Boosting energy density of the aqueous supercapacitors by employing trifluoroacetic acid as a novel high voltage electrolyte

Abstract

An effective way to increase the energy density of supercapacitors is to develop stable electrolytes with high operating potential. In this work, trifluoroacetic acid (TFA) is first employed as an aqueous acidic electrolyte with a stable operating potential of 1.4 V, a 40 % improvement in operating potential is achieved compared to the traditional acidic aqueous electrolyte. To match the TFA electrolyte, a biomass-derived hierarchical porous carbon (HPC) with a tailored pore size and ultra-large specific surface area of up to 3649.4 m2 g−1 is fabricated, which delivers a surprising specific capacitance of up to 625 F g−1 at 1 A g−1. The symmetric supercapacitor device built up by using the TFA electrolyte and the prepared electrode material can be operated stably at 1.4 V and reserve 96.6 % of initial specific capacitance after 30,000 cycles. Meanwhile, a large energy density of 19.5 Wh kg−1 at 347 W kg−1 and 19.49 Wh kg−1 at 340 W kg−1 can be delivered for the assembled normal symmetric supercapacitor and the solid-state supercapacitor, respectively. Compared to the supercapacitors using the conventional H2SO4 electrolyte, the energy density of the supercapacitor using the TFA electrolyte can be enhanced by 2.26 times without sacrificing the high-power density and outstanding cycle stability. The remarkable improvement in energy density for aqueous supercapacitors by this simple and feasible method would contribute to promoting their practical application in modern electrochemical energy storage systems.