JPH0831409A - Battery electrode and secondary battery using the same - Google Patents

Abstract

(57) [Summary] [Structure] (1) An electrode for a battery in which carbon fibers are arranged in a direction substantially perpendicular to the winding direction of the electrode plate. (2) A secondary battery using the above electrode. [Effect] According to the present invention, a high capacity battery electrode and a secondary battery using the same can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode using carbon fiber 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. Conventionally, in the carbon powder electrode, in order to adopt a method in which powder is mixed with a binder and pressure-bonded to a metal net, or slurry is applied to the metal foil, the metal net or the metal foil is used as a current collector for a terminal. Can be connected to.

On the other hand, when carbon fibers are used, since the carbon fibers themselves have high conductivity, they should have a knitted shape or a felt shape without using a current collector, and they should be sandwiched between metal current collectors. However, if the carbon fiber is sandwiched between the metal current collectors, there is a problem that the overvoltage becomes large due to the contact resistance and the capacity becomes low.

It is an object of the present invention to provide a battery electrode having a small contact resistance and a high capacity, and a secondary battery using the same.

[0008]

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

[(1) A battery electrode in which carbon fibers are arranged in a direction substantially perpendicular to the winding direction of the electrode plate.

(2) A secondary battery using the above electrode. When carbon fiber is used as the electrode material, the resistance of the carbon fiber itself is lower than that of metal by one digit or more. Therefore, in the present invention, consideration is given to the case where the electrode becomes large and the case where high current discharge is attempted. Then, an electrode plate as a current collector is used.

When the long fibers using such carbon fibers are randomly adhered to the front and back surfaces of the electrode plate, there is a problem that the carbon fibers are easily separated from the current collector when the electrode is wound. As a result of earnest studies on this problem, the present inventors have found that the above problem can be solved by an electrode plate having a structure in which carbon fibers are arranged perpendicularly to the winding direction of the electrode plate.

Since the sheet-like carbon fiber structures arranged substantially perpendicular to the winding direction are less likely to apply tension or compression to the carbon fibers as compared with the sheet-like carbon fiber structures arranged in parallel, the electrode It is difficult to peel off when it is rolled up.
Further, since it has a sheet-like structure arranged in the uniaxial direction, it has a feature that the packing density can be increased. Furthermore, in the sheet-shaped carbon fiber structure arranged in parallel in the winding direction, the carbon fibers are broken by tension or compression,
Although there is a risk of short-circuiting, which penetrates the separator, such a risk can be dramatically reduced in the structure of the present invention.

A schematic view of the battery electrode of the present invention is shown in FIG. In FIG. 1, 1 is a carbon fiber and 2 is an electrode plate.

In the present invention, the basis weight of the carbon fibers uniformly arranged in the substantially vertical direction is not particularly limited, but is 500 g / m ² or less, 10 g / m ² or more, and further 150 g / m ² or less. , 50 g / m ² or more are preferably 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 occurs, 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 above-mentioned direction substantially perpendicular to the winding direction of the electrode plate on which the carbon fibers are arranged means a direction in which the arranged carbon fibers are substantially 90 degrees with respect to the winding direction. It is preferably ± 10 degrees.

The method of integrating the carbon fiber and the electrode plate is not particularly limited, but, for example, first,
A method in which carbon fibers are uniaxially aligned to form a sheet, and the sheet-shaped carbon fibers are pressure-bonded to a metal foil by a roll press or the like. There is a method of adhering to foil. As the binder, a fluororesin typified by Teflon or polyvinylidene fluoride, a thermoplastic resin such as celluloses typified by carboxymethyl cellulose, or a thermosetting resin such as polyimide, epoxy resin, or phenol resin. It is preferably used.

By thus forming the electrode in which the carbon fiber and the electrode plate are integrated, the contact resistance can be reduced, and since the distance between the metal current collector and the carbon fiber is small, the potential difference due to the resistance of the carbon fiber also occurs. Get smaller. Therefore, it is possible to solve the problem of non-uniform doping caused by a decrease in capacity due to overvoltage due to contact resistance and a potential difference due to resistance of carbon fibers.

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 a gas of a low molecular weight organic substance, and the like. However, in addition thereto, carbon fibers obtained by baking polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenol resin, furfuryl alcohol, etc. may be used. Among these carbon fibers, it is preferable to appropriately select carbon fibers satisfying the characteristics according to the characteristics of the 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.

When the carbon fiber in the present invention is used as an electrode, it may take any form, but as described above, a cloth-like or felt-like structure or a sheet-like structure arranged in a uniaxial direction is preferable. Form. Examples of fabric-like or felt-like structures include woven fabrics, knitted fabrics, braids, laces, nets, felts, papers, nonwoven fabrics, and mats. In terms of the properties of carbon fiber and electrode characteristics,
Fabrics, felts, unidirectional arrays, etc. are preferred.

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.

As the electrode plate, a metal foil, a metal woven fabric, a metal mesh or the like is used. As the metal foil, one having a low electric resistance is preferable, and moreover, the battery is filled with a lot of carbon material as an active material. For this reason, a thin material is preferable. Specifically as the metal foil, for example, gold, silver,
Examples thereof include copper, platinum, aluminum, iron, nickel, chromium, manganese, lead, tungsten, titanium, and the like, and alloys of the above metals such as stainless steel may be used. Copper foil is most preferably used in terms of electrical resistance, thickness of metal foil, and cost.

The electrode composed of carbon fiber and electrode plate of the present invention can be used as an active electrode of various batteries,
What kind of battery such as a primary battery or a secondary battery is used is not particularly limited. 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 carbon fiber doped with cation is used. Carbon fiber doped with anions will be used for the negative electrode.
When the electrode of the present invention is used, it can be used as either 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 electrode of the present invention. It is also a preferred embodiment to use an electrode composed of another positive electrode material different from carbon fiber as the negative electrode of the constituted electrode.

As other positive electrode materials, artificial or natural graphite powder, carbon fluoride, inorganic compounds such as metals or metal oxides, and organic polymer compounds are preferably used. In this case, in a positive electrode using an inorganic compound such as a metal or a metal oxide, a 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 it is preferable that these are appropriately selected according to the required positive electrode characteristics of the battery.

Specific examples of the positive electrode material include inorganic compounds such as transition metal oxides containing alkali metals and transition metal chalcogens, conjugated polymers such as polyacetylene, polyparaphenylene, polyphenylene vinylene, polyaniline, polypyrrole and polythiophene, disulfides. Examples of the positive electrode used in ordinary secondary batteries include crosslinked polymers having a bond and thionyl chloride. Among these, in the case of a secondary battery using a non-aqueous electrolytic solution containing a lithium salt, transition metal oxides and transition metal chalcogens such as cobalt, manganese, molybdenum, vanadium, chromium, iron, copper and titanium are It is preferably used. LiCo
O 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 them, 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.

[0029]

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 negative electrode PAN-based carbon fiber Torayca T300 (manufactured by Toray Industries, Inc.)
Were aligned in a uniaxial direction to form a sheet material uniformly arranged. At this time, the carbon fiber areal weight was 60 g / m ² . Wet this sheet material with N-methylpyrrolidone,
After smoothing with a roller, thickness 15μm, width 4cm,
An electrode was produced by laminating both surfaces of a copper foil having a length of 28 cm substantially perpendicularly to the length direction (winding direction).

(2) Preparation of positive electrode Commercially available lithium carbonate (Li ₂ CO ₃ ) and basic cobalt carbonate (2CoCO ₃ 3Co (OH) ₂ ) were used in a molar ratio of 1 /.
Weigh to 1 and mix in ball mill, then 900 ℃
And heat treated for 20 hours to obtain LiCoO ₂ . This is crushed with a ball mill, artificial graphite as a conductive material, polyvinylidene fluoride (PVDF) as a binder, and N- as a solvent.
Methylpyrrolidone was used to mix LiCoO ₂ / artificial graphite / binder = 80/15/5 to prepare a positive electrode slurry, which was coated on a 15 μm thick aluminum foil, dried and pressed. The positive electrode was obtained.

(3) Preparation of Battery The two electrodes prepared in the above (1) and (2) were superposed with a separator made of porous polypropylene film (Celguard # 2500, manufactured by Daicel Chemical Industries, Ltd.) on top of each other, and the internal volume was increased. It was wound into a 5 cc battery can and vacuum dried for a whole day and night to obtain a cylindrical electrode body. The above electrode body was immersed in a glass 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.

By repeating the same procedure, 10 batteries were produced. The yield was examined by examining the presence or absence of conduction between the positive and negative electrodes using a commercially available ohmmeter. For non-defective products, the battery was used to evaluate the charge / discharge of the secondary battery.
The capacity was evaluated at a charging voltage of 4.3V and a discharge end voltage of 2.7V. Charging was performed at 100 mA for 8 hours at a constant potential, and discharging was performed at 50 mA and 1000 mA. The charging condition of the cycle characteristics is the above-mentioned condition, and the discharging current is 800
It was performed 100 times at mA. The results are shown in Table 1.

Example 2 (1) Preparation of negative electrode PAN-based carbon fiber Torayca T300 (manufactured by Toray Industries, Inc.)
Were aligned in a uniaxial direction to prepare a sheet material uniformly arranged. The carbon fiber areal weight at that time was 60 g / m ² . Polyvinylidene fluoride (PVD as binder
F) is dissolved in N-methylpyrrolidone to give a weight concentration of 10%.
A solution of was prepared. The carbon fibers uniformly arranged in the above-mentioned uniaxial direction were immersed in this solution, and PVDF was uniformly applied so as to be 6% by weight based on the weight of the carbon fibers, and the carbon fibers were smoothed by a roller. Next, the thickness of this sheet material is 15μ.
An electrode was prepared by laminating both sides of a copper foil having a length of m, a width of 4 cm, and a length of 28 cm substantially perpendicularly to the length direction (winding direction) and drying.

(2) Preparation of positive electrode and battery Preparation was carried out in the same manner as in Example 1.

Example 3 (1) Preparation of Negative Electrode An electrode was prepared in the same manner as in Example 2 except that artificial graphite was used as a conductive agent instead of the binder PVDF.

(2) Preparation of Positive Electrode and Battery An electrode was prepared in the same manner as in Example 1.

Table 1 shows the results evaluated in the same manner as in Example 1.

Example 4 (1) Preparation of Negative Electrode Same as Example 2 except that artificial graphite as a conductive agent was additionally added at a ratio of 3% by weight based on the coating amount and the weight of carbon fiber. An electrode was prepared by the method of.

(2) Preparation of Positive Electrode and Battery Preparation was carried out in the same manner as in Example 1.

The results of evaluation by the same method as in Example 1 are shown in Table 1.

Comparative Example 1 (1) Preparation of Negative Electrode An electrode was prepared in the same manner as in Example 1 except that carbon fibers uniformly arranged in the uniaxial direction were laminated in parallel with the length direction of the copper foil. .

(2) Preparation of positive electrode and battery Preparation was carried out in the same manner as in Example 1.

The results evaluated in the same manner as in Example 1 are shown in Table 1.

[0045]

[Table 1]

[0046]

According to the present invention, a high capacity battery electrode and a secondary battery using the same can be provided.

[Brief description of drawings]

FIG. 1 shows a schematic view of an electrode of the present invention.

[Explanation of symbols]

 1: Carbon fiber 2: Electrode plate

Claims (12)

[Claims] 1. A battery electrode in which carbon fibers are arranged in a direction substantially perpendicular to the winding direction of an electrode plate. 2. The battery electrode according to claim 1, wherein the electrode plate is a metal foil. 3. The weight of the carbon fiber per 1 m ² is 30 g.
The electrode for a battery according to claim 1, which is 500 g or less. 4. The battery electrode according to claim 1, wherein the conductive powder is contained in an amount of 50% by volume or less based on the carbon fiber. 5. The battery electrode according to claim 4, wherein the conductive powder is carbon powder. 6. The battery electrode according to claim 1, further comprising a binder made of a thermoplastic resin. 7. The battery electrode according to claim 6, wherein the binder is polyvinylidene fluoride. 8. The battery electrode according to claim 1, which contains a binder made of a thermosetting resin. 9. A secondary battery using the electrode according to claim 1. 10. The secondary battery according to claim 9, wherein the electrode is used as a negative electrode. 11. The secondary battery according to claim 10, wherein a transition metal oxide is used as the positive electrode. 12. The secondary battery according to claim 11, wherein the transition metal oxide is LiCoO ₂ .