JP2917317B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery using fine fibrous graphite as a negative electrode material.

[Summary of the Invention]

The present invention relates to a non-aqueous electrolyte secondary battery comprising a negative electrode, a positive electrode, and a non-aqueous electrolyte, wherein the negative electrode material has a fine fibrous shape having a half-value width of an X-ray diffraction peak corresponding to a 002 plane spacing of 1 mm or less. By using a combination of graphite and a carbonaceous material, the flatness of the discharge voltage is improved, and at the same time, excellent charge / discharge cycle characteristics are realized.

[Conventional technology]

The remarkable progress of electronic technology in recent years is
Lightening has been realized one after another. As a result, batteries that can be used as portable power sources are becoming smaller and smaller.
Light weight and high energy density are demanded.

Conventionally, aqueous batteries such as lead batteries and nickel cadmium batteries have been mainly used as secondary batteries, but these batteries exhibit excellent cycle characteristics, but are not suitable in terms of battery weight and energy density. It cannot be said that the characteristics are satisfactory.

Under such circumstances, research and development of non-aqueous electrolyte secondary batteries using lithium or a lithium alloy for the negative electrode have been actively carried out, and some of them have begun to be commercialized. This battery has excellent features of high energy density, light weight, and low self-discharge, and is expected to be widely used as the power supply for transportation.

However, when lithium or a lithium alloy is used for the negative electrode, lithium is inactivated and deposited in a powder form with repetition of a charge / discharge cycle, and lithium grows in a dendrite shape during charging, and micropores or There are drawbacks such as reaching the positive electrode through the inter-fiber voids of the separator non-woven fabric and causing an internal short circuit, which is a major obstacle to practical application.

On the other hand, a non-aqueous electrolyte secondary battery using a carbon material for the negative electrode is composed of lithium previously supported on the carbon material by a chemical or physical method, and lithium in the crystal structure of the compound used for the positive electrode active material. Or intercalation / deintercalation between carbon hexagonal mesh planes of lithium or the like present in the electrolytic solution. Dendritic precipitation of lithium metal or the like accompanying repetition of charge / discharge cycles is observed. And shows excellent life performance over several hundred times.

[Problems to be solved by the invention]

By the way, in a non-aqueous electrolyte secondary battery using a carbon material for the negative electrode, the type of carbon material used greatly affects the characteristics of the battery.

For example, when a certain type of organic polymer compound or composite is fired at a high temperature under an inert gas atmosphere, or when a carbonaceous material obtained by pulverizing cokes such as pitch coke is used, excellent life characteristics are exhibited as described above. However, the voltage change depending on the depth of discharge is large in the charge / discharge curve, and the battery capacity greatly depends on the set value of the discharge end voltage.

When artificial graphite is used, the voltage flatness during charge and discharge is excellent, but in general, not only the amount of light metal ions such as Li that can be intercalated / deintercalated is small, but also it is deactivated every cycle. This is not practical as a negative electrode material for non-aqueous electrolyte secondary batteries.

Therefore, the present invention has been proposed in view of such conventional circumstances, and has an object to provide a non-aqueous electrolyte secondary battery having excellent voltage flatness at the time of discharge and excellent charge-discharge cycle life. I do.

[Means for solving the problem]

The present inventors have studied various carbon materials as negative electrode materials for non-aqueous electrolyte secondary batteries, and have found that fine fibrous graphite exhibits excellent characteristics.

The non-aqueous electrolyte secondary battery of the present invention has been completed on the basis of this finding, and has a fibrous graphite having a half width of an X-ray diffraction peak corresponding to the 002 plane spacing of 1 mm or less, and a carbonaceous material. It comprises a negative electrode containing a material, a positive electrode, and a non-aqueous electrolyte.

In the present invention, the carbon material used for the negative electrode is prepared by introducing various hydrocarbon compounds together with a carrier gas such as hydrogen or argon into a reaction tube controlled at about 800 to 1200 ° C., and forming a catalyst (Fe, Fe / Ni alloy) in the presence of a fibrous carbon obtained by the so-called vapor phase growth method, which is formed as carbonaceous material on a substrate such as graphite or quartz glass placed in a tube in an inert gas atmosphere. 1800-3000
It was heat-treated at ℃ to obtain fine fibrous graphite. By performing the heat treatment, a graphite structure is formed, and the half value width of the X-ray diffraction peak corresponding to the spacing between the 002 faces becomes 1 ° or less.

Examples of the hydrocarbon compound as a raw material include aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, compounds in which substituents are bonded to these hydrocarbons, and mixtures thereof. Specifically, methane, propane, ethylene, benzene, naphthalene, 1,2-dichloroethylene, 1,2-dichloroethane, 1,2-dibromoethane, ethanol, anthracene, acenaphthylene, furfuryl alcohol, furfural, phenol, diphenyl, etc. Among them, aromatic hydrocarbons such as benzene are preferable.

The fine fibrous graphite used has a diameter of 1 μm or less,
The length is preferably 1 mm or less, the diameter is 0.1 μm or less,
More preferably, the length is 500 μm or less. Furthermore, it is desirable that the ratio of the diameter to the length exceeds 1:20.

The fine fibrous graphite described above may be used alone for the negative electrode, or may be used in combination with a carbonaceous material. In other words, by using a composite material in which a carbonaceous material is supported between fibers of fine fibrous graphite for the negative electrode, the energy density can be improved in addition to the good voltage flatness during discharge and the good charge / discharge cycle life. Can be.

The composite material is obtained by heating the fine fibrous carbon obtained by the vapor phase growth method to graphitize by heating to 1800 to 3000 ° C. in an inert gas atmosphere, and then converting the liquid organic polymer material or the solid organic polymer material into a solvent. It is immersed in a dissolved solution to impregnate it, and further heated to 800 to 1700 ° C. in an inert gas atmosphere to be fixed between fibers as a carbonaceous material. Hereinafter, an example of the manufacturing method will be described.

In the case of using the organic polymer material which is liquid at room temperature when producing the composite material, it is used as it is or as a solution for impregnation with a material prepared by diluting with a solvent to have an appropriate viscosity. When an organic polymer material that is solid at room temperature is used, it is dissolved in an appropriate solvent or a material obtained by uniformly dispersing particles in an appropriate dispersion medium is used as an impregnating liquid.

Then, a predetermined amount of the fine fibrous graphite is immersed in an impregnation liquid containing an organic polymer material. At this time, in order to move all the necessary amount of the organic polymer material between the fibers, it is desirable to adjust the liquid concentration so that the amount of the impregnating liquid can be entirely absorbed between the graphite fibers.

The fine fibrous graphite impregnated with a predetermined amount of the organic polymer material is dried at a temperature at which the solvent or the dispersion medium can be sufficiently removed. Next, the temperature is kept at 800 to 1700 ° C. for several hours in an inert gas atmosphere to fix the organic polymer material existing between the fine fibrous graphite as a carbonaceous material. The mixture is allowed to cool to around room temperature in an inert gas atmosphere, and the fine fibrous graphite / carbonaceous material composite material is taken out. The composite material is pulverized by a pulverizer such as a mortar, a ball mill, a vibration mill, or the like, and then classified by a sieve to remove coarse particles to obtain a negative electrode material.

As the organic polymer material for obtaining the carbonaceous material, various materials can be used, for example, polyacrylonitrile resin, vinyl acetate resin, polyvinyl alcohol resin, polyvinyl acetal resin, ABS resin, polyimide resin,
Polyvinylidene chloride resin, furfuryl alcohol resin,
Furan resin, phenol resin, polyamide resin, petroleum pitch, coal pitch and the like are used.

The solvent and the dispersion medium for obtaining the impregnating liquid may be appropriately selected according to the type of the organic polymer material.

In the case of the above-mentioned composite material, the proportion of the fine fibrous graphite in the composite material is preferably 60% by weight or more. More preferably, it is% by weight.

On the other hand, as the positive electrode material, any material may be used as long as it is used for this type of battery, but it is particularly preferable to use a material containing a sufficient amount of Li. For example, LiMn ₂ O ₄ or the general formula LiMO ₂ (where M represents at least one of Co and Ni. Therefore, for example, LiCoO ₂ and LiCo
_0.8 Ni _0.2 O ₂ ), an intercalation compound containing Li, and the like are suitable.

The non-aqueous electrolyte is prepared by appropriately combining an organic solvent and an electrolyte, and any of these organic solvents and electrolytes can be used as long as they are used for this type of battery.

For example, as the organic solvent, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran,
3-dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole and the like.

As electrolytes, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , Li
B (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiCl, LiBr and the like.

〔Example〕

Hereinafter, the present invention will be described based on specific experimental results.

First, an example of a nonaqueous electrolyte secondary battery using fine fibrous graphite alone for the negative electrode will be described.

Example 1 Using benzene as a hydrocarbon compound, vapor-phase growth was performed at 1000 ° C., and the obtained fine fibrous carbon material was heated at 2000 ° C. under an inert gas to obtain fine fibrous graphite.

FIG. 1 shows X-ray diffraction spectra of this material before and after graphitization. The device used for the measurement was a Geigerflex RAD IIC device (anti-cathode: Cu) manufactured by Rigaku Corporation.

The X-ray parameter values obtained from FIG. 1 are as shown in Table 1.

Next, using this fine fibrous graphite, a secondary battery for a coin-type nonaqueous electrolyte-based negative electrode test as shown in FIG. 2 was prototyped.

First, 0.035 g of a negative electrode mixture consisting of 80 parts by weight of fine fibrous graphite and 20 parts by weight of polyvinylidene fluoride as a binder was used.
Pressure molding was performed together with a stainless steel net (5) having a diameter of 15 mm and a wire diameter of 50 μm to obtain a disk-shaped negative electrode (4) having a diameter of 15.3 mm and a thickness of 0.2 mm. The negative electrode (4) is electrically connected to the outside of the battery through a copper current collector (6) spot-welded to the inside of a stainless steel negative electrode can (7) plated with nickel on the outside. .

On the other hand, the positive electrode (1) is composed of 85 parts by weight of LiCoO _{2 as} an active material,
1 g of a positive electrode mixture composed of 10 parts by weight of graphite as a conductive agent and 5 parts by weight of polytetrafluoroethylene as a binder was press-formed into a disk having a diameter of 15.3 mm and a height of 1.7 mm. The positive electrode (1) is electrically connected to the outside of the battery via an aluminum current collector (2) spot-welded to the inside of a stainless steel positive electrode can (3) plated with nickel on the outside. .

The positive electrode (1) and the negative electrode (4) were placed facing each other via a microporous polypropylene separator (8) after adjusting the residual moisture value to 300 ppm or less by vacuum drying.

The electrolytic solution was prepared by dissolving LiPF ₆ at a ratio of 1 mol / in an equal volume mixed solvent of propylene carbonate and 1,2-dimethoxyethane, adjusting the residual water content to 20 ppm or less, and injecting 200 µ of the solution. did.

In addition, between the positive electrode can (3) and the negative electrode can (7), a polypropylene gasket (9) having asphalt coated on its surface was disposed. Therefore, this gasket (9)
Is compressed between the negative electrode can (7) and the negative electrode can (7) by caulking of the positive electrode can (3), and the airtightness inside the battery is maintained.

With the above configuration, a coin-type negative electrode test battery (Example Battery 1) having a diameter of 20 mm and a height of 2.5 mm was assembled.

Comparative Example 1 Commercially available artificial graphite (manufactured by Lonza, KS-1) was used as a negative electrode material.
A coin-type negative electrode test battery (Comparative Battery 1) was assembled in the same manner as in Example 1 except for using 5).

Comparative Example 2 A coin-type negative electrode test battery (Comparative Example Battery 2) was assembled in the same manner as in Example 1 except that a commercially available carbonaceous material (pitch coke, manufactured by Mitsubishi Kasei Corporation) was used as the negative electrode material.

Comparative Example 3 A coin-type negative electrode test battery (Comparative Battery 3) was assembled in the same manner as in Example 1 except that a commercially available carbon fiber (no graphitization treatment) was used as the negative electrode material.

To the test cell assembled in the Examples and Comparative Examples described above, after the constant current charging until the graphite material 1g per charged amount 210mAH to the electrode area to the reference at a current density of 1 mA / cm ^2,
Similarly, the cycle of performing constant current discharge at a current density of 1 mA / cm ² until the voltage reached 2.9 V was repeated, and the charge / discharge efficiency and cycle life were examined. Note that the charge / discharge efficiency in each cycle was calculated from the formula of (discharge capacity up to 2.9 V / charge capacity) × 100.

FIG. 3 shows Example battery 1, Comparative example battery 1, and Comparative example battery.
2 shows the charge and discharge characteristics of the battery of Comparative Example 3 at the 50th cycle.

The battery 1 of the example and the battery 1 of the comparative example have good flatness of the voltage of the charge / discharge curve, and the discharge capacity does not largely change depending on the set value of the end voltage in a practical range. On the other hand, in the comparative example battery 2 and the comparative example battery 3, the voltage continuously changes depending on the charge / discharge depth, and the discharge capacity may greatly change depending on the set value of the end voltage.

FIG. 4 shows the change in charge / discharge efficiency as the number of charge / discharge cycles of these batteries increases.

In Comparative Example Battery 1 using general artificial graphite as the negative electrode material, the charge / discharge efficiency in the first cycle was almost zero, and almost no discharge was possible. The charge and discharge efficiency gradually increased after the second cycle, and stabilized at 85 to 87% after the 15th cycle.
Also in the comparative example battery 3, the initial charge / discharge efficiency tends to be low.

Therefore, when general artificial graphite is used as a negative electrode material, only a battery having a large charge / discharge cycle deterioration and a short cycle life can be obtained although the voltage flatness of the discharge curve is excellent.

On the other hand, Comparative Example Battery 2 using pitch coke, which is a common carbonaceous material, as the negative electrode material has a high charge / discharge efficiency and a long cycle life, but from the results shown in FIG. 3, flatness of the discharge voltage is required. It cannot be used for other purposes.

On the other hand, the battery of Example 1 not only showed a relatively high value of 67% in the charge and discharge efficiency in the first cycle, but also
The rise of efficiency after the cycle was fast, reaching a high charge and discharge efficiency of 99% or more in 5 to 10 cycles and stabilized. High charge / discharge efficiency means that the amount of reaction active material that cannot be charged / discharged by repeating the cycle is small, which is advantageous for designing a high-capacity practical battery. The battery 1 of the embodiment has a capacity of 50
High charge / discharge efficiency was stably maintained even after 0 cycles, and the cycle life was long.

Next, an example of a nonaqueous electrolyte secondary battery using a composite material composed of fine fibrous graphite and a carbonaceous material for a negative electrode will be described.

First, a composite material composed of fine fibrous graphite and a carbonaceous material was prepared by the following method.

<Composite Material A> Vapor-grown carbon fiber (trade name VGCF) manufactured by Showa Denko KK was used as the fine fibrous graphite.

3 g of the fine fibrous graphite was immersed in a solution of 18 g of vinyl acetate resin (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: Sakunol) in 42 g of N-methylpyrrolidone, mixed well, and allowed to absorb between the fibers. The mixture is placed in a natural convection dryer at 140 ° C for 24 hours.
Time drying was performed.

The mixture was then transferred to a quartz glass boat,
It was installed in a 90 mm quartz glass firing tube. After the inside of the firing tube was sufficiently replaced with high-purity nitrogen gas, heating was started by a horizontal tubular furnace while flowing high-purity nitrogen gas at a flow rate of 1 / min. After the carbonization reaction was first maintained at 500 ° C. for 3 hours, the temperature was further increased and the reaction was performed at 1000 ° C. for 1 hour. After cooling to room temperature while flowing high-purity nitrogen gas, the mixture was taken out to obtain 4.3 g of a fine fibrous graphite / carbonaceous material composite material.

After sufficiently pulverized in an agate mortar, the mixture was sieved with a 250-mesh sieve to obtain a composite material A.

<Composite material B> The fine fibrous graphite used was the same as the above-mentioned composite material A.

3 g of the fine fibrous graphite was immersed in a dispersion liquid in which 0.75 g of a polyimide resin (manufactured by Nippon Polyimide Co., Ltd., trade name Kelimide) was uniformly suspended in 4.25 g of N-methylpyrrolidone, mixed well, and allowed to absorb sufficiently. Was. The mixture was dried at 140 ° C. for 24 hours in a natural convection dryer.

The mixture was then transferred to a quartz glass boat,
It was set in a firing tube made of quartz glass with an inner diameter of 90 mm. After sufficiently replacing the inside of the firing tube with high-purity nitrogen gas, the flow rate
The heating was started by a horizontal tubular furnace while flowing high-purity nitrogen gas at a rate of 1 minute. After the carbonization reaction was first maintained at 500 ° C. for 3 hours, the temperature was further increased and the reaction was performed at 1000 ° C. for 1 hour. After cooling to room temperature while flowing high-purity nitrogen gas, the mixture was taken out to obtain 3.5 g of a fine fibrous graphite / carbonaceous material composite material.

This was sufficiently pulverized in an agate mortar and then sieved with a 250-mesh sieve to obtain a composite material B.

<Composite material C> The fine fibrous graphite used is the same as the above-mentioned composite material A.

3 g of the fine fibrous graphite was immersed in a dispersion liquid in which 5 g of a polyimide resin (manufactured by Nippon Polyimide Co., Ltd., trade name Kelimide) was uniformly suspended in 28.3 g of N-methylpyrrolidone, mixed well, and sufficiently absorbed. . The mixture is placed in a natural convection dryer.
Drying was performed at 140 ° C. for 24 hours.

The mixture was then transferred to a quartz glass boat,
It was set in a firing tube made of quartz glass with an inner diameter of 90 mm. After sufficiently replacing the inside of the firing tube with high-purity nitrogen gas, the flow rate
The heating was started by a horizontal tubular furnace while flowing high-purity nitrogen gas at a rate of 1 minute. After the carbonization reaction was first maintained at 500 ° C. for 3 hours, the temperature was further increased and the reaction was performed at 1000 ° C. for 1 hour. After cooling to room temperature while flowing high-purity nitrogen gas, the mixture was taken out to obtain 5.3 g of a fine fibrous graphite / carbonaceous material composite material.

This was sufficiently pulverized in an agate mortar and then sieved with a 250-mesh sieve to obtain a composite material C.

Fine fibrous graphite alone and fine fibrous graphite / carbonaceous material composite material obtained by the above method (composite material A to composite material C)
The powder X-ray diffraction spectrum of is shown in FIG. The X-ray diffractometer used for the measurement is Geigerflex RAD IIC (target: Cu) manufactured by Rigaku Corporation.

The interplanar distance of the carbon hexagonal net plane determined from FIG. 5 is equal to 3.40 ° for all four materials, and it has been confirmed that the crystal structure of fine fibrous graphite which is fundamental in the production process of the composite material is hardly changed. Was.

A coin-type non-aqueous electrolyte secondary battery as shown in FIG. 2 was prototyped in the same manner as in Example 1 except that the above-described composite material was used as a negative electrode material. The configuration of each battery was optimized for each material so that the battery capacity and the cycle life characteristics exhibited excellent secondary battery characteristics in a well-balanced manner.

Example 2 0.16 g of a negative electrode mixture composed of 90 parts by weight of a composite material A and 10 parts by weight of polyvinylidene fluoride as a binder was press-formed together with a stainless steel net (5) having a wire diameter of 0.05 mm punched out to a diameter of 15 mm. A disk-shaped negative electrode (4) having a diameter of 15.5 mm and a thickness of 0.83 mm was produced. The negative electrode (4) is electrically connected to the outside of the battery through a copper current collector (6) spot-welded to the inside of a stainless steel negative electrode can (7) plated with nickel on the outside. .

The positive electrode (1) was composed of 85 parts by weight of LiCoO _{2 as} an active material, 10 parts by weight of graphite as a conductive agent, and 5 parts by weight of polytetrafluoroethylene as a binder. It is formed by pressing into a disk having a length of 104 mm. The positive electrode (1) is electrically connected to the outside of the battery via an aluminum current collector (2) spot-welded to the inside of a stainless steel positive electrode can (3) plated with nickel on the outside. .

The positive electrode (1) and the negative electrode (4) were adjusted to a residual moisture value of 300 ppm or less by vacuum drying, and then passed through a microporous polypropylene separator (manufactured by Polyplastics, trade name: DURAGARD # 2502) (8). And set it facing.

The electrolytic solution was prepared by dissolving LiPF ₆ at a ratio of 1 mol / in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in an equal volume, adjusting this to a residual moisture value of 20 ppm or less, and injecting 120 μm thereof. did.

In addition, between the positive electrode can (3) and the negative electrode can (7), a polypropylene gasket (9) having asphalt coated on its surface was disposed. Therefore, this gasket (9)
Is compressed between the negative electrode can (7) and the negative electrode can (7) by caulking of the positive electrode can (3), and the airtightness inside the battery is maintained.

With the above configuration, a coin-type nonaqueous electrolyte secondary battery (Example Battery 2) having a diameter of 20 mm and a height of 2.5 mm was assembled.

Example 3 Same as Example 2, except that 0.15 g of a negative electrode mixture composed of 90 parts by weight of the composite material B and 10 parts by weight of polyvinylidene fluoride was worked and formed into a diameter of 15.5 mm and a height of 0.74 mm together with a stainless steel net. A coin-type non-aqueous electrolytic solution having a diameter of 20 mm and a height of 2.5 mm was prepared in the same manner as in Example 2 except that a positive electrode (1) obtained by press-molding 0.77 g of the positive electrode mixture to a diameter of 15.5 mm and a height of 1.3 mm was used. A liquid secondary battery (Example Battery 3) was assembled.

Example 4 Same as Example 2 except that 0.15 g of a negative electrode mixture composed of 90 parts by weight of the composite material C and 10 parts by weight of polyvinylidene fluoride was worked and formed into a 15.5 mm diameter and 0.65 mm height together with a stainless steel net. A coin-shaped non-aqueous electrolytic solution having a diameter of 20 mm and a height of 2.5 mm in the same manner as in Example 2 except that a positive electrode (1) obtained by press-molding 0.83 g of the positive electrode mixture to a diameter of 15.5 mm and a height of 1.22 mm was used. A liquid secondary battery (Example Battery 4) was assembled.

Example 5 As a negative electrode (2), an SG carbon disk-shaped molded product (diameter 15.3) manufactured by Showa Denko KK, which is a fine fibrous graphite / carbonaceous material composite material.
(5 mm, height 0.6 mm) was used as it was. The positive electrode (1) was obtained by press-molding 0.82 g of the same positive electrode mixture as in Example 2 to a diameter of 15.5 mm and a height of 1.21 mm. Except for this, a coin-type nonaqueous electrolyte secondary battery (Example Battery 5) having a diameter of 20 mm and a height of 2.5 mm was assembled in the same manner as in Example 2.

Comparative Example 4 0.14 g of a negative electrode mixture composed of 90 parts by weight of vapor-grown carbon fiber (trade name: VGCF) and 10 parts by weight of polyvinylidene fluoride, which is a fine fibrous graphite, manufactured by Showa Denko K.K. Negative electrode pressed to 1.03mm height (2)
And 0.57 g of the same positive electrode mixture as in Example 2 having a diameter of 15.5 mm and a height of 0.
A coin-type non-aqueous electrolyte secondary battery (comparative battery 4) having a diameter of 20 mm and a height of 2.0 mm was assembled in the same manner as in Example 2 except that the positive electrode (1) pressed to 84 mm was used. .

Although this example corresponds to an example in which fine fibrous graphite is used alone for the negative electrode, it is a comparative example in order to compare with a case where the composite material is used as the negative electrode.

First, Table 2 shows the mixture filling densities of the negative electrodes used in the batteries of Examples 2 to 5 and the battery of Comparative Example 4.

Compared to the packing density of the negative electrode consisting of fine fibrous graphite and binder only, the packing density of the negative electrode using a composite material in which a carbonaceous material is fixed between fibers is high and can be stored in the same volume This indicates that the amount of the various carbon materials is large.

Next, constant current charge / discharge tests were performed on the batteries 2 to 5 of the examples and the battery 4 of the comparative example. Charges up to 4.0V
The charge / discharge cycle was repeated, with the current being set to 6 mA for 24 hours and the discharge being 2 mA to 2.9 V.

FIG. 6 shows the cycle change of the energy density of each battery. According to this, each example battery using the composite material,
The energy density was about 10 to 50% higher than that of the battery using the fine fibrous graphite alone, and the cycle deterioration was almost comparable. For example, the energy density at the time of 50 cycles has elapsed was 70 Wh / in Comparative Example Battery 4, whereas the energy density in Example Battery 2 was 81 Wh /, an increase of about 16% as compared with Comparative Example Battery 4. At 8Wh / about 26%
In the case of the battery 4 of the embodiment, the increase was about 26% at 88 Wh /, and in the case of the battery 5 of the embodiment, the increase was about 47% at 103 Wh /.

FIG. 7 shows the discharge curve of the tenth cycle of each battery (Example batteries 2 to 4 and Comparative example battery 4). Over.

By the way, the weight ratio of the fine fibrous graphite in the composite material is estimated from the weight loss when the fine fibrous graphite / organic polymer material mixture is fired to obtain a fine fibrous graphite / carbonaceous material composite material. 70% for composite material A, composite material B
Is 90% and that of composite material C is 57%. The discharge amount of Example Battery 4 was almost equal to the discharge amount of Example Battery 3, but the flatness of the discharge curve was inferior as clearly shown in FIG. Therefore, when importance is attached to the flatness of the discharge voltage, it is preferable that the weight ratio of the fine fibrous graphite in the composite material be higher, and it is desirable that the weight ratio be 60% or more.

Also, as described in Example Battery 5, good results were obtained when a commercially available material was used for the fine fibrous graphite / carbonaceous material composite material. For example, not only the filling property is high as shown in Table 2, but also the energy density is high as shown in FIG. 6 because all of the disc-shaped negative electrode is a carbon material and can participate in the battery reaction. Further, since the fine fibrous graphite is used, the flatness of the discharge voltage is relatively good as shown in FIG. This commercially available material was a disk-shaped compact, had high hardness, and was excellent in workability during battery assembly.

The coin-type non-aqueous electrolyte secondary battery has been described above as an example. However, the present invention is not limited to this, and the battery shape and dimensions are arbitrary. For example, a button type battery, a cylindrical type battery, a spiral type cylindrical type battery, and the like also showed good results as in the previous embodiment.

〔The invention's effect〕

As is clear from the above description, in the present invention, since the composite material composed of fine fibrous graphite and carbonaceous material is used for the negative electrode, the flatness of the discharge voltage is excellent, and the cycle deterioration is small with a long time. A long-life secondary battery can be provided. The excellent flatness of the discharge voltage is advantageous in terms of circuit design of equipment using a battery. Even if the set value of the final voltage slightly fluctuates within a practical range, there is no large difference in the obtained discharge capacity.

In particular, by using a composite material including fine fibrous graphite and a carbonaceous material for the negative electrode, the filling property at the time of working and molding can be improved, and the energy density can be improved.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing X-ray diffraction spectra before and after graphitization of fine fibrous carbon. FIG. 2 is a schematic sectional view showing the configuration of the assembled coin-type battery. FIG. 3 shows a battery using only fibrous graphite as a negative electrode.
FIG. 4 is a characteristic diagram showing the charge / discharge characteristics at the cycle in comparison with a battery using another carbon material for the negative electrode, and FIG. 4 is a characteristic diagram showing a change in the charge / discharge efficiency depending on the number of repetitions of the charge / discharge cycle. FIG. 5 is a characteristic diagram showing the X-ray diffraction spectrum of the fine fibrous graphite / carbonaceous material composite material in comparison with the X-ray diffraction spectrum of the fine fibrous graphite alone. FIG. 6 is a characteristic diagram showing a cycle change of the energy density of the battery using the fine fibrous graphite / carbonaceous material composite material for the negative electrode in comparison with that of the battery using the fine fibrous graphite alone for the negative electrode. FIG. 7 is a characteristic diagram showing a discharge curve at the tenth cycle. FIG. 8 is a characteristic diagram showing a discharge curve at the 10th cycle of a battery using a commercially available fine fibrous graphite / carbonaceous material composite material for a negative electrode.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Nagaura 1-1 Shimosugishita, Takakura, Hiwada-cho, Koriyama-shi, Fukushima Prefecture 1 Inside Sony Energy Tech Koriyama Plant (56) References JP-A-62-90863 JP, A) JP-A-2-82466 (JP, A) JP-A-63-24555 (JP, A) Sharp Technical Report No. 40 (1988-10) P29-32 (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/02 H01M 4/58 H01M 10/40

Claims (2)

(57) [Claims] 1. A negative electrode comprising fine fibrous graphite having a half-width of an X-ray diffraction peak corresponding to a spacing between 002 planes of 1 ° or less and a carbonaceous material, a positive electrode, and a nonaqueous electrolyte. A non-aqueous electrolyte secondary battery comprising: 2. The composition according to claim 1, wherein the proportion of the fine fibrous graphite in the negative electrode is 60% by weight.
The non-aqueous electrolyte secondary battery according to claim 1, wherein: