Multiphysics Simulation: An IEEE Spectrum Insert
Highly Accurate Li-ion Battery SimulationMikael Cugnet
French Atomic and Alternative Energy Commission
Battery management systems (BMSs) are designed to protect the batteries and predict their charge level. They use circuit models often derived from electrochemical impedance spectroscopy (EIS) measurements to construct an equivalent circuit model (ECM) that consists of resistors and capacitors connected both in series and in parallel. Yet, ECMs do not provide any information about important cell properties like the electrode active material resistance, the reaction rate, the specific capacitance, or the diffusion coefficient.
A multiphysics model of a LiFePO4/Li half-cell can provide more information than a typical circuit model. The French Atomic and Alternative Energy Commission (CAE), France’s largest technology research organization, worked to develop a method for simulating Li-ion batteries in COMSOL Multiphysics. The first of these models includes all components of the half-cell battery, while the second specifically models the iron phosphate electrode. This allowed CAE to analyze the behavior of the material before re-designing and making the actual battery.
LiveLink™ for MATLAB® was used to process the results and receive the full impedance spectrum of the half-cell. Implementing an electric double layer in COMSOL Multiphysics helped them simulate the nonlinear behavior that is typically observed for a battery at higher operating frequencies. By using COMSOL Multiphysics to simulate a half-cell battery, they can optimize their design with an electrode material that is more conductive, and they confirmed that a model incorporating an electric double layer better reflects device behavior.
Modeling of the half cell at the macroscopic (left) and microscopic (right) level.