Mesoporous Nitrogen-Doped Carbon Nanospheres as Sulfur Matrix and a Novel Chelate-Modified Separator for High-Performance Room-Temperature Na-S 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.

Chemical and spatial dual-confinement engineering for stable Na-S batteries with approximately 100% capacity retention

Sodium-sulfur (Na-S) batteries are attracting intensive attention due to the merits like high energy and low cost, while the poor stability of sulfur cathode limits the further development. Here, we report a chemical and spatial dual-confinement approach to improve the stability of Na-S batteries. It refers to covalently bond sulfur to carbon at forms of C-S/N-C=S bonds with high strength for locking sulfur. Meanwhile, sulfur is examined to be S1-S2 small species produced by thermally cutting S8 large molecules followed by sealing in the confined pores of carbon materials. Hence, the sulfur cathode achieves a good stability of maintaining a high-capacity retention of 97.64% after 1000 cycles. Experimental and theoretical results show that Na+ is hosted via a coordination structure (N···Na···S) without breaking the C-S bond, thus impeding the formation and dissolution of sodium polysulfide to ensure a good cycling stability. This work provides a promising method for addressing the S-triggered stability problem of Na-S batteries and other S-based batteries.

Role of inorganic layers on polysulfide decomposition at sodium-metal anode surfaces for room temperature Na/S batteries

Sodium metal is a promising anode material for room-temperature sodium sulfur batteries. Due to its high reactivity, typical liquid electrolytes (e.g. carbonate-based solvents and a Na salt) can undergo reduction to form a solid electrolyte interphase (SEI) layer, with inorganic components such as Na2CO3, Na2O, and NaOH, covering the anode surface along with other SEI organic products. One of the challenges is to understand the effect of the SEI film on the decomposition of soluble sodium polysulfide molecules (e.g., Na2S8) upon shuttling from the cathode to anode during battery cycling. Here, we use ab initio molecular dynamics (AIMD) simulations to study the role of an inorganic SEI used as a model passivation layer in polysulfide decomposition. Compared to other film chemistries, it is found that the Na2CO3 film can suppress decomposition with the slowest reduction rate and the smallest amount of charge transfer towards Na2S8. The Na2CO3 film can maintain its structural properties during the simulations. In contrast, Na2O and NaOH allow some decomposed polysulfide fragments to be inserted into the SEI layer. Moreover, the decomposition of Na2S8 on both Na2O and NaOH SEI layers is more reactive with more charge transfer to Na2S8 when compared to that of Na2CO3. Thus, the ability of the SEI to suppress polysulfide decomposition is in the order: Na2CO3 > NaOH ∼ Na2O. Analyses of the density of states reveal that the Na2S8 molecule receives electrons from the Na metal directly in the presence of n-type semiconductor films of Na2CO3 and NaOH, while the charge migration behavior is different in a p-type semiconductor Na2O with the SEI film donating its electrons to the polysulfide solely. Thus, this work adds new insights into charge transfer behavior of inorganic thin film SEIs that could be present at the initial stages of SEI formation.

Core-Shell Tandem Catalysis Coupled with Interface Engineering For High-Performance Room-Temperature Na-S Batteries

The sluggish redox kinetics and shuttle effect seriously impede the large application of room-temperature sodium-sulfur (RT Na-S) batteries. Designing effective catalysts into cathode material is a promising approach to overcome the above issues. However, considering the multistep and multiphase transformations of sulfur redox process, it is impractical to achieve the effective catalysis of the entire S8 →Na2 Sx →Na2 S conversion through applying a single catalyst. Herein, this work fabricates a nitrogen-doped core-shell carbon nanosphere integrated with two different catalysts (ZnS-NC@Ni-N4 ), where isolated Ni-N4 sites and ZnS nanocrystals are distributed in the shell and core, respectively. ZnS nanocrystals ensure the rapid reduction of S8 into Na2 Sx (4 < x ≤ 8), while Ni-N4 sites realize the efficient conversion of Na2 Sx into Na2 S, bridged by the diffusion of Na2 Sx from the core to shell. Besides, Ni-N4 sites on the shell can also induce an inorganic-rich cathode-electrolyte interface (CEI) on ZnS-NC@Ni-N4 to further inhibit the shuttle effect. As a result, ZnS-NC@Ni-N4 /S cathode exhibits an excellent rate-performance (650 mAh g-1 at 5 A g-1 ) and ultralong cycling stability for 2000 cycles with a low capacity-decay rate of 0.011% per cycle. This work will guide the rational design of multicatalysts for high-performance RT Na-S batteries.

Ce-Doped Three-Dimensional Ni/Fe LDH Composite as a Sulfur Host for Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) have become the most promising choice in the new generation of energy storage/conversion equipment due to their high theoretical capacity of 1675 mAh g-1 and theoretical energy density of 2600 Wh kg-1. Nevertheless, the continuous shuttling of lithium polysulfides (LiPSs) restricts the commercial application of LSBs. The appearance of layered double hydroxides (LDH) plays a certain role in the anchoring of LiPSs, but its unsatisfactory electronic conductivity and poor active sites hinder its realization as a sulfur host for high-performance LSBs. In this paper, metal organic framework-derived and Ce ion-doped LDH (Ce-Ni/Fe LDH) with a hollow capsule configuration is designed rationally. The hollow structure of Ce-Ni/Fe LDH contains a sufficient amount of sulfur. Fe, Ni, and Ce metal ions effectively trap LiPSs; speed up the conversion of LiPSs; and firmly anchor LiPSs, thus effectively inhibiting the shuttle of LiPSs. The electrochemical testing results demonstrate that a lithium-sulfur battery with capsule-type S@Ce-Ni/Fe LDH delivers the initial discharge capacities of 1207 mAh g-1 at 0.1 C and 1056 mAh g-1 at 0.2 C, respectively. Even at 1 C, a lithium-sulfur battery with S@Ce-Ni/Fe LDH can also cycle 1000 times. This work provides new ideas to enhance the electrochemical properties of LSBs by constructing a hollow capsule configuration.

Coordinated Immobilization and Rapid Conversion of Polysulfide Enabled by a Hollow Metal Oxide/Sulfide/Nitrogen-Doped Carbon Heterostructure for Long-Cycle-Life Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are recognized as the prospective candidate in next-generation energy storage devices due to their gratifying theoretical energy density. Nonetheless, they still face the challenges of the practical application including low utilization of sulfur and poor cycling life derived from shuttle effect of lithium polysulfides (LiPSs). Herein, a hollow polyhedron with heterogeneous CoO/Co9 S8 /nitrogen-doped carbon (CoO/Co9 S8 /NC) is obtained through employing zeolitic imidazolate framework as precursor. The heterogeneous CoO/Co9 S8 /NC balances the redox kinetics of Co9 S8 with chemical adsorption of CoO toward LiPSs, effectively inhibiting the shuttle of LiPSs. The mechanisms are verified by both experiment and density functional theory calculation. Meanwhile, the hollow structure acts as a sulfur storage chamber, which mitigates the volumetric expansion of sulfur and maximizes the utilization of sulfur. Benefiting from the above advantages, lithium-sulfur battery with S-CoO/Co9 S8 /NC achieves a high initial discharge capacity (1470 mAh g-1 ) at 0.1 C and long cycle life (ultralow capacity attenuation of 0.033% per cycle after 1000 cycles at 1 C). Even under high sulfur loading of 3.0 mg cm-2 , lithium-sulfur battery still shows the satisfactory electrochemical performance. This work may provide an idea to elevate the electrochemical performance of LSBs by constructing a hollow metal oxide/sulfide/nitrogen-doped carbon heterogeneous structure.

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.

Anchoring polysulfides via a CoS2/NC@1T MoS2 modified separator for high-performance lithium–sulfur batteries

CoS2/NC@1T MoS2 synthesized by a one-step hydrothermal method forms a unique hierarchical configuration with simultaneous internal and external modifications. A lithium–sulfur battery with a CoS2/NC@1T MoS2-PP separator shows superior cycling performance.

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.

Azo-Branched Covalent Organic Framework Thin Films as Active Separators for Superior Sodium-Sulfur Batteries

Sodium-Sulfur (Na-S) batteries are outstanding for their ultrahigh capacity, energy density, and low cost, but they suffer from rapid cell capacity decay and short lifespan because of serious polysulfide shuttle and sluggish redox kinetics. Herein, we synthesize thin films of covalent organic frameworks (COFs) with azobenzene side groups branched to the pore walls. The azobenzene branches deliver dual functions: (1) narrow the pore size to the sub-nanometer scale thus inhibiting the polysulfide shuttle effect and (2) act as ion-hopping sites thus promoting the Na⁺ migration. Consequently, the Na-S battery using the COF thin film as the separator exhibits a high capacity of 1295 mA h g^-1 at 0.2 C and an extremely low attenuation rate of 0.036% per cycle over 1000 cycles at 1 C. This work highlights the importance of separator design in upgrading Na-S batteries and demonstrates the possibility of functionalizable framework materials in developing high-performance energy storage systems.

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.

A Review on the Construction of Carbon-Based Metal Compound Composite Cathode Materials 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, environmental friendliness, and ultra-high energy density. However, due to the inherent slow redox kinetics and the shuttle of polysulfides, the road of room temperature sodium-sulfur batteries to practical application is still full of difficulties. As a sulfur cathode, which is directly related to battery performance, a lot of research efforts have been devoted to it and many strategies have been proposed to solve the shuttle effect problem of sulfur cathodes. This paper analyzes the existing problems and solutions of sodium-sulfur batteries, mainly discusses and summarizes the research progress of constructing carbon-based cathode materials for sodium-sulfur batteries, and expounds the current research popular from two main directions. That is to construct advanced cathode materials based on two mechanisms of adsorption and electrocatalysis. Finally, the research direction of advanced sodium-sulfur batteries is prospected.

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.

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.

Synthesis and Hydrodynamic Modeling Study of Epoxy/Carbon Nanospheres (Epoxy-CNS) Composite Coatings for Water Filtration Applications

Coatings for filtration applications based on epoxy resin mixtures with isopropanol were synthesized using the dip-coating technique. The nanomaterials used were carbon nanospheres (CNS) synthesized by chemical vapor deposition (CVD) and commercially obtained Vulcan XC-72 (VC). The permeation flux and permeability of the coatings were determined by vacuum filtration of pure water applying different working pressures obtaining maximum values of 0.5555 cm3/s and 1.19 × 10−9 m2, respectively, for the CNS6 coating at 26,664 Pa. The minimum values obtained for the permeation flux and permeability were 0.0011 cm3/s and 1.21 × 10−11 m2, for the coating CNS3 at 39,996 Pa. This study analyzed the effect of nanomaterials and the addition of isopropanol at different volumes on the permeability of the coatings. The results show that the permeability was influenced by the number of pores present rather than by their diameter. The number of pores were obtained between the ranges 1–12 μm for all the coatings. The study of computational fluid dynamics (CFD) through a free and porous medium, showed that it is possible to accurately determine flow velocities (m/s) through and inside the composite coatings. Understanding the flow behavior is a practical strategy to predict the performance of new nanocomposite coatings.

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.

In situ implanting MnO nanoparticles into carbon nanorod-assembled microspheres enables performance-enhanced room-temperature Na–S batteries

In situ implanting MnO fine nanoparticles into carbon nanorod-assembled microspheres enables improved electrode stability and electrochemical performance via structural and compositional synergy.

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.

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.

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.

Towards high performance room temperature sodium-sulfur batteries: Strategies to avoid shuttle effect

Room temperature sodium-sulfur battery has high theoretical specific energy and low cost, so it has good application prospect. However, due to the disadvantageous reaction between soluble intermediate polysulfides and sodium anode, the capacity drops sharply, which greatly limits its practical application. In recent years, various strategies have been formulated to address the problem of polysulfides dissolution. This perspective article provides an overview of the research progress on research progress of novel cathode materials, multifunctional host, new electrolyte systems and modified separator/interlayer/anode. The challenge and prospect of the advanced strategies to suppress the polysulfides shuttle for long-life and high-efficiency room temperature sodium-sulfur batteries are proposed.

Research Progress toward Room Temperature Sodium Sulfur Batteries: A Review

Lithium metal batteries have achieved large-scale application, but still have limitations such as poor safety performance and high cost, and limited lithium resources limit the production of lithium batteries. The construction of these devices is also hampered by limited lithium supplies. Therefore, it is particularly important to find alternative metals for lithium replacement. Sodium has the properties of rich in content, low cost and ability to provide high voltage, which makes it an ideal substitute for lithium. Sulfur-based materials have attributes of high energy density, high theoretical specific capacity and are easily oxidized. They may be used as cathodes matched with sodium anodes to form a sodium-sulfur battery. Traditional sodium-sulfur batteries are used at a temperature of about 300 °C. In order to solve problems associated with flammability, explosiveness and energy loss caused by high-temperature use conditions, most research is now focused on the development of room temperature sodium-sulfur batteries. Regardless of safety performance or energy storage performance, room temperature sodium-sulfur batteries have great potential as next-generation secondary batteries. This article summarizes the working principle and existing problems for room temperature sodium-sulfur battery, and summarizes the methods necessary to solve key scientific problems to improve the comprehensive energy storage performance of sodium-sulfur battery from four aspects: cathode, anode, electrolyte and separator.

Cotton cloth templated in situ encapsulation of sulfur into carbon fibers for lithium-sulfur batteries

An in situ encapsulation strategy for embedding sulfur within carbon (S@C) fiber through a sustainable and scalable route using waste cotton cloth as a fiber template, is developed. The S@C fibers with reasonably high sulfur content of ∼71% displayed promising electrochemical performance when employed as a cathode material for a lithium sulfur battery (LSB). The S@C fibers developed herein have the potential to be used as a promising cathode material for other sulfur-based batteries as well.