JPH08102315A - Battery electrode and secondary battery using this electrode - Google Patents

Abstract

PURPOSE: To provide a battery electrode at low cost and increase discharge capacity by forming a positive electrode and/or a negative electrode with carbon fibers and arranging the electrode using carbon fibers on the outermost side. CONSTITUTION: A positive electrode 3 and/or a negative electrode 1 are/is made of carbon fibers and the electrode using carbon fibers is arranged on the outermost side. As the carbon fiber for the negative electrode 1, PAN family carbon fiber with high lithium ion doping capability is used. The electrode using carbon fiber is preferable to be formed in a cloth or a stretched sheet either one is optionally selected, and has a diameter of 1-20μm. When the carbon fiber is used in the negative electrode, the positive electrode is constituted with a positive active material 3 and a positive current collector 4. Since the thicker current collector decreases the the amount of the active material, use of metal foil is preferable. By arranging the electrode using carbon fiber on the outermost side, the amount of expensive transition metal oxide can be decreased.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, with the widespread use of portable devices such as video cameras and notebook computers, the demand for compact and high capacity batteries has increased. Most of the secondary batteries are nickel-cadmium batteries using an alkaline electrolyte, but the battery voltage is low at about 1.2 V, and it is difficult to improve the energy density. In recent years, lithium ion secondary batteries using various carbonaceous materials capable of doping and dedoping lithium ions in the negative electrode material have been proposed,
Development is active.

Among them, a battery using carbon fiber or a carbon fiber structure as a carbonaceous material is excellent in terms of chemical stability with respect to electrolyte, structural stability against volume expansion due to doping, and repeated charge / discharge characteristics. Has been done. A secondary battery using a carbon fiber or a carbon fiber structure as a negative electrode is disclosed in JP-A-60-36315.
JP-A No. 60-54181, JP-A No. 62-62
No. 103991, JP-A-62-154564, JP-A-63-58763, and JP-A-2-824.
No. 66 publication is known.

[0004]

However, such a conventional secondary battery has an insufficient charge / discharge capacity, and
On the outermost surface layer side, there is no opposing electrode, and the disadvantage is that the expensive pole material used on the outermost surface layer side cannot be used effectively.

The present invention is intended to solve the drawbacks of the prior art, and an object thereof is to provide an electrode assembly for a battery, which is inexpensive and has an excellent charge and discharge capacity, and a secondary battery using the same. And

[0006]

The present invention has the following constitution in order to achieve the above object.

That is, “(1) In a battery electrode body having a structure in which a sheet-shaped positive electrode and a sheet-shaped negative electrode are wound in a roll shape via a separator, the positive electrode and / or the negative electrode uses carbon fiber. An electrode body for a battery, which is an electrode and in which the outermost layer electrode is an electrode using carbon fiber.

(2) A secondary battery using the electrode body according to the above item (1). Is provided.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram for explaining the battery electrode body of the present invention. Note that the lead terminals and the like are omitted for clarity.

As shown in FIG. 1, the battery electrode body of the present invention has a structure wound into a roll. Although the drawing shows an example in which it is wound in a cylindrical shape, it can be arbitrarily selected as long as it has a wound structure such as a square shape or an elliptical shape.

In FIG. 1, 1 is a carbon fiber as a negative electrode material, 2 is a negative electrode current collector, 3 is a positive electrode material, 4 is a positive electrode current collector, and 5 is a separator. The feature of the present invention resides in that an electrode using carbon fiber is arranged in the outermost layer of the electrode body as shown in FIG. In the present invention, the electrode using carbon fiber may be used as either a negative electrode or a positive electrode. FIG.
As is clearer, there is no positive electrode material that opposes the carbon fiber, which is the electrode material, on the surface side of the outermost negative electrode of the electrode body, and it has not been effectively utilized. Therefore, it is more preferable to remove the carbon fiber, which is the surface side electrode material of the outermost layer electrode.

In the present invention, it is preferable to use a current collector in the electrode using carbon fiber as the pole material. The carbon fiber that can be used in the present invention is not particularly limited, but a fired organic material is preferably used.
Specifically, PAN-based carbon fiber obtained from polyacrylonitrile (PAN), pitch-based carbon fiber obtained from pitch such as coal or petroleum, cellulosic carbon fiber obtained from cellulose, gas obtained from gas of low molecular weight organic matter, etc. Examples include phase-grown carbon fibers, and in addition, carbon fibers obtained by firing polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenolic resin, furfuryl alcohol, and the like may be used. Among these carbon fibers, it is preferable to appropriately select carbon fibers satisfying the characteristics according to the characteristics of the negative electrode and the battery in which the carbon fibers are used.

Among the above carbon fibers, when used as a negative electrode of a secondary battery using a non-aqueous electrolyte containing an alkali metal salt, PAN-based carbon fibers, pitch-based carbon fibers and vapor-grown carbon fibers are used. preferable. In particular, in terms of good doping with alkali metal ions, especially lithium ions, P
AN-based carbon fiber is preferably used.

The electrode using the carbon fiber according to the present invention may have any form, but a cloth-like or felt-like structure or a uniaxially arranged sheet-like structure is a preferred form. From the viewpoint of the properties of the carbon fibers and the electrode characteristics, a woven fabric, a felt, a unidirectional array, and the like are preferable forms, and among them, it is preferable that they are arranged substantially perpendicular to the longitudinal direction of the current collector.

The diameter of the carbon fibers used in the present invention should be determined so that each form can be easily adopted, but carbon fibers having a diameter of 1 to 1000 μm are preferably used, and 1 to 20 μm is more preferable. It is also possible to use several kinds of carbon fibers having different diameters.

In the present invention, the collector used together with the carbon fiber is not particularly limited as long as it has good conductivity, but a metal having a low electric resistance is preferably used. Specific examples of the metal include gold, silver, copper, platinum, aluminum, iron, nickel, chromium, manganese, lead, tungsten, titanium, and the like. Further, stainless steel, alloys of the above metals, and the like may be used. . When the thickness of the current collector is increased, the amount of active material contained in the battery is reduced, and therefore, the metal is preferably a foil. Further, those having a small thickness are preferably used. Copper foil is most preferably used in terms of electric resistance, foil thickness and cost.

In the present invention, it is preferable to use an electrode using such carbon fiber as a negative electrode. In that case,
The positive electrode includes a positive electrode material and a positive electrode current collector. Examples of the positive electrode material include inorganic compounds such as transition metal oxides and transition metal chalcogens containing an alkali metal, polyacetylene, polyparaphenylene, polyphenylenevinylene,
Examples of the positive electrode used in ordinary secondary batteries include conjugated polymers such as polyaniline, polypyrrole, and polythiophene, crosslinked polymers having a disulfide bond, and thionyl chloride. Among these, in the case of a secondary battery using a non-aqueous electrolyte containing a lithium salt, cobalt, manganese, molybdenum, vanadium, chromium, iron,
Transition metal oxides such as copper and titanium and transition metal chalcogens are preferably used. Among them, LiCoO ₂ and LiN
Since iO ₂ has a high voltage and a large energy density, it can be preferably used. The positive electrode current collector is not particularly limited as long as it has good conductivity, but a metal having a low electric resistance is preferably used. Specific examples of the metal include gold, silver, copper, platinum, aluminum, iron, nickel, chromium, manganese, lead, tungsten, titanium, and the like. Further, stainless steel, alloys of the above metals, and the like may be used. . As the thickness of the current collector increases,
Since the amount of active material contained in the battery is reduced, the metal is preferably a foil. Further, those having a small thickness are preferably used. Aluminum foil is preferably used in terms of electrical resistance, foil thickness and cost.

The electrode body of the present invention is preferably used in a secondary battery or the like, but the electrolytic solution is not particularly limited, and a conventional electrolytic solution may be used. For example, an acid or alkaline aqueous solution or a non-aqueous solution may be used. A solvent etc. are mentioned. Among these, as an electrolytic solution for a secondary battery comprising a non-aqueous electrolytic solution containing the above-mentioned alkali metal salt, propylene carbonate,
Ethylene carbonate, γ-butyrolactone, N-methylpyrrolidone, acetonitrile, N, N-dimethylformamide, dimethylsulfoxide, tetrahydrofuran, 1,3-dioxolane, methyl formate, sulfolane,
Oxazolidone, thionyl chloride, 1,2-dimethoxyethane, diethylene carbonate and derivatives and mixtures of these are preferably used. As the electrolyte contained in the electrolytic solution, alkali metal, particularly lithium halide, perchlorate, thiocyanate, borofluoride, phosphorus fluoride, arsenic fluoride, aluminum fluoride, trifluoromethyl sulfate, etc. Is preferably used.

[0019]

EXAMPLES Specific embodiments of the present invention will be described below with reference to examples, but the present invention is not limited thereto.

Example 1, Example 2 and Comparative Example 1 (1) Preparation of Negative Electrode Commercially available PAN-based carbon fiber on both sides of a copper foil having a thickness of 10 μm ”
Torayca "T-700S (manufactured by Toray Industries, Inc.) was uniformly arranged in a substantially vertical direction to prepare a negative electrode composed of copper foil and carbon fiber.

(2) Preparation of positive electrode Commercially available lithium carbonate (Li ₂ CO ₃ ) and basic cobalt carbonate
(2CoCO ₃ .3Co (OH) ₂ ) was weighed so that the molar ratio was Li / Co = 1/1, mixed in a ball mill, and then heat treated at 900 ° C. for 20 hours to obtain LiCoO ₂ . This was crushed with a ball mill, and artificial graphite was used as a conductive material, polyvinylidene fluoride (PVdF) was used as a binder, and N-methylpyrrolidone was used as a solvent. LiCoO ₂ / artificial graphite / PVdF = 80/15/5 by weight ratio. To prepare a positive electrode slurry, and this slurry was applied onto both surfaces of an aluminum foil having a thickness of 13 μm, dried, and pressed to prepare a positive electrode.

(3) Preparation of Battery The negative electrode prepared in the above (1) and the positive electrode prepared in the above (2) were laminated with the width and length shown in Table 1 through the separator of the porous polypropylene film. In Example 1, the negative electrode was wound as the outermost layer to obtain a cylindrical electrode body. In Example 2, an electrode body was obtained in the same manner as in Example 1 except that the outermost carbon fiber on the surface layer was removed and the length was set as shown in Table 1.

In Comparative Example 1, as shown in Table 1, the electrode was prepared in the same manner as in Example 1 except that the positive electrode was made larger than the negative electrode and the positive electrode was wound so as to come to the outermost layer. Got the body

Insert these electrode bodies into an AA battery can and insert 1
The secondary batteries of Example 1, Example 2 and Comparative Example 1 were obtained by charging and sealing an electrolytic solution containing mol of lithium tetrafluoroboride.

(4) Evaluation of Battery Performance The battery performance of Example 1, Example 2 and Comparative Example 1 was evaluated under the following conditions.

At the beginning of charging, charging was started at a constant current of 200 mA, and after the charging voltage reached 4.3 V, charging was performed at a constant voltage for a total of 8 hours. Also, the discharge start-up voltage was set to 2.7 V, and the discharge current was 50 mA and 1000 mA.
The capacity was measured at.

Regarding the cycle characteristics, under the same charging conditions as above, 100 cycles were carried out at a discharge current of 800 mA, and the discharge capacity retention rate was examined.

Table 2 shows the evaluation results of the battery performance for Examples 1, 2 and Comparative Example 1 of the present invention.

As shown in Table 1, although the positive electrode lengths of Examples 1 and 2 were shorter than those of Comparative Example 1, the capacity and the cycle characteristics were equal or longer. Further, in Example 2, the cycle characteristics could be further improved.

[0030]

[Table 1]

[0031]

EFFECTS OF THE INVENTION According to the present invention, in a battery having a structure in which it is wound in a roll, by arranging an electrode using carbon fiber in the outermost layer of the electrode body, the amount of transition metal oxide which is an expensive material is used. And the battery can be manufactured at low cost. In addition, cycle characteristics are also improved. As a further improvement, when the carbon fiber which is the electrode material on the surface layer side of the outermost layer negative electrode of the electrode body is removed, that is, when the useless portion is excluded, the cycle characteristics are further improved.

[Brief description of drawings]

FIG. 1 shows a schematic view of a secondary battery of the present invention.

[Explanation of symbols]

 1: Carbon fiber 2: Negative electrode current collector 3: Positive electrode material 4: Positive electrode current collector 5: Separator

Claims (8)

[Claims] 1. A battery electrode body having a structure in which a sheet-shaped positive electrode and a sheet-shaped negative electrode are wound in a roll shape with a separator interposed therebetween, wherein the positive electrode and / or the negative electrode is an electrode using carbon fiber. The outermost layer electrode is an electrode using carbon fiber, and an electrode body for a battery. 2. The electrode body for a battery according to claim 1, wherein a current collector is used in the electrode using the carbon fiber. 3. The battery electrode body according to claim 1, wherein the active material of the outermost layer is removed from the outermost layer electrode. 4. The battery electrode body according to claim 2, wherein the current collector is made of a metal foil. 5. The battery electrode body according to claim 2, wherein the carbon fibers are arranged substantially perpendicular to the longitudinal direction of the current collector. 6. The battery electrode body according to claim 1, wherein the positive electrode comprises a transition metal oxide. 7. The transition metal oxide containing LiCoO ₂ or LiNiO ₂ as a main component.
The electrode body for a battery as described. 8. A secondary battery comprising the battery electrode body according to any one of claims 1 to 7.