Critical outlook on separator layers for solid-state lithium batteries: Solid electrolyte materials, anode interface engineering, & scalable separator production

Energy storage as batteries is important for the electrification of several different technologies including transportation. For such applications, it is also clear that the state-of-the-art lithium-ion batteries need to be improved, especially in terms of energy density, safety, and other aspects. Solid-state batteries stand out as promising candidates to fill this gap, utilizing a solid-state electrolyte separator instead of flammable liquid electrolytes soaked in polymeric membranes. This review provides a comprehensive overview of several types of solid-state electrolytes (oxides, sulphides, halides, polymer, composite), with a special focus on sulphide argyrodite solid electrolytes as promising separators which offer the best balance of performance and processability. Furthermore, we discuss the stability issues of argyrodites with next generation anodes such as Li and Si, suggesting that interface engineering strategies by thin film methods are a scalable and effective way to mitigate the stability issues at the interface. Additionally, we give an overview of the process to make solid-state electrolyte membranes which involves several steps. Although many tools and approaches are available for the fabrication of these membranes, dry processing technology is identified as an important component to the successful realization of solid-state batteries. • Inorganic (oxide, sulphide, halide), organic and composite solid electrolytes. • (Electro)chemical and mechanical stabilities between Li/Si anodes and argyrodite. • Interface engineering solutions and coating methods. • Batch and continuous production methods for solid electrolyte separator.