Multi-objective optimization of hybrid preheating strategies for Lithium-ion batteries in low temperature

The low thermal conductivity of Lithium-ion Batteries (LIBs) can result in significant temperature gradients within the LIB, if external preheating rapidly. In contrast, pulse current preheating, although slower, can realize a more uniform temperature distribution. This study combines Positive Temperature Coefficient (PTC) film heating and pulse current heating to investigate the combined effects of external and internal preheating. A three-dimensional thermal-electrochemical coupled model of LIB packs is constructed to accurately simulate the temperature field and electrochemical reactions during the preheating process. Moreover, the effects of PTC heating power, switching temperature, discharge duration, and resting duration on preheating performance are investigated. Furthermore, an L16 orthogonal array is constructed using preheating time, temperature difference, and coefficient of performance (COP) as response variables, and multivariate variance analysis and multi-objective optimization are performed to determine the hybrid preheating strategy with the shortest preheating time, smallest temperature difference, and highest COP. Ultimately, through preheating triangle analysis, a balanced preheating strategy is identified that controls the temperature difference within 2 °C, achieves a heating rate of 5.36 °C/min, and attains a COP of 0.828.