JPH03289116A - electric double layer capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electric double layer capacitor that exhibits stable performance over a long period of time.

[Conventional technology]

Electric double layer capacitors have a large capacitance and are therefore useful as backup power supplies for various electronic devices.

As shown in the cross-sectional view of FIG. 4, a conventional electric double layer capacitor is constructed by laminating a porous separator 1, polarizable electrodes 2 impregnated with an electrolyte on both sides, and a current collector 4 connected to a lead wire 3. The basic structure is such that these members are housed in an insulating container 5. Usually, the electrolyte solution is an aqueous sulfuric acid solution or an alkyl ammonium perchlorate dissolved in an appropriate organic solvent, and the polarizable electrode 2 is made of powdered activated carbon, fibrous activated carbon, carbon black, etc. Further, as the current collector 4, metals such as aluminum, stainless steel, and nickel are used. The current collector 3 is bonded to the polarizable electrode 2 by thermal spraying or bonding with an organic binder.

However, when the polarizable electrode is made of carbon material such as activated carbon, a phenomenon occurs in which a reaction current flows due to anodic oxidation during use, which reduces charging efficiency and further causes gas generation due to carbon oxidation, resulting in unreliability. Since there is a problem that leads to a decrease in properties, an attempt has been made to construct the polarizable electrode from a glassy carbon material having high oxidation resistance (Japanese Patent Application Laid-Open No. 63-244609).

In addition, conventional metal current collectors have the disadvantage that the withstand voltage of the capacitor decreases and the internal resistance gradually increases due to surface changes due to corrosion. It has also been proposed to use impermeable carbon (Japanese Patent Application Laid-Open No. 1986-1976 [Problem to be Solved by the Invention]) However, since flange carbon has a substantially non-porous structure, it has not been possible to use it as a polarizable electrode. If you try to use it, there will be a problem that the electrolyte holding capacity is insufficient.
Structures in which the current collector is made of glassy carbon or an impermeable carbon material impregnated with thermosetting resin have inferior current collecting ability compared to those made of metal, so it is necessary to There is a drawback that resistance increases.

The purpose of the present invention is to provide an electric double layer that can withstand long-term use by interposing an ultra-thin glassy carbon sheet between a metal current collector and a polarizable electrode of the conventional structure, unlike the above-mentioned prior art. We are trying to provide capacitors.

[Means to solve the problem]

The electric double layer capacitor according to the present invention for achieving the above object is obtained by baking and carbonizing aromatic polyimide resin films on both sides of a porous separator and having a thickness of 0.5 mm.
The structure is characterized by a structure in which a polarizable electrode and a metal confectionery electric body are laminated and integrated in a state where they are adjacent to each other via a glassy carbon sheet of 2m+e or less.

FIG. 1 is a sectional view showing an electric double layer capacitor according to the present invention, in which 1 is a porous separator made of a thin fibrous material such as a nonwoven synthetic fabric, and 2 is a polarizable electrode made of activated carbon, carbon black, etc. , 4 is a current collector made of metal such as argonium or stainless steel;
Reference numeral 6 denotes a glassy carbon sheet having a thickness of 0.2+o+ or less and interposed between the polarizable electrode 2 and the current collector 4 so as to separate them. In this way, the polarizable electrode 2 and the current collector 4
are stacked adjacent to each other with an extremely thin glass-like carbon sheet interposed therebetween, and housed in an insulating container 5 as a unit.

Normally, glassy carbon materials are made from thermosetting resins with a high residual carbonization rate, such as furan-based resins or phenolic resins, which are shaped into the desired shape and then fired and carbonized in a non-oxidizing atmosphere. It is manufactured by
It is extremely difficult to convert this type of resin raw material into sheet-like glass carbon with a thickness of less than 0.5 mm.

In the present invention, the glassy carbon sheet interposed between the polarizable electrode and the current collector is a smooth sheet with a thickness of 0.2 mm or less obtained by firing and carbonizing an aromatic polyimide resin film. .

As a means for forming a glassy carbon sheet with a thickness of 0.2+am or less using an aromatic bolide resin as a raw material,
Preferably, a ``Fill!'' film of an aromatic polyimide resin having a glass transition temperature (Tg) of 300°C or higher is sandwiched between carbonaceous press plates and heated at a temperature of 800 to 2100°C in a non-oxidizing atmosphere while applying pressure. At this time, by adjusting the film thickness of the aromatic polyimide resin used as a raw material and the pressing pressure during firing, a gas inorganic resin having a desired thickness in the range of 0.02 to 0.21 is adopted. It becomes possible to form a glass-like carbon sheet that is transparent and has excellent surface smoothness.

(Function) In the electric double layer capacitor according to the present invention, a polarizable electrode and a metal current collector are adjacent to each other via a glassy carbon sheet with a thickness of 0.2 mm or less obtained by firing and carbonizing an aromatic polyimide resin film. Because the electrolyte in the polarizable electrode comes into contact with the metal current collector due to the intervening action of the ultra-thin polarized film, the internal corrosion caused by corrosion of the current collector does not occur. Troubles during use such as resistance fluctuations are effectively prevented.

Therefore, an electric double layer capacitor is provided that exhibits stable performance over a long period of time without increasing the thickness of the capacitor.

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples.

Example 1 On both sides of a porous separator 1 made of a polypropylene nonwoven fabric with a thickness of 100 μm, a carbon polarizable electrode 2 and a stainless steel plate with a thickness of 100 μm are placed on both sides of a porous separator 1 made of a polypropylene nonwoven fabric with a thickness of 100 μm, via a glassy carbon sheet 6 of 0.020 m+m thickness. 5US316L)
An electric double layer capacitor (diameter 20mm, thickness 5n +
m) was prepared.

The polarizable electrode 2 is a mixture of 40 parts by weight of conductive carbon black [manufactured by Tokai Carbon ■, "TB 5500"] 5550 parts by weight of powdered activated carbon NzSA 1500 m/g) and 10 parts by weight of polytetrafluoroethylene (PTFE) powder. After that, it was pressed and formed. A sulfuric acid aqueous solution (30wtX) was used as the electrolyte.

The glassy carbon sheet 6 is made of an aromatic polyimide film with a thickness of 25 μm [manufactured by Toshi DuPont, “Kapton 1”]
00H”) between the graphite press plate and 60gf/cm.
It was produced by calcination and carbonization at 1800°C in a furnace maintained in a nitrogen gas atmosphere while applying a presser pressure of 180°C.

The characteristics of the electric double layer capacitor having the above configuration are as follows: rated voltage 1. It had high performance with Ov, capacity 0.8F, and internal resistance 0.2Ω. In addition, changes in internal resistance during charging and discharging cycles at a voltage of 0 to 0.9v were measured, and the results are shown in FIG. No change in internal resistance was observed, indicating stable performance.

Example 2 The electrolyte of Example 1 was converted into IM LiCj! 0. An electric double layer capacitor was fabricated using a propylene carbonate solution containing .

The characteristics in this case are rated voltage 3.5V, capacity 0.4F,
The internal resistance was 1.0Ω. In addition, changes in internal resistance during charging and discharging cycles at a voltage of 0 to 2V were measured, and the results are shown in FIG.

Comparative Example 1 An electric double layer capacitor corresponding to FIG. 5 was manufactured using the same structure as in Example 1 except that a glassy carbon sheet was not interposed between the polarizable electrode and the metal current collector.

The performance of this capacitor is as follows: rated voltage 0.9V, capacity 0.
It was 8F, and the internal resistance was 0.3Ω. Further, the internal resistance during charge/discharge cycles (voltage 0-0.9v) showed a change that rapidly increased after 1500 cycles, as shown in FIG. Therefore, the stability of the internal resistance was inferior to that of the structure of Example 1.

Comparative Example 2 The electrolyte of Comparative Example 1 was used as LM LiCj! An electric double layer capacitor was produced using a propylene carbonate solution containing 04 instead.

The characteristics in this case are rated voltage 3.6V, capacity 0.4F,
The internal resistance was 1.2Ω. In addition, the state of internal resistance during charge/discharge cycles (voltage 0 to 2ν) shows a change behavior that increases from around 1700 cycles, as shown in Figure 3, compared to Example 2 using the same electrolyte. It lacked stability.

[Effects of the Invention] As described above, according to the present invention, by interposing an ultra-thin glassy carbon sheet made from a specific raw material between a polarizable electrode and a metal current collector, thinness and lightness can be achieved. It becomes possible to supply an electric double layer capacitor whose stable performance is guaranteed over a long period of time without impairing the performance.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the electric double layer capacitor of the present invention, FIGS. 2 and 3 are graphs showing the relationship between the number of charge/discharge cycles and internal resistance in Examples and Comparative Examples, and FIG. 1 is a cross-sectional view showing an electric double layer capacitor with a conventional structure.

Claims (1)

[Claims] 1. On both sides of the porous separator, a polarizable electrode and a metal current collector are laminated adjacent to each other via a glassy carbon sheet with a thickness of 0.2 mm or less obtained by firing and carbonizing an aromatic polyimide resin film. An electric double layer capacitor with a double-layered structure.