Defected vanadium bronzes as improved cathodes in aqueous zinc-ion batteries
There is a growing need for fast, efficient, safe, low-cost energy storage. Aqueous zinc-ion batteries (AZIBs) may be able to address this need but suffer from fast capacity fade and poor ion diffusion kinetics; due to unstable structures and non-optimised interspacing of layered cathode materials. Herein, we propose a structural engineering strategy by synergistically inducing anionic defects and cationic groups within vanadium bronze structures to improve kinetics and boost capacity. The materials discovered and used as the cathodes in AZIBs presented a high capacity of 435 mAh g-1 at a current density of 0.2 A g-1 and excellent stability showing 95% capacity retention after 1500 cycles at 10A g-1. This combined experimental and computational study systemically indicated that rapid Zn2+ storage was achieved from both a highly porous structure, enlarged d-spacing combined with improved electron conductivity as determined by density of states calculations. The modification of vanadium bronze type cathodes achieved by controlled pre-intercalated species and tailored oxygen deficiency open up an avenue for illumination of superior material design, which is realized and proved its feasibility in this work.