Tunable Nitrogen-Doping of Sulfur Host Nanostructures for Stable and Shuttle-Free Room-Temperature Sodium-Sulfur Batteries

Synergistic Electrocatalysis and Spatial Nanoconfinement to Accelerate Sulfur Conversion Kinetics in Aqueous Zn-S Battery

Aqueous zinc batteries based on the conversion-type sulfur cathodes are promising in energy storage system due to the high theoretical energy density, low cost, and good safety. However, the multi-electron solid-state intermediate conversion reaction of sulfur cathodes generally possess sluggish kinetics, which leads to lower discharge voltage and inefficient sulfur utilization, thus suppressing the practical energy density. Herein, sulfur nanoparticles derived from metal-organic frameworks confined in situ within electrospun fibers derived sulfur and nitrogen co-doped carbon nanofibers (S@S,N-CNF) composite, which possesses yolk-shell S@C nanostructure, is fabricated through successive sulfidation, pyrolysis, and sulfide oxidation processes, and served as a high-performance cathode material for Zn-S battery. The S and N dopants on carbon can collectively catalyse sulfur reduction reaction (SRR) by lowering energy barrier and accelerating kinetics to increase discharge voltage and specific capacity. Meanwhile, the yolk-shell S@C structure with spatially confined S nanoparticle yolks is beneficial to improve charge transfer and lower activation energy, thus further expediting SRR kinetics. Furthermore, extensive density functional theory (DFT) calculations reveal that S and N dual-doping can thermodynamically and dynamically reduce the energy barrier of rate-determining step (i.e., the transformation of *ZnS4 into *ZnS2) for the overall SRR, thereby significantly accelerating SRR kinetics.

Synthesis of hierarchical porous carbon scaffold derived from red kidney bean peels for advanced Li-Se and Na-Se batteries

Incorporating selenium into high-surface-area carbon with hierarchical pores, derived from red kidney bean peels via simple carbonization/activation, yields a superior Li-Se battery cathode material. This method produces a carbon framework with 568 m2 g-1 surface area, significant pore volume, and improves the composite's electronic conductivity and stability by mitigating volume changes and reducing lithium polyselenide dissolution. The Se@ACRKB composite, containing 45 wt% selenium, shows high discharge capacities (609.13 mAh g-1 on the 2nd cycle, maintaining 470.76 mAh g-1 after 400 cycles at 0.2 C, and 387.58 mAh g-1 over 1000 cycles at 1 C). This demonstrates exceptional long-term stability and performance, also applicable to Na-Se batteries, with 421.36 mAh g-1 capacity after 200 cycles at 0.1 C. Our study showcases the potential of using sustainable materials for advanced battery technologies, emphasizing cost-effective and scalable solutions for energy storage.

Chitin-Derived Hierarchical Meso- and Microporous Carbon Enables High-Rate Sulfur Cathode of Sodium-Sulfur Batteries

Room temperature Na-S batteries are considered as a promising alternative energy storage system because of their abundant material resources and high theoretical energy density. However, the severe polysulfide shuttle effect and slow reaction kinetics hinder their practical application. Herein, a hierarchical meso- and microporous carbon with nitrogen self-doping (NSPC) is prepared using chitin as the carbon precursor and serves as a novel host to confine the sulfur (S⊂NSPC). An optimized structure of NSPC, including abundant graphite nanocrystals, large pore volume of 1.76 cm3 g-1, and large specific surface area of 2073 m2 g-1 is obtained at the carbonization temperature of 1000 °C. These merits contribute to significantly enhanced charge transfer and ion diffusion of the as-prepared S⊂NSPC-1000 cathode, which exhibits the outstanding sodium storage performance, including high reversible capacities of 1207 mAh g-1 at 0.1 C and 891 mAh g-1 at 2 C and stable cycling with a low capacity decay for 400 cycles at 1 C, among other S⊂NSPC cathodes and previously reported cathodes for Na-S batteries. This cathode can also afford stable cycling at a high sulfur loading.

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.

Molybdenum single-atoms decorated multi-channel carbon nanofibers for advanced lithium-selenium batteries

The cathode in lithium-selenium (Li-Se) batteries has garnered extensive attention owing to its superior specific capacity and enhanced conductivity compared to sulfur. Nonetheless, the adoption and advancement of Li-Se batteries face significant challenges due to selenium's low reactivity, substantial volume fluctuations, and the shuttle effect associated with polyselenides. Single-atom catalysts (SACs) are under the spotlight for their outstanding catalytic efficiency and optimal atomic utilization. To address the challenges of selenium's low chemical activity and volume expansion in Li-Se batteries, through electrospun, we have developed a lotus root-inspired carbon nanofiber (CNF) material, featured internal multi-channels and anchored with molybdenum (Mo) single atoms (Mo@CNFs). Mo single atoms significantly enhance the conversion kinetics of selenium (Se), facilitating rapid formation of Li2Se. The internally structured multi-channel CNF serves as an effective host matrix for Se, mitigating its volume expansion during the electrochemical process. The resulting cathode, Se/Mo@CNF composite, exhibits a high discharge specific capacity, superior rate performance, and impressive cycle stability in Li-Se batteries. After 500 cycles at a current density of 1 C, it maintains a capacity retention rate of 82% and nearly 100% coulombic efficiency (CE). This research offers a new avenue for the application of single-atom materials in enhancing advanced Li-Se battery performance.

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.

Double design of host and guest synergistically reinforces the Na-ion storage of sulfur cathodes

Development of room-temperature sodium-sulfur batteries is significantly hampered by the shuttle effect of soluble intermediates and intrinsically sluggish conversion kinetics. In this work, a double design host and guest strategy (i.e., implantation of a polar V₂O₃ adsorbent into a carbon substrate and selenium doping of a sulfur guest) is proposed to synergistically reinforce the electrochemical properties of sulfur electrodes in sodium ion storage. The V₂O₃ adsorbent efficiently immobilizes sulfur species via strong polar-polar interactions, while the selenium dopant improves the electronic conductivity of sulfur cathodes and accelerates the redox conversion of sulfur cathodes. The synergistic effect between the V₂O₃ adsorbent and selenium dopant is shown to inhibit the shuttle effect and improve the redox kinetics, thus realizing greatly enhanced Na-ion storage properties of sulfur cathodes. The as-designed sulfur cathode delivers a superior rate capability of 663 mA h g^-1 at 2.0 A g^-1 and demonstrates excellent cyclability of 405 mA h g^-1 over 700 cycles at 1.0 A g^-1.

Single-Atom Vanadium Catalyst Boosting Reaction Kinetics of Polysulfides in Na-S Batteries

The practical application of the room-temperature sodium-sulfur (RT Na-S) batteries is hindered by the insulated sulfur, the severe shuttle effect of sodium polysulfides, and insufficient polysulfide conversion. Herein, on the basis of first principles calculations, single-atom vanadium anchored on a 3D nitrogen-doped hierarchical porous carbon matrix (denoted as 3D-PNCV) is designed and fabricated to enhance sulfur reactivity, and adsorption and catalytic conversion performance of sodium polysulfide. The 3D-PNCV host with abundant and active V sites, hierarchical porous structure, high electrical conductivity, and strong chemical adsorption/conversion ability of V-N bonding can immobilize the polysulfides and promote reversibly catalytic conversion of polysulfides toward Na₂ S. Therefore, as-fabricated RT Na-S batteries can achieve a high reversible capacity (445 mAh g^-1 over 800 cycles at 5 A g^-1 ) and excellent rate capability (224 mAh g^-1 at 10 A g^-1 ). The electrocatalysis mechanism of sodium polysulfides is further experimentally and theoretically revealed, which provides a new strategy to develop the highly stable RT Na-S batteries.

Oxygen vacancy-mediated amorphous GeOx assisted polysulfide redox kinetics for room-temperature sodium-sulfur batteries

The practical applications of room-temperature sodium-sulfur (RT Na-S) batteries have been greatly hindered by the natural sluggish reaction kinetics of sulfur and the shuttle effect of sodium polysulfide (NaPSs). Herein, oxygen vacancy (OV)-mediated amorphous GeOx/nitrogen doped carbon (donated as GeOx/NC) composites were well designed as sulfur hosts for RT Na-S batteries. Experimental and density functional theory studies show that the introduction of oxygen vacancies on GeOx/NC can effectively immobilize polysulfides and accelerate the redox kinetics of polysulfides. Meanwhile, the micro-and mesoporous framework, acting as a reactor for storing active S, is conducive to alleviating the expansion of S during the charging/discharging process. Consequently, the S@GeOx/NC cathode affords a reversible capacity of 1017 mA h g-1 at 0.1 A g-1 after 100 cycles, outstanding rate capability of 333 mA h g-1 at 10.0 A g-1 and long lifespan cyclability of 385 mAh g-1 at 1 A g-1 after 1200 cycles. This work furnishes a new way for the rational design of metal oxides with oxygen vacancies and boosts the application for RT Na-S batteries.

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.

Porosity Engineering towards Nitrogen-Rich Carbon Host Enables Ultrahigh Capacity Sulfur Cathode for Room Temperature Potassium-Sulfur Batteries

Potassium-sulfur batteries (KSBs) are regarded as a promising large-scale energy storage technology, owing to the high theoretical specific capacity and intrinsically low cost. However, the commercialization of KSBs is hampered by the low sulfur utilization and notorious shuttle effect. Herein, we employ a porosity engineering strategy to design nitrogen-rich carbon foam as an efficient sulfur host. The tremendous micropores magnify the chemical interaction between sulfur species and the polar nitrogen functionalities decorated carbon surface, which significantly improve the sulfur utilization and conversion. Meanwhile, the abundant mesopores provide ample spaces, accommodating the large volume changes of sulfur upon reversible potassation. Resultantly, the constructed sulfur cathode delivers an ultrahigh initial reversible capacity of 1470 mAh g^-1 (87.76% of theoretical capacity) and a superior rate capacity of 560 mAh g^-1 at 2 C. Reaching the K₂S phase in potassiation is the essential reason for obtaining the ultrahigh capacity. Nonetheless, systematic kinetics analyses demonstrate that the K₂S involved depotassiation deteriorates the charge kinetics. The density functional theory (DFT) calculation revealed that the nitrogen-rich micropore surface facilitated the sulfur reduction for K₂S but created a higher energy barrier for the K₂S decomposition, which explained the discrepancy in kinetics modification effect produced by the porosity engineering.

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.

Binder-Free and High-Loading Cathode Realized by Hierarchical Structure for Potassium-Sulfur Batteries

Potassium-sulfur batteries have attracted significant research attention owing to the naturally abundant resources of potassium and sulfur, and have promising applications in large-scale energy storage systems. However, the sluggish reaction kinetics of K⁺ , low reaction activity of sulfur species, shuttling effect of polysulfides, and large volume change impede the development of these batteries. Moreover, the conventional electrode fabrication method with binders and current collectors renders it difficult to improve the areal sulfur loading and energy density. In this study, a binder-free and freestanding sulfur cathode is prepared by phase inversion and sulfurization of polyacrylonitrile. This sulfur cathode, with a hierarchically porous network, enables a high reversible capacity of 1345 mAh g^-1 and a stable cycling performance with a capacity decay of 0.15% per cycle. Importantly, areal capacities of 3.1 and 4.2 mAh cm^-2 are achieved even at high sulfur loadings of 3 and 7 mg cm^-2 , owing to the favorable electron/ion transport in the cathode. The facile preparation method and excellent electrochemical properties reported herein can pave the way for developing high-performance K-S 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.

Sulfurized Cyclopentadienyl Nanocomposites for Shuttle-Free Room-Temperature Sodium-Sulfur Batteries

A major challenge hindering the practical adoption of room-temperature sodium-sulfur batteries (NaSBs) is polysulfide dissolution and shuttling, which results in irreversible capacity decay and low Coulombic efficiencies. In this work, we demonstrate for the first time NaSBs using a ferrocene-derived amorphous sulfurized cyclopentadienyl composite (SCC) cathode. Polysulfide dissolution is eliminated via covalent bonding between the insoluble short-chain sulfur species and carbon backbone. Control experiments with a metal-free composite analogue determined that the iron species in the SCC does not have a significant role in polysulfide anchoring. Instead, the superior electrochemical performance is attributed to sulfur covalently bonded to carbon and the uniform nanoparticulate morphology of the SCC composite. In the carbonate-based electrolyte, a discharge capacity of 795 mAh g_(S)^-1 was achieved during early cycling at 0.2 C, and high Coulombic efficiencies close to 100% were maintained with capacity retention of 532 and 442 mAh g_(S)^-1 after 100 and 200 cycles, respectively.

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.