Semi-empirical ageing model for LFP and NMC Li-ion battery chemistries

LFP and NMC chemistries are currently, among the Li-ion family, the most relevant and with higher prospects technologies. This paper analyses the modelling process of the capacity decay in a Li-ion battery caused by calendar and cycling ageing. An on-line ageing estimation model valid for both LFP and NMC is developed considering the variation of the main parameters used to define the model: temperature, State of Charge and rate of charge and discharge. This model is validated from a theoretical point of view for both chemistries by comparing its performance with the data provided by manufacturers and previous ageing models. The proposed battery ageing model attains a maximum relative error of 3%, which varies depending on the battery chemistry and the specified working conditions. A further analysis regarding the model accuracy at the battery end-of-life is developed. Moreover, the model performance is validated from an experimental point of view with an NMC battery tested in the laboratory, reaching errors below 5%. In addition, a methodology for parameterizing the ageing model is proposed aiming to facilitate the application of this model into a specific battery.