Recent advances in cathodes for all-solid-state lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have been regarded as the candidate for the next-generation energy storage system due to the high theoretical specific capacity (1675 mAh/g), energy density (2600 Wh/kg) and the abundance of elemental sulfur, but the application of Li-S batteries is impeded by a series of problems. Recently, all-solid-state Li-S batteries (ASSLSBs) have drawn great attention because many drawbacks such as safety issues caused by metallic lithium anodes and organic liquid electrolytes can be overcome through the use of solid-state electrolytes (SEs). However, not only the problems brought by sulfur cathodes still exist, but more trouble arouses from the interfaces between SEs and cathodes, hampering the practical application of ASSLSBs. Therefore, in order to deal with the problems, enormous endeavors have been done on ASSLSB cathodes during the past few decades, including engineering of cathode active materials, cathode host materials, cathode binder materials and cathode structures. In this review, the electrochemical mechanism and existing problems of ASSLSBs are briefly introduced. Subsequently, the strategies for developing cathode materials and designing cathode structures are presented. Then there follows a brief discussion of SE problems and expectations, and finally, the challenges and perspectives of ASSLSBs are summarized.