Unlocking exceptional sodium ion storage capability of manganese dioxide via controllable incorporation of cation vacancies

Abstract

Defects engineering has been widely considered as a promising structure modulation strategy to realize enhanced Na+ storage in MnO2, however, incorporation of cation vacancies in a controllable manner is still in urgent need. In this study, a universal “Ion doping + Selective etching” strategy has been proposed that enables facile and controllable creation of cation vacancies in α/δ-MnO2 nanostructures. More importantly, the effects of cation vacancies on Na+ storage are found strongly correlated to the crystal structures of MnO2. 3D ion diffusion channels are formed in α-MnO2 with the formation of cation vacancies, which facilitate ion (de)intercalation under high rate conditions. In δ-MnO2, the cation vacancies mainly promote charge transfer and provide abundant Na+ insertion sites, therefore results in dramatically increased specific capacitance at low current densities. The reported work paves the way for rational design of defect structures in metal oxide framework towards enhanced charge storage capability.