Constructing Patch-Ni-Shelled Pt@Ni Nanoparticles within Confined Nanoreactors for Catalytic Oxidation of Insoluble Polysulfides in Li-S Batteries

Mo2C-MoP heterostructure regulate the adsorption energy of electrocatalysts in high-performance Li-S batteries

The cathodic polysulfides electrocatalyst, such as Mo2C, offers a promising approach to mitigate the shuttling effect by providing strong polysulfide adsorption and catalyst abilities to improve the electrochemical performance of Lithium-sulfur (Li-S) batteries. However, according to the Sabatier principle, excessive adsorption of Mo2C undermines the conversion of polysulfides. This undesirable effect can be mitigated by forming the heterostructure of Mo2C-MoP. Even more importantly, the introduction of MoP can prevent the surface gelation of Mo2C and expose more active sites. Consequently, the Li-S batteries with the Mo2C-MoP sulfur host exhibit outstanding long-term cycling stability, showcasing a mere 0.035% capacity decay per cycle over 800 cycles at 1 C. This work on the balance between adsorption capacity and catalytic active of cathodic polysulfides electrocatalyst provides a new vision for realizing a high-performance Li-S batteries.

Boosting Lean Electrolyte Lithium-Sulfur Battery Performance with Transition Metals: A Comprehensive Review

Lithium-sulfur (Li-S) batteries have received widespread attention, and lean electrolyte Li-S batteries have attracted additional interest because of their higher energy densities. This review systematically analyzes the effect of the electrolyte-to-sulfur (E/S) ratios on battery energy density and the challenges for sulfur reduction reactions (SRR) under lean electrolyte conditions. Accordingly, we review the use of various polar transition metal sulfur hosts as corresponding solutions to facilitate SRR kinetics at low E/S ratios (< 10 µL mg-1), and the strengths and limitations of different transition metal compounds are presented and discussed from a fundamental perspective. Subsequently, three promising strategies for sulfur hosts that act as anchors and catalysts are proposed to boost lean electrolyte Li-S battery performance. Finally, an outlook is provided to guide future research on high energy density Li-S batteries.

Application of Inorganic Quantum Dots in Advanced Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have emerged as one of the most attractive alternatives for post-lithium-ion battery energy storage systems, owing to their ultrahigh theoretical energy density. However, the large-scale application of Li-S batteries remains enormously problematic because of the poor cycling life and safety problems, induced by the low conductivity , severe shuttling effect, poor reaction kinetics, and lithium dendrite formation. In recent studies, catalytic techniques are reported to promote the commercial application of Li-S batteries. Compared with the conventional catalytic sites on host materials, quantum dots (QDs) with ultrafine particle size (<10 nm) can provide large accessible surface area and strong polarity to restrict the shuttling effect, excellent catalytic effect to enhance the kinetics of redox reactions, as well as abundant lithiophilic nucleation sites to regulate Li deposition. In this review, the intrinsic hurdles of S conversion and Li stripping/plating reactions are first summarized. More importantly, a comprehensive overview is provided of inorganic QDs, in improving the efficiency and stability of Li-S batteries, with the strategies including composition optimization, defect and morphological engineering, design of heterostructures, and so forth. Finally, the prospects and challenges of QDs in Li-S batteries are discussed.

Interface Engineering Toward Expedited Li2 S Deposition in Lithium-Sulfur Batteries: A Critical Review

Lithium-sulfur batteries (LSBs) with superior energy density are among the most promising candidates of next-generation energy storage techniques. As the key step contributing to 75% of the overall capacity, Li₂ S deposition remains a formidable challenge for LSBs applications because of its sluggish kinetics. The severe kinetic issue originates from the huge interfacial impedances, indicative of the interface-dominated nature of Li₂ S deposition. Accordingly, increasing efforts have been devoted to interface engineering for efficient Li₂ S deposition, which has attained inspiring success to date. However, a systematic overview and in-depth understanding of this critical field are still absent. In this review, the principles of interface-controlled Li₂ S precipitation are presented, clarifying the pivotal roles of electrolyte-substrate and electrolyte-Li₂ S interfaces in regulating Li₂ S depositing behavior. For the optimization of the electrolyte-substrate interface, efforts on the design of substrates including metal compounds, functionalized carbons, and organic compounds are systematically summarized. Regarding the regulation of electrolyte-Li₂ S interface, the progress of applying polysulfides catholytes, redox mediators, and high-donicity/polarity electrolytes is overviewed in detail. Finally, the challenges and possible solutions aiming at optimizing Li₂ S deposition are given for further development of practical LSBs. This review would inspire more insightful works and, more importantly, may enlighten other electrochemical areas concerning heterogeneous deposition processes.

Electrostatic Potential-Induced Co-N4 Active Centers in a 2D Conductive Metal-Organic Framework for High-Performance Lithium-Sulfur Batteries

The use of single-atom catalysts is a promising approach to solve the issues of polysulfide shuttle and sluggish conversion chemistry in lithium-sulfur (Li-S) batteries. However, a single-atom catalyst usually contains a low content of active centers because more metal ions lead to generation of aggregation or the formation of nonatomic catalysts. Herein, a 2D conductive metal-organic framework [Co₃(HITP)₂] with abundant and periodic Co-N₄ centers was decorated on carbon fiber paper as a functional interlayer for advanced Li-S batteries. The Co₃(HITP)₂-decorated interlayer exhibits a chemical anchoring effect and facilitates conversion kinetics, thus effectively restraining the polysulfide shuttle effect. Density functional theory calculations demonstrate that the Co-N₄ centers in Co₃(HITP)₂ feature more intense electron density and more negative electrostatic potential distribution than those in the carbon matrix as the single-atom catalyst, thereby promoting the electrochemical performance due to the lower reaction Gibbs free energies and decomposition energy barriers. As a result, the optimized batteries deliver a high rate capacity of over 400 mA h g^-1 at 4 C current and a satisfying capacity decay rate of 0.028% per cycle over 1000 cycles at 1 C. The designed Co₃(HITP)₂-decorated interlayer was used to prepare one of the most advanced Li-S batteries with excellent performance (reversible capacity of 762 mA h g^-1 and 79.6% capacity retention over 500 cycles) under high-temperature conditions, implying its great potential for practical applications.

Kinetic Acceleration of Lithium Polysulfide Conversion via a Copper-Iridium Alloying Catalytic Strategy in Li-S Batteries

To solve the shuttle effect of soluble lithium polysulfides (LiPSs), a porous N-doped carbon-supported copper-iridium alloy catalyst composite (CuIr/NC) has been synthesized and served as a modified cathode sulfur host for lithium-sulfur batteries (LSBs). The metal-organic framework-derived calcined carbon frameworks build efficient conductive channels for fast ion/electron transport. Furthermore, alloying noble metals Ir with thiophilic metal Cu provides abundant active sites to effectively capture LiPSs and accelerate the catalytic conversion process, originating from modulating the surface electronic structure of the metal Cu by introducing Ir atoms to affect the 3d-orbital distribution. All of the above are strongly supported by a range of characterization studies and density functional theory calculations. Benefiting from the above advantages, the LSBs generally show satisfactory cycling performance. Apart from exhibiting a terrific initial specific capacity of 1288 mA h g^-1 at 0.2 C, they can also keep long-term cycling stability under a high current density up to 5 C together with a slow specific capacity decay ratio (0.033%) per cycle after 1000 cycles. In addition, it is worth mentioning that a high areal capacity (4.7 mA h cm^-2) with a low E/S ratio (6.2 μL mg^-1) could still be accomplished at higher sulfur loading (4.3 mg cm^-2).

In-MOF-Derived Hierarchically Hollow Carbon Nanostraws for Advanced Zinc-Iodine Batteries

Hollow carbon materials are regarded as crucial support materials in catalysis and electrochemical energy storage on account of their unique porous structure and electrical properties. Herein, an indium-based organic framework of InOF-1 can be thermally carbonized under inert argon to form indium particles through the redox reaction between nanosized indium oxide and carbon matrix. In particular, a type of porous hollow carbon nanostraw (HCNS) is in situ obtained by combining the fusion and removal of indium within the decarboxylation process. The as-synthesized HCNS, which possesses more charge active sites, short and quick electron, and ion transport pathways, has become an excellent carrier for electrochemically active species such as iodine with its unique internal cavity and interconnected porous structure on the tube wall. Furthermore, the assembled zinc-iodine batteries (ZIBs) provide a high capacity of 234.1 mAh g^-1 at 1 A g^-1 , which ensures that the adsorption and dissolution of iodine species in the electrolyte reach a rapid equilibrium. The rate and cycle performance of the HCNS-based ZIBs are greatly improved, thereby exhibiting an excellent capacity retention rate. It shows a better electrochemical exchange capacity than typical unidirectional carbon nanotubes, making HCNS an ideal cathode material for a new generation of high-performance batteries.

Carbon Coated Metal-Based Composite Electrode Materials for Lithium Sulfur Batteries: A Review

Lithium-sulfur battery is one of the most promising secondary battery systems due to their high energy density and low material cost. During the past decade, great progress has been achieved in promoting the performances of Li-S batteries by addressing the challenges at the laboratory-level model systems. With growing attention paid to the application of Li-S batteries, new challenges at practical cell scales emerge as the bottleneck. However, challenges remain for the commercialization of lithium-sulfur batteries. The current review mainly focused on metal-based catalysts decorated-carbon materials for enhanced lithium sulfur battery performance. Firstly, the synthesis methods of various carbon-sulfur composites are discussed, as well as the influence of different material structures on the electrochemical performance. Secondly, a variety of catalysts, including metal atoms, metal oxides, sulfides, phosphides, nitrides, and carbide-decorated carbon nanomaterials, are systematically introduced to determine how lithium can be enhanced by suppressing polysulfides and promoting redox conversion reactions. Also, analyzed the multi-step electrochemical reaction mechanism of the battery during the charging and discharging process, and provide a feasible path for the practical application of high energy density lithium-sulfur batteries.

Dynamic Liquid Metal Catalysts for Boosted Lithium Polysulfides Redox Reaction

Designing efficient electrocatalysts with high electroconductivity, strong chemisorption, and superior catalytical efficiency to realize rapid kinetics of the lithium polysulfides (LiPSs) conversion process is crucial for practical lithium-sulfur (Li-S) battery applications. Unfortunately, most current electrocatalysts cannot maintain long-term stability due to the possible failure of catalytic sites. Herein, a novel dynamic electrocatalytic strategy with the liquid metal (i.e., gallium-tin, EGaSn) to facilitate LiPSs redox reaction is reported. The combined theoretical simulations and microstructure experiment analysis reveal that Sn atoms dynamically distributed in the liquid Ga matrix act as the main active catalytic center. Meanwhile, Ga provides a uniquely dynamic environment to maintain the long-term integrity of the catalytic system. With the participation of EGaSn, a tailor-made 2 Ah Li-S pouch cell with a specific energy density of 307.7 Wh kg^-1 is realized. This work opens up new opportunities for liquid-phase binary alloys as electrocatalysts for high-specific-energy Li-S batteries.

Ni3Sn2/nitrogen-doped graphene composite with chemisorption and electrocatalysis as advanced separator modifying material for lithium sulfur batteries

Lithium-sulfur batteries have been widely studied because of their advantages of abundant reserves, environmental friendliness, low cost andhighspecific capacity. However, the volume expansionand the low electrical conductivity of sulfur, and the shuttle effect of polysulfides limit their application. Herein,wesynthesizea two-dimensional layered Ni₃Sn₂/nitrogen-doped graphene (NG) composite asseparator modifying material for lithium-sulfur batteries. The Ni₃Sn₂formed by dual metal salts Ni(NO₃)₂·6H₂O and SnCl₂·2H₂O can adsorb polysulfide and catalyze its transformation to improve the electrochemical reaction kinetics. Moreover, the layered NG can not only disperse the Ni₃Sn₂particles, but alsoensure rapid electron transfer. Therefore, the lithium-sulfur battery with the Ni₃Sn₂/NG modified separator shows excellent electrochemical performance. At a current rate of 1 C, the lithium-sulfur battery with the Ni₃Sn₂/NG modified separator can provide a high initial discharge capacity of 1022.1 mAh g^-1and maintain a reversible specific capacity of 758.3 mAh g^-1after 400 cycles.

The Catalyst Design for Lithium-Sulfur Batteries: Roles and Routes

Lithium-sulfur battery is a promising candidate for next-generation high energy density batteries due to its ultrahigh theoretical energy density. However, it suffers from low sulfur utilization, fast capacity decay, and the notorious "shuttle effect" of lithium polysulfides (LiPSs) due to the sluggish reaction kinetics, which severely restrict its practical applications. Using the electrocatalyst can accelerate the redox reactions between sulfur, LiPSs and Li₂ S and suppress the shuttling of LiPSs, and thus, it is a promising strategy to solve the above problems, enabling the battery with high energy density and long cycling stability. In this personal account, we discuss the catalyst design for lithium-sulfur batteries according to the sulfur reduction reaction (SRR) and sulfur evolution reaction (SER) in the discharging and charging processes. The catalytic effects for each step in SRR and SER are highlighted and the homogenous catalysts, the selective catalysts, and the bidirectional catalysts are discussed, which can help guide the rational design of the catalysts and practical applications of lithium-sulfur batteries.

A graphene oxide scaffold-encapsulated microcapsule for polysulfide-immobilized long life lithium-sulfur batteries

Engineering high-performance cathodes for high energy-density lithium-sulfur (Li-S) batteries is quite significant to achieve commercialization. Here, we develop a graphene oxide scaffold/sulfur composite-encapsulated microcapsule (GSM) for high-performance Li-S batteries, which is prepared through the co-flow focusing (CFF) approach. The GSM-based cathode displays a high capacity of 1004 mA h g^-1 at 0.2C after cycling 200 times, a long-term cycling stability after 1000 cycles at 2C, and a good rate-performance. At temperatures of -5 °C and 45 °C, the electrochemical performance is also excellent. The computational calculations based on density functional theory (DFT) verify the high adsorption energies of the microcapsules towards polysulfides, suppressing the shuttle effect efficiently. It is expected that the GSM system developed based on the CFF method here and its high electrochemical performance will enable it to be applicable for preparing many other emerging energy-storage materials and secondary batteries.

Customized Structure Design and Functional Mechanism Analysis of Carbon Spheres for Advanced Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are attracting much attention due to their high theoretical energy density and are considered to be the predominant competitors for next-generation energy storage systems. The practical commercial application of LSBs is mainly hindered by the severe "shuttle effect" of the lithium polysulfides (LiPSs) and the serious damage of lithium dendrites. Various carbon materials with different characteristics have played an important role in overcoming the above-mentioned problems. Carbon spheres (CSs) are extensively explored to enhance the performance of LSBs owing to their superior structures. The review presents the state-of-the-art advances of CSs for advanced high-energy LSBs, including their preparation strategies and applications in inhibiting the "shuttle effect" of the LiPSs and protecting lithium anodes. The unique restriction effect of CSs on LiPSs is explained from three working mechanisms: physical confinement, chemical interaction, and catalytic conversion. From the perspective of interfacial engineering and 3D structure designing, the protective effect of CSs on the lithium anode is also analyzed. Not only does this review article contain a summary of CSs in LSBs, but also future directions and prospects are discussed. The systematic discussions and suggested directions can enlighten thoughts in the reasonable design of CSs for LSBs in near future.

A flame-retardant polyimide interlayer with polysulfide lithium traps and fast redox conversion towards safety and high sulfur utilization Li-S batteries

In recent years and following the progress made in lithium-ion battery technology, substantial efforts have been devoted to developing practical lithium-sulfur (Li-S) batteries for next-generation commercial energy storage devices. The practical application of Li-S batteries is still limited by dramatically reduced capacities, cycling instabilities, and safety issues arising from flammable components. In this study, we designed and fabricated a flame-retardant, multifunctional interlayer which integrated electroconductive networks, lithium polysulfide (LiPS) traps and catalysts to significantly elevate the electrochemical performance and safety of pristine Li-S batteries. The LiPS adsorptive polymer polyimide (PI) constrains polysulfides to the cathode region and effectively suppresses the shuttle effect. Coralloid PI/multiwalled carbon nanotube (MCNT) compounds provide plentiful reaction sites for active materials. The catalytic Ni on the metal skeleton surface notably promotes Li⁺ diffusion, lowers the redox overpotential and accelerates LiPS conversion, which improves the redox kinetics associated with sulfur-related species and significantly elevates sulfur utilization. At different current densities of 0.2 C and 0.5 C, impressive initial discharge capacities of 1275.3 mA h g^-1 and 1190.9 mA h g^-1 are attainable respectively, with high capacity retentions of 80.3% and 78.6% over 600 cycles. Besides, the multifunctional interlayer can also act as a flame-retardant layer to promote the safety of Li-S batteries by inhibiting the spread of fire. This study provides a feasible and prospective strategy that adopts a multifunctional interlayer to develop Li-S batteries with higher capacities, longer cycling lives and safer working conditions.

Polysulfide Catalytic Materials for Fast-Kinetic Metal-Sulfur Batteries: Principles and Active Centers

Benefiting from the merits of low cost, ultrahigh-energy densities, and environmentally friendliness, metal-sulfur batteries (M-S batteries) have drawn massive attention recently. However, their practical utilization is impeded by the shuttle effect and slow redox process of polysulfide. To solve these problems, enormous creative approaches have been employed to engineer new electrocatalytic materials to relieve the shuttle effect and promote the catalytic kinetics of polysulfides. In this review, recent advances on designing principles and active centers for polysulfide catalytic materials are systematically summarized. At first, the currently reported chemistries and mechanisms for the catalytic conversion of polysulfides are presented in detail. Subsequently, the rational design of polysulfide catalytic materials from catalytic polymers and frameworks to active sites loaded carbons for polysulfide catalysis to accelerate the reaction kinetics is comprehensively discussed. Current breakthroughs are highlighted and directions to guide future primary challenges, perspectives, and innovations are identified. Computational methods serve an ever-increasing part in pushing forward the active center design. In summary, a cutting-edge understanding to engineer different polysulfide catalysts is provided, and both experimental and theoretical guidance for optimizing future M-S batteries and many related battery systems are offered.

Lithium-Sulfur Battery Cathode Design: Tailoring Metal-Based Nanostructures for Robust Polysulfide Adsorption and Catalytic Conversion

Lithium-sulfur (Li-S) batteries have a high specific energy capacity and density of 1675 mAh g^-1 and 2670 Wh kg^-1 , respectively, rendering them among the most promising successors for lithium-ion batteries. However, there are myriads of obstacles in the practical application and commercialization of Li-S batteries, including the low conductivity of sulfur and its discharge products (Li₂ S/Li₂ S₂ ), volume expansion of sulfur electrode, and the polysulfide shuttle effect. Hence, immense attention has been devoted to rectifying these issues, of which the application of metal-based compounds (i.e., transition metal, metal phosphides, sulfides, oxides, carbides, nitrides, phosphosulfides, MXenes, hydroxides, and metal-organic frameworks) as sulfur hosts is profiled as a fascinating strategy to hinder the polysulfide shuttle effect stemming from the polar-polar interactions between the metal compounds and polysulfides. This review encompasses the fundamental electrochemical principles of Li-S batteries and insights into the interactions between the metal-based compounds and the polysulfides, with emphasis on the intimate structure-activity relationship corroborated with theoretical calculations. Additionally, the integration of conductive carbon-based materials to ameliorate the existing adsorptive abilities of the metal-based compound is systematically discussed. Lastly, the challenges and prospects toward the smart design of catalysts for the future development of practical Li-S batteries are presented.

Pt-NbC Composite as a Bifunctional Catalyst for Redox Transformation of Polysulfides in High-Rate-Performing Lithium-Sulfur Batteries

Accelerating the redox reaction of polysulfides via catalysis is an effective way to suppress the shuttling effect in lithium-sulfur (Li-S) cells. However, recent studies have mainly focused on the singular function of the catalyst, i.e., either oxidation or reduction of polysulfides. As such, the goal of rapid cycling of sulfur species remains to be highly desired. Herein, a Pt-carbide composite as a bifunctional catalyst was developed to simultaneously accelerate both the reduction of soluble polysulfides and the oxidation of insoluble Li₂S/Li₂S₂. Typically, a Pt-NbC composite was synthesized by growing Pt nanoparticles on the surface of NbC, and the resultant intimate interface in the hybrid is a key component for the bifunctional catalysis. During the reduction process, polysulfides could be grabbed on the surface of NbC via strong adsorption, and then these trapped polysulfides could be catalytically converted by Pt nanoparticles. During the oxidation process, both NbC and Pt exhibited catalytic activities for the dissolution of Li₂S. This process could lead to the renewal of the surface of the catalyst. By combining the sulfur cathode with a Pt-NbC-CNT (Pt-NbC anchored on a carbon nanotube)-coated separator, the cell was able to demonstrate a high initial capacity of 1382 mAh g^-1 at a current density of 0.2C. Furthermore, the cell was able to achieve an exceptional rate capability of 795 mAh g^-1 at 5C, and it was also able to show significantly inhibited self-discharge behavior. Thus, this work explores the catalyst design and the mechanism of a bifunctional catalyst for the performance enhancement in Li-S cells.

Recent Progress in High-Performance Lithium Sulfur Batteries: The Emerging Strategies for Advanced Separators/Electrolytes Based on Nanomaterials and Corresponding Interfaces

Lithium-sulfur (Li-S) batteries, possessing excellent theoretical capacities, low cost and nontoxicity, are one of the most promising energy storage battery systems. However, poor conductivity of elemental S and the "shuttle effect" of lithium polysulfides hinder the commercialization of Li-S batteries. These problems are closely related to the interface problems between the cathodes, separators/electrolytes and anodes. The review focuses on interface issues for advanced separators/electrolytes based on nanomaterials in Li-S batteries. In the liquid electrolyte systems, electrolytes/separators and electrodes system can be decorated by nano materials coating for separators and electrospinning nanofiber separators. And, interface of anodes and electrolytes/separators can be modified by nano surface coating, nano composite metal lithium and lithium nano alloy, while the interface between cathodes and electrolytes/separators is designed by nano metal sulfide, nanocarbon-based and other nano materials. In all solid-state electrolyte systems, the focus is to increase the ionic conductivity of the solid electrolytes and reduce the resistance in the cathode/polymer electrolyte and Li/electrolyte interfaces through using nanomaterials. The basic mechanism of these interface problems and the corresponding electrochemical performance are discussed. Based on the most critical factors of the interfaces, we provide some insights on nanomaterials in high-performance liquid or state Li-S batteries in the future.

Polyaniline Encapsulated Amorphous V2 O5 Nanowire-Modified Multi-Functional Separators for Lithium-Sulfur Batteries

Designing multi-functional separators is one of the effective strategies for achieving high-performance lithium-sulfur (Li-S) batteries. In this work, polyaniline (PANI) encapsulated amorphous vanadium pentoxide (V₂ O₅ ) nanowires (general formula V₂ O₅ ·nH₂ O and abbreviated as VOH) are synthesized by a facile in situ chemical oxidative polymerization method, and utilized as a basic building block for the preparation of functional interlayers on the commercial polypropylene (PP) separator, generating a VOH@PANI-PP separator with multi-functionalities. Compared to the crystalline V₂ O₅ , the amorphous V₂ O₅ shows enhanced properties of polysulfide adsorption, catalytic activity, as well as ionic conductivity. Therefore, within the VOH@PANI-PP separator, the amorphous V₂ O₅ nanowire component contributes to the strong adsorption of polysulfides, the high catalytic activity for polysulfides conversion, and the high ionic conductivity. The PANI component further strengthens the above effects, improves the electrical conductivity, and enhances the flexibility of the modified separator. Benefiting from the synergistic effects, the VOH@PANI-PP separator effectively suppresses polysulfide shuttling and improves the cycling stability of its composed Li-S batteries. This work provides a new research strategy for the development of efficient separators in rechargeable batteries by judiciously integrating the amorphous metal oxide with a conductive polymer.

Sb nanosheet modified separator for Li-S batteries with excellent electrochemical performance

An air-stable antimony (Sb) nanosheet modified separator (SbNs/separator) has been prepared by coating exfoliated Sb nanosheets (SbNs) successfully onto a pristine separator through a vacuum infiltration method. The as-prepared Li-S batteries using SbNs/separators exhibit much improved electrochemical performance compared to the ones using commercial separators. The coulombic efficiency (CE) of the Li-S battery using the SbNs/separator after the initial cycle is close to 100% at a current density of 0.1 A g-1, and 660 mA h g-1 capacity retained after 100 cycles. The rate capability of Li-S battery using SbNs/separator delivers a reversible capacity of 425 mA h g-1 when the current density increases to 1 A g-1. The improved electrochemical performance is mainly attributed to the following reasons. Firstly, the combination of physical adsorption and chemical bonding between SbNs and lithium polysulfides (LiPSs), which efficiently inhibits the shuttle phenomena of LiPSs. Secondly, the good electronic conductivity of SbNs improves the utilization of the adsorbed LiPSs, which benefits the capacity release of active materials. Lastly, the fast conversion kinetics of intermediate LiPSs caused by the catalytic effect from SbNs further suppresses the shuttle effect of LiPSs. The SbNs/separators exhibit a great potential for the future high-performance Li-S batteries.

Theoretical investigation on lithium polysulfide adsorption and conversion for high-performance Li-S batteries

Lithium-sulfur (Li-S) batteries have shown great application prospects as next-generation energy storage systems due to their high theoretical capacity and high energy density. However, the practical application of Li-S batteries is still hindered by several challenges, such as their sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs). To date, significant research has been focused on the confinement adsorption and catalytic conversion of LiPSs using theoretical or/and experimental methods. Among them, theoretical calculations are highly attractive to observe complex LiPS conversion reactions, which facilitate the rational design of S mediators for high-performance Li-S batteries. In this review, we summarize and discuss the recent advances in the adsorption and conversion of LiPSs from the viewpoint of theoretical calculations. Moreover, a set of theoretical principles to guide the screening of suitable host materials for Li-S batteries is presented and discussed. Finally, some personal insights about the future challenges and the focus of research in this field are presented, which will push a milestone step toward high-efficiency and long-life Li-S batteries.

Tuning the Band Structure of MoS2 via Co9S8@MoS2 Core-Shell Structure to Boost Catalytic Activity for Lithium-Sulfur Batteries

The introduction of a dual-functional interlayer into lithium-sulfur batteries (LSBs) provides many opportunities for restraining the "shuttle effect" and enhancing sluggish sulfur conversion kinetics. Tuning the band structure of the metal sulfide provides an opportunity to enhance its catalytic activity, which plays an important role in suppressing the "shuttle effect" of lithium polysulfides (LiPSs) in LSBs. Here were present a Co₉S₈@MoS₂ core-shell heterostructure anchored to a carbon nanofiber (Co₉S₈@MoS₂/CNF), developed as an interlayer for suppressing the shuttle effect of LiPSs. The fabricated composite heterostructure is determined to be an effective alternative material that combines the synergistic relationship between chemisorption and electrochemical catalysis. We find that the band structure of the MoS₂ shell can be effectively tuned by the Co₉S₈ core and that the Co₉S₈@MoS₂/CNF can capture the LiPSs, providing excellent catalytic ability to convert LiPSs into Li₂S₂, with subsequent transformation from Li₂S₂ to Li₂S. Importantly, high capacities of 1002 and 986 mAh g^-1 can be retained after 50 cycles with high-sulfur loadings of 6 and 10 mg cm^-2. Our results highlight the design of an atomic-scale heterostructure as a multifunctional interlayer providing a synergistic relationship between adsorption and catalysis. The net result is an effective retardation of the shuttling of LiPSs and an enhancement of the electrochemical redox reactions of LiPSs. This work shows great promise toward the development of practical applications of LSBs.

Theoretical Insights into the Favorable Functionalized Ti2C-Based MXenes for Lithium-Sulfur Batteries

Because of the high specific surface area, excellent electronic conductivity, facile Li diffusion, and rich functional groups, Ti₂C-based MXenes have been widely used to improve the electrochemical property of lithium-sulfur batteries. The complex surface functionalization (such as -OH, -S, -F, and -O) of MXenes boosts the performance but also causes controversies about the favorable functionalized surface in the electrochemical reaction during the charge and discharge process. In the present work, a theoretical study based on density functional theory has been carried out to clarify the favorable functionalized surface by comparing pristine Ti₂C and -OH-, -S-, -F-, and -O-functionalized Ti₂C surfaces from the aspects of adsorption ability, electronic conductivity, and kinetic conversion ability. It is found that compared with severe polysulfide deformation on pristine Ti₂C and Ti₂C(OH)₂ surfaces, Ti₂CO₂, Ti₂CS₂, and Ti₂CF₂ have effective polysulfide adsorption. Ti₂CO₂ has the largest surface adsorption energy, followed by Ti₂CS₂, and Ti₂CF₂ is the weakest. Meanwhile, the narrow-band gap semiconductor property of Ti₂CO₂ during adsorption indicates worse electronic conductivity than metallic Ti₂CS₂ and Ti₂CF₂. In addition, for the kinetic conversion ability, the Ti₂CS₂ surface has the fastest polysulfide conversion and Li diffusion, followed by Ti₂CF₂, and Ti₂CO₂ represents the slowest conversion and diffusion. Accordingly, because of the medium binding energy, good electronic conductivity, and fast polysulfide conversion and Li diffusion, Ti₂CS₂ is revealed to be the favorable functionalized surface. More importantly, the origin for the Ti₂CS₂ surface with medium adsorption ability represents the fastest polysulfide conversion, and Li diffusion is further clarified. The great affinity of the Ti₂CS₂ surface to the product Li₂S leads to facile polysulfide conversion. The uniform charge distribution on the Ti₂CS₂ surface contributes to the fast Li diffusion.

One-Pot Synthesis of PtNi Alloy Nanoparticle-Supported Multiwalled Carbon Nanotubes in an Ionic Liquid Using a Staircase Heating Process

High-performance PtNi alloy nanoparticle-supported multiwalled carbon nanotube composite (PtNi/MWCNT) electrocatalysts can be prepared via one-pot preparation for oxygen reduction reaction. This route of preparation utilizes the pyrolytic decomposition of metal precursors, such as Pt(acac)₂ with Ni precursors, nickel bis(trifluoromethanesulfonyl)amide (Ni[Tf₂N]₂) or nickel acetylacetonate (Ni(acac)₂), in an ionic liquid (IL), N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide ([N_1,1,1,3][Tf₂N]). Currently, there is insufficient information concerning the effect of difference in preparation conditions on the formation mechanism and catalytic activity of PtNi/MWCNT. In this article, a staircase heating process was used to investigate the PtNi alloy nanoparticle formation mechanism and catalytic activity of the resulting PtNi/MWCNT. We found that the alloy formation process, composition, and crystal structure, which directly affect the electrocatalytic activity, strongly depended on the Ni precursor species and heating process. The catalytic performance of certain PtNi/MWCNTs collected during the staircase heating process was better than that of PtNi/MWCNTs produced via the conventional heating process.

Highly Graphitized Porous Carbon-FeNi3 Fabricated from Oleic Acid for Advanced Lithium-Sulfur Batteries

Improving the electrical conductivity of sulfur, suppressing shuttle/dissolution of polysulfide, and enhancing reaction kinetics in Li-S batteries are essential for practical applications. Here, for the first time, we have used inexpensive oleic acid as a single carbon source, and have added commercial SiO₂ as a template to form a porous structure, whereas introducing Fe(NO₃ )₃ and Ni(NO₃ )₂ as catalysts to increase the degree of graphitization. Moreover, the dual metal salts Fe(NO₃ )₃ and Ni(NO₃ )₂ can also form FeNi₃ alloy, and our results show that FeNi₃ nanoparticles accelerate the kinetic conversion reactions of polysulfide. By virtue of the well-developed porous structure and high degree of graphitization, the highly graphitized porous carbon-FeNi₃ (GPC-FeNi₃ ) has high conductivity to ensure fast charge transfer, and the hierarchically porous structure facilitates ion diffusion and traps polysulfide. Thus, a GPC-FeNi₃ /S cathode displays excellent electrochemical performance. At current rates of 0.2 and 1 C, a cathode of the GPC-FeNi₃ /S composite with a sulfur content of 70 % delivers high initial discharge capacities of 1108 and 880 mA h g^-1 , respectively, and retains reversible specific capacities of 850 mA h g^-1 after 200 cycles at 0.2 C and 625 mA h g^-1 after 400 cycles at 1 C.

Tuning lithium-peroxide formation and decomposition routes with single-atom catalysts for lithium-oxygen batteries

Lithium-oxygen batteries with ultrahigh energy density have received considerable attention as of the future energy storage technologies. The development of effective electrocatalysts and a corresponding working mechanism during cycling are critically important for lithium-oxygen batteries. Here, a single cobalt atom electrocatalyst is synthesized for lithium-oxygen batteries by a polymer encapsulation strategy. The isolated moieties of single atom catalysts can effectively regulate the distribution of active sites to form micrometre-sized flower-like lithium peroxide and promote the decomposition of lithium peroxide by a one-electron pathway. The battery with single cobalt atoms can operate with high round-trip efficiency (86.2%) and long-term stability (218 days), which is superior to a commercial 5 wt% platinum/carbon catalyst. We reveal that the synergy between a single atom and the support endows the catalyst with excellent stability and durability. The promising results provide insights into the design of highly efficient catalysts for lithium-oxygen batteries and greatly expand the scope of future investigation.

A Typha Angustifolia-Like MoS2/Carbon Nanofiber Composite for High Performance Li-S Batteries

A Typha Angustifolia-like MoS₂/carbon nanofiber composite as both a chemically trapping agent and redox conversion catalyst for lithium polysulfides has been successfully synthesized via a simple hydrothermal method. Cycling performance and coulombic efficiency have been improved significantly by applying the Typha Angustifolia-like MoS₂/carbon nanofiber as the interlayer of a pure sulfur cathode, resulting in a capacity degradation of only 0.09% per cycle and a coulombic efficiency which can reach as high as 99%.

Pt/NiO Microsphere Composite as Efficient Multifunctional Catalysts for Nonaqueous Lithium-Oxygen Batteries and Alkaline Fuel Cells: The Synergistic Effect of Pt and Ni

Developing efficient and low-cost multifunctional electrocatalysts is important for electrochemical devices. In this work, a cost-effective Pt/NiO composite with very limited Pt loading (from 0.5 to 3%) was controllably synthesized through facile hydrothermal procedures. The composite demonstrated the improved catalytic performance as applied to the nonaqueous Li-O₂ batteries and the alkaline fuel cells. Regarding the alkaline fuel cells, 1% Pt/NiO composite gave rise to the best Pt distribution and thus exhibited the optimized electrochemical conductivity and properties as suggested by the significantly improved electrochemical reversibility. Meanwhile, the demonstrated 1% Pt/NiO composite presented high catalytic capability as electrode for Li-O₂ batteries, which allowed for much improved capacity utilization, high cycling stability, high initial capacity (2329 mAh/g), and no obvious voltage drop during cycling. Such multiple advantages of prepared composite electrode material offer new prospects and application as multifunctional electrocatalysts for both Li-O₂ batteries and alkaline fuel cells.