Interfacial Anode Kinetics and Its Influence on Cycling Performance of Sulfide Solid-State Batteries

Solid-state batteries (SSBs) are primarily tested in two-electrode and/or symmetric cell configurations, which may lead to under- or overestimation of degradation and failure. For long-term cycling and under dynamic conditions, the contribution of the counter electrode (anode) to fading may be substantial but is rarely reported due to lack of suitable characterization techniques. Here, we employed an advanced three-electrode cell setup to elucidate the overpotential growth and interface-related kinetic response for commonly used counter electrodes in lab-scale testing, namely, Li₄Ti₅O₁₂ and In/InLi, as well as for LiNbO₃-coated LiNi_0.85Co_0.10Mn_0.05O₂ as the working electrode (cathode) in thiophosphate-based SSB cells. This was achieved through continuous monitoring of individual electrode potentials (>1500 h) and by performing electrochemical impedance spectroscopy measurements in situ in combination with distribution of relaxation times analysis. The results reveal distinct differences in polarization and interfacial kinetics between the Li₄Ti₅O₁₂ and In/InLi anodes in practical application scenarios and how these affect cyclability and the analysis of capacity fading.