JPH11209114A - Production of graphite, lithium secondary battery and its negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a graphite production method permitting the production with a simple process, by which high graphitization degree is obtd. even if addition of a graphitized catalyst is reduced, and graphite suitable for a lithium secondary battery which has high charging and discharging characteristics and is excellent in quick charging and discharging characteristics, cycle characteristics, irreversible volume of the first cycle, etc., is produced at a reduced cost and at reduced number of stages as well, a negative electrode for the lithium secondary battery which has high charging and discharging characteristics and is excellent in quick charging and discharging characteristics, cycle characteristics, irreversible volume of the first cycle, etc., and the lithium secondary battery which has high charging and discharging characteristics and is excellent in quick charging and discharging characteristics, cycle characteristics, irreversible volume of the first cycle, etc. SOLUTION: Volatile components of the graphited catalyst generated at the graphitization stage are brought into contact with a mixture of materials before graphitization in the graphite production method incorporating a stage for obtaining the mixture of materials by mixing graphitizable aggregate or graphite, graphtizable binder and the graphitized catalyst together, a calcining stage and the graphitization stage. The negative electrode for the lithium secondary battery formed by incorporating the graphite produced by this production method and the lithium secondary battery have this negative electrode 13 and a position electrode 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a portable device,
Electric vehicles, suitable for use in power storage, etc., excellent cycle characteristics, rapid charge and discharge characteristics, excellent safety, etc., and a method for producing graphite suitable as a negative electrode material for realizing a high capacity lithium secondary battery, The present invention relates to a lithium secondary battery using the graphite and a negative electrode thereof.

[0002]

2. Description of the Related Art Conventional graphite particles include, for example, natural graphite particles,
Examples include artificial graphite particles obtained by graphitizing coke, organic polymer materials, artificial graphite particles obtained by graphitizing pitch and the like, and graphite particles obtained by pulverizing these. These particles are mixed with an organic binder and an organic solvent to form a graphite paste, the graphite paste is applied to the surface of a copper foil, and the solvent is dried to be used as a negative electrode for a lithium ion secondary battery. . For example, as shown in JP-B-62-23433,
By using graphite for the negative electrode, the problem of internal short circuit due to lithium dendrite is eliminated, and the cycle characteristics are improved.

[0003] However, natural graphite particles in which graphite crystals are developed and artificial graphite particles obtained by graphitizing coke are:
Since the bonding force between the layers of the c-axis aromatic crystal is weaker than the bonding in the plane direction of the crystal, the bonding between the graphite layers is broken by pulverization,
So-called graphite particles having a large aspect ratio are obtained. Since the scale-like graphite particles have a large aspect ratio, the scale-like graphite particles are oriented in the surface direction of the current collector when kneaded with a binder and applied to a current collector to produce an electrode. Distortion in the c-axis direction caused by the repeated insertion and extraction of lithium into and from the particles causes the destruction of the inside of the electrode, which causes not only the problem of reduced cycle characteristics but also the tendency of rapid charge / discharge characteristics to deteriorate. Further, the scale-like graphite particles having a large aspect ratio have a large specific surface area, so that they have poor adhesion to a current collector and require a large amount of binder. If the adhesion to the current collector is poor, there is a problem that the current collecting effect is reduced and the discharge capacity, rapid charge / discharge characteristics, cycle characteristics, and the like are reduced. Further, scale-like graphite particles having a large specific surface area have a problem that the irreversible capacity in the first cycle of a lithium secondary battery using the particles is large.
Furthermore, scale-like graphite particles having a large specific surface area have low thermal stability in a state where lithium is stored, and have a problem in safety when used as a negative electrode material for a lithium secondary battery. Therefore, there is a demand for graphite particles which are excellent in rapid charge / discharge characteristics, cycle characteristics, irreversible capacity in the first cycle, have a low specific surface area, and can improve safety.

[0004] Further, with the market expansion of lithium secondary batteries, there has been a demand for a large cost reduction in the materials used, and it has been necessary to improve the manufacturing process. In particular, the graphitization step requires increasing the degree of graphitization of the graphite particles in order to realize a high charge / discharge capacity, and is a step of processing the sample at an extremely high temperature of 2500 ° C. or more, so that the energy cost is high. This is a process that greatly increases the cost of the product because it takes a long time to heat and cool the furnace, and manual work such as filling and unloading the furnace is required. Further, in the graphitization step, the graphitization catalyst added at a high temperature is volatilized, and graphitization proceeds in a process in which this volatile component repeatedly bonds and decomposes with carbon in the system. Since the graphitization catalyst eventually scatters outside the system, it is necessary to add a large amount of expensive graphitization catalyst in order to achieve sufficient graphitization of carbon.

[0005]

According to the first and second aspects of the present invention, a high degree of graphitization can be obtained even with a small amount of a graphitization catalyst, high charge / discharge characteristics, and rapid charge / discharge characteristics. ,
Provided is a method for manufacturing graphite that can be manufactured in a simple process that can be manufactured at low cost together with a reduction in man-hours, in addition to a reduction in man-hours, a graphite suitable for a lithium secondary battery having excellent cycle characteristics and irreversible capacity in the first cycle. Things. The invention according to claims 3 and 4 provides a negative electrode for a lithium secondary battery having high charge / discharge characteristics, and excellent in rapid charge / discharge characteristics, cycle characteristics, irreversible capacity in the first cycle, and the like. . Claim 5
The described invention is to provide a lithium secondary battery having high charge / discharge characteristics, and excellent in rapid charge / discharge characteristics, cycle characteristics, irreversible capacity in the first cycle, and the like.

[0006]

SUMMARY OF THE INVENTION The present invention provides a process comprising the steps of mixing a graphitizable aggregate or graphite, a graphitizable binder, and a graphitizing catalyst to obtain a material mixture, a calcination step, and a graphitizing step. The present invention relates to a method for producing graphite, wherein a volatile component of a graphitization catalyst generated in the graphitization step is brought into contact with a material mixture before graphitization.
Further, the present invention provides that the graphitization step is performed using a continuous graphitization furnace, and the volatile component of the graphitization catalyst generated in the high temperature region is brought into contact with the material mixture in the low temperature region before graphitization. The present invention relates to a method for producing graphite. Further, the present invention relates to a negative electrode for a lithium secondary battery containing graphite produced by the above-mentioned production method. The present invention also relates to the negative electrode for a lithium secondary battery, wherein the mixture of graphite and an organic binder is integrated with a current collector. Further, the present invention relates to a lithium secondary battery having the negative electrode and the positive electrode.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a step of mixing a graphitizable aggregate or graphite, a graphitizable binder and a graphitizing catalyst to obtain a mixture, a firing step and a graphitizing step. The graphitization step is characterized in that a volatile component of the graphitization catalyst generated in the graphitization step is brought into contact with a material mixture before graphitization. As the graphitizable aggregate, various cokes such as fluid coke and needle coke are preferable. Examples of the graphite include natural graphite and artificial graphite. Examples of the binder which can be graphitized include various pitches such as coal-based, petroleum-based, and artificial, tar, thermosetting resin, and organic materials such as thermoplastic resins. The compounding amount of the binder is preferably 5 to 80% by weight based on the graphitizable aggregate or graphite,
It is more preferable to add 10 to 80% by weight,
More preferably, 80% by weight is added. If the amount of the binder is too large or too small, the graphite particles to be produced tend to have an increased aspect ratio and specific surface area.

[0008] The method of mixing the graphitizable aggregate or graphite and the binder is not particularly limited, and is performed using a kneader or the like, but it is preferable to mix at a temperature equal to or higher than the softening point of the binder. Specifically, when the binder is pitch, tar or the like, the temperature is preferably 50 to 300 ° C, and when the binder is a thermosetting resin, the temperature is preferably 20 to 100 ° C. As a graphitization catalyst,
For example, metals such as iron, nickel, titanium, silicon, and boron,
Graphitization catalysts such as these carbides and oxides can be used. Of these, carbides or oxides of silicon or boron are preferred. The graphitization catalyst is 0.1% based on the graphitizable aggregate or the mixture of graphite and the graphitizable binder.
-50% by weight, preferably 0.5-30% by weight, more preferably 0.5-20% by weight.
More preferably, it is added. If it is less than 0.1% by weight, the development of graphite particles becomes poor, and the charge / discharge capacity tends to decrease. On the other hand, if it exceeds 50% by weight, it becomes difficult to mix uniformly, and the workability tends to decrease.

The mixture obtained as described above is fired. The firing is preferably performed in an atmosphere in which the mixture is hardly oxidized, for example, in a nitrogen atmosphere, in an argon gas,
A method of firing in a vacuum is given. The firing temperature is 60
The temperature is preferably from 0 to 1100 ° C, and the firing time is preferably from 1 minute to 10 hours. As the form of the mixture to be fired, any of a block, a pellet, a granule, and a powder that has been pulverized in a pulverizing step can be employed. The furnace for firing may be a batch type furnace or a continuous type furnace.

[0010] In the graphitization step of the present invention, it is necessary to bring the volatile component of the graphitization catalyst generated in the graphitization step into contact with the material mixture before graphitization. It is preferable to use a furnace, and to have a mechanism for bringing the volatile components of the graphitization catalyst generated together with the graphitization of the material mixture in the high temperature region of the graphitization furnace into contact with the material mixture in the low temperature region before graphitization. Is preferred.
Here, a continuous graphitization furnace is a graphitization furnace that does not raise and cool the temperature of the entire furnace when inserting and discharging a sample in a furnace for performing graphitization. And a furnace in which the material mixture is moved, graphitized in a high-temperature region, and then the graphitized material is removed from an outlet. In general, there is a furnace having a lower temperature region on the insertion port side and the discharge port side with a high temperature region required for graphitization interposed therebetween. The movement of the material mixture in the furnace can be performed, for example, by continuously pushing the material mixture.

Regarding the temperature in the high temperature region where the graphitization is performed,
2000 ° C. or higher is preferable, 2500 ° C. or higher is preferable, and 2800 to 3200 ° C. is preferable. When this temperature is low, the development of graphite crystals becomes worse, and the graphitization catalyst tends to remain in the produced graphite particles, and in any case, the charge / discharge capacity tends to decrease.
In addition, the temperature of the lower temperature region sandwiching the high temperature region is not particularly limited as long as the temperature is lower than the high temperature region, but it is possible to insert and remove the sample mixture and the graphitized sample at the insertion port and the discharge port Any temperature is acceptable.

[0012] In the graphitization step using the continuous graphitization furnace, the volatile components of the graphitization catalyst generated in the high-temperature region in the continuous graphitization furnace are converted into a material mixture in the low-temperature region before graphitization, that is, the insertion side. Contact with the mixture in the low temperature range of Thereby, graphite having a high degree of graphitization can be obtained by reducing the amount of the graphitization catalyst. As a specific method of bringing the volatile component of the graphitization catalyst into contact with the material mixture in the low-temperature region, a method of flowing a gas in a direction opposite to the moving direction of the material mixture can be mentioned. As a gas to be used, a nitrogen gas, an argon gas or the like can be used. As a form of the continuous graphitization furnace, it is preferable that a portion in which the sample mixture moves is configured to be shielded from the outside air in order to realize the movement of the volatile component of the graphitization catalyst by gas.

The direction in which the sample mixture moves can be any of a horizontal direction, a vertical direction, an oblique direction and the like. The form of the material mixture to be inserted into the furnace may be any of block, pellet, granule, powder, etc., but the material mixture can be easily inserted and graphite can be easily removed. Pellets or granules are preferred because they can easily contact the volatile components of the graphitization catalyst and can secure a flow path for the volatile components of the graphitization catalyst in the material mixture. Here, the term "powder" refers to a product obtained by pulverizing a mixture in a pulverizing step, and the term "granular" refers to a powder obtained by using a powder method such as a tablet method, a direct granulation method, or a spray drying method. It refers to one granulated to a size of about 1 to 3 mm.

An example of a continuous graphitizing furnace used in the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a vertical continuous graphitizing furnace. This continuous graphitization furnace has a material inlet 1 and a material outlet 7, and is provided with a gas inlet 11 and a gas outlet 2 through which a non-oxidizing gas can flow in a direction opposite to the flow direction of the material. ing. The furnace core tube 8 is provided with a graphitized zone 5 which is a high temperature region, and a pre-tropical zone 3 and a cooling zone 6 which are low temperature regions on both sides thereof. Between the pre-tropical zone 3 and the graphitization zone 5, there is a volatile graphitization catalyst deposition zone 4 which is a portion where the volatilized graphitization catalyst is cooled and deposited in a low temperature region. An induction coil 9 and a temperature measuring hole 10 for heating the furnace are provided around the furnace tube 8.

In the present invention, a step of pulverizing graphite or a mixture of materials can be provided if necessary. The pulverizing step may be performed before firing, but if it is performed after obtaining the graphitized material, a process for avoiding fusion of particles in the firing step or graphitizing step as in the case of performing pulverization before firing is performed in advance. It is preferable because there is no need to perform the application. Although there is no particular limitation on the pulverizing method, a known method such as a jet mill, a vibration mill, a pin mill, a hammer mill, or the like can be used. The average particle size after pulverization is preferably 1 to 100 μm, and 10 to 50 μm.
m is more preferred. If the average particle size is too large, the surface of the prepared electrode tends to be uneven.

The graphite obtained by the above-mentioned production method can be used as a material for a negative electrode for a lithium secondary battery of the present invention. For example, an organic binder and, if necessary, a solvent are mixed, and the obtained paste is integrated with a current collector to form a negative electrode for a lithium secondary battery. The obtained paste can be formed into a shape such as a sheet or a pellet. As the organic binder, for example, polyethylene,
Polypropylene, ethylene propylene polymer, butadiene rubber, styrene butadiene rubber, butyl rubber, and high ion conductive polymer compounds can be used. Examples of the polymer compound having a high ionic conductivity include polyvinylidene fluoride, polyethylene oxide, polyepihydrin, polyphosphazene, polyacrylonitrile, and the like. Among the organic binders, a polymer compound having a large ionic conductivity is preferable, and polyvinylidene fluoride is particularly preferable.

The content of the organic binder is preferably 3 to 20% by weight based on the mixture of the graphite particles and the organic binder. The solvent is not particularly limited, and N-methyl 2-pyrrolidone, dimethylformamide, isopropanol and the like are used. The amount of the solvent is not particularly limited, as long as it can be adjusted to a desired viscosity.
It is preferable to use 30 to 70% by weight.

In order to integrate the paste with a current collector to form a negative electrode for a lithium secondary battery, there is a method in which a paste whose viscosity is adjusted is applied to, for example, a current collector and dried. As the current collector, for example, a foil or mesh of nickel, copper, or the like can be used. Further, the integration can be performed by a pressure molding method such as a roll or a press.

The negative electrode for a lithium secondary battery thus obtained can be used for lithium secondary batteries such as lithium ion secondary batteries and lithium polymer secondary batteries. In a lithium ion secondary battery, usually, the above-mentioned negative electrode is arranged with a positive electrode facing the other with a separator interposed therebetween, and an electrolyte is injected.
Further, a lithium polymer secondary battery is usually manufactured by combining a positive electrode and a solid polymer electrolyte. The lithium secondary battery of the present invention is excellent in rapid charge / discharge characteristics and cycle characteristics, has a small irreversible capacity, and is particularly excellent in safety, as compared with a lithium secondary battery using a conventional carbon material.

The material used for the positive electrode of the lithium secondary battery in the present invention is not particularly limited.
₂ , LiCoO ₂ , LiMn ₂ O _4, etc. can be used alone or as a mixture. LiClO ₄ ,
LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃
A lithium salt such as, for example, ethylene carbonate, diethyl carbonate, dimethoxyethane, dimethyl carbonate, tetrahydrofuran, so-called organic electrolyte dissolved in a non-aqueous solvent such as propylene carbonate, a solid contained in a polymer solid electrolyte such as polyvinylidene fluoride Organic electrolytes can be used.

As the separator, for example, a nonwoven fabric, a cloth, a microporous film or a combination of these, which contains a polyolefin such as polyethylene or polypropylene as a main component, can be used. FIG. 3 shows a partial cross-sectional front view of an example of a cylindrical lithium ion secondary battery.
In FIG. 3, 12 is a positive electrode, 13 is a negative electrode, 14 is a separator, 15 is a positive electrode tab, 16 is a negative electrode tab, 17 is a positive electrode cover, 18 is a battery can, and 19 is a gasket.

[0022]

Embodiments of the present invention will be described below. (Vertical Continuous Graphitizing Furnace) The continuous graphitizing furnace used in the embodiment is shown in FIG. 1 described above. FIG. 2 shows the set temperature conditions in the furnace. The core tube is made of graphite. The maximum temperature range was 3000 ° C. The structure was such that nitrogen was flowed from the furnace core tube outlet and discharged from the inlet. The fired pellets are continuously introduced from the inlet of the furnace core tube, move inside the furnace core tube, and are discharged from the outlet. The graphitization catalyst volatilized from the pellets at a high temperature moves toward the entrance side by nitrogen, and is deposited on the pellets in a low temperature region to be reused.

Example 1 (Preparation of graphite particles) Coke powder 5 having an average particle size of 5 μm
0 parts by weight, tar pitch 20 parts by weight, average particle size 48 μm
Of silicon carbide and 10 parts by weight of coal tar were mixed at 200 ° C. for 1 hour. The resulting mixture was pulverized and pressed into a pellet of φ17 mm × 8 mm. The obtained pellets were heated at 900 ° C. in a nitrogen atmosphere using an electric furnace.
The temperature was raised to calcination. Next, the fired pellets were graphitized using the continuous graphite furnace. The passage time of the graphitized zone 5 was set to one hour. Next, the graphitized pellets were pulverized to obtain graphite particles having an average particle size of 20 μm. The lattice spacing (d002) determined by X-ray diffraction of the obtained graphite particles was 0.336 nm, and the value of the crystallite size Lc was 100 nm or more.

(Preparation of negative electrode for lithium secondary battery) To 90% by weight of the obtained graphite particles, 10% by weight of polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone in solid content was added and kneaded. Thus, a graphite paste was prepared. The produced graphite paste was applied to a rolled copper foil having a thickness of 10 μm, dried, and subjected to a surface pressure of 490 MPa (0.5 ton / cm ² ).
The sample was compression-molded under the following pressure to obtain a sample electrode. The thickness of the graphite particle layer was 90 μm and the density was 1.6 g / cm ³ .

(Negative Electrode Characteristics of Graphite Particles) The prepared sample electrode was subjected to constant current charging and discharging by a three-terminal method, and evaluated as a negative electrode for a lithium secondary battery. FIG. 4 is a schematic diagram of a lithium secondary battery used in the experiment. LiPF ₆ is used as an electrolyte 21 in a glass cell 20 by ethylene carbonate (E).
C) and dimethyl carbonate (DMC) (EC: DM
C = 1: 1 (volume ratio)), and a solution dissolved at a concentration of 1 mol / liter in a mixed solvent was added thereto.
2. The separator 23 and the counter electrode 24 were stacked and arranged, and the reference electrode 25 was hung from above on the surface. Lithium metal was used for the counter electrode 24 and the reference electrode 25, and a polyethylene microporous membrane was used for the separator 23. The battery was charged to 5 mV (V vs Li / Li ⁺ ) at a constant current of 0.5 mA / cm ² . 1
V (V vs Li / Li ⁺ ). The charge capacity in the first cycle is 390 mAh / g, and the discharge capacity is 360 mAh
/ g.

Comparative Example 1 Coke, tar pitch and coal tar were mixed in the same manner as in Example 1, and mixed at 200 ° C. for 1 hour. The obtained mixture was pulverized and pressed into a pellet of φ17 × 8 mm. The temperature of the obtained pellet was increased to 900 ° C. in a nitrogen atmosphere. Next, the pellets were placed in a graphite crucible, heated to 3000 ° C. in nitrogen using a resistance heating furnace, and held for 1 hour to graphitize. Thereafter, in the same manner as in Example 1, the graphitized pellets were pulverized to obtain graphite particles. The lattice spacing (d002) of the obtained graphite particles is 0.340.
mm and the crystallite size Lc were 600 nm, and the degree of graphitization was lower than that of the example. Next, the negative electrode characteristics were evaluated in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 370 mAh / g, and the discharge capacity was 330 mAh / g, and the discharge capacity was lower than in Example 1.

Example 2 50 parts by weight of coke powder having an average particle diameter of 5 μm, 20 parts by weight of tar pitch, 2 parts by weight of silicon carbide having an average particle diameter of 48 μm and 10 parts by weight of coal tar were mixed and mixed at 200 ° C. for 1 hour. did. The obtained mixture is pulverized, and φ17 mm × 8 mm
Under pressure into pellets. Thereafter, graphite particles were obtained in the same manner as in Example 1. The lattice spacing (d002) of the obtained graphite particles is 0.337 nm, and the crystallite size Lc is 80.
It was 0 nm. Next, the negative electrode characteristics were evaluated in the same manner as in Example 1. As a result, the charge capacity in the first cycle is 38
The discharge capacity was 0 mAh / g and the discharge capacity was 345 mAh / g.

Comparative Example 2 Coke, tar pitch and coal tar were mixed in the same manner as in Example 2 and mixed at 200 ° C. for 1 hour. The obtained mixture was pulverized and pressure-formed into a pellet of φ17 mm × 8 mm. The temperature of the obtained pellet was raised to 900 ° C. in a nitrogen atmosphere, and then the pellet was placed in a graphite crucible, heated to 3000 ° C. in nitrogen using a resistance heating furnace, and held for 1 hour to graphitize. . Thereafter, the graphitized pellets were pulverized in the same manner as in Example 1 to obtain graphite particles. The lattice spacing (d002) of the obtained graphite particles is 0.339 n
m, the crystallite size Lc was 650 nm, and the degree of graphitization was lower than in the examples. Next, the negative electrode characteristics were evaluated in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 355 mAh / g and the discharge capacity was 310 mAh / g.
The discharge capacity was lower than that of.

Example 3 50 parts by weight of coke powder having an average particle diameter of 5 μm, 20 parts by weight of tar pitch, 1 part by weight of silicon carbide having an average particle diameter of 48 μm and 10 parts by weight of coal tar were mixed and mixed at 200 ° C. for 1 hour. did. The obtained mixture is pulverized, and φ17 mm × 8 mm
Under pressure into pellets. Thereafter, graphite particles were obtained in the same manner as in Example 1. The lattice spacing (d002) of the obtained graphite particles is 0.335 nm, and the crystallite size Lc is 70.
It was 0 nm. Next, the negative electrode characteristics were evaluated in the same manner as in Example 1. As a result, the charge capacity in the first cycle is 37
The discharge capacity was 0 mAh / g and the discharge capacity was 325 mAh / g.

Comparative Example 3 Coke, tar pitch and coal tar were mixed in the same manner as in Example 3 and mixed at 200 ° C. for 1 hour. The obtained mixture was pulverized and pressure-formed into a pellet of φ17 mm × 8 mm. The temperature of the obtained pellet was increased to 900 ° C. in a nitrogen atmosphere. The pellets were then placed in a graphite crucible and heated to 3000 ° C. in nitrogen using a resistance heating furnace.
Graphitization was performed by holding for a time. Thereafter, the graphitized pellets were pulverized in the same manner as in Example 1 to obtain graphite particles. The lattice spacing (d002) of the obtained graphite particles was 0.340.
nm and the crystallite size Lc were 450 nm, and the degree of graphitization was lower than that in Example 3. Next, the negative electrode characteristics were evaluated in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 335 mAh / g, and the discharge capacity was 290 mAh / g, and the discharge capacity was lower than that in Example 3.

[0031]

According to the production method according to claims 1 and 2,
Lithium secondary battery with high degree of graphitization, high charge / discharge characteristics, excellent rapid charge / discharge characteristics, cycle characteristics, irreversible capacity in the first cycle, etc. Graphite particles suitable for use can be manufactured by a simple process that can be manufactured at low cost together with a reduction in man-hours. The negative electrode for a lithium secondary battery according to claims 3 and 4,
It has high charge / discharge characteristics, and is excellent in rapid charge / discharge characteristics, cycle characteristics, irreversible capacity in the first cycle, and the like. The lithium secondary battery according to claim 5 has high charge / discharge characteristics, and is excellent in rapid charge / discharge characteristics, cycle characteristics, irreversible capacity in the first cycle, and the like.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a vertical continuous graphitizing furnace used in the present invention.

FIG. 2 is a graph showing a temperature distribution in a vertical continuous graphitizing furnace used in an example of the present invention.

FIG. 3 is a partial cross-sectional front view of a cylindrical lithium secondary battery.

FIG. 4 is a schematic view of a lithium secondary battery used for measuring charge / discharge characteristics in Examples and Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insertion port 2 Discharge port 3 Preliminary zone 4 Precipitation zone for volatile graphitization catalyst 5 Graphitization zone 6 Cooling zone 7 Discharge port 8 Reactor core tube 9 Induction coil 10 Temperature measurement hole 11 Gas inlet 12 Positive electrode 13 Negative electrode 14 Separator 15 Positive electrode tab 16 Negative electrode tab 17 Positive electrode cover 18 Battery can 19 Gasket 20 Glass cell 21 Electrolyte 22 Sample electrode (negative electrode) 23 Separator 24 Counter electrode (positive electrode) 25 Reference electrode

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01M 10/40 C04B 35/54 A (72) Inventor Jun Fujita 3-3-1 Ayukawacho, Hitachi City, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. (72) Inventor Kazuo Yamada 3-1-1 Ayukawacho, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Yamazaki Plant

Claims (5)

[Claims] 1. A method for producing graphite, comprising the steps of mixing a graphitizable aggregate or graphite, a graphitizable binder and a graphitization catalyst to obtain a material mixture, a firing step and a graphitization step. A method for producing graphite, comprising: bringing a volatile component of a graphitization catalyst generated in a process into contact with a material mixture before graphitization. 2. The graphitization step is performed using a continuous graphitization furnace, and a volatile component of the graphitization catalyst generated in the high temperature region is brought into contact with a material mixture in a low temperature region before graphitization. The method for producing graphite according to claim 1, wherein 3. A negative electrode for a lithium secondary battery comprising graphite produced by the production method according to claim 1. 4. The negative electrode for a lithium secondary battery according to claim 3, wherein a mixture of graphite and an organic binder is integrated with a current collector. 5. A lithium secondary battery comprising the negative electrode according to claim 3 or 4 and a positive electrode.