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On account of high energy density and low cost of sulfur, lithium‐sulfur (Li−S) battery has been regarded as an appealing energy storage system to date. Nevertheless, it has faced formidable challenges, mainly pertaining to the fatal shuttle effect and retarded sulfur redox kinetics. Single atom catalysts (SACs) have showcased great promise for addressing these issues owing to their maximum atom utilization efficiency, favorable catalytic activity as well as their good structural tunability at an atomic level, considerably contributing to the recent fruitful advancements in Li−S realm. In this review, we summarize the state‐of‐the‐art strategies in the coordination manipulations of SACs toward highly efficient and durable Li−S batteries. The recent advances, existing issues, and future outlooks are discussed accordingly, aiming to guide the synthetic design of SACs, propel the underlying mechanism understanding and ultimately boost the commercial viability of Li−S batteries. [ABSTRACT FROM AUTHOR]

The practical application of lithium–sulfur (Li–S) batteries has been handicapped by the notorious polysulfide shuttling and sluggish sulfur conversion kinetics. Although the functional modification of separator is readily proposed as an effective strategy to optimize the Li–S redox reactions, the excessive material dosage and invalid structural design still result in inferior electrocatalyst utilization. Herein, generic graphene‐metal selenide heterostructures (Gr‐MxSey, M = Mo, W, Mn, Cu and Zn) are controllably grown on commercial glass fiber (GF) separator employing a sequential low‐temperature chemical vapor deposition procedure. Such a tailored reservoir can not only render ample active sites but also realize the synergy of polar and catalytic framework, which maximizes the electrochemical functions in alleviating shuttle effect and guiding Li2S nucleation/decomposition. The thus‐derived Gr‐MxSey/GF separator affording favorable heatproof feature endows the Li–S battery with an outstanding cycling stability (100% capacity retention over 100 cycles at 0.2 C). Furthermore, the flexible Li–S pouch cell based on this new separator delivers good device performance (with a capacity decay of 0.25% per cycle over 100 cycles). This study offers comprehensive insight into the reliable separator design toward working Li–S batteries. [ABSTRACT FROM AUTHOR]

Single‐atom catalysts affording multifarious typed metal centers and varied coordination numbers are extensively employed in Li−S realm to promote redox kinetics. Nevertheless, the modulation of coordination environment pertaining to local atomic composition to dictate the catalytic efficiency toward sulfur electrochemistry, has remains meaningful yet unexplored thus far. In this contribution, a new type of single‐atomic iron mediator with a designed FeN3P1 coordination structure is reported to boost bidirectional polysulfide conversion in comparison with FeN4 counterpart. Theoretical calculations imply that the substitution by one P atom at the first‐coordination shell of Fe center will be beneficial to strengthen adsorption toward sulfur species and reduce energy barrier for Li2S decomposition. The bidirectional electrocatalytic behavior for polysulfide conversion via FeN3P1 mediator is confirmed by electrokinetic analysis. Consequently, the constructed Li−S battery achieves elongated lifespan with a capacity decay of 0.04% per cycle at 1.0 C and exhibits considerable capacity release of 6.2 mAh cm−2 even under a sulfur loading of 6.4 mg cm−2. This strategy of local composition engineering offers a vivid example in probing the correlation between the definitive structure of single atoms and their catalytic performance in Li−S chemistry. [ABSTRACT FROM AUTHOR]

Electrocatalyst design has stimulated considerable attention and strenuous effort to tackle a multitude of detrimental issues in lithium–sulfur (Li–S) systems, mainly pertaining to the severe polysulfide shuttle effect and sluggish sulfur redox kinetics. In this context related advances in expediting bidirectional sulfur reactions have lately surged. Nonetheless, the structure–activity correlation and electrocatalytic mechanism remain rather elusive, as a result of elusory active sites, complicated aprotic environments, and multistep conversion pathways. This review summarizes burgeoning strategies in the modulation of heterogeneous and homogeneous electrocatalysts, wherein the advanced electrokinetic measurements, operando instrumental probing, and theoretical simulations are elucidated with an emphasis on deciphering bidirectional sulfur electrochemistry. Notably, a "3s" electrocatalysis model is proposed to deepen the mechanistic understanding in this realm. Finally, a development roadmap is sketched and future research layouts are discussed, aiming in essence, to realize favorable bidirectional redox kinetics and ultimately bridge the gap between reality and ideal systems in working Li–S batteries. [ABSTRACT FROM AUTHOR]

Lithium–sulfur batteries (LSBs) are regarded as promising next‐generation energy storage systems owing to their remarkable theoretical energy density (2600 Wh kg‐1) and low cost. However, sluggish electrochemical kinetics, lithium polysulfides (LiPS) shuttling, and uncontrollable Li dendrite growth seriously hamper the commercial application of LSBs. Herein, dual‐functional 3D interconnected free‐standing fibers embedded with TiO2‐TiN heterostructures as an advanced skeleton are designed for concurrently regulating both the sulfur cathode (S/hollow TiO2‐TiN) and Li anode (Li/solid TiO2‐TiN). As a cathode skeleton, the hollow TiO2‐TiN fibers afford synergistic functions of chemical anchoring, physical confinement, and excellent electrocatalysis for LiPS. Meanwhile, the multifunctional skeleton with remarkable lithiophilicity and high conductivity can accomplish uniform Li deposition and homogeneous Li ion flux for inhibiting the growth of dendrites. Benefiting from these advantages, the full battery (S/hollow TiO2‐TiN || Li/solid TiO2‐TiN) exhibits excellent electrochemical performance, including high cycling stability (988.8 mAh g−1 after 200 cycles at 0.5 C) and impressive rate properties (639.3 mAh g−1 at 2 C). This work inaugurates a novel strategy from experimental and theoretical aspects for fabricating LSBs with robust electrochemical performance. [ABSTRACT FROM AUTHOR]

V8C7/phosphorus defect-integrated carbon (VPC) is proposed as a dual-function promoter for Li–S chemistry. The well-dispersed V8C7 and phosphorus defects exhibit ample polar sites and remarkable electron conductivity. Such rational integration of dual active centers simultaneously suppresses the shuttle effect and propels the Li–S redox reaction kinetics. Therefore, the S/VPC cathode shows an initial capacity of 1090.0 mA h g−1 and a high retention of 83.5% at 0.2C after 100 cycles and a low decay rate of 0.076% at 2C over 600 cycles. [ABSTRACT FROM AUTHOR]

Witnessing compositional evolution and identifying the catalytically active moiety of electrocatalysts is of paramount importance in Li–S chemistry. Nevertheless, this field remains elusive. We report the scalable salt‐templated synthesis of Se‐vacancy‐incorporated MoSe2 architecture (SeVs‐MoSe2) and reveal the phase evolution of the defective precatalyst in working Li–S batteries. The interaction between lithium polysulfides and SeVs‐MoSe2 is probed to induce the transformation from SeVs‐MoSe2 to MoSeS. Furthermore, operando Raman spectroscopy and ex situ X‐ray diffraction measurements in combination with theoretical simulations verify that the effectual MoSeS catalyst could help promote conversion of Li2S2 to Li2S, thereby boosting the capacity performance. The Li–S battery accordingly exhibits a satisfactory rate and cycling capability even with and elevated sulfur loading and lean electrolyte conditions (7.67 mg cm−2; 4.0 μL mg−1S). This work elucidates the design strategies and catalytic mechanisms of efficient electrocatalysts bearing defects. [ABSTRACT FROM AUTHOR]

Lithium–sulfur (Li–S) batteries have stimulated a burgeoning scientific and industrial interest owing to high energy density and low materials costs. The favorable reaction kinetics of sulfur species is a key prerequisite for pursuing their commercialization. Recent years have witnessed a wealth of investigations in terms of boosting sulfur redox via rationalizing redox mediators. Defect engineering, which allows for the effective exposure of active sites and optimization of electronic structure, has emerged expeditiously as an essential strategy to enhance polysulfide modulation, and hence expedite Li–S chemistry. Nevertheless, a comprehensive overview of defect engineering in Li–S realm is still lacking. This review emphasizes the recent advances in the rational design and polysulfide modulation strategies of different types of defective mediators. Their unique morphological configuration, superb electrochemical activity, and underlying catalytic mechanism are comprehensively summarized, aiming to deepen the understanding of defect‐mediated Li–S chemistry. Moreover, in situ evolution of defective mediators is discussed to identify the true active sites under aprotic reaction conditions. Opportunities and an outlook of this fast‐developing frontier that may lead to practical implementations of Li–S batteries are proposed. [ABSTRACT FROM AUTHOR]

Designing high‐performance electrocatalysts for boosting aprotic electrochemistry is of vital importance to drive longevous Li–S batteries. Nevertheless, investigations on probing the electrocatalytic endurance and protecting the catalyst activity yet remain elusive. Here, a ternary graphene‐TiO2/TiN (G‐TiO2/TiN) heterostructure affording conformal graphene chainmail is presented as an efficient and robust electrocatalyst for expediting sulfur redox kinetics. The G‐TiO2/TiN heterostructure synergizes adsorptive TiO2, catalytic TiN, and conductive graphene armor, thus enabling abundant anchoring points for polysulfides and sustained active sites to allow smooth bi‐directional electrocatalysis. Encouragingly, in situ crafted graphene chainmail ensures favorable protection of inner TiO2/TiN to retain their catalytic robustness towards durable sulfur chemistry. As expected, sulfur cathodes mediated by ternary G‐TiO2/TiN harvest an impressive rate capability (698.8 mAh g−1 at 5.0 C), favorable cycling stability (a low decay of 0.054% per cycle within 1000 cycles), and satisfactory areal capacity under elevated loading (delivering 8.63 mAh cm−2 at a sulfur loading of 10.4 mg cm−2). The ternary heterostructure design offers an in‐depth insight into the electrocatalyst manipulation and protection toward long lifespan Li–S batteries. [ABSTRACT FROM AUTHOR]

The rational design of electrocatalyst has readily stimulated a burgeoning interest in expediting polysulfide conversion and hence essentially restricting the "shuttle effect" in Li–S systems. Nevertheless, seldom efforts have been devoted to probing the dual‐directional polysulfide electrocatalysis to date. Herein, a CoFe alloy decorated mesoporous carbon sphere (CoFe‐MCS) serving as a promising mediator for Li–S batteries is reported. Such bimetallic alloying boosts dual‐directional electrocatalytic activity toward effective polysulfide conversion throughout detailed electroanalytic characterization, theoretical calculation, and operando instrumental probing. Accordingly, the S@CoFe‐MCS cathode harvests a stable cycling with a low capacity decay rate of 0.062% per cycle over 500 cycles at 2.0 C. More encouragingly, benefiting from the optimized redox kinetics and delicate grid architecture, printable S@CoFe‐MCS cathode achieves an excellent rate performance at a sulfur loading of 4.0 mg cm−2 and advanced areal capacity of 6.0 mAh cm−2 at 7.7 mg cm−2. This work explores non‐precious metal alloy electrocatalysts in printable cathodes toward dual‐directional polysulfide conversion, holding great potential in the pursuit of Li–S commercialization. [ABSTRACT FROM AUTHOR]

The lithium–sulfur (Li–S) battery is regarded as a next‐generation energy storage system due to its conspicuous merits in high theoretical capacity (1672 mAh g−1), overwhelming energy density (2600 Wh kg−1), and the cost‐effectiveness of sulfur. However, the practical application of Li–S batteries is still handicapped by a multitude of key challenges, mainly pertaining to fatal lithium polysulfide (LiPS) shuttling and sluggish sulfur redox kinetics. In this respect, rationalizing electrocatalytic processes in Li–S chemistry to synergize the entrapment and conversion of LiPSs is of paramount significance. This review summarizes recent progress and well‐developed strategies of the mediator design toward promoted Li–S chemistry. The current advances, existing challenges, and future directions are accordingly highlighted, aiming at providing in‐depth understanding of the sulfur reaction mechanism and guiding the rational mediator design to realize high‐energy and long‐life Li–S batteries. [ABSTRACT FROM AUTHOR]

Abstract: Lithium–sulfur (Li–S) batteries are deemed to be one of the most promising energy storage technologies because of their high energy density, low cost, and environmental benignancy. However, existing drawbacks including the shuttling of intermediate polysulfides, the insulating nature of sulfur, and the considerable volume change of sulfur cathode would otherwise result in the capacity fading and unstable cycling. To overcome these challenges, herein an in situ assembly route is presented to fabricate VS2/reduced graphene oxide nanosheets (G–VS2) as a sulfur host. Benefiting from the 2D conductive and polar VS2 interlayered within a graphene framework, the obtained G–VS2 hybrids can effectively suppress the polysulfide shuttling, facilitate the charge transport, and cushion the volume expansion throughout the synergistic effect of structural confinement and chemical anchoring. With these advantageous features, the obtained sulfur cathode (G–VS2/S) can deliver an outstanding rate capability (≈950 and 800 mAh g−1 at 1 and 2 C, respectively) and an impressive cycling stability at high rates (retaining ≈532 mAh g−1 after 300 cycles at 5 C). More significantly, it enables superior cycling performance of high‐sulfur‐loading cathodes (achieving an areal capacity of 5.1 mAh cm−2 at 0.2 C with a sulfur loading of 5 mg cm−2) even at high current densities. [ABSTRACT FROM AUTHOR]

Electrocatalysis in lithium-sulfur (Li–S) chemistry has readily stimulated extensive interests because of its irreplaceable role in realizing high-performance batteries. In this sense, achieving accelerated catalytic conversion of polysulfides is essential for the shuttle inhibition and kinetics promotion. Nonetheless, selective catalysis of sulfur reduction/evolution reaction via precise control over electrocatalytic mediators is still in its infancy. Moreover, specific catalytic role of the active metal center in dual-atom catalyst sites remains relatively unexplored. Herein, we utilize a salt-confined strategy to fabricate FeCo geminal-atom moieties dispersed on N-doped carbon support (FeCo-NC) for Li–S batteries throughout leveraging Fe and Co single-atom species with selective catalysis. The enhanced bidirectional conversion kinetics of polysulfide with the incorporation of Fe and Co atoms are uncovered throughout theoretical simulation and electrokinetic analysis. As a result, the FeCo-NC endows a rechargeable Li–S battery with excellent capacity retention rate of 98.6% after 100 cycles at 0.2 C and cycling stability with a decay rate of 0.033% per cycle over 2000 cycles at 3.0 C. More encouragingly, the assembled Li–S cell at a sulfur loading of 6.7 mg cm−2 can harvest an areal capacity of 7.13 mAh cm−2, signifying the rational design of geminal-atom mediators to dictate selective catalysis behaviors toward practical Li–S batteries. [Display omitted] • Preparing geminal-atom catalyst with high atom loading by salt-confined template strategy. • Decoupling the catalytic selectivity of the Fe and Co single-atom mediators to the sulfur redox reaction. • Deciphering optimal bidirectional electrocatalytic reaction kinetics in Li–S system. • Achieving long-lifetime and high-rate performances for Li−S batteries. [ABSTRACT FROM AUTHOR]

Achieving high-performance Li–S battery systems toward practical application. The simultaneous interface and defect engineering on graphene-oxides by direct PECVD technique accelerate the sulfur redox reaction kinetics, providing a rational strategy for designing highly active electrocatalysts targeting advanced Li–S batteries. [Display omitted] • Realizing G-oxide electrocatalyst via interface and defect engineering. • Discussing electrocatalytic mechanism of G-oxide for Li–S chemistry. • Achieving high-performance Li–S battery under practical scenarios. Li–S battery is broadly regarded as one of the most promising energy storage systems due to its prominent merits in energy density and theoretical capacity. Nevertheless, existing challenges such as formidable shuttle effect and sluggish redox kinetics hinder its practical application. Herein, we propose a universal interface and defect engineering dual-strategy to design graphene-oxide (G-oxide) hybrids as heterostructured electrocatalysts targeting promoted Li–S chemistry. The employment of direct plasma-enhanced chemical vapor deposition technique allows the in situ formation of graphene over a suite of oxide powders. Benefiting from the creation of heterointerface and carbon/oxygen defects, G-oxide realizes balanced management of polysulfide adsorption, lithium-ion migration and electron transportation, accordingly rendering bi-directional electrocatalysis behaviors for the sulfur conversion. Thus-assembled S/G-oxide cathode affords stable cycling performances even under a sulfur loading of 8.1 mg cm−2 and an electrolyte usage of 4.0 μL mg–1 S. [ABSTRACT FROM AUTHOR]

• The TCS interlayer is synthesis via facile electrospinning and carbonization. • The novel carbon skeleton is doped by nitrogen and metal tin nanoparticles. • The TCS owns uniform catalytical sites for conversion of polysulfides. • The lithium sulfur battery exhibits high initial capacities and low fading rates. Lithium-sulfur (Li-S) batteries are considered as a promising next generation battery system because of their theoretical high capacity and large energy density. However, such battery still faces many obstacles, mainly including the shuttle effect of polysulfides and sluggish reaction kinetics of the electrode actions. Herein, a freestanding metallic tin-modified and nitrogen-doped carbon-skeleton (TCS) was designed and used as the interlayer for Li-S batteries to efficiently mitigate the above issues and sustain a long lifespan. Here, the carbon-skeleton builds a high-effective conductive network for the whole interface, while the uniformly distributed metallic tin nanoparticles act as an absorbent of polysulfides and a catalyst to promote the conversion of sulfur species. As a result, both the specific capacity and cycle stability of Li-S battery are significantly improved with the assistance of the TCS interlayer. With a high sulfur content of 72.6 wt%, Li-S battery used TCS as interlayer shows an ultrahigh initial capacity of 1123.1 mA h g−1 at 0.2C and a high capacity retention of 92.8% after 100 cycles. Besides, when the sulfur areal loading increased to 3.67 mg cm−2, it still keeps a high areal capacity of 3.15 mA h cm−2 under a current density of 0.2C, and the decay rate in the first 50 cycles is only 0.0043%. As such, this work will provide a facile and practical strategy to the development of a long cycling Li-S battery. [ABSTRACT FROM AUTHOR]