Enhanced Adsorptions to Polysulfides on Graphene-Supported BN Nanosheets with Excellent Li-S Battery Performance in a Wide Temperature Range

In-situ synthesis Fe3C@C/rGO as matrix for high performance lithium-sulfur batteries at room and low temperatures

People have been focusing on how to improve the specific capacity and cycling stability of lithium-sulfur batteries at room temperature, however, on some special occasions such as cold cities and aerospace fields, the operating temperature is low, which dramatically hinders the performance of batteries. Here, we report an iron carbide (Fe3C)/rGO composite as electrode host, the Fe3C nanoparticles in the composite have strong adsorption and high catalytic ability for polysulfide. The rGO makes the distribution of Fe3C nanoparticles more disperse, and this specific structure makes the deposition of Li2S more uniform. Therefore, it realizes the rapid transformation and high performance of lithium-sulfur batteries at both room and low temperatures. At room temperature, after 100 cycles at 1C current density, the reversible specific capacity of the battery can be stabilized at 889 ± 7.1 mAh/g. Even at -40 °C, in the first cycle battery still emits 542.9 ± 3.7 mAh/g specific capacity. This broadens the operating temperature for lithium-sulfur batteries and also provides a new idea for the selection of host materials for sulfur in low-temperature lithium-sulfur batteries.

Accelerating the Rate-Determining Steps of Sulfur Conversion Reaction for Lithium-Sulfur Batteries Working at an Ultrawide Temperature Range

Wide operation temperature is the crucial objective for an energy storage system that can be applied under harsh environmental conditions. For lithium-sulfur batteries, the "shuttle effect" of polysulfide intermediates will aggravate with the temperature increasing, while the reaction kinetics decreases sharply as the temperature decreasing. In particular, sulfur reaction mechanism at low temperatures seems to be quite different from that at room temperature. Here, through in situ Raman and electrochemical impedance spectroscopy studies, the newly emerged platform at cryogenic temperature corresponds to the reduction process of Li2S8 to Li2S4, which will be another rate-determining step of sulfur conversion reaction, in addition to the solid-phase conversion process of Li2S4 to Li2S2/Li2S at low temperatures. Porous bismuth vanadate (BiVO4) spheres are designed as sulfur host material, which achieve the rapid snap-transfer-catalytic process by shortening lithium-ion transport pathway and accelerating the targeted rate-determining steps. Such promoting effect greatly inhibits severe "shuttle effect" at high temperatures and simultaneously improves sulfur conversion efficiency in the cryogenic environment. The cell with the porous BiVO4 spheres as the host exhibits excellent rate capability and cycle performance under wide working temperatures.

Reinforcing the Adsorption and Conversion of Polysulfides in Li-S Battery by Incorporating Molybdenum into MnS/MnO Nanorods

The Sabatier principle suggests that an excessive adsorption of lithium polysulfides (LiPSs) by metal compounds may hinder their conversion in the absence of a conversion module. Therefore, it is imperative to establish a synergetic effect mechanism between "strong adsorption" and "rapid conversion" for LiPSs. To achieve this coexistence, a molybdenum-doped MnS/MnO@C porous structure is designed as a multifunctional coating on the polypropylene (PP) separator. The incorporation of MnS/MnO@C enhances the adsorption capacity towards LiPSs, while molybdenum facilitates subsequent conversion. Benefiting from the synergistic effect of each component and its large specific surface area, the cell with Mo-doped MnS/MnO@C coating achieves smooth adsorption-diffusion-conversion processes and exhibits an appreciable rate performance with outstanding cycling stability. Even when sulfur loading increases to 9.68 mg cm-2 , the modified battery delivers an excellent initial areal capacity of 11.69 mAh cm-2 and maintains 6.97 mAh cm-2 after 50 cycles at 0.1 C. This study presents a promising approach to simultaneously accomplish "strong adsorption" and "rapid conversion" of polysulfides, offering novel perspectives for devising dual-functional modified separators.

Investigation of the Chemisorption-Catalysis Behavior of Sulfur Species on the Electrocatalysts Designed by Co-regulation Strategy of Anions and Cations

Li-S batteries possess high energy density and have been one of the most promising energy storage systems. For sulfur cathodes, the electrochemical performance is still seriously hindered by the polysulfide shuttling and sluggish conversion kinetics. It has been demonstrated to be one effective strategy to address the above issues via designing electrocatalysts with robust affinity and catalytic capacity towards polysulfides. However, it is still a great challenge to rapidly and economically discover high-performance electrocatalysts. Herein, using density functional theory calculation, we studied the chemisorption-catalysis behavior of sulfur species on a series of electrocatalysts (MCo2 X4 , M=Co, Zn, Cu, Ni, Fe, and Mn, X=O, S, and Se) to assess the effect of the anions and cations co-regulation on their electronic structure, chemisorption behavior, and catalytic property. FeCo2 Se4 and CuCo2 Se4 combined appropriate chemisorption with superior electronic conductivity and sulfur reduction catalytic capacity have been predicted as novel electrocatalysts for high-performance Li-S batteries. This study gives theoretical guidance for rapid discovery of high-efficient electrocatalyst to boost the electrochemical performance of sulfur cathodes.

Theoretical prediction of 2D biphenylene as a potential anchoring material for lithium-sulfur batteries

Searching for good anchoring materials that can suppress the shuttle effect is critical to large-scale commercialization of lithium-sulfur (Li-S) batteries. In this work, the adsorption behavior of lithium polysulfides (LiPSs, such as S8 and Li2Sn, n = 1, 2, 4, 6, and 8), the sulfur reduction reaction (SRR), the decomposition processes of Li2S and the diffusion behavior of Li atoms on intrinsic and doped 2D biphenylene (BIP) are systematically investigated by employing the first-principles calculation method. Calculations show that the adsorption energies of LiPSs on the electrolyte (DOL and DME) are smaller than those on the intrinsic/B doped BIP. The moderate anchoring strength (0.8-2.0 eV) between LiPSs and the BIP can effectively suppress the shuttle effect. Moreover, the Gibbs free energy barrier for SRR is 0.72/0.64 eV on intrinsic/B doped BIP. The dissociation energy barrier of Li2S on intrinsic/B doped BIP is 1.35 eV, while the diffusion energy barrier of Li atoms on intrinsic/B doped BIP is 0.18 eV/0.30 eV. Lower energy barriers are conducive to enhancing the discharging and charging efficiency. Therefore, intrinsic and B doped BIP are predicted as good anchoring materials for Li-S batteries.

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

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

Challenges and Solutions for Low-Temperature Lithium-Sulfur Batteries: A Review

The lithium-sulfur (Li-S) battery is considered to be one of the attractive candidates for breaking the limit of specific energy of lithium-ion batteries and has the potential to conquer the related energy storage market due to its advantages of low-cost, high-energy density, high theoretical specific energy, and environmental friendliness issues. However, the substantial decrease in the performance of Li-S batteries at low temperatures has presented a major barrier to extensive application. To this end, we have introduced the underlying mechanism of Li-S batteries in detail, and further concentrated on the challenges and progress of Li-S batteries working at low temperatures in this review. Additionally, the strategies to improve the low-temperature performance of Li-S batteries have also been summarized from the four perspectives, such as electrolyte, cathode, anode, and diaphragm. This review will provide a critical insight into enhancing the feasibility of Li-S batteries in low-temperature environments and facilitating their commercialization.

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

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

Efficient Regulation of Polysulfides by MoS2 /MoO3 Heterostructures for High-Performance Li-S Batteries

The notorious shuttle effect and sluggish conversion of polysulfides seriously hinder the practical application of Lithium-sulfur (Li-S) batteries. In this study, a novel architecture of MoS₂ /MoO₃ heterostructure uniformly distributed on carbon nanotubes (MoS₂ /MoO₃ @CNT) is designed and introduced into Li-S batteries via decorating commercial separator to regulate the redox reactions of polysulfides. Systematic experiments and theoretical calculations showed that the heterostructure not only provides sufficient surface affinity to capture polysulfides and acts as an active catalyst to promote the conversion of polysulfides, but also the highly conductive CNT enables rapid electron/ion migration. As a result, Li-S batteries with the MoS₂ /MoO₃ @CNT-PP separator deliver an impressive reversible capacity (1015 mAh g^-1 at 0.2 A g^-1 after 100 cycles), excellent rate capacity (873 mAh g^-1 at 5 A g^-1 ), and low self-discharge capacity loss (94.6% capacity retention after 7 days of standing). Moreover, even at an elevated temperature of 70 °C, it still exhibits high-capacity retention (800 mAh g^-1 at 1 A g^-1 after 100 cycles). Encouragingly, when the sulfur load is increased to 8.7 mg cm^-2 , the high reversible areal capacity of 6.61 mAh cm^-2 can be stably maintained after 100 cycles, indicating a high potential for practical application.

Medium-Entropy-Alloy FeCoNi Enables Lithium-Sulfur Batteries with Superb Low-Temperature Performance

Lithium-sulfur battery suffers from sluggish kinetics at low temperatures, resulting in serious polarization and reduced capacity. Here, this work introduces medium-entropy-alloy FeCoNi as catalysts and carbon nanofibers (CNFs) as hosts. FeCoNi nanoparticles are in suit synthesized in cotton-derived CNFs. FeCoNi with atomic-level mixing of each element can effectively modulate lithium polysulfides (LiPSs), multiple components making them promising to catalyze more LiPSs species. The higher configurational entropy endows FeCoNi@CNFs with extraordinary electrochemical activity, corrosion resistance, and mechanical properties. The fractal structure of CNFs provides a large specific surface area, leaving room for volume expansion and Li₂ S accumulation, facilitating electrolyte wetting. The unique 3D conductive network structure can suppress the shuttle effect by physicochemical adsorption of LiPSs. This work systematically evaluates the performance of the obtained Li₂ S₆ /FeCoNi@CNFs electrode. The initial discharge capacity of Li₂ S₆ /FeCoNi@CNFs reaches 1670.8 mAh g^-1 at 0.1 C under -20 °C. After 100 cycles at 0.2 C, the capacity decreases from 1462.3 to 1250.1 mAh g^-1 . Notably, even under -40 °C at 0.1 C, the initial discharge capacity of Li₂ S₆ /FeCoNi@CNFs still reaches 1202.8 mAh g^-1 . After 100 cycles at 0.2 C, the capacity retention rate is 50%. This work has important implications for the development of low-temperature Li-S batteries.

Ultrafine Co-Species Interspersed g-C3N4 Nanosheets and Graphene as an Efficient Polysulfide Barrier to Enable High Performance Li-S Batteries

Lithium-sulfur (Li-S) batteries are regarded as one of the promising advanced energy storage systems due to their ultrahigh capacity and energy density. However, their practical applications are still hindered by the serious shuttle effect and sluggish reaction kinetics of soluble lithium polysulfides. Herein, g-C₃N₄ nanosheets and graphene decorated with an ultrafine Co-species nanodot heterostructure (Co@g-C₃N₄/G) as separator coatings were designed following a facile approach. Such an interlayer can not only enable effective polysulfide affinity through the physical barrier and chemical binding but also simultaneously have a catalytic effect on polysulfide conversion. Because of these superior merits, the Li-S cells assembled with Co@g-C₃N₄/G-PP separators matched with the S/KB composites (up to ~70 wt% sulfur in the final cathode) exhibit excellent rate capability and good cyclic stability. A high specific capacity of ~860 mAh g^-1 at 2.0 C as well as a capacity-fading rate of only ~0.035% per cycle over 350 cycles at 0.5 C can be achieved. This bifunctional separator can even endow a Li-S cell at a low current density to exhibit excellent cycling capability, with a capacity retention rate of ~88.4% at 0.2 C over 250 cycles. Furthermore, a Li-S cell with a Co@g-C₃N₄/G-PP separator possesses a stable specific capacity of 785 mAh g^-1 at 0.2 C after 150 cycles and a superior capacity retention rate of ~84.6% with a high sulfur loading of ~3.0 mg cm^-2. This effective polysulfide-confined separator holds good promise for promoting the further development of high-energy-density Li-S batteries.

Ni Single Atoms on MoS2 Nanosheets Enabling Enhanced Kinetics of Li-S Batteries

The practical application of Li-S batteries is seriously hindered due to its shuttle effect and sluggish redox reaction, which requires a better functional separator to solve the problems. Herein, polypropylene separators modified by MoS₂ nanosheets with atomically dispersed nickel (Ni-MoS₂ ) are prepared to prevent the shuttle effect and facilitate the redox kinetics for Li-S batteries. Compared with pristine MoS₂ nanosheets, Ni-MoS₂ nanosheets exhibit both excellent adsorption and catalysis performance for overcoming the shuttle effect. Assembled with this novel separator, the Li-S batteries exhibit an admirable cycling stability at 2 C over 400 cycles with 0.01% per cycle decaying. In addition, even with a high sulfur loading of 7.5 mg cm^-2 , the battery still provides an initial capacity of 6.9 mAh cm^-2 and remains 5.9 mAh cm^-2 after 50 cycles because of the fast convention of polysulfides catalyzed by Ni-MoS₂ nanosheets, which is further confirmed by the density functional theory (DFT) calculations. Therefore, the proposed strategy is expected to offer a new thought for single atom catalyst applying in Li-S batteries.

Structural Design and Fabrication of Multifunctional Nanocarbon Materials for Extreme Environmental Applications

Extreme environments represent numerous harsh environmental conditions, such as temperature, pressure, corrosion, and radiation. The tolerance of applications in extreme environments exemplifies significant challenges to both materials and their structures. Given the superior mechanical strength, electrical conductivity, thermal stability, and chemical stability of nanocarbon materials, such as carbon nanotubes (CNTs) and graphene, they are widely investigated as base materials for extreme environmental applications and have shown numerous breakthroughs in the fields of wide-temperature structural-material construction, low-temperature energy storage, underwater sensing, and electronics operated at high temperatures. Here, the critical aspects of structural design and fabrication of nanocarbon materials for extreme environments are reviewed, including a description of the underlying mechanism supporting the performance of nanocarbon materials against extreme environments, the principles of structural design of nanocarbon materials for the optimization of extreme environmental performances, and the fabrication processes developed for the realization of specific extreme environmental applications. Finally, perspectives on how CNTs and graphene can further contribute to the development of extreme environmental applications are presented.

Enhanced Performance of Li-S Batteries due to Synergistic Adsorption and Catalysis Activity within a Separation Coating Made of Hybridized BNNSs/N-Doping Porous Carbon Fibers

Lithium-sulfur (Li-S) batteries with high theoretical energy density are considered as the most promising devices for rechargeable energy-storage systems. However, their actual applications are rather limited by the shuttle effect of lithium polysulfides (LiPSs) and the sluggish redox kinetics. Here, the boron nitride nanosheets are homodispersedly embedded into N-doping porous carbon fibers (BNNSs/CHFs) by an electrospinning technique and a subsequent in situ pyrolysis process. The hybridized BNNSs/CHFs can be smartly designed as a multifunctional separation coating onto the commercial PP membrane to enhance the electrochemical performance of Li-S batteries. As a result, the Li-S batteries with extra BNNSs/CHF modification deliver a highly reversible discharge capacity of 830.4 mA h g^-1 at a current density of 1 C. Even under 4 C, the discharge specific capacity can reach up to 609.9 mA h g^-1 and maintain at 553.9 mA h g^-1 after 500 cycles, showing a low capacity decay of 0.01836% per cycle. It is considered that the excellent performance is attributed to the synergistic effect of adsorption and catalysis of the BNNSs/CHF coating used. First, this coating can efficiently reduce the charge transfer resistance and enhance Li-ion diffusion, due to increased catalytic activity from strong electronic interactions between BNNSs and N-doping CHFs. Second, the combination of polar BNNSs and abundant pore structures within the hybridized BNNSs/CHF networks can highly facilitate an adsorption for LiPSs. Here, we believed that this work would provide a promising strategy to increase the Li-S batteries' performance by introducing hybridized BNNSs/N-doping carbon networks, which could efficiently suppress the LiPSs' shuttle effect and improve the electrochemical kinetics of Li-S batteries.

Thin Nano Cages with Limited Hollow Space for Ultrahigh Sulfur Loading Lithium-Sulfur Batteries

Owning to its various advantages, the lithium-sulfur battery is one of the research hot spots for new energy storage systems. Diverse hollow structures with specific morphologies have been used as the sulfur host materials to adsorb or/and catalyze the polysulfides, and can in particular concurrently inhibit the volume expansion during electrochemical processes in lithium-sulfur batteries. However, hollow space with a large volume will restrict the performance of the cell under high sulfur area loading, which is a very important indicator for the practical applications of the lithium-sulfur battery. Here, we report a nano thin cage cobalt acid zinc (ZnCo₂O₄) with limited hollow space as the cathode catalyst for lithium-sulfur batteries, which greatly reduces the electrode volume occupied by the hollow structure. The hollow volume of these thin cages is much smaller than those of the normally reported hollow materials in the literatue. The electrochemical performance of lithium-sulfur batteries with ZnCo₂O₄ thin cages could greatly improve due to the unique structure and the synergistic adsorption/catalytic effect of Zn/Co sites, especially at an ultrahigh S area load. Under a high S loading of 8 mg cm^-2, the cell could keep a reversible capacity of 600 mAh g^-1 after 500 cycles. Even at a sulfur loading of 10 mg cm^-2, the cell still releases a discharge capacity of 1000 mAh g^-1 which is equivalent of an area capacity of 10 mAh cm^-2. This work provides a feasible way to develop lithium sulfur batteries with a high area sulfur load. This idea provides a possible solution to develop a Li-S battery at high area S loading and move one step closer to the practical applications.

Stable Liquid-Sulfur Generation on Transition-Metal Dichalcogenides toward Low-Temperature Lithium-Sulfur Batteries

The electrochemical formation of liquid sulfur at room temperature on the basal plane of MoS₂ has attracted much attention due to the high areal capacity and rapid kinetics of lithium-liquid sulfur chemistry. However, the liquid sulfur is converted to the solid phase once it contacts the solid sulfur crystals generated from the edge of MoS₂. Thus, stable liquid sulfur cannot be formed on the entire MoS₂ surface. Herein, we report entire liquid sulfur generation on hydrogen-annealed MoS₂ (H₂-MoS₂), even under harsh conditions of large overpotentials and low working temperatures. The origins of the solely liquid sulfur formation are revealed to be the weakened interactions between H₂-MoS₂ and sulfur molecules and the decreased electrical polarization on the edges of the H₂-MoS₂. Progressive nucleation and droplet-merging growth behaviors are observed during the sulfur formation on H₂-MoS₂, signifying high areal capacities by releasing active H₂-MoS₂ surfaces. To demonstrate the universality of this strategy, other transition-metal dichalcogenides (TMDs) annealed in hydrogen also exhibit similar sulfur growth behaviors. Furthermore, the H₂ annealing treatment can induce sulfur vacancies on the basal plane and partial oxidation on the edge of TMDs, which facilitates liquid sulfur formation. Finally, liquid sulfur can be generated on H₂-MoS₂ flakes at an ultralow temperature of -50 °C, which provides a possible development of low-temperature lithium-sulfur batteries. This work demonstrates the potential of a pure liquid sulfur-lithium electrochemical system using functionalized two-dimensional materials.

Covalent organic framework wrapped by graphene oxide as an efficient sulfur host for high performance lithium-sulfur batteries

The practical application of lithium-sulfur battery is seriously limited by the loss of active substances and the deterioration of cycle stability caused by the 'shuttle effect' of lithium polysulfides (LiPSs). In this work, graphene oxide (GO) coated covalent organic framework (COF) compound materials were synthesized as sulfur host material in spray-drying process. The polar groups on COF can efficiently adsorb LiPSs through lithiophilic interaction, which can reduce the 'shuttle effect' caused by soluble LiPSs. Besides, GO in the outer layer can wrap discrete sulfur to reduce the loss of active substances, which further improves the cycle stability of the cathode. The COF@GO/S cathode exhibits a high initial specific capacity of 848.4 mAh g^-1and retains a capacity of 601.1 mAh g^-1after 500 cycles at 1 C counting with a low capacity fading of 0.058% per cycle.

Boron, nitrogen co-doped biomass-derived carbon aerogel embedded nickel-cobalt-iron nanoparticles as a promising electrocatalyst for oxygen evolution reaction

The electrocatalytic performance of oxygen evolution reaction (OER) electrocatalysts is highly reliant on the activity of its catalytic active site, which may be augmented by raising the number of active sites. In this study, nanoscaled nickel-cobalt-iron (NiCoFe) alloy was embedded on conductive boron(B), nitrogen(N) co-doped/biomass-derived carbon aerogel as an OER electrocatalyst. The synthesized electrocatalysts were calcined under different temperatures and with variable dopants. The optimal electrocatalyst (BN/CA-NiCoFe-600) demonstrated a low overpotential of 321 mV (at current density of 10 mA cm^-2) and a minute Tafel slope of 42 mV dec^-1, which was even smaller than that of IrO₂ and RuO₂. Its mass activity and specific activity were calculated to be 201.7 A g^-1, and 34.1 cm^-2_ECSA, respectively. Furthermore, the electrocatalyst showed excellent stability and durability. This work provides an easy and practical synthetic strategy for acquiring very active and durable electrocatalysts for OER.

A Li2S-based all-solid-state battery with high energy and superior safety

Safety risks stem from applying extremely reactive alkali metal anodes and/or oxygen-releasing cathodes in flammable liquid electrolytes restrict the practical use of state-of-the-art high-energy batteries. Here, we propose a intrinsically safe solid-state cell chemistry to satisfy both high energy and cell reliability. An all-solid-state rechargeable battery is designed by energetic yet stable multielectron redox reaction between Li₂S cathode and Si anode in robust solid-state polymer electrolyte with fast ionic transport. Such cells can deliver high specific energy of 500 to 800 Wh kg⁻¹ for 500 cycles with fast rate response, negligible self-discharge, and good temperature adaptability. Integrating intrinsic safe cell chemistry to robust cell design further guarantees reversible energy storage against extreme abuse of overheating, overcharge, short circuit, and mechanical damage in the air and water. This work may shed fresh insight into bridging the huge gap between high energy and safety of rechargeable cells for feasible applications and recycle.

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

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

A Lamellar Yolk-Shell Lithium-Sulfur Battery Cathode Displaying Ultralong Cycling Life, High Rate Performance, and Temperature Tolerance

The shuttling behavior and slow conversion kinetics of the intermediate lithium polysulfides are the severe obstacles for the application of lithium-sulfur (Li-S) batteries over a wide temperature range. Here, an engineered lamellar yolk-shell structure of In2 O3 @void@carbon for the Li-S battery cathode is developed for the first time to construct a powerful barrier that effectively inhibits the shuttling of polysulfides. On the basis of the unique nanochannel-containing morphology, the continuous kinetic transformation of sulfur and polysulfides is confined in a stable framework, which is demonstrated by using X-ray nanotomography. The constructed Li-S battery exhibits a high cycling capability over 1000 cycles at 1.0 C with a capacity decay rate as low as 0.038% per cycle, good rate performance, and temperature tolerance at -10, 25, and 50 °C. A nondestructive in situ monitoring method of the interfacial reaction resistance in different cycling stages is proposed, which provides a new analysis perspective for the development of emerging electrochemical energy-storage systems.

Combined enhanced redox kinetics and physiochemical confinement in three-dimensionally ordered macro/mesoporous TiN for highly stable lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with tremendous energy density possess great promise for the next-generation energy storage devices. Even though, the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) seriously restrict practical applications of Li-S batteries. Herein, a three-dimensionally ordered macro/mesoporous TiN (3DOM TiN) nanostructure is established via using poly (methyl methacrylate) PMMA spheres as template. The interconnected macro/mesoporous channels are constructed to effectively alleviate the stacking of composite materials and render a large portion of inherent active sites exposed on the surface region. Moreover, TiN exhibits high electrical conductivity, which efficiently enhances charge-transfer kinetics and guarantees the favorable electrochemical performance of sulfur cathode. More importantly, the as-prepared 3DOM TiN suppresses the shuttle effect and improves the redox kinetics significantly due to strong affinity toward LiPSs. Attributed to these unique features, the S/3DOM TiN electrode achieves an ultrahigh initial discharge capacity of 1187 mAh g^-1at 0.2 C, and stable cycling performance of 552 mAh g^-1over 500 cycles at 1 C. Meanwhile, the discharge capacity retention of 701 mAh g^-1(3.5 mAh cm^-2) can be endowed for the S/3DOM TiN electrode under high sulfur loading of 5 mg cm^-2after 100 cycles at 0.1 C. Therefore, the 3DOM TiN nanostructure electrocatalyst provides a promising path for developing practically useable Li-S batteries.

Boron nitride nanosheets wrapped by reduced graphene oxide for promoting polysulfides adsorption in lithium-sulfur batteries

The polysulfides shuttling and slow redox kinetics of sulfur-based cathodes have severely hindered the commercialization of lithium-sulfur (Li-S) batteries. Herein, distinctive three-dimensional microspheres composed of boron nitride (BN) nanosheets and reduced graphene oxide (rGO) were applied to act as efficient sulfur cathode hosts for the first time using in a spray-drying process. Using this construction, the robust microsphere structure could shorten ion diffusion pathways and supply sufficient spaces to alleviate the volumetric expansion of sulfur during lithiation. Besides, the synergistic effect between BN and rGO significantly enhanced polysulfides adsorption capability and accelerated their conversion, verified by the density functional theory (DFT) calculations and adsorption experiments. Consequently, the S-BN@rGO cathode could manifest the high initial capacity (1137 mAh g^-1 at 0.2 C) and remarkable cycling/stability performance (572 mAh g^-1 at 1 C after 500 cycles). These results shed light on a design concept of high-performance sulfur cathode host materials.

Chemical Sulfide Tethering Improves Low-Temperature Li-S Battery Cycling

Demands for energy storage and delivery continue to rise worldwide, making it imperative that reliable performance is achievable in diverse climates. Lithium-sulfur (Li-S) batteries offer a promising alternative to lithium-ion batteries owing to their substantially higher specific capacity and energy density. However, improvements to Li-S systems are still needed in low-temperature environments where polysulfide clustering and solubility limitations prohibit complete charge/discharge cycles. We address these issues by introducing thiophosphate-functionalized metal-organic frameworks (MOFs), capable of tethering polysulfides, into the cathode architecture. Compared to cells with the parent MOFs, cells containing the functionalized MOFs exhibit greater capacity delivery and decreased polarization for a range of temperatures down to -10 °C. We conduct thorough electrochemical analyses to ascertain the origins of performance differences and report an altered Li-S redox mechanism enabled by the thiophosphate moiety. This investigation is the first low-temperature Li-S study using MOF additives and represents a promising direction in enabling energy storage in extreme environments.

All-Liquid-Phase Reaction Mechanism Enabling Cryogenic Li-S Batteries

The sluggish solid-solid conversion kinetics from Li₂S₄ to Li₂S during discharge is considered the main problem for cryogenic Li-S batteries. Herein, an all-liquid-phase reaction mechanism, where all the discharging intermediates are dissolved in the functional thioether-based electrolyte, is proposed to significantly enhance the kinetics of Li-S battery chemistry at low temperatures. A fast liquid-phase reaction pathway thus replaces the conventional slow solid-solid conversion route. Spectral investigations and molecular dynamics simulations jointly elucidate the greatly enhanced kinetics due to the highly decentralized state of solvated intermediates in the electrolyte. Overall, the battery brings an ultrahigh specific capacity of 1563 mAh g^-1_{sulfur in the cathode} at -60 °C. This work provides a strategy for developing cryogenic Li-S batteries.

Manipulating Redox Kinetics of Sulfur Species Using Mott-Schottky Electrocatalysts for Advanced Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries suffer from sluggish sulfur redox reactions under high-sulfur-loading and lean-electrolyte conditions. Herein, a typical Co@NC heterostructure composed of Co nanoparticles and a semiconductive N-doped carbon matrix is designed as a model Mott-Schottky catalyst to exert the electrocatalytic effect on sulfur electrochemistry. Theoretical and experimental results reveal the redistribution of charge and a built-in electric field at the Co@NC heterointerface, which are critical to lowering the energy barrier of polysulfide reduction and Li₂S oxidation in the discharge and charge process, respectively. With Co@NC Mott-Schottky catalysts, the Li-S batteries display an ultrahigh capacity retention of 92.1% and a system-level gravimetric energy density of 307.8 Wh kg^-1 under high S loading (10.73 mg cm^-2) and lean electrolyte (E/S = 5.9 μL mg_sulfur^-1) conditions. The proposed Mott-Schottky heterostructure not only deepens the understanding of the electrocatalytic effect in Li-S chemistry but also inspires a rational catalyst design for advanced high-energy-density batteries.

Emerging of Heterostructure Materials in Energy Storage: A Review

With the ever-increasing adaption of large-scale energy storage systems and electric devices, the energy storage capability of batteries and supercapacitors has faced increased demand and challenges. The electrodes of these devices have experienced radical change with the introduction of nano-scale materials. As new generation materials, heterostructure materials have attracted increasing attention due to their unique interfaces, robust architectures, and synergistic effects, and thus, the ability to enhance the energy/power outputs as well as the lifespan of batteries. In this review, the recent progress in heterostructure from energy storage fields is summarized. Specifically, the fundamental natures of heterostructures, including charge redistribution, built-in electric field, and associated energy storage mechanisms, are summarized and discussed in detail. Furthermore, various synthesis routes for heterostructures in energy storage fields are roundly reviewed, and their advantages and drawbacks are analyzed. The superiorities and current achievements of heterostructure materials in lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), lithium-sulfur batteries (Li-S batteries), supercapacitors, and other energy storage devices are discussed. Finally, the authors conclude with the current challenges and perspectives of the heterostructure materials for the fields of energy storage.

Unifying the Clustering Kinetics of Lithium Polysulfides with the Nucleation Behavior of Li2S in Lithium-Sulfur Batteries

Within the lithium-sulfur (Li-S) battery, a wide variety of soluble lithium polysulfide intermediates form during operation. Under lean-electrolyte or low-temperature conditions, the solution coordination of polysulfides dynamically shifts to highly clustered states, which is subsequently accompanied by inhibited electrochemical kinetics. In fact, it has been shown that the tendency for polysulfides to strongly aggregate is one of the dominant kinetically limiting obstacles towards achieving adequate utilization of active material under such conditions. While this association has been noted before, it is not explicitly understood what mechanism intrinsic to polysulfide clustering curtails the electrochemical utilization of active material, particularly during the conversion to insoluble Li2S. Here, we perform a series of investigations to unify and link the kinetic constraints that arise from polysulfide clustering to the nucleation and growth behavior of Li2S. We find that there is a drastic decrease in polysulfide diffusion coefficient arising from the advent of clustering, and that this decline functionally matches that seen for the nucleation and growth rate constants for Li2S deposition. Additionally, it is found that there is a less favorable minimization of energy during Li2S nucleation, arising from the altered solvation stability of polysulfide clusters. This knowledge expands our understanding of the Li-S materials chemistry and the primary factors dictating the electrochemical behavior.

Embedding Fe3C and Fe3N on a Nitrogen-Doped Carbon Nanotube as a Catalytic and Anchoring Center for a High-Areal-Capacity Li-S Battery

The biggest obstacles of putting lithium-sulfur batteries into practice are the sluggish redox kinetics of polysulfides and serious "shuttle effect" under high sulfur mass loading and lean-electrolyte conditions. Herein, Fe₃C/Fe₃N@nitrogen-doped carbon nanotubes (NCNTs) as multifunctional sulfur hosts are designed to realize high-areal-capacity Li-S batteries. The Fe₃N and Fe₃C particles attached to NCNT can promote the conversion of polysulfides. Besides, NCNT can not only enhance the chemisorption of polysulfides but also increase the special surface area and electrical conductivity by constructing a three-dimensional skeleton network. Integrating the merits of high electrical conductivity, high catalytic activity, and strong chemical binding interaction with lithium polysulfides (LiPSs) to achieve in situ anchoring conversion, the Fe₃C/Fe₃N@NCNT multifunctional hosts realize high sulfur mass loading and accelerate redox kinetics. The novel Fe₃C/Fe₃N@NCNT/S composite cathode exhibits steady cycle ability and a high areal capacity of 9.10 mAh cm^-2 with a sulfur loading of 13.12 mg cm^-2 at 2.20 mA cm^-2 after 50 cycles.

Turning Soluble Polysulfide Intermediates Back into Solid State by a Molecule Binder in Li-S Batteries

The shuttle effect of dissolved polysulfides produced during the operation of lithium-sulfur batteries is the most serious and fundamental problem among many challenges. We propose a strategy via in situ formation of a functionalized molecule with a dual-terminal coupling function to bind the dissolved polysulfide intermediates, thus turning them back into solid-state organopolysulfide complexes by molecule binding, and then the polysulfides can be pinned on the cathode firmly. The dual-terminal coupling functional molecule binder (MB), which is formed in situ by reaction between quinhydrone (QH) and lithium, can not only bind polysulfides by reversible chemical coordination but also promote the conversion of polysulfides during cycling synchronously. In theory, with the dual-terminal coupling function, MB can bind polysulfide intermediates to copolymerize them, forming -[MB-Li₂S_n]- that has faster reaction activity and redox conversion kinetics in comparison with simple Li₂S_n. With the MB, the Li-S battery exhibits a large initial capacity of 1347 mAh g^-1 at 0.1 C. The remaining capacity of 963 mAh g^-1 at 1 C shows no obvious decay for more than 400 cycles, and the retention of the first 300 cycles can reach 96.9%, in particular. This study delivers an alternative approach to resolving the shuttle effect and achieving excellent Li-S battery performance, with the potential significance going way beyond battery systems.

Designing Advanced Lithium-based Batteries for Low-temperature Conditions

Energy-dense rechargeable batteries have enabled a multitude of applications in recent years. Moving forward, they are expected to see increasing deployment in performance-critical areas such as electric vehicles, grid storage, space, defense, and subsea operations. While this at first glance spells great promise for conventional lithium-ion batteries, all of these use-cases, unfortunately, share periodic and recurring exposures to extremely low-temperature conditions, a performance constraint where the lithium-ion chemistry can fail to perform optimally. Next-generation chemistries employing alternative anodes with increased solvent compatibility or altogether different operating mechanisms could present an avenue for overcoming many of the low-temperature hurdles intrinsic to the lithium-ion battery. In this article, we provide a brief overview of the challenges in developing lithium-ion batteries for low-temperature use, and then introduce an array of nascent battery chemistries that may be intrinsically better suited for low-temperature conditions moving forward. Specifically, we evaluate the prospects of using lithium-metal, lithium-sulfur, and dual-ion batteries for performance-critical low-temperature applications. These three chemistries are presented as prototypical examples of how the conventional low-temperature charge-transfer resistances can be overcome. However, these three chemistries also present their own unique challenges at low temperatures, highlighting the balance between traditional low-temperature electrolyte design and next-generation approaches.

A Perspective toward Practical Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have long been expected to be a promising high-energy-density secondary battery system since their first prototype in the 1960s. During the past decade, great progress has been achieved in promoting the performances of Li-S batteries by addressing the challenges at the laboratory-level model systems. With growing attention paid to the application of Li-S batteries, new challenges at practical cell scales emerge as the bottleneck. In this Outlook, the key parameters for practical Li-S batteries to achieve practical high energy density are emphasized regarding high-sulfur-loading cathodes, lean electrolytes, and limited excess anodes. Subsequently, the key scientific problems are redefined in practical Li-S batteries beyond the previous ones under ideal conditions. Finally, viable strategies are proposed to address the above challenges as future research directions.

Influence of Lithium Polysulfide Clustering on the Kinetics of Electrochemical Conversion in Lithium-Sulfur Batteries

The electrochemistry of lithium-sulfur (Li-S) batteries is heavily reliant on the structure and dynamics of lithium polysulfides, which dissolve into the liquid electrolyte and mediate the electrochemical conversion process during operation. This behavior is considerably distinct from the widely used lithium-ion batteries, necessitating new mechanistic insights to fully understand the electrochemical phenomena. Testing at low-temperature conditions presents a unique opportunity to glean new insights into the chemistry in kinetically constrained environments. Under such conditions, despite the low freezing point and favorable ionic conductivity of the glyme-based electrolyte, Li-S batteries exhibit counterintuitively poor performance. Here, we show that beyond just existing in single-molecule conformations, lithium polysulfides tend to cluster and aggregate in solution, particularly at low-temperature conditions, which subsequently constrains the kinetics of electrochemical conversion. Energetics and coordination implications of this behavior are extended towards a new framework for understanding the solution-coordination dynamics of dissolved lithium species. Based off this framework, a favorable strongly-bound lithium salt is introduced in the Li-S electrolyte to disrupt polysulfide clustered networks, enabling substantially enhanced low-temperature electrochemical performance. More broadly, this mechanistic insight heightens our understanding of polysulfide chemistry irrespective of temperature, confirming the link between the solution conformation of active material and electrochemical behavior.

Engineering Oxygen Vacancies in a Polysulfide-Blocking Layer with Enhanced Catalytic Ability

The practical application of the lithium-sulfur (Li-S) battery is seriously restricted by its shuttle effect, low conductivity, and low sulfur loading. Herein, first-principles calculations are conducted to verify that the introduction of oxygen vacancies in TiO₂ not only enhances polysulfide adsorption but also greatly improves the catalytic ability and both the ion and electron conductivities. A commercial polypropylene (PP) separator decorated with TiO₂ nanosheets with oxygen vacancies (OVs-TiO₂ @PP) is fabricated as a strong polysulfide barrier for the Li-S battery. The thickness of the OVs-TiO₂ modification layer is only 500 nm with a low areal mass of around 0.12 mg cm^-2 , which enhances the fast lithium-ion penetration and the high energy density of the whole cell. As a result, the cell with the OVs-TiO₂ @PP separator exhibits a stable electrochemical behavior at 2.0 C over 500 cycles, even under a high sulfur loading of 7.1 mg cm^-2 , and an areal capacity of 5.83 mAh cm^-2 remains after 100 cycles. The proposed strategy of engineering oxygen vacancies is expected to have wide applications in Li-S batteries.

Conductive and Catalytic VTe2@MgO Heterostructure as Effective Polysulfide Promotor for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are recognized as one of the most promising energy storage systems due to the high energy density and cost effectiveness. However, their practical implementation has still been handicapped due to notorious lithium polysulfide (LiPS) shuttle and depressed sulfur redox kinetics. It is therefore desirable to exploit key mediators synergizing electrical conductivity and electrocatalytic activity for the cathode. Herein, we report the employment of atmospheric pressure chemical vapor deposition to harness the efficient and controllable synthesis of metallic VTe₂ over particulated MgO substrates, which has scarcely been demonstrated by conventional wet-chemical synthetic routes thus far. The thus-derived VTe₂@MgO heterostructure as an efficient promotor enables effective regulation of LiPSs with respect to polysulfide capture/conversion and Li₂S decomposition. As a result, a S/VTe₂@MgO cathode with a sulfur loading of 1.6 mg cm^-2 harvests long-term cyclability with a negligible capacity decay of 0.055% per cycle over 1000 cycles at 1.0 C. Even at a sulfur loading of 6.9 mg cm^-2, the cathode still delivers electrochemical performances that can rival the state-of-the-art high-loading counterparts. Our work might offer a feasible solution for developing heterostructured promotors with multifunctionality and electrocatalytic activity for high-performance Li-S batteries.

Designing a Multifunctional Separator for High-Performance Li-S Batteries at Elevated Temperature

The practical applications of lithium-sulfur (Li-S) batteries are seriously limited by the undesirable polysulfide shuttling and lithium dendrite growth. Herein, a multifunctional membrane is designed and prepared by coating a lithiated Nafion (Li@Nafion) layer and an Al₂ O₃ layer on the two sides of a routine polymer membrane (polypropylene/polyethylene/polypropylene, PEP). The Li@Nafion layer faced to the sulfur cathode builds a "polysulfide-phobic" surface to restrain the shuttle effect via Coulomb repulsion, while the Al₂ O₃ layer with a uniform porous structure aids in regulating homogeneous Li⁺ fluxes to achieve stable Li electrodeposition. As a result, the Li//Li symmetric cell with a Li@Nafion/PEP/Al₂ O₃ (LNPA) separator realizes stable Li plating/striping even after 1000 h at a high current density (5 mA cm^-2 ). Moreover, the Li-S batteries incorporating LNPA separators not only can achieve excellent outstanding cyclic stability at an ultrahigh sulfur loading (7.6 mg cm^-2 ), but also exhibit impressive electrochemical performance at an elevated temperature (60 °C). The rational design of the LNPA separator presents new insights to develop high-performance Li-S batteries.

Two-dimensional boron nitride as a sulfur fixer for high performance rechargeable aluminum-sulfur batteries

Aluminum-ion batteries (AIBs) are regarded as promising candidates for post-lithium-ion batteries due to their lack of flammability and electrochemical performance comparable to other metal-ion batteries. The lack of suitable cathode materials, however, has hindered the development of high-performing AIBs. Sulfur is a cost-efficient material, having distinguished electrochemical properties, and is considered an attractive cathode material for AIBs. Several pioneering reports have shown that aluminum-sulfur batteries (ASBs) exhibit superior electrochemical capacity over other cathode materials for AIBs. However, a rapid decay in the capacity is a huge barrier for their practical applications. Here, we have demonstrated systematically for the first time that the two-dimensional layered materials (e.g. MoS2, WS2, and BN) can serve as fixers of S and sulfide compounds during repeated charge/discharge processes; BN/S/C displays the highest capacity of 532 mAh g-1 (at a current density of 100 mA g-1) compared with the current state-of-the-art cathode material for AIBs. Further, we could improve the life-span of ASBs to an unprecedented 300 cycles with a high Coulombic efficiency of 94.3%; discharge plateaus at ~1.15 V vs. AlCl4-/Al was clearly observed during repeated charge/discharge cycling. We believe that this work opens up a new method for achieving high-performing ASBs.

Construction of Electrocatalytic and Heat-Resistant Self-Supporting Electrodes for High-Performance Lithium-Sulfur Batteries

Boosting the utilization efficiency of sulfur electrodes and suppressing the "shuttle effect" of intermediate polysulfides remain the critical challenge for high-performance lithium-sulfur batteries (LSBs). However, most of reported sulfur electrodes are not competent to realize the fast conversion of polysulfides into insoluble lithium sulfides when applied with high sulfur loading, as well as to mitigate the more serious shuttle effect of polysulfides, especially when worked at an elevated temperature. Herein, we reported a unique structural engineering strategy of crafting a unique hierarchical multifunctional electrode architecture constructed by rooting MOF-derived CoS₂/carbon nanoleaf arrays (CoS₂-CNA) into a nitrogen-rich 3D conductive scaffold (CTNF@CoS₂-CNA) for LSBs. An accelerated electrocatalytic effect and improved polysulfide redox kinetics arising from CoS₂-CNA were investigated. Besides, the strong capillarity effect and chemisorption of CTNF@CoS₂-CNA to polysulfides enable high loading and efficient utilization of sulfur, thus leading to high-performance LIBs performed not only at room temperature but also up to an elevated temperature (55 °C). Even with the ultrahigh sulfur loading of 7.19 mg cm^-2, the CTNF@CoS₂-CNA/S cathode still exhibits high rate capacity at 55 °C.

Current Status and Future Prospects of Metal-Sulfur Batteries

Lithium-sulfur batteries are a major focus of academic and industrial energy-storage research due to their high theoretical energy density and the use of low-cost materials. The high energy density results from the conversion mechanism that lithium-sulfur cells utilize. The sulfur cathode, being naturally abundant and environmentally friendly, makes lithium-sulfur batteries a potential next-generation energy-storage technology. The current state of the research indicates that lithium-sulfur cells are now at the point of transitioning from laboratory-scale devices to a more practical energy-storage application. Based on similar electrochemical conversion reactions, the low-cost sulfur cathode can be coupled with a wide range of metallic anodes, such as sodium, potassium, magnesium, calcium, and aluminum. These new "metal-sulfur" systems exhibit great potential in either lowering the production cost or producing high energy density. Inspired by the rapid development of lithium-sulfur batteries and the prospect of metal-sulfur cells, here, over 450 research articles are summarized to analyze the research progress and explore the electrochemical characteristics, cell-assembly parameters, cell-testing conditions, and materials design. In addition to highlighting the current research progress, the possible future areas of research which are needed to bring conversion-type lithium-sulfur and other metal-sulfur batteries into the market are also discussed.

Multifunctional Ion-Sieve Constructed by 2D Materials as an Interlayer for Li-S Batteries

For Li-S batteries, the interlayer between the separator and sulfur cathode preventing lithium polysulfide (LiPS) travel across the membrane is a research hotspot. The good blocking ability for LiPSs indicates that these interlayers can promote the electrochemistry performance with high S loading. However, most of these interlayers are just used as a simple blocking wall. Such a blocking wall, for example, the lower Li⁺ ion conductivity, would often reduce the electrochemical performance, especially under large current density. Here, we report a multifunctional ion-sieve made by three two-dimensional (2D) sheets, graphitic carbon nitride (g-C₃N₄), boron nitride (BN), and graphene. A g-C₃N₄ sheet which possesses orderly channels with a size of 3 Å in the crystalline structure can effectively prevent polysulfides from passing through but allow lithium ions to pass freely, whereas a BN sheet acts as an excellent catalyst for sulfur redox, and graphene acts as an extended collector, which can promote the conductivity of the sulfur electrode region. Benefiting from the synergistic effect among these 2D materials, the ion-sieve interlayer makes the Li-S battery show excellent performance at a large rate with both high sulfur loadings and high sulfur content. In addition, the host materials are not necessary in these cells. The ion-sieve liberated a discharge capacity of about 600 mA h g^-1 after 500 cycles at 1 C, and the capacity attenuation was less than 0.01% per cycle with a 6 mg cm^-2 areal S-loading (pure S as the active material). The reversible capacity could be maintained at more than 400 mA h g^-1 at 2 C, which amounts to an area current density of 26.88 mA cm^-2.