Multi-Objective Optimization Discharge Method for Heating Lithium-Ion Battery at Low Temperatures

Lithium battery for electric vehicle exhibits poor performance in durability and discharging efficiency under cold environment, therefore the traction battery must be heated to some suitable operation temperature before charging process begins. Self-heating by discharging current of the battery is recognized as a high-efficient and cost-effective method. However, the discharging current affects both the capacity degradation rate and heating time for lithium-ion battery greatly charged at low temperatures. Therefore, the discharging strategy should be optimized based on the parameters of the battery capacity fade rate and heating time, and it’s the motivation of this research. The parameters of the Thevenin equivalent circuit model are set up and the temperature-rise model is identified by test data. To determine the optimal battery discharging current for heating, the dynamic programming algorithm is adopted The capacity fade rate and heating time is analyzed by setting different weighting factors in the heating process of battery temperatures rising from −10°C to +5°C. Compared with constant current discharging method, the multi-objective optimization self-heating method can decrease the battery capacity fade by 5.65%, the heating time is by 1.82%, and the power consumption by 3.04%. Therefore, it can be concluded that the proposed multi-objective optimization can optimize heating time and energy consumption at same time, with minimize capacity degradation.