Unveiling the role of structural water and achieving enhanced Zn-ion storage via thermal dehydration of a Ni-containing heteropolyoxovanadate cathode

Abstract

The widespread adoption of aqueous zinc-ion batteries (AZIBs) is constrained by cathode materials with limited capacity and poor structural stability. Herein, we present the systematic exploration of thermal dehydration as a strategic tool to activate a nickel-containing heteropolyoxovanadate cathode. The precursor, Na₇[NiV₁₄O₄₀]·18H₂O (Ni-NVOH), was synthesized and subsequently dehydrated to yield Na₇[NiV₁₄O₄₀] (Ni-NVO). This process removes crystalline water, optimizes the material's architecture, and opens up diffusion pathways for Zn²⁺ ions. As a result, the engineered Ni-NVO cathode delivers a high reversible capacity of 440 mAh g⁻¹ at 0.1 A g⁻¹ and exhibits good cycling stability, maintaining a high coulombic efficiency over 500 cycles at 1 A g⁻¹. This work underscores thermal dehydration as a simple yet effective strategy for activating polyoxovanadate materials, offering a valuable design principle for advanced AZIB cathodes.