Investigation of transient heat generation from high energy density Li-ion battery for effective thermal management☆

Lithium-ion batteries (LIB) with higher energy density are crucial for extending the driving range of electric vehicles (EVs). However, LIBs also generate significant heat during cycling, reducing their lifespan and increasing the risk of thermal runaway. Therefore, understanding the sources of heat generation is crucial to mitigate the thermal runaway issues and increase the lifetime. The present study estimates the total heat generated in a 5Ah 21,700 NCM cylindrical battery at various discharge rates (1C - 5C) and ambient temperatures (5 degrees C - 45 degrees C) using the electrochemical-thermal coupled (ETC) model. The total heat comprises irreversible, reversible, ohmic, and mixing heat. The irreversible and ohmic heat contributes over 75 % of the total heat in the LIBs. The former becomes more prominent at higher C-rates and elevated temperatures, while the latter dominates at lower temperatures. The results reveal that the uneven heat generation is strongly affected by fluctuations in the discharge current and surrounding temperature. The study further reveals that the heat generation at negative and positive electrodes shows contradictory behavior, impacting the battery performance. The contribution of irreversible and mixing heat is higher at the negative electrode, whereas ohmic heat dominates at the positive electrode during the discharge cycle at 25 degrees C. Reversible heat contributes significantly to the negative electrode and displays endothermic behavior at lower C rates. Our study offers in-depth insights into heat generation in a high-energy LIB cell and the individual electrodes in the cell, providing new opportunities for designing an effective thermal management system for LIBs.