AN ELECTROLYTE FOR ELECTROLYTIC CAPACITOR

Abstract: An electrolyte for electrolytic capacitor containing within an aprotic solvent a hexafluorophosphate of an organic amine compound as solute. An electrolyte for electrolytic capacitor according to the invention may conveniently be prepared by adding to an aqueous solution of hexafluorophosphate an equivalent amount of organic amine compound for reaction with subse­ quent reduction and dryness to obtain an anhydrous salt which as an approximately 10% by weight solution is then added to the aprotic solvent to prepare the resultant electro­ lyte.

Description: This invention relates to an electrolyte for an electrolytic capacitor, said electrolyte containing a hexafluorophosphate of an organic amine compound dissolved in an aprotic solvent. Hitherto, organic acids or their salts and glycol series pastes have been principally used as electrolytes for electrolytic capacitors for general purposes. The latest expansion in utilization of electronic instruments requires further improvements in the reliability and performance of capacitors, which at present suffer from the presence of undesired water in the paste and as a result an electrolyte utilising an aprotic solvent in place of an organic acid and a salt thereof and glycol paste has become attractive. The greatest obstacle to the employment of an aprotic solvent system electrolyte is the difficulty in obtaining an electrolyte of high conductivity and to achieve this an organic carboxylic acid or salt thereof which are highly soluble in aprotic solvents and which display a high degree of dissociation have been studied but success has not yet been achieved. To solve this problem and obtain a solvent with high conductivity, a solvent has been tried which produces water by the reaction between an acid and an alcohol or glycol so that water is incorporated into the aprotic solvent, but this has still not achieved sufficient conductivity, and the resulting solvent exhibits 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 research with a view to obtaining an electrolyte which is substantially nonaqueous and has a high conductivity with use of an aprotic solvent but without using any solvent in which water is formed by reaction between acids and alcohols or glycols, it has been discovered that an organic amine salt of a hexafluorophosphate has a high solubility in aprotic solvents with enhanced dissociation and displays high conductivity. According to one aspect of the invention we provide an electrolyte for an electrolytic capacitor containing a hexafluorophosphate of an organic amine compound as a soluble dissolved in an aprotic solvent. The organic amine compound preferably comprises (i) a compound containing one or two pyridine rings or (ii) a primary, secondary or tertiary amine or a quaternary ammonium compound in which in group (i) to a nitrogen atom are bonded four groups selected from 1 to 4 alkyl groups, an alkenyl group or an aryl group and 1 to 3 hydrogen atoms. The organic amine compounds for use in the capacitor of the invention preferably contain one or two pyridine rings, as described hereinafter. (1) Pyridine compounds in which one or more hydrogen atoms bonded to the pyridine carbon are replaced by alkyl group, alkenyl groups having 1 to 15 carbons, aryl group having 6 to 15 carbons or halogens, for example: α-picoline, β-picoline, γ-picoline , 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2-n-propylpyridine, 2-iso-propylpyridine, 2-n-octylpyridine, 2-vinylpyridine, 2-hexene-2-pyridine, 2-geranylpyridine, 2,3-dimethylpyridine, 2,6-dimethylpyridine, 3,4-dimethylpyridine, 3-ethyl-4-methylpyridine, 4-ethyl-2-methylpyridine, 6-ethyl-2-methylpyridine, 2,3,4-trimethylpyridine, 2,3,6-trimethylpyridine, 2,4,5-trimethylpyridine, 2,4,6-trimethylpyridine, 2-ethyl-3,5-dimethylpyridine, 2-phenylpyridine, 4-tolylpyridine, 4-mesitylpyridine, 3-chloropyridine, 3,5-dibromopyridine. (2) Dipyridine compounds in which one or more hydrogen atoms bonded to the pyridine ring are substituted by alkyl, alkenyl, aryl or halogen groups, for example: 2,2-diethyl-4,4-dipyridine, 4,4-dimethyl-2,2-dipyridine. (3) Compounds in which two pyridine rings are bonded by an alkylene group having 1 to 8 carbons or an alkenylene group having 2 to 8 carbons, for example: 1,3-di-(4-pyridine)-propane, 1,2-di-(4-pyridyl)-ethane 1,2-di-(4-pyridyl)-ethylene, 1,6-di-(4-pyridyl)-hexylene-3. (4) Quaternary ammonium compounds in which to one nitrogen atom of a pyridine ring are bonded an alkyl group, alkenyl group having 1 to 15 carbons or aryl group having 6 to 15 carbons, for example: N-ethyl-2-bromopyridine, N-vinyl-3,5-dimethylpyridine, N-phenyl-4-ethylpyridine, N-tolyl-4-butylpyridine. Further, the organic amine compound for use in the invention may be selected from primary, secondary and tertiary amines and quaternary ammonium compounds in which to one nitrogen atom are added 1 to 4 alkyl groups, alkenyl groups having 1 to 15 carbons or aryl groups having 6 to 15 carbons and 1 to 3 hydrogen atoms, for example: (1) Primary amines : methylamine, ethylamine, propylamine, iso-propylamine, butylamine, amylamine, hexylamine, vinylamine, geranylamine, aniline, benzylamine. (2) Secondary amines : dimethylamine, diethylamine, dipropylamine, diisopropylamine, divinylamine, digeranylamine, diphenylamine, ditolylamine, N-methyl.benzylamine. (3) Tertiary amines : trimethylamine, triethylamine, tripropylamine, tributyl-amine, trivinylamine, trigeranylamine, triphenylamine, N-dimethyl . benzylamine. (4) Quaternary ammonium compounds : tetramethylammonium, n-butylammonium, vinyl trimethylammonium, phenylammonium, phenyltrimethylammonium, tolyltriethylammonium, benzyltrimethylammonium. Moreover, the organic amine compound according to the invention may be preferably selected from compounds having the general formula: in which m is 0 or 1, m + n is 2 or 3, R1 indicates the presence or absence of an alkyl substituent having 1 to 3 carbon atoms and R is hydrogen, or an N-heterocyclic-di-condensed ring compound in which the nitrogen atom forms a tertiary amine or a quaternary ammonium with one or two alkyl groups having 1 to 5 carbon atoms and up to 5 conjugated double bonds are contained in the ring: N-heterocyclic-di-condensed ring compound may be selected from quinoline, 2-methylquinoline(quinaldine), isoquinoline, and their partially hydrogenated compounds or completely hydrogenated compounds (e.g. N-alkylates, indole), 3-methylindole(skatol), isoindole, pseudoindole, their partially or completely hydrogenated compounds (e.g. N-alkyl compounds). The aprotic solvent to be used in the invention may be selected from the following but is not limited thereto: (1) Amide system solvent: N-methylformamide, N-dimethylformamide, N-ethyl- formamide, N-diethylformamide, N-methylacetoamide, N-dimethylacetoamide, N-ethylacetoamide, N-diethylacetoamide, hexamethylphosphorinamide (2) Oxide compounds : di-methylsulfoxide (3) Nitrile compounds : acetonitrile (4) Cyclic esters, cyclic amides : γ-butyrolactone, N-methyl-2-pyrrolidone, ethylenecarbonate, propylenecarbonate. An electrolyte for an electrolytic capacitor according to the invention may conveniently be prepared by adding to an aqueous solution of a hexafluorophosphate an equivalent amount of an organic amine compound for reaction with subsequent reduction and drying to obtain an anhydrous salt which as an approximately 10% by weight solution is then added to the aprotic solvent to prepare the resultant electrolyte. The invention will now be illustrated by way of non-limiting examples. (Examples 1 to 12) An electrolyte for an electrolytic capacitor according to the invention utilising a 13% by weight solution of hexafluorophosphate of various organic amine compounds was tested with respect to conductivity as shown in Table 1. Results obtained at 25V 1 micro F for the electrolytes shown in examples 1 to 12 are given in Table 2. Example Initial Value 110 deg.C 1000 hours Capacity (µF) tanδ (%) Leakage Current (µA/3mins.) Capacity (µF) tanδ (%) Leakage Current (µA/3mins.) 1 1.04 0.017 0.41 0.99 0.032 0.04 2 1.01 0.051 0.37 1.99 0.063 0.05 3 1.04 0.017 0.38 1.02 0.021 0.05 4 1.04 0.019 0.40 1.01 0.033 0.03 5 1.03 0.029 0.35 0.97 0.040 0.06 6 1.04 0.021 0.38 1.01 0.029 0.04 7 1.01 0.053 0.33 0.95 0.059 0.05 8 1.01 0.052 0.31 0.96 0.061 0.07 9 1.03 0.020 0.36 0.98 0.044 0.05 10 1.01 0.050 0.35 1.00 0.063 0.04 11 1.03 0.023 0.40 0.99 0.042 0.04 12 1.03 0.037 0.37 1.01 0.031 0.06 (Ref.) 1.01 0.055 0.42 0.92 0.078 0.08 (Examples 13 to 24) Electrolytes for electrolytic capacitors according to the invention with a 13% by weight solution of hexafluorophosphate of various N-heterocyclic-di-condensed ring compounds were tested with respect to conductivity as shown in Table 3. Further, as a comparative example results obtained with a conventional standard electrolyte composed of 78% by weight of ethyleneglycol, 12% by weight of water and 10% by weight of ammonium adipate are shown in Table 3. The characteristics over a period of time of the electrolytes shown in Examples 13 to 24 and the comparative examples are shown in Table 4. Example Initial Value 110 deg.C 1000 hours Capacity (µF) tanδ (%) Leakage Current (µA/3mins.) Capacity (µF) tanδ (%) Leakage Current (µA/3mins.) 13 1.03 0.027 0.37 1.01 0.036 0.03 14 1.01 0.041 0.41 0.96 0.052 0.05 15 1.02 0.025 0.35 1.01 0.027 0.05 16 1.02 0.028 0.36 0.99 0.041 0.05 17 1.04 0.022 0.39 0.99 0.047 0.04 18 1.02 0.033 0.39 0.98 0.037 0.03 19 1.01 0.053 0.37 0.99 0.058 0.04 20 1.01 0.053 0.35 0.96 0.062 0.04 21 1.04 0.020 0.37 0.98 0.045 0.04 22 1.01 0.041 0.33 0.98 0.049 0.03 23 1.03 0.029 0.38 0.99 0.042 0.05 24 1.02 0.038 0.35 1.01 0.043 0.05 Ref. 1.01 0.055 0.42 0.92 0.078 0.08 Electrolytes according to the invention are non-aqueous electrolytes having a high conductivity, equivalent to greater than that of conventional electrolytes composed of glycols, water and organic acid salts with improved applicability in electrolytic capacitors.

Claims: An electrolyte for an electrolytic capacitor containing a hexafluorophosphate of an organic amine compound as a solute dissolved in an aprotic solvent. An electrolyte for an electrolytic capacitor according to claim 1, wherein said organic amine compound comprises (i) a compound containing one or two pyridine rings or (ii) a primary, secondary or tertiary amine or a quaternary ammonium compound in which in group (i) to a nitrogen atom are bonded four groups selected from 1 to 4 alkyl groups, an alkenyl group or an aryl group and 1 to 3 hydrogen atoms. An electrolyte for an electrolytic capacitor according to claim 2, wherein said compound containing one or two pyridine rings is a compound in which at least one hydrogen atom bonded to a carbon of a pyridine ring is replaced by an alkyl group, alkenyl group, aryl group or halogen. An electrolyte for an electrolytic capacitor according to claim 2 or 3, wherein said compound containing two pyridine rings includes a dipyridyl compound or a compound in which two pyridine rings are bonded by an alkylene group having 1 to 8 carbon atoms or an alkenylene group having 2 to 8 carbon atoms. An electrolyte for an electrolytic capacitor according to any one of claims 2 to 4, said electrolyte containing a quaternary ammonium compound which contains one or two pyridine rings in which to a nitrogen atom of a pyridine ring is added one alkyl group, alkenyl group or aryl group. An electrolyte for a electrolytic capacitor according to any one of claims 2 to 5, wherein the alkyl groups and the alkenyl group have 1 to 15 carbon atoms each and the aryl group has 6 to 15 carbon atoms. An electrolyte for an electrolytic capacitor according to claim 1, wherein said organic amine compound is a compound of the general formula, in which m is 0 or 1, m + N is 2 or 3, R1 indicates the presence or absence of an alkyl substituent having 1 to 3 carbon atoms, to form an N-heterocyclic-di-condensed ring compound and R is hydrogen, or the nitrogen atom forms a tertiary amine or a quaternary ammonium with one or two alkyl groups having 1 to 5 carbon atoms and up to 5 conjugated double bonds are contained in the ring. An electrolyte for an electrolytic capacitor according to claim 1, wherein the aprotic solvent is selected from N-methyl-formamide, N-dimethylformamide, N-ethyllformamide, N-diethylformamide, N-methylacetamide, N-dimethylacetamide, N-ethyl-acetamide, N-diethylacetamide, γ-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene, carbonate, dimethyl sulfoxide, acetonitrile or a mixture of two or more thereof.

Inventors: SHINOZAKI, FUMIHIKO NIPPON CHEMI-CON CORP., YOKOYAMA, YUTAKA NIPPON CHEMI-CON CORP.
Applicants: NIPPON CHEMI-CON CORPORATION
Application year: 1986
Main classification: H01G9
IPC codes: H01G9, H01M10