JP2001155732A - Method for preparing carbon material for negative electrode of lithium ion secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing a carbon material for a negative electrode of a lithium ion secondary cell which can stably prepare the carbon material for the negative electrode of the lithium ion secondary cell and which has a high discharge capacity at unit volume of the cell. SOLUTION: A method for preparing a carbon material for a negative electrode of a lithium ion secondary cell comprising graphitization of a carbonate obtained after a carbonization of an organic material comprises using, as an organic material, 1 or 2 or more of materials selected from (A) a coal tar, (B) a petroleum tar, (C) a coal tar pitch, (D) a petroleum pitch, (E) a mesophase microphase formed by heating a coal tar pitch, (F) a bulk meso-phase and (G) a mesophase containing pitch obtained by polymerizing condensed polycyclic aromatic hydrocarbon, preserving the hydrocarbon before graphitization in an atmosphere which does not contain substantially oxygen, and carrying out graphitization of the hydrocarbon after preservation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a carbon material for a negative electrode of a lithium ion secondary battery, and more particularly to a method for producing a carbon material for a negative electrode of a lithium ion secondary battery having a large discharge capacity.

[0002]

2. Description of the Related Art A lithium ion secondary battery has various features such as small size, light weight, large discharge capacity, high voltage and large current, and excellent cycle life. In addition, since there are few problems with environmental pollution, the demand for nickel-cadmium batteries, which have been the mainstream of batteries for portable electronic products, is expected to increase significantly as batteries for mobile phones and notebook computers. ing.

A lithium ion secondary battery is composed of a positive electrode, a negative electrode, a separator that insulates them, a non-aqueous electrolyte that is an organic electrolyte in which an electrolyte is dissolved or a non-aqueous electrolyte that is a solid electrolyte, and various safety devices. Have been. A lithium ion secondary battery is a highly safe secondary battery having no danger of ignition of lithium metal because lithium does not precipitate as a metal during charging and is stored (doped) as an ion in a negative electrode.

As the above-mentioned materials for the negative electrode, mainly,
Graphite powder having the ability to insert and extract lithium ions is used. On the other hand, when the carbonaceous powder is used as a material for a negative electrode of a lithium ion secondary battery, a high degree of graphitization and a granular (non-scale, non-needle) particle shape are required as shown below.

High degree of graphitization: The basic mechanism of insertion and extraction of lithium ions in graphite is insertion of lithium ions between graphite layers and desorption from the layers.
The maximum storage amount becomes the stoichiometric ratio of Li and C in the molecular formula LiC ₆ . Therefore, in order to improve the discharge capacity, it is necessary to use graphite having a high degree of graphitization with a sufficiently developed layered structure.

[0006] Granular (non-scale, non-needle) particle shape:
In graphite powder as a material for a negative electrode of a lithium ion secondary battery, the particle shape is regarded as important in addition to the discharge capacity. That is, when manufacturing a negative electrode of a lithium ion secondary battery,
After applying the graphite powder on the current collector plate, press it.If the particle shape is flake or needle like natural graphite, it will be easier to arrange in one direction, so that the electrolyte permeability The graphite particles are inferior or exfoliate from the current collector due to expansion and contraction due to occlusion and desorption of lithium ions.

That is, graphite powder as a material for a negative electrode of a lithium ion secondary battery is required to have a high degree of graphitization and a granular (non-scale, non-needle) particle shape.
When filling the cylindrical or prismatic battery with the graphite powder, which is the above-described negative electrode material, apply it to a thin metal sheet such as a copper foil using a binder, sandwich the separator between the positive and negative electrode sheets, and form a coil. Used by winding.

The shape of the coil is a true cylinder in the case of a cylindrical battery, and is flat in the case of a square battery. In order to increase the discharge capacity per cell unit volume in these batteries, it is necessary to increase the amount of the negative electrode material enclosed, and the method is to use the amount of the binder when applying the negative electrode material to the copper foil. And press molding at as high a density as possible.

If the surface area of the electrode sheet is small, the electric field generated in the battery cannot be efficiently collected, and the discharge capacity per unit volume of the cell decreases. Need to be molded. As described above, in the lithium ion secondary battery, various methods are used to increase the discharge capacity.

On the other hand, as described above, the graphite powder used as the material for the negative electrode is required to have a high degree of graphitization in which the layered structure is sufficiently developed in order to improve the discharge capacity. Is done. However, in the production of a carbon material for a negative electrode of a lithium ion secondary battery, even when producing a graphite powder having a high degree of graphitization,
Lot-to-lot variation in the true specific gravity, which is an indicator of the degree of graphitization, was large, and it was difficult to obtain a stable lithium ion secondary battery with a large discharge capacity.

[0011]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, reduces the variation of the true specific gravity between lots, and has a high discharge capacity per unit volume of a battery cell. It is an object of the present invention to provide a method for producing a carbon material for a negative electrode of a lithium ion secondary battery, which can stably produce a carbon material.

[0012]

SUMMARY OF THE INVENTION The present invention provides a method for producing a carbon material for a negative electrode of a lithium ion secondary battery in which an organic substance is carbonized and then the obtained carbonized substance is graphitized. A method for producing a carbon material for a negative electrode of a lithium ion secondary battery, wherein the carbonized material before application is stored in an atmosphere substantially free of oxygen, and the carbonized material after the storage is graphitized. .

In the above-mentioned present invention, the method for storing in an atmosphere substantially free of oxygen includes the step of storing the carbonized material in a container made of (A) an oxygen-impermeable material and / or Stored in a bag of permeable material, or (B) stored in an atmosphere of inert gas and / or reducing gas, or as described in (A) and
(B) It is preferable to use a combination of both (first preferred embodiment of the present invention).

[0014] In the first preferred embodiment of the present invention, the method for storing in the container made of the above-described oxygen impermeable material and / or in the bag made of the oxygen impermeable material is as follows. It is preferable to store the carbonized material in the above-described container or bag in the presence of an oxygen scavenger (second preferred embodiment of the present invention). Further, the present invention described above,
In the first preferred embodiment and the second preferred embodiment of the present invention,
The above-mentioned organic matter heat-treats (A) coal tar, (B) petroleum tar, (C) coal pitch (coal tar pitch), (D) petroleum pitch, (E) coal pitch (coal tar pitch). It is preferably one or two or more selected from the generated mesophase microspheres, (F) bulk mesophase, and (G) a mesophase-containing pitch obtained by polymerizing a condensed polycyclic aromatic hydrocarbon in the presence of a catalyst. (Third preferred embodiment to fifth preferred embodiment of the present invention).

In the present invention and the first to fifth preferred embodiments of the present invention, the above-mentioned carbonized compound is obtained by converting an organic substance into a non-oxidizing atmosphere at a temperature of 300 ° C. or more, more preferably 300 to 400 ° C. It is preferably a carbonized product obtained by heating to 1100 ° C. (the sixth preferred embodiment to the eleventh preferred embodiment of the present invention). Furthermore, in the present invention described above, in the first preferred embodiment to the eleventh preferred embodiment of the present invention, the treatment temperature in the graphitization treatment is preferably 2000 ° C. or more,
Furthermore, the processing temperature in the graphitization processing is more preferably 2500 to 3100 ° C.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The present inventors have conducted intensive studies on a method for producing a carbon material for a negative electrode of a lithium ion secondary battery capable of stably producing a lithium ion secondary battery having a high discharge capacity per unit volume of a battery cell, The following findings have been found and the present invention has been made.

That is, even when graphite powder produced by the same raw material and the same production method is used, graphite powder having a low true specific gravity, which is an index of the degree of graphitization of the graphite powder, is obtained.
It has been found that the discharge capacity of a lithium ion secondary battery using this graphite powder decreases. FIG. 2 shows the true specific gravity (the number of samples: three each) for each of the production lots (A to E) of the graphite powder.

The above graphite powder is a graphite powder produced by the following production method. [Production method of graphite powder:] Mesophase spherules generated by heat treatment of coal tar pitch are extracted with oil in tar Heat the spherulite obtained above to 400 ° C Firing the carbon powder obtained above at 1000 ° C Graphitization of the carbon powder obtained above at 3000 ° C. As shown in FIG. 2, the true specific gravity of the production lot D is lower than the production lots A to C and E.

The present inventors have conducted intensive studies on the above-mentioned causes. As a result, the graphite powders of the production lots A to C and E were produced by heating the spherulite to 400 ° C. to obtain the carbon powder. Immediately after the graphite powder was graphitized,
The graphite powder of the production lot D is a graphite powder obtained by storing the obtained carbon powder in a flexible container bag whose upper part is open to the atmosphere, storing the carbon powder for two months, and then graphitizing the carbon powder. It is presumed that the oxidation proceeded during storage in the flexible container bag and the true specific gravity decreased.

For this reason, the present inventors store carbon powder obtained by carbonizing organic substances such as mesophase microspheres in an atmosphere substantially free of oxygen, and graphitize the carbon powder after storage. An experiment of processing was performed. As a result, as shown in Examples described later, it is possible to stably manufacture a lithium ion secondary battery having a high discharge capacity per unit volume of a battery cell without causing a decrease in the true specific gravity of the graphite powder. It has become possible to produce a carbon material for a negative electrode of a lithium ion secondary battery.

That is, the present invention provides a method for producing a carbon material for a negative electrode of a lithium ion secondary battery in which an organic substance is carbonized and then the obtained carbonized substance is graphitized. This is a method for producing a carbon material for a negative electrode of a lithium ion secondary battery in which a nitride is stored in an atmosphere substantially free of oxygen, and the stored carbon is graphitized.

Hereinafter, [1] raw materials, [2] manufacturing steps, and [3] manufacturing conditions in the present invention will be described. [1] Raw material: The type of the organic substance as the raw material in the present invention is not particularly limited as long as it is an organic substance capable of obtaining carbon powder by heating or pulverizing after heating. But (A) coal tar,
(B) Petroleum tar, (C) Coal pitch (coal tar pitch), (D) Petroleum pitch, (E) Mesophase spheres produced by heat treatment of coal pitch, (F) Bulk mesophase and (G) condensation 1 selected from a mesophase-containing pitch obtained by polymerizing a polycyclic aromatic hydrocarbon in the presence of a catalyst
It is preferable that the number of species is two or more.

This is because the above-mentioned organic substances show excellent graphitization properties because they contain aromatic molecules, and in the process of carbonization and graphitization, the aromatic molecules are laminated and the degree of graphitization is high. This is because graphite powder can be obtained. Further, as the above-mentioned organic substances, coal pitch (coal tar pitch), mesophase small spheres produced by heat treatment of coal pitch (coal tar pitch), and condensed polycyclic aromatic hydrocarbons are polymerized in the presence of a catalyst. It is more preferable to use one or more selected from the mesophase-containing pitch obtained by the above method.

By using the above-mentioned organic material as a raw material, spherical or granular graphite powder can be obtained, and the particle shape [granular (non-flaky) which is required as a material for the negative electrode of a lithium ion secondary battery described above. , Non-needle shape)]. The mesophase-containing pitch obtained by polymerizing the above-mentioned mesophase small spheres and condensed polycyclic aromatic hydrocarbons can be produced by the following production method.

(Mesophase microspheres) Mesophase microspheres produced by heat treatment of coal tar pitch are extracted and separated from matrix pitch using an organic solvent such as tar medium oil, and the resulting mesophase microspheres (spherulites, mesocarbons). Microbeads). The mesophase microspheres described above had an anisotropic fraction of 5 observed with a polarizing microscope.
Preferably, it is about 100% by area.

This is because it is difficult to obtain a graphite powder having a high degree of graphitization when the anisotropic fraction is less than 5 area%. (Mesophase-containing pitch obtained by polymerizing condensed polycyclic aromatic hydrocarbon :) The above-mentioned mesophase-containing pitch is obtained by polymerizing condensed polycyclic aromatic hydrocarbon in the presence of a catalyst.

The condensed polycyclic aromatic hydrocarbon which is a raw material of the mesophase-containing pitch is selected from naphthalene, methylnaphthalene, anthracene, phenanthrene, acenaphthene, acenaphthylene, pyrene and the like.
It is preferable to use one or more kinds of condensed polycyclic aromatic hydrocarbons. Also, as a condensed polycyclic aromatic hydrocarbon,
Tar distillation oil, which is a mixture of condensed polycyclic aromatic hydrocarbons obtained by coal tar distillation, can also be used.

As the catalyst, a Lewis acid catalyst is preferred.
No. As the Lewis acid catalyst, a super strong acid catalyst and / or
Is a Lewis acid catalyst. As a super strong acid catalyst,
Hydrogen fluoride combining isocyanic acid and Bronsted acid
Boron fluoride catalyst (: HF / BF_Three), And a Lewis acid catalyst.
AlCl_Three, CuCl _TwoAnd the like.

The mesophase-containing pitch using the above-mentioned condensed polycyclic aromatic hydrocarbon as a raw material preferably has an anisotropic fraction of 80 to 100 area% as observed by a polarizing microscope. This is because when the anisotropic fraction is less than 80 area%, it is difficult to obtain a graphite material having a high degree of graphitization.

In the present invention, a mesophase-containing pitch obtained by polymerizing a condensed polycyclic aromatic hydrocarbon in the presence of a catalyst is used to obtain a light-weight mixture using a heterocyclic compound and / or a polycyclic aromatic hydrocarbon. It is more preferable to extract and remove the components and use the obtained mesophase-containing pitch. This is because the above-mentioned mesophase-containing pitch contains an isotropic pitch and a light component that is a mesophase component having a low molecular weight, and is melted during carbonization and graphitization, fusion between particles and foaming occur, and the light component is extracted in advance. This is because these problems can be solved by removing them.

[2] Manufacturing Process: FIG. 1 shows an example of a manufacturing process of a carbon material for a negative electrode (hereinafter, referred to as a carbon material for a negative electrode) of a lithium ion secondary battery according to the present invention. In the production process of the carbon material for a negative electrode shown in FIG. 1A, coal pitch (coal tar pitch) is heated to, for example, 450 ° C. to produce optically anisotropic mesophase spheres.

Next, the obtained mesophase microspheres are extracted and separated from the pitch matrix by solvent extraction using an organic solvent such as oil in tar. The obtained mesophase microspheres are dried, if necessary, preferably 30
Calcination is carried out at a temperature of 0 to 1100 ° C, more preferably 400 to 700 ° C, to obtain a carbonized product (carbon powder).

Next, the obtained carbonized product (carbon powder) is
It is stored in an atmosphere substantially free of oxygen to prevent the progress of oxidation of the carbonized material during storage. Next, the carbonized product after storage is preferably calcined at a temperature of 500 to 1100 ° C., and is preferably 2000 ° C. or more, more preferably 2000 to 1100 ° C.
Graphitization is performed at a temperature of 3100 ° C to obtain a graphite powder.

After firing at a temperature of 500 to 1100 ° C., the fired product may be stored in an atmosphere containing substantially no oxygen. In the manufacturing process shown in FIG. 1 (a), the mesophase spheres obtained by extraction and separation, the carbonized product obtained after calcination, the carbonized product obtained after calcination, the carbonized product obtained after storage, The graphite powder obtained by the treatment is
The graphite powder may be crushed or pulverized as appropriate, further classified as needed, and the particle size of the finally obtained graphite powder may be adjusted.

The graphite powder obtained in the above-described manufacturing process is
A lithium ion secondary battery having a stable and high true specific gravity and having a high discharge capacity per unit volume of a battery cell can be stably manufactured by using the graphite powder obtained in the manufacturing process of the present invention. . In the manufacturing process of the carbon material for a negative electrode shown in FIG. 1 (b), coal pitch (coal tar pitch) is heated to, for example, 450 ° C. to produce optically anisotropic mesophase microspheres.

Next, the obtained mesophase microsphere-containing heat-treated pitch is calcined in the same manner as in the manufacturing process shown in FIG. 1A to obtain a carbonized product. Next, the obtained carbonized material is stored in an atmosphere substantially free of oxygen to prevent progress of oxidation of the carbonized material during storage. next,
The carbonized product after storage is calcined and graphitized in the same manner as in the production process shown in FIG. 1A to obtain a graphite powder.

The fired product may be stored in an atmosphere containing substantially no oxygen. In the manufacturing process shown in FIG. 1 (b), the mesophase microsphere-containing heat-treated pitch, the carbonized material obtained after calcination, the carbonized material obtained after calcination, the carbonized material obtained after storage, and the graphitized material were obtained. The graphite powder is pulverized or crushed as appropriate, and further classified as necessary,
The particle size of the graphite powder finally obtained may be adjusted.

In the production process shown in FIGS. 1 (a) and 1 (b), it is preferable that the carbonized material obtained in the calcining step is stored in an atmosphere substantially free of oxygen. This is because the carbonized material obtained by the calcination tends to progress in the oxidation more than the carbonized material obtained by the calcination. In the production process of the carbon material for a negative electrode shown in FIG. 1 (c), coal pitch (coal tar pitch) is calcined (heated) at a temperature of preferably 300 to 1100 ° C, more preferably 400 to 600 ° C. ,
Obtain carbonized material.

Next, the obtained carbonized material is stored in an atmosphere substantially free of oxygen to prevent the progress of oxidation of the carbonized material during storage. Next, the carbonized material after storage is
Graphitization is performed in the same manner as in the manufacturing process shown in FIG. 1A to obtain graphite powder. In the manufacturing process shown in FIG. 1 (c), the carbonized material obtained after firing, the carbonized material after storage, and the graphite powder obtained by the graphitization treatment are appropriately ground or crushed, and And the particle size of the graphite powder finally obtained may be adjusted.

In the step of manufacturing the carbon material for the negative electrode shown in FIG.
C., more preferably 400-600.degree. C., and calcined (heated) to obtain a carbonized product. Next, the obtained carbonized material is stored in an atmosphere substantially free of oxygen to prevent progress of oxidation of the carbonized material during storage.

Next, the carbonized product after storage was replaced with the above-mentioned FIG.
Graphitization is performed in the same manner as in the production process shown in (a) to obtain graphite powder. In the manufacturing process shown in FIG. 1 (d), the mesophase-containing pitch of the raw material, the carbonized material obtained after firing, the carbonized material after storage, and the graphite powder obtained by the graphitization treatment were appropriately ground or pulverized. It may be crushed, further classified if necessary, and the particle size of the graphite powder finally obtained may be adjusted.

[3] Manufacturing conditions: Preferred manufacturing conditions in the present invention are described below. (1) Calcining (firing) step: As described above, in the present invention, the mesophase-containing pitch obtained by polymerizing the above-mentioned mesophase spherules, coal pitch (coal tar pitch), and condensed polycyclic aromatic hydrocarbon. An organic material such as is calcined or fired.

The calcining (firing) temperature in this case is preferably from 300 to 1100 ° C, more preferably from 300 to 700 ° C. This is because if the calcining (firing) temperature is lower than 300 ° C, the removal of the light components in the raw material becomes insufficient, and the subsequent carbonization, graphitization, melting of carbonized materials, fusion of particles, and foaming occur. This is because it is difficult to produce graphite powder having the required particle shape.

In this step, heat treatment is performed in a non-oxidizing atmosphere in order to prevent oxidation of the calcined product and the calcined product. (2) Method for storing carbonized material: In the present invention, as described above, the obtained carbonized material is stored in an atmosphere substantially free of oxygen.

This is because graphite powder, which is a carbon material for a negative electrode of a lithium ion secondary battery, graphitizes a carbonized material at a high temperature of 2000 ° C. or more, more preferably 2500 to 3100 ° C. This is because the carbonization step and the graphitization step are provided separately, and the firing (calcination) furnace and the graphitization furnace are separately provided. That is, from the viewpoint of the above-described steps, production schedule and production efficiency, a case where a large amount of carbonized material is produced in a short period of time and a graphitization treatment is performed after storage occurs, and in the present invention, the carbonized material is substantially converted into oxygen. To prevent oxidation of the carbonized material during storage.

As the above-mentioned preservation method,
(A) Store in a container made of oxygen-impermeable material and / or in a bag made of oxygen-impermeable material, or (B) Store in an atmosphere of inert gas and / or reducing gas. Alternatively, it is preferable to store both of the above (A) and (B) in combination. When the carbonized product is stored in the above-mentioned container or bag, it is more preferable to store it in the presence of an oxygen scavenger.

As a container made of a material impermeable to oxygen, a drum can or the like can be used. In this case, the inside of the drum is sealed. Further, as a bag made of a material impermeable to oxygen, for example, O ₂ permeability in an air atmosphere is 5 cm ^3.
/ (m ² -24h-0.098MPa) or less, more preferably a gas-sealable laminate bag having an O ₂ permeability of 2 cm ³ / (m ² -24h-0.098MPa) or less in the atmosphere can be used. .

As the inert gas, N ₂ gas, He gas, Ar gas or a mixed gas thereof can be used, and it is preferable to use N ₂ gas from the viewpoint of economy.
Further, as the reducing gas, H ₂ gas, propane gas, a mixed gas thereof, or the like can be used. Also,
The oxygen scavenger is not particularly limited as long as it is a substance having a higher reaction rate with oxygen than a carbonized material, an oxygen adsorbent, and an oxygen absorber, but from a practical viewpoint, metal powder such as iron powder. It is preferable to use

(3) Graphitization step: In the present invention, the carbonized material after storage is subjected to a graphitization treatment, preferably at a temperature of 2000 ° C. or higher. In the present invention, from the viewpoint of increasing the degree of graphitization, the higher the temperature during graphitization, the more preferable.

Further, in order to produce a graphite material having a high degree of graphitization, in which a layered structure required as a carbon material for a negative electrode of a lithium ion secondary battery is sufficiently developed, it is more preferable to use a non-oxidizing atmosphere, The graphitization treatment is performed at a temperature of 2500 ° C. or more, more preferably 2800 ° C. or more. In addition, from the viewpoint of increasing the degree of graphitization, the upper limit of the processing temperature during the graphitization is not particularly limited, but from the viewpoint of the equipment of the graphitization furnace, the processing temperature during the graphitization processing is 3100 ° C or less. It is preferred that

As described in the description of FIGS. 1 (a) and 1 (b), the carbonized material stored in an atmosphere containing substantially no oxygen
After calcination (heating) at 1100 ° C., the above-described graphitization treatment may be performed. The firing temperature is more preferably 700 to 1100
° C.

[0052]

EXAMPLES The present invention will be described below more specifically based on examples. (Example 1) Graphite powder was manufactured according to the above-described process of FIG. That is, first, coal pitch (coal tar pitch) was heated to 450 ° C. to produce mesophase microspheres, and the obtained mesophase microspheres were extracted and separated from the pitch matrix using oil in tar.

Incidentally, the anisotropy fraction of the obtained mesophase microspheres observed by a polarizing microscope was 30 area%. Next, the obtained mesophase microspheres (spherulites) were dried and calcined at 400 ° C. for 1 hour. Next, the obtained carbonized product (carbon powder) was stored in a gas-sealable laminate bag [special type of moisture-proof type manufactured by Nippon Matai Co., Ltd.] and stored for 3 months.

The O ₂ permeability of the above-mentioned laminated bag in the air atmosphere was 1.2 cm ³ / (m ² -24h-0.098 MPa). Next, the carbonized material (carbon powder) after storage is stored at 1000 ° C.
For 5 hours in a non-oxidizing atmosphere using a graphitizing furnace
The mixture was heated to 3000 ° C. and subjected to a graphitization treatment to produce a graphite powder.

Next, the true specific gravity of the obtained graphite powder was determined according to JIS.
It was measured according to R 7222 (butanol solution, using a pycnometer). Using the obtained graphite powder, a three-electrode battery shown below was assembled, and the discharge capacity was measured in a dry box under argon gas flow under the following conditions. [Cell type:] 3-electrode beaker cell Counter electrode and reference electrode: Lithium metal Working electrode: Graphite powder applied on copper foil and pressed further Working electrode production method: Graphite powder: 100 parts by weight, 10 parts by weight After mixing PVDF (polyvinylidene difluoride), N was added to the resulting mixture.
-Methylpyrrolidone was added to dissolve PVDF sufficiently and applied on copper foil.

After preliminary drying at 100 ° C., the roll was pressed using a roll press, and N-methylpyrrolidone was removed under vacuum conditions at 100 ° C. to obtain a working electrode. [Electrolyte:] As the electrolyte, 1 M lithium perchlorate was dissolved in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a ratio of 1: 1 (weight ratio).

[Charge / Discharge Test:] Using the above three-electrode battery, current density: 1.0 mA / cm ² and voltage: 2.5 for both charging and discharging.
A constant current charge / discharge test was performed under the conditions of 0 V. Table 1 shows the obtained test results. (Example 2) In Example 1 described above, the calcination temperature was set to 35.
A graphite powder was produced in the same manner as in Example 1 except that the temperature was changed to 0 ° C.

Next, the true specific gravity of the obtained graphite powder was measured in the same manner as in Example 1 described above. Using the obtained graphite powder, a three-electrode battery was assembled in the same manner as in Example 1, and a constant current charge / discharge test was performed under the same conditions as in Example 1. Table 1 shows the obtained test results.

(Example 3) Graphite powder was produced according to the process shown in FIG. That is, first, coal pitch (coal tar pitch) was fired at 500 ° C. for 5 hours. Next, the obtained carbonized product was pulverized and stored for 3 months in a container of N ₂ atmosphere.

Next, the carbonized product (carbon powder) after storage is
The mixture was heated to 3000 ° C. using a graphitization furnace to perform a graphitization treatment, thereby producing a graphite powder. Next, the true specific gravity of the obtained graphite powder was measured in the same manner as in Example 1 described above. Also,
Using the obtained graphite powder, a three-electrode battery was assembled in the same manner as in Example 1, and a constant current charge / discharge test was performed under the same conditions as in Example 1.

Table 1 shows the test results obtained. (Example 4) Graphite powder was manufactured according to the above-described process of FIG. 1 (d). That is, first, naphthalene was converted to HF / BF ₃
The mesophase-containing pitch shown below, obtained by polymerization in the presence of, was ground to 60 mesh or less.

The particle shape of the obtained powder was granular (non-scale, non-needle). [Mesophase-containing pitch:] TI (toluene-insoluble content): 75% QI (quinoline-insoluble content): 31% Anisotropic fraction observed with a polarizing microscope: 100 area% And calcined at 500 ° C. for 3 hours.

Next, the obtained carbonized product (carbon powder) is
In the same manner as in Example 1 described above, it was stored in a gas-sealable laminate bag and stored for 3 months. Next, the carbonized material (carbon powder) after storage was heated to 3000 ° C. using a graphitization furnace to perform a graphitization treatment, thereby producing a graphite powder. next,
The true specific gravity of the obtained graphite powder was measured in the same manner as in Example 1 described above.

Using the obtained graphite powder, a three-electrode battery was assembled in the same manner as in Example 1, and a constant current charge / discharge test was performed under the same conditions as in Example 1. Table 1 shows the obtained test results. (Example 5) A graphite powder was produced in the same manner as in Example 4 except that the carbonized material (carbon powder) was stored in a drum and sealed and stored.

Next, the true specific gravity of the obtained graphite powder was measured in the same manner as in Example 1 described above. Using the obtained graphite powder, a three-electrode battery was assembled in the same manner as in Example 1, and a constant current charge / discharge test was performed under the same conditions as in Example 1. Table 1 shows the obtained test results.

(Embodiment 6) In Embodiment 4 described above,
A graphite powder was produced in the same manner as in Example 4, except that the carbonized product (carbon powder) was stored in a drum and sealed and stored together with a deoxidizer. In addition, Ageless S-2000 (trade name, manufactured by Mitsubishi Gas Chemical Co., Ltd., main component: metallic iron powder) was used as the oxygen scavenger.

Next, the true specific gravity of the obtained graphite powder was measured in the same manner as in Example 1 described above. Using the obtained graphite powder, a three-electrode battery was assembled in the same manner as in Example 1, and a constant current charge / discharge test was performed under the same conditions as in Example 1. Table 1 shows the obtained test results.

(Comparative Example 1) In Example 1 described above,
A graphite powder was produced in the same manner as in Example 1 except that the calcined carbonized material (carbon powder) was stored in an air atmosphere for three months and then subjected to a graphitization treatment. Next, the true specific gravity of the obtained graphite powder was measured in the same manner as in Example 1 described above.

Using the obtained graphite powder, a three-electrode battery was assembled in the same manner as in Example 1, and a constant current charge / discharge test was performed under the same conditions as in Example 1. Table 1 shows the obtained test results. (Comparative Example 2) In Example 2, the calcined carbonized material (carbon powder) was stored in an air atmosphere for three months,
A graphite powder was produced in the same manner as in Example 2 except that the graphitization was performed.

Next, the true specific gravity of the obtained graphite powder was measured in the same manner as in Example 1 described above. Using the obtained graphite powder, a three-electrode battery was assembled in the same manner as in Example 1, and a constant current charge / discharge test was performed under the same conditions as in Example 1. Table 1 shows the obtained test results.

Comparative Example 3 In Example 3 described above,
A graphite powder was produced in the same manner as in Example 3 except that the carbonized material (carbon powder) was stored in an air atmosphere for three months and then subjected to a graphitization treatment. Next, the true specific gravity of the obtained graphite powder was measured in the same manner as in Example 1 described above.

Using the obtained graphite powder, a three-electrode battery was assembled in the same manner as in Example 1, and a constant current charge / discharge test was performed under the same conditions as in Example 1. Table 1 shows the obtained test results. (Comparative Example 4) A graphite powder was produced in the same manner as in Example 4 except that the carbonized material (carbon powder) was stored in an air atmosphere for 3 months and then subjected to a graphitization treatment. did.

Next, the true specific gravity of the obtained graphite powder was measured in the same manner as in Example 1 described above. Using the obtained graphite powder, a three-electrode battery was assembled in the same manner as in Example 1, and a constant current charge / discharge test was performed under the same conditions as in Example 1. Table 1 shows the obtained test results.

As shown in Table 1, according to the present invention,
It was possible to extremely effectively reduce the variation in the quality of graphite powder as a carbon material for negative electrodes of lithium ion secondary batteries, which had been a problem in the past, and to stably produce graphite powder with a true specific gravity of 2.20 or more. became. As a result, according to the present invention, it has become possible to stably manufacture a lithium ion secondary battery having a high discharge capacity per unit volume of a battery cell.

[0075]

[Table 1]

[0076]

According to the present invention, the variation in the quality of graphite powder as a carbon material for a negative electrode of a lithium ion secondary battery, which has been a problem in the past, can be extremely effectively reduced, and graphite powder having a high specific gravity can be obtained. It became possible to manufacture stably.
As a result, according to the present invention, it has become possible to stably manufacture a lithium ion secondary battery having a high discharge capacity per unit volume of a battery cell.

[Brief description of the drawings]

FIG. 1 is a process chart showing an example of a process for producing a carbon material for a negative electrode of a lithium ion secondary battery of the present invention.

FIG. 2 is a graph showing the true specific gravity of graphite powder for each production lot.

Claims (1)

[Claims] In a method for producing a carbon material for a negative electrode of a lithium ion secondary battery in which an organic substance is carbonized and then the obtained carbonized substance is graphitized, the carbonized substance before the graphitizing treatment is substantially removed. A method for producing a carbon material for a negative electrode of a lithium ion secondary battery, comprising storing the carbonized material after storage in an atmosphere containing no oxygen.