JP2004335874A - Nonaqueous electrolyte for electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide nonaqueous electrolyte for an electric double layer capacitor in which cycle characteristics are enhanced at the time of charging/discharging. <P>SOLUTION: Nonaqueous electrolyte for an electric double layer capacitor exhibiting enhanced characteristics at the time of charging/discharging is obtained by adding a specified diamine compound to the nonaqueous electrolyte consisting of nonaqueous solvent and electrolyte. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【発明の効果】
本発明のジアミン化合物を含有する非水電解液を用いることにより、電位窓が広くサイクル特性に優れた長期信頼性の高い電気二重層キャパシタが実現でき、その工業的意義は極めて大きい。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nonaqueous electrolyte for an electric double layer capacitor having excellent charge / discharge characteristics. More specifically, the present invention relates to a nonaqueous electrolyte for an electric double layer capacitor in which a diamine compound is contained in a nonaqueous electrolyte comprising a nonaqueous solvent and an electrolyte. Electric double layer capacitors are expected to be applied to large-scale energy storage applications such as electric vehicles, hybrid vehicles, and power storage systems, in addition to small electronic device backup power supplies that have been mainly used so far. I have.
[0002]
[Prior art]
An electric double layer capacitor is an electric storage device that uses the electric storage action of an electric double layer formed at a boundary surface between a polarizable electrode and an electrolytic solution. Such an electric double layer capacitor is generally formed by impregnating an electrolyte with a high surface area activated carbon electrode opposed to a porous separator for short circuit prevention. There are non-aqueous electrolytes and aqueous electrolytes. Non-aqueous electrolytes have a higher withstand voltage than aqueous electrolytes, and therefore have a characteristic that the energy density can be increased. In general, electric double layer capacitors store electricity by physical adsorption, and therefore have better cycle characteristics than secondary batteries. However, it is known that the capacitance decreases over time by repeating charging and discharging for a long period of time, and there is a need for an electric double layer capacitor with little deterioration in capacitance and improved cycle characteristics.
[0003]
As a conventional non-aqueous electrolyte used for an electric double layer capacitor, a solution in which a quaternary alkyl ammonium BF ₄ salt as an electrolyte is dissolved in propylene carbonate as a non-aqueous solvent is known. Attempts have also been made to improve the cycle characteristics by improving this non-aqueous electrolyte, and a description has been made of a non-aqueous electrolyte for an electric double layer capacitor containing a soluble polymer substance (for example, Patent Document 1). However, it has not been conventionally known that the cycle characteristics are improved by including a diamine compound in the electrolytic solution of the electric double layer capacitor.
[0004]
[Patent Document 1]
JP 2001-102268 A [0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a non-aqueous electrolyte for an electric double layer capacitor having improved cycle characteristics when charging and discharging.
[0006]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on a non-aqueous electrolyte for an electric double layer capacitor having the above-mentioned problems, and as a result, by including a specific diamine compound in a non-aqueous electrolyte comprising a non-aqueous solvent and an electrolyte. The present inventors have found that the potential window is widened and the cycle characteristics are improved.
[0007]
That is, the present invention provides an electric double layer in which a nonaqueous electrolytic solution comprising a nonaqueous solvent and an electrolyte shown in the following (1) and (2) contains one or more diamine compounds selected from the general formula 1. The present invention relates to a non-aqueous electrolyte for a capacitor.
(1) A non-aqueous electrolyte for an electric double layer capacitor, wherein a non-aqueous electrolyte comprising a non-aqueous solvent and an electrolyte contains one or more diamine compounds selected from the general formula 1.
_{R- (NH 2) 2 (1} )
(Wherein, R represents an organic group having 1 to 12 carbon atoms)
(2) The nonaqueous electrolysis for an electric double layer capacitor according to (1), wherein the diamine compound selected from the general formula 1 is 1,6-diaminohexane and / or 1,3-bis (aminomethyl) cyclohexane. liquid.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the invention will be described in detail. The non-aqueous electrolyte of the present invention can be usually produced by adding a diamine compound to a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent.
The diamine compound is represented by the general formula (1), specifically, ethylenediamine, 1,2-, 1,3-propanediamine, 1,2-, 1,3-, 1,4-, 2,3- Butanediamine, 1,2-, 1,3-, 1,4-, 1,5-, 2,3-, 2,4-pentanediamine, 1,2-, 1,3-, 1,4-, Saturated carbonization of 1,5-, 1,6-, 2,3-, 2,4-, 2,5-, 3,4-hexanediamine, heptanediamine, octanediamine, nonanediamine, decanediamine, undecadiamine, etc. Hydrogen diamines, o, m, aromatic diamines such as p-phenylenediamine, o, m, p-xylylenediamine, 1,2-, 1,3-, 1,4-cyclohexanediamine, 1,2- , 1,3-, 1,4-bis (aminomethyl) cyclohexane, isophoronedi Min, alicyclic diamines such as norbornane diamine, 4,5-bis (aminomethyl) dioxolane-2-one, diaminopyridine, 3,4-bis (aminomethyl) heterocyclic diamines such as sulfolane. Among these, 1,6-hexanediamine and / or 1,3-bis (aminomethyl) cyclohexane are preferable from the viewpoint of availability. In addition, these compounds shown above can be used alone or in combination of two or more.
[0009]
The amount of the diamine compound used in the present invention depends on the type of the diamine compound, the type and concentration of the electrolyte or the solvent used in the nonaqueous electrolytic solution composed of the nonaqueous solvent and the electrolyte, or the electrode used, An appropriate range is usually 1 ppm to 20 wt%, preferably 10 ppm to 10 wt%, based on the electrolyte. If the amount of the diamine compound is less than this, the effect of addition on the energy density at the time of charging and the cycle characteristics at the time of charging and discharging is small. And the generation of gas increase.
When the potential window as an index of the withstand voltage was measured for the electrolyte of the present invention, it was found that the potential window was wider than in the case where there was no additive, and that these additives had an effect of suppressing the decomposition of the electrolyte. This is probably because the diamine compound causes some reaction on the electrode surface to inactivate the electrode surface.
[0010]
The non-aqueous solvent of the non-aqueous electrolyte used in the present invention is not particularly limited, for example, propylene carbonate, ethylene carbonate, butylene carbonate, cyclic carbonate such as 1,3-dioxolan-2-one, dimethyl carbonate, Dicyclic carbonates such as diethyl carbonate and methyl ethyl carbonate, cyclic and linear ester compounds such as γ-butyrolactone, γ-valerolactone, methyl acetate and methyl propionate, and cyclic compounds such as 2-methyltetrahydrofuran and 1,2-dimethoxyethane And chain ethers, nitriles such as acetonitrile and 3-methoxypropionitrile, amides such as N, N-dimethylformamide and N, N-dimethylacetamide, sulfolane, 3-methylsulfolane, dimethylsulfoxide, ethylene Sulfur-containing compounds such as sulfides, nitro compounds such as nitromethane and nitroethane, cyclic urethanes such as 3-methyl-2-oxazolidinone, phosphorus-containing compounds such as trimethyl phosphate, and the like, preferably propylene carbonate, ethylene carbonate, and γ- Butyrolactone, acetonitrile and sulfolane, more preferably propylene carbonate. These non-aqueous solvents can be used alone or as a mixture. Further, it can be used by mixing with other additives such as a dehydrating agent, a halogen removing agent and a flame retardant.
[0011]
As the electrolyte of the non-aqueous electrolyte used in the present invention, a salt of an anion and a cation is used. Although the electrolyte is not particularly limited, for example, cations include tetraalkylammonium ions such as tetraethylammonium, trimethylethylammonium, dimethyldiethylammonium, trimethylethylammonium, tetramethylammonium, and tetra-n-butylammonium, and a nitrogen atom. Phosphonium ion replaced with phosphorus atom, N, N-dimethylpiperidinium, N, N-ethylmethylpiperidinium, N, N-diethylpiperidinium, N, N-dimethylpyrrolidinium, N, N-ethyl Methylpyrrolidinium, N, N-diethylpyrrolidinium, 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolinium, 1,3-dimethyl -1, 4, 5 6-tetrahydropyrimidium, 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidium, 1-methyl-1,8-diazabicyclo [5.4.0] undecene-7,1- Quaternary amidinium ion such as methyl-1,5-diazabicyclo [4.3.0] nonene-5, ion of a compound in which a nitrogen atom is replaced by a phosphorus atom, sulfonium ion such as trimethylsulfonium and triethylsulfonium, lithium and sodium And alkali metal ions such as potassium, alkaline earth metal ions such as calcium and magnesium, and trivalent metal ions such as aluminum. Tetraalkylammonium is preferable.
Examples of the anion include PF ₆ ⁻ , BF ₄ ⁻ , AsF ₆ ⁻ , N (RSO ₃ ) ₂ ⁻ , C (RSO ₃ ) ₃ ⁻ , SBF ₆ ⁻ , RSO ₃ ⁻ , and ClO ₄ ^−. the BF ₄ ^- is. These electrolytes can be used alone or as a mixture of two or more.
The concentration of the electrolyte in the non-aqueous electrolyte varies depending on the type of the electrolyte and the solvent used, but is usually in the range of 0.1 to 10 mol / l, preferably 0.5 to 5 mol / l.
The method of the present invention can also be used for a polymer gel electrolyte obtained by adding an electrolyte to a polymer such as polyacrylonitrile, polyethylene oxide, and polyvinylidene fluoride to form a gel.
[0012]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
The measurement of the potential window and the assembly of the cell for the charge / discharge test were performed in a glove box. The electrolyte in the non-aqueous electrolyte and the diamine compound used as an additive were all dehydrated in advance, and the electrodes, cells, etc. were used after being vacuum-dried.
[0013]
Example 1
(A) Preparation of Electrolyte Solution To a 1.8 mol / l triethylmethylammonium tetrafluoroborate propylene carbonate solution, 0.5 wt% of 1,6-hexanediamine (HDA) was added to prepare an electrolyte solution.
(B) Measurement of potential window Using an electrochemical measurement device, 5 g of the above-mentioned electrolyte solution was charged into a 20 ml glass cell, and 5 mV / g was measured using glassy carbon (diameter 3 mm) as a working electrode, a platinum wire as a counter electrode, and a silver wire as a reference electrode. The potential was swept to the anode side and the cathode side at a speed of sec. The absolute value of the potential at which a current of ± 10 μA flowed was summed to obtain a potential window. As a result, the potential window of the electrolyte was 6.5 V. Table 1 shows the results.
(C) Preparation and Evaluation of Electric Double Layer Capacitor A mixture consisting of 80 wt% of activated carbon powder (specific surface area measured by BET method using nitrogen adsorption method, 1,200 m ² / g), 10 wt% of acetylene black, and 10 wt% of polytetrafluoroethylene was prepared. After kneading, it was formed into a pressure sheet. The obtained sheet was punched out in a disk shape to form an activated carbon electrode (diameter 16 mm, thickness 0.6 mm). The electrodes were opposed to each other via a cellulose separator and housed in a stainless steel case. Thereafter, the above electrolyte was impregnated and sealed under reduced pressure.
The obtained electric double layer capacitor cell was charged to 2.7 V at 25 ° C. with a constant current of 5 mA, held for 30 minutes, and discharged to 0 V with a constant current of 5 mA to obtain an initial capacitance. The initial capacitance density was 12.8 F / cc. After that, the battery was charged to 2.7 V with a constant current of 5 mA at 70 ° C., held for 5 hours, and discharged to a voltage of 0 V with a constant current of 5 mA was repeated for 250 hours, and the rate of capacity deterioration from the initial capacity was calculated. As a result, the capacity deterioration rate was 6.3%. Table 1 shows the measurement results.
[0014]
Example 2
(A) Adjustment of electrolyte solution An electrolyte solution was prepared in the same manner as in Example 1 except that 1,3-bis (aminomethyl) cyclohexane (BAC) was used as an additive.
(B) Measurement of potential window The potential window of the electrolytic solution was measured in the same manner as in Example 1, and as a result, the potential window was 6.7 V. Table 1 shows the results.
(C) Production and evaluation of electric double layer capacitor As a result of producing and evaluating an electric double layer capacitor in the same manner as in Example 1, the initial capacitance density was 13.1 F / cc, 70 ° C. The capacity deterioration rate after charging and discharging at 7 V for 250 hours was 7.8%. Table 1 shows the measurement results.
[0015]
Comparative Example 1
(A) The procedure was the same as in Example 1 except that no additive for adjusting the electrolytic solution was added.
(B) Measurement of potential window As a result of measuring the potential window of the electrolytic solution in the same manner as in Example 1, the potential window was 5.2 V. Table 1 shows the results.
(C) Production and Evaluation of Electric Double Layer Capacitor As a result of producing and evaluating an electric double layer capacitor in the same manner as in Example 1, the initial capacitance density was 13.0 F / cc, 70 ° C. The capacity deterioration rate after charging and discharging at 7 V for 250 hours was 9.5%. Table 1 shows the measurement results.
[0016]
[Table 1]

【The invention's effect】
By using the non-aqueous electrolyte containing the diamine compound of the present invention, an electric double layer capacitor having a wide potential window and excellent cycle characteristics and high long-term reliability can be realized, and its industrial significance is extremely large.

Claims (2)

A non-aqueous electrolyte for an electric double layer capacitor, wherein a non-aqueous electrolyte comprising a non-aqueous solvent and an electrolyte contains one or more diamine compounds selected from the general formula 1.
_{R- (NH 2) 2 (1} )
(Wherein, R represents an organic group having 1 to 12 carbon atoms) The non-aqueous electrolyte for an electric double layer capacitor according to claim 1, wherein the diamine compound selected from the general formula 1 is 1,6-diaminohexane and / or 1,3-bis (aminomethyl) cyclohexane.