JPH07130355A - Electrode for secondary battery - Google Patents

Abstract

PURPOSE:To carry out uniform doping and provide high power secondary batteries by preparing electrodes for secondary batteries from carbon fiber and a metal foil. CONSTITUTION:An electrode is composed of carbon fiber and a metal foil. The shape is not especially restricted, however ones with the structure like cloth, felt, or a unidirectionally oriented sheet are preferable. One with unidirectionally oriented sheet structure is most preferable among these since the one with sheet structure can be filled at high density. An electrode with sheet structure having the unidirectionally oriented carbon fiber density preferably below 500g/m<2> and above 10g/m<2>, more preferably below 150g/m<2> and above 50g/m<2> is used. The metal foil is not specially restricted, however one with low electric resistance is preferable and thin one to fill a battery with carbon as an active material as much as possible is more preferable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode composed of carbon fiber and metal foil, and a secondary battery using the electrode.

[0002]

2. Description of the Related Art In recent years, with the widespread use of portable devices such as video cameras and notebook computers, demand for small and high capacity secondary batteries has increased. Most of the secondary batteries currently used 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. Therefore, high-energy secondary batteries have been studied using lithium metal, which is the base metal, as the negative electrode.

However, in a secondary battery in which lithium metal is used for the negative electrode, there is a risk that lithium will grow into dendrites due to repeated charging and discharging, causing a short circuit and igniting. In addition, since highly active metallic lithium is used, it is inherently dangerous, and there are many problems in using it for consumer use. In recent years, a lithium ion secondary battery using various carbonaceous materials has been devised as a device that solves such a safety problem and enables high energy peculiar to a lithium electrode. This method utilizes the fact that the carbonaceous material is doped with lithium ions during charging and has the same potential as that of metallic lithium, so that it can be used for the negative electrode instead of metallic lithium. In addition, during discharge, the doped lithium ions are dedoped from the negative electrode and return to the original carbonaceous material. When such a carbonaceous material doped with lithium ions is used as the negative electrode, there is no problem of dendrite generation, and since there is no metallic lithium, there is a feature that it is also excellent in safety, Currently, research and development are actively carried out.

As a secondary battery using an electrode using the above-mentioned carbonaceous material doped with lithium ions,
JP-A-57-208079, JP-A-58-931
76, JP-A-58-192266, JP-A-62-90863, JP-A-62-122066 and JP-A-3-66856 are known. Such a carbonaceous material is generally in the form of powder, and a polymer binder such as Teflon or vinylidene fluoride is required for molding the electrode. However, when carbon fiber or a carbon fiber structure is used as the carbonaceous material instead of powder, an electrode can be prepared without using a binder or in a small amount. Further, the carbon fiber or the carbon fiber structure is said to be excellent in terms of chemical stability with respect to the electrolyte, structural stability against volume expansion due to doping, and repeated charge / discharge characteristics. A secondary battery using such an electrode is disclosed in JP-A-60-
No. 36315, No. 60-54181, No. 62-103991, No. 62-1545.
64, JP-A-63-58763, JP-A-2
No. 82,466, etc. are known.

[0005]

However, in the case of an electrode using carbon fiber, it is difficult to electrically connect it to the metal which is the extraction electrode. In the case of carbon powder electrodes, the powder is mixed with a binder and pressed onto a metal net, or a slurry is applied to the metal foil, and this metal net or metal foil is connected to a terminal as a current collector. can do. On the other hand, in the case of carbon fiber, a method of sandwiching the end of the carbon fiber with a net-shaped or foil-shaped metal current collector has been tried so far. However, if the carbon fiber is simply sandwiched between the metal current collectors, the overvoltage increases due to contact resistance,
There is a problem of low capacity. Furthermore, when the electrode has a large area, there is a problem that the potential difference increases at a position away from the metal current collector due to the resistance of the carbon fiber, and uniform doping does not occur.

The present invention is intended to solve the drawbacks of the prior art, and an object thereof is to obtain a high-performance secondary battery which enables uniform doping in a battery using carbon fibers as electrodes. .

[0007]

The present invention has the following constitution in order to solve the above problems.

[(1) An electrode for a secondary battery, which is composed of carbon fiber and a metal foil.

(2) A secondary battery using the electrode according to the above item (1). The electrode of the present invention is characterized by being composed of carbon fiber and a metal foil, and the shape thereof is not particularly limited, but preferred embodiments will be exemplified below.

When the carbon fiber of the present invention is used as an electrode, it may have any form, but a cloth-like or felt-like structure or a uniaxially arranged sheet-like structure is a preferred form. Examples of fabric-like or felt-like structures include woven fabrics, knitted fabrics, braids, laces, nets,
Examples include felt, paper, non-woven fabric, and mat. From the point of view of carbon fiber properties and electrode characteristics, weaving and felt,
A unidirectional array or the like is preferable.

The sheet-like structure arranged in the uniaxial direction is the most preferable method because the packing density can be increased among these. In this case, it is preferable that the carbon fibers are uniformly arranged, and if the arrangement is uneven, uniform doping tends to be difficult to occur.

The unit weight of the carbon fibers uniformly arranged in the uniaxial direction is preferably 500 g / m ² or less, 10 g / m ² or more, more preferably 150 g / m ² or less,
Those having a weight of 50 g / m ² or more are used. When the basis weight is large, the thickness of the carbon fiber structure becomes large, and the resistance in the thickness direction becomes large, so that uneven doping may occur, and it tends to be difficult to use at high output. When the basis weight is small, the amount of carbon fibers of the active material in the whole negative electrode is small, so that the amount of carbon fibers that can be filled in the battery is small and the energy density of the battery tends to be low.

The carbon fiber used in the present invention is not particularly limited, and a carbonized organic material is generally used. Specifically, polyacrylonitrile (PA
N), PAN-based carbon fibers, pitch-based carbon fibers obtained from pitch such as coal or petroleum, cellulose-based carbon fibers obtained from cellulose, vapor-grown carbon fibers obtained from gas of low molecular weight organic substance, and the like. However, in addition thereto, carbon fibers obtained by firing polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenol resin, furfuryl alcohol and the like may be used. Among these carbon fibers, depending on the characteristics of the electrode and battery in which the carbon fibers are used, it is necessary to appropriately select the carbon fibers that satisfy the characteristics.

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 preferable. In particular, in terms of good doping with alkali metal ions, especially lithium ions, P
AN-based carbon fiber is preferably used.

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 preferable to use several kinds of carbon fibers having different diameters.

The metal foil in the present invention is not particularly limited, but a metal foil having a small electric resistance is preferable, and a metal foil having a small thickness for filling a large amount of carbonaceous material as an active material in the battery is preferable. preferable. The electric resistance is preferably 1.0 × 10 ^{−4 to} 1.6 × 10 ⁻⁶ Ω · cm, and the thickness is preferably 3 to 200 μm.

Specific examples of metals include gold, silver, copper, platinum, aluminum, iron, nickel, chromium, manganese,
Examples thereof include lead, tungsten, and titanium, and alloys of the above metals such as stainless steel may be used. When the thickness of the metal foil becomes thicker, the amount of the active material contained in the battery decreases, so that the foil having a small thickness is preferably used. Copper foil is preferably used in terms of electrical resistance, thickness of metal foil, and cost.

The method of integrating the sheet-shaped carbon fiber and the metal foil is not particularly limited, but for example, a method of pressure-bonding the carbon fiber to the metal foil by a roll press or the like, Teflon or polyvinylidene fluoride, etc. There is a method of adhering carbon fiber to a metal foil using a small amount of a binder.

By thus forming the electrode in which the carbon fiber and the metal foil are integrated, the contact resistance can be reduced, and the distance between the metal current collector and the carbon fiber can be reduced, so that the potential difference due to the resistance of the carbon fiber is also reduced. Get smaller. Therefore,
It is also possible to solve the problems of capacity reduction due to overvoltage caused by contact resistance and uneven doping caused by potential difference due to resistance of carbon fiber.

The electrode composed of the carbon fiber and the metal foil of the present invention can be used as an active electrode of various batteries, and what kind of battery such as a primary battery or a secondary battery is particularly limited. It is not something that will be done. Among these, it is preferably used as a negative electrode of a secondary battery. As a particularly preferable secondary battery, a secondary battery using a non-aqueous electrolytic solution containing an alkali metal salt such as lithium perchlorate, lithium borofluoride, and phosphorus hexafluoride / lithium can be mentioned.

When the electrode of the present invention is used in a non-aqueous electrolyte secondary battery containing an alkali metal salt, the cation or anion doping of carbon fiber is utilized, and the cation-doped carbon fiber is used. Carbon fiber doped with anions will be used for the negative electrode.
These should be able to be used for the positive electrode or the negative electrode depending on various characteristics of the carbon fiber, but it is not always necessary to use both electrodes as the electrodes of the present invention, and an electrode composed of the carbon fiber of the present invention for the negative electrode, It is also a preferred embodiment to use an electrode containing no carbon fiber as the positive electrode.

When an electrode containing no carbon fibers is used for the positive electrode, in addition to carbonaceous materials other than fibers, artificial or natural graphite powder, fluorinated carbon, metals or metal oxides, and other organic compounds and organic compounds are used. A molecular compound or the like can be used as the positive electrode. In this case, in the positive electrode made of an inorganic compound such as a metal or a metal oxide, charge / discharge reaction occurs by utilizing cation doping and dedoping. In the case of an organic polymer compound, a charge / discharge reaction occurs due to anion doping and undoping. As described above, various charging / discharging reaction modes are adopted depending on the substance, and these are appropriately selected according to the required positive electrode characteristics of the battery.

The positive electrode containing no carbon fiber includes inorganic compounds such as transition metal oxides and transition metal chalcogens containing alkali metal, polyacetylene, polyparaphenylene,
Examples of the positive electrode used in ordinary secondary batteries include conjugated polymers such as polyphenylene vinylene, 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,
Transition metal oxides and transition metal chalcogens such as vanadium, chromium, iron, copper and titanium are preferably used. Li
CoO ₂ and LiNiO ₂ are most preferably used because they have a high voltage and a large energy density.

The electrolytic solution of the secondary battery using the electrode of the present invention is not particularly limited, and a conventional electrolytic solution is used, and examples thereof include an acid or alkaline aqueous solution or a non-aqueous solvent. Among these, as the electrolytic solution of the secondary battery composed of the above-mentioned non-aqueous electrolytic solution containing an alkali metal salt, propylene carbonate, ethylene carbonate, γ-butyrolactone, N-methylpyrrolidone, acetonitrile, N, N-dimethylformamide, Dimethyl sulfoxide, tetrahydrofuran, 1,3-dioxolane,
Methyl formate, sulfolane, oxazolidone, thionyl chloride, 1,2-dimethoxyethane, diethylene carbonate, derivatives and mixtures of these are preferably used. The electrolyte contained in the electrolytic solution is an alkali metal,
Particularly, lithium halides, perchlorates, thiocyanates, borofluorides, phosphorous fluorides, arsenic fluorides, aluminum fluorides, trifluoromethylsulfates and the like are preferably used.

The secondary battery using the electrode of the present invention can be used as a video camera, a personal computer, a word processor, a radio-cassette, by utilizing the features of light weight, high capacity and high energy density.
It is widely applicable to portable small electronic devices such as mobile phones.

[0026]

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 (1) Preparation of Electrode Commercially available PAN-based carbon fiber "Torayca" T-300 (manufactured by Toray Industries, Inc.) was uniformly placed on a copper foil having a thickness of 15 μm in a uniaxial direction and adhered thereto. By doing so, the copper foil and the carbon fiber were integrated, and an electrode made of the copper foil and the carbon fiber having a basis weight of the carbon fiber of 100 g / m ² was prepared.

(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 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 To prepare a positive electrode slurry, and this slurry was applied onto an aluminum foil having a thickness of 15 μm, dried and pressed to obtain a positive electrode.

(3) Preparation of Battery The two electrodes prepared in the above (1) and (2) were superposed with a porous polypropylene film (Celguard # 2500, manufactured by Daicel Chemical Industries, Ltd.) interposed therebetween, A cylindrical electrode body was obtained by winding. The above electrode body was immersed in a beaker-type cell containing an electrolyte solution of propylene carbonate containing 1M lithium perchlorate, and electrode terminals were taken out from the copper foil and aluminum foil to obtain a secondary battery.

(4) Evaluation of Battery The charging evaluation of the secondary battery prepared above was performed. The current density per weight of carbon fiber is 40 mA / g constant current, 4.
Charged to 3V. The discharge capacity of the secondary battery obtained from the amount of charge discharged after charging was 320 mAh / g based on the weight of the carbon fiber used in the battery.

[0031]

EFFECTS OF THE INVENTION According to the present invention, in a battery using carbon fibers as an electrode, uniform doping is possible, so that a high performance secondary battery can be produced.

Claims (12)

[Claims] 1. An electrode for a secondary battery, comprising a carbon fiber and a metal foil. 2. An electrode for a secondary battery according to claim 1, wherein the carbon fibers are uniformly arranged in a uniaxial direction on the metal foil. 3. The unit weight of the carbon fiber is 500 g / m ² or less and 10 g / m ² or more.
The described secondary battery electrode. 4. The electrode for a secondary battery according to claim 1, wherein the basis weight of the carbon fiber is 150 g / m ² or less and 50 g / m ² or more. 5. The electrode for a secondary battery according to claim 1, wherein the metal foil is a copper foil. 6. A secondary battery using an electrode composed of carbon fiber and a metal foil. 7. The secondary battery according to claim 6, wherein the carbon fibers are uniformly arranged in a uniaxial direction on the metal foil. 8. The unit weight of the carbon fiber is 500 g / m ² or less and 10 g / m ² or more.
The secondary battery described. 9. The secondary battery according to claim 6, wherein the basis weight of the carbon fiber is 150 g / m ² or less and 50 g / m ² or more. 10. The secondary battery according to claim 6, wherein the metal foil is a copper foil. 11. A secondary battery using a transition metal oxide as a positive electrode material and the electrode according to claim 1 as a negative electrode material. 12. The transition metal is LiCoO ₂ or Li.
The secondary battery according to claim 11, which is NiO ₂ .