Characteristics of tantalum electrolytic capacitors using soluble polypyrrole electrolyte

Polypyrrole (Ppy) electrolyte solutions in various organic solvents (dimethylformamide, DMF; N-methyl-2-pyrrolidone, NMP; chloroform; trifluoroacetic acid) were prepared using Ppy powder doped with di(2-ethylhexyl)sulfosuccinate sodium salt (Ppy-DEHS) and butylnaphthalene sulfonate sodium salt (Ppy-BNS), respectively. Several tantalum electrolytic capacitors were fabricated by dip coating in these solutions and their electrical properties such as capacitance and tan δ were measured. The capacitors prepared with Ppy-DEHS electrolyte in trifluoroacetic acid showed both high capacitance and low tan δ. Usage of a Ppy electrolyte solution containing both surfactant and a coupling agent also resulted in high capacitance and low tan δ. These phenomena were interpreted in terms of electrical conductivity and chemical structure of the electrolyte, and interactions such as hydrogen bonding, radical addition reaction, covalent bonding between the tantalum oxide layer and the solvent.