Lithium–sulfur　(Li–S)　batteries　hold　great　promise　for　the　next-generation　energy　storage　system.　However,　their　commercial　applications　are　severely　hindered　by　myriads　of　drawbacks　such　as　poor　electrical　conductivity　of　sulfur,　sluggish　redox　reaction　kinetics　of　sulfur　species,　“shuttling　effect”　of　soluble　lithium　polysulfides　(LiPSs)　and　uncontrollable　dendritic　Li　growth.　Herein,　it　is　conceptually　demonstrated　that　sluggish　conversion　kinetics　of　LiPSs　is　markedly　stimulated　by　exquisite　heterointerface　modulation　at　nanoscale　level　over　transition　metal　carbides　and　nitrides.　In　this　scenario,　N-doped　carbon　coupled　with　molybdenum　nitride/carbide　(Mo2N-MoC/NC)　hybrid　nanocomposites　are　designed　through　a　one-step　carbonization-nitridation　process,　wherein　component　regulation　induced　dense　heterointerfaces　are　in　situ　produced.　Benefiting　from　high　electrical　conductivity,　strong　chemical　adsorption,　and　superior　catalytic　activity　afforded　by　dense　heterointerfaces,　the　Mo2N-MoC/NC　modified　separators　significantly　restrict　the　soluble　LiPSs　shuttling　and　simultaneously　suppress　the　Li　dendrite　generation.　The　assembled　Li–S　batteries　with　Mo2N-MoC/NC　modified　separators　exhibit　remarkable　electrochemical　performance.　Integrated　experimental　and　theoretical　results　substantiate　the　boosted　chemisorption　and　catalytic　conversion　of　LiPSs　endowed　by　such　dense　heterointerfaces.　The　work　will　open　a　new　vista　for　rationally　constructing　multifarious　heterostructured　materials　for　the　communities　of　Li-S　batteries.　©　2022　Wiley-VCH　GmbH.