Flexible Inorganic All-Solid-State Electrochromic Devices toward Visual Energy Storage and Two-Dimensional Color Tunability

Multicolor display has gradually become a sought-after trend for electrochromic devices due to its broadened application scope. Meanwhile, the advantages of inorganic electrochromic devices such as stable electrochemical performance and good energy storage ability also have great attraction in practical production applications. However, there are still huge challenges for inorganic electrochromic materials to achieve multicolor transformation due to their single-color hue change. Herein, we design an inorganic and multicolor electrochromic energy storage device (MEESD) exhibiting flexibility and all-solid-state merits. Prussian blue (PB) and MnO₂, as the asymmetrical electrodes of this MEESD, show good pseudocapacitance property, matching charge capacity, and obvious color change. As a typical electrochromic device, the MEESD shows a fast response of 0.5 s and good coloration efficiency of 144.2 cm²/C. As an energy storage device, the MEESD presents excellent rate capability and volumetric energy/power density (84.2 mWh cm^-3/23.3 W cm^-3). Its energy level can be visually monitored by color contrast and optical modulation. In the charging/discharging process, its color can obviously change to various degrees of yellow, green, and blue along with 40% wide optical modulation at 710 nm. Meanwhile, the stability of the MEESD in a common and humidity environment was analyzed in detail from electrochemical, optical, and energy storage aspects. This work provides feasible thoughts to design multifunctional electrochromic devices integrated with inorganic, flexible, all-solid-state, multicolor, and energy storage properties.