A review of the rational interfacial designs and characterizations for solid-state lithium/sulfur cells

The high theoretical specific energy of lithium/sulfur (Li/S) cells (2600 Wh/kg) has positioned the Li/S cell as one of the most promising candidates for the beyond lithium-ion cell. Despite the evident advantages, there are remaining problems mainly associated with the unique solution-based reaction chemistry involving lithium polysulfide (Li-PS) that hinder the commercialization of the Li/S cells. Incorporating solid-state electrolytes (SSEs) can avoid the Li-PS shuttle problem while preserving the benefits of Li/S cells, but it introduces other challenges related to the electrode/electrolyte solid interfaces. This topical review summarizes the current status of solid-state Li/S cells and their major challenges and discusses the recent efforts to improve cell performance and durability. Various solid-state electrolytes, including oxides, sulfides, and solid polymer electrolytes, are briefly reviewed. In particular, we focus on the recent progress to improve the interfacial properties by two major approaches, morphological and chemical modifications of the electrode/electrolyte interfaces. The design strategy and implementation to overcome the prominent issues associated with sulfur electrodes are critically discussed. Also, several electrochemical and physicochemical characterization methods to examine the electron/ion transport at the interface are outlined. Given the superior theoretical physicochemical properties of the Li/S cells, we emphasize that the inappropriate interfacial design of the solid-state Li/S cells is the major challenge to bring solid-state Li/S cells to a commercially attractive level.