Research on Charging Strategy of Lithium-ion Battery 2015-01-1192

Lithium-ion battery charging strategy affects charging time of electric vehicles, energy efficiency of entire vehicle, service life and safety. This paper focuses on the lithium iron phosphate (LiFePO4) battery, based on the battery internal mechanism and the working conditions, taking charging time, effective full-charge capacity and charge energy efficiency as the evaluation indexes.

Firstly, through a series of comparative experiments of the constant-current constant-voltage and the constant current charging strategy, the evaluation indexes variations in different temperatures and charging currents have been studied in the paper. By analyzing the respective characteristics of constant current charging phase and constant voltage charging phase in the whole charging process and their own contributions, we have found out the superiority of the constant current charging strategy. Then, through experiments of pulse current charging, which changes pulse mode, pulse period and duty ratio, the effects of various parameters above have been found. Finally, in order to shorten the charging time and relax the polarization, a new charging strategy which applies a small constant current or pulse current or constant-current pulse-current in the late constant current charging phase was proposed in this paper. By changing the value of currents and the SOC points where the current transforms to the small current charging, this paper has also gotten the data of evaluation indexes.

Through the aforementioned experiments, decisions of electric vehicle charging strategies can be partly made in different charging conditions, based on the target of shortest charging time, maximum charge capacity or highest charging efficiency.