Impedance-Based Phenomenological Analysis of Electrode-Structure-Associated and Interface-Related Contributions in Sulfide-Based All-Solid-State Battery Composite Cathodes

In sulfide-based all-solid-state battery (ASSB) composite cathodes, incomplete solid–solid contact and tortuous ionic/electronic transport pathways increase internal electrode resistance and complicate the interpretation of apparent impedance responses. Here, we present a distribution of relaxation times (DRT)-assisted phenomenological impedance approach for analyzing apparent impedance responses in terms of operational resistance components in composite cathodes based on LiNbO3-coated Ni-rich layered oxide cathode active materials. Electrochemical impedance spectroscopy was performed under controlled electrode loading, state of charge (SoC), and temperature conditions. Loading-dependent DRT analysis parameterized the apparent impedance response into five operational resistance components. The high-frequency components remained nearly unchanged or increased with increasing loading, whereas the mid- to low-frequency components generally decreased, suggesting opposite loading dependences between components tentatively associated with electrode-structural constraints and interface-related processes. SoC-dependent analysis compared relatively SoC-insensitive and SoC-sensitive operational components, while temperature-dependent analysis provided additional comparative constraints for their proposed operational interpretations by comparing their apparent activation energies. Based on these operational component correlations, a semi-empirical framework was developed to describe how the loading-dependent evolution of the DRT-deconvoluted components is reflected in the apparent impedance response. This framework helps reduce the risk of misinterpreting apparent impedance as a uniquely defined interfacial resistance and provides a practical basis for diagnosing structural limitations in high-loading ASSB composite cathodes.