Dynamic Process of Ions Transport and Cyclic Stability of WO₃ Electrochromic Film

Abstract

The dynamic process of ions transport in electrochromic WO 3 film is usually studied by electrochemical impedance spectroscopy. However, the detailed features are hidden since the ions insertion into WO 3 is a very complex process including structural deformation and phase transformations. Chronopotentiometry is an electrochemical characterization method that measures the response potential of a system under an imposed current.Compared to other dynamic characterization methods (impedance spectroscopy and CV), it allows direct access to the voltage contributions in different states of the solution-electrode system and has frequently been used to investigate kinetic effects such as adsorption and transport phenomena near electrode surface. In this study, chronopotentiometry is creatively applied to study ion transport kinetics and control ions insertion behavior in electrochromic WO 3 film. The results suggest that a large ions insertion flux at the interface of WO 3 /electrolyte could broaden ions transport channels due to the fierce lattice expansion during Li + ions insertion process, which 第 2 期 周开岭, 等: WO 3 电致变色薄膜离子传输动力过程及其循环稳定性 153 further improves the ions transportation kinetics and gifts a fast switching speed of optical performance. However, the repeating ions insertion/extraction behaviors at the interface of WO 3 /electrolyte for the long-term cycle process can reduce the size of WO 3 grains as a "ball mill effect". Especially, a large ions transport flux can aggravate the "ball mill effect". Consequently, the structure of the WO 3 film becomes very dense, which is unfavorable for ions transport and electrolyte permeation. This dense structure also leads to an irreversible accumulation of Li + ions and Li x WO 3 in the WO 3 host structure, resulting in a decay of optical modulation ability and electrochromic activity.This work offers an efficient method to analyze ion transport kinetics in intercalation materials and a new understanding of the relationship between ion transport behavior and cyclic stability of electrochromic materials.

The ion migration process and cyclic stability of voltage-induced vanadium dioxide phase transition

“…35,37 The damaged structure flattens the surface, gradually blurs the grain boundaries, fuses the grains, and gradually becomes amorphous. 52,53 In addition, the interfacial bond between the VO 2 film and the substrate weakens continuously leading to film peeling. In contrast, LiF as the electrolyte protective film can maintain the chemical stability of VO 2 and thus improve cyclic stability.…”

Effect of In Situ Heating on the Growth and Electrochromic Properties of Tungsten Trioxide Thin Films

“…Potential traps may be formed during the embedding of ions and electrons [6]. But compared with amorphous WO 3 , its crystalline state promises excellent cycling stability [7]. In response to the application of electrochromic technology, researchers have focused on performance improvement in the past and now need to consider matching color transformation and application scenarios.…”