Design of Symmetric TiO₂/LiI/TiO₂ Electrochromic Devices for Gradient Shaded Smart Windows with Enhanced Switching and Cycling Properties

Abstract Li⁺ insertion and extraction inherently impact the switching dynamics and cycling stability of inorganic electrochromic (EC) electrodes. Herein, the extraction of Li⁺ out of the TiO₂ lattice to release the electron is replaced by the charge recombination of the electron with I₃⁻ at the TiO₂‐electrolyte interface, which avoids the mechanical breakdown of the electrodes and renders self‐bleaching with no applied voltages. A device design of the same two TiO₂ nanocrystal (NC) electrodes combined with the redox lithium salt (LiI) electrolyte confers symmetric electrochromism. By applying a forward or reverse bias, the two TiO₂ electrodes alternately serve as the electrochromic electrode and exhibit voltage‐controlled gradient coloration, a maximum optical modulation of 90% at 700 nm, and a doubled cycling performance. The microstructure of the TiO₂ NC film is characterized by transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and Brunauer–Emmett–Teller methods. The electrochemical and electrochromic properties of the device are investigated using cyclic voltammetry, chronoamperometry, electrochemical impedance spectroscopy, and Mott–Schottky method.