Pack-level performance of electric vehicle batteries in second-life electricity grid energy services

Abstract

Repurposed electric vehicle (EV) batteries can provide an affordable and sustainable alternative to conventional utility-scale battery energy storage systems. While EV battery packs are often disassembled into modules or cells and repackaged for second life, the required time and labour costs can be mitigated by directly repurposing full EV battery packs when their health allows. However, the diversity among EV battery pack designs introduces uncertainty regarding their relative performance in second-life applications. This study presents experimental data demonstrating the second-life performance of EV batteries from five different EV manufacturers, featuring four unique positive electrodes, three cell formats, and three thermal management designs. All five EV batteries are tested at the pack level in their original housings, providing thermal conditions distinct from module or cell testing. The batteries are tested under 4 h, 2 h, and 1 h deep-discharge constant-power duty cycles to emulate electricity grid energy services such as energy arbitrage or peak shaving. Novel methods are employed to measure, assess, and compare battery performance in this test regime. The results show significant performance differences among the five EV battery packs, particularly between older (2012–2015) and newer (2018–2019) designs due to evolutions in energy density and thermal management. The test results are analyzed and ranked, showing that among the five tested batteries, the 2019 Tesla Model 3 battery (tested with active-liquid cooling) will provide the best overall performance in most second-life energy storage applications, while the 2015 BMW i3 battery (tested with passive-air cooling) will provide the best profit margins in applications where energy losses must be minimized. The novel experimental dataset is used to derive a number of generalized conclusions and recommendations which can be used by researchers and industrial developers to inform the modelling and design of second-life energy storage systems.