Systematic Slurry-impedance Approach via Coin Cell Platform for Microstructural Analysis of Cathode Slurries in Lithium-ion Batteries

Abstract

Understanding and controlling the internal microstructure of lithium-ion battery (LIB) slurries is a fundamental requirement for achieving high-performance electrodes. In particular, the dispersion state and particle network formed during slurry mixing strongly influence the ionic and electronic transport pathways within the electrode. Therefore, elucidating the correlation between the slurry’s internal microstructural behavior and electrode properties is crucial. Conventional rheological parameters such as viscosity and modulus, however, provide only indirect information about these electrically active particle networks because they primarily reflect mechanical responses under external deformation. Accordingly, the development of a quantitative and direct evaluation method for slurry microstructure is increasingly required. In this study, a standardized 2032-coin cell-based impedance spectroscopy framework was developed to quantitatively evaluate the microstructural characteristics of LIB slurries. By hierarchically analyzing the impedance responses of individual slurry components—including NMP solvent, PVDF binder solution, active material suspension, and conductive agent suspension—the physical origins of dielectric relaxation were identified and classified into bulk polarization at high frequency, boundary polarization at mid frequency, and electrical conduction processes at low frequency. From these individual analyses, an equivalent circuit composed of three parallel RC elements was constructed to represent the characteristic frequency responses of the cathode slurry system, enabling quantitative extraction of parameters that describe the internal particle network. The extracted resistance and capacitance components (Rnetwork and Qnetwork) exhibited strong correlations with electrode-level properties such as electronic conductivity and tortuosity, as well as with cell-level electrochemical performance including initial capacity and rate capability. Based on these correlations, the proposed framework was further applied to analyze the time-dependent evolution of slurry microstructure during storage, as well as various cathode slurry systems containing CNTs and LFP active materials. This approach establishes a reproducible and scalable methodology that directly bridges slurrylevel impedance characteristics with electrode microstructure and cell performance, providing a practical tool for process optimization and predictive electrode design.