Electrochemical Impedance Spectroscopy With Practical Rest-Times for Battery Management Applications

The State of Charge (SoC), State of Health (SoH), and State of available Power (SoaP) of Lithium-Ion Batteries (LiB) are critical quantities which cannot be measured but must be estimated by Battery Management Systems (BMS) instead. A technique known as Electrochemical Impedance Spectroscopy (EIS) provides a non-destructive way of measuring battery impedance, offering detailed insight into the battery state of operation. Several challenges must be solved in to utilize EIS as part of the BMS, including the defining of operating conditions at which to perform the sensitive EIS measurement. In laboratory conditions, several hours of rest are used to ensure a stable response of the battery, but such rest times are impractical for BMS applications. This paper proposes a methodology combining drift compensation and a Voigt-circuit used as a filter to obtain valid EIS data with short rest times under different operating conditions. Extensive tests were conducted on lithium nickel manganese cobalt (NMC) batteries to evaluate the methodology and show how the different operating conditions impact the rest time required for valid EIS measurement. The results show that rest times between 5 and 30 minutes can be used to obtain useful EIS data for a wide range of operating conditions.