Influence of heating duration on high-voltage charging durability of an activated carbon electrode for electric double layer capacitors

Phenolic-resin based steam-activated carbon fiber (ACF) for electric double layer capacitors was subjected to heattreatment at 1500°C in nitrogen. The dependence of the pore structure and the capacitance retention rate after high voltage charging (3 V, 100 h, 70°C) on the heating duration was investigated using a two-electrode cell with propylene carbonate electrolyte. The micropore-shrinkage and the removal of the oxygen-containing surface functionalities of the ACF were accomplished within a short time (5 seconds) by the heat-treatment, however a longer time (1 hour) was necessary to improve the capacitance retention rate. The Raman analysis revealed that the local ordering structure changed slowly by heat-treatment at 1500°C, suggesting the sufficiently long heat-treatment essential to the improvement of the capacitance retention rate.