Ion-exchange-induced high-performance of inverse spinel Mg2VO4 for aqueous zinc-ion batteries

Abstract

Aqueous zinc-ion batteries (ZIBs) stand out among the next generation of large-scale energy storage devices owing to their overwhelming advantages of high safety, low-cost and environmental benefit. However, this promising technology is still plagued by lack of superior cathode materials due to the inherent slow diffusion kinetics. Herein, with theoretical calculations as a guide, we proposed a new strategy to promote Zn2+ migration based on ion-exchange. Specifically, we first find the tendency of Mg2+ and Zn2+ exchange in inverse-spinel Mg2VO4 by molecular dynamics simulations. Density functional theory (DFT) calculations reveal that this ion exchange can moderate the electrostatic interaction between Zn2+ and host material, and reduce the diffusion energy barrier of Zn2+. Meanwhile, the Mg2+ of host leaves vacancies when it is detached, and both contribute to the improvement of Zn2+ diffusion kinetics. Based on theoretical calculations, we for the first time used a simple sol-gel method to synthesize inverse-spinel Mg2VO4 as an aqueous ZIBs cathode. As predicted in theoretical calculations, after optimization of Zn2+ and Mg2+ exchange, the Mg2VO4/Zn system demonstrates rewarding cyclic stability. This work provides a new insight into the development of cathode materials for high-performance ZIBs.