Diagnosis for graphite-based anode slurries via in-line electrochemical impedance spectroscopy under pipe flow

Abstract

In battery manufacturing, electrode slurries are transported through pipelines to the coating step. During pipe-flow transport, slurry microstructures can evolve and degrade electrode quality and manufacturing productivity. Conventional off-line tests inherently rely on sampling, which introduces time delay and can yield biased results because the slurry is spatially non-uniform and prone to inhomogeneity. To address these limitations, we construct a laboratory-scale pipe-flow system and directly probe undiluted electrode slurries using in-line electrochemical impedance spectroscopy (EIS) during flow. The in-line EIS distinguishes dispersant-content variations as small as 0.05 wt%. Normalization by a characteristic frequency enables quantitative comparison with conventional off-line EIS result, and the composition-dependent characteristic frequencies remain comparable despite differences in geometry. An equivalent circuit modeling (ECM) links impedance parameters to CMC-driven microstructural transitions. Below the CMC level that saturates surface adsorption, conductive particles agglomerate and the resistance decreases. Above this threshold, excess CMC remains free in the continuous phase, and the effective diffusion length scale decreases with diffusion coefficient changes, consistent with modified ionic transport. Regime-specific ECM trends remain consistent between in-line and off-line data, indicating that the pipe-flow spectra encode composition-dependent microstructural information. Power-law analyses from Ultra-small-angle neutron scattering (USANS) and rheological characterizations independently support these interpretations. Overall, this study demonstrates that in-line EIS measures high-solid slurries reliably under flow and enables real-time, structure-sensitive monitoring in industrial slurry processes.