Regulation of sulfur molecules for advanced lithium–sulfur batteries: strategies, mechanisms, and characterizations

Abstract Lithium–sulfur (Li–S) batteries have been regarded as the pinnacle in the domain of high-energy-density Li–metal batteries, mainly because of their high theoretical specific capacity and natural abundance. However, their practical implementation is chiefly impeded by the sluggish redox kinetics of lithium polysulfides (LiPSs) and the parasitic shuttle effect, which are associated with the intrinsic physiochemical properties of multiphase sulfur species. On this account, rationally regulating the properties of sulfur species at the molecular level is promising to achieve ample opportunities to circumvent these key stumbling blocks, hence driving the practical application of Li–S technology. Herein, the recent achievements in tailoring the molecular structures of sulfur species are summarized and reviewed, including low-order sulfur molecules, heteroatom-doped sulfur molecules, and LiPSs-based functional intermediates. Moreover, some advanced characterizations allowing structural and chemical environment detection of regulated sulfur species, such as X-ray absorption spectroscopy, X-ray emission spectroscopy, neutron scattering, and pair distribution function, are also discussed, aimed at propelling the theoretical and practical research of sulfur species. Finally, future perspectives on the molecular engineering of sulfur species are provided to enlighten the development of advanced Li–S batteries.