Green synthesis and applications of MXene for lithium–sulfur batteries

Lithium–sulfur batteries (LSBs) are promising electrochemical storage devices due to their incomparable theoretical energy density (2600 W h kg−1). However, the electrically nonconducting characteristic of sulfur, the shuttle effect of lithium polysulfides (LiPSs), the sluggish kinetics of Li2S2/Li2S redox reaction, and the uncontrollable growth of Li dendrite, limit the commercialization of LSBs. The mentioned issues can be resolved by designing MXene (transition–metal carbides and carbonitrides) hosts and functional separators/interlayers for LSBs. Two–dimensional (2D) MXene features high electronic conductivity, controllable structure, and abundant polar functional groups, which show a fine affinity for sulfur cathode and lithium anode. However, the synthesis methods for MXene are primarily focused on acid etching, leading to serious pollution, low yield, and a monolithic interface structure, hindering its specific application in LSBs. In this review, we provide a comprehensive overview of the conventional and environmentally friendly approaches employed in the synthesis of MXene, as well as its applications in the design of sulfur cathode, Li anode, and functional separators for LSBs. A perspective regarding future green synthesis strategies and design principles relating to sulfur cathode and Li anode is also summarized.