Activated carbon fiber sheets as polarizable electrodes of electric double layer capacitors

Activated carbon fiber sheets (ACF sheets) have been developed as polarizable electrodes of electric double layer capacitors. The ACF sheets were prepared by a paper-making process from activated carbon fibers (ACF), carbon fibers (CF), and pulps. The specific surface area of ACF sheets depended proportionally on the content of ACF and their electrical resistance decreased drastically with addition of the pitch-based CF. Natural pulps were suitable material as a binder of ACF sheets. The electric double layer capacitance of the capacitors with ACF sheets was proportional to the content of ACF and the impedance was mainly influenced by the content and the type of CF. The capacitors showed good performance over a wide temperature range (−25 to 80°C) and good charge-discharge cycle characteristics (10,000 cycles).