Development of a lifetime model for large format nickel-manganese-cobalt oxide-based lithium-ion cell validated using a real-life profile

This paper presents the development of a combined lifetime model used to estimate the capacity fade evolution and internal resistance increase of 43 Ah big capacity nickel-manganese-cobalt oxide (NMC) cell playing the leading role in the automotive industry. However, these NMC based lithium-ion cells passed through capacity fade uncertainty problems during their cycling and calendaring periods. Therefore, to investigate the nonlinear aging behavior of the NMC cell, an extensive lifetime characterization of the cell was performed with an efficient testing methodology accompanied by large and quality datasets collected for more than two years. According to the analysis result of the experimental dataset, the cycling capacity fade was strongly affected by the depth of discharge (DoD), temperature, C-rate, and slightly affected by middle state of charge (Mid-SoC). On the other hand, the calendar capacity fade was affected by high storage state of charge (SoC), and high temperature. In the previous studies, limitations related to complexity, accuracy, and computational difficulties of aging models are observed. Therefore, to compromise these challenges, in this paper, a semi-empirical fitted equivalent circuit model-based lifetime model is proposed. The validation of the developed model is performed by using a highly dynamic Worldwide Harmonized Light Vehicles Test (WLTC) profile and a root mean square error (RMSE) of 2% was found. In this study, new knowledge is gained with the developed lifetime model which benefits car manufacturers using big capacity NMC-based cells and hence can utilize the model to estimate the available capacity and lifetime of the battery cells.