Phase Transformation of VO2/rGO Composites as High‐Voltage Cathodes in Zinc‐Ion Batteries

The VO₂/rGO cathode for ZIBs: The VO₂/rGO compound structure with rGO promotes the fast electron/ion transport and stability simultaneously. It is found that the irreversible phase transition from VO₂/rGO composite to Zn₃(OH)₂V₂O₇ ⋅ 2H₂O/rGO (T-VO₂/rGO) with layered structure and a large interlayer spacing at the first charging process.

Abstract

Aqueous zinc-ion batteries (ZIBs) are becoming widely concerned candidates as stationary and safe energy storage technology. Vanadium oxides display promising role as cathodes for ZIBs owing to their inherent merits in structures and multiple valence states. However, their unsatisfactory electrical conductivity and narrow voltage window hinder the practical application. Moreover, the charge storage mechanism at the high voltage is unclear. Herein, we synthesized VO₂/rGO composites with high electrical conductivity and demonstrated an electrochemically induced phase transition from tunneled VO₂/rGO to Zn₃(OH)₂V₂O₇ ⋅ 2H₂O/rGO with a laminated structure and an enhanced interlayer spacing during the first charge to 1.6 V, which shows preferable Zn²⁺ storage capacity. Concretely, the electrochemical window of as-assembled ZIB expands to 1.6 V with a specific capacity of 329.9 mAh g⁻¹ at 0.1 A g⁻¹, exhibiting wider window compared with the ZIBs based vanadium oxide reported previously. Simultaneously, a long stable lifetime of 84 % capacity retention over 1,000 cycles can be recorded. Our work opens a new idea of design strategy to develop high-voltage ZIBs.

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