Determination of Lithium-Ion Battery Capacity for Practical Applications

Batteries are becoming highly important in automotive and power system applications. The lithium-ion battery, as the fastest growing energy storage technology today, has its specificities, and requires a good understanding of the operating characteristics in order to use it in full capacity. One such specificity is the dependence of the one-way charging/discharging efficiency on the charging/discharging current. This paper proposes a novel method for the determination of battery capacity based on experimental testing. The proposed method defines battery energy capacity as the energy actually stored in the battery, while accounting for both the charging and discharging losses. The experiments include one-way efficiency determination based on multiple cycles conducted under different operational and ambient conditions, the goal of which is to acquire the charging/discharging energies. The measured energies are corrected for one-way efficiencies to obtain values actually stored in a battery during charging or actually extracted from the battery during discharging. The proposed method is tested in a laboratory and compared against two existing baseline methods at different ambient temperatures. The results indicate that the proposed method significantly outperforms the baseline methods in terms of the accuracy of the determined battery energy capacity and state-of-energy. The prime reason for the good performance of the proposed method is that it accounts for both the operational (efficiency) and the ambient (temperature) conditions.