Measuring Dynamic Gradients in Drying Battery Electrode Coatings via Microscale Resistivity

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.