Modal analysis of lithium-ion pouch cell for state estimation and monitoring early-stage aging

Lithium-ion batteries have become a ubiquitous energy source for applications ranging from cell phones to battery-powered electric vehicles. Despite this success, state-of-charge (SOC) and state-of-health (SOH) estimation remains challenging, particularly in applications requiring high numbers of cells like battery electric vehicles . The search for reliable and accurate SOC/SOH estimation methods that are suitable for field use is a very active field of research. Mechanical methods are being pursued, leveraging the linked chemo-mechanics of cell components. This work explores the relationship between the modal response of a clamped–clamped 10 Ah NMC/graphite pouch cell and its SOC and SOH. We employ scanning laser Doppler vibrometry on a cell at 0% and 100% SOC for over 80 charge–discharge cycles. Electrochemically-induced mechanical property change is reflected in the shift in resonance frequency and the magnitude of the transmissibility curve at resonance. We also present an effective medium model (EMM) of the cell based on multiscale homogenization for use in finite-element software to simulate the cell’s modal response as a function of SOC. Results indicate that the modal response of a cell correlates with its SOC and degree of early-life aging, while the EMM provides insight about which cell components contribute to the cell’s dynamic mechanical response. • Vibrational methods for SOC and SOH estimation in early cycles of Li-ion cells. • Resonance frequency at full charge is higher than full discharge. • Resonance frequency increase with cycling in charged and discharged states. • Multiscale model of cell response aids determination of constituents responsible for aging.