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

Abstract

This study demonstrates the successful fabrication of solid-state bilayers using LiFePO₄ (LFP) cathodes and Li_1.3Al_0.3Ti_1.7(PO4)₃ (LATP)-based Composite Solid Electrolytes (CSEs) via Cold Sintering Process (CSP). By optimizing the sintering pressure, it is achieved an intimate contact between the cathode and the solid electrolyte, leading to an enhanced electrochemical performance. Bilayers cold sintered at 300 MPa and a low-sintering temperature of 150 °C exhibit high ionic conductivities (0.5 mS cm⁻¹) and stable specific capacities at room temperature (160.1 mAh g⁻¹_LFP at C/10 and 75.8 mAh g⁻¹_LFP at 1 C). Moreover, an operando electrochemical impedance spectroscopy (EIS) technique is employed to identify limiting factors of the bilayer kinetics and to anticipate the overall electrochemical behavior. Results suggest that capacity fading can occur in samples prepared with high sintering pressures due to a volume reduction in the LFP crystalline cell. This work demonstrates the potential of CSP to produce straightforward high-performance bilayers and introduces a valuable non-destructive instrument for understanding and avoiding degradation in solid-state lithium-based batteries.