Atom-Thick Interlayer Made of CVD-Grown Graphene Film on Separator for Advanced Lithium-Sulfur Batteries

A separator modified by barium titanate with macroscopic polarization electric field for high-performance lithium-sulfur batteries

The detrimental "shuttling effect" of lithium polysulfides and the sluggish kinetics of the sulfur redox reaction in lithium-sulfur batteries (LSBs) impede the practical application. Considering the high polar chemistry facilitates the anchoring of polysulfides, ferroelectric materials have gradually been employed as functionalized separators to suppress the "shuttling effect". Herein, a functional separator coated with BaTiO₃ with a macroscopic polarization electric field (poled-BaTiO₃) is designed for retarding the problematic shuttle effect and accelerating redox kinetics. Theoretical calculations and experiments revealed that resultant positive charged alignments on the poled-BaTiO₃ coating can chemically immobilize polysulfides, effectively improving the cyclic stability of LSBs. Moreover, the simultaneous reinforcement of the built-in electric field in the poled-BaTiO₃ coating can also improve Li-ion transportation for accelerating redox kinetics. Benefiting from these attributes, the as-developed LSB attains an initial discharge capacity of 1042.6 mA h g^-1 and high cyclic stability of over 400 cycles at 1 C rate. The corresponding LSB pouch cell was also assembled to validate the concept. This work is anticipated to provide new insight into the development of high-performing LSBs through engineering ferroelectric-enhanced coatings.

A Ti3C2Tx-Based Composite as Separator Coating for Stable Li-S Batteries

The nitrogen-doped MXene carbon nanosheet-nickel (N-M@CNi) powder was successfully prepared by a combined process of electrostatic attraction and annealing strategy, and then applied as the separator coating in lithium-sulfur batteries. The morphology and structure of the N-M@CNi were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectrum, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption-desorption method. The strong LiPS adsorption ability and high conductivity are associated with the N-doped carbon nanosheet-Ni modified surface. The modified separator offers the cathode of Li-S cell with greater sulfur utilization, better high-rate adaptability, and more stable cycling performance compared with the pristine separator. At 0.2 C the cell with N-M@CNi separator delivers an initial capacity of 1309 mAh g^-1. More importantly, the N-M@CNi separator is able to handle a cathode with 3.18 mg cm^-2 sulfur loading, delivering a capacity decay rate of 0.043% with a high capacity retention of 95.8%. Therefore, this work may provide a feasible approach to separator modification materials towards improved Li-S cells with improved stability.

Direct-Chemical Vapor Deposition-Enabled Graphene for Emerging Energy Storage: Versatility, Essentiality, and Possibility

The direct chemical vapor deposition (CVD) technique has stimulated an enormous scientific and industrial interest to enable the conformal growth of graphene over multifarious substrates, which readily bypasses tedious transfer procedure and empowers innovative materials paradigm. Compared to the prevailing graphene materials (i.e., reduced graphene oxide and liquid-phase exfoliated graphene), the direct-CVD-enabled graphene harnesses appealing structural advantages and physicochemical properties, accordingly playing a pivotal role in the realm of electrochemical energy storage. Despite conspicuous progress achieved in this frontier, a comprehensive overview is still lacking by far and the synthesis-structure-property-application nexus of direct-CVD-enabled graphene remains elusive. In this topical review, rather than simply compiling the state-of-the-art advancements, the versatile roles of direct-CVD-enabled graphene are itemized as (i) modificator, (ii) cultivator, (iii) defender, and (iv) decider. Furthermore, essential effects on the performance optimization are elucidated, with an emphasis on fundamental properties and underlying mechanisms. At the end, perspectives with respect to the material production and device fabrication are sketched, aiming to navigate the future development of direct-CVD-enabled graphene en-route toward pragmatic energy applications and beyond.

Development of high-energy non-aqueous lithium-sulfur batteries via redox-active interlayer strategy

Lithium-sulfur batteries have theoretical specific energy higher than state-of-the-art lithium-ion batteries. However, from a practical perspective, these batteries exhibit poor cycle life and low energy content owing to the polysulfides shuttling during cycling. To tackle these issues, researchers proposed the use of redox-inactive protective layers between the sulfur-containing cathode and lithium metal anode. However, these interlayers provide additional weight to the cell, thus, decreasing the practical specific energy. Here, we report the development and testing of redox-active interlayers consisting of sulfur-impregnated polar ordered mesoporous silica. Differently from redox-inactive interlayers, these redox-active interlayers enable the electrochemical reactivation of the soluble polysulfides, protect the lithium metal electrode from detrimental reactions via silica-polysulfide polar-polar interactions and increase the cell capacity. Indeed, when tested in a non-aqueous Li-S coin cell configuration, the use of the interlayer enables an initial discharge capacity of about 8.5 mAh cm⁻² (for a total sulfur mass loading of 10 mg cm⁻²) and a discharge capacity retention of about 64 % after 700 cycles at 335 mA g⁻¹ and 25 °C.

Lithium-sulfur batteries promise high energy density, but polysulfide shuttling acts as a major stumbling block toward practical development. Here, a redox-active interlayer is proposed to confine polysulfides, increase the cell capacity and improve cell cycle life.

Recent Advances and Strategies toward Polysulfides Shuttle Inhibition for High-Performance Li-S Batteries

Lithium-sulfur (Li-S) batteries are regarded as the most promising next-generation energy storage systems due to their high energy density and cost-effectiveness. However, their practical applications are seriously hindered by several inevitable drawbacks, especially the shuttle effects of soluble lithium polysulfides (LiPSs) which lead to rapid capacity decay and short cycling lifespan. This review specifically concentrates on the shuttle path of LiPSs and their interaction with the corresponding cell components along the moving way, systematically retrospect the recent advances and strategies toward polysulfides diffusion suppression. Overall, the strategies for the shuttle effect inhibition can be classified into four parts, including capturing the LiPSs in the sulfur cathode, reducing the dissolution in electrolytes, blocking the shuttle channels by functional separators, and preventing the chemical reaction between LiPSs and Li metal anode. Herein, the fundamental aspect of Li-S batteries is introduced first to give an in-deep understanding of the generation and shuttle effect of LiPSs. Then, the corresponding strategies toward LiPSs shuttle inhibition along the diffusion path are discussed step by step. Finally, general conclusions and perspectives for future research on shuttle issues and practical application of Li-S batteries are proposed.

Two-dimensional materials towards separator functionalization in advanced Li-S batteries

Functional separators have played important roles in improving the electrochemical performance of lithium-sulfur (Li-S) batteries by addressing the key issues of both the sulfur cathode and lithium anode. Compared with other materials that are used for separator functionalization, two-dimensional (2D) materials with atomic layer thickness and infinite lateral dimensions feature several advantages of ultra-thin laminate structure, remarkable physical properties and tunable surface chemistry, which show potential applications in separator functionalization towards addressing the issues of both the shuttle effect and formation of Li dendrites in Li-S batteries. In this review, the unique advantages of 2D materials for separator functionalization in Li-S batteries and their common construction methods are introduced. Then, recent progress and advances in the construction of 2D materials functional separators are summarized in detail towards inhibiting the shuttle effect of polysulfides and suppressing Li dendrite growth in Li-S batteries. Finally, some opportunities and challenges of 2D materials for constructing high-performance functional separators are proposed. We anticipate that this review will provide new insights into separator functionalization for developing advanced Li-S batteries.

Advances in Lithium-Sulfur Batteries: From Academic Research to Commercial Viability

Lithium-ion batteries, which have revolutionized portable electronics over the past three decades, were eventually recognized with the 2019 Nobel Prize in chemistry. As the energy density of current lithium-ion batteries is approaching its limit, developing new battery technologies beyond lithium-ion chemistry is significant for next-generation high energy storage. Lithium-sulfur (Li-S) batteries, which rely on the reversible redox reactions between lithium and sulfur, appears to be a promising energy storage system to take over from the conventional lithium-ion batteries for next-generation energy storage owing to their overwhelming energy density compared to the existing lithium-ion batteries today. Over the past 60 years, especially the past decade, significant academic and commercial progress has been made on Li-S batteries. From the concept of the sulfur cathode first proposed in the 1960s to the current commercial Li-S batteries used in unmanned aircraft, the story of Li-S batteries is full of breakthroughs and back tracing steps. Herein, the development and advancement of Li-S batteries in terms of sulfur-based composite cathode design, separator modification, binder improvement, electrolyte optimization, and lithium metal protection is summarized. An outlook on the future directions and prospects for Li-S batteries is also offered.

Ion Selective Covalent Organic Framework Enabling Enhanced Electrochemical Performance of Lithium-Sulfur Batteries

Ion selective separators with the capability of conducting lithium ion and blocking polysulfides are critical and highly desired for high-performance lithium-sulfur (Li-S) batteries. Herein, we fabricate an ion selective film of covalent organic framework (denoted as TpPa-SO₃Li) onto the commercial Celgard separator. The aligned nanochannels and continuous negatively charged sites in the TpPa-SO₃Li layer can effectively facilitate the lithium ion conduction and meanwhile significantly suppress the diffusion of polysulfides via the electrostatic interaction. Consequently, the TpPa-SO₃Li layer exhibits excellent ion selectivity with an extremely high lithium ion transference number of 0.88. When using this novel functional layer, the Li-S batteries with a high sulfur loading of 5.4 mg cm^-2 can acquire a high initial capacity of 822.9 mA h g^-1 and high retention rate of 78% after 100 cycles at 0.2 C. This work provides new insights into developing high-performance Li-S batteries via ion selective separator strategy.

Sb nanosheet modified separator for Li-S batteries with excellent electrochemical performance

An air-stable antimony (Sb) nanosheet modified separator (SbNs/separator) has been prepared by coating exfoliated Sb nanosheets (SbNs) successfully onto a pristine separator through a vacuum infiltration method. The as-prepared Li-S batteries using SbNs/separators exhibit much improved electrochemical performance compared to the ones using commercial separators. The coulombic efficiency (CE) of the Li-S battery using the SbNs/separator after the initial cycle is close to 100% at a current density of 0.1 A g-1, and 660 mA h g-1 capacity retained after 100 cycles. The rate capability of Li-S battery using SbNs/separator delivers a reversible capacity of 425 mA h g-1 when the current density increases to 1 A g-1. The improved electrochemical performance is mainly attributed to the following reasons. Firstly, the combination of physical adsorption and chemical bonding between SbNs and lithium polysulfides (LiPSs), which efficiently inhibits the shuttle phenomena of LiPSs. Secondly, the good electronic conductivity of SbNs improves the utilization of the adsorbed LiPSs, which benefits the capacity release of active materials. Lastly, the fast conversion kinetics of intermediate LiPSs caused by the catalytic effect from SbNs further suppresses the shuttle effect of LiPSs. The SbNs/separators exhibit a great potential for the future high-performance Li-S batteries.

Coordinating Adsorption and Catalytic Activity of Polysulfide on Hierarchical Integrated Electrodes for High-Performance Flexible Li-S Batteries

Lithium-sulfur (Li-S) batteries have been known to be a promising substitute because of their much higher theoretical energy density than that of traditional Li-ion batteries. However, the low utilization of sulfur caused by the poor conductivity of sulfur and shuttle of lithium polysulfides (LiPSs) severely restrict the commercial application of Li-S batteries, especially in flexible wearable devices. Herein, a hierarchical nitrogen-doped carbon nanotube (NCNT)@Co-Co₃O₄ nanowire array (NWA)-integrated electrode was developed based on the rational design of density functional theory calculations, which shows simultaneous confinement adsorption and catalysis conversion of LiPSs. In situ Raman spectra further proved that the NCNT@Co-Co₃O₄ NWAs exhibit sufficient adsorption capacity and high catalytic conversion of LiPSs. As a result, the NCNT@Co-Co₃O₄@S electrode exhibited the desirable specific capacity and excellent cyclic stability at both low and high sulfur loadings. Moreover, pouch cells with the NCNT@Co-Co₃O₄@S cathode show higher capacity under flat or bending states and longer cycle stability than that of the reported results. This work provides a new approach for the development of high-performance Li-S batteries toward future wearable electronics.

Janus Conductive/Insulating Microporous Ion-Sieving Membranes for Stable Li-S Batteries

Lithium-sulfur batteries are one of the most promising next-generation high-density energy storage systems. Despite progress, the poor electrical conductivity and cycling stability of sulfur cathodes still hinder their practical implementation. Here, we developed a facile approach for the engineering of Janus double-sided conductive/insulating microporous ion-sieving membranes that significantly enhance recharge efficiency and long-term stability of Li-S batteries. Our membrane consists of an insulating Li-anode side and an electrically conductive S-cathode side. The insulating side consists of a standard polypropylene separator, while the conductive side is made of closely packed multilayers of high-aspect-ratio MOF/graphene nanosheets having a thickness of few nanometers and a specific surface area of 996 m² g^-1 (MOF, metal-organic framework). Our models and experiments reveal that this electrically conductive microporous nanosheet architecture enables the reuse of polysulfide trapped in the membrane and decreases the polysulfide flux and concentration on the anode side by a factor of 250× over recent microporous membranes made of granular MOFs and standard battery separators. Notably, Li-S batteries using our Janus microporous membranes achieve an outstanding rate capability and long-term stability with 75.3% capacity retention over 1700 cycles. We demonstrate the broad applicability of our high-aspect-ratio MOF/graphene nanosheet preparation strategy by the synthesis of a diverse range of MOFs, including ZIF-67, ZIF-8, HKUST-1, NiFe-BTC, and Ni-NDC, providing a flexible approach for the design of Janus microporous membranes and electrically conductive microporous building blocks for energy storage and various other electrochemical applications.

Chemical Vapour Deposition of Graphene-Synthesis, Characterisation, and Applications: A Review

Graphene as the 2D material with extraordinary properties has attracted the interest of research communities to master the synthesis of this remarkable material at a large scale without sacrificing the quality. Although Top-Down and Bottom-Up approaches produce graphene of different quality, chemical vapour deposition (CVD) stands as the most promising technique. This review details the leading CVD methods for graphene growth, including hot-wall, cold-wall and plasma-enhanced CVD. The role of process conditions and growth substrates on the nucleation and growth of graphene film are thoroughly discussed. The essential characterisation techniques in the study of CVD-grown graphene are reported, highlighting the characteristics of a sample which can be extracted from those techniques. This review also offers a brief overview of the applications to which CVD-grown graphene is well-suited, drawing particular attention to its potential in the sectors of energy and electronic devices.

Balancing the Seesaw: Investigation of a Separator to Grasp Polysulfides with Diatomic Chemisorption

Lithium-sulfur (Li-S) batteries are promising next-generation high-density energy storage systems due to their advantages of high theoretical specific capacity, environmental compatibility, and low cost. However, high-order polysulfides dissolve in the electrolyte and subsequently lead to the undesired polysulfide shuttle effect, which hinders the commercialization of Li-S batteries. To tackle this issue, morpholine molecules were successfully grafted onto a commercial polypropylene separator. Density functional theory (DFT) calculations were performed and revealed that morpholine side chains could equally and reversibly grasp all the high-order polysulfides. This diatomic chemisorption adjusted the transformation process among the sulfur-related compounds. The modified separator battery possessed a discharge capacity as high as 827.8 mAh·g^-1 after 500 cycles at 0.5 C. The low capacity fading rate, symmetrical cyclic voltammogram, and retention of the electrode morphology all suggest that the diatomic equal adsorption approach can successfully suppress the polysulfide shuttle effect while maintaining excellent battery performance.

A Hierarchical Three-Dimensional Porous Laser-Scribed Graphene Film for Suppressing Polysulfide Shuttling in Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) battery is a promising next-generation rechargeable battery with high energy density. Given the outstanding capacities of sulfur (1675 mAh g^-1) and lithium metal (3861 mAh g^-1), Li-S battery theoretically delivers an ultrahigh energy density of 2567 Wh kg^-1. However, this energy density cannot be realized due to several factors, particularly the shuttling of polysulfide intermediates between the cathode and anode, which causes serious degradation of capacity and cycling stability of a Li-S battery. In this work, a simple and scalable route was employed to construct a freestanding laser-scribed graphene (LSG) interlayer that effectively suppresses the polysulfide shuttling in Li-S batteries. Thus, a high specific capacity (1160 mAh g^-1) with excellent cycling stability (80.4% capacity retention after 100 cycles) has been achieved due to the unique structure of hierarchical three-dimensional pores in the freestanding LSG.

Two-Dimensional Material-Functionalized Separators for High-Energy-Density Metal-Sulfur and Metal-Based Batteries

Functional separators have attracted much attention owing to their effectiveness in supporting the stable and safe operation of future ultrahigh-capacity electrodes, especially sulfur cathodes and metal anodes in rechargeable batteries. Among the functional materials for separator modification, two-dimensional (2 D) materials offer the unique advantages of intimate coverage, mechanical robustness, and rich surface chemistry. This Minireview summarizes up-to-date achievements in the development of 2 D material-functionalized separators to promote the application of sulfur cathodes and metal anodes. With a deep understanding of the roles of 2 D materials and their precise control in functionalizing separators, 2 D materials will find great opportunities in advancing high-energy-density rechargeable batteries.

The immobilizing polysulfide mechanism of cadmium-doping carbon aerogels via a microtemplate for high performance Li–S batteries

We develop a novel microtemplate strategy to prepare unique carbon aerogels. The designed cathode materials present excellent electrochemical performance.

Design Multifunctional Catalytic Interface: Toward Regulation of Polysulfide and Li2 S Redox Conversion in Li-S Batteries

The polysulfide shuttle effect and sluggish reaction kinetics hamper the practical applications of lithium-sulfur (Li-S) batteries. Incorporating a functional interlayer to trapping and binding polysulfides has been found effective to block polysulfide migration. Furthermore, surface chemistry at soluble polysulfides/electrolyte interface is a crucial step for Li-S battery in which stable cycling depends on adsorption and reutilization of blocked polysulfides in the electrolyte. A multifunctional catalytic interface composed of niobium nitride/N-doped graphene (NbN/NG) along the soluble polysulfides/electrolyte is designed and constructed to regulate corresponding interface chemical reaction, which can afford long-range electron transfer surfaces, numerous strong chemisorption, and catalytic sites in a working lithium-sulfur battery. Both experimental and theoretical calculation results suggest that a new catalytic interface enabled by metal-like NbN with superb electrocatalysis anchored on NG is highly effective in regulating the blocked polysulfide redox reaction and tailoring the Li₂ S nucleation-growth-decomposition process. Therefore, the Li-S batteries with multifunctional NbN/NG barrier exhibit excellent rate performance (621.2 mAh g^-1 at 3 C) and high stable cycling life (81.5% capacity retention after 400 cycles). This work provides new insights to promote Li-S batteries via multifunctional catalytic interface engineering.

Calixarene-Functionalized Porous Carbon Aerogels for Polysulfide Capture: Cathodes for High Performance Lithium-Sulfur Batteries

A cage-type composite was successfully prepared by attaching p-sulfonatocalix[4]arene to a porous activated carbon aerogel (ACA). The resulting composite showed a high specific surface area of 1620.7 m²  g^-1 and a high sulfur loading of 2.5 mg cm^-2 . The calixarene is uniformly dispersed on the carbon spheres and efficiently captures polysulfides by interaction with the sulfonate groups. Meanwhile, the cross-linked porous structure of the composite restricts the migration of polysulfides. The cathode delivers an outstanding electrochemical performance with an initial capacity of 1304.7 mAh g^-1 at 0.2 C. Furthermore, it displays excellent long-term cycling stability, maintaining 884.7 mAh g^-1 after 300 cycles at 0.5 C. Density functional theory (DFT) adsorption calculations support the strong interaction between the calixarenes and polysulfides and reveal the capture mechanism.

Graphdiyne-Modified Polyimide Separator: A Polysulfide-Immobilizing Net Hinders the Shuttling of Polysulfides in Lithium-Sulfur Battery

Graphdiyne (GDY), a new type of carbon material with an electron-rich conjugated structure, has been investigated as a separator coating layer to enhance the electrochemical performance of lithium-sulfur (Li-S) battery. Acetylenic bond (-C≡C-C≡C-) and benzene ring in the GDY coating layer are experimentally verified to reversibly attract the soluble lithium polysulfides by chemical adsorption during cycling. Meanwhile, the shuttle effect of soluble polysulfides is further physically restricted by the GDY coating layer due to the evenly distributed pores (5.42 Å) and a consistent interlayer spacing (3.65 Å) of GDY. Moreover, GDY is a conducting carbon skeleton with high Li⁺ mobility that can improve the rate performance. Hence, Li-S battery with an as-prepared GDY coating layer shows excellent electrochemical performances including superior specific capacity, excellent rate performance, and low capacity attenuation rate. The high initial discharge capacity of 1648.5 mA h g^-1 at 0.1C and 819.5 mA h g^-1 even at a high rate of 2C is achieved by this novel separator. The initial capacity of 1112.9 mA h g^-1 at 0.5C is retained to 816.7 mA h g^-1 after 200 cycles with a low attenuation rate of 0.13% per cycle. Compared with other coated separators, these results show that the GDY coating layer endows the separator with superior electrochemical performances for Li-S battery.

Scalable Salt-Templated Synthesis of Nitrogen-Doped Graphene Nanosheets toward Printable Energy Storage

Mass production of graphene powders affording high quality and environmental benignancy serves as a prerequisite for the practical usage of graphene in multiple energy storage applications. Herein, we exploit a salt-templated CVD approach to harness the direct synthesis of nitrogen-doped graphene (NG) nanosheets and related ink dispersions in a scalable, safe, efficient, and green fashion. Thus-fabricated NG accompanying large productivity, excellent electrical conductivity, and favorable solution processability possesses implications in printable energy storage devices. With the NG-based ink in hand, self-standing 3D architectures with programmable patterns can be directly printed over a myriad of substrates. Accordingly, both electrode preparation for flexible supercapacitors and separator modification in Li-S batteries can be enabled via printing by employing our NG-based composite inks. This work thus represents a practical route for mass production of graphene inks with cost-effectiveness and eco-friendliness for emerging energy storage technology.

The phase transfer effect of sulfur in lithium–sulfur batteries

The insulating elemental sulfur in a Li–S battery could be reduced to high-grade polysulfides by low-grade polysulfides from the cathode, after which they could participate in the discharging process of the Li–S battery.

Graphitic carbon nitride as polysulfide anchor and barrier for improved lithium-sulfur batteries

The poor conductivity of sulfur and the shuttle effect of soluble polysulfides have considerably hindered the practical application of lithium-sulfur (Li-S) batteries. Here, we have fabricated a three-dimensional graphitic carbon nitride/reduced graphene oxide (GCN@rGO) network as the sulfur host in Li-S batteries, where the bifunctional GCN strongly binds polysulfides through a chemical interaction and catalyzes the redox reactions of polysulfides. Additionally, GCN coating is also applied to different membranes and when these GCN-coated-membranes (GCMs) are used as separators, they are found to effectively act as the polysulfide barrier to suppress the diffusion of polysulfide intermediates to the Li anode and thus ameliorate the shuttle effect. As a result, the Li-S battery assembled from the GCN@rGO/S cathode and GCM separator exhibited a high initial specific capacity of 1000.6 mAh g^-1 at 0.1 C and 87% capacity retention with 0.066% decay per cycle over 200 charge-discharge cycles at 0.5 C.

A Polysulfide-Immobilizing Polymer Retards the Shuttling of Polysulfide Intermediates in Lithium-Sulfur Batteries

Lithium-sulfur batteries are regarded as one of the most promising candidates for next-generation rechargeable batteries. However, the practical application of lithium-sulfur (Li-S) batteries is seriously impeded by the notorious shuttling of soluble polysulfide intermediates, inducing a low utilization of active materials, severe self-discharge, and thus a poor cycling life, which is particularly severe in high-sulfur-loading cathodes. Herein, a polysulfide-immobilizing polymer is reported to address the shuttling issues. A natural polymer of Gum Arabic (GA) with precise oxygen-containing functional groups that can induce a strong binding interaction toward lithium polysulfides is deposited onto a conductive support of a carbon nanofiber (CNF) film as a polysulfide shielding interlayer. The as-obtained CNF-GA composite interlayer can achieve an outstanding performance of a high specific capacity of 880 mA h g^-1 and a maintained specific capacity of 827 mA h g^-1 after 250 cycles under a sulfur loading of 1.1 mg cm^-2 . More importantly, high reversible areal capacities of 4.77 and 10.8 mA h cm^-2 can be obtained at high sulfur loadings of 6 and even 12 mg cm^-2 , respectively. The results offer a facile and promising approach to develop viable lithium-sulfur batteries with high sulfur loading and high reversible capacities.

Biotemplating Growth of Nepenthes-like N-Doped Graphene as a Bifunctional Polysulfide Scavenger for Li-S Batteries

The practical application of lithium-sulfur (Li-S) batteries is hindered by their poor cycling stabilities that primarily stem from the "shuttle" of dissolved lithium polysulfides. Here, we develop a nepenthes-like N-doped hierarchical graphene (NHG)-based separator to realize an efficient polysulfide scavenger for Li-S batteries. The 3D textural porous NHG architectures are realized by our designed biotemplating chemical vapor deposition (CVD) approach via the employment of naturally abundant diatomite as the growth substrate. Benefiting from the high surface area, devious inner-channel structure, and abundant nitrogen doping of CVD-grown NHG frameworks, the derived separator favorably synergizes bifunctionality of physical confinement and chemical immobilization toward polysulfides, accompanied by smooth lithium ion diffusions. Accordingly, the batteries with the NHG-based separator delivers an initial capacity of 868 mAh g^-1 with an average capacity decay of only 0.067% per cycle at 2 C for 800 cycles. A capacity of 805 mAh g^-1 can further be achieved at a high sulfur loading of ∼7.2 mg cm^-2. The present study demonstrates the potential in constructing high-energy and long-life Li-S batteries upon separator modification.

Nitrogen Doped Carbon Nanosheets Encapsulated in situ Generated Sulfur Enable High Capacity and Superior Rate Cathode for Li-S Batteries

Lithium-sulfur batteries (LSBs), with large specific capacity (1,675 mAh g⁻¹), are regarded as the most likely alternative to the traditional Lithium-ion batteries. However, the intrinsical insulation and dramatic volume change of sulfur, as well as serious shuttle effect of polysulfides hinder their practical implementation. Herein, we develop three-dimensional micron flowers assembled by nitrogen doped carbon (NC) nanosheets with sulfur encapsulated (S@NC-NSs) as a promising cathode for Li-S to overcome the forementioned obstacles. The in situ generated S layer adheres to the inner surface of the hollow and micro-porous NC shell with fruitful O/N containing groups endowing both efficient physical trapping and chemical anchoring of polysulfides. Meanwhile, such a novel carbon shell helps to bear dramatic volume change and provides a fast way for electron transfer during cycling. Consequently, the S@NC-NSs demonstrate a high capacity (1,238 mAh g⁻¹ at 0.2 C; 1.0 C = 1,675 mA g⁻¹), superior rate performance with a capacity retention of 57.8% when the current density increases 25 times from 0.2 to 5.0 C, as well as outstanding cycling performance with an ultralow capacity fading of only 0.064% after 200 cycles at a high current density of 5.0 C.

Fe3O4-Decorated Porous Graphene Interlayer for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are seriously restrained by the shuttling effect of intermediary products and their further reduction on the anode surface. Considerable researches have been devoted to overcoming these issues by introducing carbon-based materials as the sulfur host or interlayer in the Li-S systems. Herein, we constructed a multifunctional interlayer on a separator by inserting Fe₃O₄ nanoparticles (NPs) in a porous graphene (PG) film to immobilize polysulfides effectively. The porous structure of graphene was optimized by controlling the oxidation conditions for facilitating ion transfer. The polar Fe₃O₄ NPs were employed to trap sulfur species via strong chemical interaction. By exploiting the PG-Fe₃O₄ interlayer with optimal porous structure and component, the Li-S battery delivered a superior cycling performance and rate capability. The reversible discharge capacity could be maintained at 732 mAh g^-1 after 500 cycles and 356 mAh g^-1 after total 2000 cycles at 1 C with a final capacity retention of 49%. Moreover, a capacity of 589 mAh g^-1 could also be maintained even at 2 C rate.