Built-In Catalysis in Confined Nanoreactors for High-Loading Li-S Batteries

CeO2/Co heterostructure encapsulated in hollow necklace-like carbon fiber as an advanced host material for high-performance lithium-sulfur batteries

The shuttle effect of lithium polysulfides (LiPSs) and the sluggish reaction kinetics of LiPSs conversion pose serious challenges to the commercial feasibility of lithium-sulfur (Li-S) batteries. To address these obstacles, herein, we construct CeO2/Co heterostructures in hollow necklace-like carbon fibers (CeO2/Co-CNFs) as the cathode host material for Li-S batteries. The specific surface area of fibers is significantly enhanced by using a template, thereby promoting the utilization efficiency of sulfur. Meanwhile, CeO2/Co-CNFs show strong conductivity, effective adsorption to LiPSs, and robust catalytic activity for LiPSs conversion. As a result, the Li-S battery with CeO2/Co-CNFs displays 961 mAh g-1 at 0.2 C, with an 86 % capacity retention rate after 100 cycles. At 2.0 C current density, the composite cathode maintains an initial discharge capacity of 782 mAh g-1, with a mere 0.044 % capacity loss per cycle. Furthermore, in situations with limited electrolytes, high sulfur loading, and high areal mass loading, the composite cathode can provide a high areal capacity of 6.2 mg cm-2 over 100 cycles. This work provides a useful approach for investigating high-performance Li-S battery cathodes.

Precisely Designed Ultra-Small CoP Nanoparticles-Decorated Hollow Carbon Nanospheres as Highly Efficient Host in Lithium-Sulfur Batteries

Designing porous carbon materials with metal phosphides as host materials holds promise for enhancing the cyclability and durability of lithium-sulfur (Li-S) batteries by mitigating sulfur poisoning and exhibiting high electrocatalytic activity. Nevertheless, it is urgent to precisely control the size of metal phosphides to further optimize the polysulfide conversion reaction kinetics of Li-S batteries. Herein, a subtlety regulation strategy was proposed to obtain ultra-small CoP nanoparticles-decorated hollow carbon nanospheres (CoP@C) by using spherical polyelectrolyte brush (SPB) as the template with stabilizing assistance from polydopamine coating, which also works as carbon source. Leveraging the electrostatic interaction between SPB and Co2+, ultra-small Co particles with sizes measuring 5.5±2.6 nm were endowed after calcination. Subsequently, through a gas-solid phosphating process, these Co particles were converted into CoP nanoparticles with significantly finer sizes (7.1±3.1 nm) compared to state-of-the-art approaches. By uniformly distributing the electrocatalyst nanoparticles on hollow carbon nanospheres, CoP@C facilitated the acceleration of Li-ion diffusion and enhanced the conversion reaction kinetics of polysulfides through adsorption-diffusion synergy. As a result, Li-S batteries utilizing the CoP@C/S cathode demonstrated an initial specific discharge capacity of 850.0 mAh g-1 at 1.0 C, with a low-capacity decay rate of 0.03 % per cycle.

Emerging Doped Metal-Organic Frameworks: Recent Progress in Synthesis, Applications, and First-Principles Calculations

Metal-organic frameworks (MOFs) are crystalline porous materials with a long-range ordered structure and excellent specific surface area and have found a wide range of applications in diverse fields, such as catalysis, energy storage, sensing, and biomedicine. However, their poor electrical conductivity and chemical stability, low capacity, and weak adhesion to substrates have greatly limited their performance. Doping has emerged as a unique strategy to mitigate the issues. In this review, the concept, classification, and characterization methods of doped MOFs are first introduced, and recent progress in the synthesis and applications of doped MOFs, as well as the rapid advancements and applications of first-principles calculations based on the density functional theory (DFT) in unraveling the mechanistic origin of the enhanced performance are summarized. Finally, a perspective is included to highlight the key challenges in doping MOF materials and an outlook is provided on future research directions.

Synergistic Effect of In2O3/NC-Co3O4 Interface on Enhancing the Redox Conversion of Polysulfides for High-Performance Li-S Cathode Materials at Low Temperatures

Lithium-sulfur (Li-S) batteries are considered as a promising energy storage technology due to their high energy density; however, the shuttling effect and sluggish redox kinetics of lithium polysulfides (LiPSs) severely deteriorate the electrochemical performance of Li-S batteries. Herein, we report a novel configuration wherein In2O3 and Co3O4 are incorporated into N-doped porous carbon as a sulfur host material (In2O3@NC-Co3O4) using metal-organic framework-based materials to synergistically tune the catalytic abilities of different metal oxides for different reaction stages of LiPSs, achieving a rapid redox conversion of LiPSs. In particular, the introduction of N-doped carbon improved the electron transport of the materials. The polar interface of In2O3 and Co3O4 anchors both long- and short-chain LiPSs and catalyzes long-chain and short-chain LiPSs, respectively, even at low temperatures. Consequently, the Li-S battery with In2O3@NC-Co3O4 cathode materials delivered an excellent discharge capacity of 1042.4 mAh g-1 at 1 C and a high capacity retention of 85.1% after 500 cycles. Impressively, the In2O3@NC-Co3O4 cathode displays superior performances at high current density and low temperature due to the enhanced redox kinetics, delivering 756 mAh g-1 at 2 C (room temperature) and 755 mAh g-1 at 0.1 C (-20 °C).

A quantitative analysis method of complex sulfide components for understanding initial capacity degradation mechanism in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are a strong contender for the new-generation battery system to meet the growing energy demand due to their significantly high energy density (2600 Wh/kg) and cost-effectiveness. However, the practical operating conditions yield an initial capacity of less than 80 % of the theoretical capacity, resulting in a limited lifespan and hindering broader application. What's worse, current mechanism, especially the evolution process of sulfides for the initial capacity degradation is not clear due to the practical difficulties of effective separation and detection of sulfur-containing components. Herein, we have developed an instrumental analysis method enabling graded leaching and quantitative determination of sulfur-containing components. This technology achieves a detection precision surpassing 99.11 %, addressing the inherent deficiency in calculating sulfur-containing components using the decrement method. Applying this method reveals that the presence of lithium polysulfides in the electrolyte (26.34 wt%) after discharging is the primary factor causing insufficient capacity utilization in Li-S batteries. This work not only demonstrates the unique behavior of Li-S batteries at high sulfur loading but also provides a systematic evaluation method to guide further research on high-energy-density batteries, and provides theoretical and technical support to promote the development of high-energy, long-life Li-S batteries.

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.

Room-temperature reversible F-ion batteries based on sulfone electrolytes with a mild anion acceptor additive

Rechargeable fluoride ion batteries (FIBs) as an emerging anion shuttle system are attracting much attention due to their potential advantages in terms of energy density, cost and safety. A liquid electrolyte system enables the FIB operation at low or room temperature due to its higher ionic conductivity than that of a solid F-ion electrolyte. However, the insolubility of fluoride salts in aprotic solvents limits the development of liquid F-ion electrolytes. Although the boron-based anion acceptors (AAs) can facilitate the dissolution of F-ion salts, they are prone to lead to a tough desolvation process for F- due to strong Lewis acidity and therefore an inferior electrochemical performance. Here, a new non-boron AA (6-thioguanine) with moderate Lewis acidity is proposed to dissolve F- in the sulfone solvent. The ionic conductivity of the corresponding electrolytes reaches a level of mS cm-1 at room temperature. A model FIB coin cell is successfully operated with high conversion reaction reversibility based on the coupled defluorination/fluorination mechanism of electrodes, enabling a low overpotential of 0.36 V and a reversible capacity of 126 mA h g-1 after 40 cycles.

Palygorskite-Derived Ternary Fluoride with 2D Ion Transport Channels for Ampere Hour-Scale Li-S Pouch Cell with High Energy Density

Although various excellent electrocatalysts/adsorbents have made notable progress as sulfur cathode hosts on the lithium-sulfur (Li-S) coin-cell level, high energy density (WG ) of the practical Li-S pouch cells is still limited by inefficient Li-ion transport in the thick sulfur cathode under low electrolyte/sulfur (E/S) and negative/positive (N/P) ratios, which aggravates the shuttle effect and sluggish redox kinetics. Here a new ternary fluoride MgAlF5 ·2H2 O with ultrafast ion conduction-strong polysulfides capture integration is developed. MgAlF5 ·2H2 O has an inverse Weberite-type crystal framework, in which the corner-sharing [AlF6 ]-[MgF4 (H2 O)2 ] octahedra units extend to form two-dimensional Li-ion transport channels along the [100] and [010] directions, respectively. Applied as the cathode sulfur host, the MgAlF5 ·2H2 O lithiated by LiTFSI (lithium salt in Li-S electrolyte) acts as a fast ionic conductor to ensure efficient Li-ion transport to accelerate the redox kinetics under high S loadings and low E/S and N/P. Meanwhile, the strong polar MgAlF5 ·2H2 O captures polysulfides by chemisorption to suppress the shuttle effect. Therefore, a 1.97 A h-level Li-S pouch cell achieves a high WG of 386 Wh kg-1 . This work develops a new-type ionic conductor, and provides unique insights and new hosts for designing practical Li-S pouch cells.

"Wane and wax" strategy: Enhanced evolution kinetics of liquid phase Li2S4 to Li2S via mutually embedded CNT sponge/Ni-porous carbon electrocatalysts

The lithium-sulfur battery (Li-S) has been considered a promising energy storage system, however, in the practical application of Li-S batteries, considerable challenges remain. One challenge is the low kinetics involved in the conversion of Li2S4 to Li2S. Here, we reveal that highly dispersed Ni nanoparticles play a unique role in the reduction of Li2S4. Ni-porous carbon (Ni-PC) decorated in situ on a free-standing carbon nanotube sponge (CNTS/Ni-PC) enriches the current response of liquid phase Li2S4 and Li2S2 around the cathode more than 8.1 and 5.7 times higher than that of the CNTS blank sample, respectively, greatly boosting the kinetics and decreasing the reaction overpotential of Li2S4 reduction (lower Tafel slope and larger current response). Thus, with the same total overpotential, more space is provided for the concentration difference overpotential, allowing the more soluble polysulfide intermediates farther away from the surface of the conductive materials to be reduced based on the "wane and wax" strategy, and significantly improving the sulfur utilization. Consequently, S@CNTS/Ni-PC delivers excellent rate performance (812.4 mAh·g-1 at 2C) and a remarkable areal capacity of 10.1 mAh·cm-2. This work provides a viable strategy for designing a target catalyst to enhance the conversion kinetics in the Li2S4 reduction process.

Cobalt-doped tin disulfide catalysts for high-capacity lithium-air batteries with high lifetime

Dual electrolyte lithium-air batteries have received widespread attention for their ultra-high energy density. However, the low internal redox efficiency of these batteries results in a relatively short operating life. SnS2 is widely used in Li-S batteries, Li-ion batteries, photocatalysis, and other fields due to the high discharge capacity in batteries. However, SnS2 suffers from low electrical conductivity and slow redox kinetics. In this study, Co-doped SnS2 is prepared by hydrothermal method for application in dual-electrolyte lithium-air batteries to study its electrochemical performance and its catalytic reaction process by DFT theory. Conductivity tests show that the Co doping enhances the electrical conductivity of the material and high transmission electron microscopy (HRTEM) results demonstrate that the Co doping of SnS2 increases the grain plane spacing and the material indicates that defects are created on the surface of the material, which is more beneficial to the electrochemical performance of the cell. Co-doped SnS2 exhibits excellent good cycling stability and high discharge capacity in a dual electrolyte lithium-air battery, maintaining a 0.7 V overpotential for 120 h at a current density of 0.1 mA cm-2, with a cell life of over 500 h and an initial discharge capacity showing excellent results up to 16 065 mA h g-1. In addition, this study explores the catalytic activity of Co-doped SnS2 based on density flooding theory (DFT). The results show that Co atoms have a synergistic effect with Sn atoms to perturb the lattice parameters. The calculations show that the catalytic activity is enhanced with the increasing of Co doping content and 3Co-Sn exhibits minimal overpotential.

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.

Recent advances in defect-engineered molybdenum sulfides for catalytic applications

Electrochemical energy conversion and storage driven by renewable energy sources is drawing ever-increasing interest owing to the needs of sustainable development. Progress in the related electrochemical reactions relies on highly active and cost-effective catalysts to accelerate the sluggish kinetics. A substantial number of catalysts have been exploited recently, thanks to the advances in materials science and engineering. In particular, molybdenum sulfide (MoSx) furnishes a classic platform for studying catalytic mechanisms, improving catalytic performance and developing novel catalytic reactions. Herein, the recent theoretical and experimental progress of defective MoSx for catalytic applications is reviewed. This article begins with a brief description of the structure and basic catalytic applications of MoS2. The employment of defective two-dimensional and non-two-dimensional MoSx catalysts in the hydrogen evolution reaction (HER) is then reviewed, with a focus on the combination of theoretical and experimental tools for the rational design of defects and understanding of the reaction mechanisms. Afterward, the applications of defective MoSx as catalysts for the N2 reduction reaction, the CO2 reduction reaction, metal-sulfur batteries, metal-oxygen/air batteries, and the industrial hydrodesulfurization reaction are discussed, with a special emphasis on the synergy of multiple defects in achieving performance breakthroughs. Finally, the perspectives on the challenges and opportunities of defective MoSx for catalysis are presented.

Furnishing Continuous Efficient Bidirectional Polysulfide Conversion for Long-Life and High-Loading Lithium-Sulfur Batteries via the Built-In Electric Field

Most catalysts cannot accelerate uninterrupted conversion of polysulfides, resulting in poor long-cycle and high-loading performance of lithium-sulfur (Li-S) batteries. Herein, rich p-n junction CoS2 /ZnS heterostructures embedded on N-doped carbon nanosheets are fabricated by ion-etching and vulcanization as a continuous and efficient bidirectional catalyst. The p-n junction built-in electric field in the CoS2 /ZnS heterostructure not only accelerates the transformation of lithium polysulfides (LiPSs), but also promotes the diffusion and decomposition for Li2 S the from CoS2 to ZnS avoiding the aggregation of lithium sulfide (Li2 S). Meanwhile, the heterostructure possesses a strong chemisorption ability to anchor LiPSs and superior affinity to induce homogeneous Li deposition. The assembled cell with a CoS2 /ZnS@PP separator delivers a cycling stability with a capacity decay of 0.058% per cycle at 1.0 C after 1000 cycles, and a decent areal capacity of 8.97 mA h cm-2 at an ultrahigh sulfur mass loading of 6 mg cm-2 . This work reveals that the catalyst continuously and efficiently converts polysulfides via abundant built-in electric fields to promote Li-S chemistry.

Squaraine-linked zwitterionic COF modified LLZTO nanoparticles for high performance polymer composite electrolytes in Li-S batteries

Lithium-sulfur (Li-S) batteries are severely restricted for practical application due to the polysulfide shuttle effect, Li dendrites and thermal runaway. The use of PEO-based polymer composite electrolytes (PCEs) as an alternative strategy suffers from limited lithium-ion conductivity with deficient long-range transfer route. Herein, Li6.4La3Zr1.4Ta0.6O12 (LLZTO) nanoparticles modified with an in situ-synthesized zwitterionic covalent organic framework layer (denoted as LLZTO@HUT4) were introduced into PEO-based PCEs. Zwitterionic HUT4 modified the lithiophobic LiOH/Li2CO3 layer on the surface of LLZTO nanoparticles, which could notably promote Li+ ion transport for superior electrochemical performance of PCEs. Additionally, the intermediate layer HUT4 located between LLZTO and PEO could further improve the mechanical properties of electrolytes due to the enhanced inorganic/organic interface compatibility and intermolecular interaction. As a result, the obtained LLZTO@HUT4-15%/PEO electrolyte exhibited a competent ionic conductivity of 0.73 mS cm-1 with a Li+ transference number of up to 0.74 at 60 °C. The assembled S@CNT|LLZTO@HUT4-15%/PEO|Li coin cell delivered a considerable initial discharge capacity of 1018 mA h g-1 at 0.2 C, with approximately 92.1% capacity retention after 100 cycles, elucidating an obviously suppressed shuttle effect.

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.

Metal-Organic Assembly Strategy for the Synthesis of Layered Metal Chalcogenide Anodes for Na+ /K+ -Ion Batteries

Layered transition metal chalcogenides (MX, M=Mo, W, Sn, V; X=S, Se, Te) have large ion transport channels and high specific capacity, making them promising for large-sized Na⁺ /K⁺ energy-storage technologies. Nevertheless, slow reaction kinetics and huge volume expansion will induce an undesirable electrochemical performance. Numerous efforts have been devoted to designing MX anodes and enhancing their electrochemical performance. Based on the metal-organic assembly strategy, nanostructural engineering, combination with carbon materials, and component regulation can be easily realized, which effectively boost the performance of MX anodes. In this Review, we present a comprehensive overview on the synthesis of MX nanostructure using the metal-organic assembly strategy, which can realize the design of MX nanostructures, based on self-sacrificial templates, host@guest tailored templates, post-modified layer and derivative templates. The preparation routes and structure evolution are mainly discussed. Then, Mo-, W-, Sn-, V-based chalcogenides used for Na⁺ /K⁺ energy storage are reviewed, and the relationship between the structure and the electrochemical performance, as well as the energy storage mechanism are emphasized. In addition, existing challenges and future perspectives are also presented.

Sheet-on-sheet ZnIn2S4@RGO-modified separators with abundant sulfur vacancies for high-performance Li-S batteries

A novel sheet-on-sheet architecture with abundant sulfur vacancies (Vs) is designed by in situ growth of flake-like ZnIn2S4 on the reduced graphene oxide (Vs-ZIS@RGO) surface, which serves as a functional layer on the separators for high-performance lithium-sulfur batteries (LSBs). Benefiting from the sheet-on-sheet architecture, the separators exhibit rapid ionic/electronic transfer, which is capable of supporting fast redox reactions. The vertically ordered ZnIn2S4 shortens the diffusion pathways of lithium-ions and the irregularly curved nanosheets expose more active sites to effectively anchor lithium polysulfides (LiPSs). More importantly, the introduction of Vs adjusts the surface or interface electronic structure of ZnIn2S4, enhancing the chemical affinity to LiPSs while accelerating conversion reaction kinetics of LiPSs. As expected, the batteries with Vs-ZIS@RGO modified separators exhibit an initial discharge capacity of 1067 mA h g-1 at 0.5C. Even at 1C, the excellent long cycle stability (710 mA h g-1 over 500 cycles) with an ultra-low decay rate of 0.055% per cycle is also attained. This work proposes a strategy of designing the sheet-on-sheet structure with rich sulfur vacancies, which provides a new perspective to rationally devise durable and efficient LSBs.

Synergistic effect of porous carbon shell confinement and catalytic conversion of nickel nanoparticle cores for improved lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are some of the most promising energy storage systems to break the ceiling of Li-ion batteries. However, the notorious shuttle effect and slow redox kinetics give rise to low sulfur utilization and discharge capacity, poor rate performance, and fast capacity decay. It is proved that the reasonable design of the electrocatalyst is one of the important ways to improve the electrochemical performance of LSBs. Here, a core-shell structure with gradient adsorption capacity for reactants and sulfur products was designed. The Ni nanoparticles core coated with graphite carbon shell was prepared by one-step pyrolysis of Ni-MOF precursors. The design takes advantage of the principle that the adsorption capacity decreases from the core to the shell, and the Ni core with strong adsorption capacity is easy to attract and capture soluble lithium polysulfide (LiPS) during the discharge/charging process. This trapping mechanism prevents the diffusion of LiPSs to the outer shell and effectively inhibits the shuttle effect. In addition, the Ni nanoparticles within the porous carbon, as the active center, expose most of the inherent active sites to the surface area, thus achieving a rapid transformation of LiPSs, significantly reducing the reaction polarization, and improving the cyclic stability and reaction kinetics of LSB. Therefore, the S/Ni@PC composites exhibited excellent cycle stability (a capacity of 417.4 mA h g-1 for 500 cycles at 1C with a fading rate of 0.11%) and outstanding rate performance (1014.6 mA h g-1 at 2C). This study provides a promising design solution of Ni nanoparticles embedded in porous carbon for high-performance, safe and reliable LSB.

Mesoporous Carbon-Based Materials for Enhancing the Performance of Lithium-Sulfur Batteries

The most promising energy storage devices are lithium-sulfur batteries (LSBs), which offer a high theoretical energy density that is five times greater than that of lithium-ion batteries. However, there are still significant barriers to the commercialization of LSBs, and mesoporous carbon-based materials (MCBMs) have attracted much attention in solving LSBs' problems, due to their large specific surface area (SSA), high electrical conductivity, and other unique advantages. The synthesis of MCBMs and their applications in the anodes, cathodes, separators, and "two-in-one" hosts of LSBs are reviewed in this study. Most interestingly, we establish a systematic correlation between the structural characteristics of MCBMs and their electrochemical properties, offering recommendations for improving performance by altering the characteristics. Finally, the challenges and opportunities of LSBs under current policies are also clarified. This review provides ideas for the design of cathodes, anodes, and separators for LSBs, which could have a positive impact on the performance enhancement and commercialization of LSBs. The commercialization of high energy density secondary batteries is of great importance for the achievement of carbon neutrality and to meet the world's expanding energy demand.

Simultaneously Suppressing Shuttle Effect and Dendrite Growth in Lithium-Sulfur Batteries via Building Dual-Functional Asymmetric-Cellulose Gel Electrolyte

Polysulfides huttling and interfacial instability of Lithium-anode are the main technical issues hindering commercialization of high-energy-density lithium-sulfur batteries. Simply addressing the problem of polysulfide shuttling or lithium dendrite growth can result in safety hazards or short lifespan. To synchronously tackle the aforementioned issues, the authors have designed an asymmetric cellulose gel electrolyte, a defective and ionized UiO66/black phosphorus heterostructure coating layer (Di-UiO66/BP) and a cationic cellulose gelelectrolyte (QACA). Defective and ionized engineered UiO66 particles significantly enhances performance of UiO66/BP layer in anchoring free polysulfides, promoting smooth and effective polysulfide conversion and expediting the redox kinetics of sulfur cathode, therefore suppressing polysulfide shuttling. QACA electrolyte with numerous cationic groups can interact with anions via electrostatic adsorption, thus enhancing lithium-ion transference number and contributing to formation of stable solid electrolyte interface to suppress lithium dendrite growth. Owing to the superior performance of QACA/Di-UiO66/BP, the final cells exhibit outstanding electrochemical performance, presenting high sulfur utilization (1420.1 mAh g^-1 at 0.1 C), high-rate capacity (665.4 mAh g^-1 at 4 C) and long cycle lifespan. This work proposes a strategy of designing asymmetric electrolytes to simultaneously address the challenges in both S-cathode and Li-anode, which contributes to advanced Li-S batteries and their practical application.

Manipulating the Spin State of Fe Sites via Fe-O-Si Bridge Bonds for Enhanced Polysulfide Redox Kinetics in the Li-S Battery

Transition metals with 3d unoccupied orbitals have superior catalytic activity, but inherent high spin suppresses their adsorption capability, leading to sluggish polysulfide conversion kinetics for Li-S batteries. Herein, we provide Fe-O-Si bridge bonds to manipulate e_g filling and induce a high-to-medium spin transition of Fe³⁺ sites, which enhances polysulfide adsorption and facilitates sulfur redox reaction kinetics. The resultant cathodes exhibit outstanding performances under high sulfur loading, which can deliver a high battery specific energy of 1061 mA h·g^-1 even after 100 cycles in Li-S pouch batteries. This work provides new insights into the kinetic and multi-step conversion mechanism of the sulfur redox reaction process, helping in the understanding and design of spin-dependent catalysts.

Nitrogen and titanium-codoped porous carbon nanocomposites derived from metal-organic framework as cathode to address polysulfides shuttle effects by Ti-assisted N-inhibiting strategy

To address the problem of shutting effect of Li-S batteries, we used Ti-based MOF as precursor to obtain a conductive matrix with dual inhibitors. The target material, namely NTiPC, shown remarkable discharge capacity with 1178 mA h g^-1, and maintained at 732 mA h g^-1 after 100 cycles. The results indicated the N- and Ti-active sites synergistic acted with conductive framework can facilitate binding reaction between matrix and polysulfides.

Catalytic Effects of Electrodes and Electrolytes in Metal-Sulfur Batteries: Progress and Prospective

Metal-sulfur (M-S) batteries are promising energy-storage devices due to their advantages such as large energy density and the low cost of the raw materials. However, M-S batteries suffer from many drawbacks. Endowing the electrodes and electrolytes with the proper catalytic activity is crucial to improve the electrochemical properties of M-S batteries. With regard to the S cathodes, advanced electrode materials with enhanced electrocatalytic effects can capture polysulfides and accelerate electrochemical conversion and, as for the metal anodes, the proper electrode materials can provide active sites for metal deposition to reduce the deposition potential barrier and control the electroplating or stripping process. Moreover, an advanced electrolyte with desirable design can catalyze electrochemical reactions on the cathode and anode in high-performance M-S batteries. In this review, recent progress pertaining to the design of advanced electrode materials and electrolytes with the proper catalytic effects is summarized. The current progress of S cathodes and metal anodes in different types of M-S batteries are discussed and future development directions are described. The objective is to provide a comprehensive review on the current state-of-the-art S cathodes and metal anodes in M-S batteries and research guidance for future development of this important class of batteries.

Artificially Layered CoSe2 Nanosheets by a Dual-Templating Strategy for High-Performance Lithium-Sulfur Batteries

Owing to the attractive merits of layered transition metal dichalcogenides (LTMDs) with van der Waals interactions, it is significant to modulate electronic structures and endow them with fascinating physiochemical properties by converting a nonlayered metal dichalcogenide into an atomic layered one. Herein, a dual-templating strategy is designed to prepare artificially layered CoSe₂ nanosheets on carbon fiber cloth (L-CoSe₂/CFC). It is found that not only the nanosheet morphology but also the layered structure is well inherited from the precursor of layered Co(OH)₂ nanosheets through a wet-solution ion-exchange approach. The as-prepared L-CoSe₂/CFC serves as an efficient multifunctional interlayer to solve the challenges of "shuttling effect" and slow multistep reaction kinetics in lithium-sulfur batteries (LSBs), thus dramatically improving their electrochemical performance. Benefiting from the L-CoSe₂ nanosheets with large interlayer spacing, strong chemical adsorption, and superior catalytic activity, L-CoSe₂/CFC promotes the anchoring of lithium polysulfides (LiPSs) and their catalytic conversion. Consequently, the L-CoSe₂/CFC cell yields a large reversible capacity of 1584 mAh g^-1 at 0.2C and a high rate capability of 987 mAh g^-1 at 4C. A high areal capacity of 4.38 mAh cm^-2 after 100 cycles at 0.2C is achieved for the high-S-loading LSB (4.6 mg cm^-2) using the L-CoSe₂/CFC interlayer.

Understanding the Catalytic Kinetics of Polysulfide Redox Reactions on Transition Metal Compounds in Li-S Batteries

Because of their high energy density, low cost, and environmental friendliness, lithium-sulfur (Li-S) batteries are one of the potential candidates for the next-generation energy-storage devices. However, they have been troubled by sluggish reaction kinetics for the insoluble Li₂S product and capacity degradation because of the severe shuttle effect of polysulfides. These problems have been overcome by introducing transition metal compounds (TMCs) as catalysts into the interlayer of modified separator or sulfur host. This review first introduces the mechanism of sulfur redox reactions. The methods for studying TMC catalysts in Li-S batteries are provided. Then, the recent advances of TMCs (such as metal oxides, metal sulfides, metal selenides, metal nitrides, metal phosphides, metal carbides, metal borides, and heterostructures) as catalysts and some helpful design and modulation strategies in Li-S batteries are highlighted and summarized. At last, future opportunities toward TMC catalysts in Li-S batteries are presented.

A Porous Hexagonal Prism Shaped C-In2-xCoxO3 Electrocatalyst to Expedite Bidirectional Polysulfide Redox in Li-S Batteries

The shuttling behavior of soluble lithium polysulfides (LPSs) extremely restricts the practical application of lithium sulfur batteries (Li-S batteries). Herein, the hollow porous hexagonal prism shaped C-In_2-xCo_xO₃ composite is synthesized to restrain the shuttle effect and accelerate reaction kinetics of LPSs. The novel hexagonal prism porous carbon skeleton not only provides a stable physical framework for sulfur active materials but also facilitates efficient electron transferring and lithium ion diffusion. Meanwhile, the polar In_2-xCo_xO₃ is equipped with strong adsorption capacity for LPSs, which is confirmed by density functional theory (DFT) calculations, helping to anchor LPSs. More importantly, the doping of Co regulates the electronic structure environment of In₂O₃, expedites the electron transmission, and bidirectionally improves the catalytic conversion ability of LPSs and nucleation-decomposition of Li₂S. Benefiting from the above advantages, the electrochemical performance of Li-S batteries has been greatly enhanced. Therefore, the C-In_2-xCo_xO₃ cathode presents a good rate performance, which exhibits a low-capacity fading rate of 0.052% per cycle over 800 cycles at 5 C. Especially, even under a high sulfur loading of 4.8 mg cm^-2, the initial specific capacity is as high as 903 mAh g^-1, together with a superior capacity retention of 85.6% after 600 cycles at 0.5 C.

Redox-Transition from Irreversible to Reversible Vitamin C by Pore Confinement in Microporous Carbon Network

Enhancement of redox-reversibility in electroactive species has been studied because of fundamental interest and their importance for energy storage systems. Various electroactive molecules suffer from redox-irreversible behavior, and this is a critical reason for their exclusion as redox electrolytes in energy storage systems. In this article, we fully demonstrated that ascorbic acid (ASC), which is an abundant but redox-irreversible molecule, can become redox-reversible when it is confined in microporous carbon regimes. From a theoretical perspective, redox-reversibility in an electrochemical reaction coupled with an irreversible chemical process can be greatly enhanced due to kinetic acceleration toward the inverse direction of the chemical reaction by accumulation of products in the nanoconfined regime. However, the kinetic acceleration in a nanoconfined domain shows limitations for enhancing the redox-reversibility, which indicates that stabilization of the species undergoing an irreversible chemical process is another important factor for redox-reversibility enhancement. The origin of nanoporous confinement of ASC and its enhanced redox-reversibility was rationalized by molecular dynamics simulations. We found that ASC-clusters of a fully protonated ASC and its conjugated base formed inside carbon pores, which would be a main driving force for its confinement in microporous carbon networks. Lastly, we demonstrated a prototype energy storage device using redox-reversible ASC in microporous carbon as the half electrode, which shows the feasibility of ASC as a possible redox electrolyte in an aqueous energy storage system.

Vacancy-Rich MoSSe with Sulfiphilicity-Lithiophilicity Dual Function for Kinetics-Enhanced and Dendrite-Free Li-S Batteries

The sluggish redox kinetics of sulfur and the uncontrollable growth of lithium dendrites are two main challenges that impede the practical applications of lithium-sulfur (Li-S) batteries. In this study, a multifunctional host with vacancy-rich MoSSe vertically grown on reduced graphene oxide aerogels (MoSSe/rGO) is designed as the host material for both sulfur and lithium. The embedding of Se into a MoS₂ lattice is introduced to improve the inherent conductivity and generate abundant anion vacancies to endow the 3D conductive graphene based aerogels with specific sulfiphilicity-lithiophilicity. As a result, the assembled Li-S batteries based on MoSSe/rGO exhibit greatly improved capacity and cycling stability and can be operated under a lean electrolyte (4.8 μL mg^-1) and a high sulfur loading (6.5 mg cm^-2), achieving a high energy density. This study presents a unique method to unlock the catalysis capability and improve the inherent lithiophilicity by heteroatom doping and defect chemistry for kinetics-enhanced and dendrite-free Li-S batteries.

Review of Multifunctional Separators: Stabilizing the Cathode and the Anode for Alkali (Li, Na, and K) Metal-Sulfur and Selenium Batteries

Alkali metal batteries based on lithium, sodium, and potassium anodes and sulfur-based cathodes are regarded as key for next-generation energy storage due to their high theoretical energy and potential cost effectiveness. However, metal-sulfur batteries remain challenged by several factors, including polysulfides' (PSs) dissolution, sluggish sulfur redox kinetics at the cathode, and metallic dendrite growth at the anode. Functional separators and interlayers are an innovative approach to remedying these drawbacks. Here we critically review the state-of-the-art in separators/interlayers for cathode and anode protection, covering the Li-S and the emerging Na-S and K-S systems. The approaches for improving electrochemical performance may be categorized as one or a combination of the following: Immobilization of polysulfides (cathode); catalyzing sulfur redox kinetics (cathode); introduction of protective layers to serve as an artificial solid electrolyte interphase (SEI) (anode); and combined improvement in electrolyte wetting and homogenization of ion flux (anode and cathode). It is demonstrated that while the advances in Li-S are relatively mature, less progress has been made with Na-S and K-S due to the more challenging redox chemistry at the cathode and increased electrochemical instability at the anode. Throughout these sections there is a complementary discussion of functional separators for emerging alkali metal systems based on metal-selenium and the metal-selenium sulfide. The focus then shifts to interlayers and artificial SEI/cathode electrolyte interphase (CEI) layers employed to stabilize solid-state electrolytes (SSEs) in metal-sulfur solid-state batteries (SSBs). The discussion of SSEs focuses on inorganic electrolytes based on Li- and Na-based oxides and sulfides but also touches on some hybrid systems with an inorganic matrix and a minority polymer phase. The review then moves to practical considerations for functional separators, including scaleup issues and Li-S technoeconomics. The review concludes with an outlook section, where we discuss emerging mechanics, spectroscopy, and advanced electron microscopy (e.g. cryo-transmission electron microscopy (cryo-TEM) and cryo-focused ion beam (cryo-FIB))-based approaches for analysis of functional separator structure-battery electrochemical performance interrelations. Throughout the review we identify the outstanding open scientific and technological questions while providing recommendations for future research topics.

A Lamellar Yolk-Shell Lithium-Sulfur Battery Cathode Displaying Ultralong Cycling Life, High Rate Performance, and Temperature Tolerance

The shuttling behavior and slow conversion kinetics of the intermediate lithium polysulfides are the severe obstacles for the application of lithium-sulfur (Li-S) batteries over a wide temperature range. Here, an engineered lamellar yolk-shell structure of In2 O3 @void@carbon for the Li-S battery cathode is developed for the first time to construct a powerful barrier that effectively inhibits the shuttling of polysulfides. On the basis of the unique nanochannel-containing morphology, the continuous kinetic transformation of sulfur and polysulfides is confined in a stable framework, which is demonstrated by using X-ray nanotomography. The constructed Li-S battery exhibits a high cycling capability over 1000 cycles at 1.0 C with a capacity decay rate as low as 0.038% per cycle, good rate performance, and temperature tolerance at -10, 25, and 50 °C. A nondestructive in situ monitoring method of the interfacial reaction resistance in different cycling stages is proposed, which provides a new analysis perspective for the development of emerging electrochemical energy-storage systems.

Engineering Catalytic CoSe-ZnSe Heterojunctions Anchored on Graphene Aerogels for Bidirectional Sulfur Conversion Reactions

Sluggish sulfur reduction and lithium sulfide (Li2 S) oxidation prevent the widespread use of lithium-sulfur (Li-S) batteries, which are attractive alternatives to Li-ion batteries. The authors propose that a transition metal selenide heterojunction (CoSe-ZnSe) catalytically accelerates bidirectional sulfur conversion reactions. A combination of synchrotron X-ray absorption spectroscopy and density functional theory calculations show that a highly active heterointerface with charge redistribution and structure distortion effectively immobilizes sulfur species, facilitates Li ion diffusion, and decreases the sulfur reduction and Li2 S oxidation energy barriers. The CoSe-ZnSe catalytic cathode exhibits high areal capacities, good rate capability, and superior cycling stability with capacity fading rate of 0.027% per cycle over 1700 cycles. Furthermore, CoSe-ZnSe heterojunctions anchored on graphene aerogels (CoSe-ZnSe@G) enhance ionic transport and catalytic activity under high sulfur loading and lean electrolyte conditions. A high areal capacity of 8.0 mAh cm-2 is achieved at an electrolyte/sulfur ratio of 3 µL mg-1 . This study demonstrates the importance of bidirectional catalytic heterojunctions and structure engineering in boosting Li-S battery performances.

Rational Design and General Synthesis of Multimetallic Metal-Organic Framework Nano-Octahedra for Enhanced Li-S Battery

Metal-organic frameworks (MOFs), which consist of central metal nodes and organic linkers, constitute a fast growing class of crystalline porous materials with excellent application potential. Herein, a series of Mn-based multimetallic MOF (bimetallic and trimetallic MIL-100) nano-octahedra are prepared by a facile one-pot synthetic strategy. The types and proportions of the incorporated elements can be tuned while retaining the original topological structure. The introduction of other metal ions is verified at the atomic level by combining X-ray absorption fine structure experiments and theoretical calculations. Furthermore, these multimetallic Mn-based MIL-100 nano-octahedra are utilized as sulfur hosts to prepare cathodes for Li-S batteries. The MnNi-MIL-100@S cathode exhibits the best Li-S battery performance among all reported MIL-100@S composite cathode materials, with a reversible capacity of ≈708.8 mAh g^-1 after 200 cycles. The synthetic strategy described herein is utilized to incorporate metal ions into the MOF architecture, of which the parent monometallic MOF nano-octahedra cannot be prepared directly, thus rationally generating novel multimetallic MOFs. Importantly, the strategy also allows for the general synthesis and study of various micro-/nanoscale MOFs in the energy storage field.

Engineering Functional Interface with Built-in Catalytic and Self-Oxidation Sites for Highly Stable Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have attracted great attention due to their high theoretical energy density. The rapid redox conversion of lithium polysulfides (LiPS) is effective for solving the serious shuttle effect and improving the utilization of active materials. The functional design of the separator interface with fast charge transfer and active catalytic sites is desirable for accelerating the conversion of intermediates. Herein, a graphene-wrapped MnCO₃ nanowire (G@MC) was prepared and utilized to engineer the separator interface. G@MC with active Mn²⁺ sites can effectively anchor the LiPS by forming the Mn-S chemical bond according to our theoretical calculation results. In addition, the catalytic Mn²⁺ sites and conductive graphene layer of G@MC could accelerate the reversible conversion of LiPS via the spontaneous "self-redox" reaction and the rapid electron transfer in electrochemical process. As a result, the G@MC-based battery exhibits only 0.038 % capacity decay (per cycle) after 1000 cycles at 2.0 C. This work affords new insights for designing the integrated functional interface for stable Li-S batteries.

Rational Design of MOF-Based Materials for Next-Generation Rechargeable Batteries

This review summarizes recent progresses in pristine metal–organic frameworks (MOFs), MOF composites, and their derivatives for next-generation rechargeable batteries including lithium–sulfur batteries, lithium–oxygen batteries, sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, and Zn–air batteries.

The design strategies for MOF-based materials as the electrode, separator, and electrolyte are outlined and discussed.

The challenges and development strategies and of MOF-related materials for battery applications are highlighted.

Metal–organic framework (MOF)-based materials with high porosity, tunable compositions, diverse structures, and versatile functionalities provide great scope for next-generation rechargeable battery applications. Herein, this review summarizes recent advances in pristine MOFs, MOF composites, MOF derivatives, and MOF composite derivatives for high-performance sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, lithium–sulfur batteries, lithium–oxygen batteries, and Zn–air batteries in which the unique roles of MOFs as electrodes, separators, and even electrolyte are highlighted. Furthermore, through the discussion of MOF-based materials in each battery system, the key principles for controllable synthesis of diverse MOF-based materials and electrochemical performance improvement mechanisms are discussed in detail. Finally, the major challenges and perspectives of MOFs are also proposed for next-generation battery applications.

Conductive Al-Doped ZnO Framework Embedded with Catalytic Nanocages as a Multistage-Porous Sulfur Host in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries possess many practical challenges including the lithium polysulfide (LiPS) "shuttle effect" and their sluggish conversion kinetics. To address these issues, a unique hierarchical porous architecture, combining highly conductive ordered macroporous skeleton and embedded microporous particles is rationally designed as a dual-effective polysulfide immobilizer and conversion promoter. In this nanoporous architecture, Al-doped ZnO (AZO) acts as a conductive macroporous framework, profiting chemical anchoring of LiPS as well as facilitating electrolyte infiltration and ion diffusion; Co nanoparticle-anchored N-doped carbon (Co-NC) derived from CoZn-metal-organic framework is embedded in the macropores to further strengthen the LiPS adsorption, catalytically accelerating conversion kinetics of LiPS simultaneously. Consequently, the Co-NC@AZO/S cathode delivers a notable rate capability of 635.5 mA h g^-1 at 5 C. A high area capacity of about 5.8 mA h cm^-2 with a mass loading of 6.8 mg cm^-2 is also achieved under a lean electrolyte (E/S = 5.7). Additionally, the Li-S pouch cells equipped with Co-NC@AZO can be extended to sulfur loading as high as 4.0 mg cm^-2, delivering a superb capability of 897.5 mA h g^-1 after 100 cycles. This work puts forward a design for stably cycled and practically viable Li-S batteries.

Defect-Rich Amorphous Iron-Based Oxide/Graphene Hybrid-Modified Separator toward the Efficient Capture and Catalysis of Polysulfides

The sluggish sulfur reduction reaction, severe shuttle effect, and poor conductivity of sulfur species are three main problems in lithium-sulfur (Li-S) batteries. Functional materials with a strong affinity and catalytic effect toward polysulfides play a key role in addressing these issues. Herein, we report a defect-rich amorphous a-Fe₃O_4-x/GO material with a nanocube-interlocked structure as an adsorber as well as an electrocatalyst for the Li-S battery. The composition and defect structure of the material are determined by X-ray diffraction, high-resolution transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy measurements. The distinctive open framework architecture of the as-engineered composite inherited from the metal-organic framework precursor ensures the stability and activity of the catalyst during extended cycles. The oxygen defects in the amorphous structure are capable of absorbing polysulfides and similarly work as catalytic centers to boost polysulfide conversion. Taking advantage of a-Fe₃O_4-x/GO on the separator surface, the Li-S battery shows a capacity over 610 mA h g^-1 at 1 C and a low decay rate of 0.12% per cycle over 500 cycles and superior rate capability. The functional material made via the low-cost synthesis process provides a potential solution for advanced Li-S batteries.

Defects Engineering of Lightweight Metal-Organic Frameworks-Based Electrocatalytic Membrane for High-Loading Lithium-Sulfur Batteries

The sluggish kinetics and shuttle effect of lithium polysulfide intermediates are the major issues that retard the practical applications of lithium-sulfur (Li-S) batteries. Herein, we introduce a defect engineering strategy to construct a defected-UiO-66-NH₂-4/graphene electrocatalytic membrane (D-UiO-66-NH₂-4/G EM) which could accelerate the conversion of lithium polysulfides in high sulfur loadings and low electrolyte/sulfur (E/S) ratio Li-S batteries. Metal-organic frameworks (UiO-66-NH₂) can be directionally chemical engraved to form concave octahedra with abundant defects. According to electrocatalytic kinetics and DFT calculations studies, the D-UiO-66-NH₂-4 architecture effectively provides ample sites to capture polysulfides via strong chemical affinity and effectively delivers electrocatalytic activity of polysulfide conversion. As a result, a Li-S battery with such an electrocatalytic membrane delivers a high capacity of 12.3 mAh cm^-2 (1013 mAh g^-1) at a sulfur loading up to 12.2 mg·_S cm^-2 under a lean electrolyte condition (E/S = 5 μL mg^-1-sulfur) at 2.1 mA cm^-2 (0.1 C). Moreover, a prototype soft package battery also exhibits excellent cycling stability with a maintained capacity of 996 mAh g^-1 upon 100 cycles.

Self-Assembly of 0D-2D Heterostructure Electrocatalyst from MOF and MXene for Boosted Lithium Polysulfide Conversion Reaction

The design of nanostructured electrocatalysts with high activity and long-term durability for the sluggish lithium polysulfide (LiPS) conversion reaction is essential for the development of high-performance lithium-sulfur (Li-S) batteries. Here, the self-assembly of bimetallic selenides on nitrogen-doped MXene (CoZn-Se@N-MX) based on the self-assembly of metal-organic framework and MXene is reported. A combination of 0D CoZn-Se nanoparticles and 2D N-MX nanosheet co-catalysts forms double lithiophilic-sulfifilic binding sites that effectively immobilize and catalytically convert LiPS intermediates. This 0D-2D heterostructure catalyst has a hierarchical porous architecture with a large active area and enables rapid Li ion diffusion, reduces the activation energy of Li₂ S deposition, and lowers the energy barrier of Li₂ S dissolution. In addition, an assembled CoZn-Se@N-MX hybrid synergistically prevents the aggregation of the CoZn-Se nanoparticles and restacking of the active areas of N-MX nanosheets during assembly and the LiPS conversion process. The Li-S battery with this 0D-2D catalyst delivers excellent rate capability, ultralong cycling life (over 2000 cycles), and a high areal capacity of 6.6 mAh cm^-2 with a low electrolyte/sulfur ratio of 5 µL mg^-1 .

Recent Progress in High-Performance Lithium Sulfur Batteries: The Emerging Strategies for Advanced Separators/Electrolytes Based on Nanomaterials and Corresponding Interfaces

Lithium-sulfur (Li-S) batteries, possessing excellent theoretical capacities, low cost and nontoxicity, are one of the most promising energy storage battery systems. However, poor conductivity of elemental S and the "shuttle effect" of lithium polysulfides hinder the commercialization of Li-S batteries. These problems are closely related to the interface problems between the cathodes, separators/electrolytes and anodes. The review focuses on interface issues for advanced separators/electrolytes based on nanomaterials in Li-S batteries. In the liquid electrolyte systems, electrolytes/separators and electrodes system can be decorated by nano materials coating for separators and electrospinning nanofiber separators. And, interface of anodes and electrolytes/separators can be modified by nano surface coating, nano composite metal lithium and lithium nano alloy, while the interface between cathodes and electrolytes/separators is designed by nano metal sulfide, nanocarbon-based and other nano materials. In all solid-state electrolyte systems, the focus is to increase the ionic conductivity of the solid electrolytes and reduce the resistance in the cathode/polymer electrolyte and Li/electrolyte interfaces through using nanomaterials. The basic mechanism of these interface problems and the corresponding electrochemical performance are discussed. Based on the most critical factors of the interfaces, we provide some insights on nanomaterials in high-performance liquid or state Li-S batteries in the future.

Metal-Organic-Framework-Derived Nanostructures as Multifaceted Electrodes in Metal-Sulfur Batteries

Metal-sulfur batteries (MSBs) are considered up-and-coming future-generation energy storage systems because of their prominent theoretical energy density. However, the practical applications of MSBs are still hampered by several critical challenges, i.e., the shuttle effects, sluggish redox kinetics, and low conductivity of sulfur species. Recently, benefiting from the high surface area, regulated networks, molecular/atomic-level reactive sites, the metal-organic frameworks (MOFs)-derived nanostructures have emerged as efficient and durable multifaceted electrodes in MSBs. Herein, a timely review is presented on recent advancements in designing MOF-derived electrodes, including fabricating strategies, composition management, topography control, and electrochemical performance assessment. Particularly, the inherent charge transfer, intrinsic polysulfide immobilization, and catalytic conversion on designing and engineering of MOF nanostructures for efficient MSBs are systematically discussed. In the end, the essence of how MOFs' nanostructures influence their electrochemical properties in MSBs and conclude the future tendencies regarding the construction of MOF-derived electrodes in MSBs is exposed. It is believed that this progress review will provide significant experimental/theoretical guidance in designing and understanding the MOF-derived nanostructures as multifaceted electrodes, thus offering promising orientations for the future development of fast-kinetic and robust MSBs in broad energy fields.

Implanting Cobalt Atom Clusters within Nitrogen-Doped Carbon Network as Highly Stable Cathode for Lithium-Sulfur Batteries

Realization of highly efficient sulfur electrochemistry, as well as the high capacity of lithium-sulfur (Li-S) batteries, can be achieved by the scientific construction of electrode host materials. In this study, using molten NaCl, a 3D porous nitrogen-doped carbon with uniformly embedded Co atom clusters (Co/PNC) is developed by pyrolyzing the precursors with NaCl at high temperatures. In the composite structure, a network carbon skeleton containing hierarchical pores acts as an advanced matrix for sulfur electrodes, and the doping of N and Co is subject to inhibit the shuttle of long-chain lithium polysulfides through chemical adsorption. The Co/PNC, with the optimized amount of Co, delivers an initial specific capacity of 1105.4 mAh g^-1 at 0.2 C with a capacity drop of only 0.064% after the cell is charged and discharged for 300 cycles at 1 C, revealing its potential in promoting the large-scale application of Li-S batteries.

Highly Lithiophilic Copper-Reinforced Scaffold Enables Stable Li Metal Anode

Lithium (Li) metal is regarded as one of the most prospective electrodes for next-generation rechargeable batteries. However, its widespread usage has been fettered by low coulombic efficiency (CE), poor cycling stability, and serious safety concerns, mainly arising from huge volumetric variation, inhomogeneous Li deposition, and dendrite growth during repeated Li plating/stripping cycles. Herein, we propose a facile one-pot electrospinning-derived highly lithiophilic nanocopper-reinforced three-dimensional-structured carbon nanofiber (Cu-CNF) as functional scaffold to stabilize the Li metal. The Cu-CNF scaffolded Li metal demonstrates homogeneous nanoplate-like Li deposition, enhanced CE, and ultrastable long lifespan cycling. As coupled with LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811), the cell possesses a remarkably stable high capacity retention of 93% over 300 cycles at 0.2 C. Furthermore, the cells paired with a thick LiFePO₄ (LFP) electrode (∼12 mg cm^-2) still can deliver a superior cycling performance even under the harsh conditions of an extremely low negative/positive electrode capacity (N/P) ratio (∼1.5) and lean electrolyte. Density functional theory calculations are performed to disclose the mechanism of the enhanced electrochemical performance of Cu-CNF scaffolded Li. This work provides a handy and cost-effective method to design superior performance Li metal anodes for practical applications.

Hierarchical Nanoreactor with Multiple Adsorption and Catalytic Sites for Robust Lithium-Sulfur Batteries

Developing high-performance cathode host materials is fundamental to solve the low utilization of sulfur, the sluggish redox kinetics, and the lithium polysulfide (LiPS) shuttle effect in lithium-sulfur batteries (LSBs). Here, a multifunctional Ag/VN@Co/NCNT nanocomposite with multiple adsorption and catalytic sites within hierarchical nanoreactors is reported as a robust sulfur host for LSB cathodes. In this hierarchical nanoreactor, heterostructured Ag/VN nanorods serve as a highly conductive backbone structure and provide internal catalytic and adsorption sites for LiPS conversion. Interconnected nitrogen-doped carbon nanotubes (NCNTs), in situ grown from the Ag/VN surface, greatly improve the overall specific surface area for sulfur dispersion and accommodate volume changes in the reaction process. Owing to their high LiPS adsorption ability, outer Co nanoparticles at the top of the NCNTs catch escaped LiPS, thus effectively suppressing the shuttle effect and enhancing kinetics. Benefiting from the multiple adsorption and catalytic sites of the developed hierarchical nanoreactors, Ag/VN@Co/NCNTs@S cathodes display outstanding electrochemical performances, including a superior rate performance of 609.7 mAh g^-1 at 4 C and a good stability with a capacity decay of 0.018% per cycle after 2000 cycles at 2 C. These properties demonstrate the exceptional potential of Ag/VN@Co/NCNTs@S nanocomposites and approach LSBs closer to their real-world application.