Comparative study of the stability of composite cathodes based on sulfide solid electrolytes for all-solid-state lithium-ion batteries

All-solid-state lithium-ion batteries (ASSLBs) offer a promising solution to the challenges faced by conventional lithium-ion batteries, particularly their thermal instability and limited energy density. This study investigates the chemical and electrochemical stabilities of two representative solid electrolytes (SEs): glass-ceramic Li₇P₃S₁₁ (LPS) and crystalline Li₆PS₅Cl (LPSCl), both synthesized via mechanical milling. Comprehensive characterization techniques are employed to assess their interfacial, chemical, and electrochemical properties in ASSLB configurations. While both SEs exhibit similar ionic conductivities and activation energies, LPSCl demonstrates markedly superior chemical stability under ambient conditions. In symmetric cell configurations, LPSCl significantly outperforms LPS, maintaining stable cycling for over 500 h with minimal increase in overpotential. This enhanced stability extends to composite cathodes, where LPSCl exhibits notably superior capacity retention to that of LPS. Advanced analytical methods, including electrochemical impedance spectroscopy and in situ X-ray diffraction (XRD) during charging–discharging, elucidate the superior interfacial stability of LPSCl. Moreover, temperature-dependent time-resolved XRD confirms that LPSCl maintains the structural integrity of LiNi_0.5Co_0.2Mn_0.3O₂ in composite cathodes at higher temperatures, highlighting its improved compatibility and safety for ASSLB applications. These findings provide critical insights into optimizing the composition and processing techniques to fully realize the potential of sulfide-based SEs for commercial ASSLBs.