Modelling the State of Charge of Lithium-ion batteries

Lithium-ion batteries are widely adopted for multiple applications ranging from mobile devices to electric vehicles. The application of Lithium-ion batteries requires an accurate modelling approach that allows for the estimation of their behaviour, namely for their state of charge (SOC). In this respect, there are several models of SOC that are available in literature. However, none of these available models considers the battery degradation and the time evolution of the SOC for each cycle. In this work, we propose a new model of the SOC of Lithium-ion batteries, based on experimental test results. The proposed model incorporates both the time evolution of the SOC as well as the life cycle. It is shown that the SOC is related to the battery voltage following a Hill function characteristic. The model is time-varying and its parameters vary according to the number of cycles. Finally the performance of the proposed model is compared with a polynomial fit based method and the benefits of this modelling approach are highlighted.