Electrolyte design for reversible metal electrodeposition-based electrochromic energy-saving devices

Reversible metal electrodeposition (RME)-based electrochromic devices have been attracting significant research interest due to their merits of low cost, simple configuration, and high extinction coefficients. As the key component in the electrochromic system, RME electrolytes with various metal ions and additives have endowed the RME device with flexible functionalities in energy-saving applications such as energy-efficient displays, smart windows, and camouflages. However, it is still challenging to research a widespread commercial application before some critical issues can be solved such as poor reversibility, low optical memory of the mirror state, and slow switching speed. Here, we offer a critical review of the recent progress of RME electrochromic devices based on aqueous, organic, ionic liquid, and eutectic electrolytes. Furthermore, the main challenges and perspectives for RME electrolytes are highlighted and discussed.