Evaluation of Acceptable Charging Current of Power Li-Ion Batteries Based on Polarization Characteristics

Battery polarization voltage characteristics of power Li-ion batteries are investigated at different charging rates. The polarization voltage is small and relatively stable in the middle state of charge (SOC) range, whereas at both ends of SOC, the polarization voltage is enlarged and varies rapidly. Meanwhile, there is an approximate linear relationship between polarization voltage and charging rate. Taking polarization time constant into account, an acceptable charging current curve is developed, which prevents charging current from being out of range. This curve takes polarization voltage and charge cutoff voltage as constraints to describe acceptable charging current value at different SOC. Based on this curve, the battery can be charged from 20% SOC to 80% SOC within 33 min. The average polarization and the maximum temperature rise are approximately equivalent to those of 0.5C constant current-constant voltage charging method. The experimental results demonstrate that the proposed charging mode can balance charging speed, charging polarization, and temperature rise.