Basal-Plane-Activated Molybdenum Sulfide Nanosheets with Suitable Orbital Orientation as Efficient Electrocatalysts for Lithium-Sulfur Batteries

Manipulating Atomic-Coupling in Dual-Cavity Boride Nanoreactor to Achieve Hierarchical Catalytic Engineering for Sulfur Cathode

The catalytic process of Li2S formation is considered a key pathway to enhance the kinetics of lithium-sulfur batteries. Due to the system's complexity, the catalytic behavior is uncertain, posing significant challenges for predicting activity. Herein, we report a novel cascaded dual-cavity nanoreactor (NiCo-B) by controlling reaction kinetics, providing an opportunity for achieving hierarchical catalytic behavior. Through experimental and theoretical analysis, the multilevel structure can effectively suppress polysulfides dissolution and accelerate sulfur conversion. Furthermore, we differentiate the adsorption (B-S) and catalytic effect (Co-S) in NiCo-B, avoiding catalyst deactivation caused by excessive adsorption. As a result, the as-prepared battery displays high reversible capacity, even with sulfur loading of 13.2 mg cm-2 (E/S=4 μl mg-1), the areal capacity can reach 18.7 mAh cm-2.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

Rechargeable metal-sulfur batteries are considered promising candidates for energy storage due to their high energy density along with high natural abundance and low cost of raw materials. However, they could not yet be practically implemented due to several key challenges: (i) poor conductivity of sulfur and the discharge product metal sulfide, causing sluggish redox kinetics, (ii) polysulfide shuttling, and (iii) parasitic side reactions between the electrolyte and the metal anode. To overcome these obstacles, numerous strategies have been explored, including modifications to the cathode, anode, electrolyte, and binder. In this review, the fundamental principles and challenges of metal-sulfur batteries are first discussed. Second, the latest research on metal-sulfur batteries is presented and discussed, covering their material design, synthesis methods, and electrochemical performances. Third, emerging advanced characterization techniques that reveal the working mechanisms of metal-sulfur batteries are highlighted. Finally, the possible future research directions for the practical applications of metal-sulfur batteries are discussed. This comprehensive review aims to provide experimental strategies and theoretical guidance for designing and understanding the intricacies of metal-sulfur batteries; thus, it can illuminate promising pathways for progressing high-energy-density metal-sulfur battery systems.

High-Throughput Calculations for Screening d- and p-Block Single-Atom Catalysts toward Li2 S/Na2 S Decomposition Guided by Facile Descriptor beyond Brønsted-Evans-Polanyi Relationship

Single-atom catalysts (SACs) are promising cathode materials for addressing issues faced by lithium-sulfur batteries. Considering the ample chemical space of SACs, high-throughput calculations are efficient strategies for their rational design. However, the high throughput calculations are impeded by the time-consuming determination of the decomposition barrier (Eb ) of Li2 S. In this study, the effects of bond formation and breakage on the kinetics of SAC-catalyzed Li2 S decomposition with g-C3 N4 as the substrate are clarified. Furthermore, a new efficient and easily-obtained descriptor Li─S─Li angle (ALi─S─Li ) of adsorbed Li2 S, different from the widely accepted thermodynamic data for predicting Eb , which breaks the well-known Brønsted-Evans-Polanyi relationship, is identified. Under the guidance of ALi─S─Li , several superior SACs with d- and p-block metal centers supported by g-C3 N4 are screened to accelerate the sulfur redox reaction and fix the soluble lithium polysulfides. The newly identified descriptor of ALi─S─Li can be extended to rationally design SACs for Na─S batteries. This study opens a new pathway for tuning the performance of SACs to catalyze the decomposition of X2 S (X = Li, Na, and K) and thus accelerate the design of SACs for alkaline-chalcogenide batteries.

Band Structure Engineering and Orbital Orientation Control Constructing Dual Active Sites for Efficient Sulfur Redox Reaction

The kinetics difference among multistep electrochemical processes leads to the accumulation of soluble polysulfides and thus shuttle effect in lithium-sulfur (Li-S) batteries. While the interaction between catalysts and representative species has been reported, the root of the kinetics difference, interaction change among redox reactions, remains unclear, which significantly impedes the catalysts design for Li-S batteries. Here, this work deciphers the interaction change among electrocatalytic sulfur reactions, using tungsten disulfide (WS2 ) a model system to demonstrate the efficiency of modifying electrocatalytic selectivity via dual-coordination design. Band structure engineering and orbital orientation control are combined to guide the design of WS2 with boron dopants and sulfur vacancies (B-WS2- x ), accurately modulating interaction with lithium and sulfur sites in polysulfide species for relatively higher interaction with short-chain polysulfides. The modified interaction trend is experimentally confirmed by distinguishing the kinetics of each electrochemical reaction step, indicating the effectiveness of the designed strategy. An Ah-level pouch cell with B-WS2- x delivers a gravimetric energy density of up to 417.6 Wh kg-1 with a low electrolyte/sulfur ratio of 3.6 µL mg-1 and negative/positive ratio of 1.2. This work presents a dual-coordination strategy for advancing evolutionarily catalytic activity, offering a rational strategy to develop effective catalysts for practical Li-S batteries.

Basal Plane-Activated Boron-Doped MoS2 Nanosheets for Efficient Electrochemical Ammonia Synthesis

Under the dual pressure of energy crisis and environmental pollution, ammonia (NH3 ) is an indispensable chemical product in the global economy. The electrocatalytic synthesis of NH3 directly from nitrogen and water using renewable electricity has become one of the most attractive and important topics. Basal plane-activated boron-doped MoS2 nanosheets (B-MoS2 ) as a non-noble metal catalyst with excellent performance for N2 electroreduction are synthesized by a facile one-step hydrothermal method. In 0.1 m Na2 SO4 solution, MoS2 nanosheets doped with 300 mg boric acid (B-MoS2 -300) give rise to a good ammonia yield rate of 75.77 μg h-1  mg-1 cat. at -0.75 V vs. RHE, and an excellent Faradaic efficiency of 40.11 % at -0.60 V vs. RHE. In addition, the B-MoS2 -300 nanosheets show good selectivity and chemical stability, and no hydrazine (N2 H4 ) by-product is generated during the reaction. 15 N isotopic labeling confirms that nitrogen in produced ammonia originates from N2 in the electrolyte. On the one hand, the high conductivity of MoS2 guarantees guarantees a high electron transfer rate from nitrogen to ammonia; on the other hand, the successful incorporation of heteroatom B enlarges the interlayer spacing of MoS2 , and the B atom can act as an active site for basal plane activation, providing more active sites for the nitrogen reduction reaction (NRR). Density functional theory calculations show that the doping of B activates the base plane of 1T-MoS2 , which makes the adsorption of N2 on the base plane easier and promotes the NRR.

N-Doping Induced Lattice Expansion of 1D Template Confined Ultrathin MoS2 Sheets to Significantly Enhance Lithium Polysulfides Redox Kinetics for Li-S Battery

Preparing MoS2 -based materials with reasonable structure and catalytic activity to enhance the sluggish kinetics of lithium polysulfides (LiPSs) conversion is of great significance for Li-S batteries (LSBs) but still remain a challenge. Hence, hollow nanotubes composed of N-doped ultrathin MoS2 nanosheets (N-MoS2 NHTs) are fabricated as efficient S hosts for LSBs by using CdS nanorods as a sacrifice template. Characterization and theoretical results show that the template effectively inhibits the excessive growth of MoS2 sheets, and N doping expands the interlayer spacing and modulates the electronic structure, thus accelerating the mass/electron transfer and enhancing the LiPSs adsorption and transformation. Benefiting from the merits, the N-MoS2 NHTs@S cathode exhibits an excellent initial capacity of 887.8 mAh g-1 and stable cycling performances with capacity fading of only 0.0436% per cycle at 1.0 C (500 cycles). Moreover, even at high S loading that of 7.5 mg cm-2 , the N-MoS2 NHTs@S cathode also presents initial excellent areal capacity of 7.80 mAh cm-2 at 0.2 C. This study offers feasible guidance for designing advanced MoS2 -based cathode materials in LSBs.

Towards Practical Application of Li-S Battery with High Sulfur Loading and Lean Electrolyte: Will Carbon-Based Hosts Win This Race?

As the need for high-energy-density batteries continues to grow, lithium-sulfur (Li-S) batteries have become a highly promising next-generation energy solution due to their low cost and exceptional energy density compared to commercially available Li-ion batteries. Research into carbon-based sulfur hosts for Li-S batteries has been ongoing for over two decades, leading to a significant number of publications and patents. However, the commercialization of Li-S batteries has yet to be realized. This can be attributed, in part, to the instability of the Li metal anode. However, even when considering just the cathode side, there is still no consensus on whether carbon-based hosts will prove to be the best sulfur hosts for the industrialization of Li-S batteries. Recently, there has been controversy surrounding the use of carbon-based materials as the ideal sulfur hosts for practical applications of Li-S batteries under high sulfur loading and lean electrolyte conditions. To address this question, it is important to review the results of research into carbon-based hosts, assess their strengths and weaknesses, and provide a clear perspective. This review systematically evaluates the merits and mechanisms of various strategies for developing carbon-based host materials for high sulfur loading and lean electrolyte conditions. The review covers structural design and functional optimization strategies in detail, providing a comprehensive understanding of the development of sulfur hosts. The review also describes the use of efficient machine learning methods for investigating Li-S batteries. Finally, the outlook section lists and discusses current trends, challenges, and uncertainties surrounding carbon-based hosts, and concludes by presenting our standpoint and perspective on the subject.

The Dual-Site Adsorption and High Redox Activity Enabled by Hybrid Organic-Inorganic Vanadyl Ethylene Glycolate for High-Rate and Long-Durability Lithium-Sulfur Batteries

Transition metal oxides (TMOs) have attracted considerable attention owing to their strong anchoring ability and natural abundance. However, their single-site adsorption toward sulfur (S) species significantly lowers the possibility of S species reacting with Li⁺ in the electrolyte and increases the reaction barrier. This study investigates molecular modification by coupling the TMO structure with Li⁺ conductive polymer ligands, and vanadyl ethylene glycolate (VEG) is successfully synthesized by introducing organic ligands into the VO_x crystal structure. In addition to the strong interaction between the VO_x and lithium polysulfides via the V-S bond, the groups in the VEG polymer ligands can reversibly couple/decouple with Li⁺ in the electrolyte. Such dual-site adsorption enables a smooth dynamic adsorption-diffusion process. Accordingly, the VEG-based Li-S cells exhibit excellent rate reversibility, cyclic stability, and a long cycle life without the addition of conducting agents. Encouragingly, the VEG-based cells also exhibit close and excellent capacity decays of 0.081%, 0.078%, and 0.095% at 0, 25, and 50 °C (1 C for 200 cycles), respectively. This work provides a novel approach for developing advanced catalysts that can realize Li-S batteries with long-term durability, fast charge-discharge properties, and applications in a wide temperature range.

Binary Sulfiphilic Nickel Boride on Boron-Doped Graphene with Beneficial Interfacial Charge for Accelerated Li-S Dynamics

The "shuttle effect" and slow conversion kinetics of lithium polysulfides (LiPSs) are stumbling block for high-energy-density lithium-sulfur batteries (LSBs), which can be effectively evaded by advanced catalytic materials. Transition metal borides possess binary LiPSs interactions sites, aggrandizing the density of chemical anchoring sites. Herein, a novel core-shelled heterostructure consisting of nickel boride nanoparticles on boron-doped graphene (Ni₃ B/BG), is synthesized through a graphene spontaneously couple derived spatially confined strategy. The integration of Li₂ S precipitation/dissociation experiments and density functional theory computations demonstrate that the favorable interfacial charge state between Ni₃ B and BG provides smooth electron/charge transport channel, which promotes the charge transfer between Li₂ S₄ -Ni₃ B/BG and Li₂ S-Ni₃ B/BG systems. Benefitting from these, the facilitated solid-liquid conversion kinetics of LiPSs and reduced energy barrier of Li₂ S decomposition are achieved. Consequently, the LSBs employed the Ni₃ B/BG modified PP separator deliver conspicuously improved electrochemical performances with excellent cycling stability (decay of 0.07% per cycle for 600 cycles at 2 C) and remarkable rate capability of 650 mAh g^-1 at 10 C. This study provides a facile strategy for transition metal borides and reveals the effect of heterostructure on catalytic and adsorption activity for LiPSs, offering a new viewpoint to apply boride in LSBs.

Novel hydrothermal synthesis of Mn-TaS3@rGO nanocomposite as a superior multifunctional mediator for advanced Li-S batteries

Because of its high theoretical capacity and energy density, the lithium-sulfur (Li-S) battery is a desirable next-generation energy storage technology. However, the shuttle effect of lithium polysulfide and the slow sulfur reaction kinetics remain significant barriers to Li-S battery application. In this work, tantalum trisulfide (TaS₃) and selective manganese-doped tantalum trisulfide (Mn-TaS₃) nanocomposites on reduced graphene oxide surface were developed via a one-step hydrothermal method for the first time and introduced as a novel multifunctional mediator in the Li-S battery. The surface engineering of Mn-TaS₃@rGO with abundant defects not only exhibits the strong adsorption performance on lithium polysulfides (LiPSs) but also demonstrates the remarkable electrocatalytic effect on both the LiPSs conversion reaction in symmetric cell and the Li₂S nucleation/dissolution processes in potentiostatic experiments, which would substantially promote the electrochemical performance of LSB. The cell assembled with Mn-TaS₃@rGO/PP modified separator could significantly improve the cell conductivity and effectively accelerate the redox conversion of active sulfur during the charging/discharging process, which delivers exceptional long-term cycling with 683 mA h g^-1 retention capacity after the 1000th cycle at 0.3C under the sulfur loading of 2.7 mg cm^-2. Even at the E/S ratio as low as 5.0 µL mg^-1, the reversible specific capacity of 692 mA h g^-1 can be offered at 0.2C over 300 cycles. This research indicates that the novel Mn-TaS₃@rGO multifunctional mediator is successfully fabricated and applied in Li-S batteries with extraordinary electrochemical performances and gives a strategy to explore the construction of a modified functional separator.

Mo-O-C Between MoS2 and Graphene Toward Accelerated Polysulfide Catalytic Conversion for Advanced Lithium-Sulfur Batteries

MoS₂ /C composites constructed with van der Waals forces have been extensively applied in lithium-sulfur (Li-S) batteries. However, the catalytic conversion effect on polysulfides is limited because the weak electronic interactions between the composite interfaces cannot fundamentally improve the intrinsic electronic conductivity of MoS₂ . Herein, density functional theory calculations reveal that the MoS₂ and nitrogen-doped carbon composite with an Mo-O-C bond can promote the catalytic conversion of polysulfides with a Gibbs free energy of only 0.19 eV and a low dissociation energy barrier of 0.48 eV, owing to the strong covalent coupling effect on the heterogeneous interface. Guided by theoretical calculations, a robust MoS₂ strongly coupled with a 3D carbon matrix composed of nitrogen-doped reduced graphene oxide and carbonized melamine foam is designed and constructed as a multifunctional coating layer for lithium-sulfur batteries. As a result, excellent electrochemical performance is achieved for Li-S batteries, with a capacity of 615 mAh g^-1 at 5 C, an areal capacity of 6.11 mAh cm^-2 , and a low self-discharge of only 8.6% by resting for five days at 0.5 C. This study opens a new avenue for designing 2D material composites toward promoted catalytic conversion of polysulfides.

Computational screening of functionalized MXenes to catalyze the solid and non-solid conversion reactions in cathodes of lithium-sulfur batteries

The poor cycling abilities of S cathodes due to the dissolution of high-order lithium polysulfides and sluggish reaction kinetics of low-order solid Li₂S hinder the commercial application of lithium-sulfur batteries. Although many hosts have been introduced into S electrodes to anchor high-order polysulfides, an effective procedure to select the hosts to improve the conversion kinetics of solid Li₂S is scarce. Using density functional theory calculations, we proposed a procedure to screen catalytic hosts for solid and non-solid reactions of Li₂S₂/Li₂S by employing the available functionalized Ti₃C₂T₂ MXenes (T = H, O, F, S, Cl, Se, Te, Br, OH, and NH), under the precondition of good anchoring abilities for high-order polysulfides. For the solid-state reactions, it was found that Ti₃C₂Se₂ is the optimal candidate for improving the reaction kinetics of solid Li₂S. Suitable catalysts for different reaction processes between molecular Li₂S₂ and Li₂S have also been proposed. We also proposed that sulfur cathodes doped with heavy atoms (Se or Te) belonging to the main group VI may significantly modify the reaction kinetics of Li₂S. These results provide guidance on synthesizing MXenes with the given surface groups as the hosts and can accelerate the step of finding out other suitable host materials.

High-Index Faceted Nanocrystals as Highly Efficient Bifunctional Electrocatalysts for High-Performance Lithium-Sulfur Batteries

Precisely regulating of the surface structure of crystalline materials to improve their catalytic activity for lithium polysulfides is urgently needed for high-performance lithium-sulfur (Li-S) batteries. Herein, high-index faceted iron oxide (Fe₂O₃) nanocrystals anchored on reduced graphene oxide are developed as highly efficient bifunctional electrocatalysts, effectively improving the electrochemical performance of Li-S batteries. The theoretical and experimental results all indicate that high-index Fe₂O₃ crystal facets with abundant unsaturated coordinated Fe sites not only have strong adsorption capacity to anchor polysulfides but also have high catalytic activity to facilitate the redox transformation of polysulfides and reduce the decomposition energy barrier of Li₂S. The Li-S batteries with these bifunctional electrocatalysts exhibit high initial capacity of 1521 mAh g^-1 at 0.1 C and excellent cycling performance with a low capacity fading of 0.025% per cycle during 1600 cycles at 2 C. Even with a high sulfur loading of 9.41 mg cm^-2, a remarkable areal capacity of 7.61 mAh cm^-2 was maintained after 85 cycles. This work provides a new strategy to improve the catalytic activity of nanocrystals through the crystal facet engineering, deepening the comprehending of facet-dependent activity of catalysts in Li-S chemistry, affording a novel perspective for the design of advanced sulfur electrodes.