NaCa 0.6 V 6 O 16 ·3H 2 O as an Ultra‐Stable Cathode for Zn‐Ion Batteries: The Roles of Pre‐Inserted Dual‐Cations and Structural Water in V 3 O 8 Layer

Abstract Rechargeable aqueous batteries with Zn 2+ 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 Zn 2+ ‐storage cyclability must be found in order for Zinc‐ion batteries (ZIBs) to find practical applications. Herein, NaCa 0.6 V 6 O 16 ·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 V 3 O 8 layered structure in NaCaVO is energetically favorable for Zn 2+ diffusion and the structural water situated between V 3 O 8 layers promotes a fast charge‐transfer and bulk migration of Zn 2+ by enlarging gallery spacing and providing more Zn‐ion storage sites. It is also found that Na + and Ca 2+ alternately suited in V 3 O 8 layers are the essential stabilizers for the layered structure, which play a crucial role in retaining long‐term cycling stability.