Pressure measurement during thermal runaway of lithium-ion batteries: Comparison of piezoelectric and piezoresistive pressure sensors

Although lithium-ion batteries (LIBs) exhibit excellent energy storage characteristics, they harbor a potential risk due to their ability to undergo thermal runaway (TR). TR is accompanied by a rise in pressure and temperature, as well as possible secondary effects (e.g. explosions). A common mitigation strategy is to house LIBs in enclosures with a high pressure resistance (e.g. flameproof enclosures). The maximum pressure that occurs is therefore an important design criterion for such enclosures. Both piezoelectric (PE) and piezoresistive (PR) sensors can be used to measure the pressure. However, it is currently unclear whether one of the two sensor types is better suited for this specific measurement task. For comparative analysis, TR experiments using a LIB (3 Ah capacity, NMC-811chemistry) are carried out in a flameproof enclosure using overheating as the failure mode. In addition to various temperature readings the pressure is recorded using both sensor types. Due to the high temperature load caused by the hot vent gases of the LIB during TR and the affinity of the PE sensors to so-called thermal shock, the measured pressure values are smaller than those measured by the PR sensors. By using PE sensors without a thermal protective layer (RTV) on the sensor membrane, the temperature can be identified as the decisive factor for the deviation. PR sensors should therefore be used for correct pressure measurement during the TR of a LIB. This study thus provides a direct performance comparison of PE and PR oil-filled sensors under thermal runaway and thermal shock conditions, recommending PR sensors as the more reliable choice for pressure assessment in lithium-ion battery safety applications. The study presents a methodologically sound evaluation framework by first validating the measurement system via controlled gas explosions, followed by testing TR under various gas atmospheres to enable a comprehensive comparison of sensor performance under realistic conditions. The vibration of the enclosure and the sensor design are also identified and discussed as disturbance variables of the pressure curve.