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

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 _0.25V ₂O ₅.nH ₂O 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.