Abstract

Cost-effective and environmentally friendly aqueous zinc-ion batteries (AZIB) 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 optimised. 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 Zn2+ diffusion over multiple length scales. Herein, we report on a new class of hydrated porous δ-Ni0.25V2O5.nH2O nanoribbons for use as an AZIB cathode. 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 favourable Zn2+ diffusion properties, arising from the atomic-level structure of the well-defined lattice channels. Furthermore, the microstructure of the asprepared 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 modelling, illustrating favourable porosity and satisfactory tortuosity.