Dissolution Of Lithium Polysulfides Research Articles

Construction of an Ohmic Contact Cathode by Two Metal Sulfides for efficient Capture and Catalysis of Polysulfide.

The slow reaction kinetics and severe shuttle effect of lithium polysulfide make Li-S battery electrochemical performance difficult to meet the demands of large electronic devices such as electric vehicles. Based on this, an electrocatalyst constructed by metal phase material (MoS2) and semiconductor phase material (SnS2) with ohmic contact is designed for inhibiting the dissolution of lithium polysulfide with improving the reaction kinetics. According to the density-functional theory calculations, it is found that the heterostructured samples with ohmic contacts can effectively reduce the reaction-free energy of lithium polysulfide to accelerate the sulfur redox reaction, in addition to the excellent electron conduction to reduce the overall activation energy. The metallic sulfide can add more sulfophilic sites to promote the capture of polysulfide. Thanks to the ohmic contact design, the carbon nanotube-MoS2-SnS2 achieved a specific capacity of 1437.2 mAhg-1 at 0.1 C current density and 805.5 mAhg-1 after 500 cycles at 1 C current density and is also tested as a pouch cell, which proves to be valuable for practical applications. This work provides a new idea for designing an advanced and efficient polysulfide catalyst based on ohmic contact.

Recent advances in carbon-based sulfur host materials for lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have been brought into focus as the development direction of the next-generation power battery system due to their high energy density, eco-friendliness, and low cost, which has a broad application prospect in the field of energy storage. However, some problems are still unresolved in the sulfur cathode, e.g., poor electric conductivity, serious volume expansion of sulfur, shuttle effect caused by easy dissolution of lithium polysulfides in the electrolyte, and slow redox reaction kinetics of sulfur species. These issues lead to poor cycle stability and rate performance, making it hard to meet the requirement for LSBs in practical applications. Since the inherent nature of sulfur is the root cause of the above problems, reasonable design of functional sulfur hosts will be an effective way to break through the current bottlenecks of LSBs. The review covers the latest research progress on carbon-based sulfur host materials of LSBs, including structural design and functional optimization strategies, aiming to prepare multifunctional sulfur host materials by integrating physical confinement, chemical adsorption, and catalytic effect towards lithium polysulfides. The obstacles and future prospects of carbon-based sulfur hosts have also been brought forward, which provides in-depth guidance for practical application of LSBs.

Modulating Ionic Conduction and Accelerating Sulfur Conversion Kinetics through Oxygen Vacancy Engineering for High‐Performance Solid‐State Lithium‐Sulfur Batteries

AbstractPoly(ethylene oxide) (PEO)‐based solid‐state lithium‐sulfur batteries (SSLSBs) have garnered considerable attention as potential energy storage solutions owing to their exceptional specific energy, ease of processing, and economic viability. Nevertheless, the inherently low Li+ conductivity of the PEO electrolyte and the inevitable dissolution of lithium polysulfides (LiPSs) within the sulfur cathode hinder the solid‐state sulfur conversion kinetics and lead to significant loss of active materials, thus posing challenges for practical applications. Herein, these concerns are addressed by incorporating oxygen vacancy enriched‐Nb22W20O102‐x (NWOx) nanorods as cathode additives in high‐performance PEO‐based SSLSBs. The uniformly dispersed NWOx nanorods effectively modify the coordination environment of Li ions by increasing the concentration of free Li ions in the PEO catholyte and alleviating the shuttle effect of dissolved LiPSs. Consequently, the developed SSLSB demonstrates excellent cyclic stability and rate capability. Specifically, it achieves a high discharge capacity of 1208.6 mAh g−1 during the initial cycle and maintains 927.8 mAh g−1 after 200 cycles at 0.1 C. Moreover, such a configuration can accommodate a high loading of active materials with stable capacity retention. Overall, this study presents an effective approach for developing solid‐state sulfur cathodes in PEO‐based SSLSBs.

N doped carbon supported cobalt/tungsten nitride Mott−Schottky heterojunction as an efficient electrocatalyst to enhance adsorption and conversion of lithium polysulfides for high-performance lithium–sulfur batteries

Lithium–sulfur batteries (LSBs) suffer from the dissolution of lithium polysulfides (LiPSs) which leading to capacity degradation and poor cycling stability. Hence, weʼve developed the Co/W3N4@NC Mott–Schottky heterostructures with built in electric field (BIF) are prepared as catalyst model to generate a built-in electric field to enhance the electrocatalytic effect on sulfur electrochemistry. Theoretical and experimental results have jointly demonstrated that the redistribution of charge and the presence of a built-in electric field at the Co/W3N4@NC heterointerface can promote the redox reaction within lithium sulfur battery during the discharge and charge processes, respectively. Experimental tests have confirmed its outstanding reversibility, achieving a capacity of 793.2 mAh·g−1 over 500 cycles at 1 C. It also shows excellent cycling performance with only 0.05 % attenuation per cycle over 800 cycles at 2 C for LSBs. Furthermore, even with a high sulfur loading of 5.5 mg·cm−2, the S@ Co/W3N4@NC cathode maintains favorable sulfur-related electrochemistry and delivers a high areal capacity of 3.61 mAh·cm−2 as well as maintaining considerable stability. This synthetic Mott–Schottky heterostructure not only amplifies the electrocatalytic effect in LSBs, but also advances the design of catalysts for advanced high-energy-density batteries.

WITHDRAWN: Progress in the advancement of medium- and high-entropy catalysts for high performance lithium-sulfur batteries

Lithium-sulfur batteries have attracted significant attention as a potential new energy storage system, thanks to their high theoretical energy density, cost-effectiveness, and environmentally friendly nature. However, the practical implementation of lithium-sulfur batteries faces inherent challenges, such as rapid capacity decay and poor cycling stability due to the dissolution of lithium polysulfides during cycling. Recent advances have made considerable progress in addressing these challenges by incorporating catalysts to facilitate redox reactions and control the shuttle effect. A notable trend in this regard is the emergence of medium- and high-entropy materials as an innovative approach to designing advanced catalysts, positioning them as promising candidates for multimetallic-based catalysts in lithium-sulfur batteries. This review examines the progress and application of medium- and high-entropy materials, including alloys, oxides, sulfides, phosphides, and prussian blue analogues, as catalysts for lithium-sulfur batteries. It explores the effects of various factors and their synergistic impacts on electrochemical performance, along with discussions on strategies of optimizing catalyst design for the improved sulfur utilization and cycling stability. Additionally, the review discusses the challenges, potential future directions, and prospects for designing medium- and high-entropy materials-based catalysts, envisioning the development of high-performance lithium-sulfur batteries for future energy storage applications.

Porous Carbon Interlayer Derived from Traditional Korean Paper for Li-S Batteries.

A carbonized interlayer effectively helps to improve the electrochemical performance of lithium-sulfur (Li-S) batteries. In this study, a simple and inexpensive carbon intermediate layer was fabricated using a traditional Korean paper called "hanji". This carbon interlayer has a fibrous porous structure, with a specific surface area of 91.82 m2 g-1 and a BJH adsorption average pore diameter of 26.63 nm. The prepared carbon interlayer was utilized as an intermediary layer in Li-S batteries to decrease the charge-transfer resistance and capture dissolved lithium polysulfides. The porous fiber-shaped carbon interlayer suppressed the migration of polysulfides produced during the electrochemical process. The carbon interlayer facilitates the adsorption of soluble lithium polysulfides, allowing for their re-utilization in subsequent cycles. Additionally, the carbon interlayer significantly reduces the polarization of the cell. This simple strategy results in a significant improvement in cycle performance. Consequently, the discharge capacity at 0.5 C after 150 cycles was confirmed to have improved by more than twofold, reaching 230 mAh g-1 for cells without the interlayer and 583 mAh g-1 for cells with the interlayer. This study demonstrates a simple method for improving the capacity of Li-S batteries by integrating a functional carbon interlayer.

Accelerated Li2S conversion in sparingly-solvating electrolytes enabled with dipole-dipole interaction for wide-temperature Li-S batteries

Utilizing sparingly-solvating electrolytes (SSEs), which suppress the dissolution of lithium polysulfides (Li2S4−8, LPSs), could reduce electrolyte consumption and thus retrieve the energy density competitiveness of lithium-sulfur batteries (LSBs). However, SSEs-based LSBs suffer from sluggish kinetics and rapid capacity degradation due to the accumulation of Li2S in the cathode. The catalytic approach, which is widely used to promote the sulfur conversion in ether-based LSBs, is rarely explored in SSEs-based LSBs due to the lack of a catalyst workable in the absence of dissolved LPSs. Here, by embedding CuS nanoparticles, which have high dipole-dipole interaction with Li2S, as polar sites into the carbon matrix of the sulfur cathode, we homogenize the Li2S deposition and accelerate the conversion kinetics. As a result, the cell with S/KB@CuS cathode realized a remarkable initial discharge capacity of 1469.5 mAh g−1 (87.7% of the theoretical value) with a reduced polarization potential (0.526V). Even at a low temperature of −15°C, the cell with S/KB@CuS cathode still delivered a capacity-retention of 799.0 mAh g−1 after 100 cycles. More importantly, the universality of the as-proposed dipole-dipole-interaction strategy is demonstrated with many other SSEs and polar additives.

Novel pentagonal carbon-based materials as multifunctional electrodes in lithium-sulfur batteries, a theoretical study

The commercialization process of lithium-sulfur batteries (LISBs) is hindered by several problems, including low electroconductivity, the dissolution of lithium polysulfides (LiPSs) and sluggish charging-discharging kinetics. Recently, two-dimensional (2D) penta-furrow structures have emerged as a distinct family of 2D structures with low mass densities, which are predicted to accelerate redox kinetics and enable sulfur conversion. Here, several novel pentagonal carbon-based substrates, including penta-graphene (penta-G) and penta-B2C (C2N, C2P, C2Si, and N2C), were first investigated in LISBs based on density functional theory (DFT) calculations. It is found that the penta-G, penta-C2P and penta-C2Si have excellent anchoring ability and can greatly improve conductivity during the whole S8/LiPSs insertion, which can effectively suppress the shuttle effect. More importantly, penta-G, penta-C2P and penta-C2Si can reduce the free energy of sulfur reduction reactions to 0.63–0.68 eV and lower the energy barriers of electrochemical conversions to 0.82–1.57 eV (Li2S dissociation) and 0.05–0.14 eV (Li-ion diffusion), thereby enhancing catalytic conversion efficiency in the discharging/charging processes. In addition, penta-G showed a much smaller volume expansion (34 %) than the 80 % value for elemental sulfur and a considerable sulfur loading amount (53.78 wt%). Our findings demonstrate that metallic pentagonal carbon-based materials could be a potential LISBs cathode material with high performance.

Multifunctional flame‐retardant co‐based interlayer for improving lithium−sulphur batteries performance

AbstractLithium–sulphur batteries (LSBs) have elicited great interest due to their remarkably high energy density. However, challenges such as the dissolution of lithium polysulfides (LiPSs), low reaction kinetics, and safety concerns associated with LSBs impede large‐scale application. In this work, a multifunctional Co‐HP‐GC interlayer was prepared using evaporation, refluxing, and impregnation procedures. Notably, after ignition, this interlayer retained its structural integrity, indicative of excellent flame retardancy and thermal stability. Furthermore, the addition of cobalt atoms augmented the cyclic performance of the batteries by expediting the redox kinetics of LiPSs transformation and electron transfer at the interface. The electrodeposition capacity of Li2S cathode with Co‐HP‐GC interlayer reached up to 199.2 mAh g−1, higher than the 155.7 mAh g−1 achieved with a graphene oxide/carbonized fibre paper (G‐CCP) interlayer. This, in turn, curtails the shuttle effect whilst improving sulphur utilization. LSBs possessing a Co‐HP‐GC interlayer demonstrated superior cyclic and rate performance. At 0.5 C, the initial specific capacity of the battery fitted with a Co‐HP‐GC interlayer was 915.8 mAh g−1, with the rate of attenuation reduced by approximately half. The strategy integrates the multifunctional flame‐retardant interlayer into various battery systems, demonstrating wide‐ranging potential applicability within the realm of LSBs.

Polyaniline-coated S/Super-P composites as cathode materials for high performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are promising alternatives to conventional lithium-ion batteries owing to their high theoretical capacity and eco-friendliness. However, their commercialization has been limited due to poor cathode conductivity and polysulfide dissolution. In this study, we synthesized a S/Super-P @ Polyaniline (S/Super-P @ PANi) composite via a straightforward high-energy ball milling (HEBM) and in-situ oxidative polymerization process. The refined sulfur and Super-P particles were encapsulated by a conductive PANi coating shell, which not only facilitated electron transfer but also inhibited the dissolution of lithium polysulfides through physical confinement and chemical adsorption. The S/Super-P @ PANi electrode showed a high initial capacity of 1185.3 mAh·g−1 at 0.1 C. Under a sulfur loading of 3.5 mg·cm−2, the electrode delivered an areal capacity of 2.8 mAh cm−2 and maintained 1.8 mAh cm−2 after 400 cycles, with a capacity decay rate of 0.08% at 0.5 C. This rational and scalable synthesis method has great potential for use in high-performance Li-S batteries.

Dual‐Functional Electrodes for High‐performance Lithium–Sulfur Cells

AbstractAt present, the commercial application of Li─S cells is impeded by many challenging issues, especially the shuttle effect of dissolved lithium polysulfides (LiPSs) and severe dendritic growth. Applying a sole kind of host material owing dual functions, including inhibiting LiPSs dissolution/shuttling andguiding Li plating/stripping, has recently become a prospective solution. Currently, a systematic review of advanced dual‐functional electrodes aiming at the cathode and anode side simultaneously is scarce. Herein, this review points at such dual‐functional electrodes and summarizes the recent progress from the select host materials to designs. First, the rough challenges and ordinary solutions on the single side of the Li─S cell are illustrated. Then, the potentials of different materials to dual‐functional electrodes are discussed, such as carbon‐based materials, single‐atom catalysts (SACs), transition metal compounds (TMCs), heterostructure hybrids (HHs), and polymers. After that, the design methods for dual‐functional electrodes with high performance are explored and summarized by slurry‐coating and self‐supporting (electrospinning (ES), 3D printing (3DP), solvent method (SM), chemistry vapor deposition (CVD) and vacuum filtration (VF)). Besides, the possibility of applying the dual‐functional electrodes to other metal‐sulfur cells is discussed. Finally, design principles and prospects in dual‐functional electrodes for future research and commercial application are proposed as guidelines.

Emerging medium- and high-entropy materials as catalysts for lithium-sulfur batteries

Lithium–sulfur batteries (LSBs) have attracted significant attention as a promising next-generation energy storage system due to their high theoretical energy density, low cost, and environmental friendliness. However, the practical implementation of LSBs faces several fundamental challenges, including the rapid capacity decay and poor cycling stability resulting from the dissolution of lithium polysulfides (LiPSs) during cycling, as well as security issues arising from the flammability of ether-based liquid electrolytes. In recent years, significant progress has been achieved in overcoming those drawbacks through the use of catalysts which play a crucial role by promoting the redox reactions and suppressing the shuttle effect. Among the main trends, the concept of medium and high entropy materials (MEMs and HEMs) has emerged as a novel approach for designing advanced functional catalysts, making them suitable multimetallic-based candidates for LSBs. This review focuses on the development and utilization of MEMs and HEMs (alloys, metal oxides, Prussian blue analogues, metal sulfides, metal phosphides, and MXenes) as both sulfur hosts and catalysts for LSBs. The roles of various elements and their synergistic effects on the electrochemical performance are discussed, along with the strategies to optimize the catalyst design for enhanced sulfur utilization and cycling stability. Furthermore, the challenges, future perspectives, and directions in designing MEMs and HEMs-based catalysts for developing high-performance and reliable LSBs are addressed, paving the way for future energy storage applications.

Degradation Mechanisms of a Li—S Cell using Commercial Activated Carbon

<p>In lithium–sulfur (Li–S) batteries, encapsulation of sulfur in activated carbon (AC) materials is a promising strategy for preventing the dissolution of lithium polysulfide into electrolytes and enhancing cycle life, because instead of solid–liquid–solid reactions, quasi-solid-state (QSS) reactions occur in the AC micropores. While a high weight fraction of sulfur in S/AC composites is essential for achieving a high energy density of Li–S cells, the deterioration mechanisms under such conditions are still unclear. In this study, we report the deterioration mechanisms during charge–discharge cycling when the discharge products overflow from the AC. Analysis using scanning electron microscopy and energy-dispersive X-ray spectrometry confirms that the sulfur in the S/AC composites migrates outside the AC as cycling progresses, and it is barely present in the AC after 20 cycles, which corresponds to the capacity decay of the cell. Impedance analysis clearly shows that the electrical resistance of the S/AC composite and the charge-transfer resistance of QSS reactions significantly increase as a result of sulfur migration. On the other hand, the charge–discharge cycling performance under limited-capacity conditions, where the discharge products are encapsulated inside the AC, is extremely stable. These results reveal the degradation mechanism of a Li–S cell with micro-porous carbon and provide crucial insights into the design of a S/AC composite cathode and its operating conditions needed to achieve stable cycling performance.</p>

Visualizing interfacial collective reaction behaviour of Li-S batteries.

Benefiting from high energy density (2,600 Wh kg-1) and low cost, lithium-sulfur (Li-S) batteries are considered promising candidates for advanced energy-storage systems1-4. Despite tremendous efforts in suppressing the long-standing shuttle effect of lithium polysulfides5-7, understanding of the interfacial reactions of lithium polysulfides at the nanoscale remains elusive. This is mainly because of the limitations of in situ characterization tools in tracing theliquid-solid conversion of unstable lithium polysulfides at high temporal-spatial resolution8-10. There is an urgent need to understand the coupled phenomena inside Li-S batteries, specifically, the dynamic distribution, aggregation, deposition and dissolution of lithium polysulfides. Here, by using in situ liquid-cell electrochemical transmission electron microscopy, we directly visualized the transformation of lithium polysulfides over electrode surfaces at the atomic scale. Notably, an unexpected gathering-induced collective charge transfer of lithium polysulfides was captured onthe nanocluster active-centre-immobilized surface. It further induced an instantaneous deposition of nonequilibrium Li2S nanocrystals from the dense liquid phase of lithium polysulfides. Without mediation of active centres, the reactions followed a classical single-molecule pathway, lithium polysulfides transforming into Li2S2 and Li2S step by step. Molecular dynamics simulations indicated that the long-range electrostatic interaction between active centres and lithium polysulfides promoted the formation of adense phase consisting of Li+ and Sn2- (2 < n ≤ 6), and the collective charge transfer in thedense phase was further verified by ab initio molecular dynamics simulations. The collective interfacial reaction pathway unveils a new transformation mechanism and deepens the fundamental understanding of Li-S batteries.

Modification of separators with neodymium oxide/graphene composite to enhance lithium-sulfur battery performance

Lithium-sulfur (Li–S) batteries have generated significant attention due to their high theoretical specific capacity and energy density among a host of energy storage power devices. Nevertheless, the lithium polysulfide dissolution shuttle that occurs within Li–S batteries will lead to capacity deterioration and inadequate cycling stability. In the paper, we proposed a measure to deal with the above problems by modifying the separator with Nd2O3/graphene composite in Li–S batteries. Graphene's special chemical properties and structural qualities make it an excellent choice for Li–S batteries. Meanwhile, Nd2O3 has a strong binding affinity with lithium polysulfide due to its low electronegativity, which exhibits Lewis's acidity and forms strong interactions with lithium polysulfide, which is strongly Lewis basic. By utilizing these advantageous properties, Li–S batteries assembling Nd2O3-decorated reduced graphite oxide modified polypropylene separators (Nd2O3/RGO/PP) demonstrate outstanding electrochemical performance, including a mere 0.0525% capacity attenuation rate under 2 C during 1000 cycles and with exceptional rate performance of 614 mAh/g even at 3 C. This study presents valuable knowledge for effectively modifying separators using rare earth oxides to incorporate graphene, ultimately promoting the practical application of Li–S batteries.

Electrochemical Characteristics of Novel Fluorinated Ether Solvent for Lithium-Sulfur Batteries

Introduction In recent years, the development of electric airplanes, large drones, and other equipment has created a need for batteries with high energy density and high power density. Lithium-sulfur batteries have been investigated as such batteries. Electrolyte solutions applying carbonate solvents and ether solvents have been developed as electrolyte for lithium-sulfur batteries1. An electrolyte with ether-based solvents is lighter than that with carbonate-based solvents, so the former is expected to be an electrolyte for lithium sulfur batteries with high energy density. However, lithium-sulfur batteries based on ether solvents have difficulty in reversible charge-discharge reactions due to the dissolution of lithium polysulfide (Li2S x ) that occurs during the charge-discharge process2. In this study, we investigate the electrochemical characteristics of electrolytes to apply a new fluorinated ether (C14) which is resistant to elution of Li2S x . Experimental Sulfur-carbon composite (S-C) was prepared by compositing activated carbon (C-novel, Toyo Tanso) and sulfur in a ratio of 35:65 by weight using a thermal impregnation method. S-C was used as the active material and mixed with acetylene black (AB, DENKA), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) to prepare a slurry. The cathode was obtained by coating the obtained slurry on an aluminum foil by a doctor blade method. An electrochemical cell was assembled with the obtained cathode as the working electrode, Li foil as the counter electrode, and LiTFSI dissolved in a mixture of dioxolane (DOL), dimethoxyethane (DME), and C14 at a concentration of 1 mol L-1 as the electrolyte. In order to clarify the electrochemical characteristics of the lithium sulfur battery with these electrolytes, constant current charge-discharge tests were conducted using the electrochemical cell described above. To clarify the coordination state of the solvent to lithium ions and lithium polysulfide in the electrolyte, IR spectra were measured for these electrolytes. Results and Discussion In the IR spectra for the solutions of Li2S x dissolved in DME, the intensity of the peak attributed to the asymmetric stretching of the C-O-C bond, which can be seen at around 1090 cm-1, increases with increasing concentration of Li2S x . The change in peak intensity appears to be due to the coordination of the structure of the diether in DME to the Li+ of Li2S x . On the other hand, in the IR spectra of Li2S x immersed in C14, the intensity of the corresponding peak was found to be similar to that of C14 only, regardless of the concentration of Li2S x . The results indicate that C14 is hard to coordinate to Li2Sx. This may be due to the fact that the functional group with fluorine in the structure of C14 is an electron-withdrawing group, which delocalizes the electrons located around O in the diether and weakens the coordinative force to Li2Sx. As a result of the constant-current charge-discharge test, it was confirmed that the voltage stagnated at about 2.3 V in the charge curves of the cell to which 1M LiTFSI / DOL : DME = 1 : 1 by vol.% was applied. The stagnation of the voltage is considered to be due to the shuttle reaction caused by the coordination of DME to lithium polysulfide and its dissolution into the electrolyte during the charge-discharge process. On the other hand, in the charge-discharge curves of the cell with 1M LiTFSI / C14, the stagnation of voltage that was observed in the cell with 1M LiTFSI / DME could not be confirmed, and it was turned out that the irreversible capacity was small. This should be due to the inability of C14 to coordinate with Li2S x . Acknowledgement A part of this research was conducted under a subcontract (JPNP15005) from the New Energy and Industrial Technology Development Organization (NEDO), a national research and development corporation. Reference 1) L. Gordin et al, ACS Appl. Mater. Interfaces, 6 (2014) 8006−80102) B. Zhang et al, ACS Energy Lett., 6 (2021) 537−546

Improvement of Lithium-Sulfur Battery Performance by Porous Carbon Selection and LiFSI/DME Electrolyte Optimization.

High-concentration lithium bis(fluorosulfonyl)imide/1,2-dimethoxyethane (LiFSI/DME) electrolytes are promising candidates for highly reversible lithium-metal anodes. However, the performance of lithium-sulfur (Li-S) batteries with a high concentration of LiFSI/DME declines because LiFSI reacts irreversibly with lithium polysulfide, which is formed during the charge-discharge process of Li-S batteries. Hence, to apply high-concentration LiFSI/DME to Li-S batteries, we investigated carbon with an appropriate pore size for use in a sulfur composite cathode and optimized the composition of high-concentration LiFSI/DME. The results showed that the combination of carbon with mesopores of 2-3 nm diameter and 3 M LiFSI in DME/1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropylether (HFE) (1:1 by vol.) provided a high-rate capability (943 mA h g-1 at a rate of 2 C). Moreover, the ratio of the 50th discharge capacity to the 2nd discharge capacity (capacity retention) improved from 50.0 to 61.6% with HFE dilution of high-concentration LiFSI/DME. The improved performance was achieved by suppressing the dissolution of lithium polysulfide, decreasing the viscosity of the electrolyte, and forming a thin solid electrolyte interface on the lithium-metal anode due to HFE dilution.

G-C3N4/MoO3 composite with optimized crystal face: A synergistic adsorption-catalysis for boosting cathode performance of lithium-sulfur batteries

The commercial application of lithium-sulfur batteries (LSBs) has been seriously hindered by the shuttle effect of lithium polysulfides (LiPSs) and their slow redox kinetics. In this work, g-C3N4/MoO3 composed of graphite carbon nitride (g-C3N4) nanoflake and MoO3 nanosheet is designed and applied to modify the separator. The polar MoO3 can form chemical bond with LiPSs, effectively slowing down the dissolution of LiPSs. And based on the principle of “Goldilocks”, LiPSs will be oxidized by MoO3 to thiosulfate, which will promote the rapid conversion from long-chain LiPSs to Li2S. Moreover, g-C3N4 can promote the electron transportation, and its high specific surface area can facilitate the deposition and decomposition of Li2S. What’s more, the g-C3N4 promotes the preferential orientation on the MoO3(021) and MoO3(040) crystal planes, which optimizes the adsorption capacity of g-C3N4/MoO3 for LiPSs. As a result, the LSBs with g-C3N4/MoO3 modified separator with a synergistic adsorption-catalysis, can achieve an initial capacity of 542 mAh g−1 at 4C with capacity decay rate of 0.0053% per cycle for 700 cycles. This work achieves the synergy of adsorption and catalysis of LiPSs through the combination of two materials, providing a material design strategy for advanced LSBs.

Spherical Sulfur-Infiltrated Carbon Cathode with a Tunable Poly(3,4-ethylenedioxythiophene) Layer for Lithium-Sulfur Batteries.

Li-S batteries have received significant attention owing to their high energy density, nontoxicity, low cost, and eco-friendliness. However, the dissolution of lithium polysulfide during the charge/discharge process and its extremely low electron conductivity hinder practical applications of Li-S batteries. Herein, we report a sulfur-infiltrated carbon cathode material with a spherical morphology and conductive polymer coating. The material was produced via a facile polymerization process that forms a robust nanostructured layer and physically prevents the dissolution of lithium polysulfide. The thin double layer composed of carbon and poly(3,4-ethylenedioxythiophene) provides sufficient space for sulfur storage and effectively prevents the elution of polysulfide during continuous cycling, thereby playing an essential role in increasing the sulfur utilization rate and significantly improving the electrochemical performance of the battery. Sulfur-infiltrated hollow carbon spheres with a conductive polymer layer demonstrate a stable cycle life and reduced internal resistance. The as-fabricated battery demonstrated an excellent capacity of 970 mA h g-1 at 0.5 C and a stable cycle performance, exhibiting ∼78% of the initial discharge capacity after 50 cycles. This study provides a promising approach to significantly improve the electrochemical performance of Li-S batteries and render them as valuable and safe energy devices for large-scale energy storage systems.

Cobalt Vanadate (Co3V2O8) Hollow Microspheres as a Polysulfide Adsorption and Conversion Catalyst for Li–S Batteries

A lithium–sulfur battery (Li–S) is considered as one of the most suitable emerging energy storage technologies for electric vehicles (EVs) due to its higher specific capacity, energy density, and low cost. However, the dissolution of lithium polysulfides (LiPS) in an electrolyte causes a huge shuttle effect, which results in poor cycle life and rate performance. Herein, Co3V2O8 (CVO) hollow microspheres have been prepared by the solvothermal method and used as catalyst additives to the sulfur electrode (cathode host). It was found that CVO acts as a bifunctional additive, the vanadium and oxygen sites immobilize the LiPS through V–S and Li–O interactions, while the cobalt site facilitates the rapid conversion of long-chain LiPS into short ones (Li2S2/Li2S). Furthermore, the hollow microspheres act as a sulfur reservoir and can confine (encapsulate) more LiPS during the electrochemical conversion process, thus inhibiting the shuttle effect. In this work, the chemical adsorption and polysulfide conversion ability of CVO is corroborated by XPS and cyclic voltammetry studies, respectively. Even at a higher sulfur loading of 5.4 mg cm–2, CVO containing the Li–S cell (denoted as S@CVO/CNT Vs Li) demonstrates an initial discharge capacity of 694 mAh g–1 at 0.5 C, and after 200 cycles, the observed capacity is 566 mAh g–1, which amounts to 81% capacity retention. Similarly, the cell delivers an excellent rate capability of up to 5 C rate. At the 1 C rate, the cell shows an initial discharge capacity of 904 mAh g–1 (S-loading of 3 mg cm–2) and 692 mAh g–1 after 300 cycles with 77% capacity retention.