Bi₂O₃ Nanosheets for Early Warning Thermal Runaway of Lithium Battery

Abstract H 2 and CO are mostly regarded as the signature products before the thermal runaway of lithium batteries. In fact, most small‐molecule gases result from the electrolyte decomposition inside the lithium battery under high temperature. The main component of electrolyte, dimethyl carbonate (DMC) can spill out of the case much earlier than H 2 and CO. Herein, it is studied that the gas production of a lithium battery before its thermal runaway, and verified that gaseous DMC is a much earlier marker to warn thermal runaway. To solve the lack of highly DMC‐sensitive sensors, a novel semiconductor gas sensor is fabricated by Bi 2 O 3 nanosheets. It performs high sensitivity and selectivity toward DMC with ultra‐low limit of detection (50 ppb) and high selectivity (>24 times). Notably, in comparison with temperature measurement and other commercial gas sensors, the as‐prepared Bi 2 O 3 sensor detecting gaseous DMC can provide an early warning over 15 min before a thermal runaway happened. So, this Bi 2 O 3 sensor has a great potential for practical application on warning thermal runaway. The in situ infrared spectroscopy and the in situ Raman spectroscopy are employed to investigate the nature behind the outstanding performances, which is ascribed to the direct interaction between electrolyte molecules and Bi 2 O 3 nanosheets.