All-solid-state lithium-ion batteries (Li-ASSBs) exhibit superior safety and energy density relative to conventional liquid electrolyte-based cells. Sulfide-based solid electrolytes (SEs) demonstrate ionic conductivities approaching those of liquid electrolytes at ambient temperature [1], alongside low interfacial resistance owing to their compliant mechanical properties [2]. However, their intrinsically poor particle cohesion mandates incorporation of polymeric binders to enable scalable roll-to-roll fabrication, which adversely impacts ionic transport.
Accurate interpretation of electrochemical impedance spectroscopy (EIS) data, a non-destructive technique widely employed to quantify ionic conductivity, remains challenging because multiple electrical equivalent circuits (EECs) can yield equally valid fits. This ambiguity risks either oversimplification or overfitting unless EEC models are strictly constrained by the underlying physicochemical principles governing electrochemical interfaces and transport phenomena [3]. To address this, we developed and validated physics-based electrical equivalent circuit (EEC) models grounded in electrochemical and microstructural principles for Li6PS5Cl/hydrogenated poly(acrylonitrile-co-butadiene) (LPSCl/HNBR) composites under blocking electrode conditions. These models incorporate distinct impedance contributions from bulk electrolyte, grain boundaries, binder interfaces, and electrode/composite interfaces, and are evaluated across variable binder loadings (2 wt%, 5 wt%, and 10 wt%) and current collectors (tungsten carbide-cobalt, nickel, Ni-plated Cu, Au-sputtered Ni-plated Cu).
Our analysis revealed that Au-sputtering prevented the current collector from engaging in side reactions with the SE composite. Additionally, two discrete EEC configurations were required to accurately capture impedance spectra at low versus moderate-to-high binder concentrations, with primary divergence observed in the high-frequency regime. Quantitative analysis indicated that increasing binder content substantially diminishes ionic conductivity by >60% at 5 wt% and >90% at 10 wt% relative to 2 wt% binder composites. These findings elucidate the binder’s importance in sulfide-based SE composite ion transport, providing critical insights for optimizing composite design in Li-ASSBs.
Full article available at https://doi.org/10.1021/acs.jpcc.5c08415

References
[1] Y. Li, S. Song, H. Kim, K. Nomoto, H. Kim, X. Sun, S. Hori, K. Suzuki, N. Matsui, R. Kanno, Science, 381, 50-53 (2023)
[2] A. Kato, M. Nose, M. Yamamoto, A. Sakuda, A. Hayashi, M. Tatsumisago, J. Ceram. Soc. Jpn., 126, 719-727 (2018)
[3] Gaddam, R. R., Katzenmeier, L., Lamprecht, X., Bandarenka, A. S. Phys. Chem. Chem. Phys. 23, 12345 (2021).