Effect of a Heterogeneous Distribution of the Conductive Additives and Binder Domain on the Impedances of Lithium-Ion Battery Electrodes

Abstract

The conductive carbon and binder are essential components of Lithium-ion battery electrodes. Their main task is to enhance the electrical connectivity and mechanical stability. Therefore, a homogeneous distribution of the carbon binder domain (CBD) throughout the electrode is desired. However, inhomogeneities can arise in the production process. At high drying rates of the wet coating, the CBD migrates to the surface of the electrode due to the drag of the evaporating solvent. This effect causes a gradient of the CBD through the thickness of the electrode. This process has two effects: (a) depletion of the CBD at the current collector, diminishing the electronic pathways and the adhesion of the electrode layer, and (b) accumulation of the CBD at the electrode surface, thus blocking pathways for Lithium transport. This is especially prominent in thick electrodes. Therefore, we investigate the effect of binder migration on the electrochemical performance of NMC622 electrodes of Lithium-ion batteries.In our simulations we use virtual electrode microstructures of NMC622 electrodes which are informed by tomography data. As it is challenging to resolve the CBD using tomographic techniques, it is distributed on a model-basis at the contact points of active material particles using an in-house structure generator[1].The valuable information derived from combining microstructure-resolved simulations with electrochemical impedance spectroscopy (EIS) on symmetric cells is used to characterize the Lithium-ion transport in the electrode pore space, including the contributions of the CBD. Additionally, half-cell discharge simulations are also conducted to analyze the effect of CBD heterogeneity on electrode performance.Through our work, we demonstrate the significance of the CBD distribution and enable predictive simulations for future battery design.[1] Hein S. et al, J. Electrochem. Soc. 2020, 167 013546 Figure 1