Ultrasonic inspection of lithium-ion batteries to detect cell safety and prevent thermal runaway

Abstract

Accurately monitoring the safety of lithium-ion batteries to prevent a thermal runaway (TR) event is of utmost importance especially in high-power applications such as electric vehicles. The fire caused by a lithium-ion battery is particularly difficult to extinguish because of its continuous emittance of highly flammable gas and its extremely high temperature. Current battery management systems (BMS) only monitor cell safety by measuring voltage, current, and temperature on the module level. Because the BMS operates on the module-level as opposed to the cell-level, these metrics can fail to predict a TR event, which may begin with individual cell failures. We report on the viability of early detection of cell damage by simultaneously monitoring voltage, current, temperature, mechanical clamping force, and ultrasonic wave transmission through individual battery cells under various electrical, mechanical, and thermal loading conditions. Time- and frequency-domain features of the acoustic signals transmitted along three propagation paths and excitation frequencies between 0.1 and 1 MHz are monitored and correlated with electrical, temperature, and force sensor data under mechanically clamped overcharge and thermal abuse scenarios. Early indicators of damage in the ultrasonic signals are presented and discussed with respect to propagation paths and known damage mechanisms in lithium-ion batteries.