An Inorganic Fiber-Polymer Composite-Based Quasi-Solid Electrolyte for High-Performance Electrochromic Devices

Electrochromic technology provides an efficient method for photothermal modulation, owing to its tunable optical absorption properties. Solid-state electrolytes provide superior safety for electrochromic devices (ECDs) compared to conventional liquid electrolytes. However, the sluggish ion diffusion in solid-state electrolytes severely impedes the response speed of ECDs. In this work, an inorganic nanofiber-polymer composite-based quasi-solid electrolyte consisting of a silica (SiO₂) nanofiber membrane and a poly(methyl methacrylate) (PMMA) polymer electrolyte was designed, which facilitated the rapid transportation of Li⁺ ions. As a nanofiller with a high aspect ratio, SiO₂ nanofibers can reduce the crystallinity of polymers. Meanwhile, the mobility and arrangement of PMMA chains near the nanofiber surfaces were altered, creating an interfacial region that facilitated ion transport. Consequently, Li⁺ ions can migrate more rapidly along the surfaces of the SiO₂ nanofibers or through the interfacial network formed around them. Moreover, the SiO₂ nanofiber membrane served as a framework that provided support for the PMMA-based polymer electrolyte. The composite quasi-solid electrolyte exhibited a high ionic conductivity (4.42 mS cm^-1 at 20 °C). The composite electrolyte-based ECD employed tungsten trioxide and vanadium pentoxide as electrodes and achieved reversible color changes between transparent light grayish and deep blue. The ECD exhibited a fast switching speed (0.96 s for coloring and 0.8 s for bleaching), a high coloration efficiency (CE = 247.36 cm² C^-1), and an outstanding cycling stability (maintaining 86% performance after 1500 cycles (54 785 s)).