Lithium-ion cell inconsistency analysis based on three-parameter Weibull probability model

The inconsistency of lithium-ion cells degrades battery performance, lifetime and even safety. The complexity of the cell reaction mechanism causes an irregular asymmetrical distribution of various cell parameters, such as capacity and internal resistance, among others. In this study, the Newman electrochemical model was used to simulate the 1C discharge curves of 100 LiMn2O4 pouch cells with parameter variations typically produced in manufacturing processes, and the three-parameter Weibull probability model was used to analyze the dispersion and symmetry of the resulting discharge voltage distributions. The results showed that the dispersion of the voltage distribution was related to the rate of decrease in the discharge voltage, and the symmetry was related to the change in the rate of voltage decrease. The effect of the cells’ capacity dominated the voltage distribution thermodynamically during discharge, and the phase transformation process significantly skewed the voltage distribution. The effects of the ohmic drop and polarization voltage on the voltage distribution were primarily kinetic. The presence of current returned the right-skewed voltage distribution caused by phase transformation to a more symmetrical distribution. Thus, the Weibull parameters elucidated the electrochemical behavior during the discharge process, and this method can guide the prediction and control of cell inconsistency, as well as detection and control strategies for cell management systems.