The non-ohmic nature of intercalation materials and the consequences for charge transport limitations

Abstract

Accurate modeling of the internal battery resistance is imperative in predicting the state of charge and state of health. A mathematical model has been developed that, in addition to the ionic transport, introduces an accurate description of the electronic transport in the porous semiconducting LiFePO4 electrodes. The model is based on the fundamental principles of electrochemistry, electrochemical kinetics, and semiconductor physics, combining them in an efficient model. This framework provides for the non-ohmic nature of semiconductor electrode materials and their current dependent conductivity. The model is validated by comparison with experimental data of Li-ion concentration profiles. It is demonstrated that the mass transport of the electrons, typically simplified or considered negligible in calculation models, have a significant influence on the electrode kinetics and therefore on the current dependent internal resistance of the battery. The accurate description of the internal resistance and the related heat production under various cycling conditions allows the design of safer battery electrode architectures. Additionally, the model allows optimization of the electrode components for various loading regime, increasing the effective energy density leading to decreasing demand for materials and costs. The present model, its principles, and methods are generally applicable and can be used for the description of the wide range of energy storage materials and systems where combined ion and electron transport takes place.