Multiregion Janus-Featured Cobalt Phosphide-Cobalt Composite for Highly Reversible Room-Temperature Sodium-Sulfur Batteries

A Critical Review on Room-Temperature Sodium-Sulfur Batteries: From Research Advances to Practical Perspectives

Room-temperature sodium-sulfur (RT-Na/S) batteries are promising alternatives for next-generation energy storage systems with high energy density and high power density. However, some notorious issues are hampering the practical application of RT-Na/S batteries. Besides, the working mechanism of RT-Na/S batteries under practical conditions such as high sulfur loading, lean electrolyte, and low capacity ratio between the negative and positive electrode (N/P ratio), is of essential importance for practical applications, yet the significance of these parameters has long been disregarded. Herein, it is comprehensively reviewed recent advances on Na metal anode, S cathode, electrolyte, and separator engineering for RT-Na/S batteries. The discrepancies between laboratory research and practical conditions are elaborately discussed, endeavors toward practical applications are highlighted, and suggestions for the practical values of the crucial parameters are rationally proposed. Furthermore, an empirical equation to estimate the actual energy density of RT-Na/S pouch cells under practical conditions is rationally proposed for the first time, making it possible to evaluate the gravimetric energy density of the cells under practical conditions. This review aims to reemphasize the vital importance of the crucial parameters for RT-Na/S batteries to bridge the gaps between laboratory research and practical applications.

A Mott-Schottky Heterojunction with Strong Chemisorption and Fast Conversion Effects for Room-Temperature Na-S Batteries

The practical application of the room-temperature sodium-sulfur (RT Na-S) batteries is currently limited by low reversible capacity and serious capacity decay due to the sluggish reaction kinetics and shuttle effect. It is necessary to design a suitable sulfur host integrated with electrocatalysts to realize effective chemisorption and catalysis of sodium polysulfides (NaPSs). Herein, under the guidance of theoretical calculation, the Mott-Schottky heterojunction with a built-in electric field composed of iron (Fe) and iron disulfide (FeS2) components anchored on a porous carbon matrix (Fe/FeS2-PC) is designed and prepared. The enhanced chemisorption effect of Fe, the fast electrocatalytic effect of FeS2, and the fast transfer effect of the built-in electric field within the Fe/FeS2 heterojunction in the cathode of RT Na-S batteries work together to effectively improve the electrochemical performance. As a result, the Fe/FeS2-PC@S cathode exhibits high reversible capacity (815 mAh g-1 after 150 cycles at 0.2 A g-1) and excellent stability (516 mAh g-1 after 600 cycles at 5 A g-1, with only 0.07% decay per cycle). The design of the Fe/FeS2 heterojunction electrocatalyst provides a new strategy for the development of highly stable RT Na-S batteries.

Enhancing Conversion Kinetics through Electron Density Dual-Regulation of Catalysts and Sulfur toward Room-/Subzero-Temperature Na-S Batteries

Room-temperature sodium-sulfur (RT Na/S) batteries have received increasing attention for the next generation of large-scale energy storage, yet they are hindered by the severe dissolution of polysulfides, sluggish redox kinetic, and incomplete conversion of sodium polysulfides (NaPSs). Herein, the study proposes a dual-modulating strategy of the electronic structure of electrocatalyst and sulfur to accelerate the conversion of NaPSs. The selenium-modulated ZnS nanocrystals with electron rearrangement in hierarchical structured spherical carbon (Se-ZnS/HSC) facilitate Na+ transport and catalyze the conversion between short-chain sulfur and Na2S. And the in situ introduced Se within S can enhance conductivity and form an S─Se bond, suppressing the "polysulfides shuttle". Accordingly, the S@Se-ZnS/HSC cathode exhibits a specific capacity of as high as 1302.5 mAh g-1 at 0.1 A g-1 and ultrahigh-rate capability (676.9 mAh g-1 at 5.0 A g-1). Even at -10 °C, this cathode still delivers a high reversible capacity of 401.2 mAh g-1 at 0.05 A g-1 and 94% of the original capacitance after 50 cycles. This work provides a novel design idea for high-performance Na/S batteries.

Defect engineering of a TiO2 anatase/rutile homojunction accelerating sulfur redox kinetics for high-performance Na-S batteries

Room-temperature sodium-sulfur (RT Na-S) batteries have the drawbacks of the poor shuttle effect of soluble sodium polysulfides (NaPSs) as well as slow sulfur redox kinetics, which result in poor cycling stability and low capacity, seriously affecting their extensive application. Herein, defect engineering is applied to construct rich oxygen vacancies at the interface of a TiO2 anatase/rutile homojunction (OV-TRA) to enhance sulfur affinity and redox reaction kinetics. Combining structural characterizations with electrochemical analysis reveals that OV-TRA well alleviates the shuttle effect of NaPSs and precipitates the deposition and diffusion kinetics of Na2S. Consequently, S/OV-TRA provides excellent electrochemical performance with a reversible capacity of 870 mA h g-1 at 0.1 C after 100 cycles and a long-term cycling capability of 759 mA h g-1 at 1 C after 1000 cycles. This work provides an effective interfacial defect engineering strategy to promote the application of metal oxides in RT Na-S batteries.

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.

Unleashing the high energy potential of zinc-iodide batteries: high-loaded thick electrodes designed with zinc iodide as the cathode

The realization of high energy is of great importance to unlock the practical potential of zinc-iodine batteries. However, significant challenges, such as low iodine loading (mostly less than 50 wt%), restricted iodine reutilization, and severe structural pulverization during cycling, compromise its intrinsic features. This study introduces an optimized, fully zincified zinc iodide loaded onto a hierarchical carbon scaffold with high active component loading and content (82 wt%) to prepare a thick cathode for enabling high-energy Zn-I2 batteries. The synergistic interactions between nitrogen heteroatoms and cobalt nanocrystals within the porous matrix not only provide forceful chemisorption to lock polyiodide intermediates but also invoke the electrocatalytic effects to manipulate efficient iodine conversion. The ZnI2 cathode could effectively alleviate continuous volumetric expansion and maximize the utilization of active species. The electrochemical examinations confirm the thickness-independent battery performance of assembled Zn-I2 cells due to the ensemble effect of composite electrodes. Accordingly, with a thickness of 300 μm and ZnI2 loading of up to 20.5 mg cm-2, the cathode delivers a specific capacity of 92 mA h gcathode-1 after 2000 cycles at 1C. Moreover, the Zn-I2 pouch cell with ZnI2 cathode has an energy density of 145 W h kgcathode-1 as well as a stable long cycle life.

Synergistic activation of P and orbital coupling effect for ultra-sensitive and selective electrochemical detection of Cd(II) over Fe-doped CoP

Despite significant advancements in the detection of cadmium (Cd(II)) based on nanomaterial adsorbability, limited research has been conducted on ultra-sensitive and selective detection mechanisms, resulting in a lack of guidance for designing efficient interface materials to detect Cd(II). Herein, reductive Fe doping on CoP facilitates an efficient Fe-Co-P electron transfer path, which renders P the electron-rich site and subsequently splits a new orbital peak that matches with that of Cd(II) for excellent electrochemical performance. The sensitivity of Cd(II) was remarkably up to 109.75 μA μM-1 on the Fe-CoP modified electrode with excellent stability and repeatability, surpassing previously reported findings. Meanwhile, the electrode exhibits exceptional selectivity towards Cd(II) ions compared to some bivalent heavy metal ions (HMIs). Moreover, X-ray absorption fine structure (XAFS) analysis reveals the interaction between P and Cd(II), which is further verified via density functional theory (DFT) calculation with the new hybrid peaks resulting from the splitting peak of P atoms coupled with the orbital energy level of Cd(II). Generally, doping engineering for specific active sites and regulation of orbital electrons not only provides valuable insights for the subsequent regulation of electronic configuration but also lays the foundation for customizing highly sensitive and selectivity sensors.

Heterostructured Co/CeO2-Decorating N-Doped Porous Carbon Nanocubes as Efficient Sulfur Hosts with Enhanced Rate Capability and Cycling Durability toward Room-Temperature Na-S Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries have gained significant interest thanks to their satisfactory energy density and abundant earth resources. Nevertheless, practical implementations of RT Na-S batteries are still impeded by serious shuttle effects of sodium polysulfide (NaPS) intermediates, sluggish redox kinetics of cathodes, and poor electronic conductivity from S-species. To solve these problems, heterostructured Co/CeO2-decorating N-doped porous carbon nanocubes (Co/CeO2-NPC) are constructed as a S support, which integrates the strong adsorption and fast conversion of NaPSs, together with superior electronic conductivity. Consequently, the as-synthesized S@Co/CeO2-NPC cathode for RT Na-S batteries exhibits improved rate performance (1275, 561.1, and 485 mAh g-1 at 0.1, 5, and 10 C, respectively) and superior cyclic durability (capacity degeneration of 0.027% per cycle after 1000 cycles at 5 C). Such a S cathode combining a heterostructure interface, hierarchical porous carbon nanocubes, and polar compositions can considerably increase electronic conductivity and promote NaPS adsorption and conversion, achieving superior performance toward RT Na-S batteries.

Spaced-Confined Janus Engineering Enables Controlled Ion Transport Channels and Accelerated Kinetics for Secondary Ion Batteries

The large grain boundary resistance between different components of the anode electrode easily leads to the low ion transport efficiency and poor electrochemical performance of lithium-/sodium-ion batteries (LIBs/SIBs). To address the issue, a Janus heterointerface with a Mott-Schottky structure is proposed to optimize the interface atomic structure, weaken interatomic resistance, and improve ion transport kinetics. Herein, Janus Co/Co2P@carbon-nanotubes@core-shell (Janus Co/Co2P@CNT-CS) refined urchin-like architecture derived from metal-organic frameworks is reported via a coating-phosphating process, where the Janus Co/Co2P heterointerface nanoparticles are confined in carbon nanotubes and a core-shell polyhedron. Such a Janus Co/Co2P heterointerface shows the strong built-in electric field, facilitating the controllable ion transport channels and the high ion transport efficiency. The Janus Co/Co2P@CNT-CS refined urchin-like architecture composed of a core-shell structure and the grafting carbon nanotubes enhances the structure stability and electronic conductivity. Benefiting from the spaced-confined Janus heterointerface engineering and synergistic effects between the core-shell structure and the grafting carbon nanotubes, the Janus Co/Co2P@CNT-CS refined urchin-like architecture demonstrates the fast ion transport rate and excellent pseudocapacitance performance for LIBs/SIBs. In this case, the Janus Co/Co2P@CNT-CS refined urchin-like architecture shows high specific capacities of 709 mA h g-1 (200 cycles) and 203 mA h g-1 (300 cycles) at a current density of 500 mA g-1 for LIBs/SIBs, respectively.

Graphene cladded cobalt phosphide nanoparticles with a sandwich structure by plasma for lithium and sodium storage

Graphene cladded cobalt phosphide nanoparticles with a sandwich structure are synthesized using Ar-H2-P plasma. In situ phosphorization and graphene reduction are achieved at the same time. Benefitting from the sandwich structure and heterointerface between CoP and RGO, the electrode delivered a high reversible capacity and durable lifespan for both lithium and sodium storage.

Polar Electrocatalysts for Preventing Polysulfide Migration and Accelerating Redox Kinetics in Room-Temperature Sodium-Sulfur Batteries

Due to the high theoretical energy density, low cost, and rich abundance of sodium and sulfur, room-temperature sodium-sulfur (RT Na-S) batteries are investigated as the promising energy storage system. However, the inherent insulation of the S₈ , the dissolution and shuttle of the intermediate sodium polysulfides (NaPSs), and especially the sluggish conversion kinetics, restrict the commercial application of the RT Na-S batteries. To address these issues, various catalysts are developed to immobilize the soluble NaPSs and accelerate the conversion kinetics. Among them, the polar catalysts display impressive performance. Polar catalysts not only can significantly accelerate (or alter) the redox process, but also can adsorb polar NaPSs through polar-polar interaction because of their intrinsic polarity, thus inhibiting the notorious shuttle effect. Herein, the recent advances in the electrocatalytic effect of polar catalysts on the manipulation of S speciation pathways in RT Na-S batteries are reviewed. Furthermore, challenges and research directions to realize rapid and reversible sulfur conversion are put forward to promote the practical application of RT Na-S batteries.

Strategies to mitigate the shuttle effect in room temperature sodium-sulfur batteries: improving cathode materials

Room-temperature sodium-sulfur batteries (RT-Na/S batteries) with high reversible capacity (1675 mA h g^-1) and excellent energy density (1274 W h kg^-1) based on abundant resources of the metal Na have become a research hotspot recently. However, the intermediate product sodium polysulfides (NaPSs) generated during the charge-discharge process are easily dissolved in the ether electrolyte and transferred from the sulfur cathode to the metallic sodium surface, resulting in rapid capacity decay (shuttle effect), which seriously affects the practical application of RT-Na/S batteries. Herein, the mechanism and recent research progress in suppressing the shuttle effect of the sulfur cathode in RT-Na/S batteries are summarized. Strategies such as carbon-based materials physically fixing NaPSs, polar materials absorbing NaPSs to reduce their dissolution, and catalytic materials accelerating the transformation of NaPSs into final products are provided. Challenges and insights into high-performance sulfur electrodes for optimizing RT-Na/S batteries are discussed.

Orthorhombic Nb2 O5 Decorated Carbon Nanoreactors Enable Bidirectionally Regulated Redox Behaviors in Room-Temperature Na-S Batteries

Regulating redox kinetics is able to spur the great-leap-forward development of room-temperature sodium-sulfur (RT Na-S) batteries, especially on propelling their Na-ion storage capability. Here, an innovative metal oxide kinetics accelerator, orthorhombic Nb2 O5 Na-ion conductor, is proposed to functionalize porous carbon nanoreactors (CNR) for S cathodes. The Nb2 O5 is shown to chemically immobilize sodium polysulfides via strong affinity. Theoretical and experimental evidence reveals that the Nb2 O5 can bidirectionally regulate redox behaviors of S cathodes, which accelerates reduction conversions from polysulfides to sulfides as well as promotes oxidation reactions from sulfides to S. In situ and ex situ characterization techniques further verify its electrochemical lasting endurance in catalyzing S conversions. The well-designed S cathode demonstrates a high specific capacity of 1377 mA h g-1 at 0.1 A g-1 , outstanding rate capability of 405 mA h g-1 at 2 A g-1 , and stable cyclability with a capacity retention of 617 mA h g-1 over 600 cycles at 0.5 A g-1 . An ultralow capacity decay rate of 0.0193% per cycle is successfully realized, superior to those of current state-of-the-art RT Na-S batteries. This design also suits emerging Na-Se batteries, which contribute to outstanding electrochemical performance as well.

Catalytic Effects of Electrodes and Electrolytes in Metal-Sulfur Batteries: Progress and Prospective

Metal-sulfur (M-S) batteries are promising energy-storage devices due to their advantages such as large energy density and the low cost of the raw materials. However, M-S batteries suffer from many drawbacks. Endowing the electrodes and electrolytes with the proper catalytic activity is crucial to improve the electrochemical properties of M-S batteries. With regard to the S cathodes, advanced electrode materials with enhanced electrocatalytic effects can capture polysulfides and accelerate electrochemical conversion and, as for the metal anodes, the proper electrode materials can provide active sites for metal deposition to reduce the deposition potential barrier and control the electroplating or stripping process. Moreover, an advanced electrolyte with desirable design can catalyze electrochemical reactions on the cathode and anode in high-performance M-S batteries. In this review, recent progress pertaining to the design of advanced electrode materials and electrolytes with the proper catalytic effects is summarized. The current progress of S cathodes and metal anodes in different types of M-S batteries are discussed and future development directions are described. The objective is to provide a comprehensive review on the current state-of-the-art S cathodes and metal anodes in M-S batteries and research guidance for future development of this important class of batteries.

Robust Room-Temperature Sodium-Sulfur Batteries Enabled by a Sandwich-Structured MXene@C/Polyolefin/MXene@C Dual-functional Separator

Room-temperature sodium-sulfur (RT-Na-S) batteries are attracting increased attention due to their high theoretical energy density and low-cost. However, the traditional RT-Na-S batteries assembled with glass fiber (GF) separators are still hindered by the polysulfide shuttle effect and sodium dendrite growth, limiting the battery's capacity and cycling stability. Here, a facile and effective method toward commercial polyolefin separators for constructing stable RT-Na-S batteries is presented. By coating commercial polypropylene membrane with core-shell structured MXene@C nanosheets, a powerful dual-functional separator with improved electrolyte wettability that can inhibit polysulfide migration and induce uniform sodium disposition is developed. More importantly, the modified separator can also accelerate the conversion kinetics of sodium polysulfides. Benefiting from these characteristics, the as-prepared RT-Na-S battery exhibits a remarkably enhanced capacity (1159 mAh g^-1 at 0.2 C) and excellent cycling performance (95.8% of capacity retention after 650 cycles at 0.5 C). This study opens a promising avenue for the development of high-performance Na-S batteries.

Challenge and Strategies in Room Temperature Sodium-Sulfur Batteries: A Comparison with Lithium-Sulfur Batteries

Metal-sulfur batteries exhibit great potential as next-generation rechargeable batteries due to the low sulfur cost and high theoretical energy density. Sodium-sulfur (Na-S) batteries present higher feasibility of long-term development than lithium-sulfur (Li-S) batteries in technoeconomic and geopolitical terms. Both lithium and sodium are alkali metal elements with body-centered cubic structures, leading to similar physical and chemical properties and exposing similar issues when employed as the anode in metal-sulfur batteries. Indeed, some inspiration for mechanism researches and strategies in Na-S systems comes from the more mature Li-S systems. However, the dissimilarities in microscopic characteristics determine that Na-S is not a direct Li-S analogue. Herein, the daunting challenges derived by the differences of fundamental characteristics in Na-S and Li-S systems are discussed. And the corresponding strategies in Na-S batteries are reviewed. Finally, general conclusions and perspectives toward the research direction are presented based on the dissimilarities between both systems. This review attempts to provide important insights to facilitate the assimilation of the available knowledge on Li-S systems for accelerating the development of Na-S batteries on the basis of their dissimilarities.

Task-Specific Janus Materials in Heterogeneous Catalysis

Janus materials are anisotropic nano- and microarchitectures with two different faces consisting of distinguishable or opposite physicochemical properties. In parallel with the discovery of new methods for the fabrication of these materials, decisive progress has been made in their application, for example, in biological science, catalysis, pharmaceuticals, and, more recently, in battery technology. This Minireview systematically covers recent and significant achievements in the application of task-specific Janus nanomaterials as heterogeneous catalysts in various types of chemical reactions, including reduction, oxidative desulfurization and dye degradation, asymmetric catalysis, biomass transformation, cascade reactions, oxidation, transition-metal-catalyzed cross-coupling reactions, electro- and photocatalytic reactions, as well as gas-phase reactions. Finally, an outlook on possible future applications is given.

Room-Temperature Sodium-Sulfur Batteries: Rules for Catalyst Selection and Electrode Design

Seeking an optimal catalyst to accelerate conversion reaction kinetics of room-temperature sodium-sulfur (RT Na-S) batteries is crucial for improving their electrochemical performance and promoting the practical applications. Herein, theoretical calculations of interfacial interactions of catalysts and polysulfides in terms of the surface adsorption state, interfacial ions migration, and electronic concentration around the Fermi level are systematically proposed as guiding principles of catalyst selection for RT Na-S batteries. As a case, MoN catalyst is accurately selected from transition metal nitrides with different d orbital electrons, and for experiment, it is introduced into the carbon nanofibers as a dual-functioning host (MoN@CNFs). The MoN@CNFs can effectively anchor polysulfides and accelerate their conversion reaction. In addition, for the sodium anode, the MoN@CNFs can also induce uniform deposition of Na and inhibit dendrite growth, which are supported by in situ characterizations and finite element simulation technique. As a result, the as-prepared RT Na-S battery displays high reversible capacity of 990 mAh g^-1 at 0.2 A g^-1 after 100 cycles and long lifespan over 1500 cycles at 2 A g^-1 . Even with high S loading of 5 mg cm^-2 , the RT Na-S battery still exhibits a high areal capacity of 2.5 mAh cm^-2 .

Electrocatalysis in Room Temperature Sodium-Sulfur Batteries: Tunable Pathway of Sulfur Speciation

Benefiting from the merits of natural abundance, low cost, and ultrahigh theoretical energy density, the room temperature sodium-sulfur (RT NaS) batteries are regarded as one of the promising candidates for the next-generation scalable energy storage devices. However, the uncontrollable sulfur speciation pathways severely hinder its practical applications. Recently, various strategies have been employed to tune the conversion pathways of sulfur, such as physical confinement, chemical inhibition, and electrocatalysis. Herein, the recent advances in electrocatalytic effects manipulate sulfur speciation pathways in advanced RT NaS electrochemistry are reviewed, including the promotion of the nearly full conversion of long-chain polysulfides, short-chain polysulfides, and small sulfur molecules. The underlying catalytic modulation mechanism that fundamentally tunes the electrochemical pathway of sulfur species is comprehensively summarized along with the design strategies for catalytic active centers. Furthermore, the challenge and potential solutions to realize the quasi-solid conversion of sulfur are proposed to accelerate the real application of RT NaS batteries.

Molybdenum Carbide Electrocatalyst In Situ Embedded in Porous Nitrogen-Rich Carbon Nanotubes Promotes Rapid Kinetics in Sodium-Metal-Sulfur Batteries

This is the first report of molybdenum carbide-based electrocatalyst for sulfur-based sodium-metal batteries. MoC/Mo₂ C is in situ grown on nitrogen-doped carbon nanotubes in parallel with formation of extensive nanoporosity. Sulfur impregnation (50 wt% S) results in unique triphasic architecture termed molybdenum carbide-porous carbon nanotubes host (MoC/Mo₂ C@PCNT-S). Quasi-solid-state phase transformation to Na₂ S is promoted in carbonate electrolyte, with in situ time-resolved Raman, X-ray photoelectron spectroscopy, and optical analyses demonstrating minimal soluble polysulfides. MoC/Mo₂ C@PCNT-S cathodes deliver among the most promising rate performance characteristics in the literature, achieving 987 mAh g^-1 at 1 A g^-1 , 818 mAh g^-1 at 3 A g^-1 , and 621 mAh g^-1 at 5 A g^-1 . The cells deliver superior cycling stability, retaining 650 mAh g^-1 after 1000 cycles at 1.5 A g^-1 , corresponding to 0.028% capacity decay per cycle. High mass loading cathodes (64 wt% S, 12.7 mg cm^-2 ) also show cycling stability. Density functional theory demonstrates that formation energy of Na₂ S_x (1 ≤ x ≤ 4) on surface of MoC/Mo₂ C is significantly lowered compared to analogous redox in liquid. Strong binding of Na₂ S_x (1 ≤ x ≤ 4) on MoC/Mo₂ C surfaces results from charge transfer between the sulfur and Mo sites on carbides' surface.

Nanostructure Engineering Strategies of Cathode Materials for Room-Temperature Na-S Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries are considered to be a competitive electrochemical energy storage system, due to their advantages in abundant natural reserves, inexpensive materials, and superb theoretical energy density. Nevertheless, RT Na-S batteries suffer from a series of critical challenges, especially on the S cathode side, including the insulating nature of S and its discharge products, volumetric fluctuation of S species during the (de)sodiation process, shuttle effect of soluble sodium polysulfides, and sluggish conversion kinetics. Recent studies have shown that nanostructural designs of S-based materials can greatly contribute to alleviating the aforementioned issues via their unique physicochemical properties and architectural features. In this review, we review frontier advancements in nanostructure engineering strategies of S-based cathode materials for RT Na-S batteries in the past decade. Our emphasis is focused on delicate and highly efficient design strategies of material nanostructures as well as interactions of component-structure-property at a nanosize level. We also present our prospects toward further functional engineering and applications of nanostructured S-based materials in RT Na-S batteries and point out some potential developmental directions.

Prussian Blue Analogues for Sodium-Ion Batteries: Past, Present, and Future

Prussian blue analogues (PBAs) have attracted wide attention for their application in the energy storage and conversion field due to their low cost, facile synthesis, and appreciable electrochemical performance. At the present stage, most research on PBAs is focused on their material-level optimization, whereas their properties in practical battery systems are seldom considered. This review aims to first provide an overview of the history and parameters of PBA materials and analyze the fundamental principles toward rational design of PBAs, and then evaluate the prospects and challenges for PBAs for practical sodium-ion batteries, hoping to bridge the gap between laboratory research and commercial reality.

A High-Efficiency Mo2 C Electrocatalyst Promoting the Polysulfide Redox Kinetics for Na-S Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries, as promising next-generation energy storage candidates, are drawing more and more attention due to the high energy density and abundant elements reserved in the earth. However, the native downsides of RT Na-S batteries (i.e., enormous volume changes, the polysulfide shuttle, and the insulation and low reactivity of S) impede their further application. To conquer these challenges, hierarchical porous hollow carbon polyhedrons embedded with uniform Mo₂ C nanoparticles are designed deliberately as the host for S. The micro- and mesoporous hollow carbon indeed dramatically enhances the reactivity of the S cathodes and accommodates the volume changes. Meanwhile, the highly conductive dispersed Mo₂ C has a strong chemical adsorption to polysulfides and catalyzes the transformation of polysulfides, which can effectively inhibit the dissolution of polysulfides and accelerate the reaction kinetics. Thus, the as-prepared S cathode can display a high reversible capacity (1098 mAh g^-1 at 0.2 A g^-1 after 120 cycles) and superior rate performance (483 mAh g^-1 at 10.0 A g^-1 ). This work provides a new method to boost the performance of RT Na-S batteries.

Review of Multifunctional Separators: Stabilizing the Cathode and the Anode for Alkali (Li, Na, and K) Metal-Sulfur and Selenium Batteries

Alkali metal batteries based on lithium, sodium, and potassium anodes and sulfur-based cathodes are regarded as key for next-generation energy storage due to their high theoretical energy and potential cost effectiveness. However, metal-sulfur batteries remain challenged by several factors, including polysulfides' (PSs) dissolution, sluggish sulfur redox kinetics at the cathode, and metallic dendrite growth at the anode. Functional separators and interlayers are an innovative approach to remedying these drawbacks. Here we critically review the state-of-the-art in separators/interlayers for cathode and anode protection, covering the Li-S and the emerging Na-S and K-S systems. The approaches for improving electrochemical performance may be categorized as one or a combination of the following: Immobilization of polysulfides (cathode); catalyzing sulfur redox kinetics (cathode); introduction of protective layers to serve as an artificial solid electrolyte interphase (SEI) (anode); and combined improvement in electrolyte wetting and homogenization of ion flux (anode and cathode). It is demonstrated that while the advances in Li-S are relatively mature, less progress has been made with Na-S and K-S due to the more challenging redox chemistry at the cathode and increased electrochemical instability at the anode. Throughout these sections there is a complementary discussion of functional separators for emerging alkali metal systems based on metal-selenium and the metal-selenium sulfide. The focus then shifts to interlayers and artificial SEI/cathode electrolyte interphase (CEI) layers employed to stabilize solid-state electrolytes (SSEs) in metal-sulfur solid-state batteries (SSBs). The discussion of SSEs focuses on inorganic electrolytes based on Li- and Na-based oxides and sulfides but also touches on some hybrid systems with an inorganic matrix and a minority polymer phase. The review then moves to practical considerations for functional separators, including scaleup issues and Li-S technoeconomics. The review concludes with an outlook section, where we discuss emerging mechanics, spectroscopy, and advanced electron microscopy (e.g. cryo-transmission electron microscopy (cryo-TEM) and cryo-focused ion beam (cryo-FIB))-based approaches for analysis of functional separator structure-battery electrochemical performance interrelations. Throughout the review we identify the outstanding open scientific and technological questions while providing recommendations for future research topics.

Continuous Carbon Channels Enable Full Na-Ion Accessibility for Superior Room-Temperature Na-S Batteries

Porous carbon has been widely used as an efficient host to encapsulate highly active molecular sulfur (S) in Li-S and Na-S batteries. However, for these sub-nanosized pores, it is a challenge to provide fully accessible sodium ions with unobstructed channels during cycling, particularly for high sulfur content. It is well recognized that solid interphase with full coverage over the designed architectures plays critical roles in promoting rapid charge transfer and stable conversion reactions in batteries, whereas constructing a high-ionic-conductivity solid interphase in the pores is very difficult. Herein, unique continuous carbonaceous pores are tailored, which can serve as multifunctional channels to encapsulate highly active S and provide fully accessible pathways for sodium ions. Solid sodium sulfide interphase layers are also realized in the channels, showing high Na-ion conductivity toward stabilizing the redox kinetics of the S cathode during charge/discharge processes. This systematically designed carbon-hosted sulfur cathode delivers superior cycling performance (420 mAh g^-1 at 2 A g^-1 after 2000 cycles), high capacity retention of ≈90% over 500 cycles at current density of 0.5 A g^-1 , and outstanding rate capability (470 mAh g^-1 at 5 A g^-1 ) for room-temperature sodium-sulfur batteries.

Two-Dimensional Titanium Carbide (Ti3C2Tx) MXenes to Inhibit the Shuttle Effect in Sodium Sulfur Batteries

Room-temperature sodium sulfur batteries (RT-NSBs) are among the promising candidates for large-scale energy storage applications because of the natural abundance of the electrode materials and impressive energy density. However, one...

Incorporated O-CoP nanosheets with an O–P interpenetrated interface as electrocatalytic cathodes for rechargeable Li–CO2 batteries

An electrocatalytic material based on oxygen-decorated CoP nanosheets with an O–P interpenetrated interface was prepared for rechargeable Li–CO2 battery cathodes.

Tessellated N-doped carbon/CoSe2 as trap-catalyst sulfur hosts for room-temperature sodium-sulfur batteries

The construction of highly conductive structure with excellent adsorption-catalytic properties to accelerate electron transfer and suppress polysulfides shuttle is considered as an effective strategy to achieve well-behaved sodium-sulfur batteries. Herein,...

An Efficient Strategy toward Multichambered Carbon Nanoboxes with Multiple Spatial Confinement for Advanced Sodium-Sulfur Batteries

Intricate hollow carbon structures possess vital function for anchoring polysulfides and enhancing the utilization of sulfur in room-temperature sodium-sulfur batteries. However, their synthesis is extremely challenging due to the complex structure. Here, a facile and efficient strategy is developed for the controllable synthesis of N/O-doped multichambered carbon nanoboxes (MCCBs) by selective etching and stepwise carbonization of ZIF-8 nanocubes. The MCCBs consist of porous carbon shells on the outside and connected carbon grids with a hollow structure on the inside, bringing about a MCCBs structure. As a sulfur host, the multichambered structure has better spatial encapsulation and integrated conductivity via the inner interconnected carbon grids, which combines the characteristics of short charge transfer path and superb physicochemical adsorption along with mechanical strength. As expected, the S@MCCBs cathode realizes decent cycle stability (0.045% capacity decay per cycle over 800 cycles at 5 A g^-1) and enhanced rate performance (328 mA h g^-1 at 10 A g^-1). Furthermore, in situ transmission electron microscopy (TEM) observation confirms the good structural stability of the S@MCCBs during the (de)sodiation process. Our work demonstrates an effective strategy for the rational design and accurate construction of intricate hollow materials for high-performance energy storage systems.

Carbonaceous Hosts for Sulfur Cathode in Alkali-Metal/S (Alkali Metal = Lithium, Sodium, Potassium) Batteries

Alkali-metal/sulfur batteries hold great promise for offering relatively high energy density compared to conventional lithium-ion batteries. By providing viable sulfur composites that can be effectively used, carbonaceous hosts as a key component play critical roles in overcoming the preliminary challenges associated with the insulating sulfur and its relatively soluble polysulfides. Herein, a comprehensive overview and recent progress on carbonaceous hosts for advanced next-generation alkali-metal/sulfur batteries are presented. In order to encapsulate the highly active sulfur mass and fully limit polysulfide dissolution, strategies for tailoring the design and synthesis of carbonaceous hosts are summarized in this work. The sticking points that remain for sulfur cathodes in current alkali-metal/sulfur systems and the future remedies that can be provided by carbonaceous hosts are also indicated, which can lead to long cycling lifetimes and highly reversible capacities under repeated sulfur reduction reactions in alkali-metal/sulfur during cycling.

Metal-based electrocatalysts for room-temperature Na-S batteries

Room-temperature sodium-sulfur (RT Na-S) batteries have recently captured intensive research attention from the community and are regarded as one of promising next-generation energy storage devices since they not only integrate the advantages in high abundance and low commercial cost of elemental Na/S but also exhibit exceptionally high theoretical capacity and energy density. Whereas, the notorious shuttle effect of soluble intermediates and sluggish kinetics remain two main obstacles for RT Na-S batteries to step into new developmental stage. Recently, impressive advancements of metal-based electrocatalysts have offered a viable solution to stabilize S cathodes and unlocked new opportunities for RT Na-S batteries. Here, we underline the recent progress on metal-based electrocatalysts for RT Na-S batteries for the first time by shedding light on this emerging but promising field. The involved metal-based electrocatalysts include metals, metal oxides, metal sulfides, metal carbides, and other metal-based catalytic species. Our emphasis is focused on the discussion of design, fabrication, and properties of these electrocatalysts as well as interactions between electrocatalysts and sodium polysulfides. Otherwise, some potential electrocatalysts for RT Na-S batteries are pointed out as well. At last, perspectives for the future development of RT Na-S batteries with S cathode electrocatalysts are offered.

Porous Heteroatom-Doped Ti3C2Tx MXene Microspheres Enable Strong Adsorption of Sodium Polysulfides for Long-Life Room-Temperature Sodium-Sulfur Batteries

The practical application of Na-S batteries is largely hindered by their low mass loading, inferior rate capability, and poor cycling performance. Herein, we report a design strategy for encapsulation of sodium polysulfides using Ti₃C₂T_x MXene. Porous nitrogen-doped Ti₃C₂T_x MXene microspheres have been synthesized by a facile synthesis method. Porous nitrogen-doped Ti₃C₂T_x MXene microspheres contain abundant pore structures and heteroatom functional groups for structural and chemical synergistic encapsulation of sodium polysulfides. Sodium-sulfur batteries, based on the as-proposed cathode, demonstrated outstanding electrochemical performances, including a high reversible capacity (980 mAh g^-1 at 0.5 C rate) and extended cycling stability (450.1 mAh g^-1 at 2 C after 1000 cycles at a high areal sulfur loading of 5.5 mg cm^-2). This MXene-based hybrid material is a promising cathode host material for polysulfide-retention, enabling high-performance Na-S batteries.

Ni@Ni3N Embedded on Three-Dimensional Carbon Nanosheets for High-Performance Lithium/Sodium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are recognized as one of the most promising next-generation energy storage devices, but their practical application is greatly limited by several obstacles, such as the highly insulating nature and sluggish redox kinetics of sulfur and the dissolution of lithium polysulfides. Herein, three-dimensional carbon nanosheet frameworks anchored with Ni@Ni₃N heterostructure nanoparticles (denoted Ni@Ni₃N/CNS) are designed and fabricated by a chemical blowing and thermal nitridation strategy. It is demonstrated that the Ni@Ni₃N heterostructure can effectively accelerate polysulfide conversion and promote the chemical trapping of polysulfides. Meanwhile, the carbon nanosheet frameworks of Ni@Ni₃N/CNS establish a highly conductive network for fast electron transportation. The cells with Ni@Ni₃N heterostructures as the catalyst in the cathode show excellent electrochemical performance, revealing stable cycling over 600 cycles with a low-capacity fading rate of 0.04% per cycle at 0.5 C and high-rate capability (594 mAh g^-1 at 3 C). Furthermore, Ni@Ni₃N/CNS can also work well in room-temperature sodium-sulfur (RT-Na/S) batteries, delivering a high specific capacity (454 mAh g^-1 after 400 cycles at 0.5 C). This work provides a rational way to prepare the metal-metal nitride heterostructures to enhance the performance both of Li-S and RT-Na/S batteries.

Mo2 N-W2 N Heterostructures Embedded in Spherical Carbon Superstructure as Highly Efficient Polysulfide Electrocatalysts for Stable Room-Temperature Na-S Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries are highly desirable for a sustainable large-scale energy-storage system due to their high energy density and low cost. Nevertheless, practical applications of RT Na-S batteries are still prevented by the shuttle effect of sodium polysulfides (NaPS), slow reaction kinetics of S, and incomplete conversion process of NaPS. Here, Mo₂ N-W₂ N heterostructures embedded in a spherical carbon superstructure (Mo₂ N-W₂ N@PC) are designed to efficiently suppress the "polysulfide shuttle" and promote NaPS redox reactions. The designed Mo₂ N-W₂ N@PC heterostructure with abundant heterointerfaces, high conductivity, and porosity can facilitate electron/ion diffusion and provide high catalytic activity for efficient NaPS conversion. The obtained Na-S battery delivers high reversible capacity with superior long-term cyclability (517 mAh g^-1 at 1 A g^-1 after 400 cycles) and unprecedented rate capability (417 mAh g^-1 at 2 A g^-1 ). Furthermore, the electrocatalysis mechanism is revealed by combining in situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), UV-vis spectra, and precipitation experiments. This work demonstrates a novel heterostructure design strategy that enables high-performance Na-S batteries.

Manipulating the Electronic Structure of Nickel via Alloying with Iron: Toward High-Kinetics Sulfur Cathode for Na-S Batteries

The sluggish conversion kinetics and severe shuttle effect in room-temperature Na-S (RT Na-S) batteries cause knotty issues, such as poor rate performance, fast capacity decay as well as low Coulombic efficiency, which seriously impede their practical application. Therefore, exploiting cost-effective and efficient electrocatalysts for absorbing soluble long-chain sodium polysulfides (NaPSs) and expediting NaPSs conversion is of paramount importance. Herein, catalyst mining is first conducted by density functional theory calculations, which reveal that the alloying of Fe into Ni can tailor the electronic structure, leading to lower reaction energy barrier for polysulfide conversion. Based on this, FeNi₃@hollow porous carbon spheres (FeNi₃@HC) as a promising sulfur host for RT Na-S batteries are rationally designed and fabricated. As expected, the S@FeNi₃@HC cathode exhibits an excellent cycling stability (591 mAh g^-1 after 500 cycles at 2 A g^-1) and outstanding rate performance (383 mAh g^-1 at 5 A g^-1). Our work demonstrates an effective strategy (i.e., alloying strategy with a rich electron state) to design superior electrocatalysts for RT Na-S batteries.

Recent Advances of Catalytic Effects in Cathode Materials for Room-Temperature Sodium-Sulfur Batteries

Electrocatalysts in room-temperature sodium-sulfur (RT-Na/S) have captured numerous attention. But, they suffered from shuttle effect and surface passivation. RT-Na/S show inferior energy-storage abilities, ascribed to the larger radii of Na-ions. Herein, the vigorous review is displayed from different kinds of metal-based traits, containing single metal, metal-based samples, and multifunctional hybrids. Through the controlling of structures and composition, the conversion reaction about liquid/solid phases would be enhanced, accompanied by the enhancements of cycling stabilities and rate properties, which enables the break-through of practical applications. The in-depth influences of catalytic effects on the Na-S reaction mechanism and the corresponding electrochemical performance in recently representative works are systematically reviewed. Particularly, this review is anticipated to propose potential research directions for further enhancement of RT-Na/S batteries.

Flower-Like Interlayer-Expanded MoS2- x Nanosheets Confined in Hollow Carbon Spheres with High-Efficiency Electrocatalysis Sites for Advanced Sodium-Sulfur Battery

The room-temperature sodium-sulfur (RT-Na/S) battery is one of the most promising technologies for low-cost energy storage. However, application of RT-Na/S batteries is currently impeded by severe shuttle effects and volume expansion that limits both energy density and cycling stability. Herein, first, the first-principal calculation is used to find that the introduction of sulfur vacancies in MoS₂ can effectively enhance polysulfide adsorption and catalytic ability as well as both the ion and electron conductivities. Then, unique MoS_{2- x} /C composite spheres are further designed and synthesized with flower-like few-layer and interlayer-enlarged MoS_{2- x} nanosheets space-confined in hollow carbon nanospheres by a "ship-in-a-bottle" strategy. With this novel design, the mass loading of S in the MoS_{2- x} /C composite can be reached to as high as 75 wt%. Owing to the synergetic effect of interlayer-expanded and few-layer MoS_{2- x} nanosheets and hollow carbon spheres matrix with high electronic/Na⁺ conductivity, the RT-Na/S batteries deliver highly stable cycle durability (capacity retention of 85.2% after 100 cycles at 0.1 A g^-1 ) and remarkable rate capability (415.7 mAh g^-1 at 2 A g^-1 ) along with high energy density. This design strategy of defect- and interlayer-engineering may find wide applications in synthesizing electrode materials for high-performance RT-Na/S batteries.

Strategies for Polysulfide Immobilization in Sulfur Cathodes for Room-Temperature Sodium-Sulfur Batteries

Room-temperature sodium-sulfur batteries are one of the most attractive energy storage systems due to their low cost and ultrahigh energy density (2600 W h kg^-1 ). During the charge/discharge process, the sulfur can react with sodium via a multistep redox reaction to obtain a high specific capacity (1675 mA h g^-1 ). However, these batteries face the difficult challenge of the "shuttle effect," which hinders their practical application. Many strategies have been employed to address this issue on sulfur electrodes, such as intact physical confinement, chemical inhibition, and electrocatalysis. In this review, the mechanisms of the abovementioned strategies are summarized, the remaining issues are clarified, and research directions are proposed for developing advanced sodium-sulfur batteries.

Metal-Organic Frameworks-Derived Nitrogen-Doped Porous Carbon Nanocubes with Embedded Co Nanoparticles as Efficient Sulfur Immobilizers for Room Temperature Sodium-Sulfur Batteries

Room temperature sodium-sulfur (RT Na-S) batteries are considered a promising candidate for energy-storage due to their high energy-density and low-cost. However, the shutting effect of polysulfides and sluggish kinetics of sulfur redox reactions still severely limit their practical implementation. Herein, a new type of 3D hierarchical porous carbonaceous nanocubes is reported as efficient sulfur hosts, composed of carbon nanotubes (CNT) and Co nanoparticles (NPs) uniformly embedded into a nitrogen-doped carbon matrix (NC). Because of the high specific surface area, large degree of graphitization, and the synergetic effects between Co NPs and N-doping, the as-designed CNTs/Co@NC electrodes not only significantly increase polysulfides immobilization, but also efficiently catalyze sulfur redox reactions, as confirmed by experimental results and DFT calculations. When tested in a RT Na-S battery, the S@CNTs/Co@NC-0.25 cathode demonstrates outstanding electrochemical performance, achieving high initial specific capacity of 1200.3 mAh g^-1 at 0.1 C, remarkable rate capability up to 5.0 C (474.2 mAh g^-1 ), and superior cyclic performance of 450.5 mAh g^-1 (292 mAh g^-1 ) after 400 cycles at 1.0 C (5.0 C). The integration of a 3D hierarchical porous architecture with well-dispersed Co NPs of an electro-catalyst provides valuable insights based on structure-adsorption-catalysis engineering for advanced RT Na-S batteries.

Tunable Electrocatalytic Behavior of Sodiated MoS2 Active Sites toward Efficient Sulfur Redox Reactions in Room-Temperature Na-S Batteries

Room-temperature (RT) sodium-sulfur (Na-S) batteries hold great promise for large-scale energy storage due to the advantages of high energy density, low cost, and resource abundance. The research progress on RT Na-S batteries, however, has been greatly hindered by the sluggish kinetics of the sulfur redox reactions. Herein, an elaborate multifunctional architecture, consisting of N-doped carbon skeletons and tunable MoS₂ sulfiphilic sites, is fabricated via a simple one-pot reaction followed by in situ sulfurization. Beyond the physical confinement and chemical binding of polarized N-doped carbonaceous microflowers, the MoS₂ active sites play a key role in catalyzing polysulfide redox reactions, especially the conversion from long-chain Na₂ S_n (4 ≤ n ≤ 8) to short-chain Na₂ S₂ and Na₂ S. Significantly, the electrocatalytic activity of MoS₂ can be tunable via adjusting the discharge depth. It is remarkable that the sodiated MoS₂ exhibits much stronger binding energy and electrocatalytic behavior compared to MoS₂ sites, effectively enhancing the formation of the final Na₂ S product. Consequently, the S cathode achieves superior electrochemical performance in RT Na-S batteries, delivering a high capacity of 774.2 mAh g^-1 after 800 cycles at 0.2 A g^-1 , and an ultrahigh capacity retention with a capacity decay rate of only 0.0055% per cycle over 2800 cycles.

The promises, challenges and pathways to room-temperature sodium-sulfur batteries

Room-temperature sodium-sulfur batteries (RT-Na-S batteries) are attractive for large-scale energy storage applications owing to their high storage capacity as well as the rich abundance and low cost of the materials. Unfortunately, their practical application is hampered by severe challenges, such as low conductivity of sulfur and its reduced products, volume expansion, polysulfide shuttling effect and Na dendrite formation, which can lead to rapid capacity fading. The review discusses the Na-S-energy-storage chemistry, highlighting its promise, key challenges and potential strategies for large-scale energy storage systems. Specifically, we review the electrochemical principles and the current technical challenges of RT-Na-S batteries, and discuss the strategies to address these obstacles. In particular, we give a comprehensive review of recent progresses in cathodes, anodes, electrolytes, separators and cell configurations, and provide a forward-looking perspective on strategies toward robust high-energy-density RT-Na-S batteries.

Enabling a Stable Room-Temperature Sodium-Sulfur Battery Cathode by Building Heterostructures in Multichannel Carbon Fibers

Room-temperature sodium-sulfur (RT Na-S) batteries are widely considered as one of the alternative energy-storage systems with low cost and high energy density. However, the both poor cycle stability and capacity are two critical issues arising from low conversion kinetics and sodium polysulfides (NaPSs) dissolution for sulfur cathodes during the charge/discharge process. Herein, we report a highly stable RT Na-S battery cathode via building heterostructures in multichannel carbon fibers. The TiN-TiO₂@MCCFs, fabricated by electrospinning and nitriding techniques, are loaded with the active material S, forming S/TiN-TiO₂@MCCFs as the cathode in a RT Na-S battery. At 0.1 A g^-1, the cathode produces the capacity of more than 640 mAh g^-1 within 100 cycles with a high Coulombic efficiency of nearly 100%. Even at 5 A g^-1, the battery still exhibites a capacity of 257.1 mAh g^-1 after 1000 cycles. Combining structural and electrochemical analyses with the first-principles calculations reveals that the incorporation of the highly electrocatalytic activity of TiN with the powerful chemisorption of TiO₂ well stabilizes S and also alleviates the shuttle effects of polysulfides. This work with simple processes and low cost is expected to promote the further development and application of metal-S batteries.

Janus Conductive/Insulating Microporous Ion-Sieving Membranes for Stable Li-S Batteries

Lithium-sulfur batteries are one of the most promising next-generation high-density energy storage systems. Despite progress, the poor electrical conductivity and cycling stability of sulfur cathodes still hinder their practical implementation. Here, we developed a facile approach for the engineering of Janus double-sided conductive/insulating microporous ion-sieving membranes that significantly enhance recharge efficiency and long-term stability of Li-S batteries. Our membrane consists of an insulating Li-anode side and an electrically conductive S-cathode side. The insulating side consists of a standard polypropylene separator, while the conductive side is made of closely packed multilayers of high-aspect-ratio MOF/graphene nanosheets having a thickness of few nanometers and a specific surface area of 996 m² g^-1 (MOF, metal-organic framework). Our models and experiments reveal that this electrically conductive microporous nanosheet architecture enables the reuse of polysulfide trapped in the membrane and decreases the polysulfide flux and concentration on the anode side by a factor of 250× over recent microporous membranes made of granular MOFs and standard battery separators. Notably, Li-S batteries using our Janus microporous membranes achieve an outstanding rate capability and long-term stability with 75.3% capacity retention over 1700 cycles. We demonstrate the broad applicability of our high-aspect-ratio MOF/graphene nanosheet preparation strategy by the synthesis of a diverse range of MOFs, including ZIF-67, ZIF-8, HKUST-1, NiFe-BTC, and Ni-NDC, providing a flexible approach for the design of Janus microporous membranes and electrically conductive microporous building blocks for energy storage and various other electrochemical applications.

Efficient suppression of the shuttle effect in Na-S batteries with an As2S3 anchoring monolayer

Sodium-sulfur batteries (NaSBs) have emerged as a promising energy storage technology for large-scale stationary applications such as smart electrical grids due to their exceptionally high energy density and cost-effectiveness. However, one of the challenging problems impeding their practical applications is the sulfur shuttle effect by which the active redox intermediates are gradually dissolved in electrolytes. In this work, we have employed first-principles density functional theory (DFT) calculations to unravel the suppression of the shuttle effect in NaSBs with a two-dimensional (2D) As2S3 monolayer as the anchoring material. We show that semiconducting As2S3 is a suitable anchoring layer to inhibit the dissolution of the polysulfide intermediates in common electrolytes because of its stronger chemical binding with sodium polysulfides than with the electrolytes. The immense adsorption is attributed to the electron donation from the unfilled S-3p states of the polysulfides to As2S3. These mechanisms increase the carrier population and consequently improve the electrical conductivity of As2S3. Hence, the use of As2S3 can both reduce the shuttle effect and enhance the cathode electron conductivity to enable improved cycling stability and coulombic efficiency of the battery.