Binder-free hierarchical VS2 electrodes for high-performance aqueous Zn ion batteries towards commercial level mass loading

Abstract

Aqueous rechargeable zinc ion batteries with advantages of low cost and high level of safety have been considered as a promising candidate for large-scale energy storage. In this work, a freestanding, binder-free cathode comprising hierarchical VS<inf>2</inf> in the 1T phase grown directly on a stainless steel mesh (VS<inf>2</inf>@SS) was developed for aqueous zinc ion batteries. The battery exhibited an excellent Zn ion storage capacity of 198 mA h g^-1 and stable cycling performance (above 80% capacity retention over 2000 cycles at 2 A g^-1). The detailed structural and chemical composition analyses revealed the phase evolution of VS<inf>2</inf> and the reversible Zn ion insertion/extraction mechanism during the charge/discharge process. Notably, with an increased mass loading of VS<inf>2</inf> over the commercial level (∼11 mg cm^-2), a long-term cycling stability with 90% capacity retention after 600 cycles (only 0.017% loss per cycle) could be achieved, which suggests that the electrodes are promising for practical applications. Furthermore, flexible solid-state Zn ion batteries were demonstrated by using the VS<inf>2</inf>@SS electrodes, and reliable electrochemical performance could be observed even after 200 cycles.