In-situ ultrasonic identification and early warning of mechanical-abuse-induced failure in lithium-ion batteries

Mechanical abuse (MA) is a major cause of thermal runaway (TR) in lithium-ion batteries (LIBs). Early warning and timely intervention against MA are crucial for safe operation. This study investigates the correlation between ultrasonic signals and MA-induced structural evolutions in LIBs. Using nail penetration (NP) and hemispherical extrusion (HE) as representative cases, the mechanisms of ultrasonic response under single-point and regional MA impacts are investigated. The NP abuse induces a progressive layer-by-layer electrode fracture, while the HE abuse causes simultaneous multi-point fractures. Based on this, the sensitivity of ultrasound to gas generation and interlayer gap formation enables accurate identification of MA types. This interpretation based on mechanism establishes a physical relationship between the ultrasonic signal and the abuse-induced evolution of internal battery structure. Furthermore, compared to conventional voltage indicators, ultrasonic signals can respond instantly to MA. It can provide early warnings up to 102.37 s and 239.13 s before the TR stage for NP and HE abuses, respectively. For the first time, this work develops an ultrasonic technique for multi-type MA identification and real-time early warning for MA-induced TR, offering a promising approach to enhancing battery safety.