JP2000012404A - Electric double-layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain improvement in capacity without damaging the characteristics of polytetrafluoroethylene as an adhesive agent at electrode foil production for an electric double-layer capacitor. SOLUTION: A polymer of at least one kind of butyl rubber (IIR), polyvinylidene fluoride(PVDF), ethylene propylene diene rubber(EPDM), natural rubber(NR), nitryl rubber(NBR), polyethylene(PE), polypropylene(PP), silicone rubber, vinyl acetate having lipophilicity or hydrophilicity higher than that of polytetrafluoroethylene(PTFE) is added to PTFE, and the wetness of activated carbon and electrolyte in the electrode is improved. Thus, the electric double- layer capacitor which improves capacity and lowering resistance is provided, while effectively utilizing the surface area of the activated carbon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double layer capacitor.

[0002]

2. Description of the Related Art An electric double layer capacitor is composed of a carbon electrode mainly composed of activated carbon and a liquid electrolyte, and stores electric charge by using an electric double layer formed at the solid-liquid interface when electricity is supplied. I do. Electric double layer capacitors use activated carbon with a large surface area and have the largest current storage capacity as a device that uses the capacitor phenomenon without electrochemical change.Therefore, in recent years, memory backup for integrated circuits and regeneration of electric vehicles It is used in energy systems and is attracting attention. As the electrolytic solution, an organic electrolytic solution obtained by dissolving a tetraalkylammonium perchlorate or a boron fluoride salt in an ethylene carbonate-based solvent or a lactone-based solvent, or an aqueous electrolytic solution of sulfuric acid or potassium hydroxide aqueous solution is used. However, the organic electrolytic solution is advantageous in terms of energy because the oxidation potential is high and the withstand voltage can be increased, and the aqueous electrolytic solution is advantageous in terms of output because the resistance can be reduced while the withstand voltage is low. In addition, since the battery operates according to a principle that does not involve an electrochemical change, it also has a feature that its life is extremely long as compared with a secondary battery. However, since the capacity is smaller than that of a secondary battery such as a lithium ion secondary battery, it is difficult for the battery to be used alone as a main power source, and further higher capacity has been desired.

[0003]

The capacity of an electric double layer capacitor depends on the main material, activated carbon, or its surface area, and it is necessary that the pore size sufficient to form an electric double layer be distributed in the activated carbon. is there. In recent years, various efforts have been made to increase the capacity, and with the advent of porous conductive polymers such as polyacene, the capacity of electric double layer capacitors has been increased. However, when theoretically considering the maximum capacity that an electric double layer capacitor can have based on the surface area of activated carbon, a capacity of about 150 F / g is generally feasible, but the actual capacity is about 10 to 15 F / g. However, the capacity of activated carbon has not been fully drawn out. This is due to the water and oil repellency of polytetrafluoroethylene (PTFE) used as a binder. PTF
E is a polymer with high chemical stability and oxidation resistance,
Although it has an excellent property that it becomes a net shape by mechanical stretching and strongly binds the conductive fine particles to ensure high conductivity, it has a problem that it prevents contact between the electrolyte and the activated carbon at the same time.

In order to solve this problem, it is effective to relatively reduce the ratio of PTFE to the conductive fine particles. However, if the ratio of the PTFE to the activated carbon electrode is less than 10%, the bonding force is weakened and the resistance increases. There is a problem that the mechanical strength is reduced.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a polymer having hydrophilicity or lipophilicity in PTF.
It is mixed with E. By mixing a polymer having hydrophilicity or lipophilicity with PTFE, the electrolyte penetrates into the pores of the activated carbon due to the hydrophilicity or lipophilicity of the added polymer without impairing the excellent properties of PTFE. The capacity of the capacitor can be increased. That is, an electrode material obtained by binding conductive fine particles and a collecting electrode with an adhesive obtained by mixing a polymer with polytetrafluoroethylene (PTFE) is used as an electrode material for an electric double layer capacitor. It is an electric double layer capacitor.

[0006] Alternatively, as an electrode material for an electric double layer capacitor, a polarizing electrode formed by mixing an adhesive obtained by mixing a polymer with polytetrafluoroethylene (PTFE) and conductive fine particles and a current collecting electrode are attached. An electric double layer capacitor using a combined electrode material.

The polymer described above is butyl rubber (IIR), polyvinylidene fluoride (PVD)
F), ethylene propylene diene rubber (EPDM), natural rubber (NR), nitrile rubber (NBR), polyethylene (PE), polypropylene (PP), silicone rubber,
An electric double-layer capacitor characterized by being at least one of vinyl acetate.

[0008] Further, the above-mentioned current collecting electrode is a foil or mesh mainly composed of at least one of aluminum, nickel and copper.

Further, the above-mentioned current collecting electrode is formed by applying a conductive rubber to a foil or a mesh mainly composed of at least one of aluminum, nickel and copper. It is.

[0010] The above-mentioned current collecting electrode is a conductive rubber sheet, which is an electric double layer capacitor.

Further, the conductive fine particles described above are at least one of activated carbon, conductive polymer, carbon black, ketjen black, acetylene black, nickel, titanium nitride, ruthenium oxide, and vanadium pentoxide. Characteristic electric double layer capacitor.

The above-mentioned polarization electrode may be made of aluminum,
An electric double-layer capacitor formed by forming a current collecting electrode by plasma spraying a metal containing at least one of nickel and copper as a main component.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS PT as an adhesive for conductive fine particles
By mixing a hydrophilic or lipophilic polymer with FE, the electrolytic solution can be permeated into the pores of activated carbon without impairing the excellent characteristics of PTFE, and the capacity of the electric double layer capacitor can be increased.

[0014]

EXAMPLE A mixture (slurry) of conductive fine particles and an adhesive was prepared with the composition shown in Table 1 using a mixer. The slurry was applied onto a collecting electrode using a roll coater, and the solvent was dried to produce a sheet-like activated carbon electrode. Note that an aluminum foil that had been etched and subjected to a chemical conversion treatment at about 2 V in advance was used as a collecting electrode.

[0015]

[Table 1]

[0016] 0.01 ml of propylene carbonate was dropped on the produced electrode, and the contact angle was measured with a cassette meter. The results shown in Table 2 were obtained. It is clear that the wettability of each of the examples is higher than that of the comparative example.

[0017]

[Table 2]

Next, as shown in FIG. 1, two activated carbon electrodes each having a lead wire connected to an activated carbon electrode cut out so as to have a predetermined area were wound through a separator paper to form a capacitor element. After drying the capacitor element, the capacitor element was impregnated with an electrolyte obtained by dissolving 0.6 mol / l of tetraethylammonium tetrafluoroborate in a solvent in which propylene carbonate and ethylene carbonate were in a ratio of 1: 1. It sealed using the aluminum case and the rubber packing, and produced 50 electric double layer capacitors each. The capacitance and resistance were measured, and the results shown in Table 3 were obtained. As is clear from Table 3, the electric double layer capacitor of the example has a larger capacity and a lower resistance value than the comparative example.
From the results shown in Table 2, it is considered that the electrode according to the present invention is easily wetted by the ethylene carbonate-based solvent which is a main component of the electrolytic solution. In addition, these capacitors
2.3 V was applied at 5 ° C., and the change over time in the characteristics was measured.
The result is shown in FIG. The embodiment has the same reliability as the comparative example.

[0019]

[Table 3]

The proportion of the polymer contained in the adhesive is effective from 20% by weight, but is preferably 50 to 90% by weight.

When the polymer to be added to the PTFE is a rubber-based polymer, a crosslinking agent may be mixed and crosslinked at the time of drying. For example, a tackifier of Taoka Chemical Co., Ltd. may be mixed as a crosslinking agent in an amount of about 10% based on the resin amount.

Further, the activated carbon electrode after the slurry is applied to the collecting electrode and dried may be pressed in a range of 500 kg / cm ^{2 or} less.

In the examples, IIR, PVDF and EPDM were used as polymers to be mixed with PTFE.
Similar effects can be obtained by using NBR, PE, PP, silicone rubber, or vinyl acetate, and a plurality of them may be used in combination.

In the examples, acetylene black was used as the conductive fine particles. However, the same applies when activated carbon, conductive polymer, carbon black, Ketjen black, nickel, titanium nitride, ruthenium oxide, or vanadium pentoxide is used. It has an effect, and a plurality of them may be used in combination.

In the embodiment, a chemically formed aluminum foil was used as the current collecting electrode. However, a foil, a mesh, or a foil or a mesh containing at least one of aluminum, nickel, and copper as a main component was coated with a conductive rubber. The same effect can be obtained by using a metal having at least one of aluminum, nickel and copper as the main component by plasma spraying.

[0026]

The electrode foil for an electric double layer capacitor according to the present invention impairs the excellent properties of PTFE by adding a polymer having hydrophilicity or lipophilicity to polytetrafluoroethylene (PTFE) as an adhesive. Thus, the electrolyte easily permeates into the pores of the activated carbon, and the capacity of the electric double layer capacitor can be increased, which is of great industrial value.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an electric double layer capacitor.

FIG. 2 Changes in capacitance and resistance value when 2.3 V is applied at 85 ° C.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Activated carbon electrode 2 Separator paper 3 Rubber packing 4 Lead wire 5 Capacitor element 6 Aluminum case

Claims (8)

[Claims] 1. An electrode material for an electric double layer capacitor, wherein an electrode material obtained by binding conductive fine particles and a collecting electrode with an adhesive obtained by mixing a polymer with polytetrafluoroethylene (PTFE) is used. Characteristic electric double layer capacitor. 2. An electrode material for an electric double layer capacitor, comprising: a polarizing electrode formed by mixing an adhesive obtained by mixing a polymer with polytetrafluoroethylene (PTFE) and conductive fine particles; and a current collecting electrode. An electric double layer capacitor characterized by using a combined electrode material. 3. The polymer according to claim 1, wherein the polymer is butyl rubber (IIR), polyvinylidene fluoride (PVDF), ethylene propylene diene rubber (E).
PDM), natural rubber (NR), nitrile rubber (NB
R), polyethylene (PE), polypropylene (P
An electric double layer capacitor characterized by being at least one of P), silicone rubber, and vinyl acetate. 4. The electric double layer capacitor according to claim 1, wherein the current collecting electrode is a foil or a mesh mainly containing at least one of aluminum, nickel and copper. 5. The current collecting electrode according to claim 1, wherein the conductive rubber is applied to a foil or a mesh mainly containing at least one of aluminum, nickel and copper. Characteristic electric double layer capacitor. 6. The electric double layer capacitor according to claim 1, wherein the current collecting electrode is a conductive rubber sheet. 7. The conductive fine particles according to claim 1, wherein the conductive fine particles are selected from the group consisting of activated carbon, conductive polymer, carbon black, Ketjen black, acetylene black, nickel, titanium nitride, ruthenium oxide, and vanadium pentoxide. An electric double layer capacitor characterized by at least one type. 8. An electric double layer capacitor comprising a current collecting electrode formed by plasma spraying a metal containing at least one of aluminum, nickel and copper on the polarized electrode according to claim 2.