Graphene Oxide as a Sulfur Immobilizer in High Performance Lithium/Sulfur Cells

Potassium Ion-Assisted Self-Assembled MXene-K-CNT Composite as High-Quality Sulfur-Loaded Hosts for Lithium-Sulfur Batteries

We successfully synthesized hybrid MXene-K-CNT composites composed of alkalized two-dimensional (2D) metal carbide and carbon nanotubes (CNTs), which were employed as host materials for lithium-sulfur (Li-S) battery cathodes. The unique three-dimensional (3D) intercalated structure through electrostatic interactions by K+ ions in conjunction with the scaffolding effect provided by CNTs effectively inhibited the self-stacking of MXene nanosheets, resulting in an enhanced specific surface area (SSA) and ion transport capability. Moreover, the addition of CNTs and in situ-grown TiO2 considerably improved the conductivity of the cathode material. K+ ion etching created a more hierarchical porous structure in MXene, which further enhanced the SSA. The 3D framework effectively confined S embedded between nanosheet layers and suppressed volume changes of the cathode composite during charging/discharging processes. This combination of CNTs and alkalized nanosheets functioned as a physical and chemical dual adsorption system for lithium polysulfides (LiPSs). When subjected to a high current at 1.0C, S@MXene-K-0.5CNT with S-loaded of 1.2 mg cm-2 had an initial capacity of 919.6 mAh g-1 and capacity decay rate of merely 0.052% per cycle after 1000 cycles. Moreover, S@MXene-K-0.5CNT maintained good cycling stability even at a high current of up to 5.0C. These impressive results highlight the potential of alkalized 2D MXene nanosheets intercalated with CNTs as highly promising cathode materials for Li-S batteries. The study findings also have prospects for the development of next-generation Li-S batteries with high energy density and prolonged lifespans.

Conformational Preference of Lithium Polysulfide Clusters Li2Sx (x = 4-8) in Lithium-Sulfur Batteries

Structures are of fundamental importance for diverse studies of lithium polysulfide clusters, which govern the performance of lithium-sulfur batteries. The ring-like geometries were regarded as the most stable structures, but their physical origin remains elusive. In this work, we systematically explored the minimal structures of Li2Sx (x = 4-8) clusters to uncover the driving force for their conformational preferences. All low-lying isomers were generated by performing global searches using the ABCluster program, and the ionic nature of the Li···S interactions was evidenced with the energy decomposition analysis based on the block-localized wave function (BLW-ED) approach and further confirmed with the quantum theory of atoms in molecule (QTAIM). By analysis of the contributions of various energy components to the relative stability with the references of the lowest-lying isomers, the controlling factor for isomer preferences was found to be the polarization interaction. Notably, although the electrostatic interaction dominates the binding energies, it contributes favorably to the relative stabilities of most isomers. The Li+···Li+ distance is identified as the key geometrical parameter that correlates with the strength of the polarization of the Sx2- fragment imposed by the Li+ cations. Further BLW-ED analyses reveal that the cooperativity of the Li+ cations primarily determines the relative strength of the polarization.

New Scalable Sulfur Cathode Containing Specifically Designed Polysulfide Adsorbing Materials

Because of its considerable theoretical specific capacity and energy density, lithium-sulfur battery technology holds great potential to replace lithium-ion battery technology. However, a versatile, low-cost, and easily scalable bulk synthesis method is essential for translating bench-level development to large-scale production. This paper reports the design and synthesis of a new scalable sulfur cathode, S@CNT/PANI/PPyNT/TiO2 (BTX). The rationally chosen cathode components suppress the migration of polysulfide intermediates via chemical interactions, enhance redox kinetics, and provide electrical conductivity to sulfur, rendering outstanding long-term cycling performance and strong initial specific capacity in terms of electrochemical performance. This cathode's cell demonstrated an initial specific capacity of 740 mA h g-1 at 0.2 C (with a capacity decay rate of 0.08% per cycle after 450 cycles).

Aqueous heterocoagulation-driven assembly of graphene oxide and polycation-coated sulfur particles for nanocomposite Li-S battery cathodes

HYPOTHESIS

Reduced graphene oxide (rGO/polycation/sulfur) composites are promising cathode materials for Li-S battery applications because homogeneously dispersed sulfur nano/micro clusters in suitable carbon hosts enable remarkable cycle life for Li-S battery cells. New, benign and economic synthesis methods based only on aqueous colloidal dispersions are demanded for achieving high dispersity grade of sulfur within the carbon host. Colloidal interactions leading to heteroaggregation between carbonaceous lamellae and polycation-modified sulphur nanoparticles at ambient conditions in water are foreseen to afford nanocomposite cathodes, which maintain excellent electrochemical performance.

EXPERIMENTS

Hydrophilic sulfur nanoparticles (SNPs) were coated by low doses of polycation (PDDA) until reaching the isoelectric point (IEP), and in high dose to achieve charge reversal. Streaming potential titrations were performed to reveal appropriate mass ratios of PPDA, SNP and GO. Positively charged SNPs formed stable heteroaggregated structures with GO, and were employed to fabricate rGO/polycation/sulphur cathodes.

FINDINGS

Charge reversal characteristics of SNPs, polycation and GO were characterized quantitatively and mass ratios of PDDA to SNP beyond IEP were found to mediate attractive interactions leading to rapid heteroaggregation between SNPs and GO and also alleviate lithium polysulfide migration. The composite cathode showed an initial discharge capacity of 522 mAhg-1 at 0.2C rate with an excellent capacity retention of 91.4 % and coulombic efficiency of 98.5% after 100 charge-discharge cycles.

Chemistry Aspects and Designing Strategies of Flexible Materials for High-Performance Flexible Lithium-Ion Batteries

In recent years, flexible and wearable electronics such as smart cards, smart fabrics, bio-sensors, soft robotics, and internet-linked electronics have impacted our lives. In order to meet the requirements of more flexible and adaptable paradigm shifts, wearable products may need to be seamlessly integrated. A great deal of effort has been made in the last two decades to develop flexible lithium-ion batteries (FLIBs). The selection of suitable flexible materials is important for the development of flexible electrolytes self-supported and supported electrodes. This review is focused on the critical discussion of the factors that evaluate the flexibility of the materials and their potential path toward achieving the FLIBs. Following this analysis, we present how to evaluate the flexibility of the battery materials and FLIBs. We describe the chemistry of carbon-based materials, covalent-organic frameworks (COFs), metal-organic frameworks (MOFs), and MXene-based materials and their flexible cell design that represented excellent electrochemical performances during bending. Furthermore, the application of state-of-the-art solid polymer and solid electrolytes to accelerate the development of FLIBs is introduced. Analyzing the contributions and developments of different countries has also been highlighted in the past decade. In addition, the prospects and potential of flexible materials and their engineering are also discussed, providing the roadmap for further developments in this fast-evolving field of FLIB research.

Engineering Strategies for Suppressing the Shuttle Effect in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are supposed to be one of the most potential next-generation batteries owing to their high theoretical capacity and low cost. Nevertheless, the shuttle effect of firm multi-step two-electron reaction between sulfur and lithium in liquid electrolyte makes the capacity much smaller than the theoretical value. Many methods were proposed for inhibiting the shuttle effect of polysulfide, improving corresponding redox kinetics and enhancing the integral performance of Li-S batteries. Here, we will comprehensively and systematically summarize the strategies for inhibiting the shuttle effect from all components of Li-S batteries. First, the electrochemical principles/mechanism and origin of the shuttle effect are described in detail. Moreover, the efficient strategies, including boosting the sulfur conversion rate of sulfur, confining sulfur or lithium polysulfides (LPS) within cathode host, confining LPS in the shield layer, and preventing LPS from contacting the anode, will be discussed to suppress the shuttle effect. Then, recent advances in inhibition of shuttle effect in cathode, electrolyte, separator, and anode with the aforementioned strategies have been summarized to direct the further design of efficient materials for Li-S batteries. Finally, we present prospects for inhibition of the LPS shuttle and potential development directions in Li-S batteries.

Designing novel monolayer and multilayer h-CSe crystals with tunable photoelectric properties

Using the first-principles method, a new structure of monolayer h-CSe was predicted, exhibiting good dynamical and thermal stability. The geometrical, electronic and optical properties of monolayer h-CSe are examined at the HSE level. Furthermore, the influences of the in-plane strain and layer number on the electric properties of the two dimensional h-CSe material are studied. The results indicate that it possesses an indirect band gap, which exhibits a rich variety of behaviors depending on the small in-plane biaxial strain. The band gap of monolayer h-CSe could be easily tuned in the energy range from 0.82 eV to 2.61 eV under small in-plane biaxial strain (from -3% to 3%). Also, a band gap transition between direct and indirect types is not found. The band gap of the h-CSe materials decreases with the increase of their layer number. In addition, it was found that these h-CSe materials show excellent optical properties, including strong light harvesting ability for the ultra-violet light range of the solar spectrum. The results obtained here indicate that monolayer h-CSe may have significant potential applications in future nanoelectronic fields.

Single-Atomic Dispersion of Fe and Co Supported on Reduced Graphene Oxide for High-Performance Lithium-Sulfur Batteries

High theoretical energy density and low cost make lithium-sulfur (LSB) batteries a promising system for next-generation energy storage. LSB performance largely depends on efficient reversible conversion of elemental sulfur to Li2S. Here, well-designed sulfur host materials including Fe or Co single atoms embedded on N-doped reduced graphene oxide (MNC/G with M = Fe or Co) are proposed to tackle the LSB challenges and enhance the electrochemical performance. Using a combination of Mössbauer spectroscopy and high-resolution scanning electron microscopy, the atomic dispersion of Co and Fe was revealed up to relatively high mass loadings. After optimization of the electrolyte/sulfur (E/S) ratio, FeNC/G shows the most promising cycle performance combining a constant high discharge capacity at low E/S values with the lowest polarization. In particular, the material FeNC/G@S with a high sulfur loading (9.4 mg cm-2) delivers a high area capacity of 7.7 mAh cm-2 under lean electrolyte conditions (6 mL g-1).

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

Developing polyoxometalate-cyclodextrin cluster-organic supramolecular framework (POM-CD-COSF) still remains challenging due to an extremely difficult task in rationally interconnecting two dissimilar building blocks. Here we report an unprecedented POM-CD-COSF crystalline structure produced through the self-assembly process of a Krebs-type POM, [Zn2 (WO2 )2 (SbW9 O33 )2 ]10- , and two β-CD units. The as-prepared POM-CD-COSF-based battery separator can be applied as a lightweight barrier (approximately 0.3 mg cm-2 ) to mitigate the polysulfide shuttle effect in lithium-sulfur batteries. The designed Li-S batteries equipped with the POM-CD-COSF modified separator exhibit remarkable electrochemical performance, attributed to fast Li+ diffusion through the supramolecular channel of β-CD, efficient polysulfide-capture ability by the dynamic host-guest interaction of β-CD, and improved sulfur redox kinetics by the bidirectional catalysis of POM cluster. This research provides a broad perspective for the development of multifunctional supramolecular POM frameworks and their applications in Li-S batteries.

A computational study on bifunctional 1T-MnS2 with an adsorption-catalysis effect for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are promising rechargeable energy storage systems with a high energy density, environmental friendliness and low cost. However, the commercialization process of Li-S batteries has been seriously hindered by the shuttling of lithium polysulfides (LiPSs) and the sluggish kinetics of conversion reaction among sulfur species. In this work, the adsorption-catalysis performance of five transition metal disulfide 1T-MS₂ (M = Mn, V, Ti, Zr, and Hf) surfaces is investigated by evaluating the adsorption energy of sulfur species, Li-ion diffusion energy barrier, decomposition energy barrier of Li₂S, and the Gibbs free energy barrier of the sulfur reduction reaction based on first-principles calculations. Our results show that the sulfiphilicity of 1T-MS₂ plays an important role in the adsorption behavior of short-chain sulfur species, in addition to lithiophilicity. Remarkably, among the five 1T-MS₂ materials, our results confirm that 1T-TiS₂ and 1T-VS₂ show excellent adsorption-catalysis performance and it is predicted that 1T-MnS₂ is an even better candidate catalyst to inhibit the shuttle effect and accelerate delithiation/lithiation kinetics. Moreover, the outstanding performance of 1T-MnS₂ persists in a solvent environment and under strain modulation. Our results not only demonstrate that 1T-MnS₂ is an excellent potential catalyst for high-performance Li-S batteries, but also provide great insights into the adsorption-catalysis mechanism during the cycling process.

Towards Practical Application of Li-S Battery with High Sulfur Loading and Lean Electrolyte: Will Carbon-Based Hosts Win This Race?

As the need for high-energy-density batteries continues to grow, lithium-sulfur (Li-S) batteries have become a highly promising next-generation energy solution due to their low cost and exceptional energy density compared to commercially available Li-ion batteries. Research into carbon-based sulfur hosts for Li-S batteries has been ongoing for over two decades, leading to a significant number of publications and patents. However, the commercialization of Li-S batteries has yet to be realized. This can be attributed, in part, to the instability of the Li metal anode. However, even when considering just the cathode side, there is still no consensus on whether carbon-based hosts will prove to be the best sulfur hosts for the industrialization of Li-S batteries. Recently, there has been controversy surrounding the use of carbon-based materials as the ideal sulfur hosts for practical applications of Li-S batteries under high sulfur loading and lean electrolyte conditions. To address this question, it is important to review the results of research into carbon-based hosts, assess their strengths and weaknesses, and provide a clear perspective. This review systematically evaluates the merits and mechanisms of various strategies for developing carbon-based host materials for high sulfur loading and lean electrolyte conditions. The review covers structural design and functional optimization strategies in detail, providing a comprehensive understanding of the development of sulfur hosts. The review also describes the use of efficient machine learning methods for investigating Li-S batteries. Finally, the outlook section lists and discusses current trends, challenges, and uncertainties surrounding carbon-based hosts, and concludes by presenting our standpoint and perspective on the subject.

High Energy Density Lithium-Sulfur Batteries Based on Carbonaceous Two-Dimensional Additive Cathodes

The increasing demand for electrical energy storage makes it essential to explore alternative battery chemistries that overcome the energy-density limitations of the current state-of-the-art lithium-ion batteries. In this scenario, lithium-sulfur batteries (LSBs) stand out due to the low cost, high theoretical capacity, and sustainability of sulfur. However, this battery technology presents several intrinsic limitations that need to be addressed in order to definitively achieve its commercialization. Herein, we report the fruitfulness of three different formulations using well-selected functional carbonaceous additives for sulfur cathode development, an in-house synthesized graphene-based porous carbon (ResFArGO), and a mixture of commercially available conductive carbons (CAs), as a facile and scalable strategy for the development of high-performing LSBs. The additives clearly improve the electrochemical properties of the sulfur electrodes due to an electronic conductivity enhancement, leading to an outstanding C-rate response with a remarkable capacity of 2 mA h cm^-2 at 1C and superb capacities of 4.3, 4.0, and 3.6 mA h cm^-2 at C/10 for ResFArGO₁₀, ResFArGO₅, and CAs, respectively. Moreover, in the case of ResFArGO, the presence of oxygen functional groups enables the development of compact high sulfur loading cathodes (>4 mg_S cm^-2) with a great ability to trap the soluble lithium polysulfides. Notably, the scalability of our system was further demonstrated by the assembly of prototype pouch cells delivering excellent capacities of 90 mA h (ResFArGO₁₀ cell) and 70 mA h (ResFArGO₅ and CAs cell) at C/10.

ZIF-67 on Sulfur-Functionalized Graphene Oxide for Lithium-Sulfur Batteries

How to overcome the problem of fast capacity fading and low sulfur utilization is the key to promote the practical applications of lithium-sulfur (Li-S) batteries. Based on the fact that sulfur-functionalized graphene oxide (GO-S) can avoid the loss of sulfur/polysulfides through the strong C-S interaction, and the zeolitic imidazolate framework (ZIF-67) can capture sulfur and catalyze lithium polysulfide (Li₂S_x, 4 ≤ x ≤ 8), the combination of ZIF-S (ZIF-67 after combining with sulfur) with GO-S can be expected to be an excellent electrode material for Li-S batteries due to the synergistic effect. Herein, ZIF-S@GO-S (n) nanocomposites (n = 1, 2, and 3 for the mass ratio of ZIF-67/GO of 4:1, 6:1, and 8:1, respectively) as the cathode materials in Li-S batteries were successfully fabricated, and ZIF-S@GO-S (2) showed better electrochemical performances and cycle stability with a high specific capacity of 1529.5 mA h g^-1 at the initial cycle and 792 mA h g^-1 after 500 cycles at 0.1 C (1 C = 1675 mA h g^-1). The fact that ZIF-S@GO-S (n) can simultaneously improve the conductivity and utilization of S (C-S···S₈ and C-S···S_xLi₂) and the conversion kinetics of Li₂S_x (4 ≤ x ≤ 8) provides a new avenue for designing and fabricating promising cathodes for high-performance Li-S batteries.

A 3D Framework with Li3 N-Li2 S Solid Electrolyte Interphase and Fast Ion Transfer Channels for a Stabilized Lithium-Metal Anode

The Li-metal anode has been recognized as the most promising anode for its high theoretical capacity and low reduction potential. However, the major drawbacks of Li metal, such as high reactivity and large volume expansion, can lead to dendrite growth and solid electrolyte interface (SEI) fracture. An in situ artificial inorganic SEI layer, consisting of lithium nitride and lithium sulfide, is herein reported to address the dendrite growth issues. Porous graphene oxide films are doped with sulfur and nitrogen (denoted as SNGO) to work as an effective lithium host. The SNGO film enables the in situ formation of an inorganic-rich SEI layer, which facilitates the transport of Li-ions, improves SEI mechanical strength, and avoids SEI fracture. In addition, COMSOL simulation results reveal that the microchannels fabricated by the 3D printing technique further shorten the Li-ion transfer pathways and homogenize heat and stress distribution in the batteries. As a result, the assembled anode shows low capacity fading of 0.1% per cycle at 2 C rate with the sulfur cathode. In addition, the high lithium utilization of the SNGO host enables the anode to provide a stable capacity at low negative/positive electrode ratios under 3 in LiS batteries.

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.

Nitrogen and titanium-codoped porous carbon nanocomposites derived from metal-organic framework as cathode to address polysulfides shuttle effects by Ti-assisted N-inhibiting strategy

To address the problem of shutting effect of Li-S batteries, we used Ti-based MOF as precursor to obtain a conductive matrix with dual inhibitors. The target material, namely NTiPC, shown remarkable discharge capacity with 1178 mA h g^-1, and maintained at 732 mA h g^-1 after 100 cycles. The results indicated the N- and Ti-active sites synergistic acted with conductive framework can facilitate binding reaction between matrix and polysulfides.

Synthesis and Electrochemical Performance of Microporous Hollow Carbon from Milkweed Pappus as Cathode Material of Lithium-Sulfur Batteries

Microtube-like porous carbon (MPC) and tube-like porous carbon-sulfur (MPC-S) composites were synthesized by carbonizing milkweed pappus with sulfur, and they were used as cathodes for lithium-sulfur batteries. The morphology and uniformity of these materials were characterized using X-ray powder diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy with an energy-dispersive X-ray analyzer, thermogravimetric analysis, and X-ray photoelectron spectrometry. The electrochemical performance of the MPC-S cathodes was measured using the charge/discharge cycling performance, C rate, and AC impedance. The composite cathodes with 93.8 wt.% sulfur exhibited a stable specific capacity of 743 mAh g^-1 after 200 cycles at a 0.5 C.

Carbon Coated Metal-Based Composite Electrode Materials for Lithium Sulfur Batteries: A Review

Lithium-sulfur battery is one of the most promising secondary battery systems due to their high energy density and low material cost. During the past decade, great progress has been achieved in promoting the performances of Li-S batteries by addressing the challenges at the laboratory-level model systems. With growing attention paid to the application of Li-S batteries, new challenges at practical cell scales emerge as the bottleneck. However, challenges remain for the commercialization of lithium-sulfur batteries. The current review mainly focused on metal-based catalysts decorated-carbon materials for enhanced lithium sulfur battery performance. Firstly, the synthesis methods of various carbon-sulfur composites are discussed, as well as the influence of different material structures on the electrochemical performance. Secondly, a variety of catalysts, including metal atoms, metal oxides, sulfides, phosphides, nitrides, and carbide-decorated carbon nanomaterials, are systematically introduced to determine how lithium can be enhanced by suppressing polysulfides and promoting redox conversion reactions. Also, analyzed the multi-step electrochemical reaction mechanism of the battery during the charging and discharging process, and provide a feasible path for the practical application of high energy density lithium-sulfur batteries.

Lithium Atom Surface Diffusion and Delocalized Deposition Propelled by Atomic Metal Catalyst toward Ultrahigh-Capacity Dendrite-Free Lithium Anode

Lithium metal anode possesses overwhelming capacity and low potential but suffers from dendrite growth and pulverization, causing short lifespan and low utilization. Here, a fundamental novel insight of using single-atomic catalyst (SAC) activators to boost lithium atom diffusion is proposed to realize delocalized deposition. By combining electronic microscopies, time-of-flight secondary ion mass spectrometry, theoretical simulations, and electrochemical analyses, we have unambiguously depicted that the SACs serve as kinetic activators in propelling the surface spreading and lateral redistribution of the lithium atoms for achieving dendrite-free plating morphology. Under the impressive capacity of 20 mA h cm^-2, the Li modified with SAC-activator exhibits a low overpotential of ∼50 mV at 5 mA cm^-2, a long lifespan of 900 h, and high Coulombic efficiencies during 150 cycles, much better than most literature reports. The so-coupled lithium-sulfur full battery delivers high cycling and rate performances, showing great promise toward the next-generation lithium metal batteries.

Multifunctional Atomic Molybdenum on Graphene with Distinctive Coordination to Solve Li and S Electrochemistry

The improvement of lithium-sulfur batteries is still impeded by notorious shuttling effect and sluggish kinetics on the S cathode, and rampant Li dendrite formation on the Li anode makes it worse. Herein, a type of single-atom dispersed Mo on nitrogen-doped graphene (Mo/NG) with a distinctive Mo-N₂ O₂ -C coordination structure first serving as a multifunctional material is designed by a structure-oriented strategy to solve Li and S electrochemistry. Mo/NG with superior intrinsic properties endowed by the unique coordination configuration adsorbs soluble polysulfides and promotes bidirectional conversion of LiPSs at the cathode side. Meanwhile, the suitable binding strength of Mo/NG with lithium ions endows it with an attractive lithiophilic feature. Specifically, Mo/NG is able to work as the adaptor to redistribute lithium ions on the interface of separator and homogenize the lithium ion flux. Due to the suitable binding ability with Li⁺ , it does not interfere with the diffusion of lithium ions across and provides tunnels exclusive to lithium ions to generate fast and homogeneous flux. Ascribed to such unique multifunctionality, Li-S batteries assembled with Mo/NG exhibit excellent electrochemical performance including long cycling stability over 1000 cycles and high areal capacities under high sulfur mass loading.

Tunnel Structure Enhanced Polysulfide Conversion for Inhibiting "Shuttle Effect" in Lithium-Sulfur Battery

The Lithium sulfur (Li-S) battery has a great potential to replace lithium-ion batteries due to its high-energy density. However, the "shuttle effect" of polysulfide intermediates (Li₂S₈, Li₂S₆, Li₂S₄, etc.) from the cathode can lead to rapid capacity decay and low coulombic efficiency, thus limiting its further development. Anchoring polysulfide and inhibiting polysulfide migration in electrolytes is one of the focuses in Li-S battery. It is well known that polar metal oxides-manganese oxides (MnO₂) are normally used as an effective inhibitor for its polysulfide inhibiting properties. Considering the natural 1D tunnel structure, MnO₂ with three kinds of typical tunnel-type were screened to study the effects of the tunnel size on the adsorption capacity of polysulfide. We found that MnO₂ with larger tunnel sizes has stronger chemisorption capacity of polysulfide. It promotes the conversion of polysulfide, and corresponding cathode exhibits better cycle reliability and rate performance in the cell comparison tests. This work should point out a new strategy for the cathode design of advanced Li-S battery by controlling the tunnel size.

Approaches to Combat the Polysulfide Shuttle Phenomenon in Li–S Battery Technology

Lithium–sulfur battery (LSB) technology has tremendous prospects to substitute lithium-ion battery (LIB) technology due to its high energy density. However, the escaping of polysulfide intermediates (produced during the redox reaction process) from the cathode structure is the primary reason for rapid capacity fading. Suppressing the polysulfide shuttle (PSS) is a viable solution for this technology to move closer to commercialization and supersede the established LIB technology. In this review, we have analyzed the challenges faced by LSBs and outlined current methods and materials used to address these problems. We conclude that in order to further pioneer LSBs, it is necessary to address these essential features of the sulfur cathode: superior electrical conductivity to ensure faster redox reaction kinetics and high discharge capacity, high pore volume of the cathode host to maximize sulfur loading/utilization, and polar PSS-resistive materials to anchor and suppress the migration of polysulfides, which can be developed with the use of nanofabrication and combinations of the PSS-suppressive qualities of each component. With these factors addressed, our world will be able to forge ahead with the development of LSBs on a larger scale—for the efficiency of energy systems in technology advancement and potential benefits to outweigh the costs and performance decay.

Multimodal Capturing of Polysulfides by Phosphorus-Doped Carbon Composites for Flexible High-Energy-Density Lithium-Sulfur Batteries

The widespread adoption of Li-ion batteries is currently limited by their unstable electrochemical performance and high flammability under mechanical deformation conditions and a relatively low energy density. Herein, high-energy-density lithium-sulfur (Li-S) batteries are developed for applications in next-generation flexible electronics and electric vehicles with long cruising distances. Freestanding high-S-loading carbon nanotubes cathodes are assembled with a phosphorus (P)-doped carbon interlayer coated on commercial separators. Strategies for the active materials and structural design of both the electrodes and separators are highly efficient for immobilizing the lithium polysulfides via multimodal capturing effects; they significantly improve the electrochemical performance in terms of the redox kinetics and cycling stability. The foldable Li-S cells show stable specific capacities of 850 mAh g^-1 over 100 cycles, achieving high gravimetric and volumetric energy densities of 387 Wh kg_cell ^-1 and 395 Wh L_cell ^-1 , respectively. The Li-S cells show highly durable mechanical flexibilities under severe deformation conditions without short circuit or failure. Finally, the Li-S battery is explored as a light-weight and flexible energy storage device aboard airplane drones to ensure at least fivefold longer flight times than traditional Li-ion batteries. Nanocarbon-based S cathodes and P-doped carbon interlayers offer a promising solution for commercializing rechargeable Li-S batteries.

Rational construction of a CNTs@VO2 nanosheets modified separator for enhancing the performance of lithium-sulfur batteries

Although lithium-sulfur (Li-S) batteries possess great potential to become the next generation of energy storage technology due to their fivefold higher energy density than commercial lithium-ion batteries, their practical application is still hindered by their poor cycling stability, especially resulting from the disturbing shuttle effect of soluble intermediates. In this study, vanadium dioxide (VO₂) nanosheets were successfully grown onto CNTs to form CNTs@VO₂ through hydrothermal and calcining processes. The hollow structure of the high conductive CNTs offers internal space and mesopores to accommodate the electrolyte combined with the polar metal oxide VO₂ nanosheets providing the chemical anchoring. The hollow binary core-shell host acting as the nanoreactor that serves as the modifier of the separator results in the intensive physical and chemical dual adsorption of lithium polysulfide species (LiPSs), promoting the conversion of long-chain LiPSs to alleviate the shuttle effect significantly and boosting the performance. In addition, the CNTs enhance the electronic conductivity and the electrolyte infiltration of the separator. Notably, the modified separator demonstrates a high initial discharge capacity of 1397 mA h g^-1 at 0.2C and retains a stable cycling ability with a reversible capacity of 965 mA h g^-1 over 200 cycles at 1C. Even for the high sulfur loading of 7.4 mg cm^-2, it can deliver a high areal capacity of 5.4 mA h cm^-2 at 0.5C.

Tailoring Mesopores and Nitrogen Groups of Carbon Nanofibers for Polysulfide Entrapment in Lithium-Sulfur Batteries

In the current work, we combined different physical and chemical modifications of carbon nanofibers through the creation of micro-, meso-, and macro-pores as well as the incorporation of nitrogen groups in cyclic polyacrylonitrile (CPAN) using gas-assisted electrospinning and air-controlled electrospray processes. We incorporated them into electrode and interlayer in Li–Sulfur batteries. First, we controlled pore size and distributions in mesoporous carbon fibers (mpCNF) via adding polymethyl methacrylate as a sacrificial polymer to the polyacrylonitrile carbon precursor, followed by varying activation conditions. Secondly, nitrogen groups were introduced via cyclization of PAN on mesoporous carbon nanofibers (mpCPAN). We compared the synergistic effects of all these features in cathode substrate and interlayer on the performance Li–Sulfur batteries and used various characterization tools to understand them. Our results revealed that coating CPAN on both mesoporous carbon cathode and interlayer greatly enhanced the rate capability and capacity retention, leading to the capacity of 1000 mAh/g at 2 C and 1200 mAh/g at 0.5 C with the capability retention of 88% after 100 cycles. The presence of nitrogen groups and mesopores in both cathodes and interlayers resulted in more effective polysulfide confinement and also show more promise for higher loading systems.

Constructing MIL-101(Cr) membranes on carbon nanotube films as ion-selective interlayers for lithium-sulfur batteries

It is of significant importance to suppress the polysulfide shuttle effect for the commercial application of lithium-sulfur batteries. Herein, continuous MIL-101(Cr) membranes were successfully fabricated on carbon nanotube films utilizing a simplein situgrowth method, aiming at constructing interlayer materials for inhibiting the shuttle effect. Owing to the suitable pore aperture and super electrolyte wettability, the as-developed MIL-101(Cr) membrane can effectively inhibit the shuttle behaviour of polysulfides while allowing the fast transport of Li-ions simultaneously, working as an ionic sieve. Additionally, this MOFs membrane is also helpful in accelerating the polysulfide catalytic conversion. Therefore, the proposed interlayer delivers an extraordinary rate capability, showing a remarkable capacity of 661.9 mAh g^-1under 5 C. Meanwhile, it also exhibits a high initial capacity of 816.1 mAh g^-1at 1 C and an exceptional durability with an extremely low capacity fading of 0.046% per cycle over 500 cycles.

Evolution of graphene oxide (GO)-based nanohybrid materials with diverse compositions: an overview

The discovery of the 2D nanostructure of graphene was in fact the beginning of a new generation of materials. Graphene itself, its oxidized form graphene oxide (GO), the reduced form of GO (RGO) and their numerous composites are associates of this generation. Out of this spectrum of materials, the development of GO and related hybrid materials has been reviewed in the present article. GO can be functionalized with metals (Ag and Mg) and metal oxides (CuO, MgO, Fe2O3, Ag2O, etc.) nanoparticles (NPs), organic ligands (chitosan and EDTA) and can also be dispersed in different polymeric matrices (PVA, PMMA, PPy, and PAn). All these combinations give rise to nanohybrid materials with improved functionality. An updated report on the chronological development of such nanohybrid materials of diverse nature has been delivered in the present context. Modifications in synthesis methodologies as well as performances and applications of individual materials are addressed accordingly. The functional properties of GO were synergistically modified by photoactive semiconductor NPs; as a result, the GO-MO hybrids acquired excellent photocatalytic ability and were able to degrade a large variety of organic dyes (MB, RhB, MO, MR, etc.) and pathogens. The large surface area of GO was successfully complemented by the NPs so that high and selective adsorption capacity towards metal ions and organic molecules as well as improved charge separation properties could be achieved. As a result, GO-MO hybrids have been considered effective materials in water purification, energy storage and antibacterial applications. GO-MO hybrids with magnetic particles have exhibited selective destruction of cancerous cells and controlled drug release properties, extremely important in the pharmaceutical field. Chitosan and EDTA-modified GO could form 3D network-like structures with strong efficiency in removing heavy metal ions and organic pollutants. GO as a filler enhanced the strength, flexibility and functional properties of common polymers, such as PVA and PVC, to a large extent while, GO-CP composites with polyaniline and polypyrrole are considered suitable for the fabrication of biosensors, supercapacitors, and MEMS as well as efficient photothermal therapy agents. In summary, GO-based hybrids with inorganic and organic counterparts have been designed, the unique properties of which are exploited in versatile fields of applications.

A New Graphitic Nitride and Reduced Graphene Oxide-Based Sulfur Cathode for High-Capacity Lithium-Sulfur Cells

Lithium-sulfur (Li-S) batteries can provide at least three times higher energy density than lithium-ion (Li-Ion) batteries. However, Li-S batteries suffer from a phenomenon called the polysulfide shuttle (PSS) that prevents the commercialization of these batteries. The PSS has several undesirable effects, such as depletion of active materials from the cathode, deleterious reactions between the lithium anode and electrolyte soluble lithium polysulfides, resulting in unfavorable coulombic efficiency, and poor cycle life of the battery. In this study, a new sulfur cathode composed of graphitic nitride as the polysulfide absorbing material and reduced graphene oxide as the conductive carbon host has been synthesized to rectify the problems associated with the PSS effect. This composite cathode design effectively retains lithium polysulfide intermediates within the cathode structure. The S@RGO/GN cathode displayed excellent capacity retention compared to similar RGO-based sulfur cathodes published by other groups by delivering an initial specific capacity of 1415 mA h g−1 at 0.2 C. In addition, the long-term cycling stability was outstanding (capacity decay at the rate of only 0.2% per cycle after 150 cycles).

Mass Production of 3D Connective Graphene Networks by Fluidized Bed Chemical Vapor Deposition and Its Application in High Performance Lithium-Sulfur Battery

Three−dimensional (3D) graphene with novel nano−architectures exhibits many excellent properties and is promising for energy storage and conversion applications. Herein, a new strategy based on the fluidized bed chemical vapor deposition (FB−CVD) process was proposed to prepare 3D graphene networks (3DGNs) with various nano−architectures. Specially designed SiC−C@graphene core/shell nanoparticles were prepared taking the advantages of the FB−CVD system, and 3DGNs with hierarchical nanostructures were obtained after removing the SiC core. The 3DGNs performed well as electrodes of lithium–sulfur batteries. The C–S cathode showed good rate performance at the current density of 0.1–2.0 C, and an initial discharge capacity of 790 mAhg⁻¹ cathode was achieved at a current density of 0.2 C. The Li−S batteries showed stabilized coulombic efficiency as high as 94% and excellent cyclic performance with an ultra low cyclic fading rate of 0.075% for the initial 280 cycles at a current density of 1.0 C. The improved electrochemical performance was ascribed to the enhanced conductivity by the connective graphene networks and the weakened shuttle effect by the special outer graphene layers. Mass production of the products was realized by the continuous FB−CVD process, which opens up new perspectives for large scale application of 3D graphene materials.

Flexible, Electrically Conductive, Nanostructured, Asymmetric Aerogel Films for Lithium-Sulfur Batteries

Lithium-sulfur batteries are afflicted with capacity fading on account of polysulfide shuttling. A novel cost-effective electrode that can hinder the polysulfide shuttling and realize high active material utilization is highly required. Here, we demonstrate a flexible, electrically conductive, nanostructured, and asymmetric hybrid cathode by integrating a high-aspect-ratio wood nanocellulose and a low-cost commercial carbon nanotube (∼$ 0.2 g^-1) into an entangled aerogel film. The vacuum filtration combined with lyophilization enables the aerogel film with quite different nanofiber/nanotube packing densities and pore structures at its two sides. The cooperative effects of the entangled building blocks and the asymmetric porous structure of the aerogel film stimulate the simultaneous increase of active sulfur loading, enhancing the electrolyte penetration, alleviating dissolution and shuttling of polysulfide ions, and promoting the fast electron transportation. The as-generated cathode exhibited a capacity fading of 0.01% per cycle over 1000 discharge/charge cycles at a 0.5 C rate (1 C = 1675 mA g^-1). The average Coulombic efficiency reached ∼99.7%.

Carbonaceous Hosts for Sulfur Cathode in Alkali-Metal/S (Alkali Metal = Lithium, Sodium, Potassium) Batteries

Alkali-metal/sulfur batteries hold great promise for offering relatively high energy density compared to conventional lithium-ion batteries. By providing viable sulfur composites that can be effectively used, carbonaceous hosts as a key component play critical roles in overcoming the preliminary challenges associated with the insulating sulfur and its relatively soluble polysulfides. Herein, a comprehensive overview and recent progress on carbonaceous hosts for advanced next-generation alkali-metal/sulfur batteries are presented. In order to encapsulate the highly active sulfur mass and fully limit polysulfide dissolution, strategies for tailoring the design and synthesis of carbonaceous hosts are summarized in this work. The sticking points that remain for sulfur cathodes in current alkali-metal/sulfur systems and the future remedies that can be provided by carbonaceous hosts are also indicated, which can lead to long cycling lifetimes and highly reversible capacities under repeated sulfur reduction reactions in alkali-metal/sulfur during cycling.

Carbon-Based Electrocatalysts for Efficient Hydrogen Peroxide Production

Hydrogen peroxide (H₂ O₂ ) is an environment-friendly and efficient oxidant with a wide range of applications in different industries. Recently, the production of hydrogen peroxide through direct electrosynthesis has attracted widespread research attention, and has emerged as the most promising method to replace the traditional energy-intensive multi-step anthraquinone process. In ongoing efforts to achieve highly efficient large-scale electrosynthesis of H₂ O₂ , carbon-based materials have been developed as 2e^- oxygen reduction reaction catalysts, with the benefits of low cost, abundant availability, and optimal performance. This review comprehensively introduces the strategies for optimizing carbon-based materials toward H₂ O₂ production, and the latest advances in carbon-based hybrid catalysts. The active sites of the carbon-based materials and the influence of coordination heteroatom doping on the selectivity of H₂ O₂ are extensively analyzed. In particular, the appropriate design of functional groups and understanding the effect of the electrolyte pH are expected to further improve the selective efficiency of producing H₂ O₂ via the oxygen reduction reaction. Methods for improving catalytic activity by interface engineering and reaction kinetics are summarized. Finally, the challenges carbon-based catalysts face before they can be employed for commercial-scale H₂ O₂ production are identified, and prospects for designing novel electrochemical reactors are proposed.

MOF-Derived Bifunctional Co0.85Se Nanoparticles Embedded in N-Doped Carbon Nanosheet Arrays as Efficient Sulfur Hosts for Lithium-Sulfur Batteries

Lithium-sulfur batteries possess the merits of low cost and high theoretical energy density but suffer from the shuttle effect of lithium polysulfides and slow redox kinetics of sulfur. Herein, novel Co_0.85Se nanoparticles embedded in nitrogen-doped carbon nanosheet arrays (Co_0.85Se/NC) were constructed on carbon cloth as the self-supported host for a sulfur cathode using a facile fabrication strategy. The interconnected porous carbon-based structure of the Co_0.85Se/NC could facilitate the rapid electron and ion transfer kinetics. The embedded Co_0.85Se nanoparticles can effectively capture and catalyze lithium polysulfides, thus accelerating the redox kinetics and stabilizing sulfur cathodes. Therefore, the Co_0.85Se/NC-S cathode could maintain a stable cycle performance for 400 cycles at 1C and deliver a high discharge specific capacity of 1361, 1001, and 810 mAh g^-1 at current densities of 0.1, 1, and 3C, respectively. This work provides an efficient design strategy for high-performance lithium-sulfur batteries with high energy densities.

Employing synergetic effect of ZnSe quantum dots and layered Ni(OH)2to boost the performance of lithium-sulfur cathodes

The low sulfur utilization, cycling instability, and sluggish kinetics are the critical obstructions to practical applications of lithium-sulfur batteries (LSBs). Constructing sulfur hosts with high conductivity, suppressed shuttle effect, and rapid kinetics is essential for their practical application in LSBs. Here, we synthetically utilized the merits of ZnSe quantum dots (QDs) and layered Ni(OH)₂to boost the performance of LSBs. A novel core-shell ZnSe-CNTs/S@Ni(OH)₂was constructed using the ZnSe-CNTs network as framework to load sulfur and following with Ni(OH)₂encapsulation. The CNT network decorated with ZnSe QDs not only serves as a conductive framework providing fast electron/ion transfer channels, but also limits polysulfide diffusion physically and chemically. Layered Ni(OH)₂, the wrinkled encapsulation, not only permits fast electron/ion transfer, but also buffers the expansion, confines active materials, and limits the polysulfide dissolution chemically. When used as a cathode, ZnSe-CNTs/S@Ni(OH)₂presents enhanced electrochemistry performance compared with ZnSe-CNTs/S and CNTs/S. The average specific capacity decreases from 1021.9 mAh g^-1at 0.2 C to 665.0 mAh g^-1at 2 C, showing rate capacity much higher than ZnSe-CNTs/S and CNTs/S. After 150 cycles, the capacity at 0.5 C slowly reduces from 926.7 to 789.0 mAh g^-1, showing high retention of 85.1%. Therefore, our investigation provides a new strategy to construct a promising sulfur cathode for LSBs.

A Polysulfides-Confined All-in-One Porous Microcapsule Lithium-Sulfur Battery Cathode

Developing emerging materials for high energy-density lithium-sulfur (Li-S) batteries is of great significance to suppress the shuttle effect of polysulfides and to accommodate the volumetric change of sulfur. Here, a novel porous microcapsule system containing a carbon nanotubes/tin dioxide quantum dots/S (CNTs/QDs/S) composite core and a porous shell prepared through a liquid-driven coaxial microfluidic method as Li-S battery cathode is developed. The encapsulated CNTs in the microcapsules provide pathways for electron transport; SnO₂ QDs on CNTs immobilize the polysulfides by strong adsorption, which is verified by using density functional theory calculations on binding energies. The porous shell of the microcapsule is beneficial for ion diffusion and electrolyte penetration. The void inside the microcapsule accommodates the volumetric change of sulfur. The Li-S battery based on the porous CNTs/QDs/S microcapsules displays a high capacity of 1025 mAh g^-1 after 100 cycles at 0.1 C. When the sulfur loading is 2.03 mg cm^-2 , the battery shows a stable cycling life of 700 cycles, a Coulombic efficiency exceeding 99.9%, a recoverable rate-performance during repeated tests, and a good temperature tolerance at both -5 and 45 °C, which indicates a potential for applications at different conditions.

Embedding Cobalt Atom Clusters in CNT-Wired MoS2 Tube-in-Tube Nanostructures with Enhanced Sulfur Immobilization and Catalyzation for Li-S Batteries

Lithium-sulfur batteries are one of the most promising next-generation energy storage systems. The efficient interconversion between sulfur/lithium polysulfides and lithium sulfide is a performance-determining factor for lithium-sulfur batteries. Herein, a novel strategy to synthesize a unique tube-in-tube CNT-wired sulfur-deficient MoS₂ nanostructure embedding cobalt atom clusters as an efficient polysulfide regulator is successfully conducted in Li-S batteries. It is confirmed that encapsulating MWCNTs into hollow porous sulfur-deficient MoS₂ nanotubes embedded with metal cobalt clusters not only can accelerate electron transport and confine the dissolution of lithium polysulfide by physical/chemical adsorption, but also can catalyze the kinetics of polysulfide redox reactions. Based on DFT calculations, in situ spectroscopic techniques, and various electrochemical studies, catalytic effects of CNT/MoS₂ -Co nanocomposite in Li-S battery are deeply investigated for the first time. The CNT/MoS₂ -Co composite cathode exhibits a very remarkable rate capability (641 mAh g^-1 at 5.0 C) and excellent cycling stability (capacity decay rate of 0.050% per cycle at 5.0 C) even at high sulfur mass loading of 3.6 mg cm^-2 . More crucially, CNT/MoS₂ -Co tube-in-tube nanostructures present a superior specific capacity of 650 mAh g^-1 in a Li-S pouch cell at 0.2 C (4.0 mg cm^-2 ).

Sulfur-Rich Polymers Based Cathode with Epoxy/Ally Dual-Sulfur-Fixing Mechanism for High Stability Lithium-Sulfur Battery

Lithium-sulfur (Li-S) batteries have attracted a great deal of attention for the next-generation energy storage devices due to their inherently high theoretical energy density, high natural abundance, and low cost. However, the dissolution of polysulfides in electrolytes and their undesirable shuttle behavior lead to poor cycling performance, which obstructs practical application. Herein, we report a dual-sulfur-fixing mechanism of epoxy/allyl compound/sulfur system to prepare poly(sulfur-random-4-vinyl-1,2-epoxycyclohexane) (SVE) copolymers as powerful cathode materials. Benefiting from the stable C-S bond and a uniform distribution of ultrafine Li₂S/S₈ in the SVE-based polymer matrix, the SVE electrodes exerted an embedding effect to reduce polysulfides migration. The thiosulfate/polythionate protective layer derived from the terminal hydroxyl group of SVE also ensured the cycle stability of SVE electrodes during cycling. As a result, optimized SVE electrodes deliver a high reversible specific capacity of 1248 mA h g^-1 at rates of 0.1 C, together with a stable cycling performance of no capacity decay per cycle over more than 400 cycles. This work provides an effective strategy for the practical application of organosulfur polymers Li-S batteries and inspires the exploration of the reaction mechanism of epoxy/allyl compound/sulfur system.

Properties of S-Functionalized Nitrogen-Based MXene (Ti2NS2) as a Hosting Material for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have received extensive attention due to their high theoretical specific capacity and theoretical energy density. However, their commercialization is hindered by the shuttle effect caused by the dissolution of lithium polysulfide. To solve this problem, a method is proposed to improve the performance of Li-S batteries using Ti₂N(Ti₂NS₂) with S-functional groups as the sulfur cathode host material. The calculation results show that due to the mutual attraction between Li and S atoms, Ti₂NS₂ has the moderate adsorption energies for Li₂S_x species, which is more advantageous than Ti₂NO₂ and can effectively inhibit the shuttle effect. Therefore, Ti₂NS₂ is a potential cathode host material, which is helpful to improve the performance of Li-S batteries. This work provides a reference for the design of high-performance sulfur cathode materials.

Three-Dimensional Engineering of Sulfur/MnO2 Composites for High-Rate Lithium-Sulfur Batteries

Herein, a three-dimensional interconnected sulfur (3DIS) system is used to construct a cathode of the lithium-sulfur battery. Compared with the traditional methods of encapsulating sulfur, the 3DIS system serves as a framework to grow MnO₂, which ensures a high sulfur content of 91.5 wt % (the ratio of sulfur/host was 10.8) and a uniform distribution of sulfur. Due to the synergistic effect of the 3D interconnected architecture and the uniform coating layer of polar MnO₂, 3DIS@MnO₂ (3DISMO) delivers a capacity of 891 mA h g^-1 after 900 cycles at 1 C. Even at a rate of 10 C, a capacity decay rate of 0.061% per cycle is achieved.