Fast Ionic Diffusion-Enabled Nanoflake Electrode by Spontaneous Electrochemical Pre-Intercalation for High-Performance Supercapacitor

Layered intercalation compounds Na x MnO 2 (x 5 0.7 and 0.91) nanoflakes have been prepared directly through wet electrochemical process with Na 1 ions intercalated into MnO 2 interlayers spontaneously. The as-prepared Na x MnO 2 nanoflake based supercapacitors exhibit faster ionic diffusion with enhanced redox peaks, tenfold-higher energy densities up to 110 Wh?kg 21 and higher capacitances over 1000 F?g 21 in aqueous sodium system compared with traditional MnO 2 supercapacitors. Due to the free-standing electrode structure and suitable crystal structure, Na x MnO 2 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.