High-performance zinc-ion batteries enabled by electrochemically induced transformation of vanadium oxide cathodes

Rechargeable aqueous zinc-ion batteries (ZIBs) have become a research hotspot in recent years, due to their huge potential for high-energy, fast-rate, safe and low-cost energy storage. To realize good electrochemical properties of ZIBs, cathode materials with prominent Zn2+ storage capability are highly needed. Herein, we report a promising ZIB cathode material based on electrochemically induced transformation of vanadium oxides. Specifically, K2V6O16.1.5H2O nanofibers were synthesized through a simple stirring method at near room temperature and then used as cathode materials for ZIBs in different electrolytes. The cathode presented superior Zn2+ storage capability in Zn(OTf)2 aqueous electrolyte, including high capacity of 321 mAh/g, fast charge/discharge ability (96 mAh/g delivered in 35 s), high energy density of 235 Wh/kg and good cycling performance. Mechanism analysis evidenced that in Zn(OTf)(2) electrolyte, Zn2+ intercalation in the first discharge process promoted K(2)V(6)O16.1.5H(2)O nanofibers to transform into Zn-3+xV(2)O(7)(OH)2.2H(2)O nanoflakes, and the latter served as the Zn2+-storage host in subsequent charge/discharge processes. Benefiting from open-framework crystal structure and sufficiently exposed surface, the Zn-3+xV(2)O(7)(OH)2.2H(2)O nanoflakes exhibited high Zn2+ diffusion coefficient, smaller charge-transfer resistance and good reversibility of Zn2+ intercalation/de-intercalation, thus leading to superior electrochemical performance. While in ZnSO4 aqueous electrolyte, the cathode material cannot sufficiently transform into Zn(3+)xV(2)O(7)(OH)2.2H(2)O, thereby corresponding to inferior electrochemical behaviors. Underlying mechanism and influencing factors of such a transformation phenomenon was also explored. This work not only reports a high-performance ZIB cathode material based on electrochemically induced transformation of vanadium oxides, but also provides new insights into Zn2+-storage electrochemistry. (C) 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.