Chemical capacitors and quaternary ammonium salts

A capacitor is an electrical device that can store energy in an electric field between a pair of closely spaced conductors. Its application as an energy storage device -an alternative to rechargeable batteries- has been receiving considerable attention. There are chemical capacitors using liquid electrolytes such as aluminum electrolytic capacitors and double-layer capacitors, and they utilize quaternary ammonium salts in their nonaqueous electrolytes. After a brief explanation of the working principles of these chemical capacitors and their requirements for electrolytes, the practical applications of quaternary ammonium salts for aluminum electrolytic capacitors and double-layer capacitors are reviewed from the historical and technological viewpoints based on research conducted in our laboratory.