Shear-Induced Deformation of Multiscale Conductive Networks in Acetylene Black Slurries Studied by Rheo-Impedance Spectroscopy

Abstract

Understanding the structural evolution of conductive additive networks under shear is essential for improving the manufacturing processes of lithium-ion battery (LiB) electrodes. In this study, we investigate the hierarchical conductive organization of acetylene black (AB) slurries under steady shear flow using rheo-impedance measurements. Viscosity measurements show that the AB network is progressively broken down under shear regardless of AB content, whereas the viscoelastic properties confirm that a fully developed particle network emerges only above approximately 2 wt%. Impedance spectroscopy resolved two dominant relaxation modes of different characteristic scales, which can be represented phenomenologically using an equivalent circuit model incorporating constant phase elements. The conductance and capacitance associated with the higher-frequency mode increase proportionally with AB loading, reflecting the growth of local conductive pathways. In contrast, the low-frequency capacitive response remained nearly constant, originating from the interfacial polarization at the electrode surface. Under steady shear flow, the low-frequency conductivity decreases markedly at low AB concentrations (∼1 wt%) due to disruption of long-range connectivity, while the high-frequency response diminished simultaneously, indicating loss of electrical connectivity between fragmented domains. At higher AB concentrations (∼4 wt%), both rheological and electrical properties remained robust against shear, demonstrating the presence of a dense and rapidly recovering network. Comparison of viscosity and conductivity reveals that apparent mechanical breakdown does not necessarily correspond to loss of electrical pathways. These findings provide new insight into the shear-resolved relaxation behavior in conductive networks and offer guidance for optimizing slurry formulation and processing conditions in LiB electrode manufacturing.