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Abstract 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, NaCa_0.6V₆O₁₆·3H₂O (NaCaVO) barnesite nanobelts are reported as an ultra‐stable ZIB cathode material. The original capacity reaches 347 mAh g⁻¹at 0.1 A g⁻¹, and the capacity retention rate is 94% after 2000 cycles at 2 A g⁻¹and 83% after 10 000 cycles at 5 A g⁻¹, respectively. Through a combined theoretical and experimental approach, it is discovered that the unique V₃O₈layered structure in NaCaVO is energetically favorable for Zn²⁺diffusion and the structural water situated between V₃O₈layers 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 V₃O₈layers are the essential stabilizers for the layered structure, which play a crucial role in retaining long‐term cycling stability.