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Insights into the improved electrochemical performance of lithium–sulfur battery with free-standing SiO2/C composite nanofiber mat interlayer

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A free-standing SiO2/C composite nanofiber mat (FS-SiO2/C-CNFM), prepared by electrospinning with heat treatments, is used as a multifunctional interlayer on the cathode side to suppress the polysulfide shuttle effect in lithium–sulfur batteries. The polysulfide adsorption and conversion capabilities of the interlayer are evaluated by a static polysulfide adsorption test and an electrochemical conversion test in an FS-SiO2/C-CNFM symmetric cell. The effects of the FS-SiO2/C-CNFM on the electrochemical properties of the lithium–sulfur batteries are studied by cyclic voltammetry, galvanostatic charge–discharge cycle tests, and electrochemical impedance spectroscopy. The FS-SiO2/C-CNFM interlayer significantly improves the specific capacity, long-cycling stability, and self- discharge behavior of the lithium–sulfur batteries. The cell with the FS-SiO2/C-CNFM interlayer has an initial discharge capacity of 1304 mA h g−1 and retains 934 mA h g−1 over 50 cycles at 0.1 C, corresponding to a capacity retention of 72% with 100% Coulombic efficiency. The improved properties are attributed to the suppression of the shuttle effect and the high reutilization of the trapped polysulfides. The adsorption/conversion mechanisms of the polysulfides of the FS-SiO2/C-CNFM interlayer are further elucidated from the results of ex situ X-ray photoelectron spectroscopy (XPS) and field-emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS) analysis.
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A study was conducted to demonstrate suppressing of self-discharge and shuttle effect of lithium–sulfur batteries with V2O5-decorated carbon nanofiber interlayer. Coin cells, composed of bare sulfur cathodes, separators, and lithium plates, were assembled by embedding the additional CNF or V2O5-decorated carbon nanofiber (VCNF) interlayers between cathodes and separators to determine the effect of V2O5-decorated interlayer on the electrochemical performances of Li–S batteries. The VCNF/Li battery was also prepared just by capitalizing VCNFs as cathode to ensure the contribution of V2O5 component to the whole capacity of S/VCNF/Li.
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The limitations in the cathode capacity compared with that of the anode have been an impediment to advance the lithium-ion battery technology. The lithium-sulphur system is appealing in this regard, as sulphur exhibits an order of magnitude higher capacity than the currently used cathodes. However, low active material utilization and poor cycle life hinder the practicality of lithium-sulphur batteries. Here we report a simple adjustment to the traditional lithium-sulphur battery configuration to achieve high capacity with a long cycle life and rapid charge rate. With a bifunctional microporous carbon paper between the cathode and separator, we observe a significant improvement not only in the active material utilization but also in capacity retention, without involving complex synthesis or surface modification. The insertion of a microporous carbon interlayer decreases the internal charge transfer resistance and localizes the soluble polysulphide species, facilitating a commercially feasible means of fabricating the lithium-sulphur batteries.
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A conductive multiwalled carbon nanotube (MWCNT) interlayer acting as a pseudo-upper current collector not only reduces the charge transfer resistance of sulfur cathodes significantly, but also localizes and retains the dissolved active material during cycling.
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Lithium/sulfur battery (LSB) is considered as one of the most promising battery systems due to its high energy density of 2600 Wh kg⁻¹. Nevertheless, the LSB suffers from some inherent problems that impede its practical application. To circumvent these problems, we grow carbon-coated ferroferric oxide (Fe3O4) nanoparticles on graphene (Fe3O4@C-G) as an effective sulfur host for LSB via a facile hydrothermal method followed by calcination. Highly conductive graphene is utilized to homogeneously deposit the carbon-coated Fe3O4 nanoparticles (Fe3O4@C), which enable rapid and steady long-distance electron transport. Moreover, the carbon coated particles of Fe3O4@C exhibit a developed micro-mesoporous structure, which not only provide space for sulfur loading to prepare a composite Sulfur/carbon-coated Fe3O4 nanoparticles on graphene (S/Fe3O4@C-G) cathode, but also provide channels for the interaction between Fe3O4 and lithium polysulfides. Furthermore, a strong chemical affinity of Fe3O4 nanoparticles coated by micro-mesoporous carbon layers towards polysulfides can be strengthened through the polar-polar interaction. Owning these advantages, the S/Fe3O4@C-G composite cathode deliver a high initial capacity of 1425 mAh g⁻¹ at 0.2 C and maintain a capacity of 1102 mAh g⁻¹ after 100 cycles.
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Nanostructured functional interlayers and separators have potential applications in high-performance lithium-sulfur (Li-S) batteries, due to their ability to suppress polysulfide (PS) shuttling. However, effective PS-trapping designs are usually accompanied by limited Li-ion diffusion, which becomes a key issue hindering practical application. Here, a nitrogen-functionalized 2D mesoporous silica nanoplate (FMSiNP) was used to construct a dense, lightweight (<0.2 mg cm-2) multi-functional interlayer using a simple casting approach, which effectively suppressed the PS shuttling, while facilitating Li+ diffusion. Able to synergistically combine the merits of strong PS trapping with fast Li+ diffusion and excellent electrolyte wettability, Li-S batteries with FMSiNP coated-interlayers show improved PS utilization and retention. These batteries additionally show a superior cycling stability capacity fading rate (0.038 % per cycle at 1.0 C over 1500 cycles), a high rate performance (discharge capacity of 574 mA h g-1 at 4.0 C), low self-discharge behaviour and a high areal capacity (2.48 mA g cm-2 over 100 cycles), when using a pure sulfur/carbon black (CB) mixture as a cathode. This rational design for multi-functional interlayers provides a facile and effective strategy to create high energy density Li-S batteries for practical applications.
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Lithium-sulfur (Li–S) batteries are attracting substantial attention because of their high energy densities and potential applications in portable electronics. However, an intrinsic property of Li–S systems, i.e., the solubility of lithium polysulfides (LiPS), hinders the commercialization of Li–S batteries. Herein, a new material, i.e., carbon nitride phosphorus (CNP), is designed and synthesized as a superior LiPS adsorbent to overcome the issues of Li–S batteries. Both the experimental results and the density functional theory (DFT) calculations confirm that CNP possesses the highest binding energy with LiPS at a P concentration of ~22% (CNP22). The DFT calculations explain the simultaneous existence of Li–N bonding and P–S coordination in the sulfur cathode when CNP22 interacts with LiPS. By introducing CNP22 into the Li–S systems, a sufficient charging capacity at a low cut-off voltage, i.e., 2.45 V, is effectively implemented, to minimize the side reactions, and therefore, to prolong the cycling life of Li–S systems. After 700 cycles, a Li–S cell with CNP22 gives a high discharge capacity of 850 mAh g−1 and a cycling stability with a decay rate of 0.041% cycle–1. The incorporation of CNP22 can achieve a high performance in Li–S batteries without concerns regarding the LiPS shuttling phenomenon.
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This study introduces an improved design of interlayer to achieve the balance between high Li+ diffusion and polysulfide inhibition in lithium-sulfur batteries. The design involves encapsulating mesoporous SiO2 nanosphere by few-layer MoS2 nanosheets via a facile one-step self-assembly to form a core-shell nanocomposite (SiO2@MoS2). SiO2@MoS2 layer overlaid on the sulfur cathode simultaneously intercepts polysulfides and ensures rapid Li+ diffusion. Few-layer MoS2 as a shell is capable of breaking up polysulfides by catalytic reaction, while mesoporous SiO2 as a core allows for physiochemical adsorption of such species; moreover, the densely packed hermetic SiO2@MoS2 nanocomposite layer provides an additional physical shield against polysulfides, realizing the full protection of the whole cathode. At the same time, the high Li+ density in the nanolayered MoS2 shell and the additional Li+ pathways created by mesoporous SiO2 core allow for fast Li+ diffusion. Thus, a pristine sulfur cathode battery with a SiO2@MoS2 interlayer exhibits an outstanding electrochemical performance with a negligible capacity decay of 0.028 % per cycle over 2500 cycles. The core-shell design suggested in this study could be extended to other nanomaterials for the optimization of Li-S battery interlayers.
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Lithium-sulfur (Li-S) batteries have attracted many attentions due to their high energy density and low-cost. However, the insulation and volume change of sulfur and high solubility of polysulfides lead to the fast decay of capacity and short cycle life. In order to solve these issues, we synthesized a novel multifunctional TiO 2 @C composite nanofibers (TiO 2 @C CNs) interlayer by electrospinning technique and subsequent heat treatment. It can significantly improve the specific capacity and long cycling stability of Li-S batteries, attributed to the effective restriction of “shuttle effect” and high reutilization of trapped active materials. Using TiO 2 @C CNs as a multifunctional interlayer, the BP2000/sulfur cathode with a high sulfur content (70 wt %) shows an initial capacity of 852 mAh g ⁻¹ at a high current rate of 4C and cycled over 2000 cycles with a fade rate of only 0.028% per cycle. The combination of metal oxides and carbon materials is facile and feasible way to archive high performance Li-S batteries.
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Lithium-sulfur batteries are well-known for their high theoretical specific capacity and high energy density. However, they face rapid capacity fading after the initial cycles due to the dissolution of polysulfides which further results in the shuttle effect. To address this issue and to protect the Li anode surface, silicon suboxide decorated stabilized polyacrylonitrile (sPAN-SiOx) fibermats are used as a freestanding interlayer on the cathode side. Polysulfides are easily captured at the cathode side by the help of complementary adsorption effect of oxygen-containing functional groups, SiOx and pyridinic-N structure of sPAN-SiOx resulting in better electrochemical cell performance. The adsorption effect of those functional groups and SiOx is confirmed by X-Ray Photoelectron Spectroscopy (XPS) analysis as obvious shifts in the binding energies and reductions of the peak intensities in the presence of polysulfides. The battery cell with sPAN-SiOx interlayer perform a discharge capacity of 646 mAh/g after 100 cycles of charge-discharge at C/5 current density which is a significant increase compared to the cells with stabilized polyacrylonitrile (sPAN) interlayer or the cells without interlayer.
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Lithium‐sulfur (Li‐S) battery based on sulfur cathodes is of great interest because of high capacity and abundant sulfur source. But the shuttling effect of polysulfides caused by charge‐discharge process results in low sulfur utilization and poor reversibility. Here, we demonstrate a good approach to improve the utility of sulfur and cycle life by synthesizing carbon nanofibers decorated with MoO2 nanoparticles (MoO2‐CNFs membrane), which plays a role of multiinterlayer inserting between the separator and the cathode for Li‐S battery. The S/MoO2‐CNFs/Li battery showed a discharge capacity of 6.93 mAh cm⁻² (1366 mAh g⁻¹) in the first cycle at a current density of 0.42 mA cm⁻² and 1006 mAh g⁻¹ over 150 cycles. Moreover, even at the highest current density (8.4 mA cm⁻²), the battery achieved 865 mAh g⁻¹. The stable electrochemical behaviors of the battery has achieved because of the mesoporous and interconnecting structure of MoO2‐CNFs, proving high effect for ion transfer and electron conductive. Furthermore, this MoO2‐CNFs interlayer could trap the polysulfides through strong polar surface interaction and increases the utilization of sulfur by confining the redox reaction to the cathode.
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Lithium-sulfur batteries were investigated as promising next-generation energy storage devices owing to their high capacity in comparison to conventional lithium-ion batteries. Nevertheless, the serious shuttle effect and sluggish redox kinetics originated from dissolution of polysulfides and insulating property of sulfur and lithium sulfide, restricted their practical applications. To overcome these stubborn problems, a robust and environment-friendly biomass carbon fiber interlayer anchored with uniformly-distributed SiO2 nanoparticles was demonstrated. Benefiting from the excellent conductivity of carbon fiber, together with the stable chemical adsorption of SiO2 for soluble polysulfides, this low-cost and lightweight interlayer could not only remarkably enhance sulfur utilization, but also efficiently capture the polysulfides by chemical entrapment strategies. With this biomass carbon [email protected]2 interlayer, the batteries delivered a high reversible capacity of 1352.8 mAh g⁻¹ at 0.1 C and enhanced capacity of 618.4 mAh g⁻¹ after 500 cycles at 1.0 C. Even up to 4.2 mg cm⁻² sulfur loading, high cycling stability was also achieved by this interlayer. We believe this robust and low-cost interlayer has a great potential for practical applications of Li–S batteries.
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One of the major challenges for practical lithium-sulfur batteries (LSBs) is to suppress the shuttle effect of the lithium polysulfides (LiPSs). Employing the polymer electrolyte instead of liquid electrolyte is an effective solution to this problem. Herein, a novel poly (propylene carbonate)-based composite gel polymer electrolyte (G-PPC-CPE) with 7.3 wt% plasticizer has been developed for LSBs. The embedded SiO2 nanoparticles act as multifunctional fillers which may improve the interfacial stability, enhance the ionic conductivity and lithium ions transference number, as well as cooperate with PPC polymer matrix to suppress the shuttle effect of LiPSs. The LSBs with G-PPC-CPE deliver a high reversible capacity of 700.5 mAh•g-1 composite (1668 mAh•g-1 sulfur) over 100 cycles, a long cycle life with 85 % capacity retention after 500 cycles and a high coulombic efficiency (~100 %). Moreover, an inhibited self-discharge behavior and a decent rate performance are obtained simultaneously. XPS analysis was used to further elucidate the interaction mechanism of nano-SiO2 and the blocking effect of G-PPC-CPE for LiPSs is more intuitively confirmed by the visual Li2S6 diffusion experiment. In brief, G-PPC-CPE guarantees good prospects for the development of the quasi-solid-state LSBs with high performance at ambient temperature.
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Favorable characteristics, such as high energy density, cost efficiency, and environmental benignity, render lithium–sulfur (Li–S) batteries a promising candidate to meet the increasing demand for efficient and economic energy-storage systems. Many efforts have been devoted to and much progress has been achieved in Li–S-battery research from both the scientific and technological viewpoints. Various tools, methods, and protocols have been developed for Li–S-battery research. Here, these advancements are summarized, from spectroscopic to electrochemical techniques, and the landscape of Li–S chemistry is painted from reactions to transport phenomena. The aim is to provide a comprehensive toolbox for Li–S-battery research and spur future development in multi-electron chemistry, multiphase conversion, and related energy-storage systems and fields.
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The most important challenge in the practical development of lithium-sulfur (Li−S) batteries is finding the suitable cathode materials. Due to the complexity of this system, various factors have been investigated during the last years, but still, the roadmap for designing the best cathode candidates is not vivid. This review attempts to create a better picture of the cathode process to pave the path for developing more practical cathode materials. The most promising candidate as the host cathode material is porous carbon nanomaterials, which are highly conductive and lightweight while having the capability of fabricating the freestanding electrodes. In this case, there is no need for a binder and current collector, and thus, a significantly higher energy density can be expected. Despite the good performance of these carbon-based sulfur cathodes, the presence of some additives anchoring the sulfur molecules to the electrode backbone seems necessary for the practical performance. Metal oxides and sulfides are among the best options, as they act as mediators in the electrochemical redox system of Li/S. Despite their similarities, these additives might mediate in the battery system via entirely different mechanisms. In addition to carbon nanomaterials, other porous materials such as metal-organic frameworks can also provide the cage-like architecture for the construction of sulfur cathode.
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In this work a new, simple and green protocol to introduce a limited content of silanol groups on the surface of an hydrophobic diatomite, in order to be slightly hydrophilic and susceptible to be silanized by bifunctional, sulfur-containing organosilanes for rubber applications, is proposed. The chemical modification was carried out at 85 °C in a solution of H2O:NaOH:H2O2. The modified diatomite was then silanized with bis(triethoxysilylpropyl) disulfide by a procedure that does not involve toxic solvent. Morphological features and elemental composition of diatomite were investigated by Field emission scanning electron microscopy coupled with Energy dispersive X-ray spectroscopy. The surface modification and silanization process were assessed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Diatomite was composed by micrometric frustules from different diatom species with pore size ranging from 25 nm to 1 μm. The spectroscopic characterizations confirmed the surface modification of diatomite with some silanols that acted as sites for silanization reaction. The silanized diatomite and the untreated one were used as filler in unvulcanized solvent-cast SBR films in order to verify that the modification does not negatively affect the polymer/filler interface and as consequence the mechanical properties. Mechanical properties of the realized samples were assessed by uniaxial tensile tests. Films filled with 10 wt% of diatomite (untreated or silanized) showed an increase of Elastic Modulus about of 50% and a decrease of the strain at break with respect to SBR samples, while the tensile strength was not significantly affected by the diatomite addition. SEM images of fracture surfaces of tested specimens showed a fine dispersion of both untreated and silanized diatomite in the polymeric matrix and the achieving of a good interfacial adhesion SBR/fillers. The silanized diatomite, as it is potentially able to bind chemically to elastomeric molecules during vulcanization process, could be used in rubber compounds as semi-reinforcing filler.
Article
Porous nanostructured V2O5 (PN-V2O5) was prepared by a facile spray pyrolysis and used as additive to synthesize sulfur/carbon/PN-V2O5 (S/C/PN-V2O5) composite by a combination of wet-ball-milling and heat treatment. The meso- and macropores in PN-V2O5 were confirmed by pore size distribution, which provided the favorable space to accommodate sulfur. The X-ray diffraction analysis showed that the crystal structures of S and V2O5 could be preserved below the heating temperature of 160 °C and that high heating temperature (200 °C) will result in reaction between S and V2O5. The pore size distribution curves of S/C/PN-V2O5 composites revealed that the penetrated S in PN-V2O5 pores mainly occupied the mesopores and macropores, which was further confirmed by a typical cross-sectional PN-V2O5 with Auger analysis. The S/C/PN-V2O5 composite cathode exhibited a discharge capacity of 632 mAh g⁻¹ after 60 cycles at the current density of 100 mA g⁻¹ and the capacity retention of S/C/PN-V2O5 electrode was 27.3% higher than that of S/C electrode, demonstrating a better cycling performance.
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The detrimental shuttle effect of lithium polysulfides in ether-based liquid electrolytes upon cycling and their reduction/deposition on the lithium metal anode surface have severely restricted the practical application of rechargeable lithium-sulfur (Li-S) batteries. Much effort has been devoted to blocking the undesirable diffusion and shuttling of lithium polysulfides. In this review, recent developments of novel configurations for Li-S batteries, including hierarchical gradient cathodes, modified separators, solid-state electrolytes and lithium anode protection, are presented. It should be emphasized that the specific energy and cycling life are the most important parameters in the future production of Li-S batteries. Moreover, there are still enormous probabilities for the further development of novel configurations to improve the performance of the current Li-S batteries for portable devices and electric vehicles. Hence, these effective and reasonable configurations represent a significant step towards the commercialization of Li-S batteries.
Article
SiO2 nanoparticle decorated polypropylene (PP) separator (PP-SiO2) has been prepared by simply immersing PP separator in the hydrolysis solution of tetraethyl orthosilicate (TEOS) with the assistance of Tween-80. After decoration, the thermal stability and the electrolyte wettability of the PP-SiO2 separator are obviously improved. When the PP-SiO2 separator is used for lithium-sulfur (Li-S) batteries, the cyclic stability and rate capability of the batteries are greatly enhanced. The capacity retention ratio of the Li-S battery configured with the PP-SiO2 separator is 64% after 200 cycles at 0.2 C, which is much higher than that configured with the PP separator (45%). Moreover, the rate capacity of the Li-S batteries using the PP-SiO2 separator reaches to 956.3 mAh g-1, 691.5 mAh g-1, 621 mAh g-1, and 567.6 mAh g-1 at the current density of 0.2 C, 0.5 C, 1 C, and 2 C, respectively. The reason could be ascribed to that the polar silica coating not only alleviate the shuttle effect, but also facilitate Li-ion migration.
Article
Although lithium-sulfur (Li-S) batteries deliver high specific energy densities, lots of intrinsic and fatal obstacles still restrict their practical application. The electrospun carbon nanofibers (CNFs) decorated with ultrafine TiO2 nanoparticles (CNF-T) was prepared and used as multi-functional interlayer to suppress the volume expansion and shuttle effect of Li-S battery. With this strategy, the CNF network with abundant space and superior conductivity can accommodate and recycle the dissolved polysulfides for the bare sulfur cathode. Meanwhile, the ultrafine TiO2 nanoparticles on CNFs work as anchoring points to capture the polysulfides with the strong interaction, making the battery perform remarkable and stable electrochemical properties. As a result, the Li-S battery with the CNF-T interlayer delivers an initial reversible capacity of 935 mAh g-1 at 1C with a capacity retention of 74.2% after 500 cycles. It is believed that this simple, low-cost and scalable method will definitely bring a novel perspective on the practical utilization of Li-S batteries.
Article
Asymmetric separators with polysulfide barrier properties consisting of porous polypropylene grafted with styrene sulfonate (PP-g-PLiSS) were characterized in lithium-sulfur cells to assess their practical applicability. Galvanostatic cycling at different C-rates with and without an electrolyte additive, and cyclic voltammetry were used to probe the electrochemical performance of the cells with the PP-g-PLiSS separators, and to compare it with the performance of the cells utilizing state-of-the-art separator, Celgard 2400. Overall, it was found that regardless of the applied cycling rate, the use of the grafted separators greatly enhances the coulombic efficiency of the cell. An appropriate Li-exchange-site ( SO3(-)) concentration at and near the surface of the separator were found to be essential to effectively suppress the polysulfide shuttle without sacrificing the Li-ion mobility through the separator, and to improve the practical specific charge of the cell.
Article
The development of advanced energy storage systems is of crucial importance to meet the ever-growing demands of electric vehicles, portable devices, and renewable energy harvest. Lithium-sulfur (Li-S) batteries, with the advantages in its high specific energy density, low cost of raw materials, and environmental benignity, are of great potential to serve as next-generation batteries. However, there are many obstacles towards the practical application of Li-S batteries such as the electrical insulating nature of sulfur, the volume expansion during lithium insertion, and the shuttle of soluble polysulfide intermediates that induces severe degradation of the cell performance. In this review, the progresses of multi-functional separators/interlayers in Li-S batteries are highlighted. The introduction of multi-functional separators/interlayers with unexpected multiple functionalities is beneficial for better sulfur utilization, efficient polysulfide diffusion inhibition, and anode protection. Multi-functional separator system with ion selective/electrical conductive polymer, sp2 and porous carbon, metal oxide modified separators, as well as interlinked free-standing nanocarbon, micro/mesoporous carbon, and other conductive interlayers have been proposed. The biomass derived materials was also included as interlayer for advanced Li-S batteries. These novel Li-S cell configurations with multi-functional separators/interlayers are especially suitable for Li-S batteries with high capacity, high stability, and high-rate performance. The opportunities of high-performance separators/interlayers and their applications in next-generation Li-S batteries were also involved. New insights on the role of working separators/interlayers in practical Li-S cells should be further explored to obtain the principle and process for advanced components for energy storage devices based on multi-electron conversion reactions.
Article
Sulfur (S)-carbon (C)-vanadium pentoxide (V2O5) composites were prepared by wet ball milling, and their physical and electrochemical properties were evaluated. Firstly, the effect of the carbon content of S-C composite electrodes on their physical and electrochemical properties was investigated. The S-C composite electrode with 60 wt.% S delivers a first discharge capacity of 1077 mAh g-1. However, its capacity markedly decreases to 606 mAh g-1 after 10 cycles, which corresponds to a capacity fading rate of 47 mAh g-1 per cycle. To improve the electrochemical performance of the S-C composite electrode, carbon was partially replaced by V2O5. The S-C-V2O5 composite electrode with a composition of 60 wt.% - S, 30 wt.% - V2O5 and 10 wt.% - C exhibits a lower capacity fading rate of 23 mAh g-1 per cycle in the first 10 cycles and better capacity retention than the S-C composite electrode over 50 cycles.
Article
A broad overview of how experimental parameters affect the performance of Li–S batteries is presented here, extending the view on these batteries beyond sophisticated conductive sulfur hosts, which have been the primary focus of many studies in recent years. The exquisite sensitivity of the Li–S system to various experimental parameters speaks to the importance of directing future research towards the entire Li–S-battery set-up, rather than just some components. The main overall goal should be to produce cells with high specific energy and energy density. These are challenging tasks and more work is required, in particular in the area of cell engineering. The achievements spotlighted in this report show that outstanding results can be obtained by suitably engineering cathodes and other cell parts, without the need to use advanced structured hosts for sulfur. A lot of stimulating, original and successful research has been done recently in the field, leading to satisfying Li–S battery performances and paving the way for more applied research, with the goal of entering a pre-application phase in Li–S battery development.
Article
Sulfur/carbon (S/C) nanocomposite-filled polyacrylonitrile (PAN) nanofibers (denoted as S/C/PAN) are synthesized as a long life and high capacity cathode material for lithium-sulfur (Li-S) batteries. In the S/C/PAN nanofibers, the sulfurized PAN matrix acts not only as ionic and electronic channels to allow Li+ and electrons to arrive at and react with the S/C nanoparticles, but also as a protective barrier to prevent the S/C nanoparticles from contacting with electrolyte, thus avoiding the discharge intermediates of sulfur to dissolve in and react with the organic carbonate electrolyte. Since the redox reaction of sulfur in the nanofibers occurs mostly at the interior S/C interface through a solid state reaction mechanism, the microstructures and electrochemical interfaces in the nanofibers cathode remain stable during repeated cycles. As a consequence, the S/C/PAN cathode demonstrate a high reversible capacity of 1179 mA h g-1 at a current rate of 200 mA g-1, a high Coulombic efficiency of ~100% after a few cycles, a good rate capability with 616 mA h g-1 at 4.0 A g-1 and a long cycling stability with 60% capacity retention over 400 cycles, showing a great prospect for Li-S battery applications.
Article
Development of advanced energy-storage systems for portable devices, electric vehicles, and grid storage must fulfill several requirements: low-cost, long life, acceptable safety, high energy, high power, and environmental benignity. With these requirements, lithium-sulfur (Li-S) batteries promise great potential to be the next-generation high-energy system. However, the practicality of Li-S technology is hindered by technical obstacles, such as short shelf and cycle life and low sulfur content/loading, arising from the shuttling of polysulfide intermediates between the cathode and anode and the poor electronic conductivity of S and the discharge product Li2 S. Much progress has been made during the past five years to circumvent these problems by employing sulfur-carbon or sulfur-polymer composite cathodes, novel cell configurations, and lithium-metal anode stabilization. This Progress Report highlights recent developments with special attention toward innovation in sulfur-encapsulation techniques, development of novel materials, and cell-component design. The scientific understanding and engineering concerns are discussed at the end in every developmental stage. The critical research directions needed and the remaining challenges to be addressed are summarized in the Conclusion. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Article
The lithium-sulfur (Li-S) battery is one of the most promising candidates for the next generation of rechargeable batteries owing to its high theoretical energy density which is four- to five-fold greater than those of state-of-the-art Li-ion batteries. However, its commercial applications have been hampered by the insulating nature of sulfur and by the poor cycling stability caused for the polysulfide shuttle phenomenon. In this work, we show that Li-S batteries with a mesoporous carbon interlayer placed between the separator and the sulfur cathode not only reduces the internal resistance of the cells but also that its intrinsic mesoporosity provides a physical place for trapping soluble polysulfides as well as to alleviate the negative impact of the large volume change of sulfur. This improvement of the active material reutilization allows to obtain a stable capacity of 1015 mAh g-1 at 0.2 C after 200 cycles despite the use of a conventional sulfur-carbon black mixture as cathode. Furthermore, we observe an excellent capacity retention (~0.1% loss per cycle, after the second cycle), thus making one step closer towards feasible Li-S battery technology for applications in electric vehicles and grid-scale stationary energy storage systems.
Article
A novel hierarchical structure carbon/sulfur composite is presented based on carbon fiber matrices, which are synthesized by electrospinning. The fibers are constituted with hollow graphitized carbon spheres formed using catalytic Ni nano-particles as hard templates. Sulfur is loaded to the carbon substrates via thermal vaporization. The structure and composition of the hierarchical carbon fiber/S composite are characterized with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and nitrogen adsorption isotherms. The electrochemical performance is evaluated by cyclic voltammetry and galvanostatic charge–discharge. The results exhibit an initial discharge capacity of 845 mA h g−1 at 0.25 C (420 mA g−1), with a retention of 77% after 100 cycles. A discharge capacity of 533 mA h g−1 is still attainable when the rate is up to 1.0 C. The good cycling performance and rate capability are contributed to the uniform dispersion of sulfur, the conductive network of carbon fibers and hollow graphitized carbon spheres.
Article
Free-standing porous carbon nanofibers with tunable surface area and pore structure have been investigated as an interlayer between the sulfur cathode and the separator to inhibit the shuttling of the intermediate polysulfides in lithium-sulfur (Li-S) batteries. Specifically, the effects of thickness, surface area, and pore size distribution of carbon nanofiber (CNF) interlayers on the performance of Li-S batteries have been studied. The carbon nanofiber interlayer not only reduces the electrochemical resistance but also localizes the migrating polysulfides and traps them, thereby improving the discharge capacity as well as cyclability. It was found that the optimum thickness of the interlayer is a critical factor to achieve good cell performance, in addition to surface area and pore structure. A high initial discharge capacity of 1549 mAh g-1 at C/5 rate, which is 92% of the theoretical capacity of sulfur, with 98% average Coulombic efficiency and 83% capacity retention after 100 cycles was obtained with a meso-microporous carbon nanofiber interlayer.
Article
The lithium-sulfur battery is receiving intense interest because its theoretical energy density exceeds that of lithium-ion batteries at much lower cost, but practical applications are still hindered by capacity decay caused by the polysulfide shuttle. Here we report a strategy to entrap polysulfides in the cathode that relies on a chemical process, whereby a host-manganese dioxide nanosheets serve as the prototype-reacts with initially formed lithium polysulfides to form surface-bound intermediates. These function as a redox shuttle to catenate and bind 'higher' polysulfides, and convert them on reduction to insoluble lithium sulfide via disproportionation. The sulfur/manganese dioxide nanosheet composite with 75 wt% sulfur exhibits a reversible capacity of 1,300 mA h g(-1) at moderate rates and a fade rate over 2,000 cycles of 0.036%/cycle, among the best reported to date. We furthermore show that this mechanism extends to graphene oxide and suggest it can be employed more widely.
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The demand for energy increases steadily with time due to population and economic growth and advances in lifestyle. As energy usage increases, concerns about environmental pollution associated with the use of fossil fuel are becoming serious. Li ion batteries have become prominent over the past two decades, particularly for portable electronics, as they offer much higher energy density than other rechargeable systems. The current Li ion technology is based on insertion-compound anode and cathode materials, which limit their charge-storage capacity and energy density. A further increase in energy density needs to be achieved through an increase in the charge-storage capacity of the anode and cathode materials or an increase in the cell voltage or both. The lithium ions produced move to the positive electrode through the electrolyte internally while the electrons travel to the positive electrode through the external electrical circuit, and thereby an electrical current is generated.
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This review is an attempt to report the latest development in lithium-sulfur batteries, namely the storage system that, due to its potential energy content, is presently attracting considerable attention both for automotive and stationary storage applications. We show here that consistent progress has been achieved, to the point that this battery is now considered to be near to industrial production. However, the performance of present lithium-sulfur batteries is still far from meeting their real energy density potentiality. Thus, the considerable breakthroughs so far achieved are outlined in this review as the basis for additional R&D, with related important results, which are expected to occur in the next few years.
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Two structures of low dielectric constant (low-k) SiOC films were elucidated in this work. Low-k thin film by remote plasma mode was mainly composed of inorganic Si–O–Si backbone bonds and some oxygen atoms are partially substituted by CH3, which lowers k value. The host matrix of low-k thin films deposited by direct plasma mode, however, was mainly composed of organic C–C bonds and “M” and “D” moieties of organosilicate building blocks, and thus the low dipole and ionic polarizabilities were the important factors on lowering k value.
Article
This study was aimed to systematically investigate the luminescence response of SiO2:Ce3+ nanophosphors with different excitation sources. The powders were synthesized by using an urea assisted combustion method. SiO2:Ce1m% samples were also annealed at 1000°C for 1h in a charcoal environment to reduce incidental Ce4+ to partial Ce3+ ions. High resolution transmission electron microscopy (HRTEM) images of the as synthesized and annealed powder samples confirmed that the particles were spherical and in the size range of 3–8nm in diameter. X-ray diffraction (XRD) and electron dispersion spectroscopy (EDS) results showed that the SiO2 was crystalline and pure. Diffused reflectance, photoluminescence (PL) and cathodoluminescence (CL) results of the SiO2:Ce3+ samples were obtained and compared with each other. The CL degradation and the surface reactions on the surface of the SiO2:Ce3+ were studied with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). A clear improvement in the chemical stability of the SiO2:Ce3+ annealed at 1000°C were obtained.