Real-time simultaneous monitoring of internal temperature and gas pressure in cylindrical cells during thermal runaway

Real-time monitoring of temperature and pressure in lithium-ion batteries provides a comprehensive insight into several failure mechanisms that collectively are associated with thermal runaway. These are characterised by elevated temperatures that triggers heat-generating decomposition processes and the release of flammable gases that rapidly degrade the battery. This study presents a new methodology that for the first-time facilities the simultaneous real-time monitoring of internal temperature and gas pressure in high-capacity 21700-format cylindrical cells. This includes the assessment of severity of thermal runaway events. The method uses a bespoke sensing system with integrated thermocouples and pressure sensors. After investigating the instrumented cells' performance and verifying sensor functionality, thermal runaway characteristics are investigated further with cell failure triggered by external heating. Results highlight the accumulation of gas pressure inside the cell, the elevation of internal cell temperature and variations in cell voltage during the different phases of cell failure: pre-vent, soft-vent, and flame generation. This study underpins developing early detection or mitigation strategies against safety hazards in lithium-ion battery systems. Moreover, the availability of unmeasured datasets supports creating mathematical models to optimise battery performance, safety and longevity.