TiO2 and Co Nanoparticle-Decorated Carbon Polyhedra as Efficient Sulfur Host for High-Performance Lithium-Sulfur Batteries

Multifunctional TiN-MXene-Co@CNTs Networks as Sulfur/Lithium Host for High-Areal-Capacity Lithium-Sulfur Batteries

The inevitable shuttling and slow redox kinetics of lithium polysulfides (LiPSs) as well as the uncontrolled growth of Li dendrites have strongly limited the practical applications of lithium-sulfur batteries (LSBs). To address these issues, we have innovatively constructed the carbon nanotubes (CNTs) encapsulated Co nanoparticles in situ grown on TiN-MXene nanosheets, denoted as TiN-MXene-Co@CNTs, which could serve simultaneously as both sulfur/Li host to kill "three birds with one stone" to (1) efficiently capture soluble LiPSs and expedite their redox conversion, (2) accelerate nucleation/decomposition of solid Li2S, and (3) induce homogeneous Li deposition. Benefiting from the synergistic effects, the TiN-MXene-Co@CNTs/S cathode with a sulfur loading of 2.5 mg cm-2 could show a high reversible specific capacity of 1129.1 mAh g-1 after 100 cycles at 0.1 C, and ultralong cycle life over 1000 cycles at 1.0 C. More importantly, it even achieves a high areal capacity of 6.3 mAh cm-2 after 50 cycles under a sulfur loading as high as 8.9 mg cm-2 and a low E/S ratio of 5.0 μL mg-1. Besides, TiN-MXene-Co@CNTs as Li host could deliver a stable Li plating/striping behavior over 1000 h.

Ultrathin Mixed Ionic-Electronic Conducting Interlayer via the Solution Shearing Technique for High-Performance Lithium-Sulfur Batteries

The commercialization of lithium-sulfur (Li-S) batteries has been hampered by diverse challenges, including the shuttle phenomenon and low electrical/ionic conductivity of lithium sulfide and sulfur. To address these issues, extensive research has been devoted to developing multifunctional interlayers. However, interlayers capable of simultaneously suppressing the polysulfide (PS) shuttle and ensuring stable electrical and ionic conductivity are relatively uncommon. Moreover, the use of thick and heavy interlayers results in an unavoidable decline in the energy density of Li-S batteries. We developed an ultrathin (750 nm), lightweight (0.182 mg cm-2) interlayer that facilitates mixed ionic-electronic conduction using the solution shearing technique. The interlayer, composed of carbon nanotube (CNT)/Nafion/poly-3,4-ethylenedioxythiophene:tetracyanoborate (PEDOT:TCB), effectively suppresses the shuttle phenomenon through the synergistic segregation and adsorption effects on PSs by Nafion and CNT/PEDOT, respectively. Furthermore, the electrical/ionic conductivity of the interlayer can be improved via counterion exchange and homogeneous Li+ ion flux/good wettability from SO3- functional group of Nafion, respectively. Enhanced sulfur utilization and reaction kinetics through polysulfide shuttle inhibition and facilitated electron/ion transfer by interlayer enable a high discharge capacity of 1029 mA h g-1 in the Li-S pouch cell under a high sulfur loading of 5.3 mg cm-2 and low electrolyte/sulfur ratio of 5 μL mg-1.

Dual-Conductive CoSe2 @TiSe2 -C Heterostructures Promoting Overall Sulfur Redox Kinetics under High Sulfur Loading and Lean Electrolyte

Although lithium-sulfur batteries (LSBs) possess a high theoretical specific capacity and energy density, the inherent problems including sluggish sulfur conversion kinetics and the shuttling of soluble lithium polysulfides (LiPSs) have severely hindered the development of LSBs. Herein, cobalt selenide (CoSe₂ ) polyhedrons anchored on few-layer TiSe₂ -C nanosheets derived from Ti₃ C₂ T_x MXenes (CoSe₂ @TiSe₂ -C) are reported for the first time. The dual-conductive CoSe₂ @TiSe₂ -C heterostructures can accelerate the conversion reaction from liquid LiPSs to solid Li₂ S and promote Li₂ S dissociation process through high conductivity and lowered reaction energy barriers for promoting overall sulfur redox kinetics, especially under high sulfur loadings and lean electrolyte. Electrochemical analysis and density functional theory calculation results clearly reveal the catalytic mechanisms of the CoSe₂ @TiSe₂ -C heterostructures from the electronic structure and atomic level. As a result, the cell with CoSe₂ @TiSe₂ -C interlayer maintains a superior cycling performance with 842.4 mAh g^-1  and a low-capacity decay of 0.031% per cycle over 800 cycles at 1.0 C under a sulfur loading of 2.5 mg cm^-2 . More encouragingly, it with a high sulfur loading of ≈7.0 mg cm^-2  still harvests a high areal capacity of ≈6.25 mAh cm^-2  under lean electrolyte (electrolyte/sulfur, E/S ≈ 4.5 µL mg^-1 ) after 50 cycles at 0.05 C.

Unraveling Polysulfide's Adsorption and Electrocatalytic Conversion on Metal Oxides for Li-S Batteries

Lithium sulfur (LiS) batteries possess high theoretical capacity and energy density, holding great promise for next generation electronics and electrical vehicles. However, the LiS batteries development is hindered by the shuttle effect and sluggish conversion kinetics of lithium polysulfides (LiPSs). Designing highly polar materials such as metal oxides (MOs) with moderate adsorption and effective catalytic activity is essential to overcome the above issues. To design efficient MOs catalysts, it is critical and necessary to understand the adsorption mechanism and associated catalytic processes of LiPSs. However, most reviews still lack a comprehensive investigation of the basic mechanism and always ignore their in-depth relationship. In this review, a systematic analysis toward understanding the underlying adsorption and catalytic mechanism in LiS chemistry as well as discussion of the typical works concerning MOs electrocatalysts are provided. Moreover, to improve the sluggish "adsorption-diffusion-conversion" process caused by the low conductive nature of MOs, oxygen vacancies and heterostructure engineering are elucidated as the two most effective strategies. The challenges and prospects of MOs electrocatalysts are also provided in the last section. The authors hope this review will provide instructive guidance to design effective catalyst materials and explore practical possibilities for the commercialization of LiS batteries.

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

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

Manipulating the Spin State of Fe Sites via Fe-O-Si Bridge Bonds for Enhanced Polysulfide Redox Kinetics in the Li-S Battery

Transition metals with 3d unoccupied orbitals have superior catalytic activity, but inherent high spin suppresses their adsorption capability, leading to sluggish polysulfide conversion kinetics for Li-S batteries. Herein, we provide Fe-O-Si bridge bonds to manipulate e_g filling and induce a high-to-medium spin transition of Fe³⁺ sites, which enhances polysulfide adsorption and facilitates sulfur redox reaction kinetics. The resultant cathodes exhibit outstanding performances under high sulfur loading, which can deliver a high battery specific energy of 1061 mA h·g^-1 even after 100 cycles in Li-S pouch batteries. This work provides new insights into the kinetic and multi-step conversion mechanism of the sulfur redox reaction process, helping in the understanding and design of spin-dependent catalysts.

Oxygen Vacancies in Bismuth Tantalum Oxide to Anchor Polysulfide and Accelerate the Sulfur Evolution Reaction in Lithium-Sulfur Batteries

The shuttling effect of soluble lithium polysulfides (LiPSs) and the sluggish conversion kinetics of polysulfides into insoluble Li₂S₂/Li₂S severely hinders the practical application of Li-S batteries. Advanced catalysts can capture and accelerate the liquid-solid conversion of polysulfides. Herein, we try to make use of bismuth tantalum oxide with oxygen vacancies as an electrocatalyst to catalyze the conversion of LiPSs by reducing the sulfur reduction reaction (SRR) nucleation energy barrier. Oxygen vacancies in Bi₄TaO₇ nanoparticles alter the electron band structure to improve instinct electronic conductivity and catalytic activity. In addition, the defective surface could provide unsaturated bonds around the vacancies to enhance the chemisorption capability with LiPSs. Hence, a multidimensional carbon (super P/CNT/Graphene) standing sulfur cathode is prepared by coating oxygen vacancies Bi₄TaO_7-x nanoparticles, in which the multidimensional carbon (MC) with micropores structure can host sulfur and provide a fast electron/ion pathway, while the outer-coated oxygen vacancies with Bi₄TaO_7-x with improved electronic conductivity and strong affinities for polysulfides can work as an adsorptive and conductive protective layer to achieve the physical restriction and chemical immobilization of lithium polysulfides as well as speed up their catalytic conversion. Benefiting from the synergistic effects of different components, the S/C@Bi₃TaO_7-x coin cell cathode shows superior cycling and rate performance. Even under a high level of sulfur loading of 9.6 mg cm^-2, a relatively high initial areal capacity of 10.20 mAh cm^-2 and a specific energy density of 300 Wh kg^-1 are achieved with a low electrolyte/sulfur ratio of 3.3 µL mg^-1. Combined with experimental results and theoretical calculations, the mechanism by which the Bi₄TaO₇ with oxygen vacancies promotes the kinetics of polysulfide conversion reactions has been revealed. The design of the multiple confined cathode structure provides physical and chemical adsorption, fast charge transfer, and catalytic conversion for polysulfides.

Carbon Nanotube-Modified Nickel Hydroxide as Cathode Materials for High-Performance Li-S Batteries

The advantages of high energy density and low cost make lithium–sulfur batteries one of the most promising candidates for next-generation energy storage systems. However, the electrical insulativity of sulfur and the serious shuttle effect of lithium polysulfides (LiPSs) still impedes its further development. In this regard, a uniform hollow mesoporous Ni(OH)₂@CNT microsphere was developed to address these issues. The SEM images show the Ni(OH)₂ delivers an average size of about 5 μm, which is composed of nanosheets. The designed Ni(OH)₂@CNT contains transition metal cations and interlayer anions, featuring the unique 3D spheroidal flower structure, decent porosity, and large surface area, which is highly conducive to conversion systems and electrochemical energy storage. As a result, the as-fabricated Li-S battery delivers the reversible capacity of 652 mAh g⁻¹ after 400 cycles, demonstrating excellent capacity retention with a low average capacity loss of only 0.081% per cycle at 1 C. This work has shown that the Ni(OH)₂@CNT sulfur host prepared by hydrothermal embraces delivers strong physical absorption as well as chemical affinity.

Manipulating the Conversion Kinetics of Polysulfides by Engineering Oxygen p-Band of Halloysite for Improved Li-S Batteries

Polar oxides are widely used as the cathodes to impede the shuttle effect in lithium-sulfur batteries, but suffer from the sluggish desorption and conversion of polysulfides due to too strong affinity of polysulfides on oxygen sites. Herein, employing halloysite as a model, an approach to overcome these shortcomings is proposed via engineering oxygen p-band center by loading titanium dioxide nanoparticles onto Si-O surface of halloysite. Using density functional theory calculations, it is predicted that electron transfer from titanium dioxide nanoparticles to interfacial O sites results in downshift of p-band center of O sites that promote desorption of polysulfides and the cleavage of Li-S and S-S, accelerating the conversion kinetics of polysulfides. The designed composite cathode material delivers outstanding electrochemical performance in Li-S batteries, outperforming the recently reported similar cathodes. The concept could provide valuable insight into the design of other catalysts for Li-S batteries and beyond.

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

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

Ni@Ni3N Embedded on Three-Dimensional Carbon Nanosheets for High-Performance Lithium/Sodium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are recognized as one of the most promising next-generation energy storage devices, but their practical application is greatly limited by several obstacles, such as the highly insulating nature and sluggish redox kinetics of sulfur and the dissolution of lithium polysulfides. Herein, three-dimensional carbon nanosheet frameworks anchored with Ni@Ni₃N heterostructure nanoparticles (denoted Ni@Ni₃N/CNS) are designed and fabricated by a chemical blowing and thermal nitridation strategy. It is demonstrated that the Ni@Ni₃N heterostructure can effectively accelerate polysulfide conversion and promote the chemical trapping of polysulfides. Meanwhile, the carbon nanosheet frameworks of Ni@Ni₃N/CNS establish a highly conductive network for fast electron transportation. The cells with Ni@Ni₃N heterostructures as the catalyst in the cathode show excellent electrochemical performance, revealing stable cycling over 600 cycles with a low-capacity fading rate of 0.04% per cycle at 0.5 C and high-rate capability (594 mAh g^-1 at 3 C). Furthermore, Ni@Ni₃N/CNS can also work well in room-temperature sodium-sulfur (RT-Na/S) batteries, delivering a high specific capacity (454 mAh g^-1 after 400 cycles at 0.5 C). This work provides a rational way to prepare the metal-metal nitride heterostructures to enhance the performance both of Li-S and RT-Na/S batteries.

Rational Design of MOF-Based Materials for Next-Generation Rechargeable Batteries

This review summarizes recent progresses in pristine metal–organic frameworks (MOFs), MOF composites, and their derivatives for next-generation rechargeable batteries including lithium–sulfur batteries, lithium–oxygen batteries, sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, and Zn–air batteries.

The design strategies for MOF-based materials as the electrode, separator, and electrolyte are outlined and discussed.

The challenges and development strategies and of MOF-related materials for battery applications are highlighted.

Metal–organic framework (MOF)-based materials with high porosity, tunable compositions, diverse structures, and versatile functionalities provide great scope for next-generation rechargeable battery applications. Herein, this review summarizes recent advances in pristine MOFs, MOF composites, MOF derivatives, and MOF composite derivatives for high-performance sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, lithium–sulfur batteries, lithium–oxygen batteries, and Zn–air batteries in which the unique roles of MOFs as electrodes, separators, and even electrolyte are highlighted. Furthermore, through the discussion of MOF-based materials in each battery system, the key principles for controllable synthesis of diverse MOF-based materials and electrochemical performance improvement mechanisms are discussed in detail. Finally, the major challenges and perspectives of MOFs are also proposed for next-generation battery applications.

Size-Dependent Cobalt Catalyst for Lithium Sulfur Batteries: From Single Atoms to Nanoclusters and Nanoparticles

The sulfur redox conversion with catalytically improved kinetics is promising to mitigate the polysulfides shuttling. While the size of electrocatalyst always brings different catalytic behaviors for various heterogeneous catalytic reactions, it is yet to be explored for Li-S batteries. Herein, a systematical study of size-dependent catalytic activity toward polysulfides conversion and the relevance to electrochemical performance are reported, by constructing Co catalysts with different atomic scales from single atoms, atomic clusters to nanoparticles. Fundamental electrocatalytic studies are focused by probing the reduction kinetics and activation energies of sulfur chemistry. The single atomic Co shows the best charge transfer/kinetic toward sulfur redox, especially for the rate-determining reaction (Li₂ S₄  ↔ Li₂ S) as demonstrated by the significantly lowered energy barrier for Li₂ S nucleation/dissolution. This is owing to stronger geometric deformation of the catalyst with lower aggregation extent when it interacts with sulfur species, thus leading to decreased Gibbs free energy changes as elucidated by DFT calculations. The superior catalytic activity of single atomic Co promises a high specific capacity (4.98 mAh cm^-2 ) at an areal loading of 4.3 mg cm^-2 over long-term cycling. The finding emphasizes the significance of the size-dependent catalytic activity to the reaction kinetics and the overall performance of Li-S batteries.

Yolk-Shell Nano ZnO@Co-Doped NiO with Efficient Polarization Adsorption and Catalysis Performance for Superior Lithium-Sulfur Batteries

Achieving strong adsorption and catalytic ability toward polar lithium polysulfide species (LiPSs) of the sulfur host in lithium-sulfur (Li-S) batteries is essential for their electrochemical cyclic stability. Herein, a strategy of "self-termination of ion exchange" is put forward to synthesize the novel yolk-shell sulfur host composed of ZnO nanoparticles confined in Co-doped NiO (CDN) polyhedron (ZCCDN). After sulfur infiltration, the obtained S/ZCCDN cathode achieves excellent performance of 738.56 mAh g^-1 after 500 cycles at 0.5 C with a very low capacity decay rate of only 0.048% per cycle. Even at 1 C, 501.05 mAh g^-1 could be retained after 500 cycles, suggesting a capacity decay ratio of only 0.076% per cycle. The good cycle performance is attributed to the improved LiPSs' conversion kinetics, which originates from ZCCDN's sturdy chemical affinity and strong catalytic ability to polar LiPSs. For the first time, by electron holography, the local interfacial polarization electric field is clarified to be existed in the material which is conducive to the capture of LiPSs and the migration of electrons and Li⁺ from the mesopores. This work provides a rational way for the use of zeolitic imidazolate frameworks (ZIFs) and development of cathode materials for Li-S batteries.

Conductive Porous Laminated Vanadium Nitride as Carbon-Free Hosts for High-Loading Sulfur Cathodes in Lithium-Sulfur Batteries

Improving the sulfur loading in cathodes is a significant challenge for practical lithium-sulfur batteries. Although carbonaceous sulfur hosts can achieve higher sulfur content and loading, the low tap densities of carbonaceous materials lead to low volumetric energy densities, restricting practical application. Here, conductive porous laminated vanadium nitride (VN) as a carbon-free sulfur host has been successfully developed to construct high tap density, high sulfur loading, and high energy density sulfur electrodes. The laminated stacking multiscale VN featuring interconnected holes possesses high storage space for sulfur loading, achieving high sulfur loading and utilization. VN@S materials' sulfur content and tap density can achieve 80 wt % and 1.17 g cm^-3, respectively. At the sulfur loading of 1.0 mg cm^-2, the VN@S cathode reaches the reversible capacity of 790 mAh g^-1 at 1 C after 200 cycles and 145.2 mAh g^-1 at 15 C after 500 cycles. Precisely, at a high sulfur loading of 12.6 mg cm^-2, the VN@S cathode delivers a reversible capacity of 518.8 mAh g^-1 (485.6 mAh cm^-3) at 0.1 C after 100 cycles.

Immobilizing Polysulfide by In Situ Topochemical Oxidation Derivative TiC@Carbon-Included TiO2 Core-Shell Sulfur Hosts for Advanced Lithium-Sulfur Batteries

The performance of lithium-sulfur (Li-S) batteries is greatly hindered by the notorious shuttle effect of lithium polysulfides (LiPSs). To address this issue, in situ topochemical oxidation derivative TiC@carbon-included TiO₂ (TiC@C-TiO₂ ) core-shell composite is designed and proposed as a multifunctional sulfur host, which integrates the merits of conductive TiC core to facilitate the redox reaction kinetics of sulfur species, and porous C-TiO₂ shell to suppress the dissolution and shuttling of LiPSs through chemisorption. A unique dual chemical mediation mechanism is demonstrated for the proposed TiC@C-TiO₂ composite that synergistically entraps LiPSs through thiosulfate/polythionate conversion coupled with strong polar-polar interaction. The morphological characterization reveals that the TiC@C-TiO₂ -based cathode can well regulate the distribution of electrode materials to retard their accumulation inside the electrode, ensuring effective contact between the active materials and electrolyte. Based on its unique function and structure, the cathode delivers an improved capacity of 1256 mAh g^-1 at 0.2C, a remarkable rate capability of 643 mAh g^-1 , and an ultralow capacity decay rate of 0.065% per cycle at 2C over 900 cycles. This work not only demonstrates a dual chemical mediation mechanism to immobilize LiPSs, but also provides a universal strategy to construct multifunctional sulfur hosts for advanced Li-S batteries.

In Situ Self-Polymerization to Form Hollow Graphitized Carbon Nanocages with Embedded Cobalt Nanoparticles for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur batteries, owing to the multi-electron participation in the redox reaction, possess enormous energy density, which has aroused much attention. Nevertheless, the detrimental shuttle effect, volume expansion, and electrical insulation of sulfur, have hindered their application. To improve the cyclability, a functional host, consisting of Co nanoparticles and N-doped hollow graphitized carbon (Co-NHGC) material, is elaborated, which has the advantages of: 1) the graphitized carbon material working as an electronic matrix to improve the utilization rate of sulfur; 2) the hollow structure relieving the stress change caused by volume expansion; 3) the rich active sites catalyze the electrochemical reaction of sulfur and entrap polysulfides. These advantages significantly improve the performance of the lithium-sulfur batteries. Accordingly, the S@Co-NHGC cathode exhibits excellent initial specific capacity, high coulombic efficiency, and excellent rate performance. This work utilizes a novel method of dopamine in situ etching of a metal-organic framework to synthetize the Co-NHGC host of sulfur, which will hopefully provide inspiration for other energy materials.

Rational design of MXene@TiO2 nanoarray enabling dual lithium polysulfide chemisorption towards high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries face a few vital issues, including poor conductivity, severe volume expansion/contraction, and especially the detrimental shuttle effect during the long-term electrochemical process. Herein, we designed a hierarchical MXene@TiO2 nanoarray via in situ solvothermal strategies followed by heat treatment. The MXene@TiO2 heterostructure achieves superior charge transfer and sulfur encapsulation. Based on the polar-polar and Lewis acid-base mechanism, the robust dual chemisorption capability to trap polysulfides can be synergistically realized through the intense polarity of TiO2 and the abundant acid metal sites of MXene. Hence, the MXene@TiO2 nanoarray as a sulfur host retains a substantially stable discharge capacity of 612.7 mA h g-1 after 500 cycles at a rate of 2 C, which represents a low fading rate of 0.058% per cycle.

Rational integration of spatial confinement and polysulfide conversion catalysts for high sulfur loading lithium-sulfur batteries

Spatial confinement is a desirable successful strategy to trap sulfur within its porous host and has been widely applied in lithium-sulfur (Li-S) batteries. However, physical confinement alone is currently not enough to reduce the lithium polysulfide (Li₂S_n, 4 ≤n≤ 8, LIPSs) shuttle effect with sluggish LIPS-dissolving kinetics. In this work, we have integrated spatial confinement with a polar catalyst, and designed a three-dimensional (3D) interconnected, Co decorated and N doped porous carbon nanofiber (Co/N-PCNF) network. This Co/N-PCNF film serves as a freestanding host for sulfur trapping, which could effectively facilitate the infiltration of electrolyte and electron transport. In addition, the polar Co species possess strong chemisorption with LIPSs, catalyzing their reaction kinetics as well. As a result of this rational design and integration, the Co/N-PCNF@S cathode with a sulfur loading of 2 mg cm^-2 exhibits a high initial discharge capacity of 878 mA h g^-1 at 1C, and maintains a discharge capacity of 728 mA h g^-1 after 200 cycles. Even with high sulfur loading of 9.33 mg cm^-2, the cathode still keeps a stable areal capacity of 7.16 mA h cm^-2 at 0.2C after 100 cycles, which is much higher than the current areal capacity (4 mA h cm^-2) of commercialized lithium-ion batteries (LIBs). This rational design may provide a new approach for future development of high-density Li-S batteries with high sulfur loading.

Architecture and Performance of the Novel Sulfur Host Material Based on Ti2O3 Microspheres for Lithium-Sulfur Batteries

Lithium-sulfur batteries are considered as promising next-generation green secondary batteries. Irrespective of the enhancement of the cycling stability or the suppression of polysulfide species shuttle, although much progress has recently been achieved, improving the conductivity of host materials and capturing the sulfide species as far as possible are still hot topics in the research of lithium-sulfur batteries nowadays. Here, we put forward a novel sulfur host architecture based on Ti₂O₃ microspheres fabricated by magnesiothermic reduction. The Ti₂O₃ microspheres possess both high electronic conductivity and excellent ability of anchoring lithium polysulfide species. The high electronic conductivity endowed by a narrow band gap can adequately activate insulative sulfur and reduce the battery resistance so that high specific capacity and excellent rate capability can be achieved, while the polar Ti₂O₃ could afford abundant polar active sites for the absorption of polysulfides for high capacity retention. As a result, Ti₂O₃ microspheres are applied in the research of lithium-sulfur batteries; excellent electrochemical performance has been revealed. The initial specific capacity is 1245 mAh g^-1 at 0.2C, with 91.57% capacity retention after 180 cycles. Even with a high areal loading of 3.6 mg cm^-2, an initial capacity of 665 mAh g^-1 at 0.5C and a good capacity retention of 70.98% after 300 cycles could be achieved. Apparently, the preparation and application of Ti₂O₃ microspheres can not only further extend the application field of the Ti-based compound but also boost the electrochemical performance of lithium-sulfur batteries.