Classification of Equivalent Circuit Models for Lithium-ion Batteries

Equivalent Circuit Models (ECMs) are the simplest models used to define the behavior of a Lithium-Ion Battery (LIB). Since their inception, many variations have been developed with the objective of improving the accuracy requirement of measuring and predicting the State of Charge (SoC) and State of Health (SoH) of a lithium-ion cell. This improvement has been fueled by the need for Electric Vehicles (EVs) to mimic the behavior of Internal Combustion Engines (ICEs) by supporting a longer drive before recharging. Despite the many variations of ECMs that are available in the literature, each one can be linked to six core models which are often adjusted by including a new parameter to reduce the modelling error. These core models are a formulation of Ordinary Differential Equations (ODEs) with an input equation as the SoC and an output equation as the terminal voltage (v) of the battery. The input equation is often similar for all the six core models. This review paper will summarize these core models and organize them in a table format, which can be used as a reference for researchers in this field. A treatment of the Root Mean Square Error (RMSE) analysis of two improved models from the core models will also be provided to demonstrate the effect of including a new parameter in the model. The analysis will be based on a Nickel Manganese Cobalt Oxide (NMC) negative electrode battery chemistry.