Illuminating the concentration dependence of charge transfer kinetics in lithium-ion battery blend-electrodes

Blending of different active materials for lithium-ion electrodes offers great opportunities to combine advantageous properties in order to achieve an overall improved cell performance. While electrochemical models for blend electrodes are readily available, the parametrization remains challenging since the contributions of the two or more blend components are difficult to distinguish and material specific and area specific parameters from literature are not always applicable. Here we present a way to directly extract the charge transfer resistance from a blend electrode using impedance spectroscopy, microstructural analysis and transmission line modeling. To differentiate between the contributions of each active material we make use of the concentration dependence of the exchange current density in intercalation electrodes. We apply and compare two theoretical derivations of concentration-dependent charge transfer kinetics to model the behavior of the two active materials. The first is the common Newman formulation and the second is a thermodynamically more consistent, non-ideal approach. When comparing the two approaches to experimental data, we find a better agreement for the non-ideal approach than for the ideal one. These findings encourage further investigations of non-ideal charge transfer formulations which could improve not only blend electrode- but also single material electrode models. • Extraction of SoC dependent exchange current density of NMC-LMO blend electrode. • Comparison of ideal and non-ideal concentration dependent charge transfer kinetics. • Better agreement with experimental data using non-ideal charge transfer kinetics.