JPH065287A - Carbon electrode and lithium secondary battery using same electrode - Google Patents

Abstract

PURPOSE:To provide a lithium secondary battery having good load properties by using a carbon electrode which is a formed body of a specified carbonaceous material for a negative pole. CONSTITUTION:A carbonaceous material formed body prepared by forming a carbon black coating layer on a granular material of an organic polymer substance and carrying out heating treatment or carbonizing treatment is used as a negative pole 5. The negative pole 5 is joined to a negative pole case 1 while having a collector 4 made of a stainless steel between them, a positive pole 7 is joined to a positive pole case 2 while having a collector 6 made of a stainless steel between them, and a separator 8 and an electrolytic liquid absorbing body 9 are set between the negative and the positive poles. Further, an organic electrolytic liquid consisting of an organic solvent and a lithium salt dissolved in the solvent is infected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon electrode and a lithium secondary battery using the same.

[0002]

BACKGROUND ART Echirenka - BONNET - in a lithium secondary battery in which an organic solvent by dissolving a lithium salt such as LiCF ₃ SO ₃ in the organic electrolyte solution, such bets, those using lithium or a lithium alloy for the negative electrode, It is easy to cause an internal short circuit, and there were problems in terms of deterioration of battery characteristics and safety.

Therefore, instead of lithium or a lithium alloy, carbonaceous materials such as activated carbon and graphite may be used as a negative electrode carrier, as disclosed in JP-A-57-208079 and JP-A-58-35881. Sho 59-143280
Publication, "Journalof Electroche
medical Society ", page 222 (1970)
), "Abstracts of the 29th Battery Symposium", page 139 (1988), etc.

In Japanese Patent Laid-Open No. 62-122066, the atomic ratio of hydrogen / carbon is less than 0.15, and the (002) plane spacing determined by X-ray wide angle diffraction is 3.37 Å or more. It has been proposed to use a carbonaceous material having a graphite-like structure having a crystallite size in the c-axis direction of 150 Å or less as a negative electrode carrier of a non-aqueous solvent battery.

When a negative electrode having such a carbonaceous material as a carrier and lithium as an active material is used, the volume energy density is sacrificed to some extent as compared with a battery having a negative electrode made of a plate of lithium or a lithium alloy. The reversibility and safety of charge and discharge are dramatically improved. Further, it is known that the use of the carbonaceous material having the above graphite-like structure gives good results in suppressing self-discharge and improving cycle characteristics.

[0006]

However, the lithium secondary battery using the above-mentioned carbonaceous material as the negative electrode carrier has a problem that the polarization is large and the capacity becomes small at the time of heavy load charging / discharging.

The present invention solves the above problems of conventional carbonaceous materials, provides a lithium secondary battery having good load characteristics, and provides a carbon electrode for a negative electrode that enables this. Has an aim.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in order to achieve the above object, and as a result, they are obtained by heat-treating a carbonaceous material having a conventional graphite-like structure with a specific coating layer. When a carbonaceous material was used as a negative electrode carrier, it was found that a high-capacity lithium secondary battery can be obtained even under heavy load charge / discharge, and the present invention was completed.

That is, the first aspect of the present invention is a molded body of a carbonaceous material obtained by providing a carbon black coating layer on a particulate matter of a carbonaceous or organic polymer substance having a graphite-like structure and subjecting it to heat treatment or carbonization treatment. According to a second aspect of the present invention, in a lithium secondary battery using an organic electrolytic solution in which a lithium salt is dissolved in an organic solvent, the above-mentioned carbon is used as a negative electrode. -The present invention relates to a lithium secondary battery characterized by using a Bon electrode.

[0010]

The carbonaceous material having a graphite-like structure in the present invention is one that can be doped with lithium ions and dedoped, and includes pyrolytic carbons, cokes,
Glassy carbons, fired bodies of organic polymer compounds, carbon fibers, activated carbon and the like can be used. As the organic polymer substance, a wide range of solid resins at room temperature such as phenol resin, polyacrylonitrile resin, cellulose resin, polyamide resin, polyamideimide resin and vinyl halide resin can be widely used.

The average particle size of the particulate matter composed of such a carbonaceous or organic polymer substance is usually about 5 to 100 μm. Since the electrical resistivity of this particulate matter is generally not sufficiently small, the lithium secondary battery using this as a negative electrode carrier has a large polarization during heavy load charging and discharging,
The capacity decreases.

In the present invention, in order to overcome the above problem, a carbon black coating layer having a low electric resistivity is provided on the above particulate matter, and the carbon black material is heat treated or carbonized to form a carbonaceous material. However, since this material itself has a low electric resistivity (volume specific resistance), a lithium secondary battery using this material as a negative electrode carrier has a small polarization at the time of heavy load charging and discharging, The utilization rate is improved, and the conventional decrease in capacity is suppressed.

When a lithium secondary battery is manufactured by mixing metal powder or the like as a conductive auxiliary material with a carbonaceous material having a conventional structure and using this as an electrode material, the polarization at the time of heavy load charging and discharging is small. The capacity increases, but since metal powder and the like do not participate in the lithium doping and de-doping reactions, the capacity per volume is smaller than that of the above-mentioned invention, which is a sufficient improvement. No effect.

In the present invention, the carbon black coating layer is formed, for example, by subjecting a particulate matter to carbon black produced by thermal decomposition of natural gas or the like at 1,500 to
What is heat-treated at a high temperature of about 3,000 ° C. may be mixed with a binder and applied, and the coating amount may be usually about 3 to 20% by weight of carbon black with respect to the particulate matter.

After forming this coating layer, it is usually 800 to 2.5
The desired carbonaceous material can be obtained by heat treatment at a temperature of about 00 ° C., or when the particulate matter is made of an organic polymer material, it is carbonized at a temperature similar to the above.

The carbon electrode of the present invention is made into a molded product having a desired shape by a conventional method using the carbonaceous material thus obtained. As an example, a slurry is prepared by dispersing the above-mentioned carbonaceous material powder and polytetrafluoroethylene powder serving as a binder thereof in a water-alcohol mixed solvent, and applying the slurry onto a wire net such as a nickel net. ，
It may be dried, then punched and formed integrally with the wire net, and then pressure-formed to a desired thickness.

FIG. 1 shows an example of the structure of the button type lithium secondary battery of the present invention in which the carbon electrode is used as a negative electrode. In the figure, 1 is a dish-shaped negative electrode can made of stainless steel, 2 is a dish-shaped positive electrode can made of stainless steel, and the bipolar cans 1 and 2 are opposed to each other, and the peripheral portions of both are made of synthetic rubber or synthetic resin. By fitting and crimping with the annular gasket 3 made of the elastic insulating material of
A flat closed container is constructed.

Inside the container, a negative electrode 5 made of the above-mentioned specific molded product joined to the negative electrode can 1 via a current collector 4 made of stainless steel, and a current collector 6 made of stainless steel in the positive electrode can 2. The positive electrode 7 joined via the
A separator 8 and an electrolyte solution absorber 9 which are interposed between 7 are loaded, and an organic electrolyte solution obtained by dissolving a lithium salt in an organic solvent is injected.

In the above-mentioned organic electrolytic solution, as the organic solvent, ethylene carbonate, propylene carbonate
1, 1.2-dimethoxyethane, γ-butyrolactone,
A polar solvent such as dioxolane is used. Further, as the lithium salt, LiCF ₃ SO ₃ , LiBF ₄ , Li
ClO ₄ , LiBφ ₄ (φ is a phenyl group), LiP
Various salts such as F ₆ and LiAsF ₆ are used.

It is needless to say that the negative electrode comprising the carbon electrode of the present invention is not limited to the button type battery shown in the figure, but can be applied to lithium secondary batteries of various shapes and structures such as a tubular type.

[0021]

As described above, by using the carbon electrode made of the molded body of the specific carbonaceous material of the present invention as the negative electrode, a lithium secondary battery having good load characteristics can be obtained. .

[0022]

EXAMPLES Next, examples of the present invention will be described to explain more specifically.

Example 1 A spherical phenol resin having an average particle diameter of 10 μm was heat-treated at 2,500 ° C. with a carbon black produced by thermal decomposition of natural gas, and 3% by weight based on the carbon black. The ratio of polytetrafluoroethylene (hereinafter, P
A slurry-like material mixed with a PTFE aqueous dispersion containing a powder (TFE) was applied to the above resin so that the carbon black was 5% by weight, and then 1,000
A carbonaceous material was obtained by carbonization at ℃.

To 30 g of this carbonaceous material, 4.7 g of pure water,
1.5 ml of a 60% by weight aqueous dispersion of PTFE powder and 2.8 ml of isopropyl alcohol were added, and the mixture was stirred for 30 minutes to form a slurry, which was dried on a nickel mesh net of 60 mesh to give a thickness after drying. Apply to 0.4mm, 2
It was dried at 00 ° C. for 1 hour. This has a diameter of 10 mm (area 0.
To prepare a carbon electrode - punched to a size of 785 cm ^2), and pressed at 10 tons / cm ^2, total thickness mosquitoes consisting of molded article of 0.3 mm.

Next, using the carbon electrode as the negative electrode,
A molded body made of LiMnO ₂ mixture having a thickness of 0.5 mm and a diameter of 10 mm is used as a positive electrode, a microporous polypropylene film is used as a separator, a polypropylene nonwoven fabric is used as an electrolytic solution absorber, and an ethylene carbonate is used as an organic electrolytic solution. And 1
A solution of LiCF ₃ SO ₃ dissolved in a mixed solvent of 2-dimethoxyethane in a volume ratio of 1: 1 in an amount of 0.6 mol / l, and a cyclic gasket made of polypropylene,
Using each of them, a button type lithium secondary battery having a structure shown in FIG. 1 was produced.

Example 2 A spherical phenol resin having an average particle diameter of 10 μm was heat-treated at 2,200 ° C. with a carbon black produced by thermal decomposition of natural gas, and 3% by weight based on the carbon black. The slurry-like material mixed with a PTFE aqueous dispersion containing the following proportion of PTFE was applied to the above resin so that the carbon black content was 5% by weight, and then 1,0
Carbonization treatment was performed at 00 ° C to obtain a carbonaceous material. A carbon electrode was prepared in the same manner as in Example 1 except that this carbonaceous material was used, and this electrode was used as a negative electrode in the same manner as in Example 1 to prepare a button-type lithium battery having the structure shown in FIG. A secondary battery was produced.

Example 3 A spherical phenol resin having an average particle diameter of 10 μm was heat-treated at 1,800 ° C. with a carbon black produced by thermal decomposition of natural gas, and 3% by weight based on this carbon black. The slurry-like material mixed with a PTFE aqueous dispersion containing the following proportion of PTFE was applied to the above resin so that the carbon black content was 5% by weight, and then 1,0
Carbonization treatment was performed at 00 ° C to obtain a carbonaceous material. A carbon electrode was prepared in the same manner as in Example 1 except that this carbonaceous material was used, and this electrode was used as a negative electrode in the same manner as in Example 1 to prepare a button-type lithium battery having the structure shown in FIG. A secondary battery was produced.

Comparative Example 1 1,000 parts of spherical phenol resin having an average particle diameter of 10 μm was used.
The carbonaceous material was carbonized at ℃ to prepare a carbon electrode using this material in the same manner as in Example 1, and this electrode was used as a negative electrode in the same manner as in Example 1 and shown in FIG. A button type lithium secondary battery having a structure was produced.

Example 4 A raw coke having an average particle size of 10 μm, which was heat-treated at 2,500 ° C. with a carbon black produced by thermal decomposition of natural gas, to obtain 3% by weight based on the carbon black. A slurry-like material mixed with a PTFE aqueous dispersion containing a proportion of PTFE was applied to the above coke at a ratio of 5% by weight of carbon black, and then 1,000.
A carbonaceous material was obtained by carbonization at ℃. A carbon electrode was prepared in the same manner as in Example 1 except that this carbonaceous material was used, and this electrode was used as a negative electrode in the same manner as in Example 1 to prepare a button-type lithium battery having the structure shown in FIG. A secondary battery was produced.

Example 5 A raw coke having an average particle diameter of 10 μm and a carbon black produced by thermal decomposition of natural gas which was heat-treated at 2,200 ° C., and the weight of the carbon black was 3% by weight. A slurry-like material mixed with a PTFE aqueous dispersion containing a proportion of PTFE was applied to the above coke at a ratio of 5% by weight of carbon black, and then 1,000.
A carbonaceous material was obtained by carbonization at ℃. A carbon electrode was prepared in the same manner as in Example 1 except that this carbonaceous material was used, and this electrode was used as a negative electrode in the same manner as in Example 1 to prepare a button-type lithium battery having the structure shown in FIG. A secondary battery was produced.

Comparative Example 2 Raw coke having an average particle size of 10 μm was carbonized at 1,000 ° C. to obtain a carbonaceous material, and this material was used in Example 1
A carbon electrode was produced in the same manner as in 1. and a button type lithium secondary battery having the structure shown in FIG. 1 was produced in the same manner as in Example 1 using this electrode as a negative electrode.

The electrical resistivity ρ∞ of each carbon electrode of Examples 1 to 5 and Comparative Examples 1 and 2 was examined. For each of the lithium secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2, 0.5 mA / cm ² and ² mA / cm ²
The discharge capacity was measured when the battery was charged and discharged at a constant current of cm ² .
The results are shown in Table 1 below. The above electrical resistivity ρ∞ was measured by the following method.

<Measurement of electric resistivity ρ∞ of carbon electrode>
After vacuum drying the measurement sample at 150 ° C. for 3 hours, the following formula (1),
As shown in (2), the resistivity ρ with respect to the compression pressure P was measured, and P was infinitely extrapolated from the plot of 1 / √P vs. ρ to obtain the electrical resistivity ρ∞.

Σ _d = 2√P / (√πH × σ _v ) (1) σ _d = r _c ′ / r × σ _v (2) (when P → ∞, σ _d = σ _v ) σ _d: apparent conductivity (Scm ^-1) σ _v: conductivity of the substance of the particle (Scm ^-1) P: compression pressure (Kg / cm ²⁾ H: hardness r _c entity of the particles': contact surface effective Radius = r _c + Δr _c (cm) Δr _c : Increase in contact circle radius r _c due to adsorption of water on the contact area (cm)

[0035]

[Table 1]

As is clear from the above test results, the lithium secondary batteries of Examples 1 to 3 and Examples 4 and 5 of the present invention are the same as those of the corresponding conventional Comparative Example 1 and Comparative Example 2, respectively. It can be seen that the load characteristics are superior to those of the lithium secondary battery.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a lithium secondary battery of the present invention.

[Explanation of symbols]

 1: Negative electrode can 2: Positive electrode can 5: Negative electrode 7: Positive electrode 8: Separator 9: Electrolyte absorber

Claims (2)

[Claims] 1. A molded product of a carbonaceous material, which is obtained by providing a carbon black coating layer on a particulate material of a carbonaceous or organic polymer substance having a graphite-like structure and subjecting it to heat treatment or carbonization. Carbon electrode. 2. A lithium secondary battery using an organic electrolytic solution in which a lithium salt is dissolved in an organic solvent, wherein the carbon electrode according to claim 1 is used as a negative electrode. battery.