Electrochemical investigation of electrochromic devices based on NiO and WO3 films using different lithium salts electrolytes

•ECDs based on NiO and WO3 films using different electrolytes were fabricated.•Effect of different electrolytes on films and ECDs was investigated.•Applied voltage distribution on NiO and WO3 electrodes in an ECD was studied.•Voltage distribution on films was unbalanced and associated with electrolyte.•Films have different impedance behavior in different states and electrolytes.

Electrochromic devices (ECDs) with different liquid electrolytes were fabricated using NiO film as counter electrode, WO3 film as working electrode. The effect of liquid electrolytes containing different lithium salts (LiClO4, LiPF6, LiTFSI) on films and ECDs was investigated, such as transmittance change, charge density, memory effect and cyclic stability. Films or ECDs using LiPF6 electrolyte have excellent electrochromic properties but low cyclic stability, compared with LiClO4 and LiTFSI electrolytes. In order to deeply understand the effect of electrolyte on films and devices, the voltage distribution of films based on an analog cell and electrochemical impedance spectroscopy (EIS) were measured and analyzed in different lithium salts electrolytes. Results show that voltage distribution and EIS characteristics of films have obvious difference in liquid LiClO4, LiPF6 and LiTFSI electrolytes. Voltage distribution on NiO and WO3 films is unbalanced and the impedance of films in bleached and colored states is different in the same electrolyte.

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