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

TL;DR

This study explores Li4Ti5O12's broadband electrochromic properties from visible to infrared, demonstrating its potential for smart windows, thermal camouflage, and temperature regulation through tunable optical and thermal characteristics.

Contribution

It reveals Li4Ti5O12's ability to switch from a semiconductor to a metal upon Li+ intercalation, enabling broadband optical and thermal modulation for advanced applications.

Findings

Large tunabilities in solar reflectance and IR emittance.

LTO exhibits stable cycling performance.

Potential for infrared camouflage and thermoregulation.

Abstract

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.