Quasi-Solid Sulfur Conversion for Energetic All-Solid-State Na−S Battery

The high theoretical energy density (1274 Wh kg⁻¹) and high safety enable the all-solid-state Na−S batteries with great promise for stationary energy storage system. However, the uncontrollable solid–liquid-solid multiphase conversion and its associated sluggish polysulfides redox kinetics pose a great challenge in tunning the sulfur speciation pathway for practical Na−S electrochemistry. Herein, we propose a new design methodology for matrix featuring separated bi-catalytic sites that control the multi-step polysulfide transformation in tandem and direct quasi-solid reversible sulfur conversion during battery cycling. It is revealed that the N, P heteroatom hotspots are more favorable for catalyzing the long-chain polysulfides reduction, while PtNi nanocrystals manipulate the direct and full Na₂S₄ to Na₂S low-kinetic conversion during discharging. The electrodeposited Na₂S on strongly coupled PtNi and N, P-codoped carbon host is extremely electroreactive and can be readily recovered back to S₈ without passivation of active species during battery recharging, which delivers a true tandem electrocatalytic quasi-solid sulfur conversion mechanism. Accordingly, stable cycling of the all-solid-state soft-package Na−S pouch cells with an attractive specific capacity of 876 mAh g_S⁻¹ and a high energy of 608 Wh kg_cathode⁻¹ (172 Wh kg⁻¹, based on the total mass of cathode and anode) at 60 °C are demonstrated.     

Mixed Anionic and Cationic Redox Chemistry in a Tetrathiomolybdate Amorphous Coordination Framework

We report the electrochemistry of a hitherto unexplored Na₂MoS₄ phase as a conversion electrode material for Na‐ and Li‐ion batteries. The material adopts an amorphous coordination polymer structure with mixed Mo and S valences. XPS and XRD analysis reveal a complex interplay between Mo and S redox chemistry, while excluding the formation of free sulfur, lithium sulfide, or other crystalline phases. Na₂MoS₄ behaves as a mixed ionic–electronic conductor, with electronic conductivity of 6.1×10^?4 S cm^?1, that permits carbon‐free application in an electrochemical cell. A reversible capacity of up to 500 mAh g^?1 was attained, corresponding to a five‐electron redox exchange, with species ranging from <Na_<1MoS₄> (highest oxidized state) to <Na_>5MoS₄> (lowest oxidized state). This study emphasizes the excellent charge‐storage performances of Na₂MoS₄ for Li‐ or Na‐ion batteries, and enriches the emerging library and knowledge of sulfide phases with mixed anionic and cationic redox properties.     

Synthesis,Crystal Structure,and Electrochemical Properties of a Simple Magnesium Electrolyte for Magnesium/Sulfur Batteries

Most simple magnesium salts tend to passivate the Mg metal surface too quickly to function as electrolytes for Mg batteries. In the present work, an electroactive salt [Mg(THF)₆][AlCl₄]₂ was synthesized and structurally characterized. The Mg electrolyte based on this simple mononuclear salt showed a high Mg cycling efficiency, good anodic stability (2.5 V vs. Mg), and high ionic conductivity (8.5 mS cm^?1). Magnesium/sulfur cells employing the as‐prepared electrolyte exhibited good cycling performance over 20 cycles in the range of 0.3–2.6 V, thus indicating an electrochemically reversible conversion of S to MgS without severe passivation of the Mg metal electrode surface.     

Toward Complete Transformation of Sodium Polysulfides by Regulating the Second-Shell Coordinating Environment of Atomically Dispersed Fe

Room temperature sodium-sulfur (RT Na-S) batteries are highly competitive as potential energy storage devices. Nevertheless, their actually achieved reversible capacities are far below the theoretical value due to incomplete transformation of polysulfides. Herein, atomically dispersed Fe-N/S active center by regulating the second-shell coordinating environment of Fe single atom is proposed. The Fe−N₄S₂ coordination structure with enhanced local electronic concentration around the Fermi level is revealed via synchrotron radiation X-ray absorption spectroscopy (XAS) and theoretical calculations, which can not only significantly promote the transformation kinetics of polysulfides, but induce uniform Na deposition for dendrite-free Na anode. As a result, the obtained S cathode delivers a high initial reversible capacity of 1590 mAh g⁻¹, nearly the theoretical value. This work opens up a new avenue to facilitate the complete transformation of polysulfides for RT Na-S batteries.     

Accelerated Multi-step Sulfur Redox Reactions in Lithium-Sulfur Batteries Enabled by Dual Defects in Metal-Organic Framework-based Catalysts

The sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs) are recognized as the main obstacles to the practical applications of the lithium-sulfur (Li−S) batteries. Accelerated conversion by catalysis can mitigate these issues, leading to enhanced Li−S performance. However, a catalyst with single active site cannot simultaneously accelerate multiple LiPSs conversion. Herein, we developed a novel dual-defect (missing linker and missing cluster defects) metal–organic framework (MOF) as a new type of catalyst to achieve synergistic catalysis for the multi-step conversion reaction of LiPSs. Electrochemical tests and first-principle density functional theory (DFT) calculations revealed that different defects can realize targeted acceleration of stepwise reaction kinetics for LiPSs. Specifically, the missing linker defects can selectively accelerate the conversion of S₈→Li₂S₄, while the missing cluster defects can catalyze the reaction of Li₂S₄→Li₂S, so as to effectively inhibit the shuttle effect. Hence, the Li−S battery with an electrolyte to sulfur (E/S) ratio of 8.9 mL g⁻¹ delivers a capacity of 1087 mAh g⁻¹ at 0.2 C after 100 cycles. Even at high sulfur loading of 12.9 mg cm⁻² and E/S=3.9 mL g⁻¹, an areal capacity of 10.4 mAh cm⁻² for 45 cycles can still be obtained.     

Unique Octupolar 2D-Polymer Frameworks as Mixed Conductors and Metal-Free Catalysts for Dual-Promoted Li and S Electrochemistry: Multi-regulation Role of Ethoxylation Chemistry

Here, we for the first time introduce ethoxylation chemistry to develop a new octupolar cyano-vinylene-linked 2D polymer framework (Cyano-OCF-EO) capable of acting as efficient mixed electron/ion conductors and metal-free sulfur evolution catalysts for dual-promoted Li and S electrochemistry. Our strategy creates a unique interconnected network of strongly-coupled donor 3-(acceptor-core) octupoles in Cyano-OCF-EO, affording enhanced intramolecular charge transfer, substantial active sites and crowded open channels. This enables Cyano-OCF-EO as a new versatile separator modifier, which endows the modified separator with superior catalytic activity for sulfur conversion and rapid Li ion conduction with the high Li⁺ transference number up to 0.94. Thus, the incorporation of Cyano-OCF-EO can concurrently regulate sulfur redox reactions and Li-ion flux in Li−S cells, attaining boosted bidirectional redox kinetics, inhibited polysulfide shuttle and dendrite-free Li anodes. The Cyano-OCF-EO-involved Li−S cell is endowed with excellent overall electrochemical performance especially large areal capacity of 7.5 mAh cm⁻² at high sulfur loading of 8.7 mg cm⁻². Mechanistic studies unveil the dominant multi-promoting effect of the triethoxylation on electron and ion conduction, polysulfide adsorption and catalytic conversion as well as previously-unexplored −CN/C−O dual-site synergistic effect for enhanced polysulfide adsorption and reduced energy barrier toward Li₂S conversion.     

Fast,Reversible Lithium Storage with a Sulfur/Long‐Chain‐Polysulfide Redox Couple

The cathodic reactions in Li–S batteries can be divided into two steps. Firstly, elemental sulfur is transformed into long‐chain polysulfides (S₈?Li₂S₄), which are highly soluble in the electrolyte. Next, long‐chain polysulfides undergo nucleation reaction and convert into solid‐state Li₂S₂ and Li₂S (Li₂S₄?Li₂S) by slow processes. As a result, the second‐step of the electrochemical reaction hinders the high‐rate application of Li–S batteries. In this report, the kinetics of the sulfur/long‐chain‐polysulfide redox couple (theoretical capacity=419 mA h g^?1) are experimentally demonstrated to be very fast in the Li–S system. A Li–S cell with a blended carbon interlayer retains excellent cycle stability and possesses a high percentage of active material utilization over 250 cycles at high C rates. The meso‐/micropores in the interlayer are responsible for accommodating the shuttling polysulfides and offering sufficient electrolyte accessibility. Therefore, utilizing the sulfur/long‐chain polysulfide redox couple with an efficient interlayer configuration in Li–S batteries may be a promising choice for high‐power applications.     

A Radical Pathway and Stabilized Li Anode Enabled by Halide Quaternary Ammonium Electrolyte Additives for Lithium-Sulfur Batteries

Passivation of the sulfur cathode by insulating lithium sulfide restricts the reversibility and sulfur utilization of Li−S batteries. 3D nucleation of Li₂S enabled by radical conversion may significantly boost the redox kinetics. Electrolytes with high donor number (DN) solvents allow for tri-sulfur (S₃⋅⁻) radicals as intermediates, however, the catastrophic reactivity of such solvents with Li anodes pose a great challenge for their practical application. Here, we propose the use of quaternary ammonium salts as electrolyte additives, which can preserve the partial high-DN characteristics that trigger the S₃⋅⁻ radical pathway, and inhibit the growth of Li dendrites. Li−S batteries with tetrapropylammonium bromide (T3Br) electrolyte additive deliver the outstanding cycling stability (700 cycles at 1 C with a low-capacity decay rate of 0.049 % per cycle), and high capacity under a lean electrolyte of 5 μL_electrolyte mg_sulfur⁻¹. This work opens a new avenue for the development of electrolyte additives for Li−S batteries.     

Synthesis,Crystal Structure,and Electrochemical Properties of a Simple Magnesium Electrolyte for Magnesium/Sulfur Batteries

Most simple magnesium salts tend to passivate the Mg metal surface too quickly to function as electrolytes for Mg batteries. In the present work, an electroactive salt [Mg(THF)₆][AlCl₄]₂ was synthesized and structurally characterized. The Mg electrolyte based on this simple mononuclear salt showed a high Mg cycling efficiency, good anodic stability (2.5 V vs. Mg), and high ionic conductivity (8.5 mS cm⁻¹). Magnesium/sulfur cells employing the as‐prepared electrolyte exhibited good cycling performance over 20 cycles in the range of 0.3–2.6 V, thus indicating an electrochemically reversible conversion of S to MgS without severe passivation of the Mg metal electrode surface.     

Porous Core–Shell CuCo2S4 Nanospheres as Anode Material for Enhanced Lithium-Ion Batteries

Porous core–shell CuCo₂S₄ nanospheres that exhibit a large specific surface area, sufficient inner space, and a nanoporous shell were synthesized through a facile solvothermal method. The diameter of the core–shell CuCo₂S₄ nanospheres is approximately 800 nm„ the radius of the core is about 265 nm and the thickness of the shell are approximately 45 nm, respectively. On the basis of the experimental results, the formation mechanism of the core–shell structure is also discussed. These CuCo₂S₄ nanospheres show excellent Li storage performance when used as anode material for lithium-ion batteries. This material delivers high reversible capacity of 773.7 mA h g⁻¹ after 1000 cycles at a current density of 1 A g⁻¹ and displays a stable capacity of 358.4 mA h g⁻¹ after 1000 cycles even at a higher current density of 10 A g⁻¹. The excellent Li storage performance, in terms of high reversible capacity, cycling performance, and rate capability, can be attributed to the synergistic effects of both the core and shell during Li⁺ ion insertion/extraction processes.     

Construction of Hierarchical Nanotubes Assembled from Ultrathin V3S4@C Nanosheets towards Alkali‐Ion Batteries with Ion‐Dependent Electrochemical Mechanisms

Ultrathin core–shell V₃S₄@C nanosheets assembled into hierarchical nanotubes (V₃S₄@C NS‐HNTs) are synthesized by a self‐template strategy and evaluated as general anodes for alkali‐ion batteries. Structural/physicochemical characterizations and DFT calculations bring insights into the intrinsic relationship between crystal structures and electrochemical mechanisms of the V₃S₄@C NS‐HNTs electrode. The V₃S₄@C NS‐HNTs are endowed with strong structural rigidness owing to the layered VS₂ subunits and interlayer occupied V atoms, and efficient alkali‐ion adsorption/diffusion thanks to the electroactive V₃S₄‐C interfaces. The resulting V₃S₄@C NS‐HNTs anode exhibit distinct alkali‐ion‐dependent charge storage mechanisms and exceptional long‐durability cyclic performance in storage of K⁺, benefiting from synergistic contributions of pseudocapacitive and reversible intercalation/de‐intercalation behaviors superior to those of the conversion‐reaction‐based Li⁺‐/Na⁺‐storage counterparts.     

Facile Stabilization of the Sodium Metal Anode with Additives: Unexpected Key Role of Sodium Polysulfide and Adverse Effect of Sodium Nitrate

Sodium metal is an attractive anode for next‐generation energy storage systems owing to its high specific capacity, low cost, and high abundance. Nevertheless, uncontrolled Na dendrite growth caused by the formation of unstable solid electrolyte interphase (SEI) leads to poor cycling performance and severe safety concerns. Sodium polysulfide (Na₂S₆) alone is revealed to serve as a positive additive or pre‐passivation agent in ether electrolyte to improve the long‐term stability and reversibility of the Na anode, while Na₂S₆‐NaNO₃ as co‐additive has an adverse effect, contrary to the prior findings in the lithium anode system. A superior cycling behavior of Na anode is first demonstrated at a current density up to 10 mA cm^?2 and a capacity up to 5 mAh cm^?2 over 100 cycles. As a proof of concept, a high‐capacity Na‐S battery was prepared by pre‐passivating the Na anode with Na₂S₆. This study gives insights into understanding the differences between Li and Na systems.     

A Four‐Electron Sulfur Electrode Hosting a Cu2+/Cu+ Redox Charge Carrier

The elemental sulfur electrode with Cu²⁺ as the charge carrier gives a four‐electron sulfur electrode reaction through the sequential conversion of S?CuS?Cu₂S. The Cu‐S redox‐ion electrode delivers a high specific capacity of 3044 mAh g^?1 based on the sulfur mass or 609 mAh g^?1 based on the mass of Cu₂S, the completely discharged product, and displays an unprecedently high potential of sulfur/metal sulfide reduction at 0.5 V vs. SHE. The Cu‐S electrode also exhibits an extremely low extent of polarization of 0.05 V and an outstanding cycle number of 1200 cycles retaining 72 % of the initial capacity at 12.5 A g^?1. The remarkable utility of this Cu‐S cathode is further demonstrated in a hybrid cell that employs an Zn metal anode and an anion‐exchange membrane as the separator, which yields an average cell discharge voltage of 1.15 V, the half‐cell specific energy of 547 Wh kg^?1 based on the mass of the Cu₂S/carbon composite cathode, and stable cycling over 110 cycles.     

Directed Dehydration of Na4Sn2S6 ⋅ 5H2O Generates the New Compound Na4Sn2S6: Crystal Structure and Selected Properties

The new thiostannate Na₄Sn₂S₆ was prepared by directed crystal water removal from the hydrate Na₄Sn₂S₆ ⋅ 5H₂O at moderate temperatures. While the structure of the hydrate comprises isolated [Sn₂S₆]⁴⁻ anions, that of the anhydrate contains linear chains composed of corner-sharing SnS₄ tetrahedra, a structural motif not known in thiostannate chemistry. This structural rearrangement requires bond-breakage in the [Sn₂S₆]⁴⁻ anion, movements of the fragments of the opened [Sn₂S₆]⁴⁻ anion and Sn−S−Sn bond formation. Simultaneously, the coordination environment of the Na⁺ cations is significantly altered and the in situ formed NaS₅ polyhedra are joined by corner- and edge-sharing to form a six-membered ring. Time-dependent in situ X-ray powder diffraction evidences very fast rehydration into Na₄Sn₂S₆ ⋅ 5H₂O during storage in air atmosphere, but recovery of the initial crystallinity requires several days. Impedance spectroscopy demonstrates a mediocre room-temperature Na⁺ ion conductivity of 0.31 μS cm⁻¹ and an activation energy for ionic transport of E_a=0.75 eV.     

Synthese und Kristallstruktur von [Na3(H2O)6,5(EtOH)][PhSnS3] · 3 EtOH

Synthesis and Crystal Structure of [Na₃(H₂O)_6,5(EtOH)][PhSnS₃] · 3 EtOH Ph₄Sn₄S₆ reacts with Na₂S · 5 H₂O in aqueous acetone to form Na₃[PhSnS₃]. Recrystallization of the crude product from ethanol leads to colourless needles of [Na₃(H₂O)_6,5(EtOH)][PhSnS₃] · 3 EtOH 1 . The crystal structure of 1 was determined by X-ray diffraction. 1 consists of [PhSnS₃]^3– anions and sodium cations which are coordinated by water, ethanol and sulfur atoms of the [PhSnS₃]^3– anions. The [PhSnS₃]^3– anion contains a tin atom which is coordinated nearly tetrahedrally by a phenyl group and three sulfur atoms. The Sn–S bonds are 237,4(2)–238,4(2) pm.     

Long‐Life Room‐Temperature Sodium–Sulfur Batteries by Virtue of Transition‐Metal‐Nanocluster–Sulfur Interactions

Room‐temperature sodium–sulfur (RT‐Na/S) batteries hold significant promise for large‐scale application because of low cost of both sodium and sulfur. However, the dissolution of polysulfides into the electrolyte limits practical application. Now, the design and testing of a new class of sulfur hosts as transition‐metal (Fe, Cu, and Ni) nanoclusters (ca. 1.2 nm) wreathed on hollow carbon nanospheres (S@M‐HC) for RT‐Na/S batteries is reported. A chemical couple between the metal nanoclusters and sulfur is hypothesized to assist in immobilization of sulfur and to enhance conductivity and activity. S@Fe‐HC exhibited an unprecedented reversible capacity of 394 mAh g^?1 despite 1000 cycles at 100 mA g^?1, together with a rate capability of 220 mAh g^?1 at a high current density of 5 A g^?1. DFT calculations underscore that these metal nanoclusters serve as electrocatalysts to rapidly reduce Na₂S₄ into short‐chain sulfides and thereby obviate the shuttle effect.     

Nickel(II)-Mediated Reversible Thiolate/Disulfide Conversion as a Mimic for a Key Step of the Catalytic Cycle of Methyl-Coenzyme M Reductase

According to the well-accepted mechanism, methyl-coenzyme M reductase (MCR) involves Ni-mediated thiolate-to-disulfide conversion that sustains its catalytic cycle of methane formation in the energy saving pathways of methanotrophic microbes. Model complexes that illustrate Ni-ion mediated reversible thiolate/disulfide transformation are unknown. In this paper we report the synthesis, crystal structure, spectroscopic properties and redox interconversions of a set of Ni^II complexes comprising a tridentate N₂S donor thiol and its analogous N₄S₂ donor disulfide ligands. These complexes demonstrate reversible Ni^II-thiolate/Ni^II-disulfide (both bound and unbound disulfide-S to Ni^II) transformations via thiyl and disulfide monoradical anions that resemble a primary step of MCR's catalytic cycle.     

Nickel(II)‐Mediated Reversible Thiolate/Disulfide Conversion as a Mimic for a Key Step of the Catalytic Cycle of Methyl‐Coenzyme M Reductase

According to the well‐accepted mechanism, methyl‐coenzyme M reductase (MCR) involves Ni‐mediated thiolate‐to‐disulfide conversion that sustains its catalytic cycle of methane formation in the energy saving pathways of methanotrophic microbes. Model complexes that illustrate Ni‐ion mediated reversible thiolate/disulfide transformation are unknown. In this paper we report the synthesis, crystal structure, spectroscopic properties and redox interconversions of a set of Ni^II complexes comprising a tridentate N₂S donor thiol and its analogous N₄S₂ donor disulfide ligands. These complexes demonstrate reversible Ni^II‐thiolate/Ni^II‐disulfide (both bound and unbound disulfide‐S to Ni^II) transformations via thiyl and disulfide monoradical anions that resemble a primary step of MCR's catalytic cycle.     

A Full Li–S Battery with Ultralow Excessive Li Enabled via Lithiophilic and Sulfilic W2C Modulation

The practical application of Li–S batteries demands low cell balance (Li_capacity/S_capacity), which involves uniform Li growth, restrained shuttle effect, and fast redox reaction kinetics of S species simultaneously. Herein, with the aid of W₂C nanocrystals, a freestanding 3D current collector is applied as both Li and S hosts owing to its lithiophilic and sulfilic property. On the one hand, the highly conductive W₂C can reduce Li nucleation overpotentials, thus guiding uniform Li nucleation and deposition to suppress Li dendrite growth. On the other hand, the polar W₂C with catalytic effect can enhance the chemisorption affinity to lithium polysulfides (LiPSs) and guarantee fast redox kinetics to restrain S species in cathode region and promote the utilization of S. Surprisingly, a full Li–S battery with ultralow cell balance of 1.5:1 and high sulfur loading of 6.06 mg cm⁻² shows obvious redox plateaus of S and maintains high reversible specific capacity of 1020 mAh g⁻¹ (6.2 mAh cm⁻²) after 200 cycles. This work may shed new sights on the facile design of full Li–S battery with low excessive Li supply.     

Bimetal-Organic Framework Nanoboxes Enable Accelerated Redox Kinetics and Polysulfide Trapping for Lithium-Sulfur Batteries

Lithium-sulfur (Li−S) batteries are considered as promising candidates for next-generation energy storage systems in view of the high theoretical energy density and low cost of sulfur resources. The suppression of polysulfide diffusion and promotion of redox kinetics are the main challenges for Li−S batteries. Herein, we design and prepare a novel type of ZnCo-based bimetallic metal–organic framework nanoboxes (ZnCo-MOF NBs) to serve as a functional sulfur host for Li−S batteries. The hollow architecture of ZnCo-MOF NBs can ensure fast charge transfer, improved sulfur utilization, and effective confinement of lithium polysulfides (LiPSs). The atomically dispersed Co−O₄ sites in ZnCo-MOF NBs can firmly capture LiPSs and electrocatalytically accelerate their conversion kinetics. Benefiting from the multiple structural advantages, the ZnCo-MOF/S cathode shows high reversible capacity, impressive rate capability, and prolonged cycling performance for 300 cycles.