Battery pack diagnostics for electric vehicles: Transfer of differential voltage and incremental capacity analysis from cell to vehicle level

Aging of lithium-ion battery cells reduces a battery electric vehicle's achievable range, power capabilities and resale value. Therefore, suitable characterization methods for monitoring the battery pack's state of health are of high interest to academia and industry and are subject to current research. On cell level under laboratory conditions, differential voltage and incremental capacity analysis are established characterization methods for analyzing battery aging. In this article, experiments are conducted on the battery electric vehicles Volkswagen ID.3 and Tesla Model 3, examining the transferability of differential voltage and incremental capacity analysis from cell to vehicle level. Hereby, the vehicles are monitored during AC charging, ensuring applicability in real-life scenarios. Overall, transferability from cell to vehicle level is given as aging-related characteristics can be detected in vehicle measurements. Hereby, loss of lithium inventory is identified as the primary cause for capacity loss in the usage time of these vehicles. Both methods have limitations, such as data quality restrictions or vehicle specific behavior, but are suitable as diagnostics tools that can enable a vehicle level state of health estimation.