Interfacial design for lithium-sulfur batteries: From liquid to solid

Li-S batteries, offering high theoretical energy density of 2600 Wh kg(-1), low cost and nontoxicity, are considered as a fascinating next-generation electric energy storage devices. However, the dissolution of the lithium polysulfides (LiPSs), shuttle effect and safety issues of Li anode notoriously pose great challenges for the commercialization of Li-S batteries. These problems derive from the interfacial issues among cathodes, separators, electrolytes and anodes, which in turn can be resolved by rational interface tailoring. This review mainly focuses on these interfacial issues in Li-S batteries with traditional liquid electrolytes and the latest research trend including gel polymer electrolytes, solid polymer electrolytes, solid inorganic electrolytes and hybrid electrolytes. In the liquid electrolyte systems, sulfur cathodes can effectively avoid severe shuttle effects and maintain stable cycling with the interfacial regulations of coatings, freestanding interlayers and separator modifications, while Li anode can be modified by protective layers, functional additives, three-dimensional current collectors and Li alloys. In quasi-solid systems (gel polymer electrolytes and hybrid electrolytes), rational designs are applied considering the utility of active materials, restraining LiPSs and suppressing Li dendrites. In all solid-state electrolyte systems (solid polymer electrolytes and solid inorganic electrolytes), the emphasis is to enhance the ionic conductivities and reduce the interfacial resistances. Mechanisms underlying these interfacial issues and corresponding electrochemical performances are discussed. Recent developments on the interfacial designs of Li-S batteries are summarized and highlighted. Based on the most critical factors of the interfaces proposed, prospectives are presented to pave the avenue for the designs of Li-S batteries.