Potassium vanadates with stable structure and fast ion diffusion channel as cathode for rechargeable aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) are feasible for grid-scale applications due to their unique attributes such as safe, sustainable, and low-cost. However, it is limited by cathode materials, which requires a stable host structure and fast channel for zinc ions diffusion. Here, we develop various kinds of potassium vanadates (K2V8O21, K0.25V2O5, K2V6O16·1.57H2O and KV3O8) as cathodes for aqueous ZIBs. K2V8O21 and K0.25V2O5 with tunnel structure can maintain a stable structure and are conducive to the faster zinc ion diffusion during repeated cycles compared to the layered KV3O8 and K2V6O16·1.57H2O that suffer from structural collapse. The optimal K2V8O21 cathode exhibits excellent zinc storage performance, with a high capacity of 247 mA h g−1 at 0.3 A g−1 and a good rate at 6 A g−1 as well as excellent cyclic stability up to 300 cycles. The results suggest K2V8O21 is a very promising cathode for aqueous ZIBs, which could be extended to construct other high-performance cathode materials with a similar crystal structure (e.g. β-Na0.33V2O5, Li0.3V2O5, Ag0.33V2O5, etc.) for zinc storage.