Experimental analysis of the effects of discharge current-rates on the parameters of the electrical equivalent circuit for NMC and LCO Li-ion batteries

Abstract

Lithium-ion batteries are widely used energy storage systems due to their higher power and energy density. The sensitivity of battery internal parameters to the operating conditions is necessary to understand their behavior better. This paper studies the effect of discharge current rates on the electrical equivalent circuit model parameters. Through cycling experimental tests, battery cells of two technologies (Lithium-Nickel-Manganese-Cobalt-Oxide (NMC) and Lithium Cobalt Oxide (LCO)) are discharged with three different current rates. The equivalent circuit model (ECM) parameters are estimated using a recursive least square algorithm with a variable forgetting factor (RLS-VFF) based on experimental data. The results also show a negligible memory effect of the C-rate current with a relative deviation of less than 3%. The estimation results also show the polarization resistance and capacitance dependency on the C-rate discharge current. However, the experimental results have shown that the series resistance is robust to the final C-rate discharge current, which makes it suitable for monitoring ageing effects.