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Catalysis is crucial to improve redox kinetics in lithium–sulfur (Li–S) batteries. However, conventional catalysts that consist of a single metal element are incapable of accelerating stepwise sulfur redox reactions which involve 16‐electron transfer and multiple Li2Sn (n = 2–8) intermediate species. To enable fast kinetics of Li–S batteries, it is proposed to use high‐entropy alloy (HEA) nanocatalysts, which are demonstrated effective to adsorb lithium polysulfides and accelerate their redox kinetics. The incorporation of multiple elements (Co, Ni, Fe, Pd, and V) within HEAs greatly enhances the catalytically active sites, which not only improves the rate capability, but also elevates the cycling stability of the assembled batteries. Consequently, HEA‐catalyzed Li–S batteries achieve a high capacity up to 1364 mAh g−1 at 0.1 C and experience only a slight capacity fading rate of 0.054% per cycle over 1000 cycles at 2 C, while the assembled pouch cell achieves a high specific capacity of 1192 mAh g−1. The superior performance of Li–S batteries demonstrates the effectiveness of the HEA catalysts with maximized synergistic effect for accelerating S conversion reactions, which opens a way to catalytically improving stepwise electrochemical conversion reactions. [ABSTRACT FROM AUTHOR]

Electrocatalysts can optimize the sulfur/sulfide reaction kinetics in Li–S batteries to compete with the loss of lithium polysulfides (LiPSs) caused by the shuttling effect. However, the design rationale of electrocatalysts to drive roundtrip sulfur/sulfide conversion is lacking. Here, pairing Lewis acidic and Lewis basic active sites to reach collective adsorption of LiPSs and simultaneous activation of electrophiles and nucleophiles in LiPSs is proposed. This concept is validated by doping polyaniline with protonated metatungstate anions, which enables reduced activation energies for both sulfur reduction reaction and sulfide oxidation reaction and results in significantly improved kinetics. Such electrocatalysts enable a Li–S battery to reach a low capacity‐decay rate of 0.029% per cycle for 1000 cycles. This work would offer insights into battery technologies where sulfur electrocatalysis will play pivotal roles. [ABSTRACT FROM AUTHOR]

The gelation of MXene promises to assemble a 3D conductive and catalytic monolith for various applications. However, controllable assembly and function customization are still challenging. Here, with a "killing two birds with one stone" initiator (metal halide, typically ZnI2), the controllable gelation of MXene is enabled, which produces a sulfur host that stabilizes not only the cathode but also the lithium metal anode for lithium‐sulfur batteries. Zn2+ cations trigger the gelation and act as linkers between MXene nanosheets (NSs), while the iodine anions as spacers avoid the NSs restacking, forming a monolith with a well‐tunable 3D structure. As a sulfur host, the formed 3D monolith with adsorptive Zn─O sites and highly accessible surface greatly enhances the sulfur redox kinetics, effectively suppressing the shuttling and sulfur loss. At the same time, iodine anions are released into the electrolyte as additives eliminating dead Li for the anode in cycling. Thus, the assembled battery shows high Coulombic efficiency (∼above 99%, even under high sulfur loading: 6.6 mg cm−2) and long cycling stability. Under the practical condition (E/S ratio: 5 µL mgs−1, sulfur loading: 5 mg cm−2), high capacity retention of >70% for 200 cycles is achieved. [ABSTRACT FROM AUTHOR]

Carbon materials are the key hosts for the sulfur cathode to improve the conductivity and confine the lithium polysulfides (LiPSs) in lithium–sulfur batteries (LSBs), owing to their high electronic conductivity and strong confinement effect. However, physical or chemical trapping methods have limitations in preventing the dissolution and accumulation of LiPSs in the electrolyte. Catalysis has emerged as a fundamental solution to accelerate the sluggish redox kinetics, and carbon materials acting as catalyst supports or direct catalysts significantly impact the reaction efficiency. Herein, the roles of carbon in the catalysis of LSBs are systematically discussed, focusing on the influence of surface area, pore structure, and surface chemistry on sulfur conversion. Then, two modification strategies, vacancy defects and heteroatom doping, that endow carbon with catalytic activity are summarized. Finally, the remaining challenges and solutions are outlined in terms of the preparation and characterization of the functional carbon in LSBs. This perspective provides essential insights and guidance for the rational design of carbon‐based catalysts in LSBs. [ABSTRACT FROM AUTHOR]

The polysulfide shuttling and electrode structure destruction caused by heterogeneous conversion reactions are the fundamental causes of the poor reversibility of high‐energy‐density lithium–sulfur (Li–S) batteries. The most direct manifestation is the unsatisfactory low Coulombic efficiency (CE). Herein the importance of CE in evaluating Li–S batteries is highlighted and a remedy is presented for such low efficiencies by in situ coating lithium sulfide (Li2S), as the cathode, with polymerizable electrolyte additives, where trithiocyanuric acid trilithium salt (TTCA‐Li) is employed for a typical demonstration. The involved reaction catalytically decreases the initial overpotential of Li2S, and the produced coating confines the shuttling of lithium polysulfides, thus inhibiting the redistribution of sulfur species and active sulfur loss upon cycling. The prototype full cell where the coated Li2S cathode couples with the Li anode has an extremely high CE of over 99.5%, while, in a Li‐free cell, the Li2S cathode well matches the lithiated silicon anode in a low N/P ratio of 1.2. This approach shows its practicality and generality through a pouch cell demonstration with a practically high Li2S loading and the extension to elemental sulfur‐based batteries by injecting the TTCA‐Li additives into cycling cells. [ABSTRACT FROM AUTHOR]

The sluggish kinetics of the sulfur evolution reaction (SER) that occur because of the high oxidation barrier of Li2S causes low sulfur utilization and the poor rate performance of lithium–sulfur batteries. However, the design of the catalysts to solve this problem is still hard to achieve because it is difficult to precisely correlate the catalytic oxidation ability with the electronic structure. Here, a layer transition metal oxide, NaxTi0.5Co0.5O2, is used as a model catalyst to probe such a correlation because it has a tunable electronic structure and good stability in the working potential window of Li–S batteries. By removing Na+, a partial phase change gradually increases the concentration of Co active sites while decreasing the work function with an upshift of the Fermi level, accelerating charge transfer on the catalyst surface and therefore improving its catalytic oxidation activity of Li2S. In particular, Na0.7Ti0.5Co0.5O2 with two‐phases coexisting effectively lowers the activation potential of Li2S, leading to minimum polarization and excellent rate performance, and even at 5.0 C, the assembled cell has a high capacity of 615 mAh g−1. This study indicates a way to optimize the electronic structure to enhance the SER, which is important for promoting the practical use of Li–S batteries. [ABSTRACT FROM AUTHOR]

Lithium sulfide (Li2S) is a promising cathode for a practical lithium‐sulfur battery as it can be coupled with various safe lithium‐free anodes. However, the high activation potential (>3.5 V) together with the shuttling of lithium polysulfides (LiPSs) bottleneck its practical uses. We are trying to present a catalysis solution to solve both problems simultaneously, specially with twinborn heterostructure to shoot off the trouble in interfacial contact between two solids, catalyst and Li2S. As a typical example, a Co9S8/Li2S heterostructure is reported here as a novel self‐catalytic cathode through a co‐recrystallization followed by a one‐step carbothermic conversion. Co9S8 as the catalyst effectively lowers the Li2S activation potential (<2.4 V) due to fully integrated and contacted interfaces and consistently promotes the conversion of LiPSs to suppress the shuttling. The obtained freestanding cathode of Co9S8/Li2S heterostructures encapsulated in three‐dimensional graphene shows a high capacity, reaching 92.6% of Li2S theoretical capacity, high rate performance (739 mAh g−1 at 2 C), and a low capacity fading (0.039% per cycle at 1 C over 900 cycles). Even under a high Li2S loading of 12 mg cm−2 and a low E/S ratio of 5μLmgLi2S−1, 86% of theoretical capacity can be utilized. [ABSTRACT FROM AUTHOR]

The introduction of sulfur redox electrocatalysts has been considered to be an effective strategy to anchor polysulfides on the cathode and reduce the energy barriers of the reactions. Due to the complexity of sulfur redox reactions (SRR/SER), there exist few descriptors to correlate the catalytic performance and the underlying electronic structures of a given catalyst, which inhibits the development of lithium−sulfur catalysts. In this article, upon mullite oxide SmMn2O5 with various substitutional defects, density functional theory calculations are used to probe the structure–property relationships. It is found that there exists no scaling relationship among the polysulfide binding energies, indicating that the catalytic performance can be tuned by a key intermediate individually. Statistical analysis of various models with different S‐containing intermediates shows that only the Li2S4 binding energy has a linear correlation with the overpotential, showing the dominant role of Li2S4 anchoring to determine the catalytic performance. The electronic structure analysis combined with machine learning further quantitatively verifies the coeffect of charge transfer, electronegativity, and work function on the binding strength of the polysulfide Li2S4. This work provides a theoretical understanding of the complex SRR/SER mechanisms and sheds light on the rational design of a sulfur redox catalyst. [ABSTRACT FROM AUTHOR]

The shuttling of soluble lithium polysulfides (LiPSs) is one of the main bottlenecks to the practical use of Li–S batteries. It is reported that in situ synthesized ultrasmall vanadium nitride nanoparticles dispersed on porous nitrogen‐doped graphene (denoted VN@NG) as a catalytic interlayer solves this problem. The ultrasmall size of VN particles provide ample triple‐phase interfaces (the reactive interfaces among VN nanocatalyst, NG conductive substrate, and electrolyte) for accelerating LiPS conversion and Li2S deposition, which greatly reduces the accumulation of LiPSs in the electrolyte and therefore inhibits the shuttle effect. Their high catalytic activity is confirmed by a reduced activation energy of the Li2S4 conversion step based on temperature‐dependent cyclic voltammetric (CV) measurements and the reduced shuttle effect is detected by in situ Raman spectra. With the VN nanocatalyst, Li–S batteries have an outstanding cycling performance with a low capacity decay rate of 0.075% per cycle over 500 cycles at 2 C. A high capacity retention of 84.5% over 200 cycles at 0.2 C is achieved with a high sulfur loading of 7.3 mg cm−2. [ABSTRACT FROM AUTHOR]

Realizing long cycling stability under a high sulfur loading is an essential requirement for the practical use of lithium–sulfur (Li–S) batteries. Here, a lamellar aerogel composed of Ti3C2Tx MXene/carbon nanotube (CNT) sandwiches is prepared by unidirectional freeze‐drying to boost the cycling stability of high sulfur loading batteries. The produced materials are denoted parallel‐aligned MXene/CNT (PA‐MXene/CNT) due to the unique parallel‐aligned structure. The lamellae of MXene/CNT/MXene sandwich form multiple physical barriers, coupled with chemical trapping and catalytic activity of MXenes, effectively suppressing lithium polysulfide (LiPS) shuttling under high sulfur loading, and more importantly, substantially improving the LiPS confinement ability of 3D hosts free of micro‐ and mesopores. The assembled Li–S battery delivers a high capacity of 712 mAh g−1 with a sulfur loading of 7 mg cm−2, and a superior cycling stability with 0.025% capacity decay per cycle over 800 cycles at 0.5 C. Even with sulfur loading of 10 mg cm−2, a high areal capacity of above 6 mAh cm−2 is obtained after 300 cycles. This work presents a typical example for the rational design of a high sulfur loading host, which is critical for the practical use of Li–S batteries [ABSTRACT FROM AUTHOR]

Lithium-sulfur batteries show great promise among future battery technologies, but their cycle life is mainly restricted by the shuttling effect of soluble lithium polysulfides (LiPSs). The catalytic conversion of LiPSs appears to be a fundamental way of suppressing this. The highly conductive metal nitrides show great potentials as high-performance catalysts, but the presence of a thin surface oxidation layer, which is normal for nanomaterials, restrains the surface electron transfer and catalytic activity. In this study, we demonstrate that the doping of the oxidation layer is an ideal solution to reviving and enhancing the catalytic activity of nitrides. As a proof of concept, sulfur-doping of a titanium nitride (TiN) oxidation layer is presented here, and the Ti S bonds formed are responsible for transmitting electrons from the conductive TiN matrix thus guaranteeing a high catalytic activity. Interfacing of Ti S with Ti O bonds at the atomic level helps realize strong trapping and fast conversion of LiPSs simultaneously. As a result, the specific capacity, rate performance, and cyclic stability are all greatly improved by the interlayer composed of sulfur-doped TiN and graphenes, which indicates a practical avenue for building high performance lithium-sulfur batteries. Image 1 • Sulfur doping of inert surface layer revives catalysis of TiN towards polysulfides. • Ti S interfacing with Ti O bonds results in fast conversion of polysulfide. • Using sulfur-doped TiN in the interlayer prolongs the cycling life of Li S batteries. [ABSTRACT FROM AUTHOR]

Abstract: Due to high energy density, low cost, and nontoxicity, lithium–sulfur (Li–S) batteries are considered as the most promising candidate to satisfy the requirement from the accelerated development of electric vehicles. However, Li–S batteries are subjected to lithium polysulfides (LiPSs) shuttling due to their high dissolution in liquid electrolyte, resulting in low columbic efficiency and poor cycling performance. Moreover, the Li metal as an indispensable anode of Li–S batteries shows serious safety issues derived from the lithium dendrite formation. The replacement of liquid electrolytes with solid‐state electrolytes (SSEs) has been recognized as a fundamental approach to effectively address above problems. In this review, the progress on applying various classes of SSEs including gel, solid‐state polymer, ceramic, and composite electrolytes to solve the issues of Li–S batteries is summarized. The specific capacity of Li–S batteries is effectively improved due to the suppression of LiPSs shuttling by SSEs, while the rate and cycling performance remain relatively poor owing to the limited ionic conductivity and high interfacial resistance. Designing smart electrode/electrolyte integrated architectures, enabling the high ionic transportation pathway and compatible electrode/electrolyte interface, may be an effective way to achieve high performance solid‐state Li–S batteries. [ABSTRACT FROM AUTHOR]

The practical application of lithium-sulfur batteries with a high energy density has been plagued by the poor cycling stability of the sulfur cathode, which is a result of the insulating nature of sulfur and the dissolution of polysulfides. Much work has been done to construct nanostructured or doped carbon as a porous or polar host for promising sulfur cathodes, although restricting the polysulfide shuttle effect by improving the redox reaction kinetics is more attractive. Herein, we present a well-designed strategy by introducing graphitic carbon nitride (g-C3N4) into a three-dimensional hierarchical porous graphene assembly to achieve a synergistic combination of confinement and catalyzation of polysulfides. The porous g-C3N4 nanosheets in situ formed inside the graphene network afford a highly accessible surface to catalyze the transformation of polysulfides, and the hierarchical porous graphene-assembled carbon can function as a conductive network and provide appropriate space for g-C3N4 catalysis in the sulfur cathode. Thus, this hybrid can effectively improve sulfur utilization and block the dissolution of polysulfides, achieving excellent cycling performance for sulfur cathodes in lithium-sulfur batteries. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) hierarchical porous graphene macrostructure coupled with uniformly distributed α-Fe 2 O 3 nano-particles (denoted Fe-PGM) was designed as a sulfur host in a lithium-sulfur battery, and was prepared by a hydrothermal method. In this hybrid structure, the α-Fe 2 O 3 nano-particles are proved to not only strongly interact with the polysulfides, but more importantly, chemically promote their transformation to insoluble species during the charge/discharge process, working as chemical barriers for the shuttling of the lithium polysulfides (LiPSs). Therefore, together with 3D hierarchical porous structure facilitating fast electron/ion transfer, Fe-PGM as a sulfur host in a cathode contributes to a high rate performance (565 mAh g −1 at a high rate of 5 C relative to 1571 mAh g −1 at 0.3 C) as well as long cyclic stability (an ultralow capacity fading rate of 0.049% per cycle over 1000 cycles at the high current rate of 5 C). [ABSTRACT FROM AUTHOR]

A carbon-sulfur hybrid with pomegranate-like core-shell structure, which demonstrates a high rate performance and relatively high cyclic stability, is obtained through carbonization of a carbon precursor in the presence of a sulfur precursor (FeS2) and a following oxidation of FeS2 to sulfur by HNO3. Such a structure effectively protects the sulfur and leaves enough buffer space after Fe3+ removal and, at the same time, has an interconnected conductive network. The capacity of the obtained hybrid is 450 mA h g−1 under the current density of 5 C. This work provides a simple strategy to design and prepare various high-performance carbon-sulfur hybrids for lithium-sulfur batteries. [ABSTRACT FROM AUTHOR]

The detrimental shuttle effect in lithium–sulfur batteries mainly results from the mobility of soluble polysulfide intermediates and their sluggish conversion kinetics. Herein, presented is a multifunctional catalyst with the merits of strong polysulfides adsorption ability, superior polysulfides conversion activity, high specific surface area, and electron conductivity by in situ crafting of the TiO2‐MXene (Ti3C2Tx) heterostructures. The uniformly distributed TiO2 on MXene sheets act as capturing centers to immobilize polysulfides, the hetero‐interface ensures rapid diffusion of anchored polysulfides from TiO2 to MXene, and the oxygen‐terminated MXene surface is endowed with high catalytic activity toward polysulfide conversion. The improved lithium–sulfur batteries deliver 800 mAh g−1 at 2 C and an ultralow capacity decay of 0.028% per cycle over 1000 cycles at 2 C. Even with a high sulfur loading of 5.1 mg cm−2, the capacity retention of 93% after 200 cycles is still maintained. This work sheds new insights into the design of high‐performance catalysts with manipulated chemical components and tailored surface chemistry to regulate polysulfides in Li–S batteries. [ABSTRACT FROM AUTHOR]

A high areal sulfur loading in a carbon-based cathode together with a high cell capacity is key to the design of lithium-sulfur batteries guaranteeing a superior energy density for use. However, a high sulfur loading produced using traditional blade coating techniques results in many technical issues such as sluggish electron/ion transport kinetics and cracking of the electrodes. Here a well designed two-step electrostatic spray deposition (ESD) technique is proposed to prepare a flexible, multilayer carbon electrode with a high sulfur areal loading, in which different carbon components by a careful selection are used for different functions in each layer. The unique "aerosol deposition" in the ESD creates buffer voids in the electrode, ensuring fast infiltration of the electrolyte and releasing the internal stress of the electrode thus avoiding the cracking of thick electrodes. With such an integrated design, the as-prepared cathode exhibits excellent flexibility, a long cyclic stability with a low capacity decay of 0.064% per cycle at 1 C for 500 cycles and a high rate capability of 736 mAh g −1  at 2 C. Moreover, a high areal sulfur loading of 9.4 mg cm −2 with an areal capacity of 6.2 mAh cm −2 at 0.1 C has been achieved. [ABSTRACT FROM AUTHOR]