Reversible Zn-driven reduction displacement reaction in aqueous zinc-ion battery

Tremendous attention has been paid to aqueous zinc-ion batteries (ZIBs) with the merits of low cost, safety and environmental benignity. Exploration of the Zn2+ ion storage mechanism is of great significance to the fundamental understanding and future practical application of advanced aqueous Zn-ion battery systems. Herein, we have observed the reduction displacement reaction mechanism upon Zn2+ insertion/extraction into/from the structure of copper pyrovanadate (Cu-3(OH)(2)V(2)O(7)2H(2)O), i.e., Zn2+ insertion would drive the reduction of Cu2+ to metallic Cu-0 particles, and also the phase transition from Cu-3(OH)(2)V(2)O(7)2H(2)O to a new phase of Zn0.25V2O5H2O. As a result, Cu-3(OH)(2)V(2)O(7)2H(2)O is able to deliver excellent electrochemical performance (e.g., a high discharge capacity of 136 mA h g(-1) can be maintained after 3000 repetitive cycles at 10 A g(-1)).