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

Abstract

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 (Cu₃(OH)₂V₂O₇·2H₂O), i.e., Zn²⁺ insertion would drive the reduction of Cu²⁺ to metallic Cu⁰ particles, and also the phase transition from Cu₃(OH)₂V₂O₇·2H₂O to a new phase of Zn_0.25V₂O₅·H₂O. As a result, Cu₃(OH)₂V₂O₇·2H₂O 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).