Testing of Commercial Electric Vehicle Battery Modules for Circular Economy Applications

Increasingly international academic and industrial communities desire to better understand, implement and improve the sustainability of vehicles that contain embedded electrochemical energy storage. Underpinning a number of studies that evaluate different circular economy strategies for the electric vehicle (EV) battery system are implicit assumptions about the retained capacity or State-of-Health (SoH) of the battery. International standards and best-practice guides exist that address the performance evaluation of both EV and HEV battery systems. However, a common theme in performance testing is that the test duration can be excessive and last for a number of hours. The aim of this research is to assess whether energy capacity and internal resistance measurements of Li-ion based modules can be optimized, reducing the test duration to a value that may facilitate further End-of-Life (EoL) options. Experimental results for a Porsche Panamera Hybrid module and a Tesla Model S P85 module that highlight a reduction of the duration of a commercial battery module characterization test by circa 70%. This reduction is accompanied by levels of measurement accuracy for retained energy capacity in the order of 1% for module test temperatures equal to 25°C. Improvement of 85% is achieved for resistance testing while still retaining levels of measurement accuracy in the order of 2% for module temperatures equal to 25°C. Based on these experimental results, a quick characterization test sequence is proposed and within a robust system test framework would allow different organizations to prioritize the relative importance of test accuracy versus experimental test time when grading used Li-ion modules.