Why Electrochromism in Li4ti5o12 Differs in the Visible and Infrared Spectrum

Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> (LTO) has been experimentally proven as a promising electrochromic material in applications of smart windows, thermal management and infrared camouflage. However, the fundamental mechanism on these phenomena is still lacking. For the first time, we fill this knowledge gap via quantitative matching the LTO's optical properties and electronic structure during charging/discharging using density functional theory. Our study suggests that the absorption of infrared is highly sensitive to intercalation of Li in the LTO lattice, in contrast with the adsorption of visible wavelengths. This unique property of LTO offers the practical ability in controlling infrared-induced heating with minimal effect on transmission of visible light. Furthermore, we also conclude that electrochemically controlled intercalation of Li causes donor states to appear, expand and move to deeper levels in the forbidden band, leading to better conductivity and lower transmittance, which is in line with the experimental results in the literature.