Design Multifunctional Catalytic Interface: Toward Regulation of Polysulfide and Li2S 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 Li₂S 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.     

Implanting Atomic Cobalt within Mesoporous Carbon toward Highly Stable Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries hold great promise to serve as next‐generation energy storage devices. However, the practical performances of Li–S batteries are severely limited by the sulfur cathode regarding its low conductivity, huge volume change, and the polysulfide shuttle effect. The first two issues have been well addressed by introducing mesoporous carbon hosts to the sulfur cathode. Unfortunately, the nonpolar nature of carbon materials renders poor affinity to polar polysulfides, leaving the shuttling issue unaddressed. In this contribution, atomic cobalt is implanted within the skeleton of mesoporous carbon via a supramolecular self‐templating strategy, which simultaneously improves the interaction with polysulfides and maintains the mesoporous structure. Moreover, the atomic cobalt dopants serve as active sites to improve the kinetics of the sulfur redox reactions. With the atomic‐cobalt‐decorated mesoporous carbon host, a high capacity of 1130 mAh g_S^?1 at 0.5 C and a high stability with a retention of 74.1% after 300 cycles are realized. Implanting atomic metal in mesoporous carbon demonstrates a feasible strategy to endow nanomaterials with targeted functions for Li–S batteries and broad applications.     

Designing a Multifunctional Separator for High‐Performance Li–S Batteries at Elevated Temperature

The practical applications of lithium–sulfur (Li–S) batteries are seriously limited by the undesirable polysulfide shuttling and lithium dendrite growth. Herein, a multifunctional membrane is designed and prepared by coating a lithiated Nafion (Li@Nafion) layer and an Al₂O₃ layer on the two sides of a routine polymer membrane (polypropylene/polyethylene/polypropylene, PEP). The Li@Nafion layer faced to the sulfur cathode builds a “polysulfide‐phobic” surface to restrain the shuttle effect via Coulomb repulsion, while the Al₂O₃ layer with a uniform porous structure aids in regulating homogeneous Li⁺ fluxes to achieve stable Li electrodeposition. As a result, the Li//Li symmetric cell with a Li@Nafion/PEP/Al₂O₃ (LNPA) separator realizes stable Li plating/striping even after 1000 h at a high current density (5 mA cm^?2). Moreover, the Li–S batteries incorporating LNPA separators not only can achieve excellent outstanding cyclic stability at an ultrahigh sulfur loading (7.6 mg cm^?2), but also exhibit impressive electrochemical performance at an elevated temperature (60 °C). The rational design of the LNPA separator presents new insights to develop high‐performance Li–S batteries.     

Robust,Ultra‐Tough Flexible Cathodes for High‐Energy Li–S Batteries

Sulfur cathodes have become appealing for rechargeable batteries because of their high theoretical capacity (1675 mA h g^?1). However, the conventional cathode configuration borrowed from lithium‐ion batteries may not allow the pure sulfur cathode to put its unique materials chemistry to good use. The solid_(sulfur)–liquid_{(polysulfides)}–solid_(sulfides) phase transitions generate polysulfide intermediates that are soluble in the commonly used organic solvents in Li–S cells. The resulting severe polysulfide diffusion and the irreversible active‐material loss have been hampering the development of Li–S batteries for years. The present study presents a robust, ultra‐tough, flexible cathode with the active‐material fillings encapsulated between two buckypapers (B), designated as buckypaper/sulfur/buckypaper (B/S/B) cathodes, that suppresses the irreversible polysulfide diffusion to the anode and offers excellent electrochemical reversibility with a low capacity fade rate of 0.06% per cycle after 400 cycles. Engineering enhancements demonstrate that the B/S/B cathodes represent a facile approach for the development of high‐performance sulfur electrodes with a high areal capacity of 5.1 mA h cm^?2, which increases further to approach 7 mA h cm^?2 on coupling with carbon‐coated separators.     

A Praline‐Like Flexible Interlayer with Highly Mounted Polysulfide Anchors for Lithium–Sulfur Batteries

The development of lithium–sulfur (Li–S) batteries is dogged by the rapid capacity decay arising from polysulfide dissolution and diffusion in organic electrolytes. To solve this critical issue, a praline‐like flexible interlayer consisting of high‐loading titanium oxide (TiO₂) nanoparticles and relatively long carbon nanofibers is fabricated. TiO₂ nanoparticles with a size gradient occupy both the external and internal of carbon fiber and serve as anchors that allow the chemical adsorption of polysulfides through a conductive nanoarchitecture. The porous conductive carbon backbone helps in the physical absorption of polysulfides and provides redox reaction sites to allow the polysulfides to be reused. More importantly, it offers enough mechanical strength to support a high load TiO₂ nanoparticle (79 wt%) that maximizes their chemical role, and can accommodate the large volume changes. Significant enhancement in cycle stability and rate capability is achieved for a readily available sulfur/multi‐walled carbon nanotube composite cathode simply by incorporating this hierarchically nanostructured interlayer. The design and synthesis of interlayers by in situ integration of metal oxides and carbon fibers via a simple route offers the potential to advance Li–S batteries for practical applications in the future.     

Self‐Supported and Flexible Sulfur Cathode Enabled via Synergistic Confinement for High‐Energy‐Density Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have attracted much attention in the field of electrochemical energy storage due to their high energy density and low cost. However, the “shuttle effect” of the sulfur cathode, resulting in poor cyclic performance, is a big barrier for the development of Li–S batteries. Herein, a novel sulfur cathode integrating sulfur, flexible carbon cloth, and metal–organic framework (MOF)‐derived N‐doped carbon nanoarrays with embedded CoP (CC@CoP/C) is designed. These unique flexible nanoarrays with embedded polar CoP nanoparticles not only offer enough voids for volume expansion to maintain the structural stability during the electrochemical process, but also promote the physical encapsulation and chemical entrapment of all sulfur species. Such designed CC@CoP/C cathodes with synergistic confinement (physical adsorption and chemical interactions) for soluble intermediate lithium polysulfides possess high sulfur loadings (as high as 4.17 mg cm^–2) and exhibit large specific capacities at different C‐rates. Specially, an outstanding long‐term cycling performance can be reached. For example, an ultralow decay of 0.016% per cycle during the whole 600 cycles at a high current density of 2C is displayed. The current work provides a promising design strategy for high‐energy‐density Li–S batteries.     

Facile Formation of a Solid Electrolyte Interface as a Smart Blocking Layer for High‐Stability Sulfur Cathode

The practical application of lithium–sulfur batteries (LSBs) is hindered by their poor cycle life, which stems mainly from the “redox shuttle reactions” of dissolved polysulfides. To develop a high‐performance cathode for LSBs, encapsulation of polysulfides with a blocking layer is potentially straightforward. Herein, a novel strategy is reported encapsulate sulfur and the electrolyte together in porous carbon spheres by using a solid electrolyte interface (SEI) that can selectively sieve Li⁺ ions while efficiently avoiding polysulfide accumulation and suppressing undesired polysulfide migration. This strategy is simple, straightforward, and effective. The carbon/sulfur cathode only needs to be cycled a few times within a voltage window of 0.3–1.0 V to form such a smart SEI, allowing the resulting cathode to exhibit superior stability extending 600 cycles. This strategy can be combined with other existing advanced sulfur cathode designs to improve the overall performance of LSBs.     

Superhierarchical Cobalt‐Embedded Nitrogen‐Doped Porous Carbon Nanosheets as Two‐in‐One Hosts for High‐Performance Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries, based on the redox reaction between elemental sulfur and lithium metal, have attracted great interest because of their inherently high theoretical energy density. However, the severe polysulfide shuttle effect and sluggish reaction kinetics in sulfur cathodes, as well as dendrite growth in lithium‐metal anodes are great obstacles for their practical application. Herein, a two‐in‐one approach with superhierarchical cobalt‐embedded nitrogen‐doped porous carbon nanosheets (Co/N‐PCNSs) as stable hosts for both elemental sulfur and metallic lithium to improve their performance simultaneously is reported. Experimental and theoretical results reveal that stable Co nanoparticles, elaborately encapsulated by N‐doped graphitic carbon, can work synergistically with N heteroatoms to reserve the soluble polysulfides and promote the redox reaction kinetics of sulfur cathodes. Moreover, the high‐surface‐area pore structure and the Co‐enhanced lithiophilic N heteroatoms in Co/N‐PCNSs can regulate metallic lithium plating and successfully suppress lithium dendrite growth in the anodes. As a result, a full lithium–sulfur cell constructed with Co/N‐PCNSs as two‐in‐one hosts demonstrates excellent capacity retention with stable Coulombic efficiency.     

Integrating Conductivity,Immobility, and Catalytic Ability into High-N Carbon/Graphene Sheets as an Effective Sulfur Host

Lithium–sulfur (Li–S) batteries are considered to be one of the most promising candidate systems for next-generation electrochemical energy storage. The major challenge of this system is the polysulfide shuttle, which results in poor cycling efficiency. In this work, a highly N-doped carbon/graphene (NC/G) sheet is designed as a sulfur host, which combines the merits of abundant N active sites and high electrical conductivity to achieve in situ anchoring–conversion of lithium polysulfides (LiPSs). Such a host not only has strong binding with LiPSs but also promotes redox kinetics, which are revealed by both experimental investigations and theoretical studies. The sulfur cathode based on the NC/G host exhibits a high initial capacity of 1380 mA h g⁻¹ and a superior cycle stability with a low capacity decay of 0.037% per cycle within 500 cycles at 2 C. Steady areal capacity with a high sulfur loading (5.6 mg cm⁻²) is also attained even without the addition of LiNO₃ in the electrolyte. This work proposes and illustrates the importance of in situ anchoring–conversion of LiPSs, offering a new strategy to design multifunctional sulfur hosts for high-performance Li–S batteries.     

Cationic Covalent‐Organic Framework as Efficient Redox Motor for High‐Performance Lithium–Sulfur Batteries

The shuttle effect of soluble lithium polysulfides (LiPSs) leads to the rapid decay of sulfur cathode, severely hindering the practical applications of lithium‐sulfur (Li‐S) batteries. To this point, a covalent‐organic framework (COF) with proper cationic sites, which can be utilized as the cathode host of high‐performance Li–S batteries, is reported. The chemical sulfur anchoring within micropores effectively suppresses the dissolution of LiPSs into the electrolyte. During the discharge step, the cationic sites can accept electrons from anode and deliver them to polysulfides to facilitate the polysulfides' disintegration. Meanwhile, the cationic sites can receive electrons from polysulfides and then send them to the anode during the charge process, which promotes the polysulfides oxidation. Thus, both experiments and computational modeling show that the cationic COF can effectively inhibit the shuttle effect of LiPSs and improve the batteries' performances. Compared with electrically neutral COFs, the cationic COF‐based batteries show much better cycling stability even at high current density, for instance, a high specific capacity of 468 mA h g^?1 is retained after 300 cycles at a current density of 4.0 C.     

Compactly Coupled Nitrogen‐Doped Carbon Nanosheets/Molybdenum Phosphide Nanocrystal Hollow Nanospheres as Polysulfide Reservoirs for High‐Performance Lithium–Sulfur Chemistry

Lithium–sulfur (Li–S) batteries have been disclosed as one of the most promising energy storage systems. However, the low utilization of sulfur, the detrimental shuttling behavior of polysulfides, and the sluggish kinetics in electrochemical processes, severely impede their application. Herein, 3D hierarchical nitrogen‐doped carbon nanosheets/molybdenum phosphide nanocrystal hollow nanospheres (MoP@C/N HCSs) are introduced to Li–S batteries via decorating commercial separators to inhibit polysulfides diffusion. It acts not only as a polysulfides immobilizer to provide strong physical trapping and chemical anchoring toward polysulfides, but also as an electrocatalyst to accelerate the kinetics of the polysulfides redox reaction, and to lower the Li₂S nucleation/dissolution interfacial energy barrier and self‐discharge capacity loss in working Li–S batteries, simultaneously. As a result, the Li–S batteries with MoP@C/N HCS‐modified separators show superior rate capability (920 mAh g^?1 at 2 C) and stable cycling life with only 0.04% capacity decay per cycle over 500 cycles at 1 C with nearly 100% Coulombic efficiency. Furthermore, the Li–S battery can achieve a high area capacity of 5.1 mAh cm^?2 with satisfied capacity retention when the cathode loading reaches 5.5 mg cm^?2. This work offers a brand new guidance for rational separator design into the energy chemistry of high‐stable Li–S batteries.     

Dual‐Function,Tunable, Nitrogen‐Doped Carbon for High‐Performance Li Metal–Sulfur Full Cell

Lithium metal–sulfur (Li–S) batteries are attracting broad interest because of their high capacity. However, the batteries experience the polysulfide shuttle effect in cathode and dendrite growth in the Li metal anode. Herein, a bifunctional and tunable mesoporous carbon sphere (MCS) that simultaneously boosts the performance of the sulfur cathode and the Li anode is designed. The MCS homogenizes the flux of Li ions and inhibits the growth of Li dendrites due to its honeycomb structure with high surface area and abundance of nitrogen sites. The Li@MCS cell exhibits a small overpotential of 29 mV and long cycling performance of 350 h under the current density of 1 mA cm^‐2. Upon covering one layer of amorphous carbon on the MCS (CMCS), an individual carbon cage is able to encapsulate sulfur inside and reduce the polysulfide shuttle, which improves the cycling stability of the Li–S battery. As a result, the S@CMCS has a maximum capacity of 411 mAh g^‐1 for 200 cycles at a current density of 3350 mA g^‐1. Based on the excellent performance, the full Li–S cell assembled with Li@MCS anode and S@CMCS cathode shows much higher capacity than a cell assembled with Li@Cu anode and S@CMCS cathode.     

Chemical Immobilization Effect on Lithium Polysulfides for Lithium–Sulfur Batteries

Despite great progress in lithium–sulfur batteries (LSBs), great obstacles still exist to achieve high loading content of sulfur and avoid the loss of active materials due to the dissolution of the intermediate polysulfide products in the electrolyte. Relationships between the intrinsic properties of nanostructured hosts and electrochemical performance of LSBs, especially, the chemical interaction effects on immobilizing polysulfides for LSB cathodes, are discussed in this Review. Moreover, the principle of rational microstructure design for LSB cathode materials with strong chemical interaction adsorbent effects on polysulfides, such as metallic compounds, metal particles, organic polymers, and heteroatom‐doped carbon, is mainly described. According to the chemical immobilizing mechanism of polysulfide on LSB cathodes, three kinds of chemical immobilizing effects, including the strong chemical affinity between polar host and polar polysulfides, the chemical bonding effect between sulfur and the special function groups/atoms, and the catalytic effect on electrochemical reaction kinetics, are thoroughly reviewed. To improve the electrochemical performance and long cycling life‐cycle stability of LSBs, possible solutions and strategies with respect to the rational design of the microstructure of LSB cathodes are comprehensively analyzed.     

A Combined Ordered Macro‐Mesoporous Architecture Design and Surface Engineering Strategy for High‐Performance Sulfur Immobilizer in Lithium–Sulfur Batteries

The practical application of lithium–sulfur (Li–S) batteries is hindered by the “shuttle” of lithium polysulfides (LiPS) and sluggish Li–S kinetics issues. Herein, a synergistic strategy combining mesoporous architecture design and defect engineering is proposed to synthesize multifunctional defective 3D ordered mesoporous cobalt sulfide (3DOM N‐Co₉S_8?x) to address the shuttling and sluggish reaction kinetics of polysulfide in Li–S batteries. The unique 3DOM design provides abundant voids for sulfur storage and enlarged active interfaces that reduce electron/ion diffusion pathways. Meanwhile, X‐ray absorption spectroscopy shows that the surface defect engineering tunes the CoS₄ tetrahedra to CoS₆ octahedra on Co₉S₈, endowing abundance of S vacancies on the Co₉S₈ octahedral sites. The ever‐increasing S vacancies over the course of electrochemical process further promotes the chemical trapping of LiPS and its conversion kinetics, rendering fast and durable Li–S chemistry. Benefiting from these features, the as‐developed 3DOM N‐Co₉S_8?x/S cathode delivers high areal capacity, superb rate capability, and excellent cyclic stability with ultralow capacity fading rate under raised sulfur loading and low electrolyte content. This design strategy promotes the development of practically viable Li–S batteries and sheds lights on the material engineering in related energy storage application.     

Single Nickel Atoms on Nitrogen‐Doped Graphene Enabling Enhanced Kinetics of Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have arousing interest because of their high theoretical energy density. However, they often suffer from sluggish conversion of lithium polysulfides (LiPS) during the charge/discharge process. Single nickel (Ni) atoms on nitrogen‐doped graphene (Ni@NG) with Ni–N₄ structure are prepared and introduced to modify the separators of Li–S batteries. The oxidized Ni sites of the Ni–N₄ structure act as polysulfide traps, efficiently accommodating polysulfide ion electrons by forming strong S_x ^2????Ni? N bonding. Additionally, charge transfer between the LiPS and oxidized Ni sites endows the LiPS on Ni@NG with low free energy and decomposition energy barrier in an electrochemical process, accelerating the kinetic conversion of LiPS during the charge/discharge process. Furthermore, the large binding energy of LiPS on Ni@NG also shows its ability to immobilize the LiPS and further suppresses the undesirable shuttle effect. Therefore, a Li–S battery based on a Ni@NG modified separator exhibits excellent rate performance and stable cycling life with only 0.06% capacity decay per cycle. It affords fresh insights for developing single‐atom catalysts to accelerate the kinetic conversion of LiPS for highly stable Li–S batteries.     

Novel Non‐Carbon Sulfur Hosts Based on Strong Chemisorption for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are considered as promising candidates for energy storage systems owing to their high theoretical capacity and high energy density. The application of Li–S batteries is hindered by several obstacles, however, including the shuttle effect, poor electrical conductivity, and the severe volume expansion of sulfur. The traditional method is to integrate sulfur with carbon materials. But the interaction between polysulfide intermediates and carbon is only weak physical adsorption, which easily leads to the escape of species from the framework (shuttle effect) of the material causing capacity loss. Recently, however, there has been a trend for the introduction of novel non‐carbon materials as sulfur hosts based on the strong chemisorption. This review highlights recent research progress on novel non‐carbon sulfur hosts based on strong chemisorption, in Li–S batteries. In comparison with carbon‐based sulfur hosts, most non‐carbon sulfur hosts have been demonstrated to be polar host materials that could efficiently adsorb polysulfide via strong chemisorption, mitigating their dissolution. The intrinsic mechanism associated with the role of non‐carbon‐based host materials in improving the performance of Li–S batteries is discussed.     

3D Printing of a V8C7–VO2 Bifunctional Scaffold as an Effective Polysulfide Immobilizer and Lithium Stabilizer for Li–S Batteries

Lithium–sulfur (Li–S) batteries have heretofore attracted tremendous interest due to low cost and high energy density. In this realm, both the severe shuttling of polysulfide and the uncontrollable growth of dendritic lithium have greatly hindered their commercial viability. Recent years have witnessed the rapid development of rational approaches to simultaneously regulate polysulfide behaviors and restrain lithium dendritic growth. Nevertheless, the major obstacles for high-performance Li–S batteries still lie in little knowledge of bifunctional material candidates and inadequate explorations of advanced technologies for customizable devices. Herein, a “two-in-one” strategy is put forward to elaborate V₈C₇–VO₂ heterostructure scaffolds via the 3D printing (3DP) technique as dual-effective polysulfide immobilizer and lithium dendrite inhibitor for Li–S batteries. A thus-derived 3DP-V₈C₇–VO₂/S electrode demostrates excellent rate capability (643.5 mAh g⁻¹ at 6.0 C) and favorable cycling stability (a capacity decay of 0.061% per cycle at 4.0 C after 900 cycles). Importantly, the integrated Li–S battery harnessing both 3DP hosts realizes high areal capacity under high sulfur loadings (7.36 mAh cm⁻² at a sulfur loading of 9.2 mg cm⁻²). This work offers insight into solving the concurrent challenges for both S cathode and Li anode throughout 3DP.     

Multifunctional Interlayer Based on Molybdenum Diphosphide Catalyst and Carbon Nanotube Film for Lithium–Sulfur Batteries

A multifunctional interlayer, composed of molybdenum diphosphide (MoP₂) nanoparticles and a carbon nanotube (CNT) film, is introduced into a lithium–sulfur (Li–S) battery system to suppress polysulfide migration. Molybdenum diphosphide acts as the catalyst and can capture polysulfides and improve the polysulfide conversion activity during the discharge/charge processes. The CNT film acts as a conductive skeleton to support the MoP₂ nanoparticles and to ensure their uniform distribution. The CNT film physically hinders polysulfide migration, acts as a current collector, and provides abundant electron pathways. The Li–S battery containing the multifunctional MoP₂/CNT interlayer exhibits excellent electrochemical performance. It delivers a reversible specific capacity of 905 mA h g^?1 over 100 cycles at 0.2 C, with a capacity decay of 0.152% per cycle. These results suggest the introduction of the multifunctional CNT/MoP₂ interlayer as an effective and practical method for producing high‐performance Li–S batteries.     

A Dual‐Function Na2SO4 Template Directed Formation of Cathode Materials with a High Content of Sulfur Nanodots for Lithium–Sulfur Batteries

The sulfur content in carbon–sulfur hybrid using the melt‐diffusion method is normally lower than 70 wt%, which greatly decreases the energy density of the cathode in lithium–sulfur (Li‐S) batteries. Here, a scalable method inspired by the commercialized production of Na₂S is used to prepare a hierarchical porous carbon–sulfur hybrid (denoted HPC‐S) with high sulfur content (≈85 wt%). The HPC‐S is characterized by the structure of sulfur nanodots naturally embedded in a 3D carbon network. The strategy uses Na₂SO₄ as the starting material, which serves not only as the sulfur precursor but also as a salt template for the formation of the 3D carbon network. The HPC‐S cathode with such a high sulfur content shows excellent rate performance and cycling stability in Li–S batteries because of the sulfur nanoparticles, the unique carbon framework, and the strong interaction between them. The production method can also be readily scaled up and used in practical Li–S battery applications.     

TiO2 Feather Duster as Effective Polysulfides Restrictor for Enhanced Electrochemical Kinetics in Lithium–Sulfur Batteries

The rechargeable lithium–sulfur battery is recognized as a promising candidate for electrochemical energy storage system because of their exceptional advance in energy density. However, the fast capacity decay of sulfur cathode caused by polysulfide dissolution and low specific capacity caused by poor electrical conductivity still impede the further development of lithium–sulfur battery. To address above issues, this study reports the synthesis of feather duster‐like TiO₂ architecture by in situ growth of TiO₂ nanowires on carbon cloth and further evaluates as sulfur host material. The strong chemical binding interaction between the polysulfides and TiO₂ feather duster efficiently restrains the shuttle effect, leading to enhanced electrochemical kinetics. Besides, the in situ grown TiO₂ NWs array also supply high surface for sulfur‐loading and fast path for electron transfer and ion diffusion. As results, the novel CC/TiO₂/S composite cathode exhibits a high capacity of 608 mA h g^?1 at 1.0 C after 700 cycles corresponding to capacity decay as low as 0.045% per cycle with excellent Coulombic efficiency higher than 99.5%.