Cellulose-based KV3O8·0·75H2O composite films and self-healing Li+ gel electrolyte for multifunctional flexible electrochromic device

Abstract

Electrochromic materials have garnered significant interest owing to their eco-friendliness, energy efficiency, and ease of use. Among these materials, vanadium-based compounds are regarded as highly promising; however, they are plagued by issues such as ion channel collapse, capacity loss, and inadequate cycling stability when employed in aqueous solutions. The present study involves the compounding of KV3O8·0·75H2O (KVO) into a network composed of linear methylcellulose, leading to the development of a self-supporting cellulose composite KVO electrochromic film. Specifically, the doping of K was found to disrupt the preferential orientation of the V2O5 (001) crystal plane and to widen the interplanar spacing to 6.9 Å. Furthermore, Cellulose was discovered to remarkably increase the viscosity of the solute (6 times) and to undertake the function of a "reinforcing agent". The methylcellulose composite KVO film's electrochromic properties were then investigated in a 1 mol L − 1 LiClO4 non-aqueous electrolyte. Consequently, the film was able to switch between green-yellow and orange-red, and it was also capable of conserving more than 67% of its charge capacity after 2000 cycles. More importantly, flexible electrochromic devices were assembled from KVO/MC films. A self-healing LiClO4/PC (LOC)-based gel electrolyte composed of Ethene, 1‑chloro‑1,2,2‑trifluoro-, polymer with 1,1‑difluoroethene (P(CTFE‑VDF)) and Li+ electrolyte was developed, which was highly compatible with the device. The device possessed a high color efficiency of 78.8 cm2 C − 1, and achieved fast response (≤5.6 s) and long service life (>77% of the charge capacity and 70% of the optical contrast after 10,000 cycles). This design presents considerable potential for the fabrication of large area (12 × 15 cm2) flexible devices.