Toward Practical High-Energy-Density Lithium-Sulfur Pouch Cells: A Review

1T-rich MoS2 nanosheets anchored on conductive porous carbon as effective polysulfide promoters for lithium-sulfur batteries

The practical applications of lithium-sulfur (Li-S) batteries have severely been hindered by notorious shuttle effect and sluggish redox kinetics of lithium polysulfide intermediates (LiPSs), which bring about rapid capacity degradation, low coulombic efficiency and poor cycling stability. In this work, 1T-rich MoS2 nanosheets are in-situ developed onto the conductive porous carbon matrix (1T-rich MoS2@PC) as efficient polysulfide promotors for high-performance Li-S batteries. The porous carbon skeleton tightly anchors MoS2 nanosheets to prevent their reaggregation and ensures accessible electrical channels, and at the same time provides a favorable confined space that promotes the generation of 1T-rich MoS2 structure. More importantly, the uniformly distributed metallic 1T-rich MoS2 nanosheets not only affords rich sulfphilic sites and high binding energy for immobilizing LiPSs, but also favors rapid electron transfer and LiPSs conversation kinetics, substantially regulating sulfur chemistry in working cells. Consequently, the Li-S cell assembled with 1T-rich MoS2@PC modified separator delivers a remarkable cycling stability with ultralow capacity decay rate of 0.067% over 500 cycles at 1C. Encouragingly, under harsh conditions (high sulfur loading of 4.78 mg cm-2 and low E/S ratio of 8 μL mg-1), a favorable electrochemical performance can still be demonstrated. This study highlights the profitable design of 1T-rich MoS2/carbon based electrocatalyst for suppressing shuttle effect and promoting catalytic conversation of LiPSs, and has the potential to be applied to in other energy storage systems.

Construction and catalysis role of a kinetic promoter based on lithium-insertion technology and proton exchange strategy for lithium-sulfur batteries

The high theoretical energy density and specific capacity of lithium-sulfur (Li-S) batteries have garnered considerable attention in the prospective market. However, ongoing research on Li-S batteries appears to have encountered a bottleneck, with unresolved key technical challenges such as the significant shuttle effect and sluggish reaction kinetics. This investigation explores the catalytic efficacy of three catalysts for Li-S batteries and elucidates the correlation between their structure and catalytic impacts. The results suggest that the combined utilization of lithium-insertion technology and a proton exchange approach for δ-MnO2 can optimize its electronic structure, resulting in an optimal catalyst (H/Li inserted δ-MnO2, denoted as HLM) for the sulfur reduction reaction. The replacement of Mn sites in δ-MnO2 with Li atoms can enhance the structural stability of the catalyst, while the introduction of H atoms between transition metal layers contributes to the satisfactory catalytic performance of HLM. Theoretical calculations demonstrate that the bond length of Li2S4 adsorbed by the HLM molecule is elongated, thereby facilitating the dissociation process of Li2S4 and enhancing the reaction kinetics in Li-S batteries. Consequently, the Li-S battery utilizing HLM as a catalyst achieves a high areal specific capacity of 4.2 mAh cm-2 with a sulfur loading of 4.1 mg cm-2 and a low electrolyte/sulfur (E/S) ratio of 8 μL mg-1. This study introduces a methodology for designing effective catalysts that could significantly advance practical developments in Li-S battery technology.

V-Doped CoSe2 Nanowire Catalysts in a 3D-Structured Electrode for Durable Li-S Pouch Cells

Lithium-sulfur (Li-S) batteries have high theoretical energy density and are regarded as a promising candidate for next-generation energy storage systems. However, their practical applications are hindered by the slow kinetics of sulfur conversion and polysulfide shuttling. In particular, large-scale pouch cells show much poor cyclability. Here, we develop a high-efficiency catalyst of V-doped CoSe2 by studying the binary CoSe2-VSe2 system and confirming its effectiveness in accelerating polysulfide conversion. The coin cell tests reveal an initial capacity of 1414 mAh g-1 at 0.1 C and 1049 mAh g-1 at 1 C and demonstrate 1000 times cyclability with a decaying rate of 0.05% per cycle. Furthermore, the assembly and construction of pouch cells were optimized with monolithic three-dimensional (3D) electrodes and a multistacking strategy. Specifically, a 3D metallic scaffold (3MS) was developed to host V-doped CoSe2 nanowires and sulfur. In addition, Janus microspheres of C@TiO2 were synthesized to capture polar polysulfides with their polar part of TiO2 and adsorb nonpolar sulfur with their nonpolar part of carbon. By integrating with 3MS, C@TiO2 microspheres can block all ion channels of 3MS and only allow Li ions in and out. These integral designs and monolithic structures enable multistacking pouch cells with high cyclability. A high-loading pouch cell was demonstrated with a total capacity of 700 mAh. The cell can be cycled for 70 times with a capacity retention of 65.7%. In brief, this work provides an integral strategy of catalyst design and overall 3D assembly for practical Li-S batteries in a large pouch cell format.

Synergistic restriction of polysulfides enabled by cobalt@carbon spheres embedded CNTs: A facile approach for constructing sulfur cathodes with high sulfur content

Despite the bright fortune of lithium-sulfur (Li-S) batteries as one of the next-generation energy storage systems owing to the ultrahigh theoretical energy density and earth-abundance of sulfur, crucial challenges including polysulfide shuttling and low sulfur content of sulfur cathodes need to be overcome before the commercial survival of sulfur cathodes. Herein, cobalt/carbon spheres embedded CNTs (Co-C-CNTs) are rationally designed as multifunctional hosts to synergistically address the drawbacks of sulfur cathodes. The host is synthesized by a facile pyrolysis using Co(OH)2 template and followed with the controllable etching process. The hierarchical porous structure owning high pore volume and surface area can buffer the volume change, physically confine polysulfides, and provide conductive networks. Besides, partially remained metallic cobalt nanoparticles are favorable for chemical adsorption and conversion of polysulfides, as validated by density functional theory simulations. With the combination of above merits, the S@Co-C-CNTs cathodes with a high sulfur content of 80 wt% present a superior initial capacity (1568 mAh g-1 at 0.1C) with ultrahigh 93.6% active material utilization, and excellent rate performance (649 mAh g-1 at 2C), providing feasible strategies for the optimization of cathodes in metal-sulfur batteries.

Healable and Conductive Two-Dimensional Sulfur Iodide for High-Rate Sodium Batteries

Self-healing functional materials can repair cracks and damage inside the battery, ensuring the stability of the battery material structure. This feature minimizes performance degradation during the charging and discharging processes, improving the efficiency and stability of the battery. Here, we have developed a novel healing conductive two-dimensional sulfur iodide (SI4) composite cathode. This process integrates both sulfur and iodine compounds into carbon nanocages, forming a SI4@C core-shell structure. This cathode design improves electrical conductivity and repairability, facilitates rapid activation, and ensures structural integrity, resulting in a typical Na-SI4 battery with high capacity and an exceptionally long cycle life. At 10.0 A g-1, the capacity of the Na-SI4 battery can still reach 217.4 mAh g-1 after more than 500 cycles, and the capacity decay rate per cycle is only 0.06%. In addition, the cathode exhibits a cascade redox reaction involving S and I, contributing to its high capacity. The in situ growth of a carbon shell further enhances the conductivity and structural robustness of the entire cathode. The flexibility and bendability of SI4@C-carbon cloth make it applicable for flexible electronic devices, providing more possibilities for battery design. The strategy of engineering a two-dimensional self-healing structure to construct a superior cathode is expected to be widely applied to other electrode materials. This study provides a new pathway for designing novel binary-conversion-type sodium-ion batteries with excellent long-term cycling performance.

Perspectives on Advanced Lithium-Sulfur Batteries for Electric Vehicles and Grid-Scale Energy Storage

Intensive increases in electrical energy storage are being driven by electric vehicles (EVs), smart grids, intermittent renewable energy, and decarbonization of the energy economy. Advanced lithium-sulfur batteries (LSBs) are among the most promising candidates, especially for EVs and grid-scale energy storage applications. In this topical review, the recent progress and perspectives of practical LSBs are reviewed and discussed; the challenges and solutions for these LSBs are analyzed and proposed for future practical and large-scale energy storage applications. Major challenges for the shuttle effect, reaction kinetics, and anodes are specifically addressed, and solutions are provided on the basis of recent progress in electrodes, electrolytes, binders, interlayers, conductivity, electrocatalysis, artificial SEI layers, etc. The characterization strategies (including in situ ones) and practical parameters (e.g., cost-effectiveness, battery management/modeling, environmental adaptability) are assessed for crucial automotive/stationary large-scale energy storage applications (i.e., EVs and grid energy storage). This topical review will give insights into the future development of promising Li-S batteries toward practical applications, including EVs and grid storage.

A Universal Electronic Structure Modulation Strategy: Is Strong Adsorption Always Correlated with High Catalysis?

Unveiling the inherent link between polysulfide adsorption and catalytic activity is key to achieving optimal performance in Lithium-sulfur (Li-S) batteries. Current research on the sulfur reaction process mainly relies on the strong adsorption of catalysts to confine lithium polysulfides (LiPSs) to the cathode side, effectively suppressing the shuttle effect of polysulfides. However, is strong adsorption always correlated with high catalysis? The inherent relationship between adsorption and catalytic activity remains unclear, limiting the in-depth exploration and rational design of catalysts. Herein, the correlation between "d-band center-adsorption strength-catalytic activity" in porous carbon nanofiber catalysts embedded with different transition metals (M-PCNF-3, M = Fe, Co, Ni, Cu) is systematically investigated, combining the d-band center theory and the Sabatier principle. Theoretical calculations and experimental analysis results indicate that Co-PCNF-3 electrocatalyst with appropriate d-band center positions exhibits moderate adsorption capability and the highest catalytic conversion activity for LiPSs, validating the Sabatier relationship in Li-S battery electrocatalysts. These findings provide indispensable guidelines for the rational design of more durable cathode catalysts for Li-S batteries.

Heterogenization-Activated Zinc Telluride via Rectifying Interfacial Contact to Afford Synergistic Confinement-Adsorption-Catalysis for High-Performance Lithium-Sulfur Batteries

The notorious shuttle effect and sluggish conversion kinetics of intermediate polysulfides (Li2S4, Li2S6, Li2S8) are severely hindered the large-scale development of Lithium-sulfur (Li-S) batteries. Rectifying interface effect has been a solution to regulate the electron distribution of catalysts via interfacial charge exchange. Herein, a ZnTe-ZnO heterojunction encapsulated in nitrogen-doped hierarchical porous carbon (ZnTe-O@NC) derived from metal-organic framework is fabricated. Theoretical calculations and experiments prove that the built-in electric field constructed at ZnTe-ZnO heterojunction via the rectifying interface contact, thus promoting the charge transfer as well as enhancing adsorption and conversion kinetics toward polysulfides, thereby stimulating the catalytic activity of the ZnTe. Meanwhile, the nitrogen-doped hierarchical porous carbon acts as confinement substrate also enables fast electrons/ions transport, combining with ZnTe-ZnO heterojunction realize a synergistic confinement-adsorption-catalysis toward polysulfides. As a result, the Li-S batteries with S/ZnTe-O@NC electrodes exhibit an impressive rate capability (639.7 mAh g-1 at 3 C) and cycling performance (70% capacity retention at 1 C over 500 cycles). Even with a high sulfur loading, it still delivers a superior electrochemical performance. This work provides a novel perspective on designing highly catalytic materials to achieve synergistic confinement-adsorption-catalysis for high-performance Li-S batteries.

Unveiling Confinement Engineering for Achieving High-Performance Rechargeable Batteries

The confinement effect, restricting materials within nano/sub-nano spaces, has emerged as an innovative approach for fundamental research in diverse application fields, including chemical engineering, membrane separation, and catalysis. This confinement principle recently presents fresh perspectives on addressing critical challenges in rechargeable batteries. Within spatial confinement, novel microstructures and physiochemical properties have been raised to promote the battery performance. Nevertheless, few clear definitions and specific reviews are available to offer a comprehensive understanding and guide for utilizing the confinement effect in batteries. This review aims to fill this gap by primarily summarizing the categorization of confinement effects across various scales and dimensions within battery systems. Subsequently, the strategic design of confinement environments is proposed to address existing challenges in rechargeable batteries. These solutions involve the manipulation of the physicochemical properties of electrolytes, the regulation of electrochemical activity, and stability of electrodes, and insights into ion transfer mechanisms. Furthermore, specific perspectives are provided to deepen the foundational understanding of the confinement effect for achieving high-performance rechargeable batteries. Overall, this review emphasizes the transformative potential of confinement effects in tailoring the microstructure and physiochemical properties of electrode materials, highlighting their crucial role in designing novel energy storage devices.

Kinetic Evaluation on Lithium Polysulfide in Weakly Solvating Electrolyte toward Practical Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are highly considered as next-generation energy storage techniques. Weakly solvating electrolyte with low lithium polysulfide (LiPS) solvating power promises Li anode protection and improved cycling stability. However, the cathodic LiPS kinetics is inevitably deteriorated, resulting in severe cathodic polarization and limited energy density. Herein, the LiPS kinetic degradation mechanism in weakly solvating electrolytes is disclosed to construct high-energy-density Li-S batteries. Activation polarization instead of concentration or ohmic polarization is identified as the dominant kinetic limitation, which originates from higher charge-transfer activation energy and a changed rate-determining step. To solve the kinetic issue, a titanium nitride (TiN) electrocatalyst is introduced and corresponding Li-S batteries exhibit reduced polarization, prolonged cycling lifespan, and high actual energy density of 381 Wh kg-1 in 2.5 Ah-level pouch cells. This work clarifies the LiPS reaction mechanism in protective weakly solvating electrolytes and highlights the electrocatalytic regulation strategy toward high-energy-density and long-cycling Li-S batteries.

Anion-Involved Solvation Structure of Lithium Polysulfides in Lithium-Sulfur Batteries

Lithium polysulfides (LiPSs) are pivotal intermediates involved in all the cathodic reactions in lithium-sulfur (Li-S) batteries. Elucidating the solvation structure of LiPSs is the first step for rational design of electrolyte and improving Li-S battery performances. Herein, we investigate the solvation structure of LiPSs and find that Li salt anions tend to enter the first solvation sheath of LiPSs and form contact ion pairs in electrolyte. The anion-involved solvation structure of LiPSs significantly influences the intrinsic kinetics of the sulfur redox reactions. In particular, the LiPS solvation structure modified by lithium bis(fluorosulfonyl)imide endows Li-S batteries with reduced polarization and enhanced rate performances under high sulfur areal loading and lean electrolyte volume conditions. This work updates the fundamental understanding of the solvation chemistry of LiPSs and highlights electrolyte engineering for promoting the performances of Li-S batteries.

Advanced Polymers in Cathodes and Electrolytes for Lithium-Sulfur Batteries: Progress and Prospects

Lithium-sulfur (Li-S) batteries, which store energy through reversible redox reactions with multiple electron transfers, are seen as one of the promising energy storage systems of the future due to their outstanding advantages. However, the shuttle effect, volume expansion, low conductivity of sulfur cathodes, and uncontrollable dendrite phenomenon of the lithium anodes have hindered the further application of Li-S batteries. In order to solve the problems and clarify the electrochemical reaction mechanism, various types of materials, such as metal compounds and carbon materials, are used in Li-S batteries. Polymers, as a class of inexpensive, lightweight, and electrochemically stable materials, enable the construction of low-cost, high-specific capacity Li-S batteries. Moreover, polymers can be multifunctionalized by obtaining rich structures through molecular design, allowing them to be applied not only in cathodes, but also in binders and solid-state electrolytes to optimize electrochemical performance from multiple perspectives. The most widely used areas related to polymer applications in Li-S batteries, including cathodes and electrolytes, are selected for a comprehensive overview, and the relevant mechanisms of polymer action in different components are discussed. Finally, the prospects for the practical application of polymers in Li-S batteries are presented in terms of advanced characterization and mechanistic analysis.

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.

High-Throughput Screening of Sulfur Reduction Reaction Catalysts Utilizing Electronic Fingerprint Similarity

The catalytic performance is determined by the electronic structure near the Fermi level. This study presents an effective and simple screening descriptor, i.e., the one-dimensional density of states (1D-DOS) fingerprint similarity, to identify potential catalysts for the sulfur reduction reaction (SRR) in lithium-sulfur batteries. The Δ1D-DOS in relation to the benchmark W2CS2 was calculated. This method effectively distinguishes and identifies 30 potential candidates for the SRR from 420 types of MXenes. Further analysis of the Gibbs free energy profiles reveals that MXene candidates exhibit promising thermodynamic properties for SRR, with the protocol achieving an accuracy rate exceeding 93%. Based on the crystal orbital Hamilton population (COHP) and differential charge analysis, it is confirmed that the Δ1D-DOS could effectively differentiate the interaction between MXenes and lithium polysulfide (LiPS) intermediates. This study underscores the importance of the electronic fingerprint in catalytic performance and thus may pave a new way for future high-throughput material screening for energy storage applications.

Optimization of the Form Factors of Advanced Li-S Pouch Cells

Lithium-sulfur (Li-S) batteries hold immense promise as next-generation energy storage due to their high theoretical energy density (2600 Wh kg⁻¹), low cost, and non-toxic nature. However, practical implementation faces challenges, primarily from Li polysulfide (LiPS) shuttling within the cathode and Li dendrite growth at the anode. Optimized electrodes/electrolytes design effectively confines LiPS to the cathode, boosting cycling performance in coin cells to up to hundreds of cycles. Scaling up to larger pouch cells presents new obstacles, requiring further research for long-term stability. A 1.45 Ah pouch cell, with optimized sulfur loading and electrolyte/sulfur ratio is developed, which delivers an energy density of 151 Wh kg-1 with 70% capacity retention up to 100 cycles. Targeting higher energy density (180 Wh kg-1 ), the developed 1Ah pouch cell exhibits 68% capacity retention after 50 cycles. Morphological analysis reveals that pouch cell failure is primarily from Li metal powdering and resulting polarization, rather than LiPS shuttling. This occurs for continuous Li ion stripping/plating during cycling, leading to dendrite growth and formation of non-reactive Li powder, especially under high currents. These issues increase ion diffusion resistance and reduce coulombic efficiency over time. Therefore, the study highlights the importance of a protected Li metal anode for achieving high-energy-dense batteries.

Enhancing Li-S Battery Performance with Limiting Li[N(SO2F)2] Content in a Sulfolane-Based Sparingly Solvating Electrolyte

By enhancing the stability of the lithium metal anode and mitigating the formation of lithium dendrites through electrolyte design, it becomes feasible to extend the lifespan of lithium-sulfur (Li-S) batteries. One widely accepted approach involves the utilization of Li[N(SO2F)2] (Li[FSA]), which holds promise in stabilizing the lithium anode by facilitating the formation of an inorganic-dominant solid electrolyte interface (SEI) film. However, the use of Li[FSA] encounters limitations due to inevitable side reactions between lithium polysulfides (LiPSs) and [FSA] anions. In this study, our focus lies in precisely controlling the composition of the SEI film and the morphology of the deposited lithium, as these two critical factors profoundly influence lithium reversibility. Specifically, by subjecting an initial charging process to an elevated temperature, we have achieved a significant enhancement in lithium reversibility. This improvement is accomplished through the employment of a LiPS sparingly solvating electrolyte with a restricted Li[FSA] content. Notably, these optimized conditions have resulted in an enhanced cycling performance in practical Li-S pouch cells. Our findings underscore the potential for improving the cycling performance of Li-S batteries, even when confronted with challenging constraints in electrolyte design.

Cement/Sulfur for Lithium-Sulfur Cells

Lithium-sulfur batteries represent a promising class of next-generation rechargeable energy storage technologies, primarily because of their high-capacity sulfur cathode, reversible battery chemistry, low toxicity, and cost-effectiveness. However, they lack a tailored cell material and configuration for enhancing their high electrochemical utilization and stability. This study introduces a cross-disciplinary concept involving cost-efficient cement and sulfur to prepare a cement/sulfur energy storage material. Although cement has low conductivity and porosity, our findings demonstrate that its robust polysulfide adsorption capability is beneficial in the design of a cathode composite. The cathode composite attains enhanced cell fabrication parameters, featuring a high sulfur content and loading of 80 wt% and 6.4 mg cm-2, respectively. The resulting cell with the cement/sulfur cathode composite exhibits high active-material retention and utilization, resulting in a high charge storage capacity of 1189 mA∙h g-1, high rate performance across C/20 to C/3 rates, and an extended lifespan of 200 cycles. These attributes contribute to excellent cell performance values, demonstrating areal capacities ranging from 4.59 to 7.61 mA∙h cm-2, an energy density spanning 9.63 to 15.98 mW∙h cm-2, and gravimetric capacities between 573 and 951 mA∙h g-1 per electrode. Therefore, this study pioneers a new approach in lithium-sulfur battery research, opting for a nonporous material with robust polysulfide adsorption capabilities, namely cement. It effectively showcases the potential of the resulting cement/sulfur cathode composite to enhance fabrication feasibility, cell fabrication parameters, and cell performance values.

Progress and Perspectives on the Development of Pouch-Type Lithium Metal Batteries

Lithium (Li) metal batteries (LMBs) are the "holy grail" in the energy storage field due to their high energy density (theoretically >500 Wh kg-1 ). Recently, tremendous efforts have been made to promote the research & development (R&D) of pouch-type LMBs toward practical application. This article aims to provide a comprehensive and in-depth review of recent progress on pouch-type LMBs from full cell aspect, and to offer insights to guide its future development. It will review pouch-type LMBs using both liquid and solid-state electrolytes, and cover topics related to both Li and cathode (including LiNix Coy Mn1-x-y O2 , S and O2 ) as both electrodes impact the battery performance. The key performance criteria of pouch-type LMBs and their relationship in between are introduced first, then the major challenges facing the development of pouch-type LMBs are discussed in detail, especially those severely aggravated in pouch cells compared with coin cells. Subsequently, the recent progress on mechanistic understandings of the degradation of pouch-type LMBs is summarized, followed with the practical strategies that have been utilized to address these issues and to improve the key performance criteria of pouch-type LMBs. In the end, it provides perspectives on advancing the R&Ds of pouch-type LMBs towards their application in practice.

Introduced Hierarchically Ordered Porous Architecture on a Separator as an Efficient Polysulfide Trap toward High-Mass-Loading Li-S Batteries

The severe shuttle effect and the depletion of active sulfur result in performance deterioration, presenting two formidable issues that must be overcome to achieve high-mass-loading lithium-sulfur batteries. Herein, we reported a composite separator by introducing carbon photonic crystals with a hierarchically ordered porous structure on a commercial separator. The ordered structure and interconnected hierarchical macro-meso-micropore network of the composite separator facilitate efficient trapping of polysulfides and rapid transport of lithium ions. The high ion diffusivity promotes the conversion of polysulfides enhancing sulfur utilization and mitigating the occurrence of "dead sulfur" on the surface of the separator. Impressively, under a high sulfur loading of 3 mg cm-2, the lithium-sulfur battery with the composite separator displayed a high reversible capacity of 1582 mA h g-1 at 0.1 C and an excellent long-term cycling performance with a decay rate of as low as 0.033% per cycle over 1500 cycles at 1 C. Surprisingly, the battery represented a high reversible capacity of 935 mA h g-1 at 0.2 C even at a sulfur loading of 6.71 mg cm-2. The design of the composite separator underscores the pivotal role of carbon architecture in improving battery performance and brings a bright prospect to enable the commercialization of high-mass-loading lithium-sulfur batteries.

Toward Stimulating the Chemistry Process for Garnet Electrolyte-Based Molten Li-S Batteries: Modulation of the End-Product in the Cathode with High Loading

Due to their low self-discharge rate, no intermediate product dissolution in the cathode, and easy recycle of electrode materials, solid electrolyte-based molten lithium sulfur batteries can be one of the highly anticipated advanced electrochemical chemistry technologies for grid-scale energy storage. However, the actual energy density and reversibility of them still face severe challenges for low active materials loading and the inherent low conductivity of sulfur and its end-products. In this work, with the iodide modulation effect, small size (∼5 nm for the primary particles) and low relative crystallinity discharge end-products in the sulfur cathode can be formed, contributing to the immense specific capacity and reversibility. As validated by theoretical calculations, iodide ions in the homogeneous molten composite cathode display a profound comprehensive effect on the chemical reaction and cycling stability. As a result, high sulfur loading (over 80 mg cm-2) with a significant utilization rate can be achieved, corresponding to a single Li-S cell of 1.39 Ah and a volumetric energy density of 528.5 Wh L-1 based on the overall cell volume; simultaneously, a prominent cycling stability during 300 cycles along with an impressive reversibility is obtained.

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.

Ultrathin Mixed Ionic-Electronic Conducting Interlayer via the Solution Shearing Technique for High-Performance Lithium-Sulfur Batteries

The commercialization of lithium-sulfur (Li-S) batteries has been hampered by diverse challenges, including the shuttle phenomenon and low electrical/ionic conductivity of lithium sulfide and sulfur. To address these issues, extensive research has been devoted to developing multifunctional interlayers. However, interlayers capable of simultaneously suppressing the polysulfide (PS) shuttle and ensuring stable electrical and ionic conductivity are relatively uncommon. Moreover, the use of thick and heavy interlayers results in an unavoidable decline in the energy density of Li-S batteries. We developed an ultrathin (750 nm), lightweight (0.182 mg cm-2) interlayer that facilitates mixed ionic-electronic conduction using the solution shearing technique. The interlayer, composed of carbon nanotube (CNT)/Nafion/poly-3,4-ethylenedioxythiophene:tetracyanoborate (PEDOT:TCB), effectively suppresses the shuttle phenomenon through the synergistic segregation and adsorption effects on PSs by Nafion and CNT/PEDOT, respectively. Furthermore, the electrical/ionic conductivity of the interlayer can be improved via counterion exchange and homogeneous Li+ ion flux/good wettability from SO3- functional group of Nafion, respectively. Enhanced sulfur utilization and reaction kinetics through polysulfide shuttle inhibition and facilitated electron/ion transfer by interlayer enable a high discharge capacity of 1029 mA h g-1 in the Li-S pouch cell under a high sulfur loading of 5.3 mg cm-2 and low electrolyte/sulfur ratio of 5 μL mg-1.

Promoting Homogeneous Zinc-Ion Transfer Through Preferential Ion Coordination Effect in Gel Electrolyte for Stable Zinc Metal Batteries

Aqueous zinc metal batteries (AZMBs) are emerging energy storage systems that are poised to replace conventional lithium-ion batteries owing to their intrinsic safety, facile manufacturing process, economic benefits, and superior ionic conductivity. However, the issues of inferior anode reversibility and dendritic plating during operation remain challenging for the practical use of AZMBs. Herein, a gel electrolyte based on zwitterionic poly(sulfobetaine methacrylate) (poly(SBMA)) dissolved with different concentrations of ZnSO4 is proposed. Two-dimensional correlation spectroscopy based on Raman analysis reveals an enhanced interaction priority between the polar groups in SBMA and the dissolved ions as electrolyte concentration increases, which establishes a robust interaction and renders homogeneous ion distribution. Attributable to the modified coordination, zwitterionic gel polymer electrolyte with 5 mol kg-1 of ZnSO4 (ZGPE-5) facilitates stable zinc deposition and improves anode reversibility. By taking advantage of preferential coordination, a symmetrical cell evaluation employing ZGPE-5 demonstrates a cycle life over 3600 h, where ZGPE-5 also exerts a beneficial effect on the full cell cycling when assembled with Zn0.25 V2 O5 cathode. This study elucidates changes in the internal ion behavior that are dependent on electrolyte concentrations and pave the way for durable AZMBs.

Zwitterionic Covalent Organic Framework Based Electrostatic Field Electrocatalysts for Durable Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are one of the most promising candidates for next-generation energy storage systems. To develop long-life LSBs, there is an urgent need to develop functional materials with higher catalytic activity toward polysulfides and reduced dendritic lithium growth. Herein, an electrostatic field electrocatalyst is designed in a zwitterionic covalent organic framework (COF) with a "two birds with one stone" ability for simultaneously overcoming obstacles in the lithium metal anode and sulfur cathode. The synergism between cationic and anionic moieties in the zwitterionic COF creates an electrostatic field for bidirectionally catalyzing S cathode conversion. Besides, the rational design of zwitterionic COF as a separator modification layer allows lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dissociation and fast lithium-ion conduction, which alleviates lithium dendrite growth and thus improves the cycling life of LSBs. This contribution not only pioneers the application of zwitterionic COF in the field of LSBs but also highlights the potential of electrostatic field electrocatalysts.

Electrochemical Enhancement of Lithium-Ion Diffusion in Polypyrrole-Modified Sulfurized Polyacrylonitrile Nanotubes for Solid-to-Solid Free-Standing Lithium-Sulfur Cathodes

The energy density of lithium-sulfurized polyacrylonitrile (Li-SPAN) batteries has chronically suffered from low sulfur content. Although a free-standing electrode can significantly reduce noncapacity mass contribution, the slow bulk reaction kinetics still constrain the electrochemical performance. In this regard, a novel electrochemically active additive, polypyrrole (PPy), is introduced to construct PAN nanotubes as a sulfur carrier. This hollow channel greatly facilitates charge transport within the electrode and increases the sulfur content. Both electrochemical tests and simulations show that the SPANPPy-1% cathode possesses a larger lithium-ion diffusion coefficient and a more homogeneous phase interface than the SPAN cathode. Consequently, significantly improved capabilities and rate properties are achieved, as well as decent exportations under high-sulfur-loading or lean-electrolyte conditions. In-situ and semi-situ characterizations are further performed to demonstrate the nucleation growth of lithium sulfide and the evolution of the electrode surface structure. This type of electrochemically active additive provides a well-supported implementation of high-energy-density Li-S batteries.

Nontraditional Approaches To Enable High-Energy and Long-Life Lithium-Sulfur Batteries

ConspectusLithium-sulfur (Li-S) batteries are promising for automotive applications due to their high theoretical energy density (2600 Wh/kg). In addition, the natural abundance of sulfur could mitigate the global raw material supply chain challenge of commercial lithium-ion batteries that use critical elements, such as nickel and cobalt. However, due to persistent polysulfide shuttling and uncontrolled lithium dendrite growth, Li-S batteries using nonencapsulated sulfur cathodes and conventional ether-based electrolytes suffer from rapid cell degradation upon cycling. Despite significant improvements in recent decades, there is still a big gap between lab research and commercialization of the technology. To date, the reported cell energy densities and cycling life of practical Li-S pouch cells remain largely unsatisfactory.Traditional approaches to improving Li-S performance are primarily focused on confining polysulfides using electronically conductive hosts. However, these micro- and mesoporous hosts suffer from limited pore volume to accommodate high sulfur loading and the associated volume change during cycling. Moreover, they fail to balance adsorption-conversion of polysulfides during charge-discharge, leading to the formation of massive dead sulfur. Such hosts are themselves electrochemically inactive, which decreases the practical energy density. In contrast, a series of nontraditional approaches, paired with advances in multiscale mechanistic understanding, have recently demonstrated exciting performance outcomes not only in conventional coin cells but also in practical pouch cells.In this Account, we first introduce our novel cathode design strategies to overcome polysulfide shuttling and sluggish redox kinetics in thick S cathodes via selenium-sulfur chemistry and cathode host engineering. Next, we gain a mechanistic understanding of Li-S batteries in various types of electrolytes via a series of spectroscopic, nuclear magnetic resonance, and electrochemical methods. Meanwhile, a novel cathode solid electrolyte interphase encapsulation strategy via nonviscous highly fluorinated ether-based electrolyte is introduced. The established selection rule by investigating how solvating power retards the shuttle effect and induces robust cathode/solid-electrolyte interphase formation is also included. We then discuss how the synergistic interactions between rational cathode structures and electrolytes can be exploited to tailor the reaction pathways and kinetics of S cathodes under high mass loading and lean electrolyte conditions. In addition, a novel interlayer design to simultaneously overcome degradation processes (polysulfide shuttling and lithium dendrite formation) and accelerate redox reaction kinetics is presented. Finally, this Account concludes with an overview of the challenges and strategies to develop Li-S pouch cells with high practical energy density, long cycle life, and fast-charging capability.

Rational Design of a High-Loading Polysulfide Cathode and a Thin-Lithium Anode for Developing Lean-Electrolyte Lithium-Sulfur Full Cells

Lithium-sulfur cells are attractive energy-storage systems because of their high energy density and the electrochemical utilization rates of the high-capacity lithium-metal anode and the low-cost sulfur cathode. The commercialization of high-performance lithium-sulfur cells with high discharge capacity and cyclic stability requires the optimization of practical cell-design parameters. Herein, a carbon structural material composed of a carbon nanotube skeleton entrapping conductive graphene is synthesized as an electrode substrate. The carbon structural material is optimized to develop a high-loading polysulfide cathode with a high sulfur loading capacity (6-12 mg cm-2 ), rate performance (C/10-C/2), and cyclic stability for 200 cycles. A thin lithium anode based on the carbon structural material is developed and exhibits long lithium stripping/plating stability for ≈2500 h with a lithium-ion transference number of 0.68. A lean-electrolyte lithium-sulfur full cell with a low electrolyte-to-sulfur ratio of 6 µL mg-1 is constructed with the designed high-loading polysulfide cathode and the thin lithium anode. The integration of all the critical cell-design parameters endows the lithium-sulfur full cell with a low negative-to-positive capacity ratio of 2.4, while exhibiting stable cyclability with an initial discharge capacity of 550 mAh g-1 and 60% capacity retention after 200 cycles.

Design principles for 2D transition metal dichalcogenides toward lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are regarded as a promising candidate for next-generation energy storage systems owing to their remarkable energy density, resource availability, and environmental benignity. Nevertheless, severe shuttling effect, sluggish redox kinetics, large volumetric expansion, and uncontrollable dendrite growth hamper the practical applications. To address these intractable issues, two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged expeditiously as an essential material strategy. Herein, this review emphasizes the development and application of 2D TMDs in Li-S batteries. It starts with introducing the fundamentals of Li-S batteries and common synthetic routes of TMDs, followed by summarizing the employment of pristine, hybrid, and defective TMDs in the realm of expediting sulfur chemistry and stabilizing lithium anode. Finally, the development roadmap and possible research directions of TMDs are proposed to offer guidance for the future design of high-performance Li-S batteries.

Beaded CoSe2-C Nanofibers for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are regarded as highly promising energy storage devices due to their high theoretical specific capacity and high energy density. Nevertheless, the commercial application of Li-S batteries is still restricted by poor electrochemical performance. Herein, beaded nanofibers (BNFs) consisting of carbon and CoSe2 nanoparticles (CoSe2/C BNFs) were prepared by electrospinning combined with carbonization and selenization. Benefitting from the synergistic effect of physical adsorption and chemical catalysis, the CoSe2/C BNFs can effectively inhibit the shuttle effect of lithium polysulfides and improve the rate performance and cycle stability of Li-S batteries. The three-dimensional conductive network provides a fast electron and ion transport pathway as well as sufficient space for alleviating the volume change. CoSe2 can not only effectively adsorb the lithium polysulfides but also accelerate their conversion reaction. The CoSe2/C BNFs-S cathode has a high reversible discharge specific capacity of 919.2 mAh g-1 at 0.1 C and presents excellent cycle stability with a low-capacity decay rate of 0.05% per cycle for 600 cycles at 1 C. The combination of the beaded carbon nanofibers and polar metal selenides sheds light on designing high-performance sulfur-based cathodes.

Vanadium Intercalation into Niobium Disulfide to Enhance the Catalytic Activity for Lithium-Sulfur Batteries

Despite their high specific energy and great promise for next-generation energy storage, lithium-sulfur (Li-S) batteries suffer from polysulfide shuttling, slow redox kinetics, and poor cyclability. Catalysts are needed to accelerate polysulfide conversion and suppress the shuttling effect. However, a lack of structure-activity relationships hinders the rational development of efficient catalysts. Herein, we studied the Nb-V-S system and proposed a V-intercalated NbS₂ (Nb₃VS₆) catalyst for high-efficiency Li-S batteries. Structural analysis and modeling revealed that undercoordinated sulfur anions of [VS₆] octahedra on the surface of Nb₃VS₆ may break the catalytic inertness of the basal planes, which are usually the primary exposed surfaces of many 2D layered disulfides. Using Nb₃VS₆ as the catalyst, the resultant Li-S batteries delivered high capacities of 1541 mAh g^-1 at 0.1 C and 1037 mAh g^-1 at 2 C and could retain 73.2% of the initial capacity after 1000 cycles. Such an intercalation-induced high activity offers an alternative approach to building better Li-S catalysts.

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.

Electrolyte Design for Improving Mechanical Stability of Solid Electrolyte Interphase in Lithium-Sulfur Batteries

Practical lithium-sulfur (Li-S) batteries are severely plagued by the instability of solid electrolyte interphase (SEI) formed in routine ether electrolytes. Herein, an electrolyte with 1,3,5-trioxane (TO) and 1,2-dimethoxyethane (DME) as co-solvents is proposed to construct a high-mechanical-stability SEI by enriching organic components in Li-S batteries. The high-mechanical-stability SEI works compatibly in Li-S batteries. TO with high polymerization capability can preferentially decompose and form organic-rich SEI, strengthening mechanical stability of SEI, which mitigates crack and regeneration of SEI and reduces the consumption rate of active Li, Li polysulfides, and electrolytes. Meanwhile, DME ensures high specific capacity of S cathodes. Accordingly, the lifespan of Li-S batteries increases from 75 cycles in routine ether electrolyte to 216 cycles in TO-based electrolyte. Furthermore, a 417 Wh kg^-1 Li-S pouch cell undergoes 20 cycles. This work provides an emerging electrolyte design for practical Li-S batteries.

Towards Practical Application of Li-S Battery with High Sulfur Loading and Lean Electrolyte: Will Carbon-Based Hosts Win This Race?

As the need for high-energy-density batteries continues to grow, lithium-sulfur (Li-S) batteries have become a highly promising next-generation energy solution due to their low cost and exceptional energy density compared to commercially available Li-ion batteries. Research into carbon-based sulfur hosts for Li-S batteries has been ongoing for over two decades, leading to a significant number of publications and patents. However, the commercialization of Li-S batteries has yet to be realized. This can be attributed, in part, to the instability of the Li metal anode. However, even when considering just the cathode side, there is still no consensus on whether carbon-based hosts will prove to be the best sulfur hosts for the industrialization of Li-S batteries. Recently, there has been controversy surrounding the use of carbon-based materials as the ideal sulfur hosts for practical applications of Li-S batteries under high sulfur loading and lean electrolyte conditions. To address this question, it is important to review the results of research into carbon-based hosts, assess their strengths and weaknesses, and provide a clear perspective. This review systematically evaluates the merits and mechanisms of various strategies for developing carbon-based host materials for high sulfur loading and lean electrolyte conditions. The review covers structural design and functional optimization strategies in detail, providing a comprehensive understanding of the development of sulfur hosts. The review also describes the use of efficient machine learning methods for investigating Li-S batteries. Finally, the outlook section lists and discusses current trends, challenges, and uncertainties surrounding carbon-based hosts, and concludes by presenting our standpoint and perspective on the subject.

Diagnosing and Correcting the Failure of the Solid-State Polymer Electrolyte for Enhancing Solid-State Lithium-Sulfur Batteries

Solid-state polymer electrolytes (SPEs) attract great interest in developing high-performance yet reliable solid-state batteries. However, understanding of the failure mechanism of the SPE and SPE-based solid-state batteries remains in its infancy, posing a great barrier to practical solid-state batteries. Herein, the high accumulation and clogging of "dead" lithium polysulfides (LiPS) on the interface between the cathode and SPE with intrinsic diffusion limitation is identified as a critical failure cause of SPE-based solid-state Li-S batteries. It induces a poorly reversible chemical environment with retarded kinetics on the cathode-SPE interface and in bulk SPEs, starving the Li-S redox in solid-state cells. This observation is different from the case in liquid electrolytes with free solvent and charge carriers, where LiPS dissolve but remain alive for electrochemical/chemical redox without interfacial clogging. Electrocatalysis demonstrates the feasibility of tailoring the chemical environment in diffusion-restricted reaction media for reducing Li-S redox failure in the SPE. It enables Ah-level solid-state Li-S pouch cells with a high specific energy of 343 Wh kg^-1 on the cell level. This work may shed new light on the understanding of the failure mechanism of SPE for bottom-up improvement of solid-state Li-S batteries.

Novel Strategy for the Formulation of High-Energy-Density Cathodes via Porous Carbon for Li-S Batteries

Porous carbon is considered an attractive host material for high-energy sulfur electrodes. This study concerns the design of a porous carbon-based sulfur electrode for the formulation of high-energy Li-S batteries. The porous carbon is impregnated with up to 80 vol.% of sulfur and a reduction in both the conductive agent and binder content. Therefore, less solvent can be used during slurry casting to inhibit crack formation following electrode drying. In addition, the utilization of two distinct electrically conducting networks enables reduced battery polarization, resulting in a battery with a capacity of 690 mAh g^-1 (even after 100 cycles). Finally, pouch cells are prepared to characterize the practical performance of the optimized cathode. This yields a capacity of 741 mAh and a cathode energy density of 1001 Wh kg^-1 . These findings are expected to guide the further development of high-energy-density cathode materials for Li-S batteries.

A COF-coated ordered porous framework as multifunctional polysulfide barrier towards high-performance lithium-sulfur batteries

The practical application of lithium-sulfur batteries (LSBs) is still hindered by the shuttle effect of lithium polysulfides (LiPS) and slow sulfur conversion kinetics. Herein, a LiPS inhibited covalent organic framework (COF)-coated conductive porous metal oxide design strategy is proposed towards the development of efficient and durable sulfur cathode in LSBs. This strategy is demonstrated by coating a TpPa-1 COF layer on cobalt-decorated titanium oxynirtide (TiO_xN_y) with a three-dimensional ordered microporous framework (3DOM) structure. In this strategy, the oxygen-deficient TiO_xN_y framework ensures a good conductivity and structural stability of the cathode during the charge/discharge process. The 3DOM macrospores provide a high capacity for sulfur accommodation and exposes active interfaces, whereas the coated TpPa-1 COF featured with ultrafine microspore offer an effective confinement of LiPS within the 3DOM framework, mitigating its shuttling effect. At the same time, the Co embedded in 3DOM TiO_xN_y servers as efficient catalyst promoting the sulfur electrochemical reaction. Attributed to these structural superiorities, the 3DOM TpPa-1@Co/TiO_xN_y/S cathode exhibits excellent performance even under high sulfur loading and low electrolyte condition. This work of using microporous COF coating with conductive macroporous metal oxides offers an effective alternative strategy for the design of practical sulfur battery.

Lithium Aluminate Nanoflakes as an Additive to Sulfur Cathodes for Enhanced Mass Transport in High-Energy-Density Lithium-Sulfur Pouch Cells Utilizing Sparingly Solvating Electrolytes

The utilization of sparingly solvating electrolytes has been reckoned as a promising approach to realizing high-energy-density lithium-sulfur batteries under lean electrolyte conditions through decoupling the electrolyte amount from sulfur utilization. However, the inferior wettability of high-concentration sparingly solvating electrolytes compromises mass transport, thereby impeding the maximum utilization of active material in sulfur cathodes. To address this issue, in this study, we incorporate lithium aluminate (LiAlO₂) nanoflakes as an additive to sulfur cathodes to enhance the mass transport by improving the percolation and accessibility of sparingly solvating electrolytes to the bulk of the electrodes. The electrochemical kinetics of LiAlO₂-containing sulfur cathodes are investigated using the galvanostatic intermittent titration technique. The Li⁺ self-diffusion coefficients of electrode materials were estimated through pulsed-field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy. Finally, a 193 Wh kg^-1 Li-S pouch cell (excluding the mass of the laminated Al pouch) is demonstrated by utilizing the LiAlO₂-incorporated sulfur cathode with a high S-loading of 4.3 mg cm^-2 in a low electrolyte/sulfur (E/S) ratio of 3 μL mg^-1. The Li-S pouch cell retains 80% of its initial specific cell capacity after 50 cycles. Our comprehensive understanding of the role of LiAlO₂ additives in enhancing the mass transport and Li⁺ self-diffusion coefficient of sulfur cathodes will contribute immensely toward the development of high-energy-density Li-S batteries under lean electrolyte conditions.

Manipulating Li2 S Redox Kinetics and Lithium Dendrites by Core-Shell Catalysts under High Sulfur Loading and Lean-Electrolyte Conditions

For practical lithium-sulfur batteries (LSBs), the high sulfur loading and lean-electrolyte are necessary conditions to achieve the high energy density. However, such extreme conditions will cause serious battery performance fading, due to the uncontrolled deposition of Li₂ S and lithium dendrite growth. Herein, the tiny Co nanoparticles embedded N-doped carbon@Co₉ S₈ core-shell material (CoNC@Co₉ S₈ NC) is designed to address these challenges. The Co₉ S₈ NC-shell effectively captures lithium polysulfides (LiPSs) and electrolyte, and suppresses the lithium dendrite growth. The CoNC-core not only improves electronic conductivity, but also promotes Li⁺ diffusion as well as accelerates Li₂ S deposition/decomposition. Consequently, the cell with CoNC@Co₉ S₈ NC modified separator delivers a high specific capacity of 700 mAh g^-1 with a low-capacity decay rate of 0.035% per cycle at 1.0 C after 750 cycles under a sulfur loading of 3.2 mg cm^-2 and a E/S ratio of 12 µL mg^-1 , and a high initial areal capacity of 9.6 mAh cm^-2 under a high sulfur loading of 8.8 mg cm^-2 and a low E/S ratio of 4.5 µL mg^-1 . Besides, the CoNC@Co₉ S₈ NC exhibits an ultralow overpotential fluctuation of 11 mV at a current density of 0.5 mA cm^-2 after 1000 h during a continuous Li plating/striping process.

Brominated flame retardants coated separators for high-safety lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have become highly promising next-generation secondary lithium batteries owing to their high theoretical energy density and abundance of sulfur. Nevertheless, the large-scale application of LSBs is still restricted by the shuttle effect of lithium polysulfide (LiPSs) and the potential fire hazard caused by flammable electrolytes. Herein, three electrolyte-insoluble brominated flame retardants (BFRs) are selected and coated on both sides of commercial polypropylene separators by a facile slurry coating method. The effects of the three BFRs on the safety and electrochemical properties of LSBs are characterized and compared. The coating modification separators greatly improves the flame retardancy of LSBs through radical elimination mechanism. The self-extinguishing time of the electrolyte is reduced from 0.66 s/mg to 0.20 s/mg. Moreover, it is demonstrated that the oxygen (O)-containing BFRs exert a significant adsorption capacity and are more advantageous than O-free BFRs in LSBs. In addition, octabromoether (BDDP) coated separator is more effective in trapping LiPSs than decabromodiphenyl ether (DBDPO) due to higher O content, which can mitigate the shuttle effect and enhance the cycle and rate performance of LSBs. This simple coating strategy for separators with BFRs offers a strongly competitive option for the large-scale production of high-safety LSBs.

CoOx nanoparticles loaded on carbon spheres with synergistic effects for effective inhibition of shuttle effect in Li-S batteries

Lithium-sulfur (Li-S) batteries, as one of the new energy storage batteries, show immense potential due to their high theoretical specific capacity and theoretical energy density. However, there are still some problems to be solved, among which the shuttle effect of lithium polysulfides is one extremely serious issue with respect to the industrial application of Li-S batteries. Rational design of electrode materials with effective catalytic conversion ability is an effective route to accelerate the conversion of lithium polysulfides (LiPSs). Herein, considering the adsorption and catalysis of LiPSs, CoO_x nanoparticles (NPs) loaded on carbon sphere composites (CoO_x/CS) were designed and constructed as cathode materials. The CoO_x NPs obtained, with ultralow weight ratio and uniform distribution, consist of CoO, Co₃O₄, and metallic Co. The polar CoO and Co₃O₄ enable chemical adsorption towards LiPSs through Co-S coordination, and the conductive metallic Co can improve electronic conductivity and reduce impedance, which is beneficial for ion diffusion at the cathode. Based on these synergistic effects, the CoO_x/CS electrode exhibits accelerated redox kinetics and enhanced catalytic activity for conversion of LiPSs. Consequently, the CoO_x/CS cathode delivers improved cycling performance, with an initial capacity of 980.8 mA h g^-1 at 0.1C and a reversible specific capacity of 408.4 mA h g^-1 after 200 cycles, along with enhanced rate performance. This work provides a facile route to construct cobalt-based catalytic electrodes for Li-S batteries, and promotes understanding of the LiPSs conversion mechanism.

n-Hexane Diluted Electrolyte with Ultralow Density enables Li-S Pouch Battery Toward >400 Wh kg-1

Lithium-sulfur (Li-S) batteries are attractive candidates for next generation energy storage devices due to their high theoretical energy density of up to 2600 Wh kg^-1 . However, the uneven deposition of lithium, the undesired shuttle of lithium polysulfides (LiPSs), and the excess weight fraction of electrolyte severely impair the practical energy density of Li-S batteries. Here, a low concentrated and nonpolar n-hexane (NH)-diluted electrolyte (named as LCDE) with ultralow-density to alleviate the above dilemmas is proposed. The nonpolar NH boosts the diffusion of lithium ion in LCDE, favoring the homogeneous deposition of lithium. This nonpolar effect also reduces the solubilities of LiPSs, promoting a quasi-solid-state transformation of sulfur chemistry, thus tremendously eradicating the shuttle of LiPSs. Most importantly, the ultra-light NH diluent enables the LCDE with an ultralow density of only 0.79 g mL^-1 , which reduces the weight of LCDE by 32.5% compared with conventional ether-based electrolyte. Owing to all the merits, the Li-S pouch cell achieves a high energy density up to 417 Wh kg^-1 . The nonpolar NH-diluted electrolyte with multifunction presented in this work provides a new and feasible direction to increase the practical energy density of Li-S batteries.

Fluorinated Covalent Organic Framework-Based Nanofluidic Interface for Robust Lithium-Sulfur Batteries

To realize the practical application of lithium-sulfur (Li-S) batteries, there is a need to inhibit uncontrolled Li deposition by facilitating Li-ion migration, and suppress the irreversible consumption of cathodes by preventing polysulfide shuttling. However, a permselective artifical membrane or interlayer which features fast ion transport but low polysulfide crossover is elusive. Here, we report the design and synthesis of a fluorinated covalent organic framework (4F-COF)-based membrane with a high permselectivity and increased battery lifespan. Combining density functional theory calculation, molecular dynamic simulation, and in situ Raman analysis, we demonstrate that fluorinated COF eliminates polysulfides shutting and dendritic lithium formation. Consequently, Li symmetrical cells demonstrate Li plating/stripping behaviors for 2000 h under 1 mA cm^-2. More importantly, Li-S batteries based on the 4F-COF/PP separator achieve cycling retention of 82.3% over 1000 cycles at 2 C, rate performance of 568.0 mA h g^-1 at 10 C, and an areal capacity of 7.60 mA h cm^-2 with a high sulfur loading (∼9 mg cm^-2). This work demonstrates that functionalizing nanochannels in COFs can impart permselectivity for energy storage applications.

Anisotropically Hybridized Porous Crystalline Li-S Battery Separators

Anisotropically hybridized porous crystalline Li-S battery separators based on porous crystalline materials that can meet the multiple functionalities of both anodic and cathodic sides are much desired for Li-S battery yet still challenging in directional design. Here, an anisotropically hybridized separator (CPM) based on an ionic liquid-modified porphyrin-based covalent-organic framework (COF-366-OH-IL) and catalytically active metal-organic framework (Ni₃ (HITP)₂ ) that can integrate the lithium-polysulfides (LiPSs) adsorption/catalytic conversion and ion-conduction sites together to directionally meet the requirements of electrodes is reported. Remarkably, the-obtained separator exhibits an exceptional high Li⁺ transference-number (t_Li+  = 0.8), ultralow polarization-voltage (<30 mV), high initial specific-capacity (921.38 mAh g^-1 at 1 C), and stable cycling-performance, much superior to polypropylene and monolayer-modified separators. Moreover, theoretical calculations confirm the anisotropic effect of CPM on the anodic side (e.g., Li⁺ transfer, LiPSs adsorption, and anode-protection) and cathodic side (e.g., LiPSs adsorption/catalysis). This work might provide a new perspective for separator exploration.

Adaptively Reforming Natural Enzyme to Activate Catalytic Microenvironment for Polysulfide Conversion in Lithium-Sulfur Batteries

Catalyzing polysulfide conversion is a promising way toward accelerating complex and sluggish sulfur redox reactions (SRRs) in lithium-sulfur batteries. Reasonable alteration of an enzyme provides a new means to expand the natural enzyme universe to catalytic reactions in abiotic systems. Herein, we design and fabricate a denatured hemocyanin (DHc) to efficiently catalyze the SRR. After denaturation, the unfolded β-sheet architectures with exposed rich atomically dispersed Cu, O, and N sites and intermolecular H-bonds are formed in DHc, which not only provides the polysulfides for a strong spatial confinement effect in microenvironment via S-O and Li···N interactions but also activates chemical channels for electron/Li⁺ transport into the Cu active center via H/Li-bonds to catalyze polysulfide conversion. As expected, the charge/discharge kinetics of DHc-containing cathodes is fundamentally improved in cyclability with nearly 100% Coulombic efficiency and capacity even under high sulfur loading (4.3 mg cm^-2) and lean-electrolyte (8 μL mg^-1) conditions.

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.

Single Nickel Atom Catalysts Enable Fast Polysulfide Redox for Safe and Long-Cycle Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have attracted great interest due to their low cost, high theoretical energy density, and environmental friendliness. However, the sluggish conversion of lithium polysulfides (LiPS) to S and Li₂ S during the charge/discharge process leads to unsatisfactory rate performance of lower to 0.1 C (1 C = 1675 mA g^-1 ) especially for Li-S pouch batteries, thus hindering their practical applications in high power batteries. Here, well-defined and monodispersed Ni single-atom catalysts (SACs) embedded in highly porous nitrogen-doped graphitic carbons (NiSA-N-PGC) are designed and synthesized to form Ni-N₄ catalytic sites at the atomic level. When serving as a bifunctional electrocatalyst, the Ni-N₄ catalytic sites cannot only promote the interfacial conversion redox of LiPS by accelerating the transformation kinetics, but also suppress the undesirable shuttle effect by immobilizing LiPS. These findings are verified by both experimental results and DFT theoretical calculations. Furthermore, Li ions show low diffusion barrier on the surface of Ni-N₄ sites, resulting in enhanced areal capacity of batteries. As a result, the Li-S battery delivers stable cycling life of more than 600 cycles with 0.069% capacity decay per cycle at a rate of 0.5 C. More importantly, the Li-S pouch cells with NiSA-N-PGC show an initial capacity of 1299 mAh g^-1 at a rate of 0.2 C even with high sulfur loading of 6 mg cm^-2 . This work opens up an avenue for developing single-atom catalysts to accelerate the kinetic conversion of LiPS for highly stable Li-S batteries.

Surface Defect Engineering of a Bimetallic Oxide Precatalyst Enables Kinetics-Enhanced Lithium-Sulfur Batteries

Developing efficient electrocatalysts to accelerate the sluggish conversion of lithium polysulfides (LiPSs) is of paramount importance for improving the performances of lithium-sulfur (Li-S) batteries. However, a consensus has not yet been reached on the in situ evolution of the electrocatalysts as well as the real catalytic active sites. Herein, defective MnV2O6 (D-MVO) is designed as a precatalyst toward LiPSs' adsorption and conversion. We reveal that the introduction of surface V defects can effectively accelerate the in situ sulfurization of D-MVO during the electrochemical cycling process, which acts as the real electrocatalyst for LiPSs' retention and catalysis. The in situ-sulfurized D-MVO demonstrates much higher electrocatalytic activity than the defect-free MVO toward LiPSs' redox conversion. With these merits, the Li-S batteries with D-MVO separators achieve superior long-term cycling performance with a low decay rate of 0.056% per cycle after 1000 cycles at 1C. Even under an elevated sulfur loading of 5.5 mg cm-2, a high areal capacity of 4.21 mAh cm-2 is still retained after 50 cycles at 0.1C. This work deepens the cognition of the dynamic evolution of the electrocatalysts and provides a favorable strategy for designing efficient precatalysts for advanced Li-S batteries using defect engineering.

Mitigating Lithium Dissolution and Polysulfide Shuttle Effect Phenomena Using a Polymer Composite Layer Coating on the Anode in Lithium-Sulfur Batteries

To mitigate lithium dissolution and polysulfide shuttle effect phenomena in high-energy lithium sulfur batteries (LISBs), a conductive, flexible, and easily modified polymer composite layer was applied on the anode. The polymer composite layer included polyaniline and functionalized graphite. The electrochemical behavior of LISBs was studied by galvanostatic charge/discharge tests from 1.7 to 2.8 V up to 90 cycles and via COMSOL Multiphysics simulation software. No apparent overcharge occurred during the charge state, which suggests that the shuttle effect of polysulfides was effectively prevented. The COMSOL Multiphysics simulation provided a venue for optimal prediction of the ideal concentration and properties of the polymer composite layer to be used in the LISBs. The testing and simulation results determined that the polymer composite layer diminished the amount of lithium polysulfide species and decreased the amount of dissolved lithium ions in the LISBs. In addition, the charge/discharge rate of up to 2.0 C with a cycle life of 90 cycles was achieved. The knowledge acquired in this study was important not only for the design of efficient new electrode materials, but also for understanding the effect of the polymer composite layer on the electrochemical cycle stability.

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.