A state of charge-aware internal preheating strategy for Li-ion batteries at low temperatures

Low temperature drastically degrades the performance of Li-ion batteries, where the usable capacity of the battery is greatly reduced. Thus, it is necessary to preheat batteries for avoiding performance degradation at low temperatures. The state of charge (SOC) variation of Li-ion batteries under preheating brings difficulty to achieve optimal heating. This paper proposes an SOC-aware internal preheating strategy for Li-ion batteries by jointly optimizing the preheating time and battery degradation. First, a coupled electrothermal-aging model is established to develop a thorough understanding of the impacts of SOC on the generation rate of internal heat. The battery model parameters are fitted within segmented SOC ranges for real-time calculation. A novel preheating strategy using multi-stage constant currents has been developed, which considers the preheating time and the battery capacity loss simultaneously. These two conflicting objectives are traded off by solving a multi-objective optimization problem. Furthermore, the particle swarm optimization algorithm is employed to obtain the Pareto front, providing the flexible preheating strategy based on users’ demands, achieving a trade-off between rapid preheating and slow battery degradation. Extensive simulations and experiments are provided to verify the effectiveness of the proposed preheating strategy.