Zinc polyacrylamide hydrogel electrolyte for quasi-solid-state electrochromic devices with low-temperature tolerance

To achieve solid-state electrochromic devices, an acceptable compromise is to use polymer electrolyte gels, which combine the merits of liquid and solid electrolytes. However, many drawbacks remain, such as inflammability, a sharp decline in ionic conductivity at zero temperature, and interfacial problems with the electrodes. Here, we introduce a polyacrylamide (PAM)-based hydrogel electrolyte containing a high concentration of zinc ion, which delivers an ionic conductivity of 63.5 mS cm−1 at room temperature and 12.8 mS cm−1 at even −30°C. Based on the PAM-Zn2+ electrolyte, we prepare a quasi-solid WO3/PAM-Zn/Zn energy storage electrochromic bifunctional device by in situ polymerization. The device exhibits excellent cycle performance (retaining 45.1% of optical contrast after 9,200 cycles) and a high areal capacity (278.3 mAh m−2 at 0.1 mA cm−2). Furthermore, larger-sized electrochromic devices also show ultra-long cycle stability and attractive anti-freeze properties. This work provides an idea for the large-scale fabrication of anti-freeze electrochromic devices with remarkable lifetimes.