Sulfur Redox Reactions Research Articles

Porosity vs carbon shell number: Key factor actually affecting the performance of multi-shelled hollow carbon nanospheres in Li-S batteries

• The pores in the carbon shells of HCNs play a key role in the Li + diffusion and Li 2 S x confinement. • Simply increasing the shell number in HCNs can not effectively confine the leakage of Li 2 S x from the S cathode. • Porous 1S-HCNs endow the S cathode with better cycling stability and rate capability than the oligoporous 2S-HCNs and 3S-HCNs do. • After 700 cycles, a capacity of 759 mAh g -1 with 63% retention is achieved for the S@1S-HCNs cathode at 0.2 C. As a type of sulfur host for lithium-sulfur batteries (LSBs), hollow carbon nanospheres (HCNs) are of particular interest due to their high electrical conductivity, available cavities, and unique morphology. However, there is a lack of in-depth study about the pivotal factors affecting their performance in LSBs. Herein, a series of multi-shelled HCNs have been prepared by a template-free method and the corresponding sulfur cathodes have been systematically investigated. A positive dependence of electrochemical properties on the specific surface area and pore volume of HCNs is confirmed. In case of low porosity of carbon shell, increasing the shell numbers in HCNs could not accelerate the Li + diffusion and restrict the dissolution of lithium polysulfide in the S@HCNs cathode. As a result, the highly porous 1S-HCNs endow the sulfur cathode with better cycling stability and rate performance than the oligoporous 2S-HCNs and 3S-HCNs do. This work may not only provide a useful reference in the design of novel sulfur hosts but also shed a light on the understanding of the complicated mechanism behind the sulfur redox reactions.

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 eg 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.

A rational design of titanium-based heterostructures as electrocatalyst for boosted conversion kinetics of polysulfides in Li-S batteries

Lithium–sulfur batteries have great potential for next-generation electrochemical storage systems owing to their high theoretical specific energy and cost-effectiveness. However, the shuttle effect of soluble polysulfides and sluggish multi-electron sulfur redox reactions has severely impeded the implementation of lithium–sulfur batteries. Herein, we prepared a new type of Ti3C2-TiO2 heterostructure sandwich nanosheet confined within polydopamine derived N-doped porous carbon. The highly polar heterostructures sandwich nanosheet with a high specific surface area can strongly absorb polysulfides, restraining their outward diffusion into the electrolyte. Abundant boundary defects constructed by new types of heterostructures reduce the overpotential of nucleation and improve the nucleation/conversion redox kinetics of Li2S. The Ti3C2–TiO2@NC/S cathode exhibited discharge capacities of 1363, and 801 mAh g−1 at the first and 100th cycles at 0.5C, respectively, and retained an ultralow capacity fade rate of 0.076% per cycle over 500cycles at 1.0C. This study provides a potential avenue for constructing heterostructure materials for electrochemical energy storage and catalysis.

High-entropy perovskite oxide nanofibers as efficient bidirectional electrocatalyst of liquid-solid conversion processes in lithium-sulfur batteries

Transition metal oxides are a class of promising host materials of sulfur for lithium-sulfur (Li-S) batteries due to their robust polysulfide adsorption, and catalytic effect on sulfur redox reaction. It is proven that the adsorption-catalysis property can benefit a lot from incorporating multiple metal elements, and high-entropy oxides (HEOs) show good competitive potential for durable Li-S batteries. Herein, HEO nanofibers are designed as bidirectional catalytic host of sulfur to promote both the reduction of soluble intermediates and the re-oxidation of insoluble products. Specifically, the high-entropy perovskite oxide La0.8Sr0.2(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 (HE-LSMO) nanofibers prepared via an electrospinning-calcination method show a unique porous fibrous structure for incorporation with sulfur. The introduced multiple metal elements can effectively modulate the binding strength of soluble polysulfides, and HE-LSMO nanofibers act as bidirectional electrocatalyst for the liquid-solid conversion processes between soluble polysulfides and insoluble Li2S, which is enabled by the high entropic contribution. As a result, the S/HE-LSMO cathode with a sulfur loading of 8.4 mg cm−2 shows a high areal capacity of 6.6 mAh cm−2 at low electrolyte/sulfur ratio of 5.3 μL mg−1, as well as good cycle stability. This work provides a foundation understanding of the bidirectional catalytic role of HEOs toward practical Li-S batteries.

Desolvation Synergy of Multiple H/Li-Bonds on an Iron-Dextran-Based Catalyst Stimulates Lithium-Sulfur Cascade Catalysis.

Traditional lithium-sulfur battery catalysts are still facing substantial challenges in solving sulfur redox reactions, which involve multistep electron transfer and multiphase transformations. Here, inspired by the combination of iron dextran (INFeD) and ascorbic acid (VC) as a blood tonic for the treatment of anemia, a highly efficient VC@INFeD catalyst is developed in the sulfur cathode, accomplishing the desolvation and enrichment of high-concentration solvated lithium polysulfides at the cathode/electrolyte interface with the assistance of multiple H/Li-bonds and resolving subsequent sulfur transformations through gradient catalysis sites where the INFeD promotes long-chain lithium polysulfide conversions and VC accelerates short-chain lithium polysulfide conversions. Comprehensive characterizations reveal that the VC@INFeD can substantially reduce the energy barrier of each sulfur redox step, inhibit shuttle effects, and endow the lithium-sulfur battery with high sulfur utilization and superior cycling stability even under a high sulfur loading (5.2mg cm-2 ) and lean electrolyte (electrolyte/sulfur ratio, ≈7µL mg-1 ) condition.

Enhancing the Catalytic Activity of Layered Double Hydroxide Supported on Graphene for Lithium–Sulfur Redox Reactions

The lithium–sulfur battery is one of the next-generation rechargeable battery candidates due to its high theoretical energy density and low cost. However, the sluggish conversion kinetics of soluble lithium polysulfides into insoluble Li2S2/Li2S leads to low sulfur utilization, retarded rate responses, and rapid capacity decay. Here, we enhance the sulfur reduction kinetics by designing and synthesizing a lamellar-structured NiFeLDH and reduced graphene oxide (rGO) composite. The assembly of a two-dimensional NiFeLDH with rGO, which has high conductivity and electrocatalytic activity, significantly enhances the electrochemical steps of sulfur reduction. The S@NiFeLDH/rGO cathode delivers an initial discharge capacity of 1014 mAh g−1 at 0.2 C and a capacity of 930 mAh g−1 after 100 cycles at 0.2 C. Even at a high current density of 1 C, the S@NiFeLDH/rGO could maintain a high capacity of 554 mAh g−1 after 400 cycles.

Electrochemical study of the redox processes of elemental sulfur in organic solvents using poly (3,4-ethylene-dioxy-thiophene) modified glassy carbon electrodes as working electrodes and ionic liquids as electrolytes

The commercial use of Lithium-sulfur batteries has been limited by their short service life due to the shuttle effect of polysulfides, which is due to the transport of polysulfides towards the anode and the formation of highly resistive deposits that passivate the electrodes. This problem can be solved by decreasing the transport of these species from the cathode to the anode and simultaneously improving the kinetics of electron transfer reactions. This work studies by electrochemical impedance spectroscopy and cyclic and ac voltammetry the redox reactions of elemental sulfur in either acetonitrile (CH3CN) or dimethyl sulfoxide (DMSO) using as a working electrode either pristine glassy carbon (GC) or GC modified with a thin film of poly-3,4-ethylenedioxythiophene (GC-PEDOT) as working electrodes. Tetrabutylammonium hexafluorophosphate (TBAPF6), 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) and 1-Butyl-3-methylimidazolium triflate ([Bmim][OTf]) were investigated as electrolytes. It was found that the kinetics of the first reduction reaction of S8 on GC is much faster in CH3CN than in DMSO and when [Bmim][OTf] is used as an electrolyte. On the other hand, it was found that PEDOT is electrocatalytic for the first reduction reaction of elemental sulfur. Finally, by encapsulating the sulfur in PEDOT it is possible to increase the retention of the sulfur species inside PEDOT upon redox cycling if pure ionic liquids are used as electrolytes.

Regulating f orbital of Tb electronic reservoir to activate stepwise and dual‐directional sulfur conversion reaction

AbstractThe sluggish kinetics in multistep sulfur redox reaction with different energy requirements for each step, is considered as the crucial handicap of lithium–sulfur (Li–S) batteries. Designing an electron reservoir, which can dynamically release electron to/accept electron from sulfur species during discharge/charge, is the ideal strategy for realizing stepwise and dual‐directional polysulfide electrocatalysis. Herein, a single Tb3+/4+ oxide with moderate unfilled f orbital is synthetized as an electron reservoir to optimize polysulfide adsorption via Tb–S and N···Li bonds, reduce activation energy barrier, expedite electron/Li+ transport, and selectively catalyze both long‐chain and short‐chain polysulfide conversions during charge and discharge. As a result, Tb electron reservoir enables stable operation of low‐capacity decay (0.087% over 500 cycles at 1 C), high sulfur loading (5.2 mg cm−2) and electrolyte‐starved (7.5 μL mg−1) Li–S batteries. This work could unlock the potential of f orbital engineering for high‐energy battery systems.image

Understanding the Catalytic Kinetics of Polysulfide Redox Reactions on Transition Metal Compounds in Li-S Batteries.

Because of their high energy density, low cost, and environmental friendliness, lithium-sulfur (Li-S) batteries are one of the potential candidates for the next-generation energy-storage devices. However, they have been troubled by sluggish reaction kinetics for the insoluble Li2S product and capacity degradation because of the severe shuttle effect of polysulfides. These problems have been overcome by introducing transition metal compounds (TMCs) as catalysts into the interlayer of modified separator or sulfur host. This review first introduces the mechanism of sulfur redox reactions. The methods for studying TMC catalysts in Li-S batteries are provided. Then, the recent advances of TMCs (such as metal oxides, metal sulfides, metal selenides, metal nitrides, metal phosphides, metal carbides, metal borides, and heterostructures) as catalysts and some helpful design and modulation strategies in Li-S batteries are highlighted and summarized. At last, future opportunities toward TMC catalysts in Li-S batteries are presented.

Unveiling the synergistic catalysis essence of trimetallic Fe-Co-Ni phosphides for lithium–sulfur chemistry

Lithium–sulfur batteries (LSBs) have emerged as prospective candidates for energy storage systems due to their high energy density and low cost of sulfur. However, the fast capacity degradation stemming from the fatal lithium polysulfide (LiPS) shuttle and sluggish redox reaction kinetic acts as the bottleneck for the real implementation of LSBs. Herein, we propose a well-designed nanosphere functionalized with trimetallic Fe-Co-Ni phosphides (FCNP) to host sulfur and promote the sulfur redox reactions. The well-dispersed trimetallic phosphides can not only enhance polarity and electron conductivity but also supply sufficient conversion sites and short sulfur evolution pathway. Therefore, the elaborated trimetallic phosphides on carbon nanosphere effectively inhibits LiPSs escaping from the cathode to anode. Further, the systematic electrochemical measurements and synchrotron X-ray three-dimensional nano-computed tomography (X-ray 3D nano-CT) results provide clear evidence that FCNP as a bidirectional electrocatalyst smoothly accelerates the generation and decomposition of Li2S. Accordingly, the S/FCNP cathode exhibits a remarkable discharge capacity of 1172.3 mA h g−1 at 0.2C in coin cell, 1164.0 mA h g−1 at 0.1C in pouch cell and the favorable cycling performance.

A Dual‐Phase Electrolyte for High‐Energy Lithium–Sulfur Batteries

AbstractDissolution of lithium polysulfides (LiPSs) is essential for fast cathode kinetics, but detrimental for anode stability, especially under lean electrolyte conditions. In this work, the phase separation phenomenon between solvents with different polarities (tetramethyl sulfone [TMS] and dibutyl ether [DBE]) is utilized to enable the design of a dual‐phase electrolyte. High‐polarity, high‐density TMS–lithium bis(trifluoromethanesulfonyl)imide–ammonium trifluoroacetate as the cathode electrolyte strongly solvates LiPSs, which propel the sulfur redox reaction. Moreover, the composite of DBE and a polymeric ion conductor serves as the anode electrolyte. The addition of DBE in the anode side effectively prevents the crossover of corrosive species (LiPSs and ammonia trifluoroacetate), enabling a significant improvement in Li‐metal anode stability. The electrode‐specific dual‐phase electrolyte design provides electrochemical performance superior to conventional electrolytes. Without additional electrode engineering, pouch cells assemble with the dual‐phase electrolyte cycle under a lean electrolyte (4 µL mg−1) and low‐Li‐excess condition (N/P = 3) for 120 cycles.

Selective catalysis of single V atoms and VN1-x nanodots enables fast polysulfides conversion in lithium–sulfur batteries

The application of lithium–sulfur (Li–S) batteries are mainly hindered by the shuttle effect of soluble polysulfides and the sluggish kinetics of sulfur redox reaction. Hence, a bidirectional catalyst, in which single vanadium (V) atoms with V-N4 coordination and vanadium nitride nanodots with abundant nitrogen vacancies (VN1-x) are decorated on nitrogen-doped carbon nanosheets (VN1-x@V-NC), was designed to modify the separators for Li–S batteries. Theoretical calculations and experiments show that V-N4 and VN1-x sites display catalytic selectivity for the formation and decomposition of Li2S, respectively. Additionally, nitrogen-deficient VN1-x displays a strong affinity toward soluble polysulfides through V-S and Li-N bonds, and polysulfides are preferentially adsorbed near the nitrogen vacancies. Specially, the strong adsorption ability facilitates the subsequent conversion reaction at the dual-site. Consequently, a Li–S battery with VN1-x@V-NC modified separator based on pure S cathode displays a stable long-term cycling performance over 500 cycles at 2C. Furthermore, the electrochemical performance of pouch cell with 4 mg cm−2 S loading demonstrates the potential of the VN1-x @V-NC modified separator for practical application.

Multi-function hollow nanorod as an efficient sulfur host accelerates sulfur redox reactions for high-performance Li-S batteries

The “shuttle effect” of lithium polysulfides (LiPSs) leads to loss of active materials and the deterioration of cycle stability, which seriously restricts the practical progress of lithium-sulfur (Li-S) batteries. The diffusion of soluble discharge intermediate is the root cause of the above problems. Herein, we synthesized a porous organic framework material (HUT-8) based on triazine network, the polar groups above the hollow structure can not only adsorb LiPSs through electron donating effect, but also anchored cobalt (II) ions provide a large number of binding sites for the in-situ growth of CoS2. This ensured maximized exposure of catalytic centre and improve their interactions with sulfur redox species under the confinement of mesopores, which can catalytically accelerate capture/diffusion of LiPSs and precipitation/decomposition of Li2S. Based on the synergistic effect of the composite materials, the CoS2-HUT-8/S cathode maintained a capacity of 583 mAh g−1 after 500 cycles at 1 C, and a minimum capacity fading rate of 0.046% per cycle. A freestanding CoS2-HUT-8/S cathode with sulfur loading of 5.2 mg cm−2 delivered a high areal capacity of 4.01 mAh cm−2 under a lean electrolyte, which would provide great potential for the practical progress of Li-S batteries.

Theoretical estimates of sulfoxyanion triple-oxygen equilibrium isotope effects and their implications

Triple-oxygen isotope (δ18O and Δ′17O) analysis of sulfate is becoming a common tool to assess several biotic and abiotic sulfur-cycle processes, both today and in the geologic past. Multi-step sulfur redox reactions often involve intermediate sulfoxyanions such as sulfite, sulfoxylate, and thiosulfate, which may rapidly exchange oxygen atoms with surrounding water. Process-based reconstructions therefore require knowledge of equilibrium oxygen-isotope fractionation factors (18α and 17α) between water and each individual sulfoxyanion. Despite this importance, there currently exist only limited experimental 18α data and no 17α estimates due to the difficulty of isolating and analyzing short-lived intermediate species. To address this, we theoretically estimate 18α and 17α for a suite of sulfoxyanions—including several sulfate, sulfite, sulfoxylate, and thiosulfate species—using quantum computational chemistry. We determine fractionation factors for sulfoxyanion “water droplets” using the B3LYP/6-31G+(d,p) method; we additionally calculate higher-order method (CCSD/aug-cc-pVTZ and MP2/aug-cc-pVTZ) scaling factors, and we qualitatively estimate the importance of anharmonic zero-point energy (ZPE) corrections using a suite of gaseous sulfoxy compounds. Methodological scaling factors greatly impact 18α predictions, whereas ZPE corrections are likely small (i.e., ⩽1‰) at Earth-surface temperatures; existing experimental data best agree with 18α predictions when including redox state-specific CCSD/aug-cc-pVTZ scaling factors. Theoretical pH- and temperature-specific bulk-solution (i.e., abundance-weighted average of all species) 18α values yield root-mean-square errors for sulfate/water, sulfite/water, and thiosulfate/water equilibrium of 4.5‰ (n=18 experimental conditions), 3.7‰ (n=27), and 2.2‰ (n=3), respectively. However, sulfate- and sulfite-system agreement improves considerably when comparing experimental results only to SO3(OH)−/H2O (RMSE = 1.6‰) and SO2(OH)−/H2O (RMSE = 2.2‰) predictions, rather than bulk solutions. This is particularly true for the sulfite system at high and low pH, when SO2(OH)− is not the dominant species. We discuss potential experimental and theoretical biases that may lead to this apparent improvement. By combining 18α and 17α predictions, we additionally estimate that sulfate, sulfite, sulfoxylate, and thiosulfate species can exhibit Δ′17O values as much as 0.199‰, 0.205‰, 0.101‰, and 0.186‰ more negative than equilibrated water at Earth-surface temperatures (reference line slope = 0.5305). This theoretical framework provides a foundation to interpret experimental and observational triple-oxygen isotope results of several sulfur-cycle processes including pyrite oxidation, microbial metabolisms (e.g., sulfate reduction, thiosulfate disproportionation), and hydrothermal anhydrite precipitation. We highlight this with several examples.

Selective catalytic oxidation of pollutant H2S over Co-decorated hollow N-doped carbon nanofibers for high-performance Li-S batteries

Hydrogen sulfide (H2S) is one of the most harmful pollutants to human health and the environment. Using carbon-based catalysts, H2S can be selectively oxidized to elemental sulfur (S) at room temperature and carbon-sulfur composites are produced, which enlightens a facile solution combining desulfurization with cathode preparation for high-performance lithium-sulfur batteries (LSBs). Herein, a heterogeneous catalyst of cobalt decorated N-doped hollow carbon nanofibers (Co-NHCFs) is designed for realizing the integrated application, in which the electron redistribution arising from long-range interactions of Co/N-doped carbon significantly promotes the oxygen radical generation and H2S dissociation, leading to its robust catalytic activity for H2S oxidation. Benefiting from the hollow framework with capacious storage space for rapid gas diffusion, the in-situ fabrication of high S-loading carbon-based cathodes (S@Co-NHCFs) used for LSBs is achieved during the H2S oxidation processing. Due to the more favorable diffusion of H2S gas than liquid S, this kind of chemical reaction-induced deposition can realize a more uniform distribution of solid S upon carbon than the traditional method by molten infusion, which, coupled with the catalysis of heterogeneous effect on the reversible sulfur-redox reaction, results in superior electrochemical performance of S@Co-NHCFs in LSBs.

Dominance of Sulfurospirillum in Metagenomes Associated with the Methane Ice Worm (Sirsoe methanicola).

Sirsoe methanicola, commonly known as the methane ice worm, is the only macrofaunal species known to inhabit the Gulf of Mexico methane hydrates. Little is known about this elusive marine polychaete that can colonize rich carbon and energy reserves. Metagenomic analysis of gut contents and worm fragments predicted diverse metabolic capabilities with the ability to utilize a range of nitrogen, sulfur, and organic carbon compounds through microbial taxa affiliated with Campylobacterales, Desulfobacterales, Enterobacterales, SAR324, Alphaproteobacteria, and Mycoplasmatales. Entomoplasmatales and Chitinivibrionales were additionally identified from extracted full-length 16S rRNA sequences, and read analysis identified 196 bacterial families. Overall, the microbial community appeared dominated by uncultured Sulfurospirillum, a taxon previously considered free-living rather than host-associated. Metagenome-assembled genomes (MAGs) classified as uncultured Sulfurospirillum predicted thiosulfate disproportionation and the reduction of tetrathionate, sulfate, sulfide/polysulfide, and nitrate. Microbial amino acid and vitamin B12 biosynthesis genes were identified in multiple MAGs, suggesting nutritional value to the host. Reads assigned to aerobic or anaerobic methanotrophic taxa were rare. IMPORTANCE Methane hydrates represent vast reserves of natural gas with roles in global carbon cycling and climate change. This study provided the first analysis of metagenomes associated with Sirsoe methanicola, the only polychaete species known to colonize methane hydrates. Previously unrecognized participation of Sulfurospirillum in a gut microbiome is provided, and the role of sulfur compound redox reactions within this community is highlighted. The comparative biology of S. methanicola is of general interest given research into the adverse effects of sulfide production in human gut microbiomes. In addition, taxonomic assignments are provided for nearly 200 bacterial families, expanding our knowledge of microbiomes in the deep sea.

MoP@NC/S cathode with multiple synergistic effect contributes to Li-S battery

Li-S battery is seen as the main technical route in high-energy density storage system because of high specific capacity. There are many challenges including volume expansion, shuttle effect and sluggish kinetics during the electrode reaction. Herein, we construct MoP nanoparticles which are embedded in N-doped carbon hollow nanostructure (MoP@NC) as host with multiple synergistic mechanism to facilitate multiphase sulfur redox reaction kinetics, inhibit polysulfide shuttle and buffer the side effects of volume expansion in Li-S battery. In consequence, MoP@NC/S cathode shows a surprisingly discharge capacity of 1587 mAh g−1 at 0.1 C, and a stable long cycle life over 1000 cycles at 1 C with low capacity loss of average 0.04% per cycle. The MoP@NC/S cathode effectively solves the essential problem and further promotes the commercialization of Li-S battery.

Defect-rich porous tubular graphitic carbon nitride with strong adsorption towards lithium polysulfides for high-performance lithium-sulfur batteries

• Nitrogen-deficient PTCN with nanotube tentacles and porous architecture was synthesized. • The introduced nitrogen defects enable more excellent intrinsic conductivity, higher adsorbability and conversion catalytic activity to LiPSs. • The vertically-rooted hollow nanotube tentacles on the PTCN surface facilitate electron conduction for sulfur redox reactions. The commercialization of the lithium-sulfur (Li-S) batteries is severely hampered by the shuttle effect and sluggish kinetics of lithium polysulfides (LiPSs). In this study, porous tubular graphitic carbon nitride (PTCN) was synthesized as the sulfur host by hydrothermal treatment, thermal shock and etching methods. By etching technology, the hollow nanotube tentacles grow on the tube wall of PTCN, the mesoporous appears on the inner wall, and a large number of nitrogen defects are introduced. The vertically-rooted hollow nanotube tentacles on the PTCN surface facilitate electron conduction for sulfur redox reactions. The hollow and porous architecture exposes plentiful active interfaces for accelerated redox conversion of polysulfide. Furthermore, the nitrogen defects in PTCN enable more excellent intrinsic conductivity, higher adsorbability and conversion catalytic activity to LiPSs. Based on the above synergetic effect, the batteries with PTCN/S cathodes realize a high discharge capacity of 504 mAh g −1 at 4 C and a stable cycling behavior over 500 cycles with a low capacity decay of 0.063% per cycle. The results indicate a promising approach todesigning a high performance electrode material for Li-S batteries. .

Understandings about functionalized porous carbon via scanning transmission x-ray microscopy (STXM) for high sulfur utilization in lithium-sulfur batteries

Functionalized porous carbons are necessary for the reversible operation of lithium-sulfur batteries (LSBs), however, their appropriate utilization and physicochemical states in the sulfur cathode are still unclear. Although numerous studies regarding distribution of sulfur in the pores of the carbon framework in the cathode have been reported, sulfur distribution and oxygen coverage on the carbon surface after sulfur infiltration have not been clearly investigated. In this study, we scrutinized the role of the pores in the oxygen-functionalized mesoporous carbon nanoparticle (O-MCN). Furthermore, we elaborated sulfur distribution, oxygen coverage, and pore utilization of O-MCN under the three different sulfur infiltration process. The soft x-ray scanning transmission x-ray microscopy (STXM) was used for the first time in the LSB system. The STXM enabled probing of local distribution of sulfur and the chemical nature of sulfur and oxygen in O-MCNs. Our findings provide a comprehensive understanding about how the sulfur infiltration process impacts the sulfur utilization during the redox reaction of sulfur in the oxygen-functionalized mesoporous carbon.

Multi-functional ZnS quantum Dots/Graphene aerogel modified separator for high performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have been considered as a promising candidate for next-generation energy storage, yet their practical application is limited by the polysulfides (PS) shuttle effect and slow kinetics of sulfur redox reaction. Despite the progress in engineering the separator for Li-S batteries, the separator with the synergistic effect of efficient PS blockage and PS conversion catalysis has not been successfully explored. Here, a zinc sulfide quantum dots/reduced graphene aerogel (ZnS-RGA) modified separator is developed for Li-S batteries. ZnS quantum dots function as the chemically LiPS-anchoring and catalytic sites that can simultaneously accelerate the sulfur redox reaction (SRR) and suppress the shuttle effect, while the 3D porous RGA further physically blocks the migration of LiPS. As a consequence, the Li-S batteries with ZnS-RGA modified separator present a high initial discharge capacity of 1211 mAh g − 1 at 0.1 C and stable cycling performance over 500 cycles at 1 C. We believe the strategy incorporating the SRR catalysts with LiPS-immobilizing separator will be an appealing way for producing high-performance Li-S devices.