Catalyzing the polysulfide conversion for promoting lithium sulfur battery performances: A review

Lithium-sulfur batteries (LSBs) are being recognized as potential successor to ubiquitous LIBs in daily life due to their higher theoretical energy density and lower cost effectiveness. However, the development of the LSB is beset with some tenacious issues, mainly including the insulation nature of the S or Li2S (the discharged product), the unavoidable dissolution of the reaction intermediate products (mainly as lithium polysulfides (LiPSs)), and the subsequent LiPSs shuttling across the separator, resulting in the continuous loss of active material, anode passivation, and low coulombic efficiency. Containment methods by introducing the high-electrical conductivity host are commonly used in improving the electrochemical performances of LSBs. However, such prevalent technologies are in the price of reduced energy density since they require more addition of amount of host materials. Adding trace of catalysts that catalyze the redox reaction between S/Li2S and Li2Sn (3 < n ≤ 8), shows ingenious design, which not only accelerates the conversion reaction between the solid S species and dissolved S species, alleviating the shuttle effect, but also expedites the electron transport thus reducing the polarization of the electrode. In this review, the redox reaction process during Li–S chemistry are firstly highlighted. Recent developed catalysts, including transition metal oxides, chalcogenides, phosphides, nitrides, and carbides/borides are then outlined to better understand the role of catalyst additives during the polysulfide conversion. Finally, the critical issues, challenges, and perspectives are discussed to demonstrate the potential development of LSBs.