Long-life Lithium-sulfur Batteries Research Articles

High-Entropy Metal Oxide-Coated Carbon Cloth as Catalysts for Long-Life Li-S Batteries.

Lithium-sulfur (Li-S) batteries with high specific energy density, low cost, and environmental friendliness of sulfur have been regarded as a competitive alternative to replace lithium-ion batteries. However, the shuttle effect and the sluggish conversion rate of lithium polysulfides (LiPSs) have seriously limited the practical application of Li-S batteries. Herein, high-entropy oxides grown on the carbon cloth (CC/HEO) are synthesized by a simple and ultrafast solution combustion method for the sulfur cathode. The as-prepared composites possess abundant HEO active sites for strong interaction with LiPSs, which can significantly promote redox kinetics. Besides, the carbon fiber substrate not only ensures high electrical conductivity but also accommodates large volume change, leading to a stable sulfur electrochemistry. Benefiting from the rational design, the Li-S batteries with CC/HEO as cathode skeleton exhibits good cyclability with a capacity decay rate of 0.057% per cycle after 1000 cycles at 2 C. More importantly, the Li-S batteries with 4.3 mg cm-2 high sulfur loading can still retain a high capacity retention of 78.2% after 100 cycles.

Effective d–p orbital hybridization of Co0.75Fe0.25P catalysts enabling high-rate and long-life lithium‒sulfur batteries

Lithium–sulfur (Li–S) batteries represent one of the potential next-generation energy storage devices. However, their commercialization is hindered by the severe shuttle effect of lithium polysulfides (LiPSs) and sluggish redox kinetics. A crucial strategy to address these issues involves the rational design of catalysts and a comprehensive understanding of interaction mechanisms between catalysts and sulfur species. In this study, Fe atoms were incorporated into CoP catalysts, and one-dimensional (1D) porous carbon-encapsulated Fe-doped CoP (Co1-xFexP@C) nanotube-like nanostructures were rationally designed and successfully synthesized. This design involves modifying the d–p orbital hybridization between the transition metal Co 3d orbitals and S 2p orbitals through the Fe 3d orbitals, thus creating catalysts with the most effective d–p orbital hybridization and, consequently, the strongest electrocatalytic activity. Detailed kinetic analysis reveals the Co0.75Fe0.25P@C catalyst, with an effective d–p orbital hybridization, can firmly anchor the LiPSs, inhibit the shuttle effect, and facilitate bidirectional Li2S redox, thereby enhancing sulfur utilization and promoting LiPS conversion. These findings enable high-rate and long-cycle-life Li–S batteries. Specifically, the Li–S battery using the Co0.75Fe0.25P@C catalyst demonstrates excellent cycling stability, with a low capacity decay rate of 0.05 % per cycle over 900 cycles at 2 C. More impressively, the Li–S battery also achieves outstanding high-rate performance, delivering 726.3 mAh g–1 at 6 C. This study introduces a new strategy for identifying catalysts with the strongest electrocatalytic activity, which holds promise for advancing the development of Li−S batteries.

Tix+ in-situ intercalation and interlayer modification via titanium foil/vanadium ion solution interface of VO2.375 as sulfur-wrapped matrix enabling long-life lithium sulfur battery

Lithium sulfur battery (LSB) has great potential as a promising next-generation energy storage system owing to ultra-high theoretical specific capacity and energy density. However, the polysulfide shuttle effect and slow redox kinetics are recognized the most stumbling blocks on the way of commercializing LSB. On this account, for the first time, we use Tix+ in-situ intercalation strategy via titanium foil/vanadium ion (V5+) solution interface to modify the layer of vanadium oxide for long cycle LSB. The inserted Tix+ strengthens interlayer interaction and enhances lithium-ion mobility rate. Meanwhile, based on density functional theory (DFT) calculation, the mixed valence of V5+/V4+ in the vanadium oxide structure reduces the stress and strain of lithium-ion intercalation through the interlayer support of titanium ions (Tix+). Also, Tix+ refines the structural stability of the sulfur wrapped composite matrix so as to facilitate the LiPSs transformation, and improve the electrochemical performances. Consequently, the Ti-VO2.375/S cathode delivers a lower capacity decay of 0.037 % per cycle over 1500 cycles with a stable coulombic efficiency around 100 %.

Selective Reduction of Multivariate Metal-Organic Frameworks for Advanced Electrocatalytic Cathodes in High Areal Capacity and Long-Life Lithium-Sulfur Batteries.

Lithium-sulfur batteries hold great promise as next-generation high-energy-density batteries. However, their performance has been limited by the low cycling stability and sulfur utilization. Herein, we demonstrate that a selective reduction of the multivariate metal-organic framework, MTV-MOF-74 (Co, Ni, Fe), transforms the framework into a porous carbon decorated with bimetallic CoNi alloy and Fe3O4 nanoparticles capable of entrapping soluble lithium polysulfides while synergistically facilitating their rapid conversion into Li2S. Electrochemical studies on coin cells containing 89 wt % sulfur loading revealed a reversible capacity of 1439.8 mA h g-1 at 0.05 C and prolonged cycling stability for 1000 cycles at 1 C/1060.2 mA h g-1 with a decay rate of 0.018% per cycle. At a high areal sulfur loading of 6.9 mg cm-2 and lean electrolyte/sulfur ratio (4.5 μL:1.0 mg), the battery based on the 89S@CoNiFe3O4/PC cathode provides a high areal capacity of 6.7 mA h cm-2. The battery exhibits an outstanding power density of 849 W kg-1 at 5 C and delivers a specific energy of 216 W h kg-1 at 2 C, corresponding to a specific power of 433 W kg-1. Density functional theory shows that the observed results are due to the strong interaction between the CoNi alloy and Fe3O4, facilitated by charge transfer between the polysulfides and the substrate.

Effect of Water As an Electrolyte Additive for Lithium Plating

Li metal anode is generally referred to as the “holy grail” of battery technology as it can deliver the highest possible energy density, which double the capacity of state of art graphite based cells1. At the heart of this advanced technology is the process of continuous plating and stripping of lithium during the cycling of the battery. Owing to the highly reactive nature of Li, this is a complicated process with several challenges2 during both plating (for e.g., dendrite formation and growth, dead lithium, continuous interface/interphase change, short circuit etc.) and stripping (void formation, pitting, broken interface/interphase layers etc.). The electrode architecture, choice of electrolyte, solid electrolyte interphase (SEI) formation, operating conditions etc. are key factors that determine overall stability of Li metal anodes. These issues get magnified when using liquid electrolytes, where continuous SEI formation leads to dead Lithium (electrically insulating) accumulation.In general, most solvents and salts employed for Li ion cells contain some amount of water as impurity even after maintaining strict conditions to keep them anhydrous. The presence of trace amount of water in combination with fluorine from either salt (LiPF6. LiTFSI, LiFSI) or solvent additives FEC can then lead to in-situ formation of HF, which has detrimental effects on Li plating. However, recently many groups have shown the beneficial effect of small amount of water as additives for Li metal anodes3,4. However, the exact mechanism of functioning of H2O as an additive is not very clear. This is partly because the formation of SEI is quite complex, especially when film forming type solvents/additives are present in the electrolyte addition to trace amounts of water.It is thus important to investigate the nucleation and growth of Li during the initial stages of plating and understand how the presence of H2O in the electrolyte affects the morphology andthe chemical nature of the deposited Li metal films. In this direction, we choose tetraglyme (4G), which is a relatively non-labile solvent towards Li plating conditions (reduction potential ~ 1.49 vs Li+/Li), as the solvent to avoid any contribution from the solvent itself on SEI formation. We then systematically study the effect of H2O on Li plating; both stand alone and in presence of various film forming additives. We show that water can indeed drastically affect the morphology and electrochemical properties of the deposited Li. Acknowledgement: This work is part of FUGELS (Functionally Graded Electrodes for Long-Life Lithium-Sulfur Batteries) project, which is a cconsortium of researchers from University of Hasselt, University of Gent, University of Antwerp, VITO, IMEC and IMOMEC.

Applications, prospects and challenges of metal borides in lithium sulfur batteries

Although the lithium-sulfur (Li-S) battery has a theoretical capacity of up to 1675 mA h g−1, its practical application is limited owing to some problems, such as the shuttle effect of soluble lithium polysulfides (LiPSs) and the growth of Li dendrites. It has been verified that some transition metal compounds exhibit strong polarity, good chemical adsorption and high electrocatalytic activities, which are beneficial for the rapid conversion of intermediate product in order to effectively inhibit the “shuttle effect”. Remarkably, being different from other metal compounds, it is a significant characteristic that both metal and boron atoms of transition metal borides (TMBs) can bind to LiPSs, which have shown great potential in recent years. Here, for the first time, almost all existing studies on TMBs employed in Li-S cells are comprehensively summarized. We firstly clarify special structures and electronic features of metal borides to show their great potential, and then existing strategies to improve the electrochemical properties of TMBs are summarized and discussed in the focus sections, such as carbon-matrix construction, morphology control, heteroatomic doping, heterostructure formation, phase engineering, preparation techniques. Finally, the remaining challenges and perspectives are proposed to point out a direction for realizing high-energy and long-life Li-S batteries.

Mott Schottky heterojunction Co/CoSe2 electrocatalyst: Achieved rapid conversion of polysulfides and Li2S deposition dissolution via built-in electric field interface effect

Rechargeable lithium-sulfur (Li-S) batteries are considered ideal candidates for the next generation of energy storage devices. However, the insulation properties of S and Li2S, as well as the notorious “shuttle effect” of lithium polysulfide, result in severe loss of active sulfur, poor redox kinetics, and rapid capacity decline. To overcome these limitations, this paper designs a self-supporting electrocatalytic electrode based on Co/CoSe2 Mott Schottky heterojunction coated carbon nanofibers (Co/CoSe2@NCNFs), and engineers it for capturing and converting polysulfides. Density functional theory calculations show that the introduction of Co/CoSe2 heterojunction effectively reduces the redox barrier of Li2S. The electron current and electron interaction at the Co/CoSe2 interface induce the redistribution of charge density in the depletion region, thus increasing the chemical reactivity of the metal semiconductor heterojunction interface, which is conducive to the ion/electron transport, polysulfide conversion and Li2S oxidation process. Therefore, the Li-S battery assembled by Co/CoSe2@NCNFs/S electrode exhibited a high initial specific capacity of 1043.3 mAh/g at 1C, and maintained a capacity of 709.9 mAh/g after 1000 cycles, with a capacity decay rate of only 0.032% per cycle. The proposed Mott Schottky heterojunction as an electrocatalyst deepens the promotion of polysulfides and Li2S in long-life Li-S batteries.

Nontraditional Approaches To Enable High-Energy and Long-Life Lithium-Sulfur Batteries.

ConspectusLithium-sulfur (Li-S) batteries are promising for automotive applications due to their high theoretical energy density (2600 Wh/kg). In addition, the natural abundance of sulfur could mitigate the global raw material supply chain challenge of commercial lithium-ion batteries that use critical elements, such as nickel and cobalt. However, due to persistent polysulfide shuttling and uncontrolled lithium dendrite growth, Li-S batteries using nonencapsulated sulfur cathodes and conventional ether-based electrolytes suffer from rapid cell degradation upon cycling. Despite significant improvements in recent decades, there is still a big gap between lab research and commercialization of the technology. To date, the reported cell energy densities and cycling life of practical Li-S pouch cells remain largely unsatisfactory.Traditional approaches to improving Li-S performance are primarily focused on confining polysulfides using electronically conductive hosts. However, these micro- and mesoporous hosts suffer from limited pore volume to accommodate high sulfur loading and the associated volume change during cycling. Moreover, they fail to balance adsorption-conversion of polysulfides during charge-discharge, leading to the formation of massive dead sulfur. Such hosts are themselves electrochemically inactive, which decreases the practical energy density. In contrast, a series of nontraditional approaches, paired with advances in multiscale mechanistic understanding, have recently demonstrated exciting performance outcomes not only in conventional coin cells but also in practical pouch cells.In this Account, we first introduce our novel cathode design strategies to overcome polysulfide shuttling and sluggish redox kinetics in thick S cathodes via selenium-sulfur chemistry and cathode host engineering. Next, we gain a mechanistic understanding of Li-S batteries in various types of electrolytes via a series of spectroscopic, nuclear magnetic resonance, and electrochemical methods. Meanwhile, a novel cathode solid electrolyte interphase encapsulation strategy via nonviscous highly fluorinated ether-based electrolyte is introduced. The established selection rule by investigating how solvating power retards the shuttle effect and induces robust cathode/solid-electrolyte interphase formation is also included. We then discuss how the synergistic interactions between rational cathode structures and electrolytes can be exploited to tailor the reaction pathways and kinetics of S cathodes under high mass loading and lean electrolyte conditions. In addition, a novel interlayer design to simultaneously overcome degradation processes (polysulfide shuttling and lithium dendrite formation) and accelerate redox reaction kinetics is presented. Finally, this Account concludes with an overview of the challenges and strategies to develop Li-S pouch cells with high practical energy density, long cycle life, and fast-charging capability.

TiO2–TiN Decorated Carbon Nanoplates Derived from NH2-MIL-125 with Efficient Polysulfide Catalytic Conversion for Long-Life Lithium–Sulfur Batteries

TiO₂–TiN Decorated Carbon Nanoplates Derived from NH₂-MIL-125 with Efficient Polysulfide Catalytic Conversion for Long-Life Lithium–Sulfur Batteries

The Structural and Electronic Engineering of Molybdenum Disulfide Nanosheets as Carbon-Free Sulfur Hosts for Boosting Energy Density and Cycling Life of Lithium-Sulfur Batteries.

The compact sulfur cathodes with high sulfur content and high sulfur loading are crucial to promise high energy density of lithium-sulfur (Li-S) batteries. However, some daunting problems, such as low sulfur utilization efficiency, serious polysulfides shuttling, and poor rate performance, are usually accompanied during practical deployment. The sulfur hosts play key roles. Herein, the carbon-free sulfur host composed of vanadium-doped molybdenum disulfide (VMS) nanosheets is reported. Benefiting from the basal plane activation of molybdenum disulfide and structural advantage of VMS, high stacking density of sulfur cathode is allowed for high areal and volumetric capacities of the electrodes together with the effective suppression of polysulfides shuttling and the expedited redox kinetics of sulfur species during cycling. The resultant electrode with high sulfur content of 89wt.% and high sulfur loading of 7.2mgcm-2 achieves high gravimetric capacity of 900.9 mAh g-1 , the areal capacity of 6.48mAh cm-2 , and volumetric capacity of 940 mAh cm-3 at 0.5 C. The electrochemical performance can rival with the state-of-the-art those in the reported Li-S batteries. This work provides methodology guidance for the development of the cathode materials to achieve high-energy-density and long-life Li-S batteries.

Revealing the enhancement mechanism of carbon-encapsulated surface-strained MoNi4 bimetallic nanoalloys toward high-stability polysulfide conversion with a wide temperature range

Bimetallic alloy catalysts, due to their more adsorption sites, more abundant electronic structures, and higher catalytic properties than single-metal ones, have attracted much interest in the field of lithium–sulfur batteries (LSBs). However, many LSBs with bimetallic alloys often suffered from their low cycling stability, which was caused by the over-strong adsorption and the bad chemical stability of the catalysts. Herein, in-situ carbon-encapsulation-induced strain relaxation strategy has been adopted to balance the adsorption and catalytic properties of the MoNi4 bimetallic nanoalloy catalyst for LSBs. As a result, the cathode with strained-MoNi4 embedded carbon nanofibers (CNF@s-MoNi4) delivers a high capacity (1632.5 mAh g−1 at 0.1 C), a superior rate capability (retaining 832.4 mAh g–1 at 5.0 C) and excellent cycling stability (decaying rate of 0.0204% per cycle over 520 cycles at 1.0 C). Even at high rates, the CNF@s-MoNi4 can keep a stable cycling capacity (827.5 mAh g–1 and 447.7 mAh g–1 after 250 cycles at 5.0 C and 10.0 C, respectively). Besides, the CNF@s-MoNi4 LSB also exhibits an excellent wide-temperature-range adaptability (-30 ∼ 50°C) and a superior dynamic bending stability. This study would provide a feasible method for developing high-capacity and long-life LSBs with a wide temperature range demand.

Single lithium–ion transport and electrochemical stability triggered by organoborate zwitterions for self-assembled PAS–co–2PEG solid electrolytes for lithium–sulfur battery

Super ion-conductive solid polymeric electrolytes (SPEs) with high lithium (Li)–ion selectivity are applied to develop high efficiency, safe, and long-life lithium–sulfur batteries (LSB). Herein, a high-performance SPE is prepared by employing organoborate zwitterions (ZBo) into the flexible self-assembled poly(arylene ether sulfone) electrolytes grafted with dual poly(ethylene glycol) segments (PAS–co–2PEG) in the presence of ionic liquid. The large dipole moment of steric bulky ZBo present in lithium–ion conductive PEG domains phase separated from mechanically reinforced PAS matrix results in the promotion of Li-salt and borate anion/ Li-cation dissociation to facilitate the Li–ion migrations. The versatile functional groups in ZBo, such as ethyl carbonate (−EC), nitrile (−CN), and PEG with high dielectric constant aids Li-hopping without ionic aggregations. Attributed to these unique features, the as-developed SPEs show not only high thermal and mechanical stability above 250 °C and 1 MPa tensile strength, but also large electrochemical stability window of 5.3 V and high ionic conductivity of 1.05 mS cm−1 along with Li-ion transfer number of ∼0.5. The corresponding S/SPE/Li cells show 99.2 % of capacity retention after 200 cycles at 0.2C rate, demonstrating the promise of the advanced development of all-solid-state LSBs.

Rational design and low-cost fabrication of multifunctional separators enabling high sulfur utilization in long-life lithium-sulfur batteries

The lithium-sulfur (Li-S) battery with an ultrahigh theoretical energy density has emerged as a promising rechargeable battery system. However, the practical applications of Li-S batteries are severely plagued by the sluggish reaction kinetics of sulfur species and notorious shuttling of soluble lithium polysulfides (LiPSs) intermediates that result in low sulfur utilization. The introduction of functional layers on separators has been considered as an effective strategy to improve the sulfur utilization in Li-S batteries by achieving effective regulation of LiPSs. Herein, a promising self-assembly strategy is proposed to achieve the low-cost fabrication of hollow and hierarchically porous Fe3O4 nanospheres (p-Fe3O4-NSs) assembled by numerous extremely-small primary nanocrystals as building blocks. The rationally-designed p-Fe3O4-NSs are utilized as a multifunctional layer on the separator with highly efficient trapping and conversion features toward LiPSs. Results demonstrate that the nanostructured p-Fe3O4-NSs provide chemical adsorption toward LiPSs and kinetically promote the mutual transformation between LiPSs and Li2S2/Li2S during cycling, thus inhibiting the LiPSs shuttling and boosting the redox reaction kinetics via a chemisorption-catalytic conversion mechanism. The enhanced wettability of the p-Fe3O4-NSs-based separator with the electrolyte enables fast transportation of lithium ions. Benefitting from these alluring properties, the functionalized separator with p-Fe3O4-NSs endows the battery with an admirable rate performance of 877 mAh g−1 at 2 C, an ultra-durable cycling performance of up to 2176 cycles at 1 C, and a promising areal capacity of 4.55 mAh cm−2 under high-sulfur-loading and lean-electrolyte conditions (4.29 mg cm−2, electrolyte/ratio: 8 µl mg−1). This study will offer fresh insights on the rational design and low-cost fabrication of multifunctional separator to strengthen electrochemical reaction kinetics by regulating LiPSs conversion for developing efficient and long-life Li-S batteries.

Vanadium dioxide plates reduced graphene oxide as sulfur cathodes for efficient polysulfides trap in long-life lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are ideal for future energy storage owing to their rich resources and high theoretical energy density. However, the easy solubility of polysulfides and the insulating properties of elemental sulfur remain a challenge. Herein, graphene decorated with vanadium dioxide (VO2) plates was designed and manufactured as a cathode matrix for battery. The polar VO2 plates can anchor the polysulfide. At the same time, the conductive rGO network not only provides electrons transport channels for electrons/ions, but also accommodates the volume changes during cycling. The electrochemical tests show that the synthesized VO2/rGO/S composites with 75.4 wt% S have a high discharge capacity of 861mAhg−1 after 100 cycles at a current density of 0.1C. The assembled battery still provides a stable specific capacity of 493.4 mAhg−1 at a current density of 0.5C after 700 cycles and the discharge of 395.8 mAhg−1 was obtained at a current density of 1C over 1000 cycles. The capacity retention rate at 1C is higher than many other vanadium oxides reported. Therefore, the outstanding performance is ascribed to the fact that the VO2 plates can alleviate the shuttle effect of polysulfides and and the graphene layer forms a good conductive network for electron transport. This research provides an avenue for the development of long-life batteries.

Two-dimensional montmorillonite-based heterostructure for high-rate and long-life lithium-sulfur batteries

In lithium-sulfur batteries, the polysulfide redox reaction kinetics is obstructed by unfavorable electron conduction and ion transportation. To address this issue, a two-dimensional (2D) heterostructure with fast ion/electron transport bi-pathways is designed herein by well integrating monolayer lithium-montmorillonite (MMT) and nitrogen-doped reduced graphene oxide (RGO). The low diffusion barrier on the Li-MMT contributes to the fast lithium ion transport, and the nearby RGO builds high electron conduction network, which enables high-efficiency adsorption-diffusion-conversion for polysulfides and achieves fast electrochemical reaction kinetics. Consequently, the lithium-sulfur batteries using the heterostructure interlayer show effective suppression towards the notorious “shuttle effect” of polysulfides, as well as deliver high initial specific capacity of 1317 mAh g−1 at 0.2 C, high rate capability of 848 mAh g−1 even at 3 C, and low capacity decay rate of 0.011% per cycle at 1 C over 200 cycles and 0.067% per cycle at 2 C over 600 cycles. The corresponding pouch cell shows high initial discharge capacity of 1542 mAh g−1 at 0.05 C. This work exhibits the potential application of the low-cost and environmentally-friendly clay as the 2D heterostructure interlayer material for realizing high-energy-density, long-lasting, and high-rate Li-S batteries.

Cobalt-doping of molybdenum phosphide nanofibers for trapping-diffusion-conversion of lithium polysulfides towards high-rate and long-life lithium-sulfur batteries

Rational design of separators is especially critical to solve the “shuttle effect” of lithium polysulfides (LiPSs) and the sluggish redox kinetics in lithium-sulfur batteries (LSBs). Here, the multi-functional nanocomposite involving Co-doped molybdenum phosphide (Co-MoP) nanofibers and porous carbon nanofibers (PCNFs) is designed and prepared through electro-blow spinning and phosphating process, which possesses multiple adsorption and catalytic sites and is acted as the functional material for LSBs separators. In this multifunctional nanocomposite, the prepared Co-MoP nanofibers can provide internal adsorption and catalytic sites for LiPSs conversion. And the interconnected nitrogen-doped PCNFs can be elaborated an efficient LiPSs mediator and accommodate the huge volume changes in the reaction process for LSBs. Benefiting from the multiple adsorptive and catalytic sites of the developed functional materials, the assembled LSBs with a Co-MoP/PCNFs modified separator display outstanding electrochemical performances, including an admirable capacity retention of 770.4 mAh g−1 after 400 cycles at 1.0 C, only 0.08 % capacity decay per cycle at 2.0 C, rate performance up to 5 C, and also decent areal capacity even under a high sulfur loading of 4.9 mg cm−2. The work provides a facile pathway towards multifunctional separators in LSBs, and it may also help deepen preparation method of MoP through the electrostatic blowing/electrospinning technology in other related energy storage fields.

A biomass-based cathode for long-life lithium-sulfur batteries

With the advantages of high conductivity and low cost, porous carbons have been considered as the most attractive host materials of sulfur cathodes in lithium-sulfur batteries (LSBs). However, LSBs always suffer short cycle life due to the “shuttle effect” of lithium polysulfide species (polysulfides), which are intermediate products during the charge/discharge processes. The weak interaction between carbon and polysulfides results in the dissolution of polysulfides from the cathodes, loss of active material of sulfur and eventually fast capacity fading. To overcome these drawbacks, we employed a biomass-derived carbon as the host material in sulfur cathodes. Results from X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen sorption reveals that this biomass-derived product is amorphous carbon and is composed of both large (>10 nm) and small (<5 nm) pores at an appropriate ratio. Using as hosts of cathodes in LSBs, the biomass-derived carbons deliver a high reversible capacity of >800 mAh/g and retain >80% of initial capacity after 200 cycles. Especially, the activated carbons exhibited an unprecedently high durability with 80% capacity retention after 400 cycles. The promising LSB performance can be ascribed to the unique porous architecture of biomass-derived carbons. The small pores in biomass-derived carbons provide more sites to anchor sulfur and polysulfides, while large pores provide channels for fast transport of ions. This is corroborated by the results from the electrochemical impedance spectroscopy (EIS), the thermogravimetric analysis (TGA) and absorption measurements.

Achieving job-synergistic polysulfides adsorption-conversion within hollow structured MoS2/Co4S3/C heterojunction host for long-life lithium–sulfur batteries

Lithium–sulfur batteries are considered one of the most promising next-generation energy storage devices owing to their ultrahigh theoretical energy density and environmental friendliness. However, the sluggish electrode reaction kinetics of the sulfur cathode and shuttle effects of lithium polysulfide (LiPSs) restrict their active material utilization and cycling stability. Herein, a hollow, free-standing MoS2/Co4S3/C heterojunction was fabricated and employed as a cathode host for high-performance lithium–sulfur batteries (LSBs). The unique hollow nanostructured MoS2/Co4S3/C can achieve job-synergistic polysulfide adsorption-conversion, in which the conductive nitrogen-doped carbon framework facilitates rapid electron/ion diffusion; polar Co4S3 species provide strong chemisorption capability and endow intrinsic catalytic sites towards LiPSs, and MoS2 serves as a nanocrystal to accelerate the reaction dynamics. As a result, MoS2/Co4S3/C/S exhibited high reversible specific capacities at 2C and was maintained at 394 mAh g−1 after 1000 cycles, with a 0.04% capacity decay rate. Impressively, the high reversible specific capacities with high sulfur loading of 4.1 mg cm−2 were maintained at 906.7 mAh g−1.

Hierarchical sparse Co nanowire/carbon nanofiber arrays as 3D Li+ gateways for high rate, long-life lithium-sulfur batteries

Lithium‑sulfur batteries (LSBs) have been investigated as promising electrochemical energy storage owing to their high theoretical energy density. However, practical applications of LSBs are still hindered by rapid capacity decay and short cycle life, especially at high rates. Here, highly hierarchical sparse Co-nanowire/carbon nanofiber/sulfur arrays (CoNws/CNFs/S) were fabricated inside porous alumina template using a combination of electrodeposition, polymer pyrolysis, and infiltration methods. As a consequence, the sulfur host structure made with CoNWs/CNFs can deliver high rate capability and cycle stability with a high capacity of 1010 mAh g-1 and a low capacity fading rate of 0.3% per cycle (after 200 cycles under a rate of 1C). Our result suggests that designing hybrid coaxial architecture could represent an attractive path to improve high power density LSBs.

Constructing a catalytic reservoir using cobalt nanoparticles-MoS2@nitrogen doped carbon nanotubes on the separator to immobilize polysulfides and accelerate their conversion for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are considered as one of the most promising electrochemical energy storage systems because of their high theoretical specific capacity and energy density. However, the shuttle effect of polysulfides and the slow redox kinetics significantly hinder their practical application. This study demonstrates a separator modification strategy that is expected to address these issues. The material for the modification is a functional carbon nanotube containing nitrogen heteroatoms and encapsulating cobalt nanoparticles. The external surface of the carbon nanotube was covered with a layer of molybdenum disulfide nanosheets (Co-MoS2@NC). The electrochemical measurements showed that the Co-MoS2@NC modified separator can inhibit the shuttle effect and promote the kinetics of the redox reaction. Both experimental investigation and the theoretical study confirmed the capability of MoS2 for the chemical adsorption and the catalytic conversion of the polysulfides. The electrochemical insight studies showed that the Li-S battery assembled with the Co-MoS2@NC modified separator has an excellent Li+ diffusion rate, enhanced rate performance (610.1 mAh g−1 at 4 C), and stable cycle life (only 0.053% capacity decay per cycle at 1 C after 1000 cycles). It is expected that this modification strategy will find its promising application for high-performance and long-life Li-S batteries.