AN ELECTROLYTE FOR ELECTROLYTIC CAPACITOR

Abstract: An electrolyte for electrolytic capacitor containing within an aprotic solvent a fluorocomplex acid salt of imidazole or imidazole derivative as solute. An electrolyte for electrolytic capacitor according to the invention may conveniently be prepared by adding one equivalent amount of imidazole or imidazole derivative to an aqueous solution of fluorocomplex acid for reaction with subsequent vacuum drying to obtain an anhydrous salt and then dissolving said anhydrous salt to an aprotic solvent until a desired conductivity is obtained, for example, as an approximately 10% by weight solution.

Description: This invention relates to an electrolyte for an electrolytic capacitor containing within an aprotic solvent a fluorocomplex acid salt of imidazole or an imidazole derivative as solute. Hitherto, organic acids or their salts and glycol series pastes have been principally used as electrolytes for electrolytic capacitors in the general purposes. The latest expansion of utilization for the electronic instruments requires more improvement and advancement in the reliability and performance of the capacitor entailing undesired problem of the presence of water in the paste and as a result an electrolyte using an aprotic solvent in place of organic acid and its salt and glycol paste has become desirable. The greatest subject of employment of the aprotic solvent system electrolyte is how to obtain an electrolyte of high conductivity, and to achieve this an organic carboxylic acid or its salt which is well soluble in the aprotic solvent and has a high degree of dissociation has been researched as a main work, but not yet succeeded. To solve the matter and obtain a high conductivity, a solvent which produces water resulting from the reaction between acids and alcohols or glycols, and even water itself is incorporated into the aprotic solvent, with still insufficient conductivity, increments of water and solute contents with poor reliability at the elevated temperature as disclosed in the Japanese patent publications No. 55-3989, 57-56763, 58-32769 and the U.S. Patent No. 4,117,531. After extensive researches and studies to obtain an electrolyte which is a substantially nonaqueous system electrolyte and has a high conductivity with the use of an aprotic solvent but without using any solvent which forms water in reaction between acids and alcohols with glycols, it has been discovered that a fluorocomplex acid salt of imidazole or an imidazole derivative has a high solubility in the aprotic solvent with an enhanced releasability and provide a high conductivity. Thus, a principal object of the invention is to provide an electrolyte of substantially non water series high conductivity with the use of an aprotic solvent. An electrolyte for electrolytic capacitor according to the invention is characterized by containing a fluorocomplex acid salt of imidazole or an imidazole derivative in an aprotic solvent as solute. The fluorocomplex acid salt of the imidazole or imidazole derivative according to the invention is represented by the following general formula, in which R₁ is a hydrogen atom or 2-cyanoethyl group, R₂ is a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a phenyl group or a benzyl group, R₃ and R₄ which may be the same or different are hydrogen atoms or alkyl groups having 1 to 8 carbon atoms and A is a fluorocomplex acid. The imidazole derivative to be preferably used in the invention may be selected from the following but not limited thereto: 2-methylimidazole; 2-ethylimidazole, 2-phenylimidazole, 2-benzylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 3-methylammonio-2-ethyl-4-methylimidazole. The fluorocomplex acid to be used in the invention may be tetrafluoroboric acid (HBF₄) or hexafluorophosphoric acid (HPF₆). The aprotic solvent to be used in the invention may be selected from the following but not limited thereto: (1) Amide system solvent: N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetoamide, N,N-dimethylacetoamide, N-ethylacetoamide, N,N-diethylacetoamide, hexamethylphosphorinamide (2) Oxide compounds: di-methylsulfoxide (3) Nitrile compounds: acetonitrile (4) Cyclic esters, cyclic amides: γ-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate. An electrolyte for an electrolytic capacitor according to the invention may conveniently be prepared by adding one equivalent amount of imidazole or imidazole derivative to an aqueous solution of a fluorocomplex acid for reaction, with subsequent vacuum drying to obtain an anhydrous salt, and then dissolving said anhydrous salt in an aprotic solvent until a desired conductivity is obtained, for example, as an approximately 10% by weight solution. (Examples 1 to 12) An electrolyte for electrolytic capacitor according to the invention will be exemplified in the following with 10% by weight solution for fluorocomplex acid salt of various imidazole or imidazole derivatives with respect to the conductivity as shown in Table 1. Further, as comparative example the conventional standard electrolytes composed of 78% by weight of ethylene glycol, 10% by weight of water and 12% by weight of ammonium adipate are shown also in Table 1. The high-temperature load test obtained at 16WV 180 micro F for electrolytes exemplified in examples 1 to 12 and the comparative example are shown as the mean value of 10 load tests in Table 2. The electrolyte according to the invention may provide a non water series electrolyte having a high conductivity equivalent to or more than the conductivity of the conventional electrolyte composed of glycols, water and organic acid salt with improved and wide applicability in design of electrolytic capacitor.

Claims: 1. An electrolyte for an electrolytic capacitor comprising an aprotic solvent and a fluorocomplex acid salt of imidazole or an imidazole derivative of general formula, in which R₁ is a hydrogen atom or 2-cyanoethyl group, R₂ is a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a phenyl group or a benzyl group, R₃ and R₄ which may be the same or different are hydrogen atoms or alkyl groups having 1 to 8 carbon atoms, and A is a fluorocomplex acid. 2. An electrolyte for an electrolytic capacitor according to clalm 1, wherein the aprotic solvent is selected from the group of N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, γ-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, dimethyl sulfoxide, acetonitrile or a mixture thereof. 3. An electrolyte for an electrolytic capacitor according to claim 1 or 2, wherein the fluorocomplex acid is tetrafluoroboric acid or hexafluorophosphoric acid.

Inventors: SHINOZAKI, FUMIHIKO C/O NIPPON CHEMI-CON CORP., YOKOYAMA, YUTAKA C/O NIPPON CHEMI-CON CORP.
Applicants: NIPPON CHEMI-CON CORPORATION
Application year: 1987
Main classification: H01G9
IPC codes: H01G9