Spinel Zn3V3O8: A high-capacity zinc supplied cathode for aqueous Zn-ion batteries

Due to the lack of high-capacity cathodes to supply adequate zinc ions for the electrochemical system, the Zn-metal anode addiction has hampered the practical application of aqueous zinc-ion batteries (AZIBs). Herein, spinel Zn3V3O8 is presented as the first kind of vanadium-based material as zinc supplied cathode for AZIBs. Benefitting from the Zn-rich feature and two-electron reaction of vanadium, Zn3V3O8 delivers a discharge capacity of 285 mA•h g−1, which is the highest record for available zinc supplied cathodes. The phase transition caused by the Zn2+ extraction from Zn3V3O8 during the first charging process forms electrochemically reversible Zn0.3V2O5-x•nH2O as the main Zn2+ host in the subsequent cycles, resulting in an excellent capacity retention of 72.6% after 2000 cycles at 5 A g−1. Due to the ability of supplying Zn2+, Zn3V3O8 ‖ carbon paper battery has been designed as a novel Zn-metal free AZIB and delivers a discharge capacity of 127 mA•h g−1 at a current density of 150 mA g−1. This paper not only provides a high-capacity zinc supplied cathode in vanadium family, but also presents a new electrochemical system of aqueous AZIBs without using Zn metal anode, which is hoped to promote the practical application of rechargeable AZIBs.