<i>Operando</i> spatiotemporal super-resolution of thermal events monitoring in lithium metal batteries

Safety challenges in high-capacity lithium metal batteries primarily arise from thermal runaway, leading to smoke emissions, fires or explosions. Real-time monitoring of internal temperature distribution is necessary to ensure safe operation and enhance cell performance. However, current methods lack dimensionality, precision, and timeliness, hindering the detection of uneven lithium deposition and localized temperature variations that drive capacity fade and safety risks. Here, we develop an <i>operando</i> spatiotemporal super-resolution thermal monitoring system capable of real-time, super-resolution temperature mapping across the lithium anode with a record-high spatial resolution of 1820 points cm^-², and a temporal resolution of 1 frame per 3 seconds. Utilizing optical frequency-domain reflectometry, an Archimedean spiral fiber configuration, and super-resolution algorithms, we capture critical thermal variations and identify hotspots during cycling. To improve thermal uniformity and reduce safety risks, we apply protective strategies, including pyramid patterning, copper mesh and polylactic acid. Cells with these measures, as monitored by our system, show reduced average temperatures, delayed capacity degradation and fewer hotspots. This innovative monitoring approach not only integrates cutting-edge optical technology with energy storage diagnostics but also establishes a robust framework for assessing thermal management strategies, thus significantly advancing the safety and energy density of lithium metal batteries for sustainable energy applications.