The rational design of poly (inoic liquid) for 4.0 V graphene-based supercapacitors

The narrow operating potential range is the main obstacle to limit the increase of energy density of supercapacitors. Surface functionalization of carbon-based electrode materials can effectively improve their electrochemical properties. In this work, a series of ionic liquid (ILs)/graphene composite electrode materials were designed and prepared using covalent and non-covalent strategies. The effects of ionic liquid modification on extending the operating voltage window, restraining self-discharge and optimizing the cycle life of devices were comprehensively studied. As a result, the non-covalent modification method can effectively reduce the defect degree of the electrodes without influencing their porosity. Meanwhile, the wettability of ILs/graphene with ILs electrolytes is improved and the self-discharge effect of the electrodes is suppressed. The resulting supercapacitors exhibited excellent stability at 4.0 V for 10,000 cycles with energy densities reaching up to 65 Wh kg^–1.