target composite graphite particles were obtained, and the battery characteristics of the composite graphite particles were evaluated in the same manner as in Example 1. Here, the mass ratio of polyethylene glycol to graphite-containing particles was 0.01.

  As a result, the capacity retention rate of the non-aqueous test cell was 94% (see Table 1), the capacity retention rate during high-temperature storage was 80% (see Table 1), and the output resistance was 4.3Ω ( (See Table 1).

  Except that the 0.1 mass% polyethylene glycol aqueous solution was replaced with a 2 mass% polyethylene glycol aqueous solution (the same polyethylene glycol as in Example 1) in “(3) Polyethylene glycol coating”, the same as in Example 1. The target composite graphite particles were obtained, and the battery characteristics of the composite graphite particles were evaluated in the same manner as in Example 1. Here, the mass ratio of polyethylene glycol to graphite-containing particles was 0.02.

  As a result, the capacity retention rate of the non-aqueous test cell was 91% (see Table 1), the capacity retention rate during high-temperature storage was 79% (see Table 1), and the output resistance was 4.5Ω ( (See Table 1).

In spherical natural graphite powder (average particle size 8 [mu] m, a specific surface area of 9.9 m ² / g) "(1) spherical natural graphite powder and acetylene black and a composite of" acetylene black (primary particle diameter 35 nm, specific surface area ^68m 2 / The mass ratio with respect to g) is 100: 0.5, and in “(3) Polyethylene glycol coating”, a 0.1 mass% polyethylene glycol aqueous solution is a 1 mass% polyethylene glycol aqueous solution (polyethylene glycol is the same as in Example 1. The target composite graphite particles were obtained in the same manner as in Example 1 except that the usage was changed to Use), and the battery characteristics of the composite graphite particles were evaluated in the same manner as in Example 1. Here, the mass ratio of acetylene black to spherical natural graphite powder was 0.005, and the mass ratio of polyethylene glycol to graphite-containing particles was 0.01.

  As a result, the capacity retention rate of the non-aqueous test cell was 90% (see Table 1), the capacity retention rate during high-temperature storage was 77% (see Table 1), and the output resistance was 4.5Ω ( (See Table 1).

  In “(2) Composite of primary composite powder and non-graphitic carbon”, the mass ratio of primary composite powder and coal-based pitch powder (softening point 86 ° C., average particle size 20 μm) is 100: 2, (3) Polyethylene glycol coating ”, except that the 0.1 mass% polyethylene glycol aqueous solution was replaced with a 2 mass% polyethylene glycol aqueous solution (the same polyethylene glycol used in Example 1). The target composite graphite particles were obtained, and the battery characteristics of the composite graphite particles were evaluated in the same manner as in Example 1. Here, the mass ratio of acetylene black to spherical natural graphite powder was 0.01, and the mass ratio of polyethylene glycol to graphite-containing particles was 0.01.

  As a result, the capacity retention rate of the non-aqueous test cell was 90% (see Table 1), the capacity retention rate during high-temperature storage was 75% (see Table 1), and the output resistance was 4.5Ω ( (See Table 1).

(Comparative Example 1)
<Manufacture of comparative samples>
Spherical natural graphite so that the mass ratio of spherical natural graphite powder (average particle size 8 μm, specific surface area 9.9 m ² / g) and coal-based pitch powder (softening point 86 ° C., average particle size 20 μm) is 100: 8. After mixing the powder and the coal-based pitch powder, the mixed powder was heated at 1300 ° C. for 1 hour in a nitrogen stream to obtain a comparative sample.

<Battery characteristics evaluation of comparative sample>
When the battery characteristics of the comparative sample were evaluated in the same manner as in Example 1, the capacity retention rate of the nonaqueous test cell was 80% (see Table 1), and the capacity retention rate during high-temperature storage was 65% ( The output resistance was 5.0Ω (see Table 1).

(Comparative Example 2)
<Manufacture of comparative samples>
(1) Preparation of non-graphitic carbon-coated spherical natural graphite powder Spherical natural graphite powder (average particle diameter 8 μm, specific surface area 9.9 m ² / g) and coal-based pitch powder (softening point 86 ° C., average particle diameter 20 μm) The spherical natural graphite powder and the coal-based pitch powder are mixed so that the mass ratio thereof becomes 100: 8, and the mixed powder is heat-treated at 1300 ° C. for 1 hour in a nitrogen stream, thereby coating the non-graphitic carbon Spherical natural graphite powder was obtained.
(2)
After putting 100 g of the above non-graphitic carbon-coated spherical natural graphite powder into 100 g of a 1% by mass polyethylene glycol aqueous solution, the mixed solution was heated to 100 ° C. and dried to obtain a comparative sample. The polyethylene glycol in the polyethylene glycol aqueous solution was manufactured by Wako Pure Chemical Industries, Ltd., and the average molecular weight displayed on the label was 500,000. The mass ratio of polyethylene glycol to non-graphitic carbon-coated spherical natural graphite powder was 0.01.

<Battery characteristics evaluation of comparative sample>
When the battery characteristics of the comparative sample were evaluated in the same manner as in Example 1, the capacity retention rate of the non-aqueous test cell was 61% (see Table 1), and the capacity retention rate during high-temperature storage was 70% ( The output resistance was 5.2Ω (see Table 1).

(Comparative Example 3)
Using the graphite-containing particles of Example 1 as a comparative sample, the battery characteristics of the graphite-containing particles were evaluated in the same manner as in Example 1.

  As a result, the capacity retention rate of the non-aqueous test cell was 90% (see Table 1), the capacity retention rate during high-temperature storage was 61% (see Table 1), and the output resistance was 4.5Ω ( (See Table 1).

(Comparative Example 4)
<Manufacture of comparative samples>
As in Example 1, except that the 0.1 mass% polyethylene glycol aqueous solution was replaced with a 3 mass% polyethylene glycol aqueous solution (polyethylene glycol used the same as in Example 1) in “(3) Polyethylene glycol coating”. Comparative samples were obtained, and the battery characteristics of the comparative samples were evaluated in the same manner as in Example 1. Here, the mass ratio of polyethylene glycol to graphite-containing particles was 0.03.

<Battery characteristics evaluation of comparative sample>
When the battery characteristics of the comparative sample were evaluated in the same manner as in Example 1, the capacity retention rate of the non-aqueous test cell was 80% (see Table 1), and the capacity retention rate during high-temperature storage was 70% ( The output resistance was 5.0Ω (see Table 1).

<Manufacture of composite graphite particles>
(1) spherical natural graphite powder, composite spherical natural graphite powder of furnace black and coal-based pitch (average particle size 8 [mu] m, a specific surface area of 9.9 m ² / g), furnace black (primary particle diameter 85 nm, specific surface area ^{20 m} 2 / g) and coal-based pitch powder (softening point 86 ° C., average particle size 20 μm) so that the mass ratio is 100: 9: 20, using a heating kneader, spherical natural graphite powder, furnace black and coal-based pitch powder. The mixture was kneaded at a temperature of 150 ° C. for 30 minutes to form a composite of spherical natural graphite powder, furnace black and coal-based pitch. Hereinafter, this composite is referred to as “composite powder”. Here, the mass ratio of furnace black to spherical natural graphite powder was 0.09, and the average particle diameter ratio of the primary particles of furnace black to spherical natural graphite powder was 0.010625.

(2) Heat treatment of composite powder The above composite powder was heat-treated at 1000 ° C. for 1 hour in a nitrogen stream to obtain graphite-containing particles. During this heat treatment, the coal-based pitch powder changed to low crystalline carbon. From the mass change before and after the heat treatment, it was confirmed that the pitch residual carbon ratio was 50%.

(3) Coating of polyethylene glycol 100 g of the graphite-containing particles described above were put into 100 g of a 1% by mass polyethylene glycol aqueous solution, and then the mixed solution was heated to 100 ° C. and dried to obtain the desired composite graphite particles. The polyethylene glycol in the polyethylene glycol aqueous solution was manufactured by Wako Pure Chemical Industries, Ltd., and the average molecular weight displayed on the label was 500,000. Here, the mass ratio of polyethylene glycol to graphite-containing particles was 0.01.

  When the battery characteristics of the composite graphite particles were evaluated in the same manner as in Example 1, the capacity retention rate of the non-aqueous test cell was 94% (see Table 2), and the capacity retention rate during high-temperature storage was 77%. Yes (see Table 2), output resistance was 4.4Ω (see Table 2).

In “(1) Composite of spherical natural graphite powder, furnace black and coal-based pitch”, spherical natural graphite powder (average particle diameter 8 μm, specific surface area 9.9 m ² / g), furnace black (primary particle diameter 85 nm, specific surface area) 20 m ² / g) and coal-based pitch powder (softening point 86 ° C., average particle diameter 20 μm) except that the mass ratio was set to 100: 15: 20. The battery characteristics of the composite graphite particles were evaluated in the same manner as in Example 1. Here, the mass ratio of furnace black to spherical natural graphite powder was 0.15.

  As a result, the capacity retention rate of the non-aqueous test cell was 90% (see Table 2), the capacity retention rate during high-temperature storage was 69% (see Table 2), and the output resistance was 4.6Ω ( (See Table 2).

(Comparative Example 5)
Using the graphite-containing particles of Example 7 as a comparative sample, the battery characteristics of the graphite-containing particles were evaluated in the same manner as in Example 1.

  As a result, the capacity retention rate of the non-aqueous test cell was 91% (see Table 2), the capacity retention rate during high-temperature storage was 58% (see Table 2), and the output resistance was 4.5Ω ( (See Table 2).

  From the above results, the composite graphite particles according to the present invention improve the high-temperature storage characteristics without degrading the charge / discharge cycle characteristics of the electrodes in the electrode formation of non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. It became clear that it was possible.

Claims (10)

Graphite-containing particles including at least a graphite part and having protrusions on the surface;
A polyether-based polymer as a main component, and a polymer film covering the graphite-containing particles,
Composite graphite particles in which the mass ratio of the polymer coating to the graphite-containing particles is in the range of 0.0001 to 0.02. The composite graphite particles according to claim 1, wherein the graphite-containing particles include graphite particles and conductive carbonaceous fine particles attached to the surface of the graphite particles. The composite graphite particles according to claim 2, wherein the conductive carbonaceous fine particles are bonded to the surface of the graphite particles with a carbon material. 4. The composite graphite particle according to claim 2, wherein a mass ratio of the conductive carbonaceous fine particles to the graphite particles is in a range of 0.003 to 0.1. 5. The composite graphitic particle according to claim 2, wherein an average particle diameter ratio of primary particles of the conductive carbonaceous fine particles to the graphite particles is in a range of 0.0003 to 0.1. The composite graphite particles according to any one of claims 1 to 5, wherein the polyether polymer has an average molecular weight within a range of 10,000 to 10,000,000. Graphite-containing particles including at least a graphite part and having protrusions on the surface;
Composite graphite particles comprising a polyether-based polymer as a main component and a polymer film covering the entire surface of the graphite-containing particles so as not to bury the protrusions. Polyether-based polymer containing graphite-containing particles containing at least a graphite part and having protrusions on the surface thereof, such that the mass ratio of the polymer coating to the graphite-containing particles is within a range of 0.0001 or more and 0.02 or less. A contact step of contacting with a polymer solution mainly composed of
A drying step of drying the graphite-containing particles brought into contact with the polymer solution.   An electrode using the composite graphite particles according to any one of claims 1 to 7 as an active material. A nonaqueous electrolyte secondary battery comprising the electrode according to claim 9.