A Quasi‐Solid Electrolytes Based on Crystalline Phase Modulation of PVDF‐HFP for High‐Performance Electrochromic Devices

Abstract A rational design of ion‐conducting layers is crucial to the performance of all‐solid‐state electrochromic devices (ECDs). However, the ECDs based on solid‐state electrolytes remain a significant challenge because of the slow ion diffusion. Herein, a quasi‐solid‐state electrolyte based on high‐polarity nanofiber membranes is prepared by electrospinning, in which ionic liquid (ILs) is combined with a poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) matrix. The obtained PVDF‐HFP/ILs gel polymer electrolytes (GPEs) showed an extremely high visible‐range transmittance (over 95%), a high ionic conductivity (5.67 mS cm −1 at 25 °C), a wide electrochemical window (4.40 V), making it an outstanding candidate to be used in ECDs as an ion‐conducting layer. The ECDs based on Prussian blue (PB) and tungsten oxide (WO 3 ) electrodes achieved a reversible color transition from transparent to dark blue, exhibiting an excellent transmittance modulation (ΔT = 90.74%), a good coloration efficiency (CE = 184.16 cm 2 C −1 ), and a good cycling stability (retained 90.78% after 1500 cycles). Additionally, the ECDs also exhibited a steady energy‐storage behavior between −20 and 50 °C and a slow self‐discharge rate, offering a viable approach to achieving high‐performance ECDs.