Analyzing the Performance Limitations of a Commercial Lithium-Ion Battery by an Impedance Based Cell Model

摘要

A complex physical lithium-ion cell model which simulates the current voltage (IU) characteristic as a function of state of charge is presented. It separately describes all loss contributions in a battery and allows interpretation of all model parameters. The operating voltage (Uop) of the cell is calculated from the difference between the open circuit voltage (UOCV) and the sum of overvoltages m' that exist when the battery is under load: U[op]=U[OCV](SOC)-e[0](SOC,I)-e[CT,C](SOC,I)-e[SEI/CT,A](SOC,I)-e[Diff,A/C](SOC,I) The individual loss contributions are measured with electrochemical impedance spectroscopy and time domain measurements, identified by a DRT-analysis [1] and quantified with a physically meaningful equivalent circuit model. The model is exemplarily parametrized to a commercial, high-power 350 mAh graphite/LiNiCoA102-LiCo02 pouch cell. For the first time, the physical background of the model allows the operator to draw conclusions about the performance-limiting factor at various application-related load profiles. Not only can the model help to choose application-optimized cell characteristics, but it can also support the battery management system when taking corrective actions during operation (such as load shifting in the battery pack).