Multi‐Scale Investigations of δ‐Ni0.25V2O5·nH2O Cathode Materials in Aqueous Zinc‐Ion Batteries

Abstract Cost‐effective and environment‐friendly aqueous zinc‐ion batteries (AZIBs) exhibit tremendous potential for application in grid‐scale energy storage systems but are limited by suitable cathode materials. Hydrated vanadium bronzes have gained significant attention for AZIBs and can be produced with a range of different pre‐intercalated ions, allowing their properties to be optimized. However, gaining a detailed understanding of the energy storage mechanisms within these cathode materials remains a great challenge due to their complex crystallographic frameworks, limiting rational design from the perspective of enhanced Zn 2+ diffusion over multiple length scales. Herein, a new class of hydrated porous δ‐Ni 0.25 V 2 O 5 .nH 2 O nanoribbons for use as an AZIB cathode is reported. The cathode delivers reversibility showing 402 mAh g −1 at 0.2 A g −1 and a capacity retention of 98% over 1200 cycles at 5 A g −1 . A detailed investigation using experimental and computational approaches reveal that the host “δ” vanadate lattice has favorable Zn 2+ diffusion properties, arising from the atomic‐level structure of the well‐defined lattice channels. Furthermore, the microstructure of the as‐prepared cathodes is examined using multi‐length scale X‐ray computed tomography for the first time in AZIBs and the effective diffusion coefficient is obtained by image‐based modeling, illustrating favorable porosity and satisfactory tortuosity.