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[Display omitted] • Polar and conductive titanium carbide is introduced for redox regulation. • Lithium sulfide plays as sulfur source in this study. • Sulfur redox and lithium sulfide precipitation are remarkably promoted. • The electrochemical characteristics of as-prepared batteries are boosted. The lithium-sulfur batteries (LSBs) have attracted more and more attention in recent years owing to its high theoretical energy density, abundant sulfur source and relatively low cost. However, the serious polysulfides shuttle and sluggish sulfur redox kinetics hinder the development and commercial application of high-performance lithium-sulfur batteries. In this paper, the titanium carbide (TiC)-decorated carbon matrix is considered as the mediator, anchor and electrocatalyst for polysulfides redox reaction. It has been proved that the conductive and polar titanium carbide can not only chemisorbs lithium polysulfides via titanium-sulfur (Ti-S) coordination, but also optimize the lithium sulfide (Li 2 S) nucleation/precipitation mechanism for better redox reaction. Especially, the graphene oxide and carbon nanotube matrix (GO-CNT) in this case can act as both host for Li 2 S loading and TiC precipitation. Accordingly, the as-fabricated lithium sulfide-graphene oxide–carbon nanotube-titanium carbide (LS-GO-CNT-TiC) cathode delivers the high initial discharge capacity of 956 mAh g−1 at 0.1C and good rate capability of 508 mAh g−1 at 2C. These results consequently manifest that the conductive and polar matrix of LS-GO-CNT-TiC can perform as a promising cathode of the high performance LSBs. [ABSTRACT FROM AUTHOR]

We present a separator modification strategy to suppress polysulfide shuttle and accelerate polysulfide conversion through transition metal coordinated g-C 3 N 4 with crystalline carbons. The Li-S batteries with Ni-C 3 N 4 /C-modified separator manifest improved electrochemical performance even at high sulfur loading and lean electrolyte condition, due to catalytic effect. • Transition metal coordinated g-C 3 N 4 with crystalline carbons is prepared. • Hybrid nanosheets efficiently prevent polysulfide diffusion by absorption effect. • This structure endows the lean-electrolyte Li-S batteries higher capacity. • Cell with Ni-C 3 N 4 /C-modified separator exhibits the best electrochemical performances. Lithium-sulfur batteries have been regarded as promising energy storage candidates because of their high energy density and low cost. However, the low electrical conductivity of sulfur, infamous polysulfides shuttle and slow redox kinetics result in fast capacity fade and poor rate capabilities. To solve these barriers, herein a modification strategy of functional separator is presented by coating transition metal coordinated graphitic carbon nitride (g-C 3 N 4) with crystalline carbons (M-C 3 N 4 /C) on the surface of a commercial separator. The coating layer exhibits both satisfactory interception ability for polysulfides shuttle and fast polysulfides conversion ability. It has been found that the uniformly distributed transition metal on g-C 3 N 4 /C acts as an active center to regulate polysulfides behavior via strong chemisorption capability and high catalytic activity towards polysulfide conversion, while the transition metal-interface guarantees the rapid electron transfer, which can consequently facilitate the utilization of active sulfur species. Notably, after considerable assessments from density functional theory calculations, spectroscopy and electrochemical performances, it can be concluded that the Ni-C 3 N 4 /C can strongly bind polysulfides and expedite polysulfides conversion kinetics as well as promote electrons/ion transfer. As a result, the lithium-sulfur batteries with Ni-C 3 N 4 /C-modified separator can deliver 999 mAh g−1 at 0.5 A g−1 with high capacity retention of 89.4% after 300 cycles. Even at a great sulfur loading of 4.6 mg cm−2 and a low electrolyte/sulfur ratio of 6 µL mg−1, a large initial capacity of 724.6 mAh g−1 is still obtained at 1.0 A g−1. The separator reported in this work initiates the exploration of transition metals coordination as dynamic regulators of high-performance lithium-sulfur batteries and also reveals an understanding of the catalytic reactions. [ABSTRACT FROM AUTHOR]