Navigating the Catholyte Landscape in All-Solid-State Batteries

All-solid-state batteries are widely regarded as the next frontier in electrochemical energy storage, offering the potential to surpass the energy density and safety limits of conventional lithium-ion batteries. Among the factors governing their performance, paramount are the choice and functionality of the solid-state electrolyte (SSE) as a catholyte within the composite positive electrode. This perspective critically examines the applicability and potential of the three most intensively studied inorganic SSE families, namely oxides, sulfides, and chlorides, as catholytes. We discuss their respective advantages, limitations, and compatibility with common cathode active materials, as well as the remaining knowledge gaps. We then assess whether any of the current SSE classes can be employed as a stand-alone SSE for all-solid-state batteries, or whether composite architectures combining multiple SSEs will ultimately be required.