Investigation of warm-up strategies and its impact on performance and ageing of electric vehicle battery pack operated at sub-zero ambient conditions

For widespread adoption of electric vehicles (EVs) across diverse climates, improving battery pack performance under extreme temperatures is essential. At sub-zero conditions, Li-ion battery kinetics become sluggish, severely limiting performance, while elevated temperatures accelerate side reactions and capacity degradation. This study investigates the effectiveness of various conduction-based heating strategies at − 20 ° C for four 59-kWh battery packs based on large-format LFP cells (40 Ah and 100 Ah prismatic; 95 Ah and 138 Ah blade cells). A mid-range EV battery pack is designed and analysed to evaluate pack-level thermal behaviour using coupled electrochemical (NTGK) and thermal diffusion models. Heating strategies including side heating (SH), bottom heating (BH), bottom-and-top heating (BTH), and BH with side aluminium plates are systematically assessed. Results show that blade cell-based packs exhibit superior thermal uniformity and reduced structural complexity compared to prismatic configurations. Among the strategies, side heating for 60-min provides the best thermal performance, achieving standard deviation ≤0.5 °C for blade cell modules and ≤ 1 °C for prismatic cell modules. Bottom heating alone results in higher peak temperatures (up to 46.6 °C) and non-uniformity, while BTH reduces peak temperature by over 12 °C. The addition of side aluminium plates enhances heat propagation and reduces temperature gradients by ∼50%. Furthermore, the impact of heating on ageing is evaluated using a 100 Ah prismatic cell under a realistic driving cycle. Results indicate that calendar ageing dominates at sub-zero conditions, and preheating significantly mitigates capacity fade. Overall, this study demonstrates that optimized heating strategies can improve thermal uniformity, reduce degradation, and extend battery life enabling more reliable EV operation in cold climates.