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.     

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.     

Delocalized Isoelectronic Heterostructured FeCoOxSy Catalysts with Tunable Electron Density for Accelerated Sulfur Redox Kinetics in Li-S batteries

High interconversion energy barriers, depressive reaction kinetics of sulfur species, and sluggish Li⁺ transport inhibit the wide development of high-energy-density lithium sulfur (Li−S) batteries. Herein, differing from random mixture of selected catalysts, the composite catalyst with outer delocalized isoelectronic heterostructure (DIHC) is proposed and optimized, enhancing the catalytic efficiency for decreasing related energy barriers. As a proof-of-content, the FeCoO_xS_y composites with different degrees of sulfurization are fabricated by regulating atoms ratio between O and S. The relationship of catalytic efficiency and principal mechanism in DIHCs are deeply understood from electrochemical experiments to in situ/operando spectral spectroscopies i.e., Raman, XRD and UV/Vis. Consequently, the polysulfide conversion and Li₂S precipitation/dissolution experiments strongly demonstrate the volcano-like catalytic efficiency of various DIHCs. Furthermore, the FeCoO_xS_y-decorated cell delivers the high performance (1413 mAh g⁻¹ at 0.1 A g⁻¹). Under the low electrolyte/sulfur ratio, the high loading cell stabilizes the areal capacity of 6.67 mAh cm⁻² at 0.2 A g⁻¹. Impressively, even resting for about 17 days for possible polysulfide shuttling, the high-mass-loading FeCoO_xS_y-decorated cell stabilizes the same capacity, showing the practical application of the DIHCs in improving catalytic efficiency and reaching high electrochemical performance.     

Enhanced Cycling Performance of All-Solid-State Li-S Battery Enabled by PVP-Blended PEO-Based Double-Layer Electrolyte

Despite the high specific capacity of Li−S battery, shuttle effect of lithium polysulfides (LiPSs) and safety issue pose a great challenge to realize its commercial application. Replacing liquid electrolyte with poly (ethylene oxide) (PEO) -based solid-state electrolyte is considered as a promising method to boost the safety, but the shuttle effect of LiPSs cannot be completely eliminated. In this work, a new kind of double-layer PEO-based polymer electrolyte is designed to restrict the LiPSs. The layer next to cathode consists of PEO and poly(vinylpyrrolidone) (PVP). The other layer consists of PEO. PVP with abundant of amide groups has been proved to have strong affinity to LiPSs. The strong interaction between LiPSs and carbonyl groups in amide is verified by Attenuated Total Reflection-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy tests. As a result, the assembled Li−S battery exhibits a specific capacity of 1100 mAh g⁻¹ and capacity retention of 347 mAh g⁻¹ after 200 cycles at 60 °C and 0.05 C, while the capacity retention of the battery without PVP-blended PEO electrolyte remains only 27 % at the same conditions.     

Origin and Acceleration of Insoluble Li2S2−Li2S Reduction Catalysis in Ferromagnetic Atoms-based Lithium-Sulfur Battery Cathodes

Accelerating insoluble Li₂S₂−Li₂S reduction catalysis to mitigate the shuttle effect has emerged as an innovative paradigm for high-efficient lithium-sulfur battery cathodes, such as single-atom catalysts by offering high-density active sites to realize in situ reaction with solid Li₂S₂. However, the profound origin of diverse single-atom species on solid-solid sulfur reduction catalysis and modulation principles remains ambiguous. Here we disclose the fundamental origin of Li₂S₂−Li₂S reduction catalysis in ferromagnetic elements-based single-atom materials to be from their spin density and magnetic moments. The experimental and theoretical studies disclose that the Fe−N₄-based cathodes exhibit the fastest deposition kinetics of Li₂S (226 mAh g⁻¹) and the lowest thermodynamic energy barriers (0.56 eV). We believe that the accelerated Li₂S₂−Li₂S reduction catalysis enabled via spin polarization of ferromagnetic atoms provides practical opportunities towards long-life batteries.     

Cooperative Catalysis of Polysulfides in Lithium-Sulfur Batteries through Adsorption Competition by Tuning Cationic Geometric Configuration of Dual-active Sites in Spinel Oxides

Fundamentally understanding the structure–property relationship is critical to design advanced electrocatalysts for lithium-sulfur (Li−S) batteries, which remains a formidable challenge. Herein, by manipulating the regulable cations in spinel oxides, their geometrical-site-dependent catalytic activity for sulfur redox is investigated. Experimental and theoretical analyses validate that the modulation essence of cooperative catalysis of lithium polysulfides (LiPSs) is dominated by LiPSs adsorption competition between Co³⁺ tetrahedral (Td) and Mn³⁺ octahedral (Oh) sites on Mn³⁺_Oh−O−Co³⁺_Td backbones. Specifically, high-spin Co³⁺_Td with stronger Co−S covalency anchors LiPSs persistently, while electron delocalized Mn³⁺_Oh with adsorptive orbital (d_z²) functions better in catalyzing specialized LiPSs conversion. This work inaugurates a universal strategy for sculpting geometrical configuration to achieve charge, spin, and orbital topological regulation in electrocatalysts for Li−S batteries.     

Sulfur‐Rich Phosphorus Sulfide Molecules for Use in Rechargeable Lithium Batteries

A new family of sulfur‐rich phosphorus sulfide molecules (P₄S_10+n ) and their electrochemical reaction mechanism with metallic Li has been explored. These P₄S_10+n molecules are synthesized by the reaction between P₄S₁₀ and S. For Li batteries, the P₄S₄₀ molecule in the series of P₄S_10+n molecules provides the highest capacity, which has a first discharge capacity of 1223 mAh g⁻¹ at 100 mA g⁻¹ and stabilizes at approximately 720 mAh g⁻¹ at 500 mA g⁻¹ after 100 cycles. This new class of sulfur‐rich P₄S_10+n molecules and its electrochemical behavior for room‐temperature Li⁺ storage could provide novel insights for phosphorus sulfide molecules and high‐energy batteries.     

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 and electrochemical performance of CeO2@CNTs/S composite cathode for Li–S batteries

The shuttle effect of lithium-sulfur (Li–S) battery is one of the crucial factors restraining its commercial application, because LiPSs (lithium polysulfides) usually leads to poor cycle life and low coulomb efficiency. Some studies have shown that metal oxides can adsorb soluble polysulfides. Herein, CeO₂ (cerium-oxide)-doped carbon nanotubes (CeO₂@CNTs) were prepared by the hydrothermal method. The polar metal oxide CeO₂ enhanced the chemisorption of the cathode to LiPSs and promoted the redox reaction of the cathode through catalysis properties. Meanwhile, the carbon nanotubes (CNTs) enhanced cathode conductivity and achieved more sulfur loading. The strategy could alleviate polysulfide shuttling and accelerate redox kinetics, improving Li–S batteries' electrochemical performances. As a result, the CeO₂@CNTs/S composite cathode showed the excellent capacity of 1437.6 mAh g⁻¹ in the current density of 167.5 mA g⁻¹ at 0.1 C, as well as a long-term cyclability with an inferior capacity decay of 0.17% per cycle and a superhigh coulombic efficiency of 100.434% within 300 cycles. The superior electrochemical performance was attributed to the polar adsorption of CeO₂ on polysulfides and the excellent conductivity of CNTs.

     

N- and S-doped ordered mesoporous carbon tubes with efficient S confinement for high-performance Li–S batteries

The insulating properties of S/Li₂S₂/Li₂S and the soluble Li₂S₄/Li₂S₆/Li₂S₈ obstruct the practical application of Li–S batteries. In this work, highly ordered N and S co-doped mesoporous carbon tubes (NSMCTBs) with high specific surface areas and large pore volume are employed to confine and improve the utilization efficiency of S species in Li–S batteries. The strong S_nLi₂?N interaction and S–S chemical bond between thiophenic S and Li₂S_n guarantee the exceptional electrochemical performance of as-prepared NSMCTBs/S cathode. A relatively high discharge capacity of 1315.2 mAh g^?1 is achieved for the first cycle at 0.5 C and maintained at 644.1 mAh g^?1 after 500 cycles. The NSMCTBs/S with high S content of up to 80%, it also delivers a discharge capacity of 1092.1 mAh g^?1 and considerable cycling performance. More importantly, the NSMCTBs/S can effectively suppress the self-discharge behavior of Li–S batteries.     

Reducing Overpotential of Solid-State Sulfide Conversion in Potassium-Sulfur Batteries

Improving kinetics of solid-state sulfide conversion in sulfur cathodes can enhance sulfur utilization of metal-sulfur batteries. However, fundamental understanding of the solid-state conversion remains to be achieved. Here, taking potassium-sulfur batteries as a model system, we for the first time report the reducing overpotential of solid-state sulfide conversion via the meta-stable S₃²⁻ intermediates on transition metal single-atom sulfur hosts. The catalytic sulfur host containing Cu single atoms demonstrates high capacities of 1595 and 1226 mAh g⁻¹ at current densities of 335 and 1675 mA g⁻¹, respectively, with stable Coulombic efficiency of ≈100 %. Combined spectroscopic characterizations and theoretical computations reveal that the relatively weak Cu-S bonding results in low overpotential of solid-state sulfide conversion and high sulfur utilization. The elucidation of solid-state sulfide conversion mechanism can direct the exploration of highly efficient metal-sulfur batteries.     

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.     

Bidirectional Tandem Electrocatalysis Manipulated Sulfur Speciation Pathway for High-Capacity and Stable Na-S Battery

The sluggish polysulfide redox kinetics and the uncontrollable sulfur speciation pathway, leading to serious shuttling effect and high activation barrier associated with sulfur cathode. We describe here the use of core–shell structured composite matrixes containing abundant catalytic sites for nearly fully reversible cycling of sulfur cathodes for Na-S batteries. The bidirectional tandem electrocatalysis provide successive reversible conversion of both long- and short-chain polysulfides, whereas Fe₂O₃ accelerates Na₂S₈/Na₂S₆ to Na₂S₄ conversion and the redox-active Fe(CN)₆⁴⁻-doped polypyrrole shell catalyzes Na₂S₄ reduction to Na₂S. The electrochemically reactive Na₂S can be readily charged back to sulfur with minimal overpotential. Simultaneously, stable cycling of Na-S pouch cell with a high reversible capacity of 696 mAh g⁻¹ is also demonstrated. The bidirectional confined tandem catalysis renders the manipulation of sulfur redox electrochemistry for practical Na-S cells.     

Topochemical Path in High Lithiation of MoS2

Lithiation of MoS₂/RGO (reduced graphite oxide) electrodes repeatedly reached experimental capacities larger than 1000 mA · g^–1, corresponding to at least 6 lithium equivalents per gram of MoS₂. At our best knowledge, a convincing explanation is still missing in literature. In most cases, phase separation into Li₂S and elemental Mo was assumed to occur. However, this can only explain capacities up to 669 mA · g^–1, corresponding to an exchange of four Li. Formation of LiMo alloys could resolve the problem but the Li/Mo system does not contain any binary phases. If signs for Li₂S formation were found, indeed experimental capacities were below 700 mAh · g^–1. Here we present a topochemical mechanism, which sustains multiple charge/discharge cycles at 1000 mAh · g^–1, corresponding to an exchange of at least 6 Li per formula unit MoS₂. This topochemical reaction route prevents decomposition into binary phases and thus avoids segregation of the components of MoS₂. Throughout the whole lithiation/delithiation process, distinct layers of Mo are preserved but extended or shrunk by slight movements and reshuffling of sulfur and lithium atoms. On addition of 6 Li per formula unit to MoS₂, all central sulfur atoms are hosted in mutual Mo–S layers such that formal S^2– and Mo^2– anions appear coordinated by lithium cations. Indeed, similar structures are known in the field of Zintl phases. Our first‐principles crystal structure prediction study describes this topological path through conversion reactions during the lithiation/delithiation processes. All optimized phases along the topological path exhibit a distinct Mo layering giving rise to a series of dominant scattering into pseudo 001 reflections perpendicular to these Mo planes. The mechanism we present here explains why such high capacities can be reached reversibly for MoS₂/RGO nano composites     

Synergistic Engineering of Defects and Heterostructures Enhance Lithium/Sodium Storage Properties of F-SnO2-x-SnS2-x Nanocrystals Supported on N,S-Graphene

Phase engineering of the electrode materials in terms of designing heterostructures, introducing heteroatom and defects, improves great prospects in accelerating the charge storage kinetics during the repeated Li⁺/Na⁺ insertion/deintercalation. Herein, a new design of Li/Na-ion battery anodes through phase regulating is reported consisting of F-doped SnO₂-SnS₂ heterostructure nanocrystals with oxygen/sulfur vacancies (V_O/V_S) anchored on a 2D sulfur/nitrogen-doped reduced graphene oxide matrix (F-SnO_2-x-SnS_2-x@N/S-RGO). Consequently, the F-SnO_2-x-SnS_2-x@N/S-RGO anode demonstrates superb high reversible capacity and long-term cycling stability. Moreover, it exhibits excellent great rate capability with 589 mAh g⁻¹ for Li⁺ and 296 mAh g⁻¹ at 5 A g⁻¹ for Na⁺. The enhanced Li/Na storage properties of the nanocomposites are not only attributed to the increase in conductivity caused by V_O/V_S and F doping (confirmed by DFT calculations) to accelerate their charge-transfer kinetics but also the increased interaction between F-SnO_2-x-SnS_2-x and Li/Na through heterostructure. Meanwhile, the hierarchical F-SnO_2-x-SnS_2-x@N/S-RGO network structure enables fast infiltration of electrolyte and improves electron/ion transportation in the electrode, and the corrosion resistance of F doping contributes to prolonged cycle stability.     

Polyoxometalate-Cyclodextrin-Based Cluster-Organic Supramolecular Framework for Polysulfide Conversion and Guest–Host Recognition in Lithium-sulfur Batteries

Developing polyoxometalate-cyclodextrin cluster-organic supramolecular framework (POM-CD-COSF) still remains challenging due to an extremely difficult task in rationally interconnecting two dissimilar building blocks. Here we report an unprecedented POM-CD-COSF crystalline structure produced through the self-assembly process of a Krebs-type POM, [Zn₂(WO₂)₂(SbW₉O₃₃)₂]¹⁰⁻, and two β-CD units. The as-prepared POM-CD-COSF-based battery separator can be applied as a lightweight barrier (approximately 0.3 mg cm⁻²) to mitigate the polysulfide shuttle effect in lithium-sulfur batteries. The designed Li−S batteries equipped with the POM-CD-COSF modified separator exhibit remarkable electrochemical performance, attributed to fast Li⁺ diffusion through the supramolecular channel of β-CD, efficient polysulfide-capture ability by the dynamic host–guest interaction of β-CD, and improved sulfur redox kinetics by the bidirectional catalysis of POM cluster. This research provides a broad perspective for the development of multifunctional supramolecular POM frameworks and their applications in Li−S batteries.     

Enhancing electrochemical conversion of lithium polysulfide by 1T-rich MoSe2 nanosheets for high performance lithium–sulfur batteries

The sluggish conversion kinetics and shuttle effect of lithium polysulfides (LiPSs) severely hamper the commercialization of lithium–sulfur batteries. Numerous electrocatalysts have been used to address these issues, amongst which, transition metal dichalcogenides have shown excellent catalytic performance in the study of lithium–sulfur batteries. Note that dichalcogenides in different phases have different catalytic properties, and such catalytic materials in different phases have a prominent impact on the performance of lithium–sulfur batteries. Herein, 1T-phase rich MoSe₂ (T-MoSe₂) nanosheets are synthesized and used to catalyze the conversion of LiPSs. Compared with the 2H-phase rich MoSe₂ (H-MoSe₂) nanosheets, the T-MoSe₂ nanosheets significantly accelerate the liquid phase transformation of LiPSs and the nucleation process of Li₂S. In-situ Raman and X-ray photoelectron spectroscopy (XPS) find that T-MoSe₂ effectively captures LiPSs through the formation of Mo-S and Li-Se bonds, and simultaneously achieves fast catalytic conversion of LiPSs. The lithium–sulfur batteries with T-MoSe₂ functionalized separators display a fantastic rate performance of 770.1 mAh/g at 3 C and wonderful cycling stability, with a capacity decay rate as low as 0.065% during 400 cycles at 1 C. This work offers a novel perspective for the rational design of selenide electrocatalysts in lithium–sulfur chemistry.     

Boosting the “Solid–Liquid–Solid” Conversion Reaction via Bifunctional Carbonate-Based Electrolyte for Ultra-long-life Potassium–Sulfur Batteries

Potassium–sulfur (K−S) batteries have attracted wide attention owing to their high theoretical energy density and low cost. However, the intractable shuttle effect of K polysulfides results in poor cyclability of K−S batteries, which severely limits their practical application. Herein, a bifunctional concentrated electrolyte (3 mol L⁻¹ potassium bis(trifluoromethanesulfonyl)imide in ethylene carbonate (EC)) with high ionic conductivity and low viscosity is developed to regulate the dissolution behavior of polysulfides and induce uniform K deposition. The organic groups in the cathode electrolyte interphase layer derived from EC can effectively block the polysulfide shuttle and realize a “solid–liquid–solid” reaction mechanism. The KF-riched solid-electrolyte interphase inhibits K dendrite growth during cycling. As a result, the achieved K−S batteries display a high reversible capacity of 654 mAh g⁻¹ at 0.5 A g⁻¹ after 800 cycles and a long lifespan over 2000 cycles at 1 A g⁻¹.     

A Supramolecular Capsule for Reversible Polysulfide Storage/Delivery in Lithium‐Sulfur Batteries

Supramolecular materials, in which small organic molecules are assembled into regular structures by non‐covalent interactions, attract tremendous interests because of their highly tunable functional groups and porous structure. Supramolecular adsorbents are expected to fully expose their abundant adsorptive sites in a dynamic framework. In this contribution, we introduced cucurbit[6]uril as a supramolecular capsule for reversible storage/delivery of mobile polysulfides in lithium‐sulfur (Li‐S) batteries to control undesirable polysulfide shuttle. The Li‐S battery equipped with the supramolecular capsules retains a high Coulombic efficiency and shows a large increase in capacity from 300 to 900 mAh g⁻¹ at a sulfur loading of 4.2 mg cm⁻². The implementation of supramolecular capsules offers insights into intricate multi‐electron‐conversion reactions and manifests as an effective and efficient strategy to enhance Li‐S batteries and analogous applications that involve complex transport phenomena and intermediate manipulation.     

Synthesis and electrochemical properties of sulfur doped-LixMnO2−ySy materials for lithium secondary batteries

Sulfur doped lithium manganese oxides (Li_xMnO_2−yS_y) were prepared by ion exchange of sodium for lithium in Na_xMnO_2−yS_y precursors obtained by a sol–gel method. These materials had the nano-crystallite size, which was composed of grain size of about 100–200 nm. Especially, Li_0.56MnO_1.98S_0.02 delivered the initial discharge capacity of 170 mAh g⁻¹ and gradually increased the discharge capacity of 220 mAh g⁻¹ until 50 cycles. Moreover, it showed an excellent cycling behavior, although its original structure transformed into the spinel phase during cycling.