A comprehensive review of hydrogen sensor for thermal runaway monitoring: fundamentals, recent advancements, and challenges.

Thermal runaway (TR) in lithium-ion batteries (LIBs) remains an intrinsic safety issue, posing significant risks of fire and explosion. Among various technologies employed to assess LIB status- including temperature, pressure, voltage, and gas measurements-gas sensors exhibit superior response speed and stronger sensing abilities. Notably, H2 has been identified as the first gas released during the TR process when compared to other gases such as CO2, CO and CH4. Furthermore, H2 serves as an indicator for the formation of trace Li dendrites, which are inducements of LIBs safety issues. Consequently, development of high performance H2 sensors is essential for providing timely early safety warning. Compared with other types of H2 sensors, chemiresistive H2 sensors have garnered significant attention owing to their good sensitivity, low cost, and easy of miniaturization and integration into LIB cells. This review presents a comprehensive overview of chemiresistive H2 sensors through classifying them into different categories based on sensing material systems. Within each category, the inherent fundamental sensing mechanisms and current strategies aimed at enhancing sensor performance have been systematically discussed. It is believed that chemiresistive H2 sensors would play an important role in TR monitoring. Moreover, a more accuracy prediction could be implemented when H2 sensors are integrated with other existing warning methods.