Simple Formalisms for the Concept of Heterogeneity in the Porous Electrodes of Lithium-Ion Batteries
Authors: Safari Mohammadhosein 
Published: July 2022

The presence of inhomogeneity in the porous electrodes of lithium-ion cells can significantly affect the active material utilization, energy/power density, and ageing dynamics of the cell, among others. 1-4 In Li-ion cells, inhomogeneity is caused by an uneven spatial distribution of the active material, carbon, binder, and electrolyte, or porous electrode micro/nanoscale properties such as the contact resistances, porosity and tortuosity. The existing literature suggests that the heterogeneity could inadvertently be introduced to the electrode with improper combination of design parameters and manufacturing steps, e.g. slurry formulation, thickness, mixing, and drying.5

Important insights into the local microstructure of the porous electrodes have been provided by FIB-SEM,6 X-ray tomography,7 or full simulation of electrode microstructure.8 Little attention has been paid, however, to develop formalisms to quantify the electrode heterogeneity and its correlation to the design parameters, manufacturing steps, and the battery performance.
In this presentation, the electrochemical and microstructural characteristics of a large group of NMC111 and NMC622 porous electrodes with different design parameters will be presented and discussed. The experimental data were obtained by preparing porous electrodes of different thickness, porosity, formulation (NMC loading and carbon/binder ratio), and surface chemistry. We spotlight the sensitivity of the energy and power density of the Li|NMC cells to the microstructural indexes including tortuosity, porosity, and effective conductivities. The experimental data were analysed with the help of modeling and simulations to introduce a simplified formalism which expresses the concept of heterogeneity in the porous electrodes of lithium-ion batteries.

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