Integrating molybdenum into zinc vanadate enables Zn3V2MoO8 as a high-capacity Zn-supplied cathode for Zn-metal free aqueous batteries

The commercialization of aqueous zinc-ion batteries (AZIBs) has been hindered by the obsession with Zn-metal anode, just like the early days of lithium-ion batteries. Developing Zn-metal free aqueous batteries (ZFABs) with superior Zn-supplied cathodes is a promising way to escape this predicament. Herein, a novel mixed transition-metal spinel, Zn3V2MoO8, has been synthesized via a sol-gel technique and proposed as a Zn-supplied cathode material. Utilizing the synergistic effect of vanadium and molybdenum, Zn3V2MoO8 can provide a high capacity of 360.3 mA h g-1 at 100 mA g-1, which is the state-of-the-art in existing Zn-supplied cathodes, and the capacity retention is 82% over 700-4500 cycles at 10 A g-1. The mechanism is that Zn3V2MoO8 undergoes a phase transition to Zny(V,Mo)2O5-x·nH2O in the initial charge, and then protons and zinc ions intercalate/deintercalate concurrently into/from the new host. To construct ZFABs with a Zn3V2MoO8 cathode, two non-zinc materials (brass and 9,10-anthraquinone) are used as anodes. Thereby, the Zn3V2MoO8||9,10AQ battery reveals a more satisfactory electrochemical performance, with a stable capacity of 100.4 mA h g-1 lasting for 200 cycles, which provides a feasible scheme for the practical application of AZIBs.