Pre-detection of thermal runaway in Li-ion 18650 batteries via temperature and voltage: the importance of temperature measurement location

This study establishes a phenomenological method for detecting and categorising the stages of thermal runaway in 18650 lithium-ion batteries. Using surface temperature and voltage measurements at nine specific locations on the cell, we define three distinct stages of thermal runaway. Experiments were conducted across six states of charge (SOCs), with thermal runaway induced using an electrical resistance heater. Our findings reveal that the rate of temperature change (°C/s) serves as a critical early indicator for detecting thermal runaway. Specifically, the initial stage is identified when the cell voltage drops to zero (0 V), concurrent with a temperature increase rate exceeding 13.6 °C/s at the negative terminal. The venting phase is characterised by a temperature change rate below −2.8 °C/s at the positive terminal, signifying the release of oxidising gases. In the final explosive reaction stage, flames may occur, and thermal runaway propagation can be prevented by detecting temperature thresholds exceeding 205.5 °C at TC #1 and 50.1 °C at TC #9. These findings provide actionable guidelines for the strategic placement of sensors and post-incident root cause analysis, ultimately contributing to safer battery operation and improved thermal management in lithium-ion battery applications.