Modal analysis of lithium-ion batteries for estimation of state of charge and state of health

Abstract

The robustness and safety of battery-operated systems will become critically important as society transitions away from fossil fuels. In the foreseeable future, lithium-ion batteries will be used for high-power, high-capacity applications such as electric vehicles and renewable energy storage. In these applications, which require thousands of cells, existing battery management systems do not monitor the operating conditions of each cell. Variability in temperature and pressure can affect a cell’s state of charge (SOC) or state of health (SOH). This environmental loading coupled with cell-to-cell variability makes SOC/SOH estimation very difficult. Inaccurate measurements of SOC/SOH can reduce the lifespan of battery systems or lead to accidental overcharge and thermal runaway. We present modal analysis as a viable approach to estimate SOC/SOH for electrically cycled cells. Modal tests are performed using laser Doppler vibrometry on 10 Ah Nickel–Manganese–Cobalt pouch cells at 0% and 100% SOC across more than 30 cycles. Changes in the resonance frequencies of the cell are correlated with SOC/SOH to provide an understanding of how the mechanical properties of cell components change as a function of charge level and aging. This work demonstrates that modal analysis may be used as a tool for regular battery maintenance to improve battery safety.