Fractional models of lithium-ion batteries with application to state of charge and ageing estimation

Abstract

The lithium-ion batteries are currently used for a wide variety of mobile applications due to their high energy/power density and operating voltage. However, they also suffer from some limitations that force car manufacturers to associate them to a Battery Management System (BMS) that diagnoses and control the battery pack in real time. To carry out an accurate battery diagnosis, the BMS uses models of each cell in the pack. In this paper a two fractional models of lithium-ion cell are proposed. They result from several simplifications of an electrochemical model involving several partial differential equations. The very low number of parameters in the simpler proposed model permits their adjustment with a very simple procedure. It is then shown how this model can be used for State of Charge (SOC) and ageing estimation. As due to ageing cell and model behavior mismatch, a solution is proposed to define if the model parameters adjustment is required.