Investigation of the polarization effect in lithium iron phosphate battery for electric vehicles

The polarization effect is an significant and complex phenomenon of the lithium iron phosphate battery. An electrical method is applied in analysis of the effect. Based on a equivalent circuit model, a modified hybrid pulse power characterization (HPPC) test is used for identification of ohmic resistance and polarization resistance, which are two parameters reflecting the polarization degree. The analysis based on experiment data shows different polarization resistance when the state-of-charge (SOC), current magnitude or cell degradation changes. The polarization effect can be taken in advantage to calculate the equilibrium potential and enhance the instantaneous power.