A robust UV-curable ion-liquid gel electrolyte for high-performance polymer-based electrochromic devices

Abstract

Electrolyte plays a vital role in balancing charges and facilitating ion transportation in electrochromic devices (ECDs). Meanwhile, mechanical performance is a crucial aspect worth noting in practical applications for preventing short circuit of the ECDs and counter electrode layers. Herein, a quasi-solid gel electrolyte (GE) with a robust polymer framework and high mechanical properties was constructed through a combination of “soft chain” epoxy acrylate (EA) and “hard chain” VEIMPF₆ monomer with EMIMTFSI and LiTFSI as the ion sources. After optimizing the component ratio, the electrolyte GE3-Li2 showed the best properties, including a high ionic conductivity of 1.52 × 10⁻³ S cm⁻¹, over 85% of optical transmittance in the visible region and good mechanical strength, such as a tensile strength of 0.56 MPa, adhesion strength of 1.385 MPa, and elongation at break of 426%. The resultant three polymer-based ECDs based on this electrolyte demonstrated outstanding electrochromic performance, retaining electrochromic behaviors even after performing hundreds of bending, flexing and pressing tests. These results indicate that the designed robust gel electrolyte is suitable for practical application in polymer-based ECDs.