Functional catalysts for polysulfide conversion in Li–S batteries: from micro/nanoscale to single atom

Lithium−sulfur (Li–S) batteries have the advantages of low-cost and ultra-high energy density (2600 Wh·kg⁻¹), which have attracted considerable attention. However, the practical application of Li–S batteries still suffers various intractable problems, such as low electrical conductivity, significant volume expansion, and the shuttle effect of sulfur cathode. Up to now, many tremendous efforts and significant progress have been devoted to settle these problems. One of the most effective strategies is that introducing metal-based compounds (e.g., metal oxides, -sulfides, -nitrides, carbides, -phosphate, single-metal compounds) to enhance the electrochemical performance of S cathode benefiting from superior adsorption/catalytic ability toward Li₂S_n (n = 1, 2, 4, 8). In this review, we summarized the recent advances in the application of micro/nanoscale catalysts in Li–S system and highlighted the catalytic effect of single-atom compounds. Finally, the challenges and the future research prospects of single-atom catalysts were discussed.