Soluble Lithium Polysulfides Research Articles

Synergistic mechanisms of nitrogen configurations in sulfur hosts and their enhancement of electrochemical performance in lithium‑sulfur batteries

Lithium‑sulfur batteries (LSBs) have attracted a lot of attention due to their high theoretical capacity and energy density. However, the cathode material for LSBs is limited by the low conductivity of sulfur and its products, as well as volume fluctuations during charging and discharging, and the shuttle effect of soluble lithium polysulfide. In this work, a cathode sulfur host material Nitrogen-doped porous carbon materials (N-PCM) was synthesized, doped with Pyridine N and Pyrrolic N, using melamine and glycine as nitrogen sources, silicon dioxide as template. The synthesis method characterized by controllable nitrogen content and nitrogen configurations. The results of the electrochemical performance test indicate that the composite N-PCM/S exhibits a higher capacity and enhanced cycling stability. At a rate of 0.1C, N-PCM/S demonstrates an initial discharge capacity of up to 1308 mAh/g. At 2C, the initial discharge capacity is 603 mAh/g, while maintaining a reversible capacity of 543 mAh/g after 400 cycles. The capacity decay rate is only 0.025 % per cycle, showcasing excellent cycle stability. Additionally, the N-PCM/S exhibits excellent electrochemical performance under electrolyte-poor conditions. The results showed that the synergistic effect of different nitrogen configurations significantly enhanced the adsorption and catalytic conversion of polysulfide by sulfur hosts, accelerate the reaction rate of polysulfide.

Trace amounts of MoB MBene with layered configuration trigger catalytic converter of polysulfide

The formation of soluble lithium polysulfide severely limits the performance of the reversible capacity and cycle stability in lithium‑sulfur batteries. Herein, a carbon fiber cathode of LiS battery is proposed, and the two-dimensional metal boride material MoB MBene is selected as the catalyst of lithium‑sulfur battery. Theoretical calculations and experimental data have confirmed that MoB MBene performs exceptionally well in adsorbing polysulfides and preventing the shuttle effect. It also expedites the solid-liquid-solid phase transition and efficiently decrease the Li2S breakdown energy barrier. MoB MBene not only anchors polysulfides by generating MoS bonds in LiS redox reaction, but also accelerates the kinetics of polysulfide conversion by lowering the energy barrier of polysulfides conversion. By adopting MoB MBene as a catalyst, a lithium‑sulfur battery achieved a long cycle life (with only 0.0779 % attenuation after 800 cycles at 1C) and a high initial discharge capacity (1105 mAh g−1). This work could provide new perspectives on using MBene as a catalyst for LiS chemistry.

Pyridinic-N-rich single-atom vanadium catalysts boost conversion kinetics of polysulfides for high performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are promising next-generation energy storage devices possessing a high theoretical energy density, but their practical deployment has been hindered by the notorious shuttle effect and sluggish conversion kinetics of soluble lithium polysulfides (LiPSs). In this work, single-atom vanadium catalysts (V-SACs) embedded in pyridinic-N-rich carbon are developed through a simple one-step polymer-assisted pyrolysis approach, which can effectively adsorb LiPSs and remarkably boost the kinetics of LiPSs conversion. The Li-S cells comprising pyridinic-N-rich V-SACs as the sulfur host display an initial discharge capacity of 921.1 mAh g−1 at 1 C and retain a capacity of 605.8 mAh g−1 after 500 cycles, showing a low decay rate of 0.068 % per cycle. Even with a high sulfur loading of 6.5 mg cm−2 and a low electrolyte/sulfur ratio of 7.5 μL mg−1, the cell still delivers a high initial areal capacity of 8.1 mAh cm−2 at 0.05 C. Comprehensive experimental studies and density functional theory (DFT) calculations demonstrate that the abundant pyridinic-N sites and vanadium single atoms afford more chemisorption sites for LiPSs and synergistically promote LiPSs conversion kinetics, resulting in enhanced electrochemical performance compared to the Li-S cells without V-SACs.

A yarn-ball-shaped graphene microsphere-coated separator design for enhanced electrochemical performance in Li-S batteries

Lithium-sulfur batteries (LSBs) present a promising alternative to conventional lithium-ion (Li-ion) batteries due to their high energy density and theoretical capacity. However, their practical application is hindered by issues such as poor sulfur utilization, highly soluble lithium polysulfides (LiPSs), and rapid capacity decay. This study introduces an innovative cell configuration using a separator coated with reduced graphene oxide/carbon nanotube (rGO/CNT) microspheres. The rGO/CNT-coated separator aims to enhance electron transfer, confine LiPSs within the cathode region, and mitigate their migration to the anode. In particular, the LSB cell with an rGO/CNT-modified separator delivers an impressive initial capacity of 1482 mAh g−1 and demonstrates a low capacity decay rate of 0.09% per cycle. The highly conductive rGO/CNT-coated separator enhances active material utilization even at high rates, resulting in a significant capacity of 824 mAh g−1 at 4C. Furthermore, the rGO/CNT-modified separator shows an impressive capacity of 895 mAh g−1 under high sulfur loading of 4.8 mg cm−2 with long-term cycling performance. The results demonstrate that the rGO/CNT-coated separator significantly enhances sulfur reutilization, reduces capacity decay, and improves the electrochemical stability of LSBs. This configuration simplifies the manufacturing process and offers a viable solution for the practical application of LSBs.

Hierarchical van der Waals heterostructure with dual-defect sites for bidirectionally catalyzing Li2S nucleation and decomposition in lithium-sulfur batteries

The lithium‑sulfur batteries hold a promising option for the next generation of energy storage systems. Nevertheless, the shuttle effect of soluble lithium polysulfides and their slow reaction kinetics lead to extremely low efficiency and poor stability, thereby limiting the commercial viability of lithium‑sulfur batteries. Herein, MoSe2/Ti3C2 van der Waals heterostructure is synthesized with a dual-defect strategy, and its electrocatalytic performance is further improved through solution coating treatment (SCT), which involves the addition of glucose during the hydrothermal process. The conductive Ti3C2 scaffold effectively inhibits the aggregation of MoSe2 nanoflakes, thereby validating a larger active surface area. Meanwhile, the nitrogen dopant and selenium vacancy dual-defects in MoSe2 provide abundant active sites for anchoring polysulfides and catalyzing their conversion. As a result, the synergistic interaction between MoSe2 and Ti3C2 bidirectionally catalyzes the Li2S nucleation and decomposition through a heterointerface effect. The lithium‑sulfur battery equipped with MoSe2/Ti3C2-SCT heterostructure modified separator exhibits outstanding discharge specific capacity of 1496.9 mAh g−1 at 0.1C, and a low decay rate per cycle of 0.059 % after 500 cycles at 1C. The discharge specific capacity recovers to 89.3 % of the initial capacity when the current density is decreased from 5C to 0.1C. This work highlights the potential of defect engineering in transition metal selenides to enhance the performance of lithium‑sulfur batteries. It offers a new approach to designing composite electrocatalysts for high-performance lithium‑sulfur batteries.

First-principles investigations to evaluate FeN2 as an electrocatalyst to improve the performance of Li–S batteries

The high energy density, low cost, and environmental sustainability of lithium-sulfur (Li–S) batteries render them highly promising as next-generation energy storage devices. Nevertheless, the commercial advancement of Li–S batteries faces obstacles, including the limited conductivity of sulfur, the shuttle effect of lithium polysulfides (LiPSs), and the suboptimal efficiency of the discharging/charging process. Based on the theoretical calculation of density functional, the potential application of an FeN2 single-layer as a catalyst in Li–S batteries to overcome the abovementioned problems is studied. The results show that the FeN2 single-layer molecules have a metal electron structure and soluble LiPSs can effectively coordinate and bond with FeN2. Improving the overall conductivity and anchoring effect of sulfur can effectively inhibit the shuttle effect caused by LiPSs. It is worth noting that the FeN2 single-molecule membrane has dual functions, and it has electrocatalytic activity on both the sulfur reduction reaction and the Li2S decomposition reaction, thus improving the conversion efficiency of the discharging and charging processes. These findings may provide a reference for the development of high-performance Li–S batteries.

High-entropy sulfides enhancing adsorption and catalytic conversion of lithium polysulfides for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with high energy density suffer from the soluble lithium polysulfide species. Traditional metal sulfides containing a single metal element used as electrocatalysts for Li-S batteries commonly have limited catalytic abilities to improve battery performance. Herein, based on the Hume-Rothery rule and solvothermal method, the high-entropy sulfide NiCoCuTiVSx derived from Co9S8 was designed and synthesized, to realize the combination of small local strain and excellent catalytic performance. With all five metal elements (Ni, Co, Cu, Ti, and V) capable of chemical interactions with soluble polysulfides, NiCoCuTiVSx exhibited strong chemical confinement of polysulfides and promoted fast kinetics for polysulfides conversion. Consequently, the S/NiCoCuTiVSx cathode can maintain a high discharge capacity of 968.9 mA h g−1 after 200 cycles at 0.5 C and its capacity retention is 1.3 times higher than that of S/Co9S8. The improved cycle stability can be attributed to the synergistic effect originating from the multiple metal elements, coupled with the reduced nucleation and activation barriers of Li2S. The present work opens a path to explore novel electrocatalyst materials based on high entropy materials for the achievement of advanced Li-S batteries.

Synergistic Interaction of Strongly Polar Zinc Selenide and Highly Conductive Carbon Nanoframeworks Accelerates Redox Kinetics of Polysulfides.

Lithium-sulfur batteries (LSBs) have become strong competitors in secondary battery systems because of their superior theoretical capacity and energy density. However, due to the serious shuttle effect of soluble long-chain lithium polysulfides (LiPSs) and the slow solid-solid reaction kinetics, LSBs face some specific challenges, such as a short cycle life and low rate performance. The introduction of selenide/carbon composites derived from zeolite imidazolate frameworks (ZIFs) into separator coatings is a direct and effective solution to the aforementioned problems. Here, a zinc selenide/carbon catalyst material (ZnSe@C) was constructed and employed to modify commercial polypropylene (PP) separators to accelerate the conversion of intermediates. The highly polar ZnSe effectively fixes the active material on the cathode side by transferring electrons between elements with LiPSs and improves the utilization rate of sulfur. Concurrently, the highly conductive carbon nanoskeleton generated following the pyrolysis of ZIF-8 ensures the rapid transfer of charges during the catalytic reaction. The prepared ZnSe@C has a large specific surface area (250.07 m2 g-1) and mesoporous ratio (78.03%), which not only enhances adsorption and catalysis but also promotes the penetration of the electrolyte and the transport of Li+. Based on this, ZnSe@C/PP separator cells exhibit a low average capacity decay rate of 0.051% per cycle after 500 cycles at 1 C.

Janus-type monolayer M2SSe (M = Ga, In, B, and al) as sulfur host materials for lithium-sulfur batteries: A first-principles study

Lithium-sulfur batteries (LSBs) are notable for their outstanding energy density, economic viability, and environmental friendliness, positioning them as a leading option for future energy storage solutions. Nevertheless, the insulation of sulfur, the shuttle effect, and the sluggish redox kinetics limit their application. Hence, finding a suitable sulfur host material is critical to improve the performance of LSBs. In this work, the comprehensive calculations of adsorption configurations, electronic properties, and Gibbs free energy during catalytic processes are conducted to reveal the unique advantages of Janus-type monolayer M2SSe (M = Ga, In, B, and Al) as a potential sulfur host material. The calculated results indicate that M2SSe monolayers exhibit semiconducting properties and effectively adsorb soluble lithium polysulfides, thereby enhancing the conductivity and response speed of LSBs, and suppressing the shuttle effect. Moreover, M2SSe exhibits bifunctional electrocatalytic ability, improving the conversion of lithium polysulfide during charging and discharging, thus effectively accelerating the redox kinetics of LSBs. Among the Janus-type M2SSe series, the Se-side of In2SSe exhibits the most promising characteristics. This study indicates that Janus-type monolayer M2SSe (M = Ga, In, B, and Al) effectively serves as a sulfur host material for LSBs, overcoming critical challenges and improving overall performance.

Unique flake-shaped sulfur morphology favored by the binder-free electrophoretically deposited TiO2 layer as a promising cathode structure for Li-S batteries

Metal oxides have been extensively studied as catalyst additives in Li-S batteries due to their high affinity for soluble lithium polysulfides (LiPSs). The present study developed a novel carbon nanomaterials- and binder-free 3D sulfur host by electrophoretic deposition (EPD) of TiO2 nanoparticles on carbon fiber paper (CFP). Benefiting from the unique well-connected TiO2 porous layer formed by EPD, the initial discharge capacity of Li-S battery was increased from 1160 mAh g−1 in conventional cast TiO2/binder/S cathode (Cast:CFP/PVDF/TiO2/S) to 1310 mAh g−1 in the EPD:CFP/TiO2/S cathode, along with an overpotential drop of 16 %. Electron microscopic studies at 100% state-of-charge (SoC) revealed that while notorious sulfur particulates were formed on Cast:CFP/PVDF/TiO2/S, the surface of EPD:CFP/TiO2/S was covered with flake-shaped sulfur precipitates. The formation of sulfur flakes effectively suppressed pulverization in EPD:CFP/TiO2/S, leading to superior electrochemical performance and cycle life. Microstructural studies and real-time EIS investigations revealed that sulfur flakes nucleated across the Li2S matrix at the initial stages of charge and grew vertically from the sulfur/TiO2 interface. The preferential growth mechanism of sulfur flakes was attributed to the superior surface conductance of the EPD-TiO2 film enabled by the ordered clusters formed during EPD, enhancing the kinetics of electrocatalytic reactions of polysulfides at the TiO2/sulfur interface. Our results show that developing novel methods to modify the morphology of secondary sulfur upon cycling is critical for enhancing charge-discharge performance in Li-S batteries.

Unveiling the Reaction Mystery Between Lithium Polysulfides and Lithium Metal Anode in Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are widely regarded as one of the most promising next-generation high-energy-density energy storage devices. However, soluble lithium polysulfides (LiPSs) corrode Li metal and deteriorate the cycling stability of Li-S batteries. Understanding the reaction mechanism between LiPSs and Li metal anode is imperative. Herein, the reaction rate and products of LiPSs with Li metal anode, the composition and structure of the as-generated solid electrolyte interphase (SEI), and the mechanism of lithium nitrate (LiNO3) additives for inhibiting the corrosion reactions are systematically unveiled. Concretely, LiPSs react with Li metal anode more rapidly than Li salt and generate a Li2S-rich SEI. The Li2S-rich SEI is highly reactive with LiPSs, which exacerbates the formation of dendritic Li and the continuous corrosion of active Li. LiNO3 functions dominantly by modulating the solvation structure of LiPSs and inherently reducing the reactivity of LiPSs, rather than the conventional understanding of LiNO3 participating in the formation of SEI. This work reveals the reaction mechanism between LiPSs and Li metal anode and inspires rational regulating of the solvation structure of LiPSs for stabilizing Li metal anode in Li-S batteries.

Scalable Ni12P5-Coated Carbon Cloth Cathode for Lithium–Sulfur Batteries

As a better alternative to lithium-ion batteries (LIBs), lithium–sulfur batteries (LSBs) stand out because of their multi-electron redox reactions and high theoretical specific capacity (1675 mA h g−1). However, the long-term stability of LSBs and their commercialization are significantly compromised by the inherently irreversible transition of soluble lithium polysulfides (LiPS) into solid short-chain S species (Li2S2 and Li2S) and the resulting substantial density change in S. To address these issues, we used activated carbon cloth (ACC) coated with Ni12P5 as a porous, conductive, and scalable sulfur host material for LSBs. ACC has the benefit of high electrical conductivity, high surface area, and a three-dimensional (3D) porous architecture, allowing for ion transport channels and void spaces for the volume expansion of S upon lithiation. Ni12P5 accelerates the breakdown of Li2S to increase the efficiency of active materials and trap soluble polysulfides. The highly effective Ni12P5 electrocatalyst supported on ACC drastically reduced the severity of the LiPS shuttle, affected the abundance of adsorption–diffusion–conversion interfaces, and demonstrated outstanding performance. Our cells achieved near theoretical capacity (>1611 mA h g−1) during initial cycling and superior capacity retention (87%) for >250 cycles following stabilization with a 0.05% decay rate per cycle at 0.2 C.

Revealing a volcano correlation of sulfur reduction catalytic activity and elements doping in cobalt-based sulfides for Li-S batteries

The effective utilization of Li-S batteries still necessitates the incorporation of an efficient catalytic medium to address the challenges posed by shuttle effects and sluggish reaction kinetics. Furthermore, the structure-activity relationship of catalysts for the sulfur reduction reaction remains inadequately understood. In this study, we utilize Co9S8 as a template to investigate the correlation between the doping of co-periodic elements (Fe, Ni, Cu and Zn) and their catalytic effects on the sulfur reduction reaction. There is a “volcano peak” correlation between the catalytic performance and the type of doped elements from Fe to Zn, and research indicates that the Ni-doped Co9S8 (NCS) demonstrates superior performance compared to other samples. The NCS not only maintains the inherent advantages of Co9S8 but also effectively lowers the apparent activation energy necessary for Li-S batteries. Consequently, this enhancement facilitates a more rapid and complete conversion of soluble lithium polysulfides, thereby endowing Li-S batteries with an enhanced reaction kinetics. When the sulfur areal loading is elevated to 5.2 mg cm−2, the maximum areal capacity of the cell can attain 5.2 mAh cm−2 at 0.05 C. This work further substantiates the efficacy of the element doping strategy in enhancing the catalytic performance of reduction reaction catalysts, and it also offers significant insights or considerations for the development of practical catalysts, thereby facilitating the practical application of Li-S batteries.

Metal–Organic Frameworks with Axial Cobalt–Oxygen Coordination Modulate Polysulfide Redox for Lithium–Sulfur Batteries

AbstractAlthough the ultrahigh theoretical energy density and cost‐effectiveness, lithium–sulfur (Li‐S) batteries suffer from sluggish conversion kinetics and the shuttling effect of soluble lithium polysulfides (LiPSs). Herein, conductive hexagonal cobalt‐organic framework (Co‐HTP) nanosheets are anchored in situ on carboxyl graphene (CG) substrates and serve as host catalysts to modulate the polysulfide redox. Substantial characterizations identify that the local coordination environment of the quadrilateral Co–N4 units transforms into an asymmetric penta‐coordinated O–Co–N4 with axial Co─O coordination, which triggers spin polarization and remarkable electron delocalization of Co 3d orbital. The higher spin state and lower local electron density of the O–Co–N4 sites induce more active electronic states in Co‐HTP/CG and facilitate orbital hybridization with polysulfides to form more stable bond orders. Such optimized electronic structure significantly accelerates redox kinetics and enhances the adsorption strength of polysulfides. These merit the lithium–sulfur battery based on Co‐HTP/CG with a high reversible capacity, impressive rate capability, and prolonged cycling performance over 500 cycles. This work will enrich the design philosophy of modulating the spintronic structure of electrocatalysts for advanced Li–S batteries and beyond.

Pd quantum dots supported on rhombic dodecahedral porous carbons connected by CNTs as multifunctional electrocatalysts for Li–S batteries

Lithium sulfide (Li2S) is considered as one of the promising cathode materials for secondary batteries owing to its high lithium storage capacity and low–cost advantage of sulfur. However, the commercial application of Li2S is hindered by the sluggish reaction kinetics of electrochemical conversion from Li2S to S and the shuttle effect of their soluble lithium polysulfides (LiPSs). Herein, we report a multifunctional electrocatalyst composed of 5.9 wt% Pd quantum dots supported on rhombic dodecahedral porous carbons connected by CNTs (Pd@RDPC–CNT) to improve the electrochemical reaction kinetics of Li2S and to alleviate the shuttle effect of LiPSs. The Pd@RDPC–CNT/Li2S nanocomposite exhibits a low first activation barrier of 2.56 V and fast reaction kinetics with a high reversible capacity of 1119 mAh g−1 at 0.2 A g−1, very close to the theoretical capacity of 1166 mAh g−1. The superior electrochemical performance including high reversible capacity, good rate capability and long–term cycling stability over 1000 cycles can be attributed to the multifunctional electrocatalyst of Pd@RDPC–CNT with high catalytic activation, strong LiPSs adsorption and high electronic/ionic conductivity, which is demonstrated by our experimental results and DFT calculation results. This study provides a way to apply Li2S to secondary batteries by using multifunctional electrocatalysts.

Facilitating sulfur species capture and bi-directional redox in Li-S batteries with single-atomic Co-O2N2 coordination structure

Lithium-sulfur (Li-S) batteries suffer from the shuttle effect of soluble lithium polysulfides (LiPSs) and slow redox kinetics, significantly limiting their practical application. Although single-atom catalysts (SACs) offer a promising strategy to address these challenges, designing materials with optimal adsorption force and high catalytic activity remains a grand challenge. Here, we present a cobalt (Co)-based SAC with unique Co-O2N2 coordination structures for Li-S batteries. Both experimental and theoretical studies demonstrate that O, N-coordinated Co single atoms anchored on a porous carbon framework (Co/NOC) effectively capture LiPSs and dramatically catalyze bidirectional polysulfide conversion. The expanded carbon layer spacing facilitates lithium ions diffusion and maximizes the exposure of active sites. As a result, Li-S batteries incorporating Co/NOC as separators exhibit outstanding rate performance (906.6 mAh g−1 at 3 C) and exceptional cycling stability, even at −10 °C. Furthermore, with a high sulfur loading of 12.0 mg cm−2, the areal specific capacity reaches up to 12.36 mAh cm−2. This work provides some useful insights for the design of high-performance SACs for Li-S batteries.

Synergistic Electrocatalyst-Cathode Architecture for Stable Long-Term Cycling Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are a promising candidate for next-generation energy storage owing to the high theoretical capacity of sulfur (1,675 mAh g−1). However, the intrinsically low electrical conductivity of sulfur and complex multistep electrolyte-mediated redox reactions involving soluble lithium polysulfide intermediates engender critical challenges toward practical realization. Specifically, migration and diffusion of higher-order lithium polysulfides provokes continuous loss of active sulfur species, yielding premature capacity fade. Electrochemical kinetics also remain sluggish due to the insulating nature of sulfur cathodes, which require engineering designs to accelerate charge transfer.Rational morphological and compositional cathode tuning represents a compelling strategy for addressing fundamental Li-S limitations. Herein, we develop an extended cathode architecture composed of a porous carbon nanotube network decorated with homogenously dispersed nanocatalysts. Electron microscopy and spectroscopy analysis verify platinum group metals are well-incorporated both within internal channels and external surface sites of conductive carbon nanotubes. The composite framework affords multifaceted functionality arising from synergistic chemical and structural attributes of components. Nanocatalyst sites demonstrate a pronounced chemical affinity toward soluble polysulfide intermediates, effectively localizing them within cathode, minimizing diffusional losses toward the anode. This anchoring phenomenon is complemented by the inherent microporosity of the high-surface-area nanotube network, further obstructing polysulfide migration through a confinement effects. Concurrently, noble metal nanoparticles facilitate the redox conversion of trapped higher-order polysulfides into solid Li2S alleviating the precipitation of electrically insulating discharge products. The excellent electrical conductivity of CNTs ensures efficient charge transport to all incorporated sulfur active materials, further maximizing reversible utilization.As a result of complementary polysulfide confinement and electrocatalytic conversion functionalities, Li-S coin cells exhibit enhanced reversible capacities exceeding 900 mAh g−1 for over 500 cycles at 0.558 A g−1. Notably, over 500 cycles, minimal capacity decay of 0.018% per cycle and 92% retention of the initial capacity are obtained at moderate sulfur loadings highlighting the exceptional cycling stability enabled by engineered cathodes. Outstanding rate performance is also demonstrated with the delivery of 854 mAh g−1 capacity at a very high current density of 1.675 A g−1. Our rationally designed cathode architecture provides critical mechanistic insight toward addressing fundamental bottlenecks to progress Li-S technologies.

Oriented structural design of MXene electrodes for lithium sulfur catalysis

The lithium-sulfur reaction can contribute to the chemical electrical energy conversion capacity due to the multi-level ion/electron transfer process. However, the appearance of soluble intermediate products prevents efficient electron transfer, making it impossible to achieve stable cycling and capacity contribution. Restricted catalysis provides a solution for inhibiting the shuttle of soluble lithium polysulfides. Herein, MXene aerogel with optimized channel utilization is designed as S host according to the polysulfide control strategy of localization, adsorption, and catalysis. With the help of the results of oriented channels, the polysulfide conversion process is optimized, providing a comprehensive scheme for inhibiting the shuttle effect. Lithium sulfur catalytic batteries have achieved high capacity and stable cycling. This system provides a comprehensive solution for lithium sulfur reaction catalysis and a new perspective for the functional application of MXene based lithium sulfur batteries.

Nitrogen-Doped TiO2- x(B)/MXene Heterostructures for Expediting Sulfur Redox Kinetics and Suppressing Lithium Dendrites.

Practical application of lithium-sulfur (Li-S) batteries is severely impeded by the random shuttling of soluble lithium polysulfides (LiPSs), sluggish sulfur redox kinetics, and uncontrollable growth of lithium dendrites, particularly under high sulfur loading and lean electrolyte conditions. Here, nitrogen-doped bronze-phase TiO2(B) nanosheets with oxygen vacancies (OVs) grown in situ on MXenes layers (N-TiO2- x(B)-MXenes) as multifunctional interlayers are designed. The N-TiO2- x(B)-MXenes show reduced bandgap of 1.10eV and high LiPSs adsorption-conversion-nucleation-decomposition efficiency, leading to remarkably enhanced sulfur redox kinetics. Moreover, they also have lithiophilic nature that can effectively suppress dendrites growth. The cell based on the N-TiO2- x(B)-MXenes interlayer under sulfur loading of 2.5mg cm-2 delivers superior cycling performance with a high specific capacity of 690.7 mAh g-1 over 600 cycles at 1.0 C. It still has a notable areal capacity of 6.15 mAh cm-2 after 50 cycles even under a high sulfur loading of 7.2mg cm-2 and a low electrolyte-to-sulfur (E/S) ratio of 6.4 µL mg-1. The Li-symmetrical battery with the N-TiO2- x(B)-MXenes interlayer showcases a low over-potential fluctuation with 21.0mV throughout continuous lithium plating/stripping for 1000h. This work offers valuable insights into the manipulation of defects and heterostructures to achieve high-energy Li-S batteries.

Hollow and Porous N‐Doped Carbon Framework as Lithium‐Sulfur Battery Interlayer for Accelerating Polysulfide Redox Kinetics

AbstractLithium‐sulfur batteries (LSBs) have become one of the most powerful candidates for next‐generation battery technologies due to their high theoretical energy density and low cost. However, the notorious shuttle effect of soluble lithium polysulfides (LiPSs) and sluggish conversion reaction kinetics cause low sulfur utilization and inferior cycle life. Rational catalyst design on hierarchical pore structures and composition optimization is highly desired to realize synergetic enrichment, accommodation, and catalytic redox capacity of sulfur species. In this consideration, the hollow and porous N‐doped carbon framework is prepared, in which Co nanoparticles (NPs) are evenly embedded (denoted as Co‐HMCF) to modulate electron cloud density of carbons. Electrochemical tests and density functional theory (DFT) calculations demonstrate that Co‐HMCF could simultaneously deliver superior catalytic activity in accelerating LiPSs conversion as well as Li2S nucleation/decomposition to improve overall sulfur redox kinetics. Consequently, the Co‐HMCF interlayer significantly improves the battery performance, including high discharge capacity output (1538 mAh g−1 at 0.2 C), stable long‐term cycle (0.047% capacity decay per cycle for 800 cycles at 1.0 C), and exceptional rate capacity (582 mAh g−1 at 5.0 C).