Li4Ti5O12: A Visible-to-Infrared Broadband Electrochromic Material for Optical and Thermal Management.

Broadband electrochromism from visible to infrared wavelengths is attractive for applications like smart windows, thermal-camouflage, and temperature control. In this work, the broadband electrochromic properties of Li4Ti5O12 (LTO) and its suitability for infrared-camouflage and thermoregulation are investigated. Upon Li+ intercalation, LTO changes from a wide band-gap semiconductor to a metal, causing LTO nanoparticles on metal to transition from a super-broadband optical reflector to a solar absorber and thermal emitter. Large tunabilities of 0.74, 0.68 and 0.30 are observed for the solar reflectance, mid-wave infrared (MWIR) emittance and long-wave infrared (LWIR) emittance respectively. The values exceed, or are comparable to notable performances in the literature. A promising cycling stability is also observed. MWIR and LWIR thermography reveal that the emittance of LTO-based electrodes can be electrochemically tuned to conceal them amidst their environment. Moreover, under different sky conditions, LTO shows promising solar heating and sub-ambient radiative cooling capabilities depending on the degree of lithiation and device design. The demonstrated capabilities of LTO make LTO-based electrochromic devices highly promising for infrared-camouflage applications in the defense sector, and for thermoregulation in space and terrestrial environments.