TW202043145A - Method for manufacturing negative-electrode material for li-ion secondary cell - Google Patents

Abstract

This invention aims at providing a method for manufacturing a negative-electrode material for a lithium ion secondary cell with excellent productivity. The method for manufacturing negative-electrode material for a lithium ion secondary cell of this invention includes the following steps: a filling step: filling the interior of a bag with graphite precursor powder, then, degassing and depressurizing the interior of the bag, and maintaining a depressurized state; and a graphitizing step: heating the bag obtained in the filling step and filled with the graphite precursor powder and maintaining the interior in the depressurized state to graphitize the graphite precursor powder.

Description

Method for manufacturing negative electrode material for lithium ion secondary electrode

The present invention relates to a method for manufacturing a negative electrode material for lithium ion secondary batteries.

Graphite particles of negative electrode materials for lithium ion secondary batteries are generally produced by graphitizing graphite precursors.

The process of obtaining stone-ground powder as a product from the graphite precursor powder of the raw material. Patent Document 1 describes mixing/stirring the graphite precursor with a binder such as coal tar, pitch, or synthetic resin, and pulverizing the mixture. The material is put into a mold and press-formed to form a graphite precursor molded body. The graphite precursor molded body is fired (graphitized) at 2000°C or higher in a non-oxidizing environment to form a graphitized molded body, which is then graphitized into A method of crushing the shape to produce graphite powder.

In addition to the graphite powder manufacturing method described in Patent Document 1, there is also the graphite precursor powder of the raw material is charged into a crucible, and the powder is directly fired (graphitized) at 2000°C or higher to obtain graphite powder as a product的方法。 The method. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 11-171519

[The problem to be solved by the invention]

However, according to the method for producing graphite powder described in Patent Document 1, in order to obtain graphite powder as a product, it is necessary to pulverize the graphitized molded body obtained by graphitizing the graphite precursor molded body. Therefore, the manufacturing method becomes complicated and the productivity may be poor. Furthermore, in the step of pulverizing the graphitized molded body, the graphite particles may be damaged and the battery characteristics may decrease.

In addition, the method of directly graphitizing the graphite precursor powder of the raw material in the crucible in the powder state is compared with the method of graphitizing the graphite precursor molded body described in Patent Document 1. Since the packing density is lower, it can be used at one time. The amount of graphitization is small, and industrial productivity cannot be said to be good.

Therefore, the subject of the present invention is to provide a method for producing a negative electrode material for lithium ion secondary batteries with excellent productivity. [Means to solve the problem]

The inventors of the present invention have repeated their active research to solve the above-mentioned problems and found that when graphite precursor powder is filled inside the bag, and then the inside of the bag is maintained in a degassed and depressurized state, the filling density is It becomes higher, and the pulverization of the graphitized mass is not necessary, thus completing the present invention.

That is, the present invention provides the following [1]. [1] A method for manufacturing a negative electrode material for lithium ion secondary electrodes, which has the following steps: The graphite precursor powder is filled inside the bag, and then the inside of the bag is degassed, depressurized, and the filling step of maintaining the decompressed state, and A graphitization step in which the aforementioned graphite precursor powder is filled with the aforementioned graphite precursor powder obtained in the aforementioned filling step and the bag is maintained in an internally reduced pressure state to be heated to graphitize the aforementioned graphite precursor powder. [Invention Effect]

According to the present invention, it is possible to provide a method for manufacturing a negative electrode material for a lithium ion secondary battery with excellent productivity.

In the present invention, when "~" is used to indicate a range, the range includes both sides of "~". For example, the range expressed as "A~B" includes A and B.

[Method of manufacturing negative electrode material for lithium ion secondary battery] The manufacturing method of the negative electrode material for lithium ion secondary battery of the present invention has the following steps: the graphite precursor powder is filled inside the bag, and then the inside of the bag is degassed, depressurized, and the depressurized state is maintained. , And a graphitization step in which the above-mentioned graphite precursor powder is filled with the above-mentioned graphite precursor powder obtained in the above-mentioned filling step, and the above-mentioned bag is maintained in a decompressed state by heating to graphitize the above-mentioned graphite precursor powder.

The method for manufacturing the negative electrode material for lithium ion secondary batteries of the present invention can achieve high productivity because the filling density of the carbon powder is increased, and the pulverization of the graphitized agglomerates is not necessary.

(Raw materials and additives) The graphite precursor powder of the raw material and the binder and graphitization catalyst that can be mixed with the graphite precursor and used in the manufacturing method of the present invention are described.

"Graphite Precursor Powder" The graphite precursor powder, which is the raw material of graphite particles for lithium ion secondary batteries, is not particularly limited if it is a graphitizable powder material. For example, coal tar pitches and/or resins can be heat-treated at 300°C to 1200°C. . The heat treatment environment can be an oxidizing environment in the atmosphere, or a non-oxidizing environment in nitrogen or argon. However, when the heat treatment is above 700°C, a non-oxidizing environment is preferred.

Examples of the above-mentioned coal tar pitches include, for example, coal tar, light bitumen oil, medium bitumen oil, heavy bitumen oil, naphthalene oil, anthracene oil, tar pitch, bitumen oil, mesophase pitch, oxygen-crosslinked petroleum pitch, and heavy oil. .

Examples of the above-mentioned resins include thermoplastic resins such as polyvinyl alcohol (PVA) and polyacrylic acid, and thermosetting resins such as phenol resin and furan resin.

As the graphite precursor, it is preferably a fired product or calcined product of medium carbon spheres, and more preferably a fired product of medium carbon spheres. Since the method for manufacturing the negative electrode material for lithium ion secondary batteries of the present invention does not require pulverization after graphitization, compared with the case of pulverization after graphitization, the mesophase structure of graphite particles is not easily destroyed and is not easily damaged as a negative electrode material Excellent characteristics.

The carbon-to-carbon spheres can be heated by, for example, coal tar pitch or petroleum-based pitch at a temperature of 350°C to 500°C for 10 minutes to 6 hours, and the optically anisotropic spheres generated in the pitch can be extracted by solvent. Obtained by filtration. Calcinate the carbon spheres obtained here in a non-oxidizing environment at a temperature of about 200°C to 500°C for 2 hours to 10 hours to obtain a calcined product. Calcined at a temperature of about 600°C to 1200°C After 2 hours to 10 hours, the finished product can be obtained. Both the calcined product and the sintered product can be crushed and adjusted in particle size to make graphite precursor powder.

In the production method of the present invention, the graphite precursor powder of the raw material is preferably one whose particle size is adjusted by pulverization.

(Volatile matter of graphite precursor) The aforementioned graphite precursor may also contain volatile matter. The volatile content of the graphite precursor is not particularly limited as long as it does not adversely affect the characteristics of the graphite particles for lithium ion secondary batteries obtained. However, it is preferably 10% by mass or less relative to the total mass of the graphite precursor, and more preferably It is 5% by mass or less, and more preferably 2% by mass or less.

(Average particle size of graphite precursor) The average particle size of the graphite precursor is not particularly limited, but is preferably 1 to 50 μm, more preferably 3 to 35 μm, and still more preferably 5 to 20 μm. In addition, in the present invention, the average particle size of the graphite precursor is determined by a laser diffraction particle size distribution meter, and the cumulative degree of particle size distribution is calculated as a volume percentage of 50% particle size (50% particle size, D50, median path).

"Binder" The manufacturing method of the negative electrode material for lithium ion secondary batteries of the present invention does not need to mix a binder in the graphite precursor, and it is desirable not to mix it, but it will not adversely affect the characteristics of the graphite particles obtained for lithium ion secondary batteries Within the range, it is okay to mix adhesives. As the above-mentioned binder system, for example, PVA, pitch, phenol resin, etc. are appropriately selected. The amount of the binder when mixing the binder in the graphite precursor is not particularly limited as long as it does not adversely affect the characteristics of the graphite particles for lithium ion secondary batteries obtained, but it is relative to the total mass of the graphite precursor , Preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 2% by mass or less. The method of mixing the graphite precursor and the binder is not particularly limited, but it is better to mix above the softening temperature of the binder. The temperature varies with the type of binder used, but it is preferably 80-350°C.

"Graphitization Catalyst" The method for manufacturing the negative electrode material for lithium ion secondary batteries of the present invention can also mix graphitization catalysts in the graphite precursor within the range that does not adversely affect the properties of the graphite particles for lithium ion secondary batteries obtained. When the graphitization catalyst is mixed with the graphite precursor and graphitized, it has the effect of improving the crystallinity of the graphite powder obtained. As the graphitization catalyst, for example, at least one of metals such as silicon, boron, iron, titanium, and nickel, and oxides or carbides of these metals can be used. The amount of graphitization catalyst when the graphitization catalyst is mixed with the graphite precursor is not particularly limited as long as it does not adversely affect the characteristics of the graphite particles for lithium ion secondary batteries obtained, but it is relative to graphite. The total mass of the precursors is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 2% by mass or less.

(Filling step and graphitization step) The filling step and graphitization step of the manufacturing method of the present invention are described.

"Filling Steps" The filling step is a step of filling the graphite precursor powder inside the bag, and then degassing and depressurizing the inside of the bag, and maintaining the reduced pressure state.

(Filling the bag of graphite precursor) The material of the bag filled with the graphite precursor (hereinafter sometimes referred to as the "bag") is not particularly limited, but it is preferably polyethylene or polypropylene whose residual carbon rate is close to zero, which will volatilize during graphitization. In addition, the thickness of the bag is not particularly limited, but it is preferably a thickness that does not break when the graphite precursor is filled. In addition, the size of the bag is not particularly limited, and can be appropriately selected depending on the size of the crucible used in the graphitization step described later, the amount of graphite powder produced, and the like. In addition, the filling amount of the graphite precursor is not particularly limited, but can be appropriately selected according to the size of the bag, the size of the crucible used in the graphitization step described later, the amount of graphite powder produced, and the like.

(filling) In the filling step, the graphite precursor of the raw material can be individually filled with one graphite precursor in one bag, or two or more graphite precursors can be combined and filled in one bag. In addition, when two or more graphite precursors are filled in the same bag, the graphite precursors may be attached to each other, buried, or compounded. Furthermore, the graphite precursor can also be used by attaching, embedding, or compounding carbonaceous or graphite fibers, amorphous hard carbon and other carbon precursor materials, organic materials, or inorganic materials.

(Maintenance of degassing and decompression) By degassing and depressurizing the inside of the bag filled with the graphite precursor, the filling density of the graphite precursor is increased to increase the filling density, the bag is sealed, and the inside of the bag is maintained at a reduced pressure. Degassing can be performed using, for example, a vacuum compressor (manufactured by Kotobuki Environmental Equipment Co., Ltd.). The air pressure inside the bag after degassing and pressure reduction is preferably about 0 Pa to 2000 Pa.

"Graphitization Step" The graphitization step is a step of graphitizing the graphite precursor powder by heating the bag with the graphite precursor powder filled inside and maintaining the internal pressure-reduced state obtained from the filling step.

Graphitization is performed by heating the graphite precursor powder filled in the bag maintained in a reduced pressure state.

The temperature (heating temperature) during the graphitization treatment is not particularly limited if it is the temperature at which the graphite precursor powder can graphitize, but it is preferably 2000°C to 3200°C, more preferably 2500°C to 3200°C, and still more It is 2800℃~3200℃. If the heating temperature during graphitization is within this range, the crystallinity of the graphite particles can be prevented from developing excessively.

The time during the graphitization treatment (heating time) is not particularly limited as long as the graphite precursor powder can be graphitized, but it is preferably 5 minutes to 30 hours, more preferably 30 minutes to 20 hours.

The environment during the graphitization treatment is not particularly limited as long as it does not hinder the graphitization of the graphite precursor powder, but it is preferably a non-oxidizing environment. The non-oxidizing environment may be an inert gas environment using inert gas such as argon, helium, or nitrogen, or a reducing environment using reducing gas such as hydrogen or carbon monoxide gas. The best environment is in argon gas flow or nitrogen gas flow.

The temperature distribution during the temperature increase during the graphitization treatment and the temperature distribution during heating are not particularly limited, but may be in various forms such as a linear temperature increase and a stepwise temperature increase in which the temperature is maintained at regular intervals. It can also be kept at a temperature below 2000°C for a specific time.

The method of graphitization treatment is not particularly limited, but it is preferably heated in a state enclosed in a graphite crucible or the like. [Example]

[Example 1] (Production of anode material) "Preparation of Graphite Precursor Powder" The coal tar containing 0.5% by mass of free carbon (xylene insoluble fraction (QI)) was heat-treated at 350°C for 0.5 hours, and then heat-treated at 450°C for 0.2 hours to generate mesophase carbon spheres. Use asphalt heavy oil (boiling point: 200~300℃) to extract asphalt from coal tar after heat treatment. From the pitch matrix, the mesocarbon pellets are recovered by filtration. The resulting mesophase carbon spheres are calcined at 500°C in a rotary kiln. The obtained calcined mesocarbon spheres (5 mass% volatile content) were crushed, and the average particle size was adjusted to 15 μm. The particle size adjusted product was fired at 1000° C. so that the volatile content was 2% by mass or less (the finished product of mesophase carbon pellet fired).

"Filling Steps" The resulting fired product is put into a polyethylene (PE) bag adjusted in advance to fit the size of the graphite crucible, and the opening of the bag is melt-sealed in a state of degassing under reduced pressure.

"Graphitization Step" The graphite crucible was enclosed in this state, and the temperature was increased at a temperature increase rate of 1000° C./hour in an argon environment, and graphitization treatment was performed at 3000° C. for 3 hours. In the graphitization step, the bag decomposed and disappeared, and the obtained graphite powder was removed by a vibrating sieve with a mesh size of 53 μm to prepare a negative electrode material.

(Making of negative electrode mixture paste) 98 parts by mass of the produced negative electrode material, 1 part by mass of carboxymethyl cellulose and 1 part by mass of styrene-butadiene rubber were put into water and stirred to prepare a negative electrode mixture paste.

(Production of working electrode (negative electrode)) Coat the prepared negative electrode mixture paste on copper foil with uniform thickness, evaporate and dry the solvent at 90°C in a vacuum, and press the negative electrode mixture layer with a roller press to press the electrode The density is adjusted to 1.70g/cm ³ . The copper foil and the negative electrode mixture layer were punched into a circle shape with a diameter of 15.5 mm, and a working electrode (negative electrode) formed by the current collector and the negative electrode mixture adhered to the current collector was produced.

(Production of counter electrode (positive electrode)) Press the lithium metal foil against the nickel mesh and punch it into a circle with a diameter of 15.5mm to make a current collector made of the nickel mesh and a lithium metal foil (0.5 mm thick) adhered to the current collector Opposite (positive).

(Electrolyte solution, separator) Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent of 33% by volume of ethylene carbonate and 67% by volume of ethyl methyl carbonate at a concentration of 1 mol/L to prepare a non-aqueous electrolyte. The prepared non-aqueous electrolyte was impregnated in a polypropylene porous body (thickness 20 μm) to produce a separator impregnated with the electrolyte.

(Evaluation of the production of batteries) The button type secondary battery shown in Fig. 1 was produced as an evaluation battery. The outer packaging cup 1 and the outer packaging can 3 are sealed together with an insulating gasket 6 at their peripheral edges. A current collector 7a made of nickel mesh, a circular counter electrode (positive electrode) 4 made of lithium foil, a separator sheet impregnated with electrolyte, are laminated in order from the inner surface of the outer can 3 5. A battery system composed of a current collector (negative electrode) 7b made of copper foil with a negative electrode mixture attached. In the aforementioned evaluation battery, the separator 5 impregnated with electrolyte was sandwiched between the current collector 7b and the counter electrode 4 closely attached to the current collector 7a, and then the current collector 7b was housed in the outer cup 1 and The counter pole 4 is housed in the outer can 3, the outer cup 1 and the outer can 3 are combined together, and then a flange gasket 6 is interposed between the outer cup 1 and the outer can 3, and the two peripheral edges are sealed together While making.

(Negative characteristics) The charge and discharge characteristics were measured by the following method. The results are shown in Table 1. Carry out 0.9mA constant current charging until the circuit voltage reaches 1mV, switch to constant voltage charging when the circuit voltage reaches 1mV, and then calculate the charging capacitance (unit: mAh/g) from the energization amount during which the current value becomes 20μA. Then, stop for 10 minutes. Next, perform constant current discharge at a current value of 0.9mA until the circuit voltage reaches 1.5V, and calculate the discharge capacitance (unit: mAh/g) from the amount of energization in the meantime. Set this as the first cycle. In this test, the process of absorbing lithium ions on the negative electrode material is called charging, and the process of detaching lithium ions from the negative electrode material is called discharging. Calculate the loss by "charging capacitor in the first cycle"-"discharging capacitor in the first cycle". The larger the discharge capacitance, the larger the battery capacitance, and the better the negative characteristics. The smaller the loss, the better the charge and discharge efficiency and the better the negative electrode characteristics.

(The average particle size) The cumulative degree of the particle size distribution measured with a laser diffraction particle size distribution meter (LMS-2000e, manufactured by Seishin Enterprise Co., Ltd.) is calculated as a volume percentage of 50% of the particle size (median diameter, 50% particle size).

(Specific surface area) Using a powder analyzer (Macsorb (registered trademark), manufactured by MOUNTECH), it was determined by the BET one-point method of nitrogen adsorption.

(Volatile matter) Measure the volatile content according to "11. Quantitative Method of Fixed Carbon Content" of JIS K 2425:2006. That is, 1 g of the sample (graphite precursor powder) was measured into a crucible, and heated at 430°C for 30 minutes without a lid. Subsequently, a double crucible was made, heated at 800 for 30 minutes to remove volatile matter, and the weight reduction rate of the sample was set as the volatile matter.

(Filling density) From the inner volume of the crucible and the mass of the graphite precursor powder filled in the crucible, calculate when filling in the crucible (the bag (filled with graphite precursor powder) is filled in the crucible, and the powder is filled in the crucible. ) Of the filling density. In addition, the mass of the graphite precursor powder is obtained by the difference between the mass of the crucible after filling and the mass of the crucible before filling. Calculate the filling density of the mold during press molding from the volume and mass of the molded product.

(Criteria for judging whether to crush after graphitization) After graphitization, whether it is necessary to pulverize the system to give light vibration, it is judged as "not required" when the massive graphite powder disintegrates, and as "necessary" when it is not disintegrated.

[Example 2] Except that the calcined mesocarbon spheres in Example 1 was pulverized to an average particle diameter of 3 μm, a negative electrode mixture was prepared in the same manner as in Example 1, a negative electrode was produced, a lithium ion secondary battery was produced, and characteristics were evaluated. The evaluation results are also shown in Table 1 below.

[Example 3] Except that the calcined mesocarbon spheres (5% by mass of volatile matter) obtained in Example 1 were pulverized to an average particle diameter of 3 μm and the subsequent firing treatment was not performed, the negative electrode mixture was prepared in the same manner as in Example 1, and the negative electrode was produced. Fabrication of lithium ion secondary batteries and performance evaluation. The evaluation results are also shown in Table 1 below.

[Example 4] Except that the calcined mesocarbon spheres (5% by mass of volatile matter) obtained in Example 1 were pulverized to an average particle diameter of 15 μm and the subsequent firing treatment was not performed, a negative electrode mixture was prepared in the same manner as in Example 1, and a negative electrode was produced. Fabrication of lithium ion secondary batteries and performance evaluation. The evaluation results are also shown in Table 1 below.

[Example 5] Except that the calcined mesocarbon spheres (5% by mass of volatile matter) obtained in Example 1 were pulverized to an average particle size of 10 μm and the subsequent firing treatment was not performed, a negative electrode mixture was prepared in the same manner as in Example 1, and a negative electrode was produced. Fabrication of lithium ion secondary batteries and performance evaluation. The evaluation results are also shown in Table 1 below.

[Comparative Example 1] Except that no filling step was performed in Example 1, a negative electrode mixture was prepared in the same manner as in Example 1, a negative electrode was produced, a lithium ion secondary battery was produced, and characteristics were evaluated. The evaluation results are also shown in Table 1 below.

[Comparative Example 2] Except that no filling step was performed in Example 2, the negative electrode mixture was prepared, the negative electrode was produced, the lithium ion secondary battery was produced, and the characteristics were evaluated in the same manner as in Example 2. The evaluation results are also shown in Table 1 below.

[Comparative Example 3] The fired product of mesocarbon small spheres (with a volatile content of 2% by mass or less) obtained in Example 1 was placed in a mold, and a pressure (0.5 ton/cm ² ) was applied to try to shape it. However, the fired product does not become lumpy and cannot be formed. Therefore, the graphitization step was not implemented afterwards. Moreover, in Comparative Example 3, since the volatile content of the burned product of the graphite precursor of the mesocarbon small spheres is less than 2% by mass, and the binder is not mixed, it is considered that the molded body cannot be formed by pressing only with the mold.

[Comparative Example 4] Except that the calcined mesocarbon spheres (5 mass% volatile content) obtained in Example 1 were placed in a mold, and press-molded with a pressure (0.5 ton/cm ² ). Since an agglomerate was obtained, the graphitization treatment was performed in the same manner as in Example 1. In the same manner as in Example 1, a negative electrode mixture was prepared, a negative electrode was produced, a lithium ion secondary battery was produced, and characteristics were evaluated. The evaluation results are also shown in Table 1 below. In addition, unlike Comparative Example 3, in Comparative Example 4, since the volatile content of the burned product of the graphite precursor of the mesocarbon pellets is 5 mass%, it is considered that even if the binder is not separately mixed, the pressure is pressed by the mold. It can also be a formed body.

[Comparative Example 5] Except that the calcined mesocarbon small spheres obtained in Example 2 (with a volatile content of 5% by mass) were placed in a mold, and molded under pressure (0.5 ton/cm ² ). Since an agglomerate was obtained, the graphitization treatment was performed in the same manner as in Example 2. In the same manner as in Example 1, a negative electrode mixture was prepared, a negative electrode was produced, a lithium ion secondary battery was produced, and characteristics were evaluated. The evaluation results are also shown in Table 1 below. Also, similar to Comparative Example 4, in Comparative Example 5, since the volatile content of the burned product of the graphite precursor of the mesocarbon pellets is 5 mass%, it is considered that even if the binder is not separately mixed, the pressure is applied by the mold. It can also be a formed body.

[Comparative Example 6] Except that no filling step was performed in Example 4, the negative electrode mixture was prepared in the same manner as in Example 4, the negative electrode was produced, the lithium ion secondary battery was produced, and the characteristics were evaluated. The evaluation results are also shown in Table 1 below.

[Comparative Example 7] Except that no filling step was performed in Example 5, the negative electrode mixture was prepared in the same manner as in Example 5, the negative electrode was produced, the lithium ion secondary battery was produced, and the characteristics were evaluated. The evaluation results are also shown in Table 1 below.

[Result explanation] In Example 1, due to the high packing density of the graphite precursor powder before graphitization and the need for pulverization after graphitization treatment, the productivity is excellent, and it is believed that the production cost of negative electrode materials for lithium ion secondary batteries can be reduced. In Examples 2 and 3, although a smaller graphite precursor powder with an average particle size of 3μm was also used, the packing density can be increased, and the pulverization treatment after graphitization treatment is not required, so the productivity is excellent, and it is believed that the lithium ion can be reduced Production cost of negative electrode materials for secondary batteries.

In the case of Examples 4 and 5 in which calcined mesophase carbon spheres with different average particle diameters are used as the graphite precursor, the packing density of the graphite precursor powder before graphitization is also increased, and pulverization after graphitization treatment is not required It has excellent productivity due to processing, and it is believed that the production cost of negative electrode materials for lithium ion secondary batteries can be reduced. Furthermore, using the graphite particles (negative material for lithium ion secondary batteries) obtained in Examples 1 to 5 as the negative electrode material, the negative electrode produced corresponds to the average particle size, and comparative examples 1, 2, and 6 compared with the previous product were obtained. , 7 The same discharge capacitance and loss. In addition, since the loss value depends on the average particle size of the graphite particles, when comparing the loss values, it is necessary to compare the values with approximately the same average particle size.

In Comparative Example 1, the graphite precursor powder is filled in a crucible and graphitized. Although the filling density in the crucible is not low, the productivity decreases due to the use of the crucible, which does not meet the requirements of the present invention.

Comparative Example 2 is a case where the graphite precursor powder with an average particle size of 3μm is filled in a crucible for graphitization, but the filling density of the crucible is 0.3g/cm ³ which is low, so it is caused by the use of the crucible The productivity is reduced and does not reach the required level of the present invention.

Comparative Examples 6 and 7 due to the packing density of the crucible were ^{0.7g / cm 3, 0.5g / cm} 3 and less, so the use of the crucible caused by the production of reduced, does not reach the required level according to the present invention.

Comparative Example 3 could not be shaped and could not be graphitized.

Although the packing density of the graphite precursor powder molded body in Comparative Examples 4 and 5 is not low, since pulverization is required after the graphitization treatment, the productivity is lowered and does not reach the required level of the present invention.

In addition, the graphite particles (negative material for lithium ion secondary batteries) obtained in Comparative Examples 4 and 5 were used as the negative electrode material. Although it corresponds to the average particle size, the discharge capacity of the evaluation battery is equivalent to that of Examples 1-3. , But the loss is greater than that of Examples 1 to 3, and the performance of the negative electrode is poor.

According to the method of manufacturing a negative electrode material for a lithium ion secondary battery of the present invention, compared with a method of filling a large amount of graphite precursor powder in a crucible and pressing a mold to produce a molded body of the graphite precursor powder, it has excellent productivity and has Help reduce manufacturing costs.

1: exterior cup 2: negative electrode mixture 3: External cans 4: opposite pole (positive) 5: spacer 6: Insulating gasket 7a: collector 7b: Current collector (negative electrode)

Fig. 1 is a schematic cross-sectional view of an evaluation battery used to evaluate the battery characteristics of the negative electrode.

1: exterior cup

2: negative electrode mixture

3: External cans

4: opposite pole (positive)

5: spacer

6: Insulating gasket

7a: collector

7b: Current collector (negative electrode)

Claims (1)

A method for manufacturing a negative electrode material for a lithium ion secondary battery, which has the following steps: The graphite precursor powder is filled inside the bag, and then the inside of the bag is degassed, depressurized, and the filling step of maintaining the decompressed state, and A graphitization step in which the aforementioned graphite precursor powder is filled with the aforementioned graphite precursor powder obtained in the aforementioned filling step, and the aforementioned bag is maintained in an internally reduced pressure state to be heated to graphitize the aforementioned graphite precursor powder.

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