Study on Thermal Runaway Behavior and Early Warning Algorithm of Ternary Lithium Battery Pack Under Preload Force

Overcharging is a primary cause of thermal runaway in ternary lithium‐ion batteries, often leading to serious safety incidents. Early detection of thermal runaway during overcharging is therefore critical. This study investigates a 5 Ah ternary lithium battery pack, applying appropriate preload force to simulate real‐world conditions. Various overcharge experiments are conducted under different conditions, and changes in battery voltage, temperature, and expansion force are thoroughly analyzed. The results indicate that under the same initial conditions, higher charging rates accelerate the temperature rise in the lithium battery. Additionally, the internal gas generation rate increases, causing a faster rise in edge pressure and leading to earlier battery cracking. Building on these findings, a three‐level early warning algorithm is developed, which comprehensively considers voltage, temperature, and expansion force changes. Experimental validation demonstrates that this algorithm can accurately identify the current stage of thermal runaway and detect the transition to the third warning stage 604 s before complete failure, thus providing critical protection for the safe operation of the battery pack. This study offers valuable guidance for enhancing the monitoring and early warning capabilities of battery management systems.