Electrochemical Response of Cold-Sintered Cathode-Hybrid Electrolyte Bilayers: Deep Insights into the Determining Kinetic Mechanisms via Operando Electrochemical Impedance Characterization

[EN] This study reports the fabrication of solid-state bilayers combining LiFePO4 (LFP) cathodes with Li1.3Al0.3Ti1.7(PO4)3 (LATP)-based composite solid electrolytes using a cold sintering process. By optimizing sintering pressure, intimate cathode–electrolyte contact is achieved, resulting in improved electrochemical performance. Bilayers cold-sintered at 300 MPa and 150 degrees C show high ionic conductivity (about 0.5 mS cm-1) and stable room-temperature capacities (160.1 mAh g-1 of LFP at C/10 and 75.8 mAh g-1 of LFP at 1 C). Operando electrochemical impedance spectroscopy is used to identify kinetic limitations and predict overall behavior. The results indicate that capacity fading may occur at higher pressures due to volume contraction of the LFP crystal cell. Overall, the work highlights cold sintering as a simple route to high-performance solid-state bilayers and demonstrates operando EIS as a non-destructive tool to understand and mitigate degradation in solid-state lithium batteries.