High energy density Li-ion capacitor assembled with all graphene-based electrodes

To meet the higher requirement of energy storage units, novel devices combining high power performance of supercapacitor and high energy density of Li-ion battery are in urgent demand. Herein we designed and fabricated a Li-ion capacitor device, which is composed of an electrochemical double layer capacitance electrode as the positive electrode and a Li-ion battery type electrode as the negative electrode. Both electrodes consist of graphene-based active materials: a three-dimensional graphene-based porous carbon material with ultrahigh specific surface area, appropriate pore size distribution and excellent conductivity for the positive electrode, and a flash-reduced graphene oxide with open-pore structure and superior rate capability for the negative electrode. With the benefit of the Li-ion capacitor structure, the device exhibits a comprehensive and excellent electrochemical performance in terms of high operating voltage (4.2 V), ultrahigh energy density of 148.3 Wh kg−1 (with power density of 141 W kg−1), maximum power density of 7800 W kg−1 (with energy density kept at 71.5 Wh kg−1) and long cycle life. Such a superior performance indicates that the Li-ion capacitor could be a promising novel energy storage device for wide applications in fast, high efficient and long life energy storage systems.