Superior Performance Asymmetric Supercapacitors Based on Flake-like Co/Al Hydrotalcite and Graphene

Flake-like Co/Al layered double hydroxides (Co/Al LDHs) were synthesized by using a facile and free-template hydrothermal method. Reduced graphene oxide (rGO) is obtained by a simple, clean and controlled hydrothermal reduction route to convert graphene oxide (GO) to stable graphene solution which avoided reductant. Because of their unique structure, both materials exhibit excellent electrochemical performances, which the maximum specific capacitance of Co/Al LDHs is 1158F/g and rGO is 223.2F/g. An asymmetric capacitor incorporating the LDHs as the positive electrode and the rGO as the negative electrode was fabricated. The experimental results indicate that the optimized asymmetric supercapacitor shows intriguing performances with a maximum specific capacitance of 97.5 F/g and high energy density of 34.7Wh/kg at a cell voltage of 1.6V. A good electrochemical stability with 93% specific capacitance retained was demonstrated after consecutive 2000 cycle numbers. Because of the large mass loading and high energy density, this device after 2000 cycles still drives a red light-emitting-diode (LED). This impressive result presented here may have outstanding potential in commercial applications. (C) 2014 Elsevier Ltd. All rights reserved.