Ultra-strong ionic liquid-based polymer composite electrolyte for high performance electrochromic devices

Polymer electrolytes are the key composite for all-solid electrochromic devices due to their unique properties including high ionic conductivity, good flexibility, etc. However, such applications are still impeded by the poor mechanical strength. In this study, novel quasi-solid polymer/ionic liquid composite electrolyte is constructed and the tensile strength is greatly enhanced by coupling epoxy composite with glass fibers (GFs) as the reinforcement. The tensile strength of the composite electrolyte is tripled and reaches 7.6 MPa after optimizing the content of GFs with the ionic conductivity of 1.75 × 10−5 S cm−1. Then, a dual-coloring electrochromic device fabricated with the composite electrolyte presents excellent switching stability (18000 cycles, >180000 s), fast response (˂2 s), ultra-high coloring efficiency (η = 451 cm2/C) and low driving voltage (±1 V). In addition, a substrate-free and flexible electrochromic device based on the composite electrolyte is successfully assembled, which demonstrates remarkable electrochromic behaviors, unique flexibility and mechanical stability. This work may promote the development of low-cost, easily-assembled, ultrahigh-flexible and high-performance electrochromic devices.