High-capacity lithium sulfur battery and beyond: a review of metal anode protection layers and perspective of solid-state electrolytes

Li metal has the highest specific capacity (3860 mA h g⁻¹) and the lowest electrochemical potential (− 3.04 V vs. SHE) of available metal anodes. Together with the high specific capacity of sulfur cathodes (1670 mA h g⁻¹), Li metal–S batteries are a promising candidate to achieve high energy density batteries for electric vehicles and future industry. However, Li metal anodes suffer from corrosive reactions with electrolytes, a theoretically infinite volume change, and the growth of dendrites during electrochemical cycling. To realize the practical application of Li metal–S batteries, protective layers or artificial solid-electrolyte interphase (ASEI) layers have been applied to the surface of Li metal. These ASEI layers demonstrate capabilities to suppress the growth of dendrites and mitigate side reactions, which enhance the performance and safety of Li metal anodes in liquid-electrolyte systems, though there are still limitations and challenges. The development of solid-state electrolytes as artificial SEIs provides a promising route to suppress the issues of dendrite formation and the polysulfide “shuttle effect” in Li–S chemistry; however, the improvement in the interfacial compatibility and stability between the Li metal and the solid-state electrolyte is crucially needed. In this review, we summarize different types of ASEI layers used to protect Li metal, especially in Li–S batteries, with both liquid- and solid-electrolyte systems. We also briefly introduce the concept of anode protection of Mg metal and its application in Mg–S batteries. Perspectives regarding the further development and improvement of ASEI layers for Li metal and Mg metal are discussed.