AN ELECTROLYTE FOR ELECTROLYTIC CAPACITOR

Abstract: An electrolyte for electrolytic capacitor containing within an aprotic solvent a fluorocomplex acid salt of a N-­ heterocyclic compound as solute. An electrolyte for electrolytic capacitor according to the invention may conveniently be prepared by adding to an aqu­ eous solution of fluorocomplex acid salt an equivalent amount of N-heterocyclic compound for reaction with subse­ quent dryness at reduced pressure to obtain an anhydrous salt which is then added to the aprotic solvent to prepare the resultant electrolyte having desired conductivity.

Description: This invention relates to an electrolyte for an electrolytic capacitor containing within an aprotic solvent, a fluorocomplex acid salt of a N-heterocyclic compound 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 via 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 N-heterocyclic compound salt of a fluorocomplex acid has a high solubility in the aprotic solvent with an enhanced releasability and provides a high conductivity. Thus, a principal object of the invention is to provide an electrolyte of substantially non water series high conductivity with use of an aprotic solvent. An electrolyte for an electrolytic capacitor according to the invention is characterized by containing a fluorocomplex acid salt of N-heterocyclic compound in an aprotic solvent as solute. The electrolyte for the electrolytic capacitor according to the present invention is characterized by containing within an aprotic solvent a fluorocomplex acid salt of a N-heterocyclic compound of general formula, in which R is H or C x H 2x + 1 or (C x H 2x + 1 )₂; R₁ is an alkyl group having 1 to 5 carbon atoms; n is an integer of 0 to 3; a plus b equals 4 or 5; A is a fluorocomplex acid, and where the (CH₂) and (CH) groups take any arrangement, and when a plus b equals 4, x is 1 and both n and b are 0, and where a plus b equals 5, x is an integer of 1 to 6 and both n and b are the same integer of 0 to 3, the R group(s) being attatched to the CH group(s). As one group of said N-heterocyclic compounds, piperidine and piperidine derivatives may be given, the general formulas being as follows: in which R₁ is an alkyl group having 1 to 6 carbon atoms; n is an integer of 0 to 3; the nitrogen atom forms a secondary, or a tertiary amine or a quaternary ammonium via R taking H or 1 to 2 alkyl groups having 1 to 5 carbon atoms respectively; and A is a fluorocomplex acid. For example, concrete compounds are such as 2-methylpiperidine, 3-methylpiperidine, 4-methylpiperidine, 1,2-dimethylpiperidine, 1,4-dimethylpiperidine, 2,3-dimethylpiperidine, 2,4-dimethylpiperidine, 2,5-dimethylpiperidine, 2,6-dimethylpiperidine, 2,3,6-trimethylpiperidine, 2,4,6-trimethylpiperidine, 2-methyl-5-ethylpiperidine, 2-phenylpiperidine, 3-phenylpiperidine, 4-phenylpiperidine and quaternary ammonium compounds of said above piperidine compounds in which each their nitrogen atom is alkylated, such as N-methyl, N,N-dimethyl, N-ethyl, N,N-diethyl, N-n-propyl, N,N-di-n-propyl, N-n-butyl, N,N-di-n-buthyl, N-isobutyl, N,N-diisobutyl, N-n-amyl, N,N-di-n-amyl, N-isoamyl, N,N-diisoamyl. As another group of said N-heterocyclic compound, pyrrolidine or N-methylpyrrolidine compounds may be given, having the general formulas as follows: in which the nitrogen atom forms a secondary, a tertiary amine or a quaternary ammonium via R taking H or one or two methyl groups respectively; and A is a fluorocomplex acid. For example, concrete compounds are such as tetrafluoroborate or hexafluorophosphate of pyrrolidine, N-methylpyrrolidine, or N,N-dimethylpyrrolidinium. The aprotic solvent to be used in the invention may be selected from the followings 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. The fluorocomplex acid for the present invention is preferably tetrafluoroboric acid (HBF₄), or hexafluorophosphoric acid (HPF₆). An electrolyte for an electrolytic capacitor according to the invention may conveniently be prepared by adding to an aqueous solution of a fluorocomplex acid salt an equivalent amount of N-heterocyclic compound for reaction with subsequent drying at reduced pressure to obtain an anhydrous salt which is then added to the aprotic solvent to prepare the resultant electrolyte having desired conductivity. (Examples 1 to 14) An electrolyte for an electrolytic capacitor according to the invention will be exemplified in the followings with 10% by weight solution for fluorocomplex acid salts of piperidine, piperidine derivatives, pyrrolidine and pyrrolidine compounds as various N-heterocyclic compounds as shown in Table 1. Further, as comparative example the conventional standard electrolytes composed of 78% by weight of ethyleneglycol, 12% by weight of water and 10% by weight of ammonium adipate are also shown in Table 1. The high-temperature load test obtained at 16V 1000 micro F for electrolytes exemplified in examples 1 to 14 and comparative example are shown 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 containing within an aprotic solvent a fluorocomplex acid salt of a N-heterocyclic compound of general formula, in which R is H or C x H 2x + 1 or (C x H 2x + 1 )₂; R₁ is an alkyl group having 1 to 5 carbon atoms; n is an integer of 0 to 3; a plus b equals 4 or 5; A is a fluorocomplex acids, and where the (CH₂) and (CH) groups take any arrangement, and when a plus b equals 4, x is 1 and both n and b are 0, and when a plus b equals 5, x is an integer of 1 to 6 and both n and b are the same integer of 0 to 3 the R group(s) being attatched to the (CH) group(s). 2. An electrolyte for an electrolyte capacitor according to claim 1, wherein said N-heterocyclic compound is a fluorocomplex acid salt of piperidine or a piperidine derivative of general formula, in which R₁ is an alkyl group having 1 to 6 carbon atoms; n is an integer of 0 to 3; the nitrogen atom forms a secondary, or a tertiary amine or a quaternary ammonium via R taking H or 1 to 2 alkyl groups having 1 to 5 carbon atoms respectively; and A is a fluorocomplex acid. 3. An electrolyte for an electrolytic capacitor according to claim 1, wherein said N-heterocyclic compound is a fluorocomplex acid salt of pyrrolidine or an N-methylpyrrolidine compound of general formula, in which the nitrogen atom forms a secondary, or a tertiary amine or a quaternary ammonium via R taking H or one or two methyl groups respectively; and A is a fluorocomplex acid. 4. An electrolyte for an electrolytic capacitor according to anyone of claims 1 to 3, wherein the aprotic solvent is selected from 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. 5. An electrolyte for an electrolytic capacitor according to anyone of claims 1 to 4, wherein the fluorocomplex acid is tetrafluoroboric acid or hexafluorophosphoric acid.

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