JPH08180868A - Carbon material for lithium secondary battery negative electrode, its manufacture, carbon electrode and nonaqueous electrolytic lithium secondary battery - Google Patents

Abstract

PURPOSE: To provide a carbon material (carbon electrode) having a large lithium storing quantity, and a method for manufacturing it, and also provide a nonaqueous electrolytic lithium secondary battery with long charging and discharging cycle life and high discharging capacity. CONSTITUTION: A carbon material in which the C-axial crystallite size Lc determined from X-ray diffraction is not more than 20Å, the value of 1÷(Lc÷d002+1) is 0.17 or more when the 002 surface spacing is d002, and oxygen content is less than 3wt.% is used as a negative electrode 3. A petroleum or petroleum pitch, aromatic resin, mesocarbon microbead or polymer material is baked under inert or reductive atmosphere to form a negative electrode carbon material.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a carbon material for a negative electrode of a non-aqueous electrolyte lithium secondary battery and a method for producing the same. The present invention relates to a carbon electrode for a negative electrode of a non-aqueous electrolyte lithium secondary battery. The present invention relates to a novel non-aqueous electrolyte lithium secondary battery.

[0002]

2. Description of the Related Art With the miniaturization of electronic devices, high energy density of batteries is required. BACKGROUND ART A lithium secondary battery using lithium as a negative electrode active material has attracted attention as a type of high energy density secondary battery. In a conventional lithium secondary battery, metallic lithium is used as a negative electrode material, and a positive electrode containing lithium and an electrolytic solution in which a salt is dissolved in an aprotic organic solvent are used. However, when metallic lithium is used as the material for the negative electrode, there is a problem that lithium dendrite is deposited on the surface of the negative electrode due to repeated charging and discharging, especially when used as a secondary battery. This lithium dendrite grows through the diaphragm and has a high risk of short circuit with the positive electrode. Therefore, the secondary battery using metallic lithium as the material for the negative electrode has a shortcoming that the cycle life of charging / discharging is short.

As one method for solving this problem,
It has been proposed to use graphite as the material for the negative electrode.
In this method, graphite is used as a negative electrode, and a positive electrode containing lithium and a nonaqueous electrolytic solution are used. In this way, when charging,
In the negative electrode, lithium is occluded in the graphite layered structure,
A graphite intercalation compound containing lithium is produced. During discharge, lithium in the graphite intercalation compound of the negative electrode is released from the carbon layer and returns to the positive electrode.

Under extreme conditions of high temperature and high pressure, C ₂ Li is formed by a chemical reaction between graphite and lithium. However, in a lithium secondary battery using graphite as a negative electrode, when an intercalation compound of graphite and lithium is produced by electrochemical charging, one lithium is coordinated with six carbons (C ₆ It is known to have the maximum discharge capacity when it becomes Li), and theoretically, the discharge capacity of the negative electrode can be increased up to 372 mAh / g-carbon.

On the other hand, the inventor of the present invention has found that when an amorphous carbon material is used as the negative electrode material, the theoretical discharge capacity is 372 mAh / g-ca when graphite is used.
It has been found that a battery exceeding rbon may be obtained in some cases. This suggests that a bonding state other than intercalation in the graphite intercalation compound exists as a bonding state between the carbon atom and lithium. Conventionally, the detailed mechanism has been unknown.

On the other hand, various attempts have been made to relate the discharge capacity when a carbon material is used as a negative electrode to the physical parameters of the carbon material. For example, as such a parameter, 0 of the carbon material used for the negative electrode is used.
02 side of the plane spacing (d002), crystallite size in the C-axis direction (Lc), specific surface area, Raman spectroscopy R value (the amorphous structure peak intensity of 1360 cm ^-1 based on the based on the crystal structure 1580 cm ^-1 It is the ratio to the peak intensity, and the smaller R is, the higher the crystallinity is), the H / C atomic ratio, the pore size distribution, the pore volume, the line width between peaks of the first derivative absorption spectrum of ESR, the specific gravity, etc. Is being considered.

However, an attempt to uniformly explain the discharge capacity when a carbon material is used as a negative electrode by the structure of the carbon material and these parameters has not been successful.

[0008]

SUMMARY OF THE INVENTION The present invention has been proposed in view of such conventional circumstances, and new parameters relating to the structure and physical properties of the carbon material and the non-aqueous electrolyte lithium secondary battery containing the carbon material. Find the correlation with the discharge capacity when used as the negative electrode of, and based on the correlation,
An object of the present invention is to provide a carbon material for a negative electrode of a non-aqueous electrolyte lithium secondary battery having a large lithium storage capacity and a discharge capacity equal to or higher than the theoretical discharge capacity of a graphite electrode, a method for producing the same, and a carbon electrode. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery having a long charge / discharge cycle life and a high discharge capacity.

[0009]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present inventors have conducted a long-term study, and as a result,
Scientifically clarified the lithium storage mechanism for carbon materials with a small crystallite size, and based on this storage mechanism,
The correlation between the new parameters for the crystal structure of the carbon material and the discharge capacity when used as the material for the negative electrode was found. That is, according to the knowledge of the present inventors, it is possible to explain that the theoretical discharge capacity of graphite exceeds 372 mAh / g-carbon by using a carbon material having a small crystallite size as the negative electrode. Furthermore, this correlation has led to the acquisition of knowledge for obtaining a negative electrode material having an extremely large discharge capacity. The present invention has been completed based on such findings.

According to the present invention, the crystallite size Lc in the C-axis direction determined by X-ray diffraction is 20 angstroms or less, and 0
Non-aqueous electrolyte lithium secondary battery negative electrode in which 1 / (Lc / d002 + 1) has a value of 0.17 or more and the oxygen content is 3% by weight or less, where d002 (angstrom) is the surface spacing of 02 surfaces. Related to carbon materials for automobiles. In the present invention, a carbon raw material is heat-treated at 650 to 1100 ° C in an inert atmosphere, and further 650 to 1100 ° C in a reducing atmosphere.
The present invention relates to the method for producing a carbon material for a negative electrode, which is characterized in that the heat treatment is performed at The present invention relates to a carbon electrode for a negative electrode of a non-aqueous electrolyte lithium secondary battery comprising the carbon material for a negative electrode. The present invention relates to a non-aqueous electrolyte lithium secondary battery having the carbon electrode as a negative electrode and an electrode containing lithium as a positive electrode.

Carbon Material for Negative Electrode of Non-Aqueous Electrolyte Secondary Battery The carbon material for negative electrode of non-aqueous electrolyte lithium secondary battery of the present invention has a crystallite size Lc in the C-axis direction of 20 angstroms or less determined by X-ray diffraction. Is preferably 7 to 20 angstroms, more preferably 7 to 10 angstroms, and 1 ÷ (Lc ÷ when the surface spacing of 002 surfaces is d002.
The value of d002 + 1) (hereinafter, also referred to as X value) is 0.17 or more, preferably 0.20 or more, more preferably 0.2 to
0.33, particularly preferably 0.2 to 0.25 and having an oxygen content of 3% by weight or less, preferably 2% by weight or less,
It is more preferably 1% by weight or less, and particularly preferably 0.5% by weight or less.

A carbon material having Lc of more than 20 angstrom, that is, a carbon material having a high degree of crystallinity, is used as a material for a negative electrode of a secondary battery. It causes the decomposition of the electrolytic solution, which causes the deterioration of cycle characteristics and the decrease of charge / discharge efficiency. On the other hand, in the case of a carbon material having a small Lc, the surface area of the crystallite becomes large and the discharge capacity becomes large. The discharge capacity of the negative electrode using the carbon material with X smaller than 0.17 is less than 370 mAh / g.

The carbon material for the negative electrode of the present invention is preferably a carbon material having no functional group such as —OH or —COOH in the end portion of the carbon layer, that is, a carbon material having a low oxygen content. Carbon materials that do not have a functional group such as —OH and —COOH in the end portion of the carbon layer tend to have a larger lithium occlusion amount as compared with those having these functional groups. When used as a material, the discharge capacity tends to be larger. In addition, the value of the oxygen content in the present specification is a value measured by a combustion method, and specifically, a value measured as follows.

CHN Corder of Yanaco Analytical Industry
Using MT-5 type device, 1 to 3 with helium gas flow
A mg sample is decomposed at 950 ° C. to 1050 ° C., the generated gas is sent to the detection unit at a constant rate by a quantitative pump, and oxygen is quantitatively analyzed using antipyrine as a reference substance.

The form of the carbon material of the present invention is not particularly limited, and may be any of powder form, granular form, spherical form, fibrous form, film form and the like.

Production of carbon material for negative electrode of non-aqueous electrolyte secondary battery
Method The carbon material for a negative electrode of the present invention is a carbon raw material in an inert atmosphere or a reducing atmosphere at 650 to 1100 ° C.,
Preferably 650 to 1000 ° C., more preferably 650
It can be manufactured by heat treatment (baking) at ˜900 ° C., more preferably 700 to 800 ° C. As the carbon raw material, an organic material such as an easily graphitizable material, a non-graphitizable material, and a polymer material (synthetic and natural) can be used.

Typical organic materials used as starting materials (carbon materials) are: a) petroleum pitch, coal pitch,
b) a carbonizable polymer material (polymer), specifically,
Furan resin, polyacrylonitrile, rayon, cellulose, polycarbonate, and the like, c) aromatic resin in which an aromatic component is crosslinked with a crosslinking agent, and d) mesocarbon microbeads (MCMB) can be mentioned. Especially when it is carried out industrially, it is preferable to use the organic material a), b) or d) from the viewpoint of the characteristics and cost of the obtained carbon material. As the carbon raw material, these organic materials can be used alone or as a mixture.

In the present invention, the carbon material is carbonized by heat treatment. Regarding a specific heat treatment method, a suitable method differs depending on the characteristics of the carbon raw material to be used, and there is no particular limitation, and the carbon material of the present invention having the above characteristics may be obtained. For example, when using a coal-based or petroleum-based pitch as a carbon raw material, a known method,
For example, after infusibilizing by heating at 300 to 350 ° C. in air, it is preferable to perform heat treatment under the temperature condition of the above specific range. The specific means for heat-treating the carbon raw material is not particularly limited, and heat treatment means generally used in the production of carbon materials, such as an electric furnace and a gas furnace, can be used.

In the present invention, the heat treatment of the carbon raw material is performed in an inert atmosphere and then in a reducing atmosphere.
The inert atmosphere includes various inert gases such as nitrogen gas, argon, and helium under vacuum. The reducing atmosphere includes various reducing gases such as a mixed gas of an inert gas and hydrogen gas or an atmosphere of pure hydrogen gas. From the viewpoint of characteristics when the obtained carbon material is used as the carbon material for the negative electrode, it is preferable to heat-treat the carbon raw material in an inert atmosphere and then further heat it in a reducing atmosphere, specifically, a hydrogen atmosphere. . Carbon raw material (carbon raw material heat-treated in an inert atmosphere)
Is heat-treated in a reducing atmosphere to remove functional groups such as —OH and —COOH in the end portion of the carbon layer.

As a method for creating a reducing atmosphere, for example, in a space for heat treating a carbon raw material, for example, in an electric furnace,
A hydrogen atmosphere can be created by filling an inert gas such as nitrogen or argon and then circulating hydrogen.
The flow rate of hydrogen in this case is 0.2 m per 1 g of carbon raw material.
It is 1 / min or more, preferably about 0.25 to 0.60 ml / min, more preferably about 0.25 to 0.40 ml / min.

Carbon Electrode for Negative Electrode of Non-Aqueous Electrolyte Secondary Battery The carbon electrode of the present invention is a molded product of the carbon material of the present invention or a carbon material of another kind, such as carbon fiber or activated carbon. When the mixture of the carbon material of the present invention and the carbon fiber is used as the carbon material forming the molded body of the mixture, the proportion of the carbon fiber used is 15% by weight or less, preferably 5 to 15% with respect to the carbon material. It is good to set it as the weight%, More preferably, it is about 5-10 weight%. The use of carbon fibers or activated carbon can improve the discharge capacity of the carbon electrode for the negative electrode. However, if the proportion of carbon fiber or activated carbon used is too high, the discharge capacity of the carbon electrode for negative electrode tends to decrease.

In producing the carbon electrode, an additive other than the carbon material such as a binder can be used for the carbon material, if necessary. A fluorinated hydrocarbon polymer such as polytetrafluoroethylene can be used as the binder of the carbon material. The amount of the additive other than the carbon material is not particularly limited and may be adjusted within a range in which the adverse effect on the characteristics of the carbon electrode is small, specifically, 30% by weight or less based on the total amount of the carbon material, It is preferably 20% by weight or less, more preferably 10% by weight or less.

The shape of the carbon electrode of the present invention is not particularly limited and can be appropriately selected depending on the type and shape of the battery used. The carbon electrode of the present invention is suitable as a negative electrode of a non-aqueous electrolyte lithium secondary battery from the viewpoint of charge / discharge cycle life and discharge capacity.

Non-Aqueous Electrolyte Lithium Secondary Battery The non- aqueous electrolyte lithium secondary battery of the present invention relates to a lithium secondary battery using a carbon material having a small crystallite size as a material for a negative electrode. , By using the battery component such as the carbon electrode (negative electrode), the positive electrode, the electrolytic solution, the separator, the current collector, the gasket, the sealing plate, and the case of the present invention which has the carbon material of the present invention as a constituent Can be assembled by. FIG. 1 schematically shows an example of a lithium secondary battery.

An electrode containing lithium is used as the positive electrode. For example, an electrode using an intercalation compound containing a composite metal oxide represented by the general formula LiMO ₂ (where M represents at least one of Co, Ni, and Fe) as a positive electrode active material, an intercalation compound containing lithium. Is preferable, and particularly an electrode using LiCoO ₂ exhibits good characteristics as a positive electrode of a lithium secondary battery.

As the electrolytic solution, a non-aqueous electrolytic solution prepared by dissolving one or more electrolytes in a non-aqueous solvent can be used. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, tetrahydrofuran, 2-
Methyltetrahydrofuran, dioxolane, 4-methyldioxolane, sulfolane, 1,2-dimethoxyethane, dimethylsulfoxide, acetonitrile, N, N-
An aprotic solvent such as dimethylformamide, diethylene glycol or dimethyl ether can be used. The non-aqueous solvent used in the present invention,
Particularly preferred ether solvents that are stable even under a strong reducing atmosphere, for example, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane and the like.

As the electrolyte, salts which generate anions that are difficult to solvate, such as LiPF ₆ , LiClO ₄ , and L
_{iBF 4, LiClF 4, LiAsF 6} , LiSb
F ₆ , LiAlO ₄ , LiAlCl ₄ , LiPF ₆ , L
Salts containing lithium such as iCl and LiI can be used. As the separator, a liquid-retaining material, for example, a polyolefin-based porous film such as a porous polypropylene nonwoven fabric can be used.

The non-aqueous electrolyte lithium secondary battery of the present invention comprises:
It can be suitably used in a wide range of applications such as power sources for portable electronic devices, backup power sources for various memories and solar batteries, and electric vehicles.

[0029]

In a lithium secondary battery using graphite having a large crystallite size as a negative electrode, an intercalation compound is formed between carbon atoms of the graphite and lithium by charging, and lithium is released from graphite by discharging. At this time, theoretically,
A maximum discharge capacity of 372 mAh / g is obtained. On the other hand, the present inventor has found that when a carbon material having a small crystallite size is used as the negative electrode, a lithium secondary battery having a discharge capacity exceeding 372 mAh / g can be obtained.

The discharge capacity of the lithium secondary battery depends on the amount of lithium stored in the negative electrode. That is, the larger the amount of lithium stored in the negative electrode, the larger the discharge capacity. FIG. 2 shows a model showing the lithium storage mechanism of the carbon electrode of the present invention. In the lithium secondary battery of the present invention, lithium is occluded in the negative electrode by charging. It is considered that these lithiums have three kinds of bonding states with the carbon atom of the negative electrode.

First, lithium is occluded between the carbon layers in the laminated structure of the negative electrode to form an intercalation compound. The electronic state of lithium occluded in this bonded state is considered to be the same as the electronic state of lithium occluded in the graphite electrode because it exists between the carbon layers. Lithium occluded in such a bound state is called Li _L. Here, since a carbon material with a small crystallite size has a stacking irregularity of the carbon surface, the carbon layer has no correlation with the adjacent carbon layer. It seems that the tacaration cannot be combined. Therefore, the amount of lithium occluded in the laminated structure is C ₆ Li.
Is smaller than Then, it is predicted that Li _L decreases as the crystallite size decreases.

Second, it is considered that the carbon atoms at the end portion of the carbon layer which cannot intercalate with lithium are laterally bonded with lithium to form a charge transfer compound as shown in FIG. Lithium occluded in such a bound state is called Li _E. It is expected that Li _E will increase as the crystallite size decreases.

Thirdly, as shown in FIG. 2, it is conceivable that lithium is occluded by carbon atoms on the crystallite surface to form a charge transfer compound. It is considered that the electronic state of lithium stored in this bonded state is the same as the electronic state of lithium stored in the end portion. L of this kind of lithium
Call i _S. When the crystallite size becomes smaller, Li
_S is expected to increase. The above Li _E and L
i _S is believed to be similar to lithium in lithium-doped polyacetylene.

Li _L inserted between carbon layers is called intercalation lithium. In addition, Li _E occluded at the end portion of the carbon layer and Li _S occluded on the surface of the crystallite are referred to as doping lithium. In the intercalation lithium and the doping lithium, the 2S electrons of lithium all move to the LUMO (lowest unoccupied molecular orbital) of the carbon negative electrode to stabilize the system. Therefore, these lithiums become ionic lithium. The total amount Li _{T of} lithium occluded in the carbon electrode (negative electrode) is shown by the following formula, and the discharge capacity of the negative electrode depends on Li _T.

The Li _T = Li _L + Li _E + Li _S graphite crystal structure has a carbon 6-membered ring plane developed two-dimensionally,
Based on a three-dimensional laminated structure. Since the crystallite size of graphite is generally large, most of the lithium occluded by the negative electrode using graphite enters the carbon layer and becomes Li _L. In the case of graphite, Li _E and Li _S are too small as compared with Li _L and can be ignored. Theoretically, Li _L can store up to C ₆ Li.

On the other hand, when the crystallite size of the carbon material used for the negative electrode becomes small, Li _E and Li _S increase, and it cannot be ignored compared with Li _L. As shown in the model in FIG. 2, in the present invention, the smaller the crystallite size of the carbon material used for the negative electrode, the more Li _S and L
It is considered that the negative electrode discharge capacity increases due to the increase in i _E. That is, in the present invention,
The reduction of Li _L due to the small crystallite size is
It is considered that the increase in Li _E and Li _S sufficiently compensates for this.

Further, Li _E depends on the kind of atoms in the end portion of the carbon layer. That is, -OH is added to the end portion of the carbon layer,
When a functional group such as —COOH is present, lithium cannot generate a charge transfer compound with the carbon atom in the end portion of the carbon layer, and Li _E is reduced. This reflects the fact that the discharge capacity of the negative electrode can be further increased by using a carbon material having no functional group such as —OH and —COOH in the end portion of the carbon layer in the present invention. .

Furthermore, Li _S depends on the size of the surface area of the crystallite. Lc is the stacking height of the layer surfaces, d002 is the interplanar spacing of the carbon layers, and the value of Lc / d002 + 1 represents the number of carbon layers stacked per one crystallite. Usually, as the number of stacked layers increases, that is, as Lc increases, the surface area of the crystallite decreases. That is, the reciprocal of Lc / d002 + 1 is considered to be proportional to the surface area of the crystallite of the carbon material. Therefore, the larger the X value, that is, the value of 1 / (Lc / d002 + 1), the larger Li _{S and} the larger the discharge capacity. This reflects the fact that the discharge capacity is further increased when a carbon material having a large crystallite surface area is used in the present invention.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to embodiments.

Example 1 [Preparation of carbon raw material] Double amount of hydrogenated anthracene oil was added to coal tar pitch having a softening point of 100 ° C., quinoline insoluble content of 0.2% and benzene insoluble content of 30%, and the mixture was heated at 6 ° C. at 430 ° C.
The mixture was heated for 0 minutes, and the hydrogenated anthracene oil was removed at 300 ° C. under reduced pressure to obtain reduced pitch. Next, nitrogen gas was introduced into this reduced pitch to obtain a mesophase pitch having a softening point of 310 ° C., a quinoline insoluble content of 50%, a benzene insoluble content of 98%, and a mesophase content of 90% or more.

[Manufacture of Carbon Material for Negative Electrode] The mesophase pitch obtained as described above is melted, shaped into a ribbon-shaped carbon raw material film through a slit, and heated at 300 to 350 ° C. in an air atmosphere to make it infusible. I went. The ribbon-shaped infusible carbon film thus obtained was carbonized at 1000 ° C. in an inert gas atmosphere to prepare a carbon film having a width of 8 mm and a thickness of 0.01 mm, and then continuously heated to 1000 ° C. in a hydrogen gas atmosphere at 30 ° C. Heat treatment was performed for a minute. When the obtained ribbon-shaped carbon film was subjected to X-ray diffraction, the interlayer distance d002 was 3.48 angstrom, C
The crystallite size Lc in the axial direction was 16 angstrom (X value is 0.179).

[Production of Lithium Secondary Battery] The obtained ribbon-shaped carbon film was cut into a length of 20 mm, and the upper end portion was sandwiched by clips to form a carbon electrode (negative electrode). A negative electrode test cell was constructed by using a solution of LiClO ₄ dissolved in propylene carbonate at a concentration of 1 mol / liter as an electrolytic solution and metallic lithium as a counter electrode (positive electrode).

[Measurement of Discharge Capacity] The test cell was charged and discharged at a constant current of a current density of 50 mAh / g-carbon. X-ray diffraction parameter of carbon film used for negative electrode [Lc (angstrom), d002 (angstrom), X value (= 1 ÷ (Lc ÷ d002 + 1))]
Then, the oxygen content was measured and the discharge capacity was measured. The results are shown in Table 1.

The charging and discharging conditions were as follows: Charging: charging to 10 mV against metallic lithium,
Next, the battery was charged at a constant voltage of 10 mV, and when the current reached an equilibrium current (usually about 1 × 10 ^{−5 to} 5 × 10 ⁻⁶ A), the charging was terminated; 2.0
The discharge was terminated when the voltage exceeded V.

Example 2-4 [Production of Carbon Material for Negative Electrode] The procedure of Example 1 was repeated, except that mesophase pitch was used as a raw material of the carbon film and the firing temperature of the infusible carbon film was changed. That is, the mesophase pitch is melted and formed into a ribbon-shaped carbon film through a slit, and the mesophase pitch is heated to 300 in an air atmosphere.
It was made infusible by heating at ~ 350 ° C. After firing the obtained ribbon-shaped infusible carbon film under different temperature conditions in an inert gas atmosphere, subsequently, in a hydrogen gas atmosphere, heat treatment is performed at the same temperature as the firing temperature for 30 minutes,
Three different types of carbon materials (Examples 2 to 4) were produced.

The firing temperature of the infusible film in each example is as follows: Example 2: 810 ° C., Example 3: 750 ° C., Example 4: 700 ° C.

[Preparation of Lithium Secondary Battery] A negative electrode test cell was constructed in the same manner as in Example 1 except that the ribbon-shaped carbon film thus obtained was used as the carbon material for the negative electrode.

[Measurement of Discharge Capacity] With respect to the ribbon-shaped carbon film produced under the above conditions, X-ray diffraction parameters were determined in the same manner as in Example 1 to measure oxygen content and discharge capacity. The results are shown in Table 1.

Example 5 [Manufacture of Carbon Material for Negative Electrode] In the same manner as in Example 1, mesophase pitch was melted and formed into a ribbon-shaped carbon film through a slit, and 300-350 in an air atmosphere.
It was made infusible by heating at ℃. The obtained ribbon-shaped infusible carbon film was carbonized at 1000 ° C. in an inert gas atmosphere.

[Production of Lithium Secondary Battery] A negative electrode test cell was constructed in the same manner as in Example 1 except that the ribbon-shaped carbon film thus obtained was used as the negative electrode.

[Measurement of Discharge Capacity] With respect to the ribbon-shaped carbon film produced under the above conditions, X-ray diffraction parameters were determined in the same manner as in Example 1 to measure the oxygen content and the discharge capacity.

Examples 6-8 In the same manner as in Example 1, the mesophase pitch was melted, formed into a ribbon-shaped carbon film through a slit, and heated at 300 to 350 ° C. in an air atmosphere to make it infusible.
The obtained ribbon-shaped infusible carbon film was fired in an inert gas atmosphere to prepare three types of carbon materials (Examples 6-8) having different firing temperatures. The firing temperature is as follows.

Example 6: 810 ° C, Example 7: 750 ° C, Example 8: 700 ° C.

[Preparation of Lithium Secondary Battery] A negative electrode test cell was constructed in the same manner as in Example 1 except that the ribbon-shaped carbon film thus obtained was used as the negative electrode carbon material.

[Measurement of Discharge Capacity] Regarding the ribbon-shaped carbon film (Example 6-8) produced under the above conditions, the X-ray diffraction parameters were determined in the same manner as in Example 1.
The oxygen content was measured and the discharge capacity was measured. The results are shown in Table 1.

[0056]

Table 1 Lc d002 X value Discharge capacity Oxygen content (mAh / g) (wt%) Example 1 16 3.48 0.179 400 0.05 Example 2 15 3.50 0.189 480 0.08 Example 3 14 3.51 0.200 510 0.10 Example 4 13 3.52 0.213 530 0.10 Example 5 16 3.48 0.179 306 0.50 Example 6 15 3.50 0 .189 407 0.90 Example 7 14 3.51 0.200 440 1.40 Example 8 13 3.52 0.213 460 2.40 .

Examples 9 and 10 [Production of carbon material for negative electrode] 3 kg of dehydrated coal tar
heat treatment under a pressure of cm ^{2 at} a temperature of 385 ° C. for 14 hours, and the generated spherulites are separated using a high temperature centrifuge,
After washing with light oil and medium oil, it was dried at 150 ° C. for 3 hours under a nitrogen gas atmosphere. The obtained MCMB (mesocarbon microbeads) was heat-treated at 800 ° C. for 1 hour in an inert gas atmosphere, and then heat-treated at 800 ° C. for 30 minutes in a hydrogen gas atmosphere to obtain a powdery carbon material (d002 = 3). .52 Angstrom, Lc =
15 angstrom, X = 0.19, oxygen content = 0.
10% by weight).

[Preparation of Composite Carbon Electrode] Next, MCMB after this heat treatment and pitch-based carbon fiber (d002 = 3.45 angstrom) were mixed at a mixing ratio as shown in Table 2, and 100 parts by weight of the mixture. On the other hand, 10 parts by weight of polytetrafluoroethylene (D-1 manufactured by Daikin Industries, Ltd.) was mixed, uniformly stirred in a liquid phase (in water), and then dried to obtain a paste. The obtained paste-like composite carbon material 30
mg is crimped onto a nickel mesh as a current collector,
A carbon electrode (negative electrode) was produced by vacuum drying at 200 ° C. for 6 hours.

[Preparation of Lithium Secondary Battery] A carbon electrode (Example 9) prepared as described above or a carbon electrode (Example 10) prepared in the same manner as above except that no pitch-based carbon fiber was used. LiClO as negative electrode and positive electrode
₄ as the electrolytic solution at a concentration of 1 mol / liter, LiCl
Propylene carbonate in which O ₄ was dissolved was used as a separator, and a polypropylene nonwoven fabric was used to manufacture a lithium secondary battery having a structure shown in FIG.

[Measurement of Discharge Capacity] The charge / discharge characteristics of the obtained secondary battery were measured by constant current charge / discharge of 0.1 mA / cm ² . Charging is performed to 0.01 V against metallic lithium and then at 0.01 V at a constant voltage, and the current becomes a balanced current (usually about 1 × 10 ^{−5 to} 5 × 10 ⁻⁶ A). I finished charging. The discharge capacity was the capacity up to the time when the battery voltage exceeded 2.0V.

[0061]

[Table 2] The discharge capacity of the battery using the pitch-based carbon fiber used as the mixed material as the electrode is 150 mAh / g.
However, if the pitch-based carbon fiber is added to the carbon material of the present invention in an amount of 5 to 1,
A battery using a composite carbon electrode mixed with 5 wt% can obtain a high discharge capacity. That is, the discharge capacity of Example 9 including the pitch-based carbon fiber was generally higher than that of Example 10, which is an effect of the composite carbon electrode.

Example 11 A carbonized precursor was obtained by heat-treating an organic polymer polycarbonate as a starting material at 700 ° C. for 3 hours under vacuum. Next, the carbonization precursor was fired in a hydrogen atmosphere at 700 ° C. for 30 minutes to obtain a carbon material. The obtained carbon material was cooled and then pulverized to prepare a carbon electrode in the same manner as in Example 9 except that carbon fiber was not used.
The line diffraction parameters were evaluated in the same manner as in Example 1,
The negative electrode discharge capacity was measured by the same method as in Example 9. Further, the oxygen content of the obtained carbonaceous material was measured. The results are shown in Table 3.

Example 12 An organic polymer polycarbonate was used as a starting material and heat-treated at 700 ° C. for 3 hours under vacuum to obtain a carbonization precursor. Next, the carbonization precursor was fired at 700 ° C. for 120 minutes in a hydrogen atmosphere to obtain a carbon material. After cooling, the mixture was pulverized, the X-ray diffraction parameter was evaluated by the same method as in Example 1, and the negative electrode discharge capacity was measured by the same method as in Example 9. Further, the oxygen content of the obtained carbonaceous material was measured. The results are shown in Table 3.

Example 13 An organic polymer polycarbonate was used as a starting material (carbon material) and heat-treated at 700 ° C. for 3 hours under vacuum to obtain a carbon material. The obtained carbon material was cooled and then pulverized to prepare a carbon electrode in the same manner as in Example 9, and its X-ray diffraction parameter was evaluated in the same manner as in Example 1 to measure the negative electrode discharge capacity. The measurement was performed in the same manner as in Example 9. Further, the oxygen content of the obtained carbonaceous material was measured. The results are shown in Table 3.

[0065]

Table 3 Lc d002 X value Discharge capacity Oxygen content (mAh / g) (wt%) Example 11 7.60 3.72 0.329 610 1.0 Example 12 7.54 3.73 0.331 650 0.1 Example 13 7.64 3.71 0.327 550 3.0 .

The discharge capacities of Examples 11 and 12 are higher than those of Example 13. This is because the functional groups such as -COOH and -OH in the end portion of the carbon layer of the carbon material used for the carbon electrode (negative electrode) are reduced by firing in a hydrogen atmosphere, so that the stored Li _E increases and the discharge capacity increases. It is considered to be a thing.

Correlation between X Value and Discharge Capacity Based on the results of the respective examples in which the oxygen content is 0.1% by weight or less, the X value, that is, the value of 1 / (Lc / d002 + 1) and the discharge of the negative electrode. The correlation of capacity is shown in FIG. As shown in FIG. 3, it can be seen that the discharge capacity increases as the X value increases, and that a discharge capacity of 370 mAh / g or higher can be obtained when the X value is 0.17 or higher.

[0068]

As is clear from the results of the examples, according to the present invention, a new parameter (L) relating to crystals of a carbon material having a newly found correlation with discharge capacity is obtained.
Since the characteristics of the carbon material for the negative electrode are defined based on (c and X value), the lithium occlusion amount is large by utilizing this relationship.
It is possible to provide a non-aqueous electrolyte lithium secondary battery having a discharge capacity equal to or higher than the theoretical capacity of a graphite electrode.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view schematically showing an example of a non-aqueous electrolyte lithium secondary battery.

FIG. 2 is a schematic diagram showing a state of lithium occluded in a carbon electrode.

FIG. 3 is a graph showing the correlation between the X value and the discharge capacity of the carbon material for negative electrode in the non-aqueous electrolyte lithium secondary battery of the present invention.

[Explanation of symbols]

 1 Positive Electrode 2 Separator 3 Negative Electrode 4 Case 5 Sealing Plate 6 Current Collector 7 Insulating Packing

Front page continuation (72) Inventor Chiharu Yamaguchi 4-1-2 Hiranocho Chuo-ku, Osaka City, Osaka Prefecture Osaka Gas Co., Ltd.

Claims (8)

[Claims] 1. A crystallite size Lc in the C-axis direction determined by X-ray diffraction is 20 angstroms or less, and when the 002 plane spacing is d002 (angstrom), 1 ÷
A carbon material for a non-aqueous electrolyte lithium secondary battery negative electrode, which has a value of (Lc ÷ d002 + 1) of 0.17 or more and an oxygen content of 3% by weight or less. 2. A carbon material for a negative electrode of a non-aqueous electrolyte lithium secondary battery, which has a value of 1 ÷ (Lc ÷ d002 +1) of 0.20 or more and an oxygen content of 1.0% by weight or less. 3. A carbon raw material is added under an inert atmosphere to 6
The method for producing a carbon material for a negative electrode according to claim 1, wherein the heat treatment is performed at 50 to 1100 ° C., and further the heat treatment is performed at 650 to 1100 ° C. in a reducing atmosphere. 4. The carbon raw material 1 is subjected to a heat treatment under a reducing atmosphere.
The method for producing a carbon material for a negative electrode according to claim 3, which is performed in a hydrogen atmosphere at a flow rate of 0.2 ml / min or more per g. 5. The organic material comprising at least one selected from the group consisting of petroleum-based pitch, coal-based pitch, aromatic resin, mesocarbon microbeads and polymer material as the carbon raw material. 4. The method for producing the carbon material for a negative electrode according to 4. 6. A carbon electrode for a negative electrode of a non-aqueous electrolyte lithium secondary battery, which comprises the carbon material for a negative electrode according to claim 1 as a constituent element. 7. A non-aqueous electrolyte lithium secondary containing the mixture of the carbon material for negative electrode according to claim 1 and carbon fiber as a constituent element, and the content of carbon fiber is 5 to 15% by weight of the carbon material. Composite carbon electrode for battery negative electrode. 8. A non-aqueous electrolyte lithium secondary battery having the carbon electrode according to claim 6 or 7 as a negative electrode and an electrode containing lithium as a positive electrode.