Effects of C-Rate on the Thermal Behavior of Commercial Lithium-Ion Pouch Cells with Different Aging Histories for a Successful Second-Life Transition

Second-life applications are becoming increasingly popular as they enable enhancement of sustainability and economic efficiency. However, the transition from the first to the second life of batteries introduces safety challenges due to different operating conditions and previous degradation mechanisms. This study investigates the safety implications of high currents in aged cells. Thermal behavior upon cycling with different C-rates, ranging from 0.5 to 4.0 C, was analyzed using commercial 50 Ah NMC/C pouch cells. The tested cells had different aging histories, including minimal cycling and real age. The results revealed a consistent thermal pattern upon cycling, particularly a significant heat generation phase occurring at the end of discharge (3.6–3.0 V), independent of battery age. At higher C-rates, heat generation intensified. While no direct correlation was found between aging and certain thermal parameters, such as absolute maximum temperature and temperature difference, direct correlations were identified with the temperature increase rate and interquartile range. These correlations were linked to reduced thermal conductivity and battery state of health. This study highlights the critical role of considering C-rate, especially for aged cells, emphasizing the need to evaluate the expected current in the second-life application to avoid rapid temperature rises and ensure safety.