A high energy density asymmetric supercapacitor based on a CoNi-layered double hydroxide and activated carbon

A high performance asymmetric supercapacitor was fabricated using a CoNi-layered double hydroxide (CoNi-LDH) as the positive electrode and activated carbon as the negative electrode in an electrolyte of 6 M aqueous KOH. The supercapacitor can be cycled reversibly in a wide potential window of 0-1.5 V and exhibits a remarkable energy density of 46.3 Wh·kg−1 at a power density of 102.3 W·kg−1, a high energy density of 25.6 Wh·kg−1 even at a high power density of 1704.5 W·kg−1 These values are much higher than those of a symmetric supercapacitor using only activated carbon (6.9 Wh·kg−1). The results can be ascribed to the high specific capacitance and rate capability of the CoNi-LDH, and the complementary potential windows of the two electrodes that increase the working voltage of the supercapacitor. The supercapacitor also exhibits stable cycling with a 84.5% capacitance retention after 1000 cycles.