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

Abstract

Layered intercalation compounds Na\(_{x}\)MnO\(_{2}\) (x = 0.7 and 0.91) nanoflakes have been prepared directly through wet electrochemical process with Na\(^{+}\) 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\(^{-1}\) and higher capacitances over 1000 F·g\(^{-1}\) 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.