Thermochromic nanoreflectors for battery safety

Abstract

We present thermochromic nanophotonic reflectors as a rapid, real-time visual sensing platform for temperature monitoring on battery surfaces. These devices consist of a nanoscale tellurium (Te) layer sandwiched between a metallic mirror and a transparent protective layer. Using the solid-to-quasi-liquid phase transition of Te below 80 °C, the reflectors exhibit reversible, sub-second optical changes in response to thermal stimuli. When exposed to open flame, mimicking thermal runaway scenarios, the reflectors effectively track heat propagation across the battery surface. Furthermore, we demonstrate practical applicability by visualizing temperature dynamics during standard charge–discharge cycles of commercial lithium-ion batteries and smartphones. This work highlights the potential of Te-based thermochromic nanophotonic reflectors as compact, wireless, and intuitive thermal sensors for enhancing battery safety in real-world electronic systems.