Interfacial Charge Transfer and Zinc Ion Intercalation and Deintercalation Dynamics in Flexible Multicolor Electrochromic Energy Storage Devices

Bifunctional electrochromic devices integrating electrochromism and energy storage have attracted extensive attention in recent years. Here, zinc-ion-intercalation-based multicolor electrochromic energy storage devices (EESDs) based on a free-standing Zn2+-based polymeric electrolyte membrane (ZPEM) and a nanocrystal-in-glass V2O5 thin film were constructed. Evolution of the interlayer spacing, V–O-related bonds, and chemical compositions of the V2O5 thin films with zinc ion intercalation and deintercalation is elaborated in a liquid Zn(CF3SO3)2-propylene carbonate (PC) electrolyte. Impressively, highly reversible multi-electrochromism among greenish-blue, yellowish-green, greenish-yellow, faint-yellow, yellowish-orange, and reddish-orange colors is observed in both flexible V2O5 thin films and flexible ZPEM/V2O5/indium tin oxide (ITO) EESDs, which enjoy the benefits from the free channel originating from the large interlayer spacing, the buffering effect of the amorphous phase in the host nanocrystal-in-glass V2O5 matrix, the robust electrostatic interactions between the host V2O5 and guest Zn2+, and Faradaic redox reactions at the Zn2+/V2O5 active interface. The flexible multicolor EESD based on zinc ion intercalation and deintercalation exhibits remarkable electrochromic and energy storage performance with a high transmittance modulation of 57.88%, an excellent coloration efficiency of 36.91 cm2 C–1, a superior specific capacitance of 51 μF cm–2, an enhanced rate capacity, and a pseudocapacitive feature, making it a promising candidate for cost-efficient, environmentally friendly, and bifunctional electrochromic devices.