An Electric Double-Layer Capacitor With Activated Carbon Fiber Electrodes

An electric double-layer capacitor with activated carbon fiber (ACF) electrodes has been developed. The capacitor features ultrahigh capacitance (0.033 F-0.68 F) in a small thin structure (13.5-mm diameter x 8 mm or 21.5-mm diameter x 9 mm). A technique for carbonization and activation of the phenolic resin-based fiber and a plasma spraying technique for the metal electrodes enabled us to make the small-size capacitor for memory backup use and as a replacement for small-size batteries. Micropores larger than 2 nm in diameter in the ACF effectively work to form an electric double layer which results in a highperformance capacitor over a wide temperature range from -25 to 70°C.