Lithium-sulfur　batteries　(LSBs)　are　appealing　energy　storage　systems　by　virtue　of　the　high　theoretical　energy　density　and　abundant　resources　of　sulfur.　However,　the　sluggish　redox　reaction　kinetics　and　shuttle　effect　of　soluble　lithium　polysulfides　(LiPSs)　seriously　restrict　their　practical　applications.　Searching　for　highly　efficient　and　low　cost　electrocatalysts　towards　LiPSs　conversion　is　one　of　the　most　promising　approaches　to　relieve　the　shuttle　effect　and　enhance　the　sulfur　utilization.　In　this　work,　we　first　demonstrate　the　application　of　ternary　iron　molybdenum　nitride　hybridized　with　nitrogen-doped　carbon,　denoted　as　(Fe0.81Mo0.19)MoN2/NC　composite,　as　an　advanced　separator　modifier　to　boost　the　bidirectional　catalytic　conversion　of　LiPSs.　Impressively,　the　as-fabricated　LSBs　with　(Fe0.81Mo0.19)MoN2/NC　modified　separator　display　an　ultrahigh　initial　discharge　capac-ity　of　1366.1　mAh　g-1　at　0.1　C　and　still　remains　a　high　value　of　809.1　mAh　g-1　at　a　high　rate　of　4　C.　Furthermore,　a　remarkable　discharge　capacity　of　569.2　mAh　g-1　is　retained　when　cycling　at　a　high　rate　of　1　C　for　700　cycles　(corresponding　to　a　low　attenuation　rate　of　0.065　%　per　cycle),　indicating　the　good　long-term　cycling　stability.　The　excellent　performance　could　be　attributed　to　the　multiple　advantages　of　high　electrical　conductivity,　numerous　active　sites,　strong　adsorption　ability　and　excellent　catalytic　activity,　thereby　effectively　suppressing　the　shuttle　effect　of　LiPSs.　The　present　work　indicates　that　the　ternary　transition　metal　nitrides　could　be　promising　separator　modifiers　for　high-performance　LSBs.