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

Theoretical evaluation of monolayer MA2Z4 (M = Ti, Zr, or Hf; A = Si or Ge; and Z = P or As) family as promising candidates for lithium-sulfur batteries

Rechargeable lithium-sulfur (Li-S) batteries have been considered as a potential energy storage system due to their high theoretical specific energy. However, their practical commercial application has been hindered by unresolved key issues. One promising approach to overcoming these challenges is the development of anchoring materials with exceptional performance. In this work, we conducted detailed evaluations of twelve types of MA2Z4 (M = Ti, Zr, or Hf; A = Si or Ge; and Z = P or As) monolayers as potential Li-S battery electrodes through first-principles calculations. Our results indicate that these monolayers can effectively immobilize Li2Sn species, preventing them from dissolving into the electrolyte and preserving intact Li2Sn conformations. The high electrical conductivity of these monolayers can be perfectly retained after S8/L2Sn clusters adsorption. Furthermore, the MA2P4 monolayers demonstrate superior catalytic performance for the sulfur reduction reaction (SRR) compared to the MA2As4 counterparts, whereas the MA2As4 monolayers exhibit lower decomposition energy barriers. Our current work indicates that these MA2Z4 monolayers hold significant promise as electrode materials for Li-S batteries.

Entrapment and Reactivation of Polysulfides in Conductive Amphiphilic Covalent Organic Frameworks Enabling Superior Capacity and Stability of Lithium-Sulfur Batteries

Inhibiting the shuttle of polysulfides is of great significance for promoting the practical application of lithium-sulfur batteries (LSBs). Here, an imine-linked covalent organic framework@carbon nanotube (COF@CNT) interlayer composed of triazine and boroxine rings is constructed between the sulfur cathode and the separator for polysulfides reception and reutilization. The introduction of CNT imparts the conductor characteristic to the interlayer attributed to electron tunneling in thin COF shell, and creates a hierarchical porous architecture for accommodating polysulfides. The uniform distribution of amphiphilic adsorption sites in COF microporous structure not only enables efficient entrapment of polysulfides while allowing the penetration of Li+ ions, but also provides a stable electrocatalytic channel for bidirectional conversion of active sulfur to achieve the substantially improved capacity and stability. The interlayer-incorporated LSBs deliver an ultrahigh capacity of 1446 mA g-1 at 0.1C and an ultralow capacity decay rate of 0.019% at 1C over 1500 cycles. Even at an electrolyte/sulfur ratio of 6 µL mg-1, an outstanding capacity of 995 mAh g-1 and capacity retention of 74.1% over 200 cycles at 0.2C are obtained. This work offers a compelling polysulfides entrapment and reactivation strategy for stimulating the study on ultra-stable LSBs.

Ionic Liquid-Assisted Synthesis of Higher Loaded Ni/Fe Dual-Atom Catalysts in N, F, B Codoped Carbon Matrix for Accelerated Sulfur Reduction Reaction

In response to mitigating the severe shuttle effect within lithium-sulfur batteries, single-atom catalysts have emerged as one of the most effective solutions. Here, N, F, B codoped porous hollow carbon nanocages (NFB-NiFe@NC) with high Ni and Fe doping are rationally designed and synthesized using ionic liquids (ILs) as dopants. The introduction of ILs inhibits the growth of zeolitic imidazolate framework-8 (ZIF8), resulting in NFB-ZIF8 precursors with smaller particle sizes, enabling higher loading dual-atom catalysts. Meanwhile, the abundant heteroatoms increase the reactive sites and alter the carbon matrix's nonpolar intrinsic properties, thus enhancing the chemisorption of polysulfides. The synergistic interaction of the heteroatoms with Ni and Fe dual-atoms ultimately promotes the catalytic conversion kinetics of polysulfides. As a result of these beneficial properties, the cells prepared using the NFB-NiFe@NC modified separator exhibit significantly improved performance, including a high initial capacity of 1448 mAh g-1 at 0.2 C. Even at a high S-loading of 7.6 mg cm-2, the ideal area capacity of 8.38 mAh cm-2 can still be maintained at 0.1 C. New insights are provided here for designing highly loaded dual-atom catalysts for application in lithium-sulfur batteries.

Theoretical Design and Study of a Single-Atom Catalyst in Lithium-Sulfur Batteries: Edge-Type FeN4 Active Site Electron Density Redistribution Driven by Heteroatoms

Lithium-sulfur (Li-S) batteries are considered to be the most promising next-generation high energy density storage systems. However, they still face challenges, such as the shuttle effect of lithium polysulfides (LiPSs) and slow sulfur oxidation-reduction kinetics. In this work, heteroatom (P and S)-doped edge-type Fe single-atom catalytic materials (FeN4S2/P2-DG) for sulfur reduction reactions (SRRs) and sulfur oxidation reactions in Li-S batteries are investigated using density functional theory calculations. Theoretical analysis suggests that compared to planar Fe-N4 fragments, the charge density accumulation around edge-type Fe-N4 fragments in S- or P-doped structures is higher. Furthermore, the doping of P or S reduces the electron filling state of Fe_3d orbitals, leading to a decrease in electron occupancy in the antibonding orbitals, which is beneficial for the formation of d-p orbital hybridization, strengthening the anchoring strength of FeN4P2/S2-DG for S8/LiPSs. Specifically, FeN4P1,2-DG showed the lowest free energy barriers (0.57 eV) for SRRs and reduced the dissociation energy barrier of Li2S from 1.85 eV (for planar FeN4-G) to 0.96 eV during the charging process, demonstrating excellent catalytic ability. Additionally, this theoretical study provides further insights into the application of graphene-supported single-atom catalyst materials as anchoring materials for Li-S batteries.

Metal-N Coordination in Lithium-Sulfur Batteries: Inhibiting Catalyst Passivation

Lithium-sulfur (Li-S) batteries exhibit great potential as the next-generation energy storage techniques. Application of catalyst is widely adopted to accelerate the redox kinetics of polysulfide conversion reactions and improve battery performance. Although significant attention has been devoted to seeking new catalysts, the problem of catalyst passivation remains underexplored. Herein, we find that metal-N coordination has a previously overlooked role in preventing the catalyst passivation. In the case of nickel, the Ni catalyst reacts with S8 to produce NiSx compounds on the surface, leading to catalyst passivation and slow the kinetics of LiPSs conversion. In contrast, when Ni is coordinated with N (typically Ni-N4), S8 remains stable on the surface. The Ni-N4 exhibits excellent resistance to passivation and rapid kinetics of LiPSs conversion. Consequently, the sulfur cathode with Ni-N4 exhibits a high rate capability of 604.11 mAh g-1 at 3 C and maintains a low capacity decay rate of 0.046 % per cycle over 1000 cycles at 2 C. Furthermore, preventing S passivation in M-N coordination applies not only to Ni-N4 but also to various coordination numbers and transition metals. This study reveals a new aspect of metal-N coordination in inhibiting catalyst passivation, improving our understanding of catalysts in Li-S batteries.

Natural biomass derived single-atom catalysts for energy and environmental applications

Single atom catalysts (SACs) excel in various chemical processes, including electrocatalysis and industrial chemistry, due to their efficiency. In contrast to chemically synthesized precursors, biomass offers a greener and more cost-effective approach for SACs fabrication. To date, over forty types of SACs have been synthesized using natural sources like starch, cellulose, lignin, hemicellulose, proteins, and chitin. These catalysts incorporate metals such as Fe, Co, Ni, Cu, Zn, Mn, and Pt. This review concentrates on the preparation of SACs from biomass, exploring innovative techniques and their extensive applications in energy conversion and environmental conservation, including but not limited to reactions involving oxygen reduction, oxygen evolution, and hydrogen evolution. It also discusses current challenges and prospective advancements in this domain. This paper updates and expands on the knowledge of SACs derived from biomass, aiming to foster the development of more effective, low-cost catalyst materials from natural sources.

Synergistic Effect of Lactam and Pyridine Nitrogen on Polysulfide Chemisorption and Electrocatalysis in Lithium Sulfur Batteries

Sulfur undergoes various changes, including the formation of negative charge-bearing lithium polysulfides during the operation of Li-S batteries. Dissolution of some of the polysulfides in battery electrolytes is one of the reasons for the poor performance of Li-S batteries. The charge injection into the sulfur and polysulfides from the electrode is also a problem. To address these issues, a small-molecule additive, 3,6-di(pyridin-4-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, was designed and synthesized with carbonyl oxygen atoms and two types of nitrogen. The pyridinic nitrogen increases the electronegativity of the carbonyl oxygen atoms. The pyridinic nitrogen, carbonyl oxygen, and lactam nitrogen provide multiple binding sites concurrently to the polysulfides, which increases the binding efficiency between the additive and polysulfides. A control molecule without the pyridine moiety displayed decreased binding to lithium polysulfides. Furthermore, the band edges of lithium polysulfide and 3,6-di(pyridin-4-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione are commensurate for efficient charge transfer between them, leading to the efficient electrocatalysis of lithium polysulfides. The cyclic voltammogram of the Li-S battery fabricated with 3,6-di(pyridin-4-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione exhibited sharp and well-defined peaks, confirming the formation of Li2Sy (where y varies between one and eight) from S8. These Li-S batteries showed a specific capacity of 950 mA h/g at 0.5 C, with a capacity retention of 70% at the 300th cycle. The pyridine-free control molecule, 3,6-diphenyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, showed relatively poor performance in a Li-S battery.

Two-dimensional phosphorus carbides (β-PC) as highly efficient metal-free electrocatalysts for lithium-sulfur batteries: a first-principles study

Li-S batteries are considered as the next-generation batteries due to their exceptional theoretical capacity. However, their practical application is hampered by the shuttling effects of lithium polysulfides (LiPSs) and the sluggish Li2S decomposition, particularly the slow conversion from Li2S2 to Li2S. Addressing these challenges, the quest for effective catalysts that can accelerate the conversion of LiPSs and enhance the performance of Li-S batteries is crucial. In this study, we explored the electrocatalytic activity of two-dimensional phosphorus carbides (β0-PC and β1-PC) in Li-S batteries based on first-principles calculations. Our findings reveal that these materials demonstrate optimal binding strengths (ranging from 1.09 to 1.83 eV) with long-chain LiPSs, effectively preventing them from dissolving into the electrolyte. Additionally, they show remarkable catalytic activity during the sulfur redox reaction (SRR), with ΔG being only 0.37 eV for β0-PC and 0.13 eV for β1-PC. The low energy barrier induced by β-PC enhances ion migration barrier and significantly expedites the charge/discharge cycles of Li-S batteries. Furthermore, we investigated the conversion dynamics of Li2S2 to Li2S, employing the computational lithium electrode (CLE) model. The excellent performance in these aspects underscores the potential of these materials as electrocatalysts for Li-S batteries, paving the way for advanced high-efficiency energy storage solutions.

Immobilization and Catalytic Conversion of Polysulfide by In-Situ Generated Nickel in Hollow Carbon Fibers for High-Rate Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered promising energy-storage systems because of their high theoretical energy density, low cost, and eco-friendliness. However, problems such as the shuttle effect can result in the loss of active materials, poor cyclability, and rapid capacity degradation. The utilization of a structural configuration that enhances electrochemical performance via dual adsorption-catalysis strategies can overcome the limitations of Li-S batteries. In this study, an integrated interlayer structure, in which hollow carbon fibers (HCFs) were modified with in-situ-generated Ni nanoparticles, was prepared by scalable one-step carbonization. Highly hierarchically porous HCFs act as the carbon skeleton and provide a continuous three-dimensional conductive network that enhances ion/electron diffusion. Ni nanoparticles with superior anchoring and catalytic abilities can prevent the shuttle effect and increase the conversion rate, thereby promoting the electrochemical performance. This synergistic effect resulted in a high capacity retention of 582 mAh g-1 at 1 C after 100 cycles, providing an excellent rate capability of up to 3 C. The novel structure, wherein Ni nanoparticles are embedded in cotton-tissue-derived HCFs, provides a new avenue for enhancing electrochemical performance at high C rates. This results in a low-cost, sustainable, and high-performance hybrid material for the development of practical Li-S batteries.

Atomic-Level Catalyst Coupled with Metal Oxide Heterostructure for Promoting Kinetics of Lithium-Sulfur Batteries

Despite the low competitive cost and high theoretical capacity of lithium-sulfur (Li-S) batteries, their practical application is severely hindered by the lithium polysulfide (LiPS) shuttling and low conversion efficiency. Herein, the electronic structure of hollow Titanium dioxide nanospheres is tunned by single Iron atom dopants that can cooperatively enhance LiPS absorption and facilitate desired redox reaction in practical Li-S batteries, further suppressing the notorious shuttle effect, which is consistent with theoretical calculations and in situ UV/vis investigation. The obtained electrode with massive active sites and lower energy barrier for sulfur conversions exhibits exceptional cycling stability after 500 cycles and high capacity under the sulfur loading of 10.53 mg cm-2. In particular, an Ah-level Li-S pouch cell is fabricated, further demonstrating that the synthetic strategy based on atomic-level design offers a promising route toward practical high-energy-density Li-S batteries.

[2+1] Cycloadditions Modulate the Hydrophobicity of Ni-N4 Single-Atom Catalysts for Efficient CO2 Electroreduction

Microenvironment regulation of M-N4 single-atom catalysts (SACs) is a promising way to tune their catalytic properties toward the electrochemical CO2 reduction reaction. However, strategies that can effectively introduce functional groups around the M-N4 sites through strong covalent bonding and under mild reaction conditions are highly desired. Taking the hydrophilic Ni-N4 SAC as a representative, we report herein a [2+1] cycloaddition reaction between Ni-N4 and in situ generated difluorocarbene (F2C:), and enable the surface fluorocarbonation of Ni-N4, resulting in the formation of a super-hydrophobic Ni-N4-CF2 catalyst. Meanwhile, the mild reaction conditions allow Ni-N4-CF2 to inherit both the electronic and structural configuration of the Ni-N4 sites from Ni-N4. Enhanced electrochemical CO2-to-CO Faradaic efficiency above 98 % is achieved in a wide operating potential window from -0.7 V to -1.3 V over Ni-N4-CF2. In situ spectroelectrochemical studies reveal that a highly hydrophobic microenvironment formed by the -CF2- group repels asymmetric H-bonded water at the electrified interface, inhibiting the hydrogen evolution reaction and promoting CO production. This work highlights the advantages of [2+1] cycloaddition reactions on the covalent modification of N-doped carbon-supported catalysts.

Single Atom Catalysts Based on Earth-Abundant Metals for Energy-Related Applications

Anthropogenic activities related to population growth, economic development, technological advances, and changes in lifestyle and climate patterns result in a continuous increase in energy consumption. At the same time, the rare metal elements frequently deployed as catalysts in energy related processes are not only costly in view of their low natural abundance, but their availability is often further limited due to geopolitical reasons. Thus, electrochemical energy storage and conversion with earth-abundant metals, mainly in the form of single-atom catalysts (SACs), are highly relevant and timely technologies. In this review the application of earth-abundant SACs in electrochemical energy storage and electrocatalytic conversion of chemicals to fuels or products with high energy content is discussed. The oxygen reduction reaction is also appraised, which is primarily harnessed in fuel cell technologies and metal-air batteries. The coordination, active sites, and mechanistic aspects of transition metal SACs are analyzed for two-electron and four-electron reaction pathways. Further, the electrochemical water splitting with SACs toward green hydrogen fuel is discussed in terms of not only hydrogen evolution reaction but also oxygen evolution reaction. Similarly, the production of ammonia as a clean fuel via electrocatalytic nitrogen reduction reaction is portrayed, highlighting the potential of earth-abundant single metal species.

Regulating Sulfur Redox Kinetics by Coupling Photocatalysis for High-Performance Photo-Assisted Lithium-Sulfur Batteries

Challenges such as shuttle effect have hindered the commercialization of lithium-sulfur batteries (LSBs), despite their potential as high-energy-density storage devices. To address these issues, we explore the integration of solar energy into LSBs, creating a photo-assisted lithium-sulfur battery (PA-LSB). The PA-LSB provides a novel and sustainable solution by coupling the photocatalytic effect to accelerate sulfur redox reactions. Herein, a perovskite quantum dot-loaded MOF material serves as a cathode for the PA-LSB, creating built-in electric fields at the micro-interface to extend the lifetime of photo-generated charge carriers. The band structure of the composite material aligns well with the electrochemical reaction potential of lithium-sulfur, enabling precise regulation of polysulfides in the cathode of the PA-LSB system. This is attributed to the selective catalysis of the liquid-solid reaction stage in the lithium-sulfur electrochemical process by photocatalysis. These contribute to the outstanding performance of PA-LSBs, particularly demonstrating a remarkably high reversible capacity of 679 mAh g-1 at 5 C, maintaining stable cycling for 1500 cycles with the capacity decay rate of 0.022 % per cycle. Additionally, the photo-charging capability of the PA-LSB holds the potential to compensate for non-electric energy losses during the energy storage process, contributing to the development of lossless energy storage devices.

Practical four-electron zinc-iodine aqueous batteries enabled by orbital hybridization induced adsorption-catalysis

The successive I-/I0/I+ redox couples in the four-electron zinc-iodine aqueous battery (4eZIB) is plagued by the instability of the electrophilic I+ species, which could either be hydrolyzed or be neutralized by the I3- redox intermediates. We present an adsorption-catalysis approach that effectively suppresses the hydrolysis of ICl species and also provides an enhanced reaction kinetics to surpass the formation of triiodide ions. We elucidate that the improved stability is attributed to the pronounced orbital hybridization between the d orbitals of Fe-N4 moieties (atomic Fe supported on nitrogen doped carbon) and the p orbitals of iodine species (I2 and ICl). Such d-p orbital hybridization leads to enhanced adsorption for iodine species, increased energy barrier for proton detachment from the ICl·HOH intermediate during hydrolysis, and efficient catalysis of the iodine redox reactions with high conversion efficiency. The proposed 4eZIB demonstrates practical areal capacity (>3 mAh cm-2) with a near-unity coulombic efficiency, high energy density of 420 Wh kg-1 (based on cathode mass), and long-term stability (over 10,000 cycles). Even at -20 °C, the battery exhibits stable performance for over 1000 cycles with high iodine utilization ratio.

Ni Single-Atom Bual Catalytic Electrodes for Long Life and High Energy Efficiency Zinc-Iodine Batteries

Zinc-iodine batteries (Zn-I2) are extremely attractive as the safe and cost-effective scalable energy storage system in the stationary applications. However, the inefficient redox kinetics and "shuttling effect" of iodine species result in unsatisfactory energy efficiency and short cycle life, hindering their commercialization. In this work, Ni single atoms highly dispersed on carbon fibers is designed and synthesized as iodine anchoring sites and dual catalysts for Zn-I2 batteries, and successfully inhibit the iodine species shuttling and boost dual reaction kinetics. Theoretical calculations indicate that the reinforced d-p orbital hybridization and charge interaction between Ni single-atoms and iodine species effectively enhance the confinement of iodine species. Ni single-atoms also accelerate the iodine conversion reactions with tailored bonding structure of I─I bonds and reduced energy barrier for the dual conversion of iodine species. Consequently, the high-rate performance (180 mAh g-1 at 3 A g-1), cycling stability (capacity retention of 74% after 5900 cycles) and high energy efficiency (90% at 3 A g-1) are achieved. The work provides an effective strategy for the development of iodine hosts with high catalytic activity for Zn-I2 batteries.

Single-atom catalysts based on C2N for sulfur cathodes in Na-S batteries: a first-principles study

Several major roadblocks, including the "shuttle effect" caused by the dissolved higher-order sodium polysulfides (NaPSs), extremely poor conductivity of sulfur cathodes, and sluggish conversion kinetics of charging-discharging reactions, have hindered the commercialization of sodium-sulfur batteries (NaSBs). In our study, representative C2N-based single-atom catalysts (SACs), TM@C2N (TM = Fe, Ni and V), are proposed to improve the comprehensive performance of NaSBs. Based on first-principles calculations, we first discuss in detail the anchoring behavior of all adsorption systems, TM@C2N/(S8 and NaPSs). The results indicate that compared to pristine C2N, TM@C2N substrates exhibit a stronger capability to capture S8/NaPSs clusters through physical/chemical binding, with V@C2N showing the most outstanding capability ranging from -2.37 to -5.03 eV. The density of states analysis reveals that metallic properties can be well maintained before and after adsorption of polysulfides. More importantly, TM@C2N configurations can greatly reduce the energy barriers of charging and discharging reactions, thereby accelerating the conversion efficiency of NaSBs. It is worth mentioning that V@C2N has lower charge-discharge energy barriers and Na ion migration rates, since the embedded TM atom weakens the strong binding of Na+ in the N6 cavity of C2N. The intrinsic mechanism analysis reveals that the interaction between the d orbitals of V and the p orbitals of S leads to the weakening of Na-S bonds, which can not only effectively inhibit the shuttle effect, but also promote the dissociation of Na2S. Overall, this work not only offers excellent catalytic materials, but also provides vital guidance for designing SACs in NaSBs.

Relay-Type Catalysis by a Dual-Metal Single-Atom System in a Waste Biomass Derivative Host for High-Rate and Durable Li-S Batteries

An environmental-friendly and sustainable carbon-based host is one of the most competitive strategies for achieving high loading and practicality of Li-S batteries. However, the polysulfide conversion reaction kinetics is still limited by the nonuniform or monofunctional catalyst configuration in the carbon host. In this work, we propose a catalysis mode based on "relay-type" co-operation by adjacent dual-metal single atoms for high-rate and durable Li-S batteries. A discarded sericin fabric-derived porous N-doped carbon with a stacked schistose structure is prepared as the high-loading sulfur (84 wt %) host by a facile ionothermal method, which further enables the uniform anchoring of Fe/Co dual-metal single atoms. This multifunctional host enables superior lithiophilic-sulfiphilic and electrocatalytic capabilities contributed by the "relay-type" single-atom modulation effects on different conversion stages of liquid polysulfides and solid Li2S2/Li2S, leading to the suppression of the "shuttle effect", alleviation of nucleation and decomposition barriers of Li2Sx, and acceleration of polysulfide conversion kinetics. The corresponding Li-S batteries exhibit a high specific capacity of 1399.0 mA h g-1, high-rate performance up to 10 C, and excellent cycling stability over 1000 cycles. They can also endure the high sulfur loading of 8.5 mg cm-2 and the lean electrolyte condition and yield an areal capacity as high as 8.6 mA h cm-2. This work evidentially demonstrates the potential of waste biomass reutilization coupled with the design of a single-atom system for practical Li-S batteries with high energy density.

Enhancing Zn2+ Storage Performance by Constructing the Interfaces Between VO2 and Co-N-C Layers

Vanadium oxides have aroused attention as cathode materials in aqueous zinc-ion batteries (AZIBs) due to their low cost and high safety. However, low ion diffusion and vanadium dissolution often lead to capacity decay and deteriorating stability during cycling. Herein, vanadium dioxides (VO2) nanobelts are coated with a single-atom cobalt dispersed N-doped carbon (Co-N-C) layer via a facile calcination strategy to form Co-N-C layer coated VO2 nanobelts (VO2@Co-N-C NBs) for cathodes in AZIBs. Various in-/ex situ characterizations demonstrate the interfaces between VO2 layers and Co-N-C layers can protect the VO2 NBs from collapsing, increase ion diffusion, and enhance the Zn2+ storage performance. Additional density functional theory (DFT) simulations demonstrate that Co─O─V bonds between VO2 and Co-N-C layers can enhance interfacial Zn2+ storage. Moreover, the VO2@Co-N-C NBs provided an ultrahigh capacity (418.7 mAh g-1 at 1 A g-1), outstanding long-term stability (over 8000 cycles at 20 A g-1), and superior rate performance.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

Rechargeable metal-sulfur batteries are considered promising candidates for energy storage due to their high energy density along with high natural abundance and low cost of raw materials. However, they could not yet be practically implemented due to several key challenges: (i) poor conductivity of sulfur and the discharge product metal sulfide, causing sluggish redox kinetics, (ii) polysulfide shuttling, and (iii) parasitic side reactions between the electrolyte and the metal anode. To overcome these obstacles, numerous strategies have been explored, including modifications to the cathode, anode, electrolyte, and binder. In this review, the fundamental principles and challenges of metal-sulfur batteries are first discussed. Second, the latest research on metal-sulfur batteries is presented and discussed, covering their material design, synthesis methods, and electrochemical performances. Third, emerging advanced characterization techniques that reveal the working mechanisms of metal-sulfur batteries are highlighted. Finally, the possible future research directions for the practical applications of metal-sulfur batteries are discussed. This comprehensive review aims to provide experimental strategies and theoretical guidance for designing and understanding the intricacies of metal-sulfur batteries; thus, it can illuminate promising pathways for progressing high-energy-density metal-sulfur battery systems.

Chlorine bridge bond-enabled binuclear copper complex for electrocatalyzing lithium-sulfur reactions

Engineering atom-scale sites are crucial to the mitigation of polysulfide shuttle, promotion of sulfur redox, and regulation of lithium deposition in lithium-sulfur batteries. Herein, a homonuclear copper dual-atom catalyst with a proximal distance of 3.5 Å is developed for lithium-sulfur batteries, wherein two adjacent copper atoms are linked by a pair of symmetrical chlorine bridge bonds. Benefiting from the proximal copper atoms and their unique coordination, the copper dual-atom catalyst with the increased active interface concentration synchronously guide the evolutions of sulfur and lithium species. Such a delicate design breaks through the activity limitation of mononuclear metal center and represents a catalyst concept for lithium-sulfur battery realm. Therefore, a remarkable areal capacity of 7.8 mA h cm-2 is achieved under the scenario of sulfur content of 60 wt.%, mass loading of 7.7 mg cm-2 and electrolyte dosage of 4.8 μL mg-1.

Preparation of highly dispersed Ni single-atom doped ultrathin g-C3N4 nanosheets by metal vapor exfoliation for efficient photocatalytic CO2 reduction

Single-atom photocatalysts can modulate the utilization of photons and facilitate the migration of photogenerated carriers. However, the preparation of single-atom uniformly doped photocatalysts is still a challenging topic. Herein, we propose the preparation of Ni single-atom doped g-C3N4 photocatalysts by metal vapor exfoliation. The Ni vapor produced by calcining nickel foam at high temperature accumulates in between g-C3N4 layers and poses a certain vapor pressure to destroy the interlayer van der Waals forces of g-C3N4. Individual metal atoms are doped into the structure while exfoliating g-C3N4 into nanosheets by metal vapor. Upon optimization of Ni content, the Ni single atom doped g-C3N4 nanosheets with 2.81 wt% Ni exhibits the highest CO2 reduction performance in the absence of sacrificial agents. The generation rates of CO and CH4 are 19.85 and 1.73 μmol g-1h-1, respectively. The improved photocatalytic performance is attributed to the anchoring Ni of single atoms on g-C3N4 nanosheets, which increases both carrier separation efficiency and reaction sites. This work provides insight into the design of photocatalysts with highly dispersed single-atom.

Tandem Catalysis inside Double-Shelled Nanocages with Separated and Tunable Atomic Catalyst Sites for High Performance Lithium-Sulfur Batteries

Single-atomic catalysts are effective in mitigating the shuttling effect and slow redox kinetics of lithium polysulfides (LiPSs) in lithium-sulfur (Li-S) batteries, but their ideal performance has yet to be achieved due to the multi-step conversion of LiPSs requiring multifunctional active sites for tandem catalysis. Here double-shelled nano-cages (DSNCs) have been developed to address this challenge, featuring separated and tunable single-atom sites as nano reactors that trigger tandem catalysis and promote the efficient electrochemical conversion of LiPSs. This enables high capacity and durable Li-S batteries. The DSNCs, with inner Co-N4 and outer Zn-N4 sites (S/CoNC@ZnNC DSNCs), exhibit a high specific capacity of 1186 mAh g-1 at 1 C, along with a low capacity fading rate of 0.063% per cycle over 500 cycles. Even with a high sulfur loading (4.2 mg cm-2) and a low E/S ratio (6 µL mg-1), the cell displays excellent cycling stability. Moreover, the Li-S pouch cells are capable of stable cycling for more than 160 cycles. These results demonstrate the feasibility of driving successive sulfur conversion reactions with separated active sites, and are expected to inspire further catalyst design for high performance Li-S batteries.

Regulating the coordination environment of single atom catalysts anchored on C3N monolayer for Li-S battery by first-principles calculations

Owing to the extremely high theoretical specific capacity and energy density, the catalytic materials of lithium-sulfur (Li-S) batteries are widely explored. The "shuttle effect", poor electrode conductivity, and slow charge-discharge reaction dynamics are some of the key issues that have seriously hampered their commercialization process. Herein, based on the density-functional-theory (DFT), the catalytic performances of a series of single-atom catalysts (SACs) designed by regulating the N-content around coordination center in C3N (TM@N2C2/N3C/N4-C3N (TM = Ti, V, Fe, Co, Ni)), are systematically analyzed and evaluated. Among all the constructed SACs, Ti-centered configurations with fewer d electrons, especially for the Ti@N2C2-C3N, have the remarkable catalytic effect in improving the electron conductivity, trapping soluble polysulfides and accelerating the redox reaction. The in-depth mechanism indicates that the interaction between d orbital of Ti, mainly the splitting [Formula: see text] , and p orbital of S is the key factor for achieving high-effective adsorption. More importantly, the integral value of crystal orbital Hamiltonian population (ICOHP) of the Li-S bond in the adsorbed Li2S can serve as an excellent descriptor for evaluating the overall catalytic ability of substrates. Our work has vital guiding significance for designing high-performance SACs of Li-S batteries.

Phosphorous-Based Heterostructure for the Effective Catalysis of Polysulfide Reactions with Phase Changes in High-Sulfur-Loading Lithium-Sulfur Batteries

High sulfur loading and long cycle life are the design targets of commercializable lithium-sulfur (Li-S) batteries. The sulfur electrochemical reactions from Li2 S4 to Li2 S, which account for 75% of the battery's theoretical capacity, involve liquid-to-solid and solid-to-solid phase changes in all Li-S battery electrolytes in use today. These are kinetically hindered processes that are exacerbated by a high sulfur loading. In this study, it is observed that an in situ grown bimetallic phosphide/black phosphorus (NiCoP/BP) heterostructure can effectively catalyze the Li2 S4 to Li2 S reactions to increase the sulfur utilization at high sulfur loadings. The NiCoP/BP heterostructure is a good polysulfide adsorber, and the electric field prevailing at the Mott-Schottky junction of the heterostructure can facilitate charge transfer in the Li2 S4 to Li2 S2 liquid-to-solid reaction and Li+ diffusion in the Li2 S2 to Li2 S solid-state reaction. Consequently, a sulfur cathode with the NiCoP/BP catalyst can deliver a specific capacity of 830 mAh g-1 at the sulfur loading of 6 mg cm-2 for 500 cycles at the 0.5 C rate. High sulfur utilization is also possible at a higher sulfur loading of 8 mg cm-2 for 440 cycles at the 1 C rate.

The heterointerface effect to boost the catalytic performance of single atom catalysts for sulfur conversion in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are considered as one of the promising next-generation energy storage devices due to their characteristics of high energy density and low cost. However, the shuttle effect and sluggish conversion of lithium polysulfide (LiPs) have hindered their commercial applications. To address these issues, in our previous works, we have screened several highly efficient single atom catalysts (SACs) (MN4@G, M = V, Mo and W) with atomically dispersed transition metal atoms supported by nitrogen doped graphene based on high throughput calculations. Nevertheless, they still suffer from low loading of metal centers and unsatisfactory capability for accelerating the reaction kinetics. To tackle such problems, based on first-principles calculations, we systematically investigated the heterointerface effect on the catalytic performance of such three MN4@G toward sulfur conversion upon forming heterostructures with 5 typical two-dimensional materials of TiS2, C3N4, BN, graphene and reduced graphene oxide. Guided by efficient descriptors proposed in our previous work, we screened VN4@G/TiS2, MoN4@G/TiS2 and WN4@G/TiS2 possessing low Li2S decomposition barriers of 0.54, 0.44 and 0.41 eV, respectively. They also possess enhanced capabilities for catalyzing the sulfur reduction reaction as well as stabilizing soluble LiPs. More interestingly, the heterointerface can enhance the capability of the carbon atoms far away from the metal centers for trapping LiPs. This work shows that introducing a heterointerface is a promising strategy to boost the performance of SACs in Li-S batteries.

Kinetic Promoters for Sulfur Cathodes in Lithium-Sulfur Batteries

ConspectusLithium-sulfur (Li-S) batteries have attracted worldwide attention as promising next-generation rechargeable batteries due to their high theoretical energy density of 2600 Wh kg-1. The actual energy density of Li-S batteries at the pouch cell level has significantly exceeded that of state-of-the-art Li-ion batteries. However, the overall performances of Li-S batteries under practical working conditions are limited by the sluggish conversion kinetics of the sulfur cathodes. To overcome the above challenge, various kinetic promotion strategies have been proposed to accelerate the multiphase and multi-electron cathodic redox reactions between sulfur, lithium polysulfides (LiPSs), and lithium sulfide. Nowadays, kinetic promoters have been massively employed in sulfur cathodes to achieve Li-S batteries with high energy densities, high rates, and long lifespans. A comprehensive and timely summary of cutting-edge kinetic promoters for sulfur cathodes is of great essence to afford an in-depth understanding of the unique Li-S electrochemistry.In this Account, we outline the recent efforts on the design of sulfur cathode kinetic promoters for advanced Li-S batteries. The latest progress is discussed in detail regarding heterogeneous, homogeneous, and semi-immobilized kinetic promoters. Heterogeneous promoters, representatively known as electrocatalysts, function mainly by reducing the energy barriers of the interfacial electrochemical reactions. The working mechanism, activity regulation strategies, and reconstitution/deactivation processes of the heterogeneous promoters are reviewed to provide guiding principles for rational design. In comparison, homogeneous promoters are able to fully contact with the reaction interfaces and regulate the electron/ion-inaccessible reactants in working Li-S batteries. Redox mediators and redox comediators are typical homogeneous promoters. The former establishes extra chemical reaction pathways to circumvent the originally sluggish steps and boost the overall kinetics, while the latter fundamentally modifies the LiPS molecules to enhance their redox kinetics. For semi-immobilized promoters, the active units are generally anchored on the cathode substrate through flexible chains with mobile characteristics. Such a design endows the promoter with both heterogeneous and homogeneous characteristics to comprehensively regulate the multiphase sulfur redox reactions involving both mobile and immobile reactants.Overall, this Account summarizes the fundamental electrochemistry, design principles, and practical promotion effects of the various kinetic promoters used for the sulfur cathodes in Li-S batteries. We believe that this Account will provide an in-depth and cutting-edge understanding of the unique sulfur electrochemistry, thereby providing guidance for further development of high-performance Li-S batteries and analogous rechargeable battery systems.

Origin of Phase Engineering CoTe2 Alloy Toward Kinetics-Reinforced and Dendrite-Free Lithium-Sulfur Batteries

Slow electrochemistry kinetics and dendrite growth are major obstacles for lithium-sulfur (Li-S) batteries. The investigations over the polymorph effect require more endeavors to further access the related catalyst design principles. Herein, the systematic evaluation of CoTe2 alloy with two polymorphs regarding sulfur reduction reaction (SRR) and lithium plating/stripping is reported. As disclosed by theoretical calculations and electrochemical measurements, the orthorhombic (o-) and hexagonal (h-) CoTe2 make a substantial difference. The reactivity origin of the CoTe2 polymorphs is explored. The higher position of d-band centers for the Co atoms on the o-CoTe2 leads to a higher displacement of the antibonding state; the lower antibonding state occupancy, the more effective the interaction with the sulfide moieties and lithium. Hence, o-CoTe2 annihilates h-CoTe2 and exhibits better catalysis and more uniform lithium deposition, consolidated by excellent performance of full cell made of o-CoTe2 . It keeps stable charging/discharging for 800 cycles at 0.5 C with only 0.055% capacity decay per cycle and even achieves an areal capacity of 6.5 mAh cm-2 at lean electrolyte and high sulfur loading of 6.4 mg cm-2 . This work establishes the mechanistic perspective about the catalysts in Li-S batteries and provides new insight into the unified solution.

Anion-doped polypyrrole three-dimensional framework enables adsorption and conversion in lithium-sulfur batteries

Inhibiting the shuttle effect and propelling polysulfide conversion by introducing a suitable sulfur container has been proven as a promising strategy to enhance the cycle life of lithium-sulfur (Li-S) batteries. Here, a unique three-dimensional (3D) inter-connected framework assembled with SO42--doped polypyrrole (PPy-SO4) nanowires is proposed. The doping SO42- anion in a polymer skeleton could confine lithium polysulfides (LiPSs) by polar-polar interaction to inhibit the shuttle effect and enhance the conductivity of PPy to accelerate polysulfide conversion. Moreover, the electrostatic coupling between SO42- anion and Li+, as well as between -N+- and Sn2-, at polypyrrole /electrolyte interface can effectively regulate the redox kinetics of polysulfide. Besides, the inter-connected framework creates a large contact surface for sulfur and high-flux paths for electron transport. Consequently, the Li-S batteries assembled with PPy-SO4/S cathode exhibit a stable capacity of 501 mAh g-1 after 350 cycles at 1C, showing a low decay rate of 0.09% per cycle. Notably, the efficiency of the anion doping strategy is further verified in the pouch cell, realizing a capacity of 480 mAh g-1 after 250 cycles. This work illustrates that anion doping with rational structural design is a feasible solution to boost the electrochemical performance of Li-S batteries.

Surface design for high ion flux separator in lithium-sulfur batteries

Addressing the shuttle effect is a critical challenge in realizing practical applications of lithium-sulfur batteries. One promising avenue refers to the surface modification of separators, transitioning them from closed to open structures. In the current investigation, a high ion flux separator was devised by means of MnO2 self-assembly onto a Porous Polypropylene (PP) separator, subsequently coupling it with biochar. The separator exhibited favorable ion and electronic conductivity. Moreover, it adeptly captured and transformed polysulfides into Li2S2/Li2S, cyclically curbing the mobility of Polysulfide lithium (LiPSs). In addition, this augmentation in the kinetic conversion of LiPSs during the electrochemical process translated into an impressive discharge specific capacity and area capacity of 939 mAh/g and 4 mAh cm-2, respectively. Moreover, this innovative design methodology provides an alternative avenue for future separator designs within lithium-sulfur batteries.

High-Throughput Calculations for Screening d- and p-Block Single-Atom Catalysts toward Li2 S/Na2 S Decomposition Guided by Facile Descriptor beyond Brønsted-Evans-Polanyi Relationship

Single-atom catalysts (SACs) are promising cathode materials for addressing issues faced by lithium-sulfur batteries. Considering the ample chemical space of SACs, high-throughput calculations are efficient strategies for their rational design. However, the high throughput calculations are impeded by the time-consuming determination of the decomposition barrier (Eb ) of Li2 S. In this study, the effects of bond formation and breakage on the kinetics of SAC-catalyzed Li2 S decomposition with g-C3 N4 as the substrate are clarified. Furthermore, a new efficient and easily-obtained descriptor Li─S─Li angle (ALi─S─Li ) of adsorbed Li2 S, different from the widely accepted thermodynamic data for predicting Eb , which breaks the well-known Brønsted-Evans-Polanyi relationship, is identified. Under the guidance of ALi─S─Li , several superior SACs with d- and p-block metal centers supported by g-C3 N4 are screened to accelerate the sulfur redox reaction and fix the soluble lithium polysulfides. The newly identified descriptor of ALi─S─Li can be extended to rationally design SACs for Na─S batteries. This study opens a new pathway for tuning the performance of SACs to catalyze the decomposition of X2 S (X = Li, Na, and K) and thus accelerate the design of SACs for alkaline-chalcogenide batteries.

GO-CoNiP New Composite Material Modified Separator for Long Cycle Lithium-Sulfur Batteries

Lithium-sulfur batteries with high capacity are considered the most promising candidates for next-generation energy storage systems. Mitigating the shuttle reaction and promoting catalytic conversion within the battery are major challenges in the development of high-performance lithium-sulfur batteries. To solve these problems, a novel composite material GO-CoNiP is synthesized in this study. The material has excellent conductivity and abundant active sites to adsorb polysulfides and improve reaction kinetics within the battery. The initial capacity of the GO-CoNiP separator battery at 1 C is 889.4 mAh g-1 , and the single-cycle decay is 0.063% after 1000 cycles. In the 4 C high-rate test, the single-cycle decay is only 0.068% after 400 cycles. The initial capacity is as high as 828.2 mAh g-1 under high sulfur loading (7.3 mg cm-2 ). In addition, high and low-temperature performance tests are performed on the GO-CoNiP separator battery. The first cycle discharge reaches 810.9 mAh g-1 at a low temperature of 0 °C, and the first cycle discharge reaches 1064.8 mAh g-1 at a high temperature of 60 °C, and both can run stably for 120 cycles. In addition, in situ Raman tests are conducted to explain the adsorption of polysulfides by GO-CoNiP from a deeper level.

Transition Metal Phosphides: The Rising Star of Lithium-Sulfur Battery Cathode Host

Lithium-sulfur batteries (LSBs) with ultra-high energy density (2600 W h kg-1 ) and readily available raw materials are emerging as a potential alternative device with low cost for lithium-ion batteries. However, the insulation of sulfur and the unavoidable shuttle effect leads to slow reaction kinetics of LSBs, which in turn cause various roadblocks including poor rate capability, inferior cycling stability, and low coulombic efficiency. The most effective way to solve the issues mentioned above is to rationally design and control the synthesis of the cathode host for LSBs. Transition metal phosphides (TMPs) with good electrical conductivity and dual adsorption-conversion capabilities for polysulfide (PS) are regarded as promising cathode hosts for new-generation LSBs. In this review, the main obstacles to commercializing the LSBs and the development processes of their cathode host are first elaborated. Then, the sulfur fixation principles, and synthesis methods of the TMPs are briefly summarized and the recent progress of TMPs in LSBs is reviewed in detail. Finally, a perspective on the future research directions of LSBs is provided.

A nitrogen-rich two dimensional covalent organic framework with multiple carbonyls as a highly efficient anchoring material for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries, as next generation energy storage systems, have gained considerable attention due to their high energy density, low cost, and environmental friendliness. However, the practical applications of Li-S batteries are presently hindered by several issues, such as the low conductivity of sulfur species, the shuttle effect of polysulfides, and poor conversion efficiency in discharging/charging processes. In this study, using density functional theory (DFT)-based computations, we propose a two dimensional (2D) covalent organic framework (COF) with triquinoxalinylene (TQ) and benzoquinone (BQ) units in its skeleton, namely, TQBQCOF, as a promising sulfur host material for high-performance Li-S batteries. We have found that the TQBQCOF is a semiconductor with a band gap of 1.16 eV. After the adsorption of LiPSs the TQBQCOF becomes metallic in nature, which ensures its excellent electronic conductivity. The moderate adsorption energies of the TQBQCOF to the soluble LiPSs can effectively suppress the shuttle effect of polysulfides. Notably, the TQBQCOF also shows high catalytic activity for the sulfur reduction reactions (SRR) in the discharge process and Li2S decomposition in the charging process of Li-S batteries. The Gibbs free energy barrier for the SRR is 0.22 eV, while the decomposition barrier of a Li2S molecule on the TQBQCOF is only 0.04 eV, ensuring the rapid charging and discharging processes of Li-S batteries.

Single-atom site catalysis in Li-S batteries

With their high theoretical energy density, Li-S batteries are regarded as the ideal battery system for next generation electrochemical energy storage. In the last 15 years, Li-S batteries have made outstanding academic progress. Recently, research studies have placed more emphasis on their practical application aspects, which puts forward strict requirements for the loading of S cathodes and the amount of electrolytes. To meet the above requirements, electrode catalysis design is of crucial significance. Among all the catalysts, single-atom site catalysts (SASCs) are considered to be ideal catalyst materials for the commercialization of Li-S batteries due to their high activity and highest utilization of catalytic sites. This perspective introduces the kinetic mechanism of S cathodes, the basic concept and synthesis strategy of SASCs, and then systematically summarizes the research progress of SASCs for S cathodes and, the related functional interlayers/separators in recent years. Finally, the opportunities and challenges of SASCs in Li-S batteries are summarized and prospected.

Core-Shell Tandem Catalysis Coupled with Interface Engineering For High-Performance Room-Temperature Na-S Batteries

The sluggish redox kinetics and shuttle effect seriously impede the large application of room-temperature sodium-sulfur (RT Na-S) batteries. Designing effective catalysts into cathode material is a promising approach to overcome the above issues. However, considering the multistep and multiphase transformations of sulfur redox process, it is impractical to achieve the effective catalysis of the entire S8 →Na2 Sx →Na2 S conversion through applying a single catalyst. Herein, this work fabricates a nitrogen-doped core-shell carbon nanosphere integrated with two different catalysts (ZnS-NC@Ni-N4 ), where isolated Ni-N4 sites and ZnS nanocrystals are distributed in the shell and core, respectively. ZnS nanocrystals ensure the rapid reduction of S8 into Na2 Sx (4 < x ≤ 8), while Ni-N4 sites realize the efficient conversion of Na2 Sx into Na2 S, bridged by the diffusion of Na2 Sx from the core to shell. Besides, Ni-N4 sites on the shell can also induce an inorganic-rich cathode-electrolyte interface (CEI) on ZnS-NC@Ni-N4 to further inhibit the shuttle effect. As a result, ZnS-NC@Ni-N4 /S cathode exhibits an excellent rate-performance (650 mAh g-1 at 5 A g-1 ) and ultralong cycling stability for 2000 cycles with a low capacity-decay rate of 0.011% per cycle. This work will guide the rational design of multicatalysts for high-performance RT Na-S batteries.

2D Materials Beyond Post-AI Era: Smart Fibers, Soft Robotics, and Single Atom Catalysts

Recent consecutive discoveries of various 2D materials have triggered significant scientific and technological interests owing to their exceptional material properties, originally stemming from 2D confined geometry. Ever-expanding library of 2D materials can provide ideal solutions to critical challenges facing in current technological trend of the fourth industrial revolution. Moreover, chemical modification of 2D materials to customize their physical/chemical properties can satisfy the broad spectrum of different specific requirements across diverse application areas. This review focuses on three particular emerging application areas of 2D materials: smart fibers, soft robotics, and single atom catalysts (SACs), which hold immense potentials for academic and technological advancements in the post-artificial intelligence (AI) era. Smart fibers showcase unconventional functionalities including healthcare/environmental monitoring, energy storage/harvesting, and antipathogenic protection in the forms of wearable fibers and textiles. Soft robotics aligns with future trend to overcome longstanding limitations of hard-material based mechanics by introducing soft actuators and sensors. SACs are widely useful in energy storage/conversion and environmental management, principally contributing to low carbon footprint for sustainable post-AI era. Significance and unique values of 2D materials in these emerging applications are highlighted, where the research group has devoted research efforts for more than a decade.

Effect of Heterostructure-Modified Separator in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries with high energy density and low cost are the most promising competitor in the next generation of new energy reserve devices. However, there are still many problems that hinder its commercialization, mainly including shuttle of soluble polysulfides, slow reaction kinetics, and growth of Li dendrites. In order to solve above issues, various explorations have been carried out for various configurations, such as electrodes, separators, and electrolytes. Among them, the separator in contact with both anode and cathode is in a particularly special position. Reasonable design-modified material of separator can solve above key problems. Heterostructure engineering as a promising modification method can combine characteristics of different materials to generate synergistic effect at heterogeneous interface that is conducive to Li-S electrochemical behavior. This review not only elaborates the role of heterostructure-modified separators in dealing with above problems, but also analyzes the improvement of wettability and thermal stability of separators by modification of heterostructure materials, systematically clarifies its advantages, and summarizes some related progress in recent years. Finally, future development direction of heterostructure-based separator in Li-S batteries is given.

Rational design of MXene-based single atom catalysts for Na-Se batteries from sabatier principle

Na-Se batteries have attracted great attention because of their high-energy density and low cost, though the shuttle effect of polyselenides and sluggish reaction dynamics still limit their practical applications. Herein, MXenes were decorated with single zinc atom as selenium hosts, and the effect of interfacial electrochemical reaction was studied via first-principles simulation. The embedding of single zinc atom into MXenes was found to enhance the anchoring ability to inhibit the shuttle effect. However, Zn-MXenes as single atom catalysts had different effects on interfacial electrochemical reactions, which can be attributed to the increased interaction strengths between Zn-MXenes and polyselenides. For Ti-based MXenes, the enhanced interaction was found to be beneficial for the electrochemical reaction, whereas the overly strong anchoring strength of Zn-Cr2CO2 would inhibit charging-discharging kinetics. Therefore, the matching of MXenes and metal atoms should be considered to adjust the anchoring ability based on the Sabatier principle. This work provides new insights into the design of SACs and high-performance Na-Se batteries.

Deciphering the Influence of Anionic Electrons of Surface-Functionalized Two-Dimensional Electrides in Lithium-Sulfur Batteries

Using transition metal compounds as sulfur hosts is regarded as a promising approach to suppress the polysulfide shuttle and accelerate redox kinetics for lithium-sulfur (Li-S) batteries. Herein, we report that a new kind of compound, electrides (exotic ionic crystalline materials in which electrons serve as anions), is efficient sulfur hosts for Li-S batteries for the first time. Based on the first-principles calculations, we found that two-dimensional (2D) electrides M2C (M = Sc, Y) exhibit unprecedentedly strong binding strength toward sulfur species and surface functionalization is necessary to passivate their activity. The 2D electrides modified with the F-functional group exhibit the best performance in terms of the adsorption energy and sulfur reduction process. A comparative study with a nonelectride reveals that the anionic electrons (AEs) of electrides aid in anchoring the soluble polysulfides. These results open an avenue for the application of electrides in Li-S batteries.

Vanadium as Auxiliary for Fe-V Dual-Atom Electrocatalyst in Lithium-Sulfur Batteries: "3D in 2D" Morphology Inducer and Coordination Structure Regulator

The undesirable shuttling behavior, the sluggish redox kinetics of liquid-solid transformation, and the large energy barrier for decomposition of Li2S have been the recognized problems impeding the practical application of lithium-sulfur batteries. Herein, inspired by the spectacular catalytic activity of the Fe/V center in bioenzyme for nitrogen/sulfur fixation, we design an integrated electrocatalyst comprising N-bridged Fe-V dual-atom active sites (Fe/V-N7) dispersed on ingenious "3D in 2D" carbon nanosheets (denoted as DAC), in which vanadium induces the laminar structure and regulates the coordination configuration of active centers simultaneously, realizing the redistribution of the 3d-orbital electrons of Fe centers. The high coupling/conjunction between Fe/V 3d electrons and S 2p electrons shows strong affinity and enhanced reactivity of DAC-Li2Sn (1 ≤ n ≤ 8) systems. Thus, DAC presents strengthened chemisorption ability toward polysulfides and significantly boosts bidirectional sulfur redox reaction kinetics, which have been evidenced theoretically and experimentally. Besides, the well-designed "3D in 2D" morphology of DAC enables uniform sulfur distribution, facilitated electron transfer, and abundant active sites exposure. Therefore, the assembled Li-S cells present outstanding cycling stability (637.3 mAh g-1 after 1000 cycles at 1 C) and high rate capability (711 mAh g-1 at 4 C) under high sulfur content (70 wt %).

Guiding maps of solvents for lithium-sulfur batteries via a computational data-driven approach

Practical realization of lithium-sulfur batteries requires designing optimal electrolytes with controlled dissolution of polysulfides, high ionic conductivity, and low viscosity. Computational chemistry techniques enable tuning atomistic interactions to discover electrolytes with targeted properties. Here, we introduce ComBat (Computational Database for Lithium-Sulfur Batteries), a public database of ∼2,000 quantum-chemical and molecular dynamics properties for lithium-sulfur electrolytes composed of solvents spanning 16 chemical classes. We discuss the microscopic origins of polysulfide clustering and the diffusion mechanism of electrolyte components. Our findings reveal that polysulfide solubility cannot be determined by a single solvent property like dielectric constant. Rather, observed trends result from the synergistic effect of multiple factors, including solvent C/O ratio, fluorination degree, and steric hindrance effects. We propose binding energy as a proxy for Li+ dissociation, which is a property that impacts the ionic conductivity. The insights obtained in this work can serve as guiding maps to design optimal lithium-sulfur electrolyte compositions.

Recent Progress for Concurrent Realization of Shuttle-Inhibition and Dendrite-Free Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have become one of the most promising new-generation energy storage systems owing to their ultrahigh energy density (2600 Wh kg-1 ), cost-effectiveness, and environmental friendliness. Nevertheless, their practical applications are seriously impeded by the shuttle effect of soluble lithium polysulfides (LiPSs), and the uncontrolled dendrite growth of metallic Li, which result in rapid capacity fading and battery safety problems. A systematic and comprehensive review of the cooperative combination effect and tackling the fundamental problems in terms of cathode and anode synchronously is still lacking. Herein, for the first time, the strategies for inhibiting shuttle behavior and dendrite-free Li-S batteries simultaneously are summarized and classified into three parts, including "two-in-one" S-cathode and Li-anode host materials toward Li-S full cell, "two birds with one stone" modified functional separators, and tailoring electrolyte for stabilizing sulfur and lithium electrodes. This review also emphasizes the fundamental Li-S chemistry mechanism and catalyst principles for improving electrochemical performance; advanced characterization technologies to monitor real-time LiPS evolution are also discussed in detail. The problems, perspectives, and challenges with respect to inhibiting the shuttle effect and dendrite growth issues as well as the practical application of Li-S batteries are also proposed.

In Situ 1D Carbon Chain-Mail Catalyst Assembly for Stable Lithium-Sulfur Full Batteries

The main obstacles for the commercial application of Lithium-Sulfur (Li-S) full batteries are the large volume change during charging/discharging process, the shuttle effect of lithium polysulfide (LiPS), sluggish redox kinetics, and the indisciplinable dendritic Li growth. Especially the overused of metal Li leads to the low utilization of active Li, which seriously drags down the actual energy density of Li-S batteries. Herein, an efficient design of dual-functional CoSe electrocatalyst encapsulated in carbon chain-mail (CoSe@CCM) is employed as the host both for the cathode and anode regulation simultaneously. The carbon chain-mail constituted by carbon encapsulated layer cross-linking with carbon nanofibers protects CoSe from the corrosion of chemical reaction environment, ensuring the high activity of CoSe during the long-term cycles. The Li-S full battery using this carbon chain-mail catalyst with a lower negative/positive electrode capacity ratio (N/P < 2) displays a high areal capacity of 9.68 mAh cm-2 over 150 cycles at a higher sulfur loading of 10.67 mg cm-2 . Additionally, a pouch cell is stable for 80 cycles at a sulfur loading of 77.6 mg, showing the practicality feasibility of this design.

Enhancing Electron Conductivity and Electron Density of Single Atom Based Core-Shell Nanoboxes for High Redox Activity in Lithium Sulfur Batteries

Herein, an integrated structure of single Fe atom doped core-shell carbon nanoboxes wrapped by self-growing carbon nanotubes (CNTs) is designed. Within the nanoboxes, the single Fe atom doped hollow cores are bonded to the shells via the carbon needles, which act as the highways for the electron transport between cores and shells. Moreover, the single Fe atom doped nanobox shells is further wrapped and connected by self-growing carbon nanotubes. Simultaneously, the needles and carbon nanotubes act as the highways for electron transport, which can improve the overall electron conductivity and electron density within the nanoboxes. Finite element analysis verifies the unique structure including both internal and external connections realize the integration of active sites in nano scale, and results in significant increase in electron transfer and the catalytic performance of Fe-N4 sites in both Li2 Sn lithiation and Li2 S delithiation. The Li-S batteries with the double-shelled single atom catalyst delivered the specific capacity of 702.2 mAh g-1 after 550 cycles at 1.0 C. The regional structure design and evaluation method provide a new strategy for the further development of single atom catalysts for more electrochemical processes.

Application of Inorganic Quantum Dots in Advanced Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have emerged as one of the most attractive alternatives for post-lithium-ion battery energy storage systems, owing to their ultrahigh theoretical energy density. However, the large-scale application of Li-S batteries remains enormously problematic because of the poor cycling life and safety problems, induced by the low conductivity , severe shuttling effect, poor reaction kinetics, and lithium dendrite formation. In recent studies, catalytic techniques are reported to promote the commercial application of Li-S batteries. Compared with the conventional catalytic sites on host materials, quantum dots (QDs) with ultrafine particle size (<10 nm) can provide large accessible surface area and strong polarity to restrict the shuttling effect, excellent catalytic effect to enhance the kinetics of redox reactions, as well as abundant lithiophilic nucleation sites to regulate Li deposition. In this review, the intrinsic hurdles of S conversion and Li stripping/plating reactions are first summarized. More importantly, a comprehensive overview is provided of inorganic QDs, in improving the efficiency and stability of Li-S batteries, with the strategies including composition optimization, defect and morphological engineering, design of heterostructures, and so forth. Finally, the prospects and challenges of QDs in Li-S batteries are discussed.

Boosting Lean Electrolyte Lithium-Sulfur Battery Performance with Transition Metals: A Comprehensive Review

Lithium-sulfur (Li-S) batteries have received widespread attention, and lean electrolyte Li-S batteries have attracted additional interest because of their higher energy densities. This review systematically analyzes the effect of the electrolyte-to-sulfur (E/S) ratios on battery energy density and the challenges for sulfur reduction reactions (SRR) under lean electrolyte conditions. Accordingly, we review the use of various polar transition metal sulfur hosts as corresponding solutions to facilitate SRR kinetics at low E/S ratios (< 10 µL mg-1), and the strengths and limitations of different transition metal compounds are presented and discussed from a fundamental perspective. Subsequently, three promising strategies for sulfur hosts that act as anchors and catalysts are proposed to boost lean electrolyte Li-S battery performance. Finally, an outlook is provided to guide future research on high energy density Li-S batteries.

Atomically Dispersed Fe-N4 and Ni-N4 Independent Sites Enable Bidirectional Sulfur Redox Electrocatalysis

Single-atom catalysts (SACs) with high atom utilization and outstanding catalytic selectivity are useful for improving battery performance. Herein, atomically dispersed Ni-N₄ and Fe-N₄ dual sites coanchored on porous hollow carbon nanocages (Ni-Fe-NC) are fabricated and deployed as the sulfur host for Li-S battery. The hollow and conductive carbon matrix promotes electron transfer and also accommodates volume fluctuation during cycling. Notably, the high d band center of Fe in Fe-N₄ site demonstrates strong polysulfide affinity, leading to an accelerated sulfur reduction reaction. Meanwhile, Li₂S on the Ni-N₄ site delivers a metallic property with high S 2p electron density of states around the Femi energy level, enabling a low sulfur evolution reaction barrier. The dual catalytic effect on Ni-Fe-NC endows sulfur cathode high energy density, prolonged lifespan, and low polarization.

Edge Coordination of Ni Single Atoms on Hard Carbon Promotes the Potassium Storage and Reversibility

Hard carbon is the most promising anode for potassium-ion batteries (PIBs) due to its low cost and abundance, but its limited storage capacity remains a major challenge. Herein, edge coordination of metal single atoms is proved to be an effective strategy for promoting potassium storage in hard carbon for the first time, taking B, N co-doped hard carbon nanotubes anchored by edge Ni-N₄ -B atomic sites (Ni@BNHC) as an example. It is revealed that edge Ni-N₄ -B can provide active sites for interlayer adsorption of K⁺ and that Ni atoms can facilitate the reversibility of K⁺ storage on N and B atoms. Furthermore, an unprecedentedly reversible K⁺ storage capacity of 694 mAh g^-1 at 0.05 A g^-1 is realized by introducing commercial carbon nanotubes. This work provides a new perspective for the application of single-atom engineering and the design of high-performance carbon anodes for PIBs.

Dual Active Sites of Oversaturated Fe-N5 and Fe2 O3 Nanoparticles for Accelerating Redox Kinetics of Polysulfides

The shuttling effect and sluggish reaction kinetics are the main bottlenecks for the commercial viability of lithium-sulfur (Li-S) batteries. Metal-nitrogen-carbon single atom catalysts have attracted much attention to overcoming these obstacles due to their novel electrocatalytic activity. Herein, a novel cooperative catalytic interface with dual active sites (oversaturated Fe-N₅ and polar Fe₂ O₃ nanocrystals) are co-embedded in nitrogen-doped hollow carbon spheres (Fe₂ O₃ /Fe-SA@NC) is designed by fine atomic regulation mechanism. Both experimental verifications and theoretical calculations disclose that the dual active sites (Fe-N₅ and Fe₂ O₃ ) in this catalyst (Fe₂ O₃ /Fe-SA@NC) tend to form "FeS" and "LiN/O" bond, synchronically enhancing chemical adsorption and interface conversion ability of polysulfides, respectively. Specially, the Fe-N₅ coordination with 3D configuration and sulfiphilic superfine Fe₂ O₃ nanocrystals exhibit the strong adsorption ability to facilitate the subsequent conversion reaction at dual-sites. Meanwhile, the nitrogen-doped hollow carbon spheres can promote Li⁺ /electron transfer and physically suppress polysulfides shuttling. Consequently, Li-S battery with the Fe₂ O₃ /Fe-SA@NC-modified separator exhibits a high capacity retention of 78% after 800 cycles at 1 C (pure S cathode, S content: 70 wt.%). Furthermore, the pouch cell with this separator shows good performance at 0.1 C for practical application (S loading: 4 mg cm^-2 ).

Metal-Organic-Framework-Derived 3D Hierarchical Matrixes for High-Performance Flexible Li-S Batteries

Lithium-sulfur (Li-S) batteries have shown exceptional theoretical energy densities, making them a promising candidate for next-generation energy storage systems. However, their practical application is limited by several challenging issues, such as uncontrollable Li dendrite growth, sluggish electrochemical kinetics, and the shuttling effect of lithium polysulfides (LiPSs). To overcome these issues, we designed and synthesized hierarchical matrixes on carbon cloth (CC) by using metal-organic frameworks (MOFs). ZnO nanosheet arrays were used as anode hosts (CC-ZnO) to enable stable Li plating and stripping. The symmetric cell with CC-ZnO@Li was demonstrated to have enhanced cycling stability, with a voltage hysteresis of ∼25 mV for over 800 h at 1 mA cm^-2 and 1 mAh cm^-2. To address the cathode challenges, we developed a multifunctional CC-NC-Co cathode host with physical confinement, chemical anchoring, and excellent electrocatalysis. The full cells with CC-ZnO@Li anodes and CC-NC-Co@S cathodes exhibited excellent electrochemical performance, with long cycling life (0.02% and 0.03% capacity decay per cycle when cycling 900 times at 0.5 C and 600 times at 1 C, respectively) and outstanding rate performance (793 mAh g^-1 at 4 C). Additionally, the pouch cell based on the flexible CC-ZnO@Li anode and CC-NC-Co@S cathode showed good stability in different bending states. Overall, our study presents an effective strategy for preparing flexible Li and S hosts with hierarchical structures derived from MOF, which can pave the way for high-performance Li-S batteries.