JPS6235609A - 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] [Industrial application fields] The present invention relates to an electric double layer capacitor.

[Prior Art] Conventionally, perchlorates, hexafluorophosphates, fluoroborates, trifluoromethanesulfonates, etc. have been proposed as solutes for electrolytes for electric double layer capacitors (Unexamined Japanese Patent Publication No. No. 49-6824, No. 50-44463, No. 59-
(Refer to each publication No. 2324097). However, when these known solutes are used, the resulting capacitors are not yet satisfactory in terms of withstand voltage, capacitance value, self-discharge, etc. [Problems to be Solved by the Invention] The present invention solves the following problems: This is an attempt to solve the above-mentioned problems in the prior art, and the object is to provide an electric double layer capacitor that has excellent withstand voltage, capacity, and self-discharge.

[Means for Solving the Problems] That is, the present invention provides an electric double layer capacitor that utilizes an electric double layer formed at the interface between a polarizable electrode and an electrolyte, in which trifluoromethanesulfonic acid is used as a solute in the electrolyte. This is an electric double layer capacitor characterized by using 42 CF3 S03 M (M is an alkali metal such as Li, Na, or ammonium). In the present invention, trifluoromethanesulfonic acid f! is used as the solute of the electrolyte. ! CF3 S03M (M is an alkali metal, ammonium) is important. By employing such a solute, a capacitor with excellent withstand voltage and capacity and less self-discharge can be obtained.

The concentration of such solute in the electrolyte is 0.1 to 3. O
M, particularly preferably 0.3 to 1.5M. If the concentration is too low, losses will increase due to an increase in internal resistance, while if it is too high, problems such as a decrease in stability due to precipitation of solutes in cold weather may occur. .

In the present invention, the type of solvent is not particularly limited, and various conventionally known or well-known solvents can be employed, among which electrochemically stable non-aqueous solvents such as propylene carbonate, γ-butyrolactone, Acetonitrile, dimethylformamide, 1,2-dimethoxyethane, sulfolane or nitromethane are preferred. Among these, especially propylene carbonate, γ-butyrolactone, acetic acid,
Particular preference is given to using nitriles. Preferably, such solvents are used in substantially anhydrous form.

Furthermore, the type of polarizable electrode is not limited, but activated carbon or activated carbon fiber, which is electrochemically inert to the electrolytic solution and has a large specific surface area, can be preferably employed.

The electric double layer capacitor of the present invention can be manufactured by filling the electrolytic solution as described above between polarizable electrodes that have been processed and formed to match the shape of the capacitor, and sealing the electrolytic solution in a case.

[Example] Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. In addition, in the following Examples and Comparative Examples, the test apparatus was assembled as follows.

First, activated carbon fibers on the cathode side (
Specific surface area 2000g/g, 3.14cm2.0.4mm
thickness), polypropylene nonwoven fabric separator (4.9cm
2,0.4mm thick), anode side activated carbon m fiber (3,14c+
02.2 mm thick) are placed one on top of the other. At this time, the activated carbon fibers are placed completely opposite each other with a separator in between.

Next, a polytetrafluoroethylene ring having threads on both the inside and outside surfaces is screwed into the container to fix the positions of the activated carbon Na fibers and the separator.

Then, a threaded polytetrafluoroethylene cup with a platinum wire mesh aggregate (200 mesh) attached to the tip of the platinum lead wire was screwed into the opening of the ring, and the continuity between the platinum I ord wire and the nickel container was measured using an LCR meter. Complete the set by checking with the two terminal method. Note that the platinum lead wire is drawn out to the outside through a hole provided in the center of the rod.

Using the test apparatus assembled as described above, the capacitor characteristics were evaluated using various electrolytes consisting of the combinations of solutes and solvents shown in Table 1.

The evaluation items were the decomposition voltage of the electrolyte, which is an indicator of capacity and withstand voltage, and the voltage drop during open circuit, which is an indicator of self-discharge characteristics, and each was measured using the following procedure.

To measure the capacity, first set the separator impregnated with the specified electrolyte and the activated carbon Na fibers in a container, and then turn on at 1.8V.
Perform time constant voltage charging. Thereafter, constant current discharge was performed at 1 mA, and the time required for the voltage between the terminals during discharge to reach Ov was measured, and the capacity was calculated from that value.

Table 1 Table 2 Decomposed voltage is determined by setting the test capacitor in the same way as when measuring capacity, applying DC voltage, and leakage current (L) after 10 minutes.
C) was measured, and the sharp rising point of LC with respect to the time of application was taken as the decomposition voltage of the electrolytic solution.

To test the self-discharge property, set the test capacitor in the same way as when measuring capacity, and then charge it at a constant voltage of 1.8V for 1 hour. After that, the circuit was opened, the voltage drop across the terminals was measured, and the rate of decrease was calculated from the voltage during charging.

The results of the above test are shown in Table 1. In addition, the number in Table 1 +
1.12, numbers 5 and 6 in Table 2 show conventional examples for comparison.

[Effect of the invention] The capacitor of the present invention has both capacitance and #voltage.

It is excellent in terms of self-discharge, and in a particularly preferred embodiment, it is excellent in terms of self-discharge. This results in an improvement of approximately 15% in terms of electrical strength, approximately 18% in withstand voltage, and 66% in self-discharge.

Claims (1)

[Claims] 1. In an electric double layer capacitor that utilizes an electric double layer formed at the interface between a polarizable electrode and an electrolyte, trifluoromethanesulfonate CF_3SO_3M (M is Li, Na, etc.) is used as a solute in the electrolyte. , an alkali metal such as K, ammonium salt). 2. The electric double layer capacitor according to claim 1, wherein the solute concentration is 0.1 to 3M. 3. The electric double layer capacitor according to claim 1, wherein M is an alkali metal such as ammonium, Li, Na, or K.