In-situ electrochemical conversion of Na5V12O32@graphene for enhanced cycle stability in aqueous zinc ion batteries

HYPOTHESIS:Na5V12O32 (NVO) is a potential cathode for aqueous zinc ion batteries (AZIBs). However, it suffers severe capacity decay due to the dissolution of the active material. The structural design may be an effective solution to the problem. EXPERIMENTS:Herein, we construct a typical two-dimensional hierarchical structure of Na5V12O32@graphene (NVO@G) via a facile molten salt method. FINDINGS:The capacity fading problem is solved by the in-situ conversion of NVO@G to a more stable hierarchical system during cycling. The in-situ formed zinc pyrovanadate (Zn3V2O7(OH)2·2H2O, ZVO) nanosheets on the surface of graphene exhibits excellent zinc-ion storage stability. The presence of graphene induces the growth of NVO nanobelts to construct the typical two-dimensional hierarchical structure. Additionally, the in-situ conversion makes the formed ZVO nanosheets contact with graphene better. Benefitting from the hierarchical nanostructure and in-situ phase conversion, the NVO@G electrode shows excellent long-term stability (96.4% retention after 340 cycles at 0.3 A g-1, 85.7% retention after 4400 cycles at 5 A g-1) and high zinc ion storage capacity (220 mAh g-1 at 0.3 A g-1), which is superior to those of most electrode materials previously reported.