High-Performance Aqueous Zn2+/Al3+ Electrochromic Batteries based on Niobium Tungsten Oxides

Electrochromic energy storage devices (EESDs) are incorporating electrochromic and energy storage functions, which can visually display energy storage levels in real-time to promote the next generation of transparent battery development. However, their performances are still limited for practical applications. Herein, a self-powered EESD based on complex niobium tungsten oxide is designed using aqueous Zn2+ and hybrid Zn2+/Mn+ (Mn+ = Al3+, Mg2+, and K+) electrolytes. The results reveal that the use of Zn2+/Al3+ hybrid electrolyte achieves superior electrochromic performances including a short self-coloring time, high optical contrast, and excellent cyclic stability. Furthermore, it is also found that the self-coloring process is accompanied by a high discharged capacity of niobium tungsten oxide, with high optical modulation in the Zn2+/Al3+ hybrid electrolyte. The detailed mechanism on the performances of EESD using various electrolytes is systematically studied. This work provides a simple and effective strategy for an aqueous and self-powered EESD with high optical contrast and good cycle stability.