Secondary batteries with high energy density, high specific energy and long cycle life have attracted increasing research attention as required for ground and aerial electric vehicles and large-scale stationary energy-storage. Lithium–sulfur (Li–S) batteries are considered as a particularly promising candidate because of their high theoretical performance and low cost of active materials. In spite of the recent progress in both fundamental understanding and developments of electrode and electrolyte materials, the practical use of liquid electrolyte-based Li–S batteries is still hindered by their poor cycling performance and safety concerns. Solid-state Li–S batteries have the potential to overcome these challenges. In this review, the mechanisms of Li ion transport and the basic requirements of solid-state electrolytes are discussed. We focus on recent advances in various solid-state Li–S battery systems, from quasi-solid-state to all-solid-state Li–S batteries. We also describe the remaining challenges and plausible solutions, including improved designs and compositions of electrode materials, solid-state electrolytes and the electrode/electrolyte interfaces. Though many fundamental and technological issues still need to be resolved to develop commercially viable technologies, solid-state Li–S batteries offer an attractive opportunity to address the present limitations.
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