Flexible and rechargeable electrochromic aluminium-ion battery based on tungsten oxide film electrode

Abstract

Electrochromic (EC) energy storage devices that possess characteristics of energy storage and electrochromism are highly desirable and have increasingly attracted research interests, whilst devices that can be stretched or are flexible have received very little attention. Herein, we report a flexible and rechargeable aluminium (Al) ion EC battery (ECB), which consists of a WO3 film as positive electrode, PET/ITO as substrate, Al sheet as negative electrode, aluminum trichloride (AlCl3) aqueous solution as electrolyte, and absorptive glass mat (AGM) as electrolyte carrier and separator. The ECB exhibits a high specific capacity of 142 mAhg−1, while demonstrating reversible color transitions between white (bleached state) and dark blue (colored state) during the cyclic charge/discharge processes. Furthermore, the ECB can work at bending angles of 0-80° with a capacity retention of 92.3% after 40 bending cycles. The flexibility of the ECB is ascribed to the flexible, porous, and highly stable features of the AGM as well as the deformability of the PET/ITO substrate. The potential widow of the ECB can be largely enhanced by connecting small-sized ECBs internally in series while maintaining the energy density unchanged. The present study demonstrates that the ECB using the AGM as the electrolyte carrier and separator may have great potentials for the construction of both flexible, portable electronics and smart windows.