Impedance reduction in lithium-ion batteries via non-contact ultrasonic excitation using electromagnetic acoustic transducers

The performance of lithium-ion batteries is strongly influenced by internal resistance, which increases significantly at low temperatures and limits charge transfer and capacity. This study investigates a non-contact ultrasonic excitation approach using an electromagnetic acoustic transducer to reversibly reduce the impedance of commercial lithium-ion pouch cells. Continuous ultrasound at 35 kHz was applied during electrochemical impedance spectroscopy and charging tests at different temperatures. The results show that ultrasonic excitation lowers the mid- and low-frequency impedance associated with charge-transfer and diffusion processes, while the high-frequency ohmic resistance remains unchanged. The impedance reduction develops gradually during excitation and is fully reversible. At 0 °C, ultrasound-assisted charging results in increased capacity and a faster charging time compared to the reference case. These findings show that ultrasonic excitation can contribute to mitigating the performance limitations of lithium-ion batteries in cold environments by improving charge transfer and reducing internal resistance, highlighting its potential for practical low-temperature charging support. • Contactless ultrasonic excitation applied to Li-ion pouch cells. • Ultrasound reduces mid- and low-frequency impedance. • Impedance reduction is reversible and strongest at low temperature. • Enhanced low-temperature charge acceptance during CC–CV charging. • Ultrasound mitigates low-temperature impedance limitations.