Research on pulse charging current of lithium-ion batteries for electric vehicles in low-temperature environment

The scale of the electric vehicle (EV) industry is expanding in the current new energy industry reform. Lithium-ion batteries (LIBs) have also gotten a lot of interest as the power source for EVs. However, the safety and remaining life of LIB are highly tied to the charging strategy adopted. Particularly, fast charging at low temperatures can cause lithium to deposit on the anode of the battery, intensifying heat production and even evolving into thermal runaway of the battery. Based on the simplified battery Alternating current (AC) impedance model, the optimal frequency of pulse current is analyzed. Considering the influence of state of charge (SOC) and temperature on the battery impedance, a three-dimensional response surface about the optimal frequency, temperature and SOC was established using Mendeley data. To simulate LIB pulse strategy charging in a cold environment, the equivalent circuit model (ECM) is coupled with a simple battery heating model. The three-dimensional response surface is employed to instantly determine the pulse frequency. The simulation results demonstrate that both the bi-directional pulse current charging strategy with optimal frequency and the positive pulse current charging strategy with optimal frequency have faster charging time and better temperature rise effect than the constant current (CC) charging strategy, and can significantly eliminate the polarization voltage of the battery at low temperatures.