An aqueous symmetrical supercapacitor with high bulk pseudocapacitance induced by phase transformation of MnO2

Abstract

The faradaic redox reaction related to pseudocapacitance that occurs in the bulk of electrode materials can benefit the supercapacitors’ energy storage performance. In this work, a 2D layered α-MnO2 electrode with bulk pseudocapacitance that expands during the electrochemical energy storage process is obtained by a controllable phase transformation of 2D δ-MnO2. This 2D layered material possesses both high capacitance (306.8 F/g at 1 A/g) and superior cycle stability (84.4% after 5000 rounds) owing to its high bulk pseudocapacitance proportion based on the 2D layered structure and stable phase of α-MnO2. Furthermore, a symmetrical device constructed with the 2D layered α-MnO2 electrode also possesses a high energy density of 38.9 W h/kg at a power density of 870.3 W/kg, and it retains 18.1 W h/kg at a power density of 5.8 × 104 W/kg. The results given above reveal that 2D layered α-MnO2, after undergoing phase transformation, can raise the bulk pseudocapacitance utilization and further strengthen the supercapacitors’ energy storage capacity.