# Measuring Dynamic Gradients in Drying Battery Electrode Coatings via Microscale Resistivity

## TL;DR

This study uses a low-cost method to track how shear rate affects the drying process and microstructure of battery electrodes, influencing performance.

## Contribution

A cost-effective four-line probe device is used to study dynamic microstructural changes during electrode drying under different shear rates.

## Key findings

- Electrode resistances at different depths reveal distinct microstructural evolution for high and low shear rates.
- Low shear rates lead to carbon particle aggregation and sedimentation during early drying stages.
- A carbon-rich top layer forms during drying for both shear rates, validated by EFM and EDS imaging.

## Abstract

In situ techniques for probing the microstructural evolution
of
lithium-ion battery (LIB) electrodes are often limited by the cost
or accessibility. This study demonstrates the use of a simple and
cost-effective four-line probe device to measure dynamic electrode
microstructures at varying penetration depths and to explain the effects
of shear during coating on the transient and final electrode microstructure.
Previous studies report superior performance for LIB electrodes coated
at a high shear rate over those coated at a low shear rate. The researchers
postulated that this was due to a difference in carbon connectivity
in the final dried electrode, and this difference was partially supported
by energy dispersive spectroscopy (EDS) atomic distribution analysis.
In this study, we revisit these coating conditions at high and low
shears to determine the time evolution effect of shear on the carbon
microstructure formed during drying. The electrode resistances at
different penetration depths clearly show a difference in the dynamic
microstructure for different shear rates, indicating different drying
mechanisms. Heuristic drying models are used to interpret resistivity
data of the two electrodes and propose the drying mechanisms. For
example, at low shear rates, there is obvious aggregation and sedimentation
of carbon particles at early times. Furthermore, we observed the formation
of a carbon-rich top layer during drying for both shear rates. Electrochemical
fluorescence microscopy (EFM) and EDS imaging of the final dried electrode
validate the observations determined from the resistivity measurements
and modeling. Overall, these results use a low-cost, in situ method
to offer a comprehensive understanding of how the shear rate influences
the microstructural development of composite electrodes during drying
and its implications for battery performance.