One-step hydrothermal synthesis of Nb5+-doped α-MnO2 nanoparticle for high-performance asymmetric supercapacitor electrode material

Expanding the stable voltage window and specific capacitance of supercapacitor electrode materials remains a key scientific challenge due to the low energy density of supercapacitors. In this study, starting from the problem of low specific capacitance caused by the limited electron transfer rate due to the low conductivity of MnO 2 , a simple and economical hydrothermal method was used to doping different contents of Nb 5+ ions, which replaced some Mn 4+ ions in the α-MnO 2 lattice, thereby causing certain changes in the charge density and band structure of α-MnO 2 , and effectively improving its conductivity. In addition, Nb 5+ -doped α-MnO 2 effectively alters its morphology and surface area, providing a large surface area for ion and electron transport. The optimized Nb-MnO 2 electrode has a voltage window widened from 0.8 V to 1.2 V in a 1 M Na 2 SO 4 electrolyte, with a specific capacitance of 587 F/g with in the 1.2 V wide voltage window, while the undoped MnO 2 has a specific capacitance of only 131 F/g. A 2 V asymmetric supercapacitor is constructed with activated carbon AC as the negative electrode, providing a high energy density of 57 Wh/kg at a power density of 1010 W/kg in a 3 M KOH electrolyte. In addition, at a current density of 5 A/g, the capacitance retention rate of 84.85% was maintained after 5000 charge–discharge cycles. This work is a valuable foundation for the future exploration of wide voltage window and high-performance aqueous electrolyte asymmetric supercapacitors.