Ultrasonic spectroscopy for in situ early detection and dynamic monitoring of lithium plating in lithium-ion batteries

<h2>Summary</h2> Lithium (Li) plating can significantly degrade lithium-ion battery (LIB) performance, posing safety risks. Detecting and monitoring Li plating, especially in its onset stage, is challenging due to its complex and unpredictable nature. This study introduces an ultrasonic spectroscopy method for <i>in situ</i> early detection of mild Li plating and monitoring its development within commercial LIBs. A wave model predicts the ultrasonic spectrum from a multi-layer and saturated porous battery structure. Controlled experiments are conducted at both room and low temperatures. At room temperature, the ultrasonic amplitude generally increases during battery charging. However, at low temperature, the transmission amplitude at the resonance frequency shows a clear decrease during the same charging process. The opposite trend of amplitude change enables highly sensitive and reliable detection of early-stage Li plating with minimal interference from factors such as state-of-charge (SOC) variations. The method is further evaluated by tracking Li plating growth during real-world fast-charging scenarios.