Research on safety warning characteristics of battery based on temperature and force coupling signals

As the core power source for electric vehicles, renewable energy grid connected systems, and portable electronic devices, the safety are the most crucial problem. Compared to single-parameter warning systems, multi-parameter warning systems significantly enhance reliability. This research focuses on lithium iron phosphate (LFP) batteries, commonly used in energy storage, and investigates the coupling relationship between temperature and force parameters during experiments where overheating induces thermal runaway (TR). The findings reveal that as the state of charge (SOC) increases, the venting time of the battery initially rises and then declines, whereas the TR time exhibits the opposite trend. An increase in the lithium-ion battery (LIB) surface temperature and a decrease in battery capacity can further shorten the venting and TR times. Notably, the temperature changes at the positive electrode tab are the most sensitive indicators. Key warning thresholds are defined as the time when the force change rate first reaches 19.6 N/s, and when the temperature at the positive electrode tab hits its first peak and subsequently returns to zero. Furthermore, the relationship between the warning time prior to safety vent opening and SOC is accurately described by a cubic polynomial fit of y = 0.00355x³-0.8872x² + 62.72x-728 and y = -0.00107x³ + 0.149x²-7.013x + 307, respectively. However, under low- temperature heating conditions that trigger TR, the force change rate is more commonly used as a warning threshold for safety vent opening and TR than the temperature change rate. The findings of this study provide a robust scientific foundation and valuable technical support for the design and operation of battery early warning systems, thereby enhancing the safety of energy storage systems utilizing LIBs.