Generalized Analytical Model for Capacity Evaluation of Automotive-Grade Lithium Batteries

In this study, an analytical model is represented for evaluation of remaining charge state of commercial automotive-grade lithium batteries. The model is elaborated for evaluation of battery remaining charge state under dynamic loads and various temperature conditions, which is typical for operation of batteries being parts of electric or hybrid electric vehicles. It is proved that use of the Peukert equation as a part of an analytical model leads to a restriction of field-of-use for those models as the Peukert equation is not applicable under small discharge rates. It has been also shown that in modern analytical models, the usually used temperature dependencies are not applicable at extremely low and extremely high temperatures of battery discharge. The reason is that they do not take into account neither the presence of a negative thermal critical point, under which the battery capacity output becomes equal to zero, nor a limitation of a capacity growth in conditions of a temperature increase. The represented analytical model solves such problems to a large extent and provides with a good prediction accuracy for battery remaining state of charge (relative error is not more than 4%).