Engineering vanadium vacancies to accelerate ion kinetics for high performance zinc ion battery.

Vanadium dioxide (VO) has attracted significant attention in aqueous zinc ion batteries (AZIBs) owing to their desirable theoretical specific capacity originated from multiple electrons transfer reaction and special crystal structure. However, sluggish electrochemical kinetics leads to inferior electrochemical storage performance. Herein, rich vanadium vacancies were introduced in tunnel VO to boost Zn diffusion, increasing charge storage capacity and lengthen lifespan. The structural analyses of X-ray diffraction data refinement and X-ray photoelectron spectroscopy confirm that vanadium vacancies adjust the valence of vanadium, simultaneously shrink unit cell, thus improving structural stability. Theoretical calculations and the corresponding electrochemical measurements elucidate vacancy diffusion mechanism effectively enhance Zn diffusion and electron transfer by reduced Zn migration barrier and charge transfer activation energy. The resulted vacancy-rich cathode exhibits an improved electrochemical stability and kinetics, yielding unprecedented cycling performance at low currents (332 mA h g after 200 cycles at 0.1 A g) and excellent rate capability of 184 mA h g at 20 A g as well as long-term stability at 20 A g. This work is anticipated to promote the development of next generation AZIBs and offer distinguishing inspiration for design of electrode systems.