JPH0362295B2 - - Google Patents

Abstract

PURPOSE:To obtain an electric dipole layer capacitor having excellent withstanding voltage, capacitance and long-term reliability by using specific salt as a solute in an electrolyte. CONSTITUTION:Salt represented by formula I is employed as a solute in an electrolyte. In formula I, m=0-10 and n=0-10 hold (m and n are not brought to zero simultaneously), R represents a hydrogen atom, a 1-15 C alkyl group, an allyl group or a 6-15 C aryl group, and X represents BF4, PF6, ClO4, AsF6, SbF6, AlCl4 or RfSO3 (Rf represents 1-8 C fluoroalkyl group). Accordingly, an electric double-layered capacitor having a low capacitance deterioration rate under the conditions of a high temperature owing to high withstanding voltage and high long-term reliability is acquired.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an electric double layer capacitor. [Prior Art] Conventionally, electrolytic solutions used in electric double layer capacitors include electrochemical solutions such as alkali metal salts and tetraalkylammonium salts of perchloric acid, hexafluorophosphoric acid, tetrafluoroboric acid, or trifluoromethanesulfonic acid. It is known that a stable solute is dissolved in a polar organic solvent (JP-A-49-68254,
Publications such as JP-A-50-44463 and JP-A-59-232409). [Problems to be solved by the invention] However, electric double layer capacitors using these known solutes have the problem that sufficient performance cannot be obtained in terms of withstand voltage, capacitance value, long-term reliability, etc. It was hot. The present invention solves the above-mentioned problems and achieves a withstand voltage,
The objective is to provide an electric double layer capacitor with excellent capacity and long-term reliability. [Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and is an electric double layer that utilizes an electric double layer formed at the interface between a polarizable electrode and an electrolyte. In capacitors, the solute in the electrolyte is expressed by the general formula

[expression] or

[Formula] (In the formula, m = 0 to 10, n = 0 to 10, (m and n cannot be 0 at the same time) R is a hydrogen atom, an alkyl group having 1 to 15 carbon atoms, allyl group, or an aryl group having 6 to 15 carbon atoms,
is BF ₄ , PF ₆ , ClO ₄ , AsF ₆ , SbF ₆ , AlCl ₄ or
R _f SO ₃ (R _f is a fluoroalkyl group having 1 to 8 carbon atoms)
shows. ) The present invention provides an electric double layer capacitor characterized by being a salt represented by: As the solute of the electrolytic solution used in the present invention, it is necessary to use a salt represented by the above general formula. In these general formulas, m and n are 0 to 10, preferably 0 to 5 (however, m and n cannot be 0 at the same time), and R is a hydrogen atom or has a carbon number of 1 to 15, preferably 1.
-4 alkyl group, allyl group, or aryl group having 6 to 15 carbon atoms, preferably 6 to 10 carbon atoms. Examples of preferable alkyl groups include methyl group, ethyl group, propyl group, and butyl group. Examples of preferable aryl groups include phenol group (C ₆ H ₅ ^- ), tolyl group (CH ₃ ,
C ₆ H ₄ ⁻ ), naphthyl group (C ₁₀ H ₇ ⁻ ), and the like. Also, X is BF ₄ , PF ₆ , ClO ₄ , AsF ₆ , SbF ₆ ,
AlCl ₄ or R _f SO ₃ (R _f is a fluoroalkyl group having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms) is preferably used. [Function] The appropriate concentration of such a solute (electrolyte) in the electrolytic solution is 0.1 to 3.0M/, especially 0.5 to 3.0M/.
It is appropriate to set it to 1.5M/. If this concentration is too low, internal resistance increases and capacity decreases. On the other hand, if the temperature is too high, problems such as solute precipitation and decreased stability may occur when the temperature is lowered. The solvent for the electrolyte used in the present invention is not particularly limited, and includes propylene carbonate, butylene carbonate, γ-butyrolactone, acetonitrile, dimethylformamide,
1,2-dimethoxyethane, sulfolane, nitromethane, etc. are preferably used alone or in appropriate mixtures. Regarding the material of the polarizable electrode used in the present invention,
Although not particularly limited, it is preferable to use activated carbon powder or activated carbon fiber that is electrochemically inert to the electrolyte and has a large non-surface area. In particular, an electrode made by adding a binder such as polytetrafluoroethylene (PTFE) to activated carbon powder, roll-molding it into a sheet, and more preferably stretching it uniaxially or biaxially, has a capacitance per unit volume. It is preferably used because it has excellent strength and long-term reliability. As the separator interposed between the pair of polarizable electrodes in the present invention, a normal separator made of polypropylene fiber nonwoven fabric, glass fiber mixed nonwoven fabric, etc. can be used. Examples Next, examples and comparative examples will be specifically described based on the drawings. A unit cell (diameter 20 mm, thickness 2.0 mm) of a coin-type electric double layer capacitor as shown in FIG. 1, which is common to the examples and comparative examples of the present invention, was prepared in the following manner. First, 10% by weight of polytetrafluoroethylene was added to activated carbon powder (non-surface area: 2000 m ² /g) and formed into a sheet by wet kneading. The sheet thus obtained was punched out into a disk shape, and polarizable electrodes 1 and 2 (diameter 15 mm,
The polarizable electrodes 1 and 2 were placed facing each other with a separator 3 made of nonwoven polypropylene fibers interposed therebetween, and then placed in a stainless steel cap 4.
and an outer container consisting of a stainless steel can 5. Next, a predetermined electrolyte is injected into the unit cell, and the polarizable electrodes 1 and 2 and the separator 3 are
After the electrolyte was sufficiently impregnated into the container, the ends of the cap 4 and the can 5 were caulked and sealed via a polypropylene packing 6 to integrate them. Using the unit cell of the electric double layer capacitor manufactured as described above, the initial voltage when a voltage of 2.8 V was applied to each cell using various electrolytes shown in Table 1 at a concentration of 1.0 M After measuring the capacitance and internal resistance, we then measured the capacity after storage at 70°C for 1000 hours while applying a voltage of 2.8V to this cell, and calculated the capacity deterioration rate (%) from the initial capacity. . The results of these measurements are shown in Table 1. In addition, the internal resistance measured by the AC two-terminal method (frequency 1 KHz) is also shown. [Effects of the Invention] As explained above, according to the present invention, an electric double layer capacitor having a high withstand voltage, a low rate of capacity deterioration under high temperature conditions, and high long-term reliability can be obtained.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a partial sectional view showing one embodiment of an electric double layer capacitor according to the present invention. 1, 2... Polarizable electrode, 3... Separator, 4... Cap, 5... Can, 6... Packing.

Claims (1)

[Scope of 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, the solute of the electrolyte has the general formula [Formula] or [Formula] (where m = 0 to 10, n = 0 to 10, (m and n cannot be 0 at the same time) R is a hydrogen atom, an alkyl group with 1 to 15 carbon atoms, an allyl group, or an allyl group with 6 to 15 carbon atoms represents the aryl group of
represents BF ₄ , PF ₆ , ClO ₄ , AsF ₆ , SbF ₆ , AlCl ₄ , or R _f SO ₃ (R _f is a fluoroalkyl group having 1 to 8 carbon atoms). ) An electric double layer capacitor characterized by being a salt represented by: 2. The electric double layer capacitor according to claim 1, wherein the solute concentration is 0.1 to 3.0 mol/solvent.