Experiment Studies of Charging Strategy for Lithium-Ion Batteries 2019-01-0792

Regarding the lithium-ion batteries used in the electric vehicle, charging time and charging efficiency are the concern of the public. In this paper, a lot of experiments were conducted to investigate the common charging strategies, including the CC-CV (constant current-constant voltage) charging and the pulse current charging, for the LiFePO₄ batteries, which are still widely used in commercial vehicles. Charging temperature and the charging current in the CC phase are the main influence factors to be studied for the CC-CV charging strategy, and the contribution of the CC phase and CV phase to the whole charging is analyzed from three aspects, including the time percent, charging energy efficiency and the capacity of battery at different temperatures and charging current. Regarding the pulse charging strategy, the pulse frequency is determined from the perspective of energy loss, then the experiments for pulse charging with different pulse mode, different duty cycle, as well as different charging temperature and charging current were conducted to study the characteristic of pulse charging. In order to eliminate the battery polarization, we optimized the charging current at the end of charging before the battery voltage reaches the cut-off voltage, and the optimization including transforming the large current to a small charging current or pulse charging current. The experiment result indicates that, small charging current can not only cut down the charging time, but also improves the charging efficiency. This strategy is suitable for fast charging of lithium-ion batteries. Finally, some constructive suggestions for the determination of charging strategy are provided according to the above experiment results.