Electrochemically Activated Vanadium Oxide Cathode for Advanced Aqueous Zn-Ion Batteries.

The search for large-capacity and high-energy-density cathode materials for aqueous Zn-ion batteries is still challenging. Here, an electrochemical activation strategy to boost the electrochemical activity of a carbon-confined vanadium trioxide (VO@C) microsphere cathode is demonstrated. Tunnel-structured VO undergoes a complete phase transition to a layered, amorphous, and oxygen-deficient ZnVO·HO on the first charge, thus allowing subsequent (de)intercalation of zinc cations on the basis of the latter structure, which can be regulated by the amount of HO in the electrolyte. The electrode thus delivers excellent stability with a significantly high capacity of 602 mAh g over 150 cycles upon being subjected to a low-current-rate cycling, as well as a high-energy density of 439.6 Wh kg and extended life up to 10000 cycles with a 90.3% capacity retention. This strategy will be exceptionally desirable to achieve ultrafast Zn-ion storage with high capacity and energy density.