Thermal management requirements in battery packs: An analysis of the effects of battery degradation

Battery degradation significantly affects a battery's thermal behaviour. This study developed a cell-level thermal model by considering the effects of ageing on both irreversible and reversible heat generation. A degradation-aware electro-thermal framework for battery packs with a pack-level electrical model and a thermal resistance network of a heat pipe-fan (HP-F)–based battery thermal management system (BTMS) was constructed for this research. The model predictions were validated using experiments at cell and pack levels, with root mean square errors within 2 °C and 1 °C, respectively. According to this framework, the thermal behaviour and management requirements of battery packs under different states of health (SOH) were analysed. The results demonstrated that aged batteries generate more heat due to increased internal resistance, leading to elevated average temperature (ΔTaᵥe) and temperature differences (Tdiff) within the pack. At 20 °C and 1C discharge, the ΔTaᵥe of a pack with SOH = 85 % increases by 51.72 % compared to SOH = 100 %, and the maximum Tdiff grows by 51.3 %. Enhanced cooling decreases the average temperature but enlarges temperature gradients, especially in aged packs, necessitating balanced control. As the battery ages, the required cooling intensity decreases under uniformity constraints but increases under temperature control needs, imposing stricter demands on thermal management design. Under HP-F-based BTMS, when SOH ≥87 %, the appropriate airflow ratio increases with cooling demands. When SOH<87 %, a constant airflow ratio is maintained to balance temperature, uniformity and energy consumption.