NaCa0.6V6O16•3H2O as an Ultra-Stable Cathode for Zn-Ion Batteries: The Roles of Pre-Inserted Dual-Cations and Structural Water in V3O8 Layer

Rechargeable aqueous batteries with Zn2+ as a working-ion are promising candidates for grid-scale energy storage because of their intrinsic safety, low-cost, and high energy-intensity. However, suitable cathode materials with excellent Zn2+-storage cyclability must be found in order for Zinc-ion batteries (ZIBs) to find practical applications. Herein, NaCa0.6V6O16 center dot 3H(2)O (NaCaVO) barnesite nanobelts are reported as an ultra-stable ZIB cathode material. The original capacity reaches 347 mAh g(-1) at 0.1 A g(-1), and the capacity retention rate is 94% after 2000 cycles at 2 A g(-1) and 83% after 10 000 cycles at 5 A g(-1), respectively. Through a combined theoretical and experimental approach, it is discovered that the unique V3O8 layered structure in NaCaVO is energetically favorable for Zn2+ diffusion and the structural water situated between V3O8 layers promotes a fast charge-transfer and bulk migration of Zn2+ by enlarging gallery spacing and providing more Zn-ion storage sites. It is also found that Na+ and Ca2+ alternately suited in V3O8 layers are the essential stabilizers for the layered structure, which play a crucial role in retaining long-term cycling stability.