Asymmetric electrochemical capacitors with high energy and power density based on graphene/CoAl-LDH and activated carbon electrodes

Asymmetric electrochemical capacitors (ECs) consisting of composites of reduced graphene oxide (RGO) and CoAl layered double hydroxide (LDH) as positive electrode, activated carbon (AC) as negative electrode (RGO/LDH//AC) and 6 M KOH solution as electrolyte were achieved. RGO/LDH was synthesized by a facile solution method in one step under mild conditions. Owing to its wide operating voltage window of 0–1.75 V and the utilization of RGO, the RGO/LDH//AC capacitor exhibited excellent electrochemical properties with a maximum energy density of 35.5 W h kg−1, much higher than those of LDH//AC (25.1 W h kg−1) and AC//AC (6.3 W h kg−1) electrochemical capacitors. Moreover, the devices also showed a high power density of 8.75 kW kg−1 and long cycle life of ∼90% retention after 6000 cycles at the current density of 4 A g−1. Such high-performance asymmetric electrochemical capacitors offer great promise in the application of energy storage systems.