JP3159754B2 - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To easily realize an electrically conductive sheet having a low temperature and superior corrosion resistance and liquid impermeability by forming a conductive sheet from a gas impermeable carbide sheet which is produced by firing cellulosic fiber, carbon powders and phenolic resin. CONSTITUTION:A mixed manufactured sheet is produced from 25-60wt.% cellulosic fiber, a PVA and 3-25wt.% graphite powder by a paper making method, and this sheet is soaked in a solution of phenolic resin. A sufficiently impregnated paper sheet is then dried, so that a prepreg sheet is obtained. The amount or resin to be immersed (solid content) is set to 35-65wt.%. Eight prepreg sheets are laminated, and these laminated sheets are sandwiched between graphite plates. The sandwiched laminated sheets are then subjected to curing by heating under pressure, so that a laminated sheet is obtained. This laminated sheet is sandwiched between graphite plates, and then gradually heated in a nitrogen atmosphere. The temperature of the laminated sheet is increased so that it can be completely carbonized, whereby a gas impermeable carbide sheet is obtained. The thickness of this conductive sheet is set to 0.3-0.7mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor using an electric double layer formed at an interface between an electrode surface and an electrolytic solution, and more particularly, to a conductive sheet (conductive sheet) on the outer surface of the electric double layer capacitor. Collector electrode).

[0002]

2. Description of the Related Art The basic structure of an electric double layer capacitor is shown in FIG.
The polarizable electrode 1 containing an electrolytic solution is divided by an ion-permeable and non-electron-conductive separator 2, and a conductive electrode serving as a collecting electrode is formed on the outer surface of each of the polarized electrodes 1. The sheet 3 is joined, and a sealing material 4 for preventing electrolyte leakage is arranged around the sheet 3.

[0003] Since a polarizing electrode needs to be chemically stable and have a large surface area, carbon materials (such as activated carbon powder and fibers) are often used. As the form of the polarized electrode, (1) a paste made of an electrolytic solution such as a sulfuric acid aqueous solution and a powder such as activated carbon (for example,
JP-A-62-130506, JP-A-63-244
609, JP-A-2-174210),
(2) A porous carbon former which is used by impregnating an electrolyte with an electrolytic solution, wherein the carbon former is obtained by foaming, carbonizing and activating a phenolic resin former (for example, see JP-A-2-29)
No. 7915), and those obtained by activating, shaping and carbonizing meso pitch (for example, JP-A-2-297915).
(3) An example in which a woven fabric of activated carbon fibers or the like is impregnated with an electrolytic solution (for example, JP-A-64-82514).

[0004] As the conductive sheet, (1) a laminated sheet of an adhesive layer made of ethylene resin and carbon black and a base material layer made of ethylene resin (and / or propylene resin) and carbon black (for example, JP-A-63-181412) and (2) a rubber material in which conductive carbon is dispersed (for example, JP-A-2-174210) have been proposed.

[0005]

The characteristics that the conductive sheet should have are that the electric resistance is low (low resistance), that it is not corroded by an electrolyte (such as sulfuric acid) (corrosion resistance), and that the electrolyte does not leak (liquid). Is impermeable). All of the above-mentioned conventional conductive sheets have relatively high electric resistance. In addition, a general carbon molded product (a product obtained by forming a pitch with a powder of coke or the like and carbonizing it) has a small liquid permeability and is not easily formed into a thin plate.

An object of the present invention is to provide a conductive sheet having these three characteristics and easy to manufacture.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to dispose a pair of polarizable electrodes via an ion-permeable and non-electron-conductive separator, and connect a conductive sheet to both outer surfaces of the polarized electrodes. In the electric double layer capacitor, the conductive sheet is constituted by a sheet of gas-impermeable carbide obtained by firing cellulosic fiber, carbon (including graphite) fine powder, and phenol resin.

[0008] The proportion of these components cellulosic fiber, carbon fines and phenolic resin is 25-60.
%, Preferably 3 to 25% and 35 to 65% by weight. Cellulose fibers are easy to make paper, but a small amount (20% by weight or less) of polyacrylonitrile or polyvinyl alcohol fibers can be added to maintain the strength of the papermaking sheet. These act as a binder between the cellulose fibers and improve the sheet strength.

Polyacrylonitrile is melt-carbonized during firing after resin impregnation, and thus does not significantly affect the strength of the carbonized sheet. Polyvinyl alcohol is decomposed and volatilized during firing, and does not contribute to the strength of the carbonized sheet. In any case, if the amount is too large, the strength of the sheet after carbonization is reduced.
The content is preferably 0% by weight or less. The conductive sheet preferably has a thickness of 0.3 to 0.7 mm and an electric resistivity of 5 mΩ · cm or less.

As the cellulosic fibers, pulp usually used for paper is suitable, and short cellulose fibers such as rayon and cotton may be used. The fibers are formed into a sheet, and therefore a papermaking method is easy and preferable. In that case, the fiber length is desirably 5 mm or less. Further, commercially available paper, in particular, filter paper may be used. The carbon fine powder is preferably a graphite fine powder crushed to about 50 μm or less in order to enhance conductivity. The phenol resin is preferably of a resol type, and the fiber sheet is impregnated with an uncured liquid. In order to facilitate the impregnation, it is desirable to add an organic solvent such as acetone to the phenol resin for adjusting the viscosity. In the present specification, the amount of the phenol resin is indicated by the amount of resin solid content.

[0011] In order to produce the conductive sheet according to the present invention, basically, paper such as pulp is impregnated with a phenol resin, carbon fine powder is added at the time of paper making or impregnation, and then dried. Then, the resin is cured and fired at a high temperature to obtain a gas-impermeable carbide sheet. Further, the dried impregnated sheets may be laminated and pressure-bonded before curing, and pressure-bonding and curing may be simultaneously performed by hot pressing.

The cellulose fiber is used in an amount of 25 to 65% by weight (preferably 30 to 50% by weight) in order to facilitate papermaking and maintain the strength of the sheet. 35 to 65% by weight (preferably 40 to 60% by weight) in order to fill the carbon fines between the fibers and to maintain the carbon fines between the fibers.
5% by weight (preferably 10 to 20% by weight).

[0013] The polyacrylonitrile and polyvinyl alcohol fibers added additionally are suitably mixed with the cellulose fibers in the papermaking process, and the graphite fine powder is suitably mixed during the papermaking process or the impregnation with the phenol resin. In the case where the sheet is included at the same time as the carbon fine powder is impregnated with the resin, the cellulose fiber is made into a paper (sheet) by a known method (after a commercially available paper is prepared), and the viscosity is reduced with an organic solvent. The carbon fine powder is mixed with the phenol resin solution which has been easily impregnated and mixed well, and the sheet is immersed and impregnated in the resin solution, and at the same time, the carbon fine powder is uniformly dispersed throughout the sheet. The impregnation amount is adjusted by passing the sheet pulled up from the resin solution between rolls as necessary. Also,
This impregnation amount can also be adjusted by adjusting the resin concentration with an organic solvent.

The sheet impregnated with the resin and the carbon fine powder is dried at 120 to 180 ° C. to obtain a prepreg sheet. When this prepreg sheet is thick (0.5 to
(Thickness of about 1.0 mm), it can be cured and fired as it is to obtain a conductive sheet of a gas-impermeable carbide. However, if the thickness is large, it is difficult to make paper and it is difficult to uniformly infiltrate the resin and carbon fine powder at the time of impregnation, so that the prepreg sheet is thin (0.2 to It is desirable to make a plurality of the layers, and press, cure, and fire them.

The curing is carried out by heating to 150 to 200 ° C., and at this time, it is preferable to compress the prepreg sheet with a graphite plate or the like by applying a pressure of 0.5 to 10 kg / cm ² .
Prevents large air holes in the sheet due to compression,
Furthermore, in the case of lamination, the adhesion between the sheets is improved. Next, the cured sheet is fired under an inert atmosphere,
If the temperature rise at that time is too early, the decomposition and volatilization of the resin and the fiber proceed rapidly, causing the generation of large pores.
C. for about 20 to 100 hours. It is desirable to heat to 800 ° C. or higher in order to obtain a gas-impermeable carbide, and there is no particular limitation on the maximum firing temperature, and it is possible to heat up to about 3000 ° C. in the same manner as ordinary carbonization of carbon. . In particular, firing at a high temperature is preferable because impurities can be volatilized and removed. Further, it is preferable that the sheet is sandwiched between graphite plates so as not to be warped during the firing, and then the firing is performed.

[0016]

In the conductive sheet of the electric double layer capacitor according to the present invention, since the phenol resin is sufficiently penetrated between the cellulose fibers and is cured and baked in a state of covering the carbon fine powder, it is carbonized. ) It is obtained as a gas-impermeable carbide sheet with almost no rate, and its electrical resistivity is also 5 mΩ ·
cm and smaller. The thickness of the conductive sheet is 0.3 to 0.5.
A thickness of 7 mm is preferable. If the thickness is larger than 7 mm, the electric resistance increases, which is disadvantageous for downsizing of the electric double layer capacitor itself. On the other hand, if it is thin, the mechanical absolute strength is weak and the handling property is deteriorated.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings with reference to embodiments and comparative examples of the present invention. Example 1 70% by weight of beaten cellulosic fiber (wood pulp: Canadian freeness), PVA (Kuraray Co., Ltd., V
PB105, 1 denier, 4 mm length) 10% by weight and graphite fine powder having a particle size of 30 μm or less (VFG- manufactured by Showa Denko KK)
30): From 20% by weight, a mixed sheet was obtained by a conventional papermaking method. This sheet had a thickness of 0.2 mm. The sheet was immersed in a phenol resin solution dissolved in ethyl alcohol to be sufficiently impregnated, pulled up, and dried at 150 ° C. for 1 minute to obtain a prepreg sheet. The resin impregnation amount (solid content) was 51% by weight.

Eight of these prepreg sheets are laminated, sandwiched between graphite plates, heated at 150 ° C. while pressurizing at 10 kg / cm ² , and held for 10 minutes to cure, thereby obtaining a thickness of 1.0 mm.
Was obtained. Next, the laminate was heated gradually in a non-oxidizing atmosphere (nitrogen atmosphere) while being sandwiched between graphite plates to prevent warping, and heated to 1000 ° C. for 4 days to completely laminate the laminate. It was carbonized into a gas-impermeable carbide sheet. After cooling to room temperature by natural cooling, the graphite plate was removed to obtain a conductive sheet having a thickness of 0.6 mm.

This conductive sheet has an electric resistivity of 2.1 m.
Ω · cm and air permeability (gas passage rate) is 2.3 × 10
^-10 cm ² / sec (nitrogen gas, 1 atm, room temperature), flexural strength was 1630 kg / cm ² , and bulk density was 1.63 g / cm ³ . The conductive sheet thus manufactured can be used for the electric double layer capacitor shown in FIG. At such an air permeability, the electrolyte contained in the polarizable electrode hardly leaks out, and the gas impermeable carbide sheet is not corroded by the electrolyte.

[0020]

As described above, a conductive sheet having excellent characteristics of low resistance, liquid impermeability and corrosion resistance can be easily obtained by using a papermaking method. When used in a multilayer capacitor, the internal resistance of the capacitor can be reduced and the reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a basic configuration of an electric double layer capacitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Polarizable electrode 2 ... Separator 3 ... Conductive sheet 4 ... Sealant

Claims (5)

(57) [Claims] 1. An electric double layer capacitor in which a pair of polarizable electrodes are disposed via an ion-permeable, non-electron conductive separator, and conductive sheets are bonded to both outer surfaces of the polarized electrodes. The electric double layer capacitor, wherein the conductive sheet is formed of a sheet of gas impermeable carbide obtained by firing cellulosic fiber, carbon fine powder, and phenol resin. 2. The use ratio of the cellulosic fiber, carbon fine powder and phenol resin is 25 to 60% by weight,
The electric double layer capacitor according to claim 1, wherein the content is 25% by weight and 35 to 65% by weight. 3. An electric double-layer capacitor in which a pair of polarizable electrodes is disposed via an ion-permeable and non-electron-conductive separator, and a conductive sheet is bonded to both outer surfaces of the polarized electrodes. The conductive sheet is characterized by being constituted by a sheet of a gas-impermeable carbide obtained by firing cellulosic fiber, carbon fine powder, phenol resin, and at least one additional component of polyacrylonitrile fiber and polyvinyl alcohol fiber. Electric double layer capacitor. 4. The use ratio of the cellulosic fiber, carbon fine powder, phenol resin and additional component is 25 to 60% by weight, 3 to 25% by weight, 35 to 65% by weight and 20% by weight or less. The electric double layer capacitor according to claim 3, wherein 5. The conductive sheet has a thickness of 0.3 to 0.3.
4. The electric double layer capacitor according to claim 1, wherein the electric double layer capacitor has a thickness of 0.7 mm and an electric resistivity of 5 m [Omega] .cm or less.