Enhancing cycling stability of iodine electrodeposition electrochromic devices Assisted by liquid active adhesion material

Electrochromic devices based on non-metallic iodine (I 2 ) electrodeposition feature a simple structure, low cost, and high optical contrast but suffer from poor cycling stability due to the low conductivity of solid I 2 and the formation of dead iodine. Herein, 1-methyl-3-propylimidazolium ions (MPI + ) are introduced into an I − -containing water-in-salt electrolyte, enabling the concurrent generation of solid I 2 and liquid MPII 3 under anodic oxidation. The liquid MPII 3 enhances the I 2 adhesion and interfacial contact, providing a self-healing effect that suppresses dead iodine while improving charge transport and reaction kinetics. As a result, the electrochromic device exhibits outstanding overall performance, including a high optical modulation of 69.2 %, fast switching speeds with coloring/bleaching times of 6.9/11.9 s, and excellent cycling durability with optical contrast retention exceeding 100 % after 20,000 cycles. Furthermore, a large-area dual-deposition electrochromic device with an active area of 100 cm 2 was successfully fabricated, demonstrating high modulation and uniform coloration capability. This work provides a new strategy and technical foundation for the design and practical development of high-performance solid-state deposition-type electrochromic devices.