Electrolyte for electrolytic capacitor

An electrolyte for electrolytic capacitors containing within an aprotic solvent a hexafluorophosphate of an organic amine compound as solute; wherein said organic amine compound is a compound containing one or two pyridine rings; or a primary, secondary or tertiary amine.

An electrolyte for electrolytic capacitor containing within an aprotic 
solvent a hexafluorophosphate salt 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 subsequent 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 electrolyte. 
FIELD OF THE INVENTION 
This invention relates to an electrolyte for electrolytic capacitors 
containing within an aprotic solvent a hexafluorophosphate salt of an 
organic amine compound as solute. 
BACKGROUND OF THE INVENTION 
Hitherto, organic acids or salts thereof and glycol series pastes have been 
principally used as electrolytes for electrolytic capacitors in the 
general purposes. The latest expansion of utilization for 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 salts thereof and glycol 
paste has come to receive attention. 
The greatest subject of employment of the aprotic solvent system 
electrolyte is how to obtain an electrolyte of high conductivity and to 
acheive this an organic carboxylic acid or its salt which is readily 
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 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. Pat. 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 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 an organic amine salt of hexafluorophosphate has a high 
solubility in the aprotic solvent with an enhanced releasability and 
provides a high conductivity. 
SUMMARY OF THE INVENTION 
Thus, a principal object of the invention is to provide an electrolyte of 
substantially non water series high conductivity, using an aprotic 
solvent. 
An electrolyte for electrolytic capacitor according to the invention is 
characterized by containing a hexafluorophosphate salt of an organic amine 
compound in the aprotic solvent as solute. 
PREFERRED EMBODIMENTS OF THE INVENTION 
The organic amine compounds according to the invention are preferably 
selected from the compound groups containing 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 group having 1 to 15 
carbons, aryl group having 6 to 15 carbons or halogen: 
.alpha.-picoline, .beta.-picoline, .gamma.-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-dimethyl-pyridine, 
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-tri-methylpyridine, 
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: 
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: 
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) Quatenary ammonium compounds in which to one nitrogen atom of pyridine 
are bonded an alkyl group, an alkenyl group having 1 to 15 carbons or an 
aryl group having 6 to 15 carbons: 
N-ethyl-2-bromopyridine, N-vinyl 3,5-dimethylpyridine, 
N-phenyl-4-ethylpyridine, N-tolyl-4-butylpyridine. 
Further, the organic amine compound according to the invention may 
preferably be selected from primary, secondary tertiary amines and 
quaternary ammonium compounds in which to one nitrogen atom are added 1 to 
4 alkyl groups, alkenyl group having 1 to 15 carbons or aryl group having 
6 to 15 carbons and 1 to 3 hydrogen atoms. 
(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 the carbon of a hexafluorophosphate salt having a 
general formula, 
##STR1## 
in which m is 0 or 1, m+n is 2 or 3, R.sub.1 is presence or nonpresence of 
alkyl substituent having 1 to 3 carbon atoms, R is hydrogen or 
N-heterocyclic-di-condensed ring compound in which a nitrogen atom forms a 
tertiary amine or a quaternary ammonium with one or two alkyl groups 
having 1 to 5 carbon atoms and 0 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 partial 
hydrogenated compound or complete hydrogenated compound and, as those 
compounds, N-alkylates, indole, 3-methylindole(skatol), isoindole, 
pseudoindole, their partial or complete hydrogenated compound and, as 
those compounds, N-alkyl compounds. 
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-dimethylformamide, N-ethylformamide, 
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: 
.gamma.-butyrolactone, N-methyl-2-pyrrolidone, ethylenecarbonate, 
propylenecarbonate. 
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 subsequent 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 electrolyte.