Pack-Level Electrochemical Impedance Spectroscopy in EV Batteries Enabled by a DC Fast Charger

In order to reliably operate Lithium-ion battery systems at their maximum power capability, it is advantageous to track the battery electrical impedance. Direct-Current Fast Charging (DCFC) stations provide a low-cost opportunity to introduce in-situ impedance measurements through the shared use of new hardware across many users. The feasibility of DCFC-based EV battery pack impedance measurement is explored in this work. To the authors’ knowledge, this is the first published measurement and analysis of impedance data from a commercial EV dc charging plug. A custom 50 kW CHAdeMO-interface DCFC is implemented, featuring electrochemical impedance spectroscopy with 5 A perturbation current at 400V, up to 3.1 kHz. The high-voltage system impedance is measured for a prototype EV featuring a custom 27kWh battery pack, and a 2015 Nissan Leaf EV through the CHAdeMO port. It is found that while the vehicle-level impedance is significantly affected by the DCFC charging cable and internal vehicle components, battery impedance variation due to temperature can still be detected. This work motivates the future development of charger-side battery diagnostics, including 1) large-scale vehicle fleet battery health monitoring, 2) data collection for improved battery degradation modeling, and 3) direct information exchange with EVs for battery performance optimisation.