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While the sulfur conversion reaction kinetics in Li–S batteries is nowadays improved by the use of appropriate electrocatalysts, it remains a challenge for the batteries to perform well under the lean electrolyte condition where polysulfide shuttle, electrode passivation and the loss of electrolyte due to side reactions, are aggravated. These challenges are addressed in this study by the tandem use of a polysulfide conversion catalyst and a redox–targeting mediator in a gel sulfur cathode. Specifically, the gel cathode reduces the polysulfide mobility and hence the polysulfide shuttle and the passivation of the lithium anode by the crossover polysulfides. The redox mediator restrains the deposition of inactive sulfur species in the cathode thereby enabling the Fe–N and Co–N co–doped carbon catalyst to prolong its catalytic activity. Consequently, the integrated catalytic system is able to increase the discharge capacity of high–loading (6.8 mg cm–2) lean–electrolyte (4.0 µL mg–1) Li–S batteries from ∼630 to ∼1316 mAh g–1, concurrently with an improvement of the cycle life (600 cycles with 46% capacity retention at 1.0 mA cm−2). Redox mediator assisted catalysis in a gel cathode is therefore an effective strategy to extend the application of the sulfur conversion catalyst in lean electrolyte Li–S batteries.

Utilizing catalysts to accelerate the redox kinetics of lithium polysulfides (LiPSs) is a promising strategy to alleviate the shuttle effect of lithium−sulfur (Li−S) batteries. Nevertheless, most of the reported catalysts are only effective for LiPSs reduction, resulting in the devitalization of catalysts over extended cycles as a consequence of the continuous accumulation of Li2S passivation layer. The situation gets even worse when employing mono-directional catalyst with poor electron conductivity because the charge transfer for the decomposition of solid Li2S is severely hampered. Herein, a high-conductive and dual-directional catalyst Co3C decorated on porous nitrogen-doped graphene-like structure and carbon nanotube (Co3C@PNGr-CNT) is fabricated as sulfur host, which not only promotes the precipitation of Li2S from LiPSs during discharge but also facilitates the decomposition of Li2S during subsequent charge, as evidenced by the reduced activation energies for both reduction and oxidation processes. Furthermore, the long-term catalytic stability of Co3C is corroborated by the reversible evolution of Co–C bond length over extended cycles as observed from X-ray absorption fine structure results. As a consequence, the fabricated Co3C@PNGr-CNT/S cathode delivers a low capacity decay of 0.043% per cycle over 1000 cycles at 2 C. Even at high sulfur loading (15.6 mg cm−2) and low electrolyte/sulfur (E/S) ratio (∼8 μL mg−1) conditions, the battery still delivers an outstanding areal capacity of 11.05 mAh cm−2 after 40 cycles. This work provides a rational strategy for designing high-efficient bidirectional catalyst with single component for high-performance Li-S batteries.

The homogeneous distribution of nano-sulfur onto 3D structures for the development of high-performance Li-S batteries (LSBs) is a top concern to solve the low utilization of sulfur, sluggish redox kinetics, and lithium polysulfide (LiPS) shuttle effect. Herein, a novel “egg tray” hierarchical architecture of confining and uniformly distributing nano-sulfur into a 3D holey graphene (HG) framework with polyaniline crosslinking (3DHG/NS/CPANI) via photo-assisted method was designed for high-mass-loading LSB cathode. Notably, HG contains both conductive skeletons as electron transfer paths and abundant void spaces in favor of homogenous sulfur anchoring. This configuration improves the contact between nano-sulfur and graphene for effective charge transportation and provides buffering space for volume variations during electrochemical processes. Moreover, a facile photo-assisted method was developed to cross link HG with polyaniline to act as an efficient polysulfide adsorbent, allowing nano-sulfur (NS) to be firmly embedded into the holes of graphene through physical and chemical effects, thus prohibiting the dissolution and shuttle effect of polysulfide. Considering these advantages, the prepared 3DHG/NS/CPANI electrode exhibited excellent performance with high sulfur utilization and specific capacity, resulting in specific discharge capacities at 0.5 and 1 C of 1082 and 921 mA h −1, respectively, and small capacity decay of 0.04% per cycle over 500 cycles at 1 C. The strategy in this work, which synergistically combines morphology control, nano-sulfur positioning, and structural engineering to enhance the electrochemical performance for Li−S batteries, will offer a valuable reference to energy storage and conversion advances.

The defect engineering shows great potential in boosting the conversion of lithium polysulfides intermediates for high energy density lithium-sulfur batteries (LSBs), yet the catalytic mechanisms remain unclear. Herein, the oxygen-defective Li4Ti5O12-x hollow microspheres uniformly encapsulated by N-doped carbon layer (OD-LTO@NC) is delicately designed as an intrinsically polar inorganic sulfur host for the research on the catalytic mechanism. Theoretical simulations have demonstrated that the existence of oxygen deficiencies enhances the adsorption capability of spinel Li4Ti5O12 towards soluble lithium polysulfides. Some -S-S- bonds of the Li2S6 on the defective Li4Ti5O12 surface are fractured by the strong adsorption force, which allows the inert bridging sulfur atoms to be converted into the susceptible terminal sulfur atoms, and reduces the activation energy of the polysulfide conversion in some degree. In addition, with the N-doped carbon layer, secondary hollow microspheres architecture built with primary ultrathin nanosheets provide a large amount of void space and active sites for sulfur storage, adsorption and conversion. The as-designed sulfur host exhibits a remarkable rate capability of 547 mAh g−1 at 4 C (1 C=1675 mA g−1) and an outstanding long-term cyclability (519 mAh g−1 after 1000 cycles at 3 C). Besides, a high specific capacity of 832 mAh g−1 is delivered even after 100 cycles under a high sulfur mass loading of 3.2 mg cm−2, indicating its superior electrochemical performances. This work not only provides a strong proof for the application of oxygen defect in the adsorption and catalytic conversion of lithium polysulfides, but offers a promising avenue to achieve high performance LSBs with the material design concept of incorporating oxygen-deficient spinel structure with hierarchical hollow frameworks.

Introducing defects into 2D materials can increase the coordinatively unsaturated sites that are usually also catalytically active sites. How does the level of defects influence catalytic performance and how to take advantage of defects to optimize the 2D materials? In this work, anionic Se vacancies and edge dislocations are regulated in 2D WSe2 as a model of transition metal dichalcogenide host material for the sulfur cathode. The defective 2D WSe2 with different W/Se ratios are quantitatively investigated the influence of the defects on enhancing the cathodic process in lithium sulfur (Li-S) batteries. With a moderate level of defects, WSe1.51 shows the optimal performance for adsorbing polysulfides, catalysing polysulfides conversion, and promoting liquid-solid transformation, all of which are crucial steps for Li-S battery. The corresponding sulfur cathode delivers a high initial areal capacity of 11.3 mAh cm −2, and excellent cycle stability with a decay rate of 0.025% during 1000 cycles at 1C rate. Even in a pouch cell, the excellent cyclability and flexibility are still available. The results show the feasibility of enhancing the catalytic ability of 2D transition metal dichalcogenide by controlling the level of defects by which a long-cycle and high-energy Li-S rechargeable battery can be achieved.

Despite having advantages of safety and dominating consumer and electric vehicle market, the progress of aqueous rechargeable battery research is hindered by low capacity anode materials. A game-changing strategy is to use an environmentally benign aqueous electrolyte with earth abundance Na-ion and sulfur. Sulfur promises to be a next-generation electrode material due to its high theoretical capacity and energy density. But the practical application of elemental sulfur in aqueous electrolyte suffer from sharp capacity decay due to the dissolution of polysulfides. Herein, we report 70 % elemental sulfur along with CoS2 and 1‑butyl‑3-methylimidazolium o,o-bis(2-ethylhexyl) dithiophosphate (BMIm-DDTP) ionic liquid (IL) as anode (S@CoS2-IL) for aqueous rechargeable sodium-ion/sulfur batteries (ARSSB) in 2 M aq. Na2SO4 electrolyte.The S@CoS2-IL anode delivers an outstanding capacity of 977 mA h g−1 (> 91 % of the theoretical capacity of elemental sulfur i.e. 1070 mA h g−1), at 0.5 C with a stable cycling performance over 100 cycles with > 98 % of capacity retention at 2 C with 100 % of coulombic efficiency. A negligible loss of S was confirmed by UV–Vis spectroscopy and potentiometric titration and anchoring of polysulfide at S@CoS2-IL anode were evidenced by NMR, ESI-mass, Raman and X-ray photoelectron spectroscopy. The synergy between highly active CoS2 and BMIm-DDTP IL from the dynamic coordination of dithiophosphate with CoS2 provides easy access for polysulfides anchoring and fast reaction kinetics which effectively suppresses the dissolution of discharge polysulfides and HS−. The full cell studies using S@CoS2-IL anode with standard Na0.44MnO2 cathode demonstrate an outstanding capacity of 778 mA h g−1 w.r.t the weight of S and 104.98 mA h g−1 (of total electrodes weight), which is close to the theoretical capacity of 109 mA h g−1 with 100 % coulombic efficiency and 91.8 % capacity retention over 400 cycles at 2 C. The excellent performance of this aqueous battery chemistry shows that S@CoS2-IL anode has great potential towards practical application in ARSSB.

Lithium-sulfur (Li-S) batteries have attracted extensive attention in the field of energy storage due to their high energy density and low cost. However, conundrums such as severe polarization, poor cyclic performance originating from shuttle effect of lithium polysulfides and sluggish sulfur redox kinetics are stumbling blocks for their practical application. Herein, a novel sulfur cathode integrating sulfur and polyvinylpyrrolidone(PVP)-derived N-doped porous carbon nanofibers (PCNFs) with embedded CoF3 and YF3 nanoparticles are designed and prepared though the electrostatic blowing technology and carbonization process. The unique flexible PCNFs with embedded polar CoF3 and YF3 nanoparticles not only offer enough voids for volume expansion to maintain the structural stability during the electrochemical process, but also promote the physical encapsulation and chemical entrapment of all sulfur species. Moreover, the uniform distribution of YF3/CoF3 nanoparticles also can expose more binding active sites to lithium polysulfide and present more catalytic sites to the greatest extent. Therefore, the assembled cells with the prepared cathode exhibited stable performances with an outstanding initial capacity of 1055.2 mAh g−1 and an extended cycling stability of 0.029% per cycle during the 300 cycles at 0.5C. Even at a high sulfur loading of 2.1 mg cm−2, The YF3/CoF3 doped-PCNFs exhibited a high discharge specific capacity of 1038 mAh g−1, and the decay rate is also as low as 0.05% over 1000 cycles. This work shares a convenient and safe strategy for the synthesis of multi-dimension, dual-functional and stable superstructure electrode for advanced Li-S batteries.

The sluggish redox kinetic and shuttle effect of polysulfides still obstruct the commercial application of lithium-sulfur (Li-S) batteries. Herein, a nanocomposite consisting of well-dispersed and lamellar-like shape CoS anchored on g-C3N4 nanosheets (CoS@g-C3N4) is prepared firstly, and then it is integrated on a polypropylene membrane combined with little conductive Ketjen black (KB) to fabricate a multifunctional and quite thin interlayer, with a thickness of only ∼ 2.1 um and areal mass loading of ∼ 0.07 mg·cm−2. The as-prepared interlayer firstly can capture polysulfides by Li-N bond as well as Lewis acid-base interaction between CoS and polysulfide anions (Sn2-), and more importantly, it also displays a positive effect on catalyzing the redox conversion of intermediate polysulfides. As expected, a Li-S cell assembled with this modified separator and high sulfur content cathode displays an excellent electrochemical performance, with specific capacity of ∼ 1290 mAh g−1 at 0.2C and a low fading rate of 0.03% per cycle after 500 cycles at 1.0C. Furthermore, a high sulfur mass loading of ∼ 4.0 mg·cm−2 electrode paired with this multifunctional separator exhibits a stable specific capacity of ∼ 600 mAh g−1 after 250 cycles under 0.1C. This work can give some guides to rational design a quite thin and light interlayer for improving the utilization of sulfur species, with little damage to the energy density and Li ion transportation in Li-S batteries.

Lithium-Sulfur (Li-S) batteries are very competitive in energy storage equipment due to their high theoretical capacity and low cost of raw materials. However, the serious polysulfide "shuttle effect", volume expansion effect and slow conversion reaction kinetics of Li−S batteries during the charge/discharge cycle process still need to be resolved urgently. Herein, we prepared a novel sulfur host of SnO2-decorated MoS2 hollow microspheres (SnO2-MoS2 HMSs). The unique hollow structure provides enough space to accommodate a large amount of sulfur and effectively adapts to its large volume expansion during charge and discharge process. On the other hand, the SnO2 nanoparticles that attached to the surface of the MoS2 nanosheets will accelerate the catalysis of MoS2 and enhance the bonding strength with the polysulfide intermediates through the S−Sn−O chemical bond, which further inhibits the shuttle effect. The newly synthesized SnO2-MoS2 HMSs cathode has achieved excellent electrochemical performance. The initial discharge specific capacity of 1326.4 mAh g−1 was obtained at 0.2 C, and after 100 cycles, the specific capacity of the SnO2-MoS2 HMSs/S cathode only decreased slightly to 1183.8 mAh g−1, its capacity retention rate reaching as high as 89.2%. We expect the newly synthesized hollow structured MoS2 with SnO2 decoration provides a new strategy for the construction of Li-S battery cathode materials.

The practical applications of lithium sulfur battery is impeded by the lithium polysulfide shuttling and sluggish redox kinetics. To address the issues, herein, a multifunctional host is developed by the combination of nitrogen, phosphorus co-doped carbon fiber (NPCF) and CoS2 towards boost the soluble polysulfides adsorption and transformation. Benefiting from the NPCF originated from biomass cattail fibers, a high conductive network is provided, and shuttle effect is reduced due to the strong chemical interaction between abundant heteroatom polar sites and lithium polysulfides. Moreover, the electrocatalytic CoS2 on the carbon skeleton facilitate lithium polysulfides conversion and lithium sulfide deposition based on the density functional theory calculations and experiments. The efficient lithium polysulfides entrapment and subsequent electrocatalytic conversion improve dynamic stability during cycling, especially for rate capability. With these advantageous features, the electrode with NPCF/CoS2 host can deliver a good rate capability (903 and 782 mAh g−1 at 1C and 2C, respectively) and stable cycling performance with an ultra-low capacity decay of 0.014% per cycle at 1C. Notably, the cell can achieve a high areal capacity of 4.96 mA h cm−2 under an elevated sulfur loading of 5.0 mg cm−2. Overall, the improvement on the electrochemical performance ascertains the validity of the design strategy based on synergy engineering, which is a highly suitable approach for energy storage and conversion application.

S@pPAN has become promising cathode materials in rechargeable batteries due to its high compressed density, low E/S ratio, no polysulfide dissolution, no self-discharge, and stable cycling. However, it is a big challenge to enhance its sulfur content which determines its practical specific capacity. Herein, we prepare crosslinked PAN as precursor, leading to effective enhancement of sulfur content up to 55 wt% and a reversible specific capacity of 838 mAh g-1composites at 0.2C. Because of the microporous structure and high specific area, crosslinked PAN provides more space to accommodate sulfur molecule and improve the interfacial reaction of S@pPAN as well. This work provides a promising direction to design S@pPAN for lithium sulfur batteries with high energy density.

Elemental sulfur, an industrial by-product from petroleum industries worldwide, has drawn sufficient attention to researchers. The limited scope of application has caused a colossal surplus amount of elemental sulfur stacked in the open places. Several polysulfide synthesis processes, including condensation, free-radical process, and ionic copolymerization technique, were used but resulted in unstable products. A new polymerization technique, termed inverse vulcanization, has been introduced, which enabled different types of crosslinkers for polysulfide production and their scopes to explore numerous applications. The current paper concisely reviews the evolution and advances of using vegetable oils and plant extracts in inverse vulcanization to produce polysulfides. The alluring applications and properties have also been discussed briefly.

Multivalent metal–sulfur (M-S, where M = Mg, Al, Ca, Zn, Fe, etc.) batteries offer unique opportunities to achieve high specific capacity, elemental abundancy and cost-effectiveness beyond lithium-ion batteries (LIBs). However, the slow diffusion of multivalent-metal ions and the shuttle of soluble polysulfide result in impoverished reversible capacity and limited cycle performance of M−S (Mg–S, Al–S, Ca–S, Zn–S, Fe–S, etc.) batteries. It is a necessity to optimize the electrochemical performance, while deepening the understanding of the unique electrochemical reaction mechanism, such as the intrinsic multi-electron reaction process, polysulfides dissolution and the instability of metal anodes. To solve these problems, we have summarized the state-of-the-art progress of current M−S batteries, and sorted out the existing challenges for different multivalent M−S batteries according to sulfur cathode, electrolytes, metallic anode and current collectors/separators, respectively. In this literature, we have surveyed and exemplified the strategies developed for better M−S batteries to strengthen the application of green, cost-effective and high energy density M−S batteries.

Molybdenum disulfide (MoS2) is a promising anode material for lithium-ion batteries (LIBs) because of its high theoretical capacity. But its rapid capacity decay due to poor conductivity, structure pulverization, and polysulfide dissolution presents challenges for practical applications. In this work, an innovative cationic surfactant templating route to one-step synthesizing epitaxial few-layer MoS2@N-doped carbon (EF-MoS2@NC) core–shell hollow structures is developed via an electrostatic interaction S+X−I+ pathway. Compared with general hard-template strategies, the soft-template method proposed here is simplified, avoiding the cumbersome coating and template removal process. The internal hollow space and outer NC protective layer can accommodate the large volumetric expansion of MoS2 and preserve the structural integrity of the electrode preventing polysulphide dissolution. When evaluated as anode materials for LIBs, the core–shell EF-MoS2@NC hollow spheres achieve a high discharge capacity of 928 mA h g−1 after 100 cycles at 0.1 A g−1. More importantly, a reversible capacity of 829 mA h g−1 could be obtained at 1.0 A g−1 after 1000 cycles, which demonstrates good stability.

Modifying separator with metal oxides has been considered as a strong strategy to inhibit the shuttling of soluble polysulfide in the lithium-sulfur battery (Li-S battery). Manganese dioxide (MnO2), one kind of transition metal oxide, is widely applied to decorate the PP (Polypropylene) separator. However, the fabrication by physical coating is always multistep and complicated. Here, we design a simple and fast method to chemically decorate separator. Based on the oxidizing property of acidic KMnO4 solution, the PP separator was oxidized and an ultrathin self-assembled MnO2 layer was directly constructed on one side of separator, by immersing in acidic KMnO4 solution for only 1 h. The self-assembled MnO2 layer has the synergistic effect of adsorption and catalytic conversion on polysulfides, which can effectively inhibit the shuttle effect. It can also help battery to maintain excellent electrochemical kinetics in the electrochemical cycle and maintain the effective recycling of active substances. As a result, the shuttling of polysulfide is greatly prohibited by this novel functional separator, and cycling stability is outstandingly improved, with a low-capacity decaying of 0.058% after 500 cycles at 0.5C. The rapid and simple modification method proposed in this study has a certain reference value for the future large-scale application of lithium-sulfur battery.

Lithium-sulfur batteries (LSBs) are attractive candidates for post-lithium-ion battery technologies because of their ultrahigh theoretical energy density and low cost of active cathode materials. However, the commercialization of LSBs remains extremely challenging primarily due to poor cycling performance and safety concerns, which are inherently caused by low conductivity of S8 and Li2S, severe polysulfide shuttling, and high polarization by solid Li2S2/Li2S deposition. Catalytic materials could facilitate the large-scale practical application of LSBs by overcoming all these challenges. In this review, we investigate the sulfur species evolution in LSBs and explore the roles of catalytic materials in charge/discharge processes, highlighting the catalysis of solid S8 to liquid polysulfides and solid Li2S2 to Li2S. Furthermore, we offer systematic strategies from atomic to macro levels, including defect engineering, morphology engineering and catalyst compositing, to enhance catalysis efficiency in terms of sulfur supercooling, fast charge transfer, thiosulfate generation, disulfide bond cleavage, tuneable Li2S growth and Li2S decomposition enhancement. The design and availability of the proposed catalytic materials will further advance LSB technology from coin cells and pouch cells to the subsequent commercialization scale.

Facilitating polysulfide conversion by electrocatalysis is a promising strategy to suppress shuttle effect in lithium-sulfur (Li-S) batteries, yet the active sites in electrocatalysts are gradually passivated by continuous formation of Li2S passivation layer over cycling, making it challenging to achieve steady conversion of sulfur species. Herein, a strategy of reactive Li2S collaborated with dual-directional Fe3C electrocatalyst is proposed to achieve fast and continuous conversion of sulfur species for drastically boosting the performance of Li-S batteries. During the reduction process, reactive Li2S with unique three-dimensional porous structure is precipitated on Fe3C surface, which not only shortens ion/electron diffusion path but also exposes and retains more active sites in Fe3C. While for the following oxidation process, Fe3C also promotes the decomposition of reactive Li2S to refresh electrocatalyst surface. Therefore, the high catalytic activity of Fe3C is well retained during the entire electrochemical process, as verified by comprehensive experimental and theoretical calculation results. Eventually, Fe3C enables stable operation of high-areal-capacity Li-S batteries (> 6.0 mAh cm−2) under a wide-temperature range (-10 to 40 °C). Our strategy of coupling reactive Li2S with a bidirectional electrocatalyst provides a new avenue for developing high-energy and wide-temperature Li-S batteries.

Lithium–sulfur (Li–S) battery is highly regarded as a promising next-generation energy storage device but suffers from sluggish sulfur redox kinetics. Probing the behavior and mechanism of the sulfur species on electrocatalytic surface is the first step to rationally introduce polysulfide electrocatalysts for kinetic promotion in a working battery. Herein, crystalline lithium sulfide (Li2S) is exclusively observed on electrocatalytic surface with uniform spherical morphology while Li2S on non-electrocatalytic surface is amorphous and irregular. Further characterization indicates the crystalline Li2S preferentially participates in the discharge/charge process to render reduced interfacial resistance, high sulfur utilization, and activated sulfur redox reactions. Consequently, crystalline Li2S is proposed with thermodynamic and kinetic advantages to rationalize the superior performances of Li–S batteries. The evolution of solid Li2S on electrocatalytic surface not only addresses the polysulfide electrocatalysis strategy, but also inspires further investigation into the chemistry of energy-related processes.

Lithium-sulfur (Li-S) batteries are considered to be promising candidates for next-generation storage systems. However, the practical applications are still hindered by the severe capacity decay, mainly caused by the large volume change, polysulfide shuttle and sluggish sulfur conversion kinetics. Herein, hollow urchin-like Mn3O4 (HU-Mn3O4) microspheres as sulfur hosts have been synthesized by the hydrothermal method and calcination treatment, aiming to prevent the polysulfide dissolution (benefiting from the strong polysulfide anchoring effect of Mn3O4) and alleviate the volume expansion of sulfur (benefiting from the special hollow structure). Meanwhile, the urchin-like thorny surface also facilitates the rapid ion/electron transfer and the abundant active sites for the fast sulfur redox kinetics. When used as the sulfur host in Li-S batteries, the S@HU-Mn3O4 cathode delivers a high initial capacity of 1137.4 mAh g−1 with a slow capacity decay of 0.042% after 200 cycles at 0.2 C. Even under the conditions of lean electrolyte (E/S = 7 mL g−1) and low N/P ratio (N/P = 2.1), the S@HU-Mn3O4 cathode still enables a stable cycling performance with a high gravimetric energy density (202 Wh kg cell−1), demonstrating its great potential in the development of future practical Li-S battery materials.

Tracking the S oxidation pathway in sulfide-bearing mine waste-rock piles is complicated by variations in water content, O2 and Fe3+ concentrations, microbial diversity, mineralogy, the occurrence of a variety of S species associated with incomplete oxidation, and nonlinear coupling between physicochemical processes. Synchrotron-based S K-edge X-ray absorption near edge structure (XANES) spectroscopy facilitates the identification and quantification of S species (i.e., S2-, S22-, S8, S2O32-, and SO42-) in a naturally weathered mine waste-rock pile containing pyrite, sphalerite, galena, pyrrhotite, and chalcopyrite. Mineralogy-dependent polysulfide and thiosulfate pathways both affect the S oxidation within the waste-rock pile. Currently, the polysulfide pathway, with S8 as the intermediate S species, generates high concentrations of dissolved metals (from the rapid oxidation of monosulfides including sphalerite, galena, pyrrhotite, and chalcopyrite). As these monosulfides are depleted, the thiosulfate pathway of pyrite oxidation, including intermediate oxidation products (i.e., S8 and S2O32-), will become the dominant oxidation pathway, resulting in the potential for generation of additional acidic drainage. This information highlights the importance of identifying the sulfide-mineral oxidation reaction pathways when attempting to estimate acid generation potential, and when developing remediation strategies for the storage and management of sulfide-bearing waste rock.

Under high sulfur loading, high sulfur content and low electrolyte/sulfur ratio (E/S), the practical application of lithium sulfur (Li–S) batteries is seriously limited by the negative and slow kinetics of polysulfide. Here, a freestanding sulfur cathode based on nitrogen doped porous carbon fiber/vertical graphene (NF@VG) composites is proposed. Porous structure and nitrogen doping effectively enhance absorption of polysulfides through physical confinement and chemical action, while vertical graphene network greatly promotes electron transfer and boosts the catalytic conversion kinetics of polysulfides. Therefore, the as-prepared sulfur cathode exhibits an initial capacity of 738 mAh g−1, and a maintained capacity of 609 mAh g−1 after 600 cycles with only 0.029% capacity fading per cycle at 1 C rate at a sulfur loading of 7 mg cm−2. In addition, the battery displays an areal capacity of 12.8 mAh cm−2 under high sulfur loading (13 mg cm−2), high sulfur content (81.6 wt%), and low E/S (4.8 μL mg−1), indicating that the NF@VG composite fibers are highly competitive as sulfur host for Li–S batteries.

In order to overcome the shuttling effect of soluble polysulfides in lithium-sulfur (Li-S) batteries, we have designed and synthesized a creative MoS2-MoO3/carbon shell (MoS2-MoO3/CS) composite by a H2O2-enabled oxidizing process under mild conditions, which is further used for separator modification. The MoS2-MoO3 heterostructures can conform to the CS morphology, forming two-dimensional nanosheets, and thus shorten the transport path of lithium ion and electrons. Based on our theoretical calculations and experiments, the heterostructures show strong surface affinity toward polysulfides and good catalytic activity to accelerate polysulfide conversion. Benefiting from the above merits, the Li-S battery with a MoS2-MoO3/CS modified separator exhibits good electrochemical performance: it delivers a high discharge capacity of 1531 mAh g-1 at 0.2 C; the initial capacity can be maintained by 92% after 600 cycles at 1 C, and the discharge capacity decay rate is only 0.0135% per cycle. Moreover, the MoS2-MoO3/CS battery still achieves good cycling stability with 78% capacity retention after 100 cycles at 0.2 C with a high sulfur loading of 5.9 mg cm-2. This work offers a facile design to construct the MoS2-MoO3 heterostructures for high-performance Li-S batteries, and may also improve one's understanding on the heterostructure contribution during polysulfide adsorption and conversion.

During the past decades, lithium-sulfur batteries have obtained great attention due to their advantages as energy storage systems, which have high specific capacity and energy density. However, the real applications were hindered by many challenges, especially the shuttle effect of the polysulfide from the cathode to the anode side. This is attributed that the traditional PP films could not prevent the polysulfide migration from the cathode to the anode side. Therefore, it is an efficient method to develop a modified film, which could inhibit the polysulfide shuttle effect. Based on this idea, we prepared molybdenum sulfide–modified (MS modified) film as separators in the lithium-sulfur batteries, which were obtained by coating the molybdenum sulfide on the surface of the traditional PP films. The electrochemical results indicate that the Li–S battery by using MS–modified films exhibits excellent electrochemical performance.

High-entropy alloys (HEAs), as a special heterostructure, possesses many exclusive advantages, including the inherited merits from each component and the synergistic regulation of electronic properties, which has a great potential for catalyzing complicated redox conversions. Herein, we reveal that the synthesized nano-HEA plays a unique role in the multi-electron and multiphase conversions of lithium polysulfides (LiPSs) in lithium-sulfur batteries (Li-S). Owing to the strong affinity with LiPSs, nano-HEA enriches the activity of LiPSs around the electrode more than 17 times higher than that of the control sample (without nano-HEA addition), significantly reducing the concentration polarization. In addition, the activation polarization was greatly suppressed by the nano-HEA catalyst, which is demonstrated by the lower Tafel slope, higher exchange current density, and the larger current response from the scanning electrochemical microscopy (SECM). Besides, the smooth and continuous redistribution of surface charge is further revealed by DFT calculation, benefiting the multi-electron reactions of LiPSs. As a result, Li-S batteries assembled with nano-HEA modified separators delivered outstanding capacity retention rates of 83.3% (2 C after 500 cycles in coin cell) and 82% (0.1 C 150 cycles in pouch cell), respectively.

More and more attentions have been attracted by lithium-sulfur batteries (Li-S), owing to the high energy density for the increasingly advanced energy storage system.While the poor cycling stability, due to the inherent polysulfide shuttle, seriously hampered their practical application. Recently, some polar hosts, like single metal oxides and sulfides, have been employed as hosts to interact with polysulfide intermediates. However, due to the inherent poor electrical conductivity of these polar hosts, a relatively low specific capacity is obtained. Herein, a spinel-type bimetal sulfide NiCo2S4 through a Prussian blue analogue derived methodology is reported as the novel host of polysulfide, which enables high-performance sulfur cathode with high Coulombic efficiency and low capacity decay. Notably, the Li-S battery with NiCo2S4-S composites cathode still maintains a capacity of 667 mA h g-1 at 0.5 C after 300 cycles, and 399 mA h g-1 at 1 C after 300 cycles. Even after 300 cycles at the current density of 0.5 C, the capacity decays by 0.138% per cycle at high sulfur loading about 3 mg cm-2. And the capacity decays by 0.026% per cycle after 1000 cycles, when the rate is 1 C. More importantly, the cathode of NiCo2S4-S composite shows the outstanding discharge capacity, owing to its good conduction, high catalytic ability and the strong confinement of polysulfides.

Recently, safety issues associated with the practical application of lithium–sulfur (Li–S) batteries have attracted tremendous concern. Herein, a nonflammable 3D porous framework is constructed from functional boron nitride nanosheets (f-BNNSs) supported on a scaffold of continuous functional carbon nanotubes (f-CNTs) as a bifunctional host for Li–S batteries. The unique 3D porous structure with high thermal conductivity provides a well-distributed heat field with smooth and ultrafast heat-conduction channels during continuous battery operation even at a high temperature, thereby ensuring timely and effective heat transfer and avoiding the thermal runaway caused by accumulated heat and excessive local temperature. The incombustible f-BNNSs act as a physical flame-retardant barrier to prevent the occurrence and spread of combustion. In addition, the uniform electric field with low local current density inhibit the growth of Li dendrites, avoiding the excessive local temperature caused by the formation of an uneven thermal field. The abundant polar functional groups effectively suppress polysulfide shuttling, reducing the extra heat accumulation generated by severe electrode polarization. This work provides a “two-in-one” strategy for realizing high-safety batteries via a “prevention and post-treatment” method that combines thermal field regulation and flame retardancy, and thus promotes the commercial development of Li–S batteries.

Commercial lithium sulfur batteries are hindered by unstable and unreliable cycling performances due to the dissolution and shuttle of lithium polysulfides. Defect engineering with plentiful active sites and high surface binding energies to restrain polysulfides dissolution and promote the redox conversion polysulfides. Here, we present a nano carbon intercalated by W18O49 nanorods composite materials as functional sulfur host. With high W/O ratio of 0.367 in tungsten oxide famliy (WOx), W18O49 achieves abundant oxygen vacancy in intrinsic atomic structure. These oxygen vacancies not only provide stable active sites to stabilize the Li2S but also immobilize polysulfides by strong coulombic interactions of W-S and Li-O bondings. Accordingly, this cathode achieves stable long cycling performance with decay rate of 0.038 % per cycle at 2 C for 1200 cycles. With high sulfur loading of 6.4 mg·cm−2, the cathode also shows stable cycling at 0.2 C for 150 cycles. This immobilizations of polysulfides by oxygen vacancy engineering in W18O49 is referential for developing commercial useable Li-S batteries.

Atom-intercalated transition metal disulfides (TMDs) have attached much attention mainly due to their highly improved conductivity. But it is few reported that the atom intercalation can enable the TMDs have unexpected catalytic properties, caused by the unit-cell deformation in them. In this work, a type of V0.25-intercalated VS2 (V5S8) nanoflakes was designed via a direct vulcanization method combining Kirkendall heat diffusion effect, and used as the promotor for lithium-sulfur batteries (LSBs). The V5S8 possesses a NiAs crystal structure, in which V atoms occupy the interlayer spacing between VS2 monolayers, which will unavoidably cause the unit-cell deformation. As expected, the CNF@V5S8/S cathodes show a specific capacity of 1260 mAh g−1 at 0.2 C, and can keep 73.65% of the capacity with charge/discharge rate increasing 10 times; while the CNF@VS2/S ones can only retain 54.0% of the initial capacity. Moreover, the CNF@V5S8/S cathodes show an ultralow decay rate of only 0.0312% per cycle for 1500 cycles at 5 C. Furthermore, the catalysis effect of V5S8 on the conversion of lithium polysulfide (Li2Sn, n = 1, 2, 4, 6 and 8) and S8 clusters were systematically discusses. Besides, the V5S8 can further enable LSBs achieve a high areal capacity (8.2 mAh cm−2 with sulfur loading of 7.8 mg cm−2) and a high dynamic flexible stability at bending angle between 0 and 180 °.

Rechargeable aluminum batteries are believed as a promising next-generation energy-storage system due to abundant low-cost Al sources and high volumetric specific capacity. The Al-storage cathodes, however, are plagued by strong electrostatic interaction between host materials and carrier ions, leading to large overpotential and undesired cycling stability as well as sluggish ion diffusion kinetics. Herein, sulfur-linked carbonyl polymer based on perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) as the cathode materials for ABs is proposed, which demonstrates a small voltage polarization (135 mV), a reversible capacity of 110 mAh g−1 at 100 mA g−1 even after 1200 cycles, and rapid Al-storage kinetics. Compared with PTCDA, the sulfide polymer possesses higher working voltage because of its lower LUMO energy level according to theoretical calculation. The ordered carbonyl active sites in sulfide polymer contribute to the maximized material utilization and rapid ion coordination and dissociation, resulting in superior rate capability. Besides, the bridged thioether bonds endow the polysulfide with robust and flexible structure, which inhibits the dissolution of active materials and improves cycling stability. This work implies the importance of ordered arrangement of redox active moieties for organic electrode, which provides the theoretical direction for the structural design of organic materials applied in multivalent-ion batteries.

Li2S, which features a high theoretical capacity of 1,166 mA·h g-1, is an attractive cathode material for developing high-energy-density lithium-sulfur batteries. However, pristine Li2S requires a high activation voltage of 4.0 V, which degrades both the electrolyte and electrode, leading to poor cycling performance. In an effort to reduce the activation overpotential, in this study, we investigate the use of P2S5 in an advanced Li2S-P2S5 catholyte and demonstrate a new synthetic approach that enables facile and low-temperature processing. Our findings show the P2S5 additive generates two thiophosphates with high ionic conductivities in the catholyte, which improve the activation efficiency and the electrochemical utilization. To further improve this advanced catholyte design, we also investigate two modified Li2S-P2S5 catholytes based on carbon black (to strengthen the conductivity) and dilute polysulfide (Li2S6; to amplify the reaction activity). Our analysis indicates that the optimal Li2S-P2S5-Li2S6 catholyte attains high ionic conductivity and strong reaction kinetics, achieving a high charge-storage capacity of 700 mA·h g-1 with a long-term cyclability of 200 cycles.

Designing sulfur host materials with unique functions such as physical constraint or chemical catalysis to suppress the shuttle effect and promote the fast conversion of polysulfides is a prerequisite for lithium-sulfur batteries (LSBs). Herein, we construct hollow Co(OH)2 nanotubes connected by Ti3C2Tx nanosheets (denoted as Co(OH)2@Ti3C2Tx) as host materials for sulfur through a simple self-assembly method at room temperature. The large void spaces of Co(OH)2 nanotubes not only confine higher sulfur loading but also mitigate the volumetric expansion in the process of lithiation. Moreover, the conductive Ti3C2Tx layers facilitate fast electron transfer and catalyze the transition of sulfur based on the terminations on the surface. Combining those two materials can also act as an efficient polysulfide anchor to enable outstanding electrochemical performance. The Co(OH)2@Ti3C2Tx@S cathode presents a high discharge capacity of 1400 mAh g-1 at 0.1C and long-cycling stability at 1C for 500 cycles. Moreover, the obtained capacity of Li2S precipitation and the dissolution capacity reach 193.3 and 291.1 mAh g-1, respectively. Consequently, this work demonstrates a facile strategy to design multifunctional materials that effectively confine the polysulfides and enhance the performance of LSBs.

Further development of lithium–sulfur (Li–S) batteries is restricted by the insulation of sulfur and the shuttle effect of lithium polysulfide (LiPSs). Herein, we propose a multifunctional freestan...

Ambient-temperature sodium-sulfur batteries are an appealing, sustainable, and low-cost alternative to lithium-ion batteries due to their high material abundance and specific energy of 1274 W h kg-1. However, their viability is hampered by Na polysulfide (NaPS) shuttling, Na loss due to side reactions with the electrolyte, and dendrite formation. Here, we demonstrate that a solid-electrolyte interphase rich in inorganic components can be realized at both the sulfur cathode and the Na anode by tweaking the solvation structure of the electrolyte. This transforms the sulfur redox process from conventional dissolution-precipitation chemistry into a quasi-solid-state reaction, which eliminates NaPS shuttling and facilitates dendrite-free Na-metal plating and stripping. With the solvated ionic liquid electrolyte structure, a high initial capacity of 922 mA h g-1 with a capacity fade of as low as 0.10% per cycle over 300 cycles was achieved. The scalability of this approach to pouch cells with practically necessary parameters demonstrates its potential for practical viability.

Lithium-sulfur batteries (LSBs) are considered the most likely replacement for conventional lithium–ion batteries in next-generation high-energy output solutions based on their high specific capacity (1675 mAh g−1) and high-energy density (2600 Wh kg−1). But, there are some problems that need to be solved urgently. In this work, an environmentally friendly, green, and low-cost ZIF-67-derived cobalt-based sulfate material (CoSO4) combined with carbon nanotubes was proposed as a sulfur host material. Experiments show that the addition of CoSO4 can significantly enhance the transformation of polysulfide and suppress the shuttle effect. The best performance is the CNT-CoSO4-2/S, which has an initial capacity of 1356.9 mAh g−1 at 0.1 C current density. Furthermore, long-term cycle test was carried out at a current density of 0.2 C; the coulombic efficiency was above 98.63% after 200 cycles. This work demonstrates the potential of cobalt-based sulfates as cathode materials for lithium–sulfur batteries.