Internal short circuits because of deformation or melting down of separators have been recognized as a root cause for many thermal runaway (TR) events of high-energy-density (HED) lithium-ion batteries (LIBs). Ceramic coating of the polyolefin separators is a promising strategy but generally hinders ionic conduction. In this study, we demonstrate that co-coating the separators with boehmite ceramics and Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) solid-state electrolytes could markedly improve the safety of LIBs while mitigating detrimental effects on electrochemical performance. We assembled HED (~350 Wh/kg) lithium-ion pouch cells with nickel-rich Li(Ni_0.9Co_xMn_0.1-x)O₂ cathodes, silicon-based/graphite blended anodes, and co-coated separators of varying thicknesses. It is found that LATP reacts with the organic liquid electrolytes and lithium to generate a robust solid-electrolyte-interface-filled LATP layer during the formation, which can prevent the thermal deformation of separators. During the thermal abusive tests, the battery's TR failure thresholds raised from 146.2 to 162.0 ℃. Correspondingly, the direct failure cause of the cell TR hurdled the separator malfunction to the thermochemical reactions of the nickel-rich cathodes. Additionally, pouch cells exhibited impressive electrochemical performance, maintaining a capacity retention of 87.99% after 500 cycles at 1C.

All-solid-state lithium batteries are considered as the priority candidates for next-generation energy storage devices due to their better safety and higher energy density. As the key part of solid-state batteries, solid-state electrolytes have made certain research progress in recent years. Among the various types of solid-state electrolytes, sulfide electrolytes have received extensive attention because of their high room-temperature ionic conductivity and good moldability. However, sulfide-based solid-state batteries are still in the research stage. This situation is mainly due to the fact that the application of sulfide electrolytes still faces challenges in particular of interfacial issues, mainly including chemical and electrochemical instability, unstable interfacial reaction, and solid–solid physical contact between electrolyte and electrode. Here, this review provides a comprehensive summary of the existing interfacial issues in the fabrication of sulfide-based solid-state batteries. The in-depth mechanism of the interfacial issues and the current research progress of the main coping strategies are discussed in detail. Finally, we also present an outlook on the future development of sulfide-based solid-state batteries to guide the rational design of next-generation high-energy solid-state batteries.