Supercapacitors and lithium ion batteries combined are promising hybrid energy storage for portable products, electric vehicles, and smart grid applications. However, the major scientific challenge in this system is to significantly increase the energy density of supercapacitors or raise the power density of lithium ion battery to enhance flexibility for various energy demands.

This study aims to extend the energy density while maintain high specific capacitance through modification of electrodes with graphene oxide (GO) based materials. To prevent leakage of electrolyte, gel polymer electrolyte (GPE) consisting of lithium salt is selected, and it is also able to enhance the mechanical property of the capacitor. GO synthesized by chemical methods from graphite powder is employed because chemically functionalized surface of GO sheet can exhibit derived hydroxyl groups, epoxy groups, and active edges with carboxylic acid groups. Engineering of these functional groups in GO can potentially affect the surface adsorption and in turn improve the performance of capacitors.

In this study, modification of GO surface is conducted and its effects on the all-solid-state supercapacitor are investigated. Characterizations of functionalized graphene oxide have been conducted with x-ray diffraction (XRD), scanning electron microscopy (SEM), and FTIR. Electrochemical performance of these electrodes is investigated using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy.