Stable Zn–WO3 battery with a ZnCl2 water-in-salt electrolyte

Transition metal oxide, WO3, has shown great potential in zinc-ion rechargeable batteries as cathode material, yet the poor structural stability and low capacity significantly hindered its further application. Herein, a 30 m water-in-salt electrolyte (WiSE) was rationally designed to construct a stable Zn–WO3 battery. The relatively fewer free water molecules and lower desolvation barrier of [ZnCl4]2- ions in ZnCl2 WiSE not only resulted in a wide electrochemical stability window, low depth of discharge, high reduction potential but also contributed to the limited dissolution of WO3 and high electrochemical corrosion resistance. As a result, the assembled Zn–WO3 battery with 30 m ZnCl2 WiSE achieved a specific capacity of 94.8 mAh g−1 at 0.1 A g−1, energy density of 18.9 Wh kg−1 at a power density of 747.3 W kg−1 and capacitance retention of 94.8% after 1,000 cycles at a high rate of 1 A g−1. Furthermore, a flexible quasi-solid-state Zn–WO3 battery was fabricated using ZnCl2 WiSE without adding adhesives, demonstrating great potential for the next-generation energy storage application.