Mechanistic Insights of Zn2+ Storage in Sodium Vanadates

Rechargeable aqueous zinc-ion batteries (ZIBs) with high safety and low-cost are highly desirable for grid-scale energy storage, yet the energy storage mechanisms in the current cathode materials are still complicated and unclear. Hence, several sodium vanadates with NaV3O8-type layered structure (e.g., Na5V12O32 and HNaV6O16 center dot 4H(2)O) and beta-Na0.33V2O5-type tunneled structure (e.g., Na0.76V6O15) are constructed and the storage/release behaviors of Zn2+ ions are deeply investigated in these two typical structures. It should be mentioned that the 2D layered Na5V12O32 and HNaV6O16 center dot 4H(2)O with more effective path for Zn2+ diffusion exhibit higher ion diffusion coefficients than that of tunneled Na0.76V6O15. As a result, Na5V12O32 delivers higher capacity than that of Na0.76V6O15, and a long-term cyclic performance up to 2000 cycles at 4.0 A g(-1) in spite of its capacity fading. This work provides a new perspective of Zn2+ storage mechanism in aqueous ZIB systems.