Abstract

Layered intercalation compounds Na_xMnO₂ (x = 0.7 and 0.91) nanoflakes have been prepared directly through wet electrochemical process with Na⁺ ions intercalated into MnO₂ interlayers spontaneously. The as-prepared Na_xMnO₂ nanoflake based supercapacitors exhibit faster ionic diffusion with enhanced redox peaks, tenfold-higher energy densities up to 110 Wh.kg^-1 and higher capacitances over 1000 F.g^-1 in aqueous sodium system compared with traditional MnO₂ supercapacitors. Due to the free-standing electrode structure and suitable crystal structure, Na_xMnO₂ nanoflake electrodes also maintain outstanding electrochemical stability with capacitance retention up to 99.9% after 1000 cycles. Besides, pre-intercalation effect is further studied to explain this enhanced electrochemical performance. This study indicates that the suitable pre-intercalation is effective to improve the diffusion of electrolyte cations and other electrochemical performance for layered oxides, and suggests that the as-obtained nanoflakes are promising materials to achieve the hybridization of both high energy and power density for advanced supercapacitors.