Semi-empirical ageing model development of Traction battery

Abstract

Abstract In this thesis work a semi-empirical model for lithium-ion battery calendar ageing and cycling ageing behaviour was built based on several ageing factors. For the calendar ageing, the factors include State of Charge (SOC), temperature and storage time. For the cycling ageing, the factors include Full Equivalent Cycles (FEC), temperature, Depth of Discharge (DOD), C-rate and middle-SOC. More than six groups of independent research data and two different chemistry of lithium-ion batteries, Lithium Nickel-Manganese-Cobalt Oxide (NMC) are included (NMC111 and NMC442). The developed ageing model can be used for several different type of cells. The primary tool for data analysis and modelling is Matlab. This thesis investigates the relations of ageing factors and their influence on the degradation of batteries in the final model. Then the obtained model was validated and managed to be fitted for three different batteries’ ageing data with minor adjustments. An ageing model was acquired with separated calendar ageing and cycling ageing. The RMSE of each data sets is from 1.5-1.9 which is considered good to use for prediction. Besides, the stressed factors of the ageing model have been studied in order to provide input parameters for the required applications in a BMS. The research shows that the storage time has an important influence on the calendar ageing process. The storage temperature is more important than the storage SOC. Regarding cycling ageing, the FEC plays an important role in the ageing process.The cycling temperature and the SOC window are more important than the C-rate.