Unravelling the proton hysteresis mechanism in vacancy modified vanadium oxides for High-Performance aqueous zinc ion battery

•Proton hysteresis was, for first time, observed in zinc-ion batteries.•Oxygen vacancy promotes the conductivity and intercalation of Zn2+ and H+.•The new cathodes deliver excellent rate and long-term cycling performance. Rechargeable aqueous zinc-ion batteries, as one of the most promising next-generation energy storage devices, have attracted increasing attentions because of their low cost, environmental benignity, and intrinsic safety. However, their practical application is severely hindered by the low energy density, unsatisfying power density, and poor long-term cycling stability. Herein, a hierarchical vacancy-modified vanadium oxide coated by soft carbon layer is elaborately designed as cathodes for zinc ion batteries. Consequently, the vanadium oxide cathodes deliver an ultrahigh capacity of 587 mAh/g at 0.1 A/g, highly enhanced rate performance with a reversible capacity of 367 mAh/g at 20 A/g, and excellent long-term cycling stability with a decay rate of 0.0058% per cycle after 5000 cycles, which are among the best performances of vanadium-based cathodes. More importantly, an intriguing phenomenon of proton hysteresis was, for the first time, observed during the electrochemical processes. Based on the experimental results and theoretical calculations, we demonstrate that the synergistic effect of vacancy and proton hysteresis on the excellent electrochemical performance in zinc ion batteries. This work not only demonstrates the huge potential of the deliberately designed vanadium oxide in practical application, but also provides a refreshing understanding of the electrochemical mechanism in zinc ion batteries.