Pore-scale modeling of capillary-driven binder migration during battery electrode drying

TL;DR

This paper develops a pore-scale model to accurately simulate capillary-driven binder migration during electrode drying in sodium-ion batteries, highlighting the importance of microstructural effects for process optimization.

Contribution

It introduces a spatially resolved continuum model that explicitly accounts for capillary transport, improving microstructure-resolved predictions of binder migration during drying.

Findings

Smaller particles lead to more uniform binder distribution.

Higher evaporation rates and surface tension increase binder gradients.

Solvent viscosity has minor effects unless hydrophilic or hydrophobic behaviors are involved.

Abstract

Sodium-ion batteries employing hard carbon electrodes are considered a drop-in technology for lithium-ion batteries. Electrode drying is a critical manufacturing step, as binder migration during pore emptying impacts the mechanical integrity and electrical performance of the electrode. Existing modeling approaches predominantly rely on the film shrinkage phase in a one dimensional way or neglect the capillary transport, resulting in a lack of physically consistent microstructure resolved predictions of binder migration. In this work, a spatially resolved pore scale continuum model is extended to explicitly describe capillary driven binder transport during pore emptying. The model is applied to hard carbon microstructures with varying mean particle diameters. The simulations reveal that smaller particle sizes lead to a more homogeneous binder distribution, whereas higher evaporation rates and increased surface tension promote stronger binder gradients. Variations in solvent viscosity show only a minor influence on binder migration, as long as no hydrophilic or hydrophobic behavior is present. Finally, the simulations demonstrate that an explicit description of capillary transport and microstructural effects is essential for accurately predicting binder migration and provides a basis for the targeted optimization of electrode drying processes.