Combined cycling and calendar capacity fade modeling of a Nickel-Manganese-Cobalt Oxide Cell with real-life profile validation

This paper presents the development of a semi-empirical combined lifetime model for a Nickel Manganese Cobalt Oxide (NMC) cathode and a graphite anode based cell, considered as one of the most promising candidates for the automotive industry. The development of this model was based on a thorough understanding of the degradation behavior of a 20-Ah NMC cell, based on the analysis of the results of an extensive test-matrix using 146 cells. This test-matrix was designed around four impact factors: temperature (25–45°C), Depth-of-Discharge (100–20% DoD), middle State-of-Charge (80–20% Mid-SoC) and current rates (C/3 to 2C). Gathering sufficient data for a mathematical model requires a huge time-investment, and the measurements gathered over the course of 2.5years offer a unique insight in the aging behavior of the NMC cells used in this study. Experimental results for cycling aging indicated that the capacity loss was strongly affected by the Depth-of-Discharge and temperature. For calendar aging, an initial increase in capacity was observed when stored at low State-of-Charges, due to electrochemical milling, while the deterioration of the capacity was affected most by high storage State-Of-Charges and storage temperatures. The developed combined lifetime model showed an error of less than 5% RMS compared to the measurement results after a Worldwide harmonized Light vehicles Test (WLTC) was applied for 18months.