Electrochromic properties of Li4Ti5O12: From visible to infrared spectrum

Recently, Li4Ti5O12 (LTO) has been experimentally proven as a promising broadband electrochromic material for applications like smart windows, thermal management, and infrared camouflage. However, a detailed understanding of the fundamental mechanism of these phenomena is still lacking, especially how and why the optical spectrum changes with lithiation. We fill this knowledge gap by performing a detailed analysis of LTO's optical properties during charging/discharging via a robust study of the density functional theory (DFT). Our study suggests that the absorption of infrared light is highly sensitive to intercalation of Li in the LTO lattice, in contrast to that of visible wavelengths. This unique characteristic of LTO offers an effective mechanism in controlling infrared radiation intensity with minimal attenuation on the transmission of visible light. Furthermore, the DFT study also reveals that the electrochemical intercalation of Li introduces donor states which will gradually expand and move to deeper levels in the forbidden band. This electronic structure change leads to better conductivity and lower transmittance, which is in line with the experimental observation in the literature.