Optimal external heating resistance enabling rapid compound self-heating for lithium-ion batteries at low temperatures

Low-temperature preheating to achieve effective thermal management for lithium-ion batteries is a crucial enabler for the efficient and safe operation of electric vehicles in cold conditions. Effective heating is yet challenging due to its implementation complexity and a tricky balance of the heating performance. Here, we develop a lightweight compound self-heating system involving two external light aluminum heaters, which recycle the discharge energy contributing to external heating. Basic electrical and thermal modeling for the compound self-heating system is performed and experimentally validated. We adopt four key but conflicting heating metrics: heating time, heating efficiency, battery degradation, and temperature uniformity, to optimize the resistance of external heaters with the adaptive particle swarm optimization method. We thus propose a rapid compound self-heating strategy that can conveniently warm the battery up with 32.49 °C·min⁻¹. Experimental results under different states-of-charge and temperatures confirm the good adaptability of the proposed heating strategy. Comparison experiments with the unheated battery demonstrate the proposed heating strategy improves discharge power, charge power, and discharge energy by over 7.4 times, 19.0 times, and 109.9%, respectively. With the optimal external aluminum heaters, battery available discharge energy is enhanced by above 70.4%, implying a huge step forward to boost battery performance.