Metal–Sulfur Battery Cathodes Based on PAN–Sulfur Composites

Atomic cobalt as an efficient electrocatalyst in sulfur cathodes for superior room-temperature sodium-sulfur batteries

The low-cost room-temperature sodium-sulfur battery system is arousing extensive interest owing to its promise for large-scale applications. Although significant efforts have been made, resolving low sulfur reaction activity and severe polysulfide dissolution remains challenging. Here, a sulfur host comprised of atomic cobalt-decorated hollow carbon nanospheres is synthesized to enhance sulfur reactivity and to electrocatalytically reduce polysulfide into the final product, sodium sulfide. The constructed sulfur cathode delivers an initial reversible capacity of 1081 mA h g-1 with 64.7% sulfur utilization rate; significantly, the cell retained a high reversible capacity of 508 mA h g-1 at 100 mA g-1 after 600 cycles. An excellent rate capability is achieved with an average capacity of 220.3 mA h g-1 at the high current density of 5 A g-1. Moreover, the electrocatalytic effects of atomic cobalt are clearly evidenced by operando Raman spectroscopy, synchrotron X-ray diffraction, and density functional theory.

Boosting the Electrochemical Performance of Li-S Batteries with a Dual Polysulfides Confinement Strategy

Lithium-sulfur (Li-S) batteries have attracted more and more attention because they represent one of the most promising candidates to satisfy emerging energy storage demands. The biggest challenge regarding the application of the Li-S battery is to suppress the polysulfide shuttle while maintaining a high sulfur loading mass. Here, a dual polysulfide confinement strategy is designed by confinement of sulfur in polydopamine-coated MXene nanosheets (denoted as S@Mxe@PDA) that performs as a high-performance cathode for Li-S cells owing to their inherently high underlying metallic conductivity and chemical bonding and strong chemical adsorption to lithium polysulfides (LPs). This dual LPs confinement strategy is supported by the results of density functional theory calculations. It is demonstrated that the S@Mxe@PDA cathode exhibits outstanding electrochemical properties, including high reversible capacity (1044 mAh g^-1 after 150 cycles at 0.2 C), superior rate capability (624 mAh g^-1 at 6 C) and excellent cycling stability (556 mAh g^-1 after 330 cycles at 0.5 C with 4.4 mg cm^-2 sulfur loading). This work offers a facile and effective method for boosting Li-S batteries into practical applications.

A high performance lithium-ion-sulfur battery with a free-standing carbon matrix supported Li-rich alloy anode

A high-performance lithium-ion–sulfur battery has been built by using a carbon supported Li-rich alloy anode and sulfurized polyacrylonitrile (S@pPAN) cathode.

Although the lithium–sulfur battery exhibits high capacity and energy density, the cycling performance is severely retarded by dendrite formation and side-reactions of the lithium metal anode and the shuttle effect of polysulfides. Therefore, exploring lithium rich-alloy (or compound) anodes and suppressing the shuttling of polysulfides have become practical technical challenges for the commercialization of lithium–sulfur batteries. Here, a lithium ion sulfur full battery system combining a lithium-rich Li–Si alloy anode and sulfurized polyacrylonitrile (S@pPAN) cathode has been proposed. The free-standing CNF matrix supported Li–Si alloy anode is prepared by a simple and effective method, which is practical for scale-up production. The obtained Li–Si alloy anode demonstrates high cycling stability without dendrite growth, while the use of the S@pPAN cathode avoids the shuttle effect in carbonate electrolytes. The constructed Li–Si/S@pPAN battery could be cycled more than 1000 times at 1C and 3000 times at 3C, with a capacity fading rate of 0.01% and 0.03% per cycle. The exceptional performance should originate from the stable integrated anode structure and the excellent compatibility of the S@pPAN cathode and Li–Si alloy anode with carbonate electrolytes.

Advances in Cathode Materials for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) represent a promising energy storage technology, and they show potential for next-generation high-energy systems due to their high specific capacity, abundant constitutive resources, non-toxicity, low cost, and environment friendliness. Unlike their ubiquitous lithium-ion battery counterparts, the application of LSBs is challenged by several obstacles, including short cycling life, limited sulfur loading, and severe shuttling effect of polysulfides. To make LSBs a viable technology, it is very important to design and synthesize outstanding cathode materials with novel structures and properties. In this review, we summarize recent progress in designs, preparations, structures, and properties of cathode materials for LSBs, emphasizing binary, ternary, and quaternary sulfur-based composite materials. We especially highlight the utilization of carbons to construct sulfur-based composite materials in this exciting field. An extensive discussion of the emerging challenges and possible future research directions for cathode materials for LSBs is provided.

Exploring Chemical, Mechanical, and Electrical Functionalities of Binders for Advanced Energy-Storage Devices

Tremendous efforts have been devoted to the development of electrode materials, electrolytes, and separators of energy-storage devices to address the fundamental needs of emerging technologies such as electric vehicles, artificial intelligence, and virtual reality. However, binders, as an important component of energy-storage devices, are yet to receive similar attention. Polyvinylidene fluoride (PVDF) has been the dominant binder in the battery industry for decades despite several well-recognized drawbacks, i.e., limited binding strength due to the lack of chemical bonds with electroactive materials, insufficient mechanical properties, and low electronic and lithium-ion conductivities. The limited binding function cannot meet inherent demands of emerging electrode materials with high capacities such as silicon anodes and sulfur cathodes. To address these concerns, in this review we divide the binding between active materials and binders into two major mechanisms: mechanical interlocking and interfacial binding forces. We review existing and emerging binders, binding technology used in energy-storage devices (including lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, and supercapacitors), and state-of-the-art mechanical characterization and computational methods for binder research. Finally, we propose prospective next-generation binders for energy-storage devices from the molecular level to the macro level. Functional binders will play crucial roles in future high-performance energy-storage devices.

Sulfur Diffusion within Nitrogen-Doped Ordered Mesoporous Carbons Determined by in Situ X-ray Scattering

The low intrinsic conductivity of sulfur necessitates conductive additives, such as mesoporous carbons, to the cathode to enable high-performance metal-sulfur batteries. Simultaneous efforts to address polysulfide shuttling have introduced nitrogen-doped carbons to provide both conductivity and suppressed shuttling because of their strong interaction with sulfur. The strength of this interaction will impact the ability to fill the mesopores with sulfur via melt infusion. Here, we systematically investigate how nitrogen doping influences the rate that molten sulfur can infiltrate the mesopores and the overall extent of pore filling of highly ordered mesoporous doped carbons using in situ small angle X-ray scattering (SAXS). The similarity in electron density between molten sulfur and the soft carbon framework of the mesoporous material leads to a precipitous decrease in the scattered intensity associated with the ordered structure as voids are filled with sulfur. As the nitrogen doping increases from 1 to 20 at. %, the effective diffusivity of sulfur in the mesopores decreases by an order of magnitude (2.7 × 10^-8 to 2.3 × 10^-9 cm/s). The scattering becomes nearly invariant within 20 min of melt infiltration at 155 °C for all but the most doped carbon, which indicates that submicron-sized mesoporous carbon particles can be filled rapidly. Additionally, the nitrogen doping decreases the sulfur content that can be accommodated within the mesopores from 95% of the mesopores filled without doping to only 64% filled with 20 at. % N as determined by the residual scattering intensity. Sulfur does not crystallize within the mesopores of the nitrogen-doped carbons, which is further indicative of the strong interactions between the nitrogen species and sulfur that can inhibit polysulfide shuttling. In situ SAXS provides insights into the diffusion of sulfur in mesopores and how the surface chemistry of nitrogen-doped carbon appears to significantly hinder the infiltration by sulfur.

Use of Tween Polymer To Enhance the Compatibility of the Li/Electrolyte Interface for the High-Performance and High-Safety Quasi-Solid-State Lithium-Sulfur Battery

Lithium metal batteries have attracted increasing attention recently due to their particular advantages in energy density. However, as for their practical application, the development of solid-state lithium metal batteries is restricted because of the poor Li/electrolyte interface, low Li-ion conductivity, and irregular growth of Li dendrites. To address the above issues, we herein report a high Li-ion conductivity and compatible polymeric interfacial layer by grafting tween-20 on active lithium metal. Sequential oxyethylene groups in tween-grafted Li (TG-Li) improve the ion conductivity and the compatibility of the Li/electrolyte interface, which enables low overpotentials and stable performance over 1000 cycles. Consequently, the poly(ethylene oxide)-based solid-state lithium-sulfur battery with TG-Li exhibits a high reversible capacity of 1051.2 mA h g^-1 at 0.2 C (1 C = 1675 mA h g^-1) and excellent stability for 500 cycles at 2 C. The decreasing concentration of the sulfur atom with increasing Ar⁺ sputtering depth indicates that the polymer interfacial layer works well in suppressing polysulfide reduction to Li₂S/Li₂S₂ on the metallic Li surface even after long-term cycling.

Structural Design of Lithium–Sulfur Batteries: From Fundamental Research to Practical Application

Abstract

Lithium–sulfur (Li–S) batteries have been considered as one of the most promising energy storage devices that have the potential to deliver energy densities that supersede that of state-of-the-art lithium ion batteries. Due to their high theoretical energy density and cost-effectiveness, Li–S batteries have received great attention and have made great progress in the last few years. However, the insurmountable gap between fundamental research and practical application is still a major stumbling block that has hindered the commercialization of Li–S batteries. This review provides insight from an engineering point of view to discuss the reasonable structural design and parameters for the application of Li–S batteries. Firstly, a systematic analysis of various parameters (sulfur loading, electrolyte/sulfur (E/S) ratio, discharge capacity, discharge voltage, Li excess percentage, sulfur content, etc.) that influence the gravimetric energy density, volumetric energy density and cost is investigated. Through comparing and analyzing the statistical information collected from recent Li–S publications to find the shortcomings of Li–S technology, we supply potential strategies aimed at addressing the major issues that are still needed to be overcome. Finally, potential future directions and prospects in the engineering of Li–S batteries are discussed.

Graphical Abstract

A pyrolyzed polyacrylonitrile/selenium disulfide composite cathode with remarkable lithium and sodium storage performances

As a special class of cathode materials for lithium-sulfur batteries, pyrolyzed polyacrylonitrile/sulfur (pPAN/S) can completely solve the polysulfide dissolution problem and deliver reliable performance. However, the applicable S contents of pPAN/S are usually lower than 50 weight % (wt %), and their capacity utilizations are not sufficient, both of which greatly limit their energy densities for commercial applications. We report a pyrolyzed polyacrylonitrile/selenium disulfide (pPAN/SeS₂) composite with dramatically enhanced active material content (63 wt %) and superior performances for both lithium and sodium storage. As a result, pPAN/SeS₂ delivers high capacity of >1100 mAh g^-1 at 0.2 A g^-1 for Li storage with extremely stable cycle life over 2000 cycles at 4.0 A g^-1. Moreover, when applied in a room temperature Na-SeS₂ battery, pPAN/SeS₂ achieves superior capacity of >900 mAh g^-1 at 0.1 A g^-1 and delivers prolonged cycle life over 400 cycles at 1.0 A g^-1.

A new ether-based electrolyte for lithium sulfur batteries using a S@pPAN cathode

An ether-based electrolyte of 4 M LiFSI/DBE is proposed to match both Li metal anodes and a S@pPAN cathode.

An in situ chemically and physically confined sulfur–polymer composite for lithium–sulfur batteries with carbonate-based electrolytes

A sulfur–polymer composite synthesized by one-step thermal sulfurization of PANI is proposed to show excellent long-term cycling stability in carbonate-based electrolytes.

Sulfur nanocomposite as a positive electrode material for rechargeable potassium–sulfur batteries

A room temperature K–S cell with carbonate electrolyte exhibits a promising electrochemical performance.

Self-assembled N-graphene nanohollows enabling ultrahigh energy density cathode for Li-S batteries

Functional porous carbon materials are widely used to solve the low conductivity and shuttle effect of Li-S batteries; however, the common carbon/sulfur composite electrodes based on traditional technology (with conducting agents and binders) make it difficult for a battery to work stably at an ultra-high sulfur loading of 10 mg cm^-2. Herein, an appropriate content of sulfur was injected into a pomegranate-like structure self-assembled with nanohollows (PSSN) of N-graphene. The Li-PSSN/S battery based on traditional technology displays a large-capacity, high-rate and long-life at an ultra-high areal-sulfur loading of 10.1 mg cm^-2. The excellent performance with ultra-high areal-sulfur loading can be attributed to the hierarchal nanohollows with graphene-shells being in close contact to build a 3D-electronic conduction network and promoting electrolyte adsorption into the entire electrode to maintain rapid Li-ion transport, while stopping the shuttle-effect via the strong interaction of polysulfide with the doped N elements on graphene-shells. In addition, the exact sulfur content can provide just enough space to maintain the huge volume change and constant thickness of the S-electrodes during the charge-discharge process to enhance the cycling stability.

Atomic Sulfur Anchored on Silicene, Phosphorene, and Borophene for Excellent Cycle Performance of Li-S Batteries

Dissolution of intermediate lithium polysulfides (LiPS) is an inevitable obstacle for the solid sulfur-based cathode in Li-S batteries. For the first time, herein, atomic sulfur is incorporated into silicene, phosphorene, and borophene to intrinsically eliminate the dissolution of LiPS. The small molecular sulfur species are anchored on the silicene surface with stronger Si-S interaction than the P-S and B-S ones. Meanwhile, a high atomic sulfur coverage (63.1 wt %) is achieved in silicene and concomitantly stabilizes the silicene layer. For the S₃-covered silicene, a high theoretical capacity of 857 mA h g^-1 is achieved with slight dissolution of LiPS originated from the loss of interior S atoms that are not directly bound with silicene surface. By realizing the elemental S₂ coverage on silicene with large surface area, the Li⁺ ions can react fast with the S₂ species, leading to a high theoretical capacity of 891 mA h g^-1 without dissolution and migration of the intermediate LiPS. Most interestingly, the discharge products of atomic layer of lithium sulfides on silicene surface exhibit completely different behaviors from the traditional discharge products of solid Li₂S, which can function as effective adsorption and activation sites for the conversion of LiPS from long chain to short chain by accelerated redox reaction. The present study gains some key insights into how the atomic sulfur contributes to the intrinsic shuttle inhibition and offers a feasible way to design the atomic sulfur-based cathode materials of Li-S batteries with better electrochemical performance.

More Reliable Lithium-Sulfur Batteries: Status, Solutions and Prospects

Lithium-sulfur (Li-S) batteries have attracted tremendous interest because of their high theoretical energy density and cost effectiveness. The target of Li-S battery research is to produce batteries with a high useful energy density that at least outperforms state-of-the-art lithium-ion batteries. However, due to an intrinsic gap between fundamental research and practical applications, the outstanding electrochemical results obtained in most Li-S battery studies indeed correspond to low useful energy densities and are not really suitable for practical requirements. The Li-S battery is a complex device and its useful energy density is determined by a number of design parameters, most of which are often ignored, leading to the failure to meet commercial requirements. The purpose of this review is to discuss how to pave the way for reliable Li-S batteries. First, the current research status of Li-S batteries is briefly reviewed based on statistical information obtained from literature. This includes an analysis of how the various parameters influence the useful energy density and a summary of existing problems in the current Li-S battery research. Possible solutions and some concerns regarding the construction of reliable Li-S batteries are comprehensively discussed. Finally, insights are offered on the future directions and prospects in Li-S battery field.

Constructing hierarchical sulfur-doped nitrogenous carbon nanosheets for sodium-ion storage

Hierarchical sulfur-doped nitrogenous carbon (S/NC) and nitrogenous carbon (NC) nanosheets are successfully fabricated by carbonization of their corresponding precursor polymers which are synthesized through the polymerization reaction of dianhydride and multi-amine compounds. Hierarchical S/NC nanosheets deliver greatly enhanced reversible capacity, compared with hierarchical NC nanosheets, of 280 mAh g^-1 at a current density of 100 mA g^-1 after 300 cycles. It is found that the introduction of sulfur species in carbon skeleton results in increasing the turbostratic structures, rather than enlarging the interlayer distances, for boosting the specific capacity of sodium-ion storage. The turbostratic structures and sulfur dopant existed in the carbon can offer more active sites for the sodium-ion storage. Carbon-based materials doped with sulfur are capable of improving the sodium-ion storage property, which can broaden the horizon of designing a string of outstanding carbon materials for the future energy storage technologies.

Electrochemical Properties of Sulfurized-Polyacrylonitrile Cathode for Lithium-Sulfur Batteries: Effect of Polyacrylic Acid Binder and Fluoroethylene Carbonate Additive

Sulfurized carbonized polyacrylonitrile (S-CPAN) is a promising cathode material for Li-S batteries owing to the absence of polysulfide dissolution phenomena in the electrolyte solutions and thus the lack of a detrimental shuttle mechanism. However, challenges remain in achieving high performance at practical loading because of large volume expansion of S-CPAN electrodes and lithium anode degradation at high current densities. To mitigate this problem, we propose a novel cell design including poly(acrylic acid) (PAA) binder for improved integrity of the composite electrodes and fluoroethylene carbonate (FEC) as additive in the electrolyte solutions for stabilizing the lithium metal surface. As a result, these cells delivered high initial discharge capacity of 1500 mAh g^-1 and a superior cycling stability ∼98.5% capacity retention after 100 cycles, 0.5 C rate, and high sulfur loading of 3.0 mg cm^-2. Scaled-up 260 mAh pouch cells are working very well, highlighting the practical importance of this work.

Stabilized Lithium-Sulfur Batteries by Covalently Binding Sulfur onto the Thiol-Terminated Polymeric Matrices

Despite the low competitive cost and high theoretical capacity of lithium-sulfur battery, its practical application is severely hindered by fast capacity fading and limited capacity retention mainly caused by the polysulfide dissolution problem. Here, this paper reports a new strategy of using thiol-terminated polymeric matrices to prevent polysulfide dissolution, which exhibits an initial capacity of 829.1 mAh g^-1 , and the exceptionally stable capacity retention of ≈84% at 1 C after 200 cycles, and excellent cycling stability with a low mean decay rate of 0.048% after 600 cycles. Significantly, in situ UV/vis spectroscopy analysis of the electrolyte upon battery cycling is performed to verify the function of preventing polysulfide dissolution by means of strongly anchoring discharge products of lithium sulphides. Moreover, density functional theory calculations reveal that the breakage of the linear sulfur chains results in the less soluble short-chain polysulfides due to the formation of the covalently crosslinked discharge products, which avoids the production of soluble long-chain polysulfide and minimizes the shuttle effect. These results exhibit an alternative for the stabilization of the electrochemical performance of lithium-sulfur batteries.

Designing solid-liquid interphases for sodium batteries

Secondary batteries based on earth-abundant sodium metal anodes are desirable for both stationary and portable electrical energy storage. Room-temperature sodium metal batteries are impractical today because morphological instability during recharge drives rough, dendritic electrodeposition. Chemical instability of liquid electrolytes also leads to premature cell failure as a result of parasitic reactions with the anode. Here we use joint density-functional theoretical analysis to show that the surface diffusion barrier for sodium ion transport is a sensitive function of the chemistry of solid–electrolyte interphase. In particular, we find that a sodium bromide interphase presents an exceptionally low energy barrier to ion transport, comparable to that of metallic magnesium. We evaluate this prediction by means of electrochemical measurements and direct visualization studies. These experiments reveal an approximately three-fold reduction in activation energy for ion transport at a sodium bromide interphase. Direct visualization of sodium electrodeposition confirms large improvements in stability of sodium deposition at sodium bromide-rich interphases.

The chemistry at the interface between electrolyte and electrode plays a critical role in determining battery performance. Here, the authors show that a NaBr enriched solid–electrolyte interphase can lower the surface diffusion barrier for sodium ions, enabling stable electrodeposition.

Electrostatic Polysulfides Confinement to Inhibit Redox Shuttle Process in the Lithium Sulfur Batteries

Cationic polymer can capture polysulfide ions and inhibit polysulfide shuttle effect in lithium sulfur (Li-S) rechargeable batteries, enhancing the Li-S battery cycling performance. The cationic poly[bis(2-chloroethyl) ether-alt-1,3-bis[3-(dimethylamino) propyl]urea] quaternized (PQ) with a high density quaternary ammonium cations can trap the lithium polysulfide through the electrostatic attraction between positively charged quaternary ammonium (R₄N⁺) and negatively charged polysulfide (S_x^2-). PQ binder based sulfur electrodes deliver much higher capacity and provide better stability than traditional polyvinylidene fluoride (PVDF) binder based electrodes in Li-S cells. A high sulfur loading of 7.5 mg/cm² is achieved, which delivers a high initial areal capacity of 9.0 mAh/cm² and stable cycling capacity at around 7.0 mAh/cm² in the following cycles.

Molecularly Imprinted Polymer Enables High-Efficiency Recognition and Trapping Lithium Polysulfides for Stable Lithium Sulfur Battery

Using molecularly imprinted polymer to recognize various target molecules emerges as a fascinating research field. Herein, we applied this strategy for the first time to efficiently recognize and trap long-chain polysulfides (Li₂S_x, x = 6-8) in lithium sulfur battery to minimize the polysulfide shuttling between anode and cathode, which enables us to achieve remarkable electrochemical performance including a high specific capacity of 1262 mAh g^-1 at 0.2 C and superior capacity retention of over 82.5% after 400 cycles at 1 C. The outstanding performance is attributed to the significantly reduced concentration of long-chain polysulfides in electrolyte as evidenced by in situ UV/vis spectroscopy and Li₂S nucleation tests, which were further confirmed by density functional theory calculations. The molecular imprinting is demonstrated as a promising approach to effectively prevent the free diffusion of long-chain polysulfides, providing a new avenue to efficiently recognize and trap lithium polysulfides for high-performance lithium sulfur battery with greatly suppressed shuttle effect.

Lithium Batteries with Nearly Maximum Metal Storage

The drive for significant advancement in battery capacity and energy density inspired a revisit to the use of Li metal anodes. We report the use of a seamless graphene-carbon nanotube (GCNT) electrode to reversibly store Li metal with complete dendrite formation suppression. The GCNT-Li capacity of 3351 mAh g^-1_GCNT-Li approaches that of bare Li metal (3861 mAh g^-1_Li), indicating the low contributing mass of GCNT, while yielding a practical areal capacity up to 4 mAh cm^-2 and cycle stability. A full battery based on GCNT-Li/sulfurized carbon (SC) is demonstrated with high energy density (752 Wh kg^-1 total electrodes, where total electrodes = GCNT-Li + SC + binder), high areal capacity (2 mAh cm^-2), and cyclability (80% retention at >500 cycles) and is free of Li polysulfides and dendrites that would cause severe capacity fade.

Integrated Design of MnO2 @Carbon Hollow Nanoboxes to Synergistically Encapsulate Polysulfides for Empowering Lithium Sulfur Batteries

Lithium sulfur batteries (LSBs) with high theoretical energy density are being pursued as highly promising next-generation large-scale energy storage devices. However, its launch into practical application is still shackled by various challenges. A rational nanostructure of hollow carbon nanoboxes filled with birnessite-type manganese oxide nanosheets (MnO₂ @HCB) as a new class of molecularly-designed physical and chemical trap for lithium polysulfides (Li₂ S_x (x = 4-8)) is reported. The bifunctional, integrated, hybrid nanoboxes overcome the obstacles of low sulfur loading, poor conductivity, and redox shuttle of LSBs via effective physical confinement and chemical interaction. Benefiting from the synergistic encapsulation, the developed MnO₂ @HCB/S hybrid nanoboxes with 67.9 wt% sulfur content deliver high specific capacity of 1042 mAh g^-1 at the current density of 1 A g^-1 with excellent Coulombic efficiency ≈100%, and retain improved reversible capacity during long term cycling at higher current densities. The developed strategy paves a new path for employing other metal oxides with unique architectures to boost the performance of LSBs.

Microporous Carbon Polyhedrons Encapsulated Polyacrylonitrile Nanofibers as Sulfur Immobilizer for Lithium-Sulfur Battery

Microporous carbon polyhedrons (MCPs) are encapsulated into polyacrylonitrile (PAN) nanofibers by electrospinning the mixture of MCPs and PAN. Subsequently, the as-prepared MCPs-PAN nanofibers are employed as sulfur immobilizer for lithium-sulfur battery. Here, the S/MCPs-PAN multicomposites integrate the advantage of sulfur/microporous carbon and sulfurized PAN. Specifically, with large pore volume, MCPs inside PAN nanofibers provide a sufficient sulfur loading. While PAN-based nanofibers offer a conductive path and matrix. Therefore, the electrochemical performance is significantly improved for the S/MCPs-PAN multicomposite with a suitable sulfur content in carbonate-based electrolyte. At the current density of 160 mA g^-1_sulfur, the S/MPCPs-PAN composite delivers a large discharge capacity of 789.7 mAh g^-1_composite, high Coulombic efficiency of about 100% except in the first cycle, and good capacity retention after 200 cycles. In particular, even at 4 C rate, the S/MCPs-PAN composite can still release the discharge capacity of 370 mAh g^-1_composite. On the contrary, the formation of the thick SEI layer on the surface of nanofibers with a high sulfur content are observed, which is responsible for the quick capacity deterioration of the sulfur-based composite in carbonate-based electrolyte. This design of the S/MCPs-PAN multicomposite is helpful for the fabrication of stable Li-S battery.

Freestanding reduced graphene oxide-sulfur composite films for highly stable lithium-sulfur batteries

Freestanding reduced graphene oxide-sulfur (rGO-S) composite films were fabricated by combining solution infiltration of sulfur into solvated rGO films with freeze-drying. Such rGO-S composite films can directly serve as the cathodes of lithium-sulfur (Li-S) batteries. The nanostructured architecture of rGO-S composite films considerably improved the cycling stability of Li-S batteries.

Highly Stable Sodium Batteries Enabled by Functional Ionic Polymer Membranes

A sodium metal anode protected by an ion-rich polymeric membrane exhibits enhanced stability and high-Columbic efficiency cycling. Formed in situ via electropolymerization of functional imidazolium-type ionic liquid monomers, the polymer membrane protects the metal against parasitic reactions with electrolyte and, for fundamental reasons, inhibits dendrite formation and growth. The effectiveness of the membrane is demonstrated using direct visualization of sodium electrodeposition.

Decoration of Silica Nanoparticles on Polypropylene Separator for Lithium-Sulfur Batteries

A SiO₂ nanoparticle decorated polypropylene (PP) separator (PP-SiO₂) has been prepared by simply immersing the 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 956.3, 691.5, 621, and 567.6 mAh g^-1 at the current density of 0.2, 0.5, 1, and 2 C, respectively. The reason could be ascribed to that the polar silica coating not only alleviates the shuttle effect but also facilitates Li-ion migration.

Inkjet-Printed Lithium-Sulfur Microcathodes for All-Printed, Integrated Nanomanufacturing

Improved thin-film microbatteries are needed to provide appropriate energy-storage options to power the multitude of devices that will bring the proposed "Internet of Things" network to fruition (e.g., active radio-frequency identification tags and microcontrollers for wearable and implantable devices). Although impressive efforts have been made to improve the energy density of 3D microbatteries, they have all used low energy-density lithium-ion chemistries, which present a fundamental barrier to miniaturization. In addition, they require complicated microfabrication processes that hinder cost-competitiveness. Here, inkjet-printed lithium-sulfur (Li-S) cathodes for integrated nanomanufacturing are reported. Single-wall carbon nanotubes infused with electronically conductive straight-chain sulfur (S@SWNT) are adopted as an integrated current-collector/active-material composite, and inkjet printing as a top-down approach to achieve thin-film shape control over printed electrode dimensions is used. The novel Li-S cathodes may be directly printed on traditional microelectronic semicoductor substrates (e.g., SiO₂ ) or on flexible aluminum foil. Profilometry indicates that these microelectrodes are less than 10 µm thick, while cyclic voltammetry analyses show that the S@SWNT possesses pseudocapacitive characteristics and corroborates a previous study suggesting the S@SWNT discharge via a purely solid-state mechanism. The printed electrodes produce ≈800 mAh g^-1 S initially and ≈700 mAh g^-1 after 100 charge/discharge cycles at C/2 rate.

Sulfur-Rich Phosphorus Sulfide Molecules for Use in Rechargeable Lithium Batteries

A new family of sulfur-rich phosphorus sulfide molecules (P₄ S_10+n ) and their electrochemical reaction mechanism with metallic Li has been explored. These P₄ S_10+n molecules are synthesized by the reaction between P₄ S₁₀ and S. For Li batteries, the P₄ S₄₀ molecule in the series of P₄ S_10+n molecules provides the highest capacity, which has a first discharge capacity of 1223 mAh g^-1 at 100 mA g^-1 and stabilizes at approximately 720 mAh g^-1 at 500 mA g^-1 after 100 cycles. This new class of sulfur-rich P₄ S_10+n molecules and its electrochemical behavior for room-temperature Li⁺ storage could provide novel insights for phosphorus sulfide molecules and high-energy batteries.

Greatly Suppressed Shuttle Effect for Improved Lithium Sulfur Battery Performance through Short Chain Intermediates

The high solubility of long-chain lithium polysulfides and their infamous shuttle effect in lithium sulfur battery lead to rapid capacity fading along with low Coulombic efficiency. To address above issues, we propose a new strategy to suppress the shuttle effect for greatly enhanced lithium sulfur battery performance mainly through the formation of short-chain intermediates during discharging, which allows significant improvements including high capacity retention of 1022 mAh/g with 87% retention for 450 cycles. Without LiNO₃-containing electrolytes, the excellent Coulombic efficiency of ∼99.5% for more than 500 cycles is obtained, suggesting the greatly suppressed shuttle effect. In situ UV/vis analysis of electrolyte during cycling reveals that the short-chain Li₂S₂ and Li₂S₃ polysulfides are detected as main intermediates, which are theoretically verified by density functional theory (DFT) calculations. Our strategy may open up a new avenue for practical application of lithium sulfur battery.

Improving the capacity of lithium–sulfur batteries by tailoring the polysulfide adsorption efficiency of hierarchical oxygen/nitrogen-functionalized carbon host materials

O/N-functionalization of hierarchical carbon is demonstrated to be effective in enhancing the adsorption capacity for lithium polysulfide and thus the reversible capacity of Li–S cells.

Influence of cations in lithium and magnesium polysulphide solutions: dependence of the solvent chemistry

The disproportionation and dissociation equilibria of chemically prepared “Li₂S₈” and “MgS₈” solutions are studied in a variety of solvents.

Chloride-Reinforced Carbon Nanofiber Host as Effective Polysulfide Traps in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) battery is one of the most promising alternatives for the current state-of-the-art lithium-ion batteries due to its high theoretical energy density and low production cost from the use of sulfur. However, the commercialization of Li-S batteries has been so far limited to the cyclability and the retention of active sulfur materials. Using co-electrospinning and physical vapor deposition procedures, we created a class of chloride-carbon nanofiber composites, and studied their effectiveness on polysulfides sequestration. By trapping sulfur reduction products in the modified cathode through both chemical and physical confinements, these chloride-coated cathodes are shown to remarkably suppress the polysulfide dissolution and shuttling between lithium and sulfur electrodes. From adsorption experiments and theoretical calculations, it is shown that not only the sulfide-adsorption effect but also the diffusivity in the vicinity of these chlorides materials plays an important role on the reversibility of sulfur-based cathode upon repeated cycles. Balancing the adsorption and diffusion effects of these nonconductive materials could lead to the enhanced cycling performance of an Li-S cell. Electrochemical analyses over hundreds of cycles indicate that cells containing indium chloride-modified carbon nanofiber outperform cells with other halogenated salts, delivering an average specific capacity of above 1200 mAh g-1 at 0.2 C.

A Flexible Nanostructured Paper of a Reduced Graphene Oxide-Sulfur Composite for High-Performance Lithium-Sulfur Batteries with Unconventional Configurations

Flexible nanostructured reduced graphene oxide-sulfur (rGO-S) composite films are fabricated by synchronously reducing and assembling GO sheets with S nanoparticles on a metal surface. The nanostructured architecture in such composite films not only provides effective pathways for electron transport, but also suppresses the diffusion of polysulfides. Furthermore, they can serve as the cathodes of flexible Li-S batteries.

A sulfur host based on titanium monoxide@carbon hollow spheres for advanced lithium-sulfur batteries

Lithium–sulfur batteries show advantages for next-generation electrical energy storage due to their high energy density and cost effectiveness. Enhancing the conductivity of the sulfur cathode and moderating the dissolution of lithium polysulfides are two key factors for the success of lithium–sulfur batteries. Here we report a sulfur host that overcomes both obstacles at once. With inherent metallic conductivity and strong adsorption capability for lithium-polysulfides, titanium monoxide@carbon hollow nanospheres can not only generate sufficient electrical contact to the insulating sulfur for high capacity, but also effectively confine lithium-polysulfides for prolonged cycle life. Additionally, the designed composite cathode further maximizes the lithium-polysulfide restriction capability by using the polar shells to prevent their outward diffusion, which avoids the need for chemically bonding all lithium-polysulfides on the surfaces of polar particles.

The promise of lithium-sulfur batteries with higher energy densities than lithium-ion is hindered by the insulating nature of sulfur and dissolution of polysulfides. Here the authors design titanium monoxide/carbon hollow nanospheres that overcome both obstacles, enabling improved electrochemical properties.