Non-destructive testing of lithium-ion batteries via analysis of bending modes

Lithium-ion batteries are crucial for portable electronics, electromobility, and stationary energy storage, playing a critical role in global decarbonization goals. Tracking battery performance during their lifetime ensures reliability, as various degradation mechanisms affect their operation. These changes may alter mechanical properties and thus understanding the complex relationship between electrochemistry, heat transfer, and mechanical properties therefore remains a key research challenge. Elastodynamic inspection methods, such as ultrasonic and vibrational analysis, have shown promise in detecting mechanical changes under varying states of charge (SOC) and state of health (SOH). Recent research has demonstrated the shift in the fundamental resonance frequency is a reliable metric of the SOC and SOH of Nickel-Manganese-Cobalt (NMC) pouch cells. This study presents an analysis of flexural modes for NMC cells at 0% and 100% SOC over 80 charge–discharge cycles. We employ spatial filtering to extract and enhance the response of the first three modes. We observe a correlation between the resonance frequency and the SOC/SOH for all the modes explored. The trends in resonance frequency and quality factor versus cycle from the data are explored and we propose model-based methods to extract insights regarding the evolution of mechanical properties that exploit higher modes as a function of charge level and aging.