Shielding Polysulfide Intermediates by an Organosulfur-Containing Solid Electrolyte Interphase on the Lithium Anode in Lithium-Sulfur Batteries

Polysulfide chemistry in metal-sulfur batteries

Renowned for their high theoretical energy density and cost-effectiveness, metal-sulfur (M-S) batteries are pivotal in overcoming the current energy storage bottlenecks and accelerating the transition toward a cleaner society. Polysulfides (PSs) serve as essential intermediates in M-S batteries and bridge the electrochemical redox processes of sulfur, playing a decisive role in controlling the electrode behaviors and regulating the battery performances. Understanding PS chemistry across diverse battery environments is key to advancing M-S batteries. This review aims to provide a comprehensive overview of the PS chemistry in high-energy-density battery systems and outline future research directions. The compositions, properties, and characterization methods of PSs are introduced to facilitate a fundamental understanding of the PS chemistry in working batteries. Following this, a thorough examination of the chemical and electrochemical behaviors of PSs and their impacts on electrode performances is conducted to deepen the insights into the PS reactions in batteries. Building on this foundation, representative PS regulation strategies are discussed, focusing on molecular modification, solvation optimization, and interfacial regulation, to achieve superior M-S battery performances. Challenges of PSs in practical M-S batteries are finally analyzed, and perspectives on the future research trends of PS chemistry are presented.

Revealing the Coordination and Mediation Mechanism of Arylboronic Acids Toward Energy-Dense Li-S Batteries

Lithium-sulfur (Li─S) batteries offer a promising avenue for the next generation of energy-dense batteries. However, it is quite challenging to realize practical Li─S batteries under limited electrolytes and high sulfur loading, which may exacerbate problems of interface deterioration and low sulfur utilization. Herein, the coordination and mediation chemistry of arylboronic acids that enable energy-dense and long-term-cycling Li─S batteries is proposed. The coordination chemistry between NO3 - and arylboronic acids breaks the resonance configuration of NO3 - and thermodynamically promotes its reduction on the anode, contributing to a mechanically robust interface. The mediation chemistry between lithium arylborate and polysulfides distorts S─S/Li─S bonds, alters the rate-determining step from Li2S4→Li2S2 to Li2S6→Li2S4, and homogeneously accelerates the sulfur redox kinetics. Li─S batteries using 3,5-bis(trifluoromethyl)phenylboronic acid (BPBA) show excellent cycling stability (1000 cycles with a low capacity decay rate of 0.033% per cycle) and a high energy density of 422 Wh kg-1 under aggressive chemical environments (high sulfur loading of 17.4 mg cm-2 and lean electrolyte operation of 3.6 mL gS -1). The basic mechanism of coordination and mediation chemistry can be extended to other arylboronic acids with different configurations and compositions, thus broadening the application prospect of arylboronic acids in the electrolyte engineering of Li─S batteries.

Shortening the Reaction Pathway of Sulfur Redox Kinetics with 2,5-Dichloro-1,4-Benzoquinone to Minimize the Shuttle Effect in Lithium-Sulfur Batteries

The low active material utilization, sluggish sulfur redox kinetics, and formation of unstable interfacial layers remain critical challenges in lithium-sulfur (Li-S) batteries. To minimize these effects, 2, 5-dichloro-1,4-benzoquinone (DCBQ) was demonstrated in this study as an electrolyte additive. Leveraging its unique symmetrical structure, DCBQ interacted with polysulfides during charge and discharge cycles to form insoluble symmetric cyclic organic polysulfide intermediates. These intermediates served as a cathode-electrolyte interphase (CEI) by attaching to the sulfur cathode surface, which mitigated the shuttle effect by reducing the accumulation of insoluble Li2S and suppressing polysulfide dissolution. In the presence of DCBQ, the discharge pathway for Li2S6 transitioned from Li2S6 → Li2S4 → Li2S2 → Li2S to a shortened sequence of Li2S6 → Li2S3 → Li2S, enhancing sulfur utilization and streamlining redox processes. On the anode side, the formation of LiCl and intermediate compounds contributed to an organic-inorganic solid-electrolyte interface (SEI), which protected the lithium anode, improved the Li+ diffusion coefficient (6.63 × 10-11 cm2 S-1), and eventually enhanced the battery's cycling stability. Consequently, the Li-S battery that included the DCBQ additive exhibited nearly 100% Coulombic efficiency at a rate of 0.2 C. It showed an initial discharge-specific capacity of 992.24 mAh g-1 and experienced a low-capacity degradation of just 0.45% per cycle over 120 cycles. These results highlight the effectiveness of DCBQ as an electrolyte additive in enhancing both the performance and stability of the battery.

Single-step laser-printed integrated sulfur cathode toward high-performance lithium-sulfur batteries

Lithium-sulfur batteries are expected to supersede existing lithium-ion batteries due to the high theoretical energy density of sulfur cathodes (positive electrodes). Unfortunately, inefficient redox reactions and the "shuttle effect" hinder their commercial development. Assembling high-performance nanostructured sulfur host materials into a sulfur cathode presents a viable solution. However, fabricating host materials and preparing sulfur cathodes involve complicated, multistep, and labor-intensive processes under varying temperatures and conditions, raising concerns about efficiency and cost in practical production. Herein, we propose a single-step laser printing strategy to prepare high-performance integrated sulfur cathodes. During the high-throughput laser-pulse irradiation process, the precursor donor is activated, producing jetting particles that include in-situ synthesized halloysite-based hybrid nanotubes, sulfur, and glucose-derived porous carbon. After laser printing, a composite layer, containing host materials, active materials, and conductive components, is uniformly coated onto a carbon fabric acceptor, forming an integrated sulfur cathode. The laser-printed sulfur cathodes exhibit high reversible capacity and low capacity attenuation during cycling measurements. Furthermore, the laser-printed high-loading samples show high performance in both coin and pouch lithium-sulfur cells. This strategy would simplify the fabrication process in lithium-sulfur battery industry and inspire advancements in other battery research.

Revitalizing Li-S batteries: the power of electrolyte additives

Lithium-sulfur (Li-S) batteries have garnered significant attention as promising next-generation energy storage solutions due to their high energy density and cost efficiency. However, the broad adoption of Li-S batteries is impeded by several critical issues. These include the intrinsically low conductivities of sulfur (S) and lithium sulfide (Li2S), the polysulfide shuttle effect, and dendrite formation on the lithium (Li) electrode, among other challenges. Overcoming these obstacles is crucial to realizing the full potential of Li-S batteries. A key step towards improving Li-S battery performance is the optimization of electrolytes, with a particular focus on enhancing cell cyclability, rate capability, safety, and lifespan. This review examines the current advancements in various electrolyte additive options, including their concepts, designs, and materials, and how the electrolyte's final chemical and physical properties influence the overall performance of Li-S batteries. The aim is to provide a comprehensive framework for the rational selection of future electrolyte additives for Li-S batteries, based on the available concepts, and to evaluate the existing electrolyte additives.

Integrated Design of Homogeneous/Heterogeneous Copper Complex Catalysts to Enable Synergistic Effects on Sulfur and Lithium Evolution Reactions

Fatal polysulfide shuttling, sluggish sulfur redox kinetics and detrimental lithium dendrites have curtailed the real discharge capacity, working lifespan and safety of lithium-sulfur (Li-S) batteries. Organic small molecule promotors as one type of emerging active catalysts can fulfil the management of the electrochemical species evolution behaviors. Herein, an integrated engineering is organized by synthesizing dual chlorine-bridge enabled binuclear copper complex (Cu2(phen)2Cl2) and its derivative generated in electrolyte (Cu-ETL) as the heterogeneous and homogeneous catalyst, respectively. The well-designed Cu-ETL with a optimized concentration of 0.25 wt% as a homogeneous enabler offers highly utilized Cu centers and the sufficient interface contact for guiding the Li2S nucleation/decomposition reactions. The Cu2(phen)2Cl2 loaded on carbon spheres as an interlayer (Cu-INT) can break through the catalytic limitation resulting from the saturated concentration of Cu-ETL and thus offers an extended manipulation effect. Benefiting from the synergistic effect, the Li-S battery shows stable cycling at 3 C upon 500 cycles with a capacity degradation rate as low as 0.029 % per cycle. Of specific note, an actual cell energy density of 372.1 Wh kg-1 is harvested by a 1.2 Ah-level soft-packaged pouch cell, implying a chance for requiring the demand of high-energy batteries.

Engineering Electrolytes with Transition Metal Ions for the Rapid Sulfur Redox and In Situ Solidification of Polysulfides in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have been pursued due to their high theoretical energy density and superb cost-effectiveness. However, the dissolution-conversion mechanism of sulfur inevitably leads to shuttle effects and interface passivation issues, which impede Li-S battery practical application. Herein, the approach of adopting transition metal salts (CoI2) to engineering the electrolyte is proposed. Different from anchored transition metal catalysts in the cathode, soluble cobalt ions can chemically reduce and solidify polysulfides, alleviating the dependence of sulfur conversion on the conductive interface while suppressing the shuttle effect. Importantly, all elements in CoI2 are in the lowest valence state and solid complexes are formed after the redox reaction, which prevents the migration of high valent Co3+ to the anode, thus overcoming the poor compatibility between redox mediator and Li anode. Notably, I3- has the function of eliminating dead sulfur and dead lithium, which we apply to Li-S batteries. After activating I3- at a certain frequency, Li-S batteries indeed achieve a longer and more stable cycle life. By combining the regulatory behavior of anions and cations, the electrolyte is engineered for Li-S batteries with high capacity, long lifespan, and excellent rate performance.

Advances in Functional Organosulfur-Based Mediators for Regulating Performance of Lithium Metal Batteries

Rechargeable lithium metal batteries (LMBs) are promising next-generation energy storage systems due to their high theoretical energy density. However, their practical applications are hindered by lithium dendrite growth and various intricate issues associated with the cathodes. These challenges can be mitigated by using organosulfur-based mediators (OSMs), which offer the advantages of abundance, tailorable structures, and unique functional adaptability. These features enable the rational design of targeted functionalities, enhance the interfacial stability of the lithium anode and cathode, and accelerate the redox kinetics of electrodes via alternative reaction pathways, thereby effectively improving the performance of LMBs. Unlike the extensively explored field of organosulfur cathode materials, OSMs have garnered little attention. This review systematically summarizes recent advancements in OSMs for various LMB systems, including lithium-sulfur, lithium-selenium, lithium-oxygen, lithium-intercalation cathode batteries, and other LMB systems. It briefly elucidates the operating principles of these LMB systems, the regulatory mechanisms of the corresponding OSMs, and the fundamentals of OSMs activity. Ultimately, strategic optimizations are proposed for designing novel OSMs, advanced mechanism investigation, expanded applications, and the development of safe battery systems, thereby providing directions to narrow the gap between rational modulation of organosulfur compounds and their practical implementation in batteries.

Organic Thiolate as Multifunctional Salt for Rechargeable Lithium-Sulfur Batteries

The practical application of lithium-sulfur (Li-S) batteries is hindered by the severe shuttle effect of soluble polysulfide intermediates and the unstable lithium anode interface. Conventional lithium salts (e.g., LiPF6, LiTFSI) just serve as conducting salts to provide necessary free lithium cations for internal ion transport, lacking full utilization of the anions. Herein, lithium 4-fluorobenzenethiolate (F-PhSLi) as a multifunctional salt for rechargeable Li-S batteries, which is able to chemically react with sulfur to alter the redox pathway of sulfur cathode, accelerate the sulfur redox kinetics, and inhibit the shuttle effect of polysulfides is reported. Meanwhile, due to the redox activity of F-PhSLi, the reactive electrolyte can offer additional capacity. In addition, it also can construct a stable LiF-rich solid electrolyte interface layer on the lithium metal anode. Such reactive electrolyte endows Li-S batteries with ultrahigh discharge specific capacity, improved sulfur utilization, long-term storage ability, enhanced rate capability, and outstanding low-temperature performance. This work presents a new solution for developing high performance Li-S batteries.

An Electrolyte Engineered Homonuclear Copper Complex as Homogeneous Catalyst for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries suffer from severe polysulfide shuttle, retarded sulfur conversion kinetics and notorious lithium dendrites, which has curtailed the discharge capacity, cycling lifespan and safety. Engineered catalysts act as a feasible strategy to synchronously manipulate the evolution behaviors of sulfur and lithium species. Herein, a chlorine bridge-enabled binuclear copper complex (Cu-2-T) is in situ synthesized in electrolyte as homogeneous catalyst for rationalizing the Li-S redox reactions. The well-designed Cu-2-T provides completely active sites and sufficient contact for homogeneously guiding the Li2S nucleation/decomposition reactions, and stabilizing the lithium working interface according to the synchrotron radiation X-ray 3D nano-computed tomography, small angle neutron scattering and COMSOL results. Moreover, Cu-2-T with the content of 0.25 wt% approaching saturated concentration in electrolyte further boosts the homogeneous optimization function in really operated Li-S batteries. Accordingly, the capacity retention of the Li-S battery is elevated from 51.4% to 86.3% at 0.2 C, and reaches 77.0% at 1.0 C over 400 cycles. Furthermore, the sulfur cathode with the assistance of Cu-2-T realizes the stable cycling under the practical scenarios of soft-packaged pouch cell and high sulfur loading (6.5 mg cm-2 with the electrolyte usage of 4.5 µL mgS -1).

Recent Progress of Advanced Functional Separators in Lithium Metal Batteries

As a representative in the post-lithium-ion batteries (LIBs) landscape, lithium metal batteries (LMBs) exhibit high-energy densities but suffer from low coulombic efficiencies and short cycling lifetimes due to dendrite formation and complex side reactions. Separator modification holds the most promise in overcoming these challenges because it utilizes the original elements of LMBs. In this review, separators designed to address critical issues in LMBs that are fatal to their destiny according to the target electrodes are focused on. On the lithium anode side, functional separators reduce dendrite propagation with a conductive lithiophilic layer and a uniform Li-ion channel or form a stable solid electrolyte interphase layer through the continuous release of active agents. The classification of functional separators solving the degradation stemming from the cathodes, which has often been overlooked, is summarized. Structural deterioration and the resulting leakage from cathode materials are suppressed by acidic impurity scavenging, transition metal ion capture, and polysulfide shuttle effect inhibition from functional separators. Furthermore, flame-retardant separators for preventing LMB safety issues and multifunctional separators are discussed. Further expansion of functional separators can be effectively utilized in other types of batteries, indicating that intensive and extensive research on functional separators is expected to continue in LIBs.

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.

Molecular Engineering toward Robust Solid Electrolyte Interphase for Lithium Metal Batteries

Lithium-metal batteries (LMBs) with high energy density are becoming increasingly important in global sustainability initiatives. However, uncontrollable dendrite seeds, inscrutable interfacial chemistry, and repetitively formed solid electrolyte interphase (SEI) have severely hindered the advancement of LMBs. Organic molecules have been ingeniously engineered to construct targeted SEI and effectively minimize the above issues. In this review, multiple organic molecules, including polymer, fluorinated molecules, and organosulfur, are comprehensively summarized and insights into how to construct the corresponding elastic, fluorine-rich, and organosulfur-containing SEIs are provided. A variety of meticulously selected cases are analyzed in depth to support the arguments of molecular design in SEI. Specifically, the evolution of organic molecules-derived SEI is discussed and corresponding design principles are proposed, which are beneficial in guiding researchers to understand and architect SEI based on organic molecules. This review provides a design guideline for constructing organic molecule-derived SEI and will inspire more researchers to concentrate on the exploitation of LMBs.

Solid Electrolyte Interphase Recombination on Graphene Nanoribbons for Lithium Anode

The practical application of lithium metal batteries is hindered by the lithium dendrite issue, which is seriously affected by the composition and structure of the solid electrolyte interphase (SEI). Modifying the SEI can regulate lithium dendrite formation and growth. Here, we experimentally realize a Li protective layer of LiTFSI-ether electrolyte induced a natural SEI grafted on graphene nanoribbons (SEI@GNRs) via their in situ reactions. The experimental results and theoretical calculations uncover that the 3D structure of SEI@GNRs can reduce the local current density and Li+ flux. The natural SEI in SEI@GNRs, especially the rich inorganic species of LiF, Li3N, and Li2S, decreases the Li+ nucleation overpotential, makes Li+ ion deposition and nucleation uniform, and isolates electron transport. Their synergetic effect suppresses Li dendrite formation and growth, increasing the electrochemical performance of lithium metal batteries. The design strategy is beneficial for the development of lithium metal batteries.

Engineering Strategies for Suppressing the Shuttle Effect in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are supposed to be one of the most potential next-generation batteries owing to their high theoretical capacity and low cost. Nevertheless, the shuttle effect of firm multi-step two-electron reaction between sulfur and lithium in liquid electrolyte makes the capacity much smaller than the theoretical value. Many methods were proposed for inhibiting the shuttle effect of polysulfide, improving corresponding redox kinetics and enhancing the integral performance of Li-S batteries. Here, we will comprehensively and systematically summarize the strategies for inhibiting the shuttle effect from all components of Li-S batteries. First, the electrochemical principles/mechanism and origin of the shuttle effect are described in detail. Moreover, the efficient strategies, including boosting the sulfur conversion rate of sulfur, confining sulfur or lithium polysulfides (LPS) within cathode host, confining LPS in the shield layer, and preventing LPS from contacting the anode, will be discussed to suppress the shuttle effect. Then, recent advances in inhibition of shuttle effect in cathode, electrolyte, separator, and anode with the aforementioned strategies have been summarized to direct the further design of efficient materials for Li-S batteries. Finally, we present prospects for inhibition of the LPS shuttle and potential development directions in Li-S batteries.

Stable Lithium-Sulfur Batteries Ensured by GeS2 and α-S8 Lattice Matching During the Charge Process

The charge process of lithium-sulfur batteries (LSBs) is a process in which molecular polarity decreases and the volume shrinks gradually, which is the process most likely to cause lithium polysulfides (LiPSs) loss and interfacial collapse. In this work, GeS2 is utilized, whose (111) lattice plane exactly matches with the (113) lattice of α-S8 , to solve these problems. GeS2 can regulate the interconversion-deposition behavior of S-species during the charge process. Soluble LiPSs can be spontaneously adsorbed on the GeS2 surface, then obtain electrons and eventually convert to α-S8 molecules. More importantly, the α-S8 molecules will crystallize uniformly along the (111) lattice plane of GeS2 to maintain a stable cathode-electrolyte interface. Therefore, outstanding charge/discharge LSBs are successfully accomplished.

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

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

Organosulfur Materials for Rechargeable Batteries: Structure, Mechanism, and Application

Lithium-ion batteries have received significant attention over the last decades due to the wide application of portable electronics and increasing deployment of electric vehicles. In order to further enhance the performance of the batteries and overcome the capacity limitations of inorganic electrode materials, it is imperative to explore new cathode and functional materials for rechargeable lithium batteries. Organosulfur materials containing sulfur-sulfur bonds as a kind of promising organic electrode materials have the advantages of high capacities, abundant resources, tunable structures, and environmental benignity. In addition, organosulfur materials have been widely used in almost every aspect of rechargeable batteries because of their multiple functionalities. This review aims to provide a comprehensive overview on the development of organosulfur materials including the synthesis and application as cathode materials, electrolyte additives, electrolytes, binders, active materials in lithium redox flow batteries, and other metal battery systems. We also give an in-depth analysis of structure-property-performance relationship of organosulfur materials, and guidance for the future development of organosulfur materials for next generation rechargeable lithium batteries and beyond.

Tuning Li Nucleation by a Hybrid Lithiophilic Protective Layer for High-Performance Lithium Metal Batteries

Lithium (Li) metal has been recognized as the most promising anode material for next-generation rechargeable batteries. However, the practical application of Li anodes is hampered by the growth of Li dendrites. To address this issue, a robust and uniform Sb-based hybrid lithiophilic protective layer is designed and built by a facile in situ surface reaction approach. As evidenced theoretically and experimentally, the as-prepared hybrid protective layer provides outstanding wettability and fast charge-transfer kinetics. Moreover, the lithiophilic Sb embedded in the protective layer provides a rich site for Li nucleation, which effectively reduces the overpotential and induces uniform Li deposition. Consequently, the symmetric cell exhibits a long lifespan of over 1600 h at 1 mA cm^-2 and 1 mAh cm^-2 with a low voltage polarization. Furthermore, excellent cycling stability is also obtained in Li-S full cells (60% capacity retention in 800 cycles at 1 C) and Li||LFP full cells (74% capacity retention in 500 cycles at 5 C). This work proposed a facile but efficient strategy to stabilize the Li metal anode.

Modulating Electron Conducting Properties at Lithium Anode Interfaces for Durable Lithium-Sulfur Batteries

The lithium (Li) ion and electron diffusion behaviors across the actual solid electrolyte interphase (SEI) play a critical role in regulating the Li nucleation and growth and improving the performance of lithium-sulfur (Li-S) batteries. To date, a number of researchers have pursued an SEI with high Li-ion conductivity while ignoring the Li dendrite growth caused by electron tunneling in the SEI. Herein, an artificial anti-electron tunneling layer with enriched lithium fluoride (LiF) and sodium fluoride (NaF) nanocrystals is constructed using a facile solution-soaking method. As evidenced theoretically and experimentally, the LiF/NaF artificial SEI exhibits an outstanding electron-blocking capability that can reduce electron tunneling, resulting in dendrite-free and dense Li deposition beneath the SEI, even with an ultrahigh areal capacity. In addition, the artificial anti-electron tunneling layer exhibits improved ionic conductivity and mechanical strength, compared to those of routine SEI. The symmetric cells with protected Li electrodes achieve a stable cycling of 1500 h. The LiF/NaF artificial SEI endows the Li-S full cells with long-term cyclability under conditions of high sulfur loading, lean electrolyte, and limited Li excess. This study provides a perspective on the design of the SEI for highly safe and practical Li-S batteries.

Direct Tracking of Additive‐Regulated Evolution on the Lithium Anode in Quasi‐Solid‐State Lithium–Sulfur Batteries

The complicated problems confronted by lithium (Li) anode hinder the practical application of quasi‐solid‐state lithium‐sulfur (QSSLS) batteries. However, the interfacial processes and reaction mechanisms, which are still vague, pose challenges to disclose. Herein, the insoluble sulfides stacking and Li dendrites growth on the Li anode are real‐time monitored via in‐situ atomic force microscopy inside the working QSSLS batteries. In the LiNO3‐added electrolyte, it is detected that the formation process of solid electrolyte interphase (SEI) involves two stages, forming loose nanoparticles (NPs, ≈102 nm) at the open circuit potential and dense NPs (≈74 nm) during discharging owing to the synergism of Li polysulfides (LiPSs) and LiNO3. The compact SEI film not only blocks the erosion of LiPSs but also homogenizes the Li deposition behaviors, leading to the electrochemical performance enhancement of QSSLS batteries. These straightforward insights uncover the additive‐manipulated morphological/chemical evolution and interfacial properties and thus facilitate the improvement of QSSLS batteries.

Facile Replacement Reaction Enables Nano-Ag-Decorated Three-Dimensional Cu Foam as High-Rate Lithium Metal Anode

In developing advanced lithium (Li) metal batteries with high-energy density, excellent cycle stability, and high-rate capability, it is imperative to resolve dendrite growth and volume expansion during repeated Li plating/stripping. 3D hosts featuring lithiophilic sites are expected to realize both spatial control and dendrite inhibition over Li nucleation. Herein, this work prepares silver (Ag) nanoparticle-decorated 3D copper (Cu) foam via a facile replacement reaction. The 3D host provides rigid skeleton to accommodate volume expansion during cycling. Ag nanoparticles show micro-structural affinity to guide efficient nucleation of Li, leading to reduced overpotential and enhanced electrochemical kinetics. As the result, under an ultrahigh current density of 10 mA cm^-2, Cu@Ag foam/Li half cells demonstrate outstanding Coulombic efficiency (CE) of 97.2% more than 100 cycles. Also, Cu@Ag foam-Li symmetric cells sustain preeminent cycling over 900 h with a small voltage hysteresis of 32.8 mV at 3 mA cm^-2. Moreover, the Cu@Ag foam-Li||LiFePO₄ full cell demonstrates a high discharge capacity of 2.33 mAh cm^-2 over 200 cycles with an excellent CE up to 99.9% at 0.6C under practical conditions (N/P = 1.3, 17.4 mg cm^-2 LiFePO₄). Notably, the full cell with LiFePO₄ exhibits a higher areal capacity of 1 mAh cm^-2 over 700 cycles under a high rate of 5C, corresponding to capacity retention up to 100% (N/P = 3, 17.4 mg cm^-2 LiFePO₄). This study provides a novel and simple strategy for constructing high-rate and long-life Li metal batteries.

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

Lithium-sulfur (Li-S) batteries promise great potential as high-energy-density energy-storage devices due to their ultrahigh theoretical energy density of 2600 Wh kg^-1 . Evaluation and analysis on practical Li-S pouch cells are essential for achieving actual high energy density under working conditions and affording developing directions for practical applications. This review aims to afford a comprehensive overview of high-energy-density Li-S pouch cells regarding 7 years of development and to point out further research directions. Key design parameters to achieve actual high energy density are addressed first, to define the research boundaries distinguished from coin-cell-level evaluation. Systematic analysis of the published literature and cutting-edge performances is then conducted to demonstrate the achieved progress and the gap toward practical applications. Following that, failure analysis as well as promotion strategies at the pouch cell level are, respectively, discussed to reveal the unique working and failure mechanism that shall be accordingly addressed. Finally, perspectives toward high-performance Li-S pouch cells are presented regarding the challenges and opportunities of this field.

Biomass-Derived Lenthionine Enhanced by Radical Receptor for Rechargeable Lithium Battery

Organic compounds with tunable structures and high capacities are promising electrode materials for batteries. Cyclic organosulfide (i. e., lenthionine), as a natural material that can provide excellent ratio of effective atoms (S) and non-efficient atoms (C, H, and others), has a high theoretical specific capacity of 853.6 mAh g^-1 . However, the multiphase transformation causes rapid capacity decay and hysteresis of charge/discharge voltage plateaus. To overcome these issues, a receptor, phenyl disulfide (PDS), was introduced to truncate subsequent transformations directly from the source and change the reaction path, inhibit the capacity decay, and improve the cycling stability. After 500 cycles, the capacity retention was 81.1 % with PDS, which was in sharp contrast to that (35.6 %) of the control cell. This study helps to understand the electrochemistry mechanism of biomass-derived lenthionine used as a high-capacity cathode material for rechargeable lithium batteries, also offering a strategy to overcome its inherent issues.

Shielding polysulfides enabled by a biomimetic artificial protective layer in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are widely considered to be next-generation storage technologies due to their high energy density, low cost and non-toxicity. However, the soluble lithium polysulfides (LiPS) migrating to the anode side inevitably causes side reactions with the Li anode, resulting in severe corrosion of the Li anode, loss of active materials, and rapid battery failure. Therefore, it is necessary to develop effective strategies to avoid LiPS exposure to Li anodes. Herein, a stable UiO-66-ClO₄/PDMS (PDUO-Cl) biomimetic protective layer is rationally constructed by the drip coating method. The PDUO-Cl protective layer can effectively suppress the side reaction of Li metal with LiPSs/electrolyte and homogenize the Li⁺ flux, thus avoiding corrosion of the Li metal anode. As a result, the symmetric cell with the PDUO-Cl protective layer delivers a stable cycle performance greater than 1400 h under a current density of 0.5 mA cm^-2. The Li-S batteries with a PDUO-Cl protective layer still show relatively better rate performance and cycling stability (69% after 100 cycles at 0.1 C). This work provides new insights into the design of protective strategies for Li anodes in Li-S batteries.

High-Density Oxygen Doping of Conductive Metal Sulfides for Better Polysulfide Trapping and Li2 S-S8 Redox Kinetics in High Areal Capacity Lithium-Sulfur Batteries

Exploring new materials and methods to achieve high utilization of sulfur with lean electrolyte is still a common concern in lithium-sulfur batteries. Here, high-density oxygen doping chemistry is introduced for making highly conducting, chemically stable sulfides with a much higher affinity to lithium polysulfides. It is found that doping large amounts of oxygen into NiCo2 S4 is feasible and can make it outperform the pristine oxides and natively oxidized sulfides. Taking the advantages of high conductivity, chemical stability, the introduced large Li-O interactions, and activated Co (Ni) facets for catalyzing Sn 2- , the NiCo2 (O-S)4 is able to accelerate the Li2 S-S8 redox kinetics. Specifically, lithium-sulfur batteries using free-standing NiCo2 (O-S)4 paper and interlayer exhibit the highest capacity of 8.68 mAh cm-2 at 1.0 mA cm-2 even with a sulfur loading of 8.75 mg cm-2 and lean electrolyte of 3.8 µL g-1 . The high-density oxygen doping chemistry can be also applied to other metal compounds, suggesting a potential way for developing more powerful catalysts towards high performance of Li-S batteries.

Constructing MIL-101(Cr) membranes on carbon nanotube films as ion-selective interlayers for lithium-sulfur batteries

It is of significant importance to suppress the polysulfide shuttle effect for the commercial application of lithium-sulfur batteries. Herein, continuous MIL-101(Cr) membranes were successfully fabricated on carbon nanotube films utilizing a simplein situgrowth method, aiming at constructing interlayer materials for inhibiting the shuttle effect. Owing to the suitable pore aperture and super electrolyte wettability, the as-developed MIL-101(Cr) membrane can effectively inhibit the shuttle behaviour of polysulfides while allowing the fast transport of Li-ions simultaneously, working as an ionic sieve. Additionally, this MOFs membrane is also helpful in accelerating the polysulfide catalytic conversion. Therefore, the proposed interlayer delivers an extraordinary rate capability, showing a remarkable capacity of 661.9 mAh g^-1under 5 C. Meanwhile, it also exhibits a high initial capacity of 816.1 mAh g^-1at 1 C and an exceptional durability with an extremely low capacity fading of 0.046% per cycle over 500 cycles.

Advances of Organosulfur Materials for Rechargeable Metal Batteries

Battery materials have become a hotspot in the academic research. Organosulfur compounds are considered as a promising class of cathode materials for rechargeable metal batteries. They have attracted increasing attention in recent years after a long-term stagnancy since 1980s. Recent studies have focused on the understanding of redox mechanism of linear organosulfur molecules R-Sn -R with defined structures. In addition, some new organosulfur compounds are developed. The reversible sulfursulfur (SS) bond breakage/formation of organosulfur in batteries makes them applicable as functional materials in batteries. In this review, new organosulfur materials including molecules, polymers, and composites are introduced. In the following, organosulfur-inorganic hybrid materials are discussed, which have shown unique redox process and enhanced battery performance. In the third part, organosulfur additives are used in Li-S batteries, which can improve the formation of solid-electrolyte interphase (SEI) and alter the redox pathways of sulfur cathodes. In the fourth part, organosulfur materials used in other metal batteries are introduced. Lastly, a summary and some perspectives are given. This review presents an overview of the recent advances of organosulfur materials in batteries and provides guidance for the future development of these materials.

Highly catalytically active CoSe2 supported on nitrogen-doped three dimensional porous carbon as a cathode for high-stability lithium-sulfur battery

Lithium-sulfur batteries, promising secondary energy storage devices, were mainly limited by its unsatisfactory cyclability owing to inefficient reversible conversion of sulfur and lithium sulfide on the cathode during the discharge/charging process. In this study, nitrogen-doped three-dimensional porous carbon material loaded with CoSe 2 nanoparticles (CoSe 2 -PNC) is developed as a cathode for lithium-sulfur battery application. A combination of CoSe 2 and nitrogen-doped porous carbon can efficiently improve the cathode activity and its conductivity, resulting in enhanced redox kinetics of the charge/discharge process. The obtained electrode exhibits a high discharge specific capacity of 1139.6 mAh g -1 at a current density of 0.2 C. After 100 cycles, its capacity remained at 865.7 mAh g -1 corresponding to a capacity retention of 75.97%. In a long-term cycling test, a discharge specific capacity of 546.7 mAh g -1 was observed after 300 cycles performed at a current density of 1 C.

Organophosphorus Hybrid Solid Electrolyte Interphase Layer Based on LixPO4 Enables Uniform Lithium Deposition for High‐Performance Lithium Metal Batteries

Lithium metal is a promising anode candidate for the next‐generation rechargeable battery system because of its highest specific capacity and lowest potential. However, low Coulombic efficiency (CE) and the formation of Li dendrites during the cycling process seriously hinder its practical application. Here, an organophosphorus hybrid flexible solid electrolyte interphase (SEI) layer is proposed based on a surface chelation strategy using phytic acid (PA) as Li metal surface treatment chemicals. Different from the traditional SEI layer, the polynuclear complex between PA and Li+ serves as a “connecter” in this SEI layer, which not only ensures its mechanical flexibility but also improves its lithiophilic property and ionic conductivity. With these advantages, the Li || Cu cells exhibit a high CE of 99.0% over 500 cycles at a current density of 0.5 mA cm−2. Li || Li symmetrical cells can also maintain a stable Li plating/stripping process over 2500 h at a high current density of 10.0 mA cm−2. Besides, all Li metal batteries (Li || S, Li || NCM, Li || LFP et al.) based on this strategy exhibit long cycling life and high capacity retention. This surface chelation strategy is believed to offer a new avenue to fabricate a stable and efficient SEI layer for practical application of Li metal batteries.

Low-Density Fluorinated Silane Solvent Enhancing Deep Cycle Lithium-Sulfur Batteries' Lifetime

The lithium metal anode (LMA) instability at deep cycle with high utilization is a crucial barrier for developing lithium (Li) metal batteries, resulting in excessive Li inventory and electrolyte demand. This issue becomes more severe in capacity-type lithium-sulfur (Li-S) batteries. High-concentration or localized high-concentration electrolytes are noted as effective strategies to stabilize Li metal but usually lead to a high electrolyte density (>1.4 g mL^-1 ). Here we propose a bifunctional fluorinated silane-based electrolyte with a low density of 1.0 g mL^-1 that not only is much lighter than conventional electrolytes (≈1.2 g mL^-1 ) but also form a robust solid electrolyte interface to minimize Li depletion. Therefore, the Li loss rate is reduced over 4.5-fold with the proposed electrolyte relative to its conventional counterpart. When paired with onefold excess LMA at the electrolyte weight/cell capacity (E/C) ratio of 4.5 g Ah^-1 , the Li-S pouch cell using our electrolyte can survive for 103 cycles, much longer than with the conventional electrolyte (38 cycles). This demonstrates that our electrolyte not only reduces the E/C ratio but also enhances the cyclic stability of Li-S batteries under limited Li amounts.

Isomeric Organodithiol Additives for Improving Interfacial Chemistry in Rechargeable Li-S Batteries

Lithium-sulfur (Li-S) batteries have a high theoretical specific energy; however, their performance is plagued by the shuttle effect of lithium polysulfides and the instability of the lithium anode interface. Great efforts have been made using electrolyte additives to address the issues. Herein, we report a class of electrolyte additives, i.e., benzenedithiols (BDTs). Among the three isomers of BDTs, 1,4-BDT shows the best effect on the performance improvement of a Li-S battery because it can bond more sulfur atoms than the other two. The functionality of 1,4-BDT on the cathode and anode involves the chemical reactions of thiol groups. The S-S bonds were generated from 1,4-BDT and sulfur through oligomerization, which change the original redox path of sulfur and inhibit the shuttle effect of lithium polysulfides. In addition, 1,4-BDT can form a smooth and stable solid-electrolyte interphase (SEI), which can enable the Li/Li symmetric cell with an ultralow overpotential of 0.08 V at a high current density of 5 mA cm^-2 for over 300 h. The Li-S cell with 1,4-BDT displays the highest cycling stability at a C/5 rate, with an initial capacity of 1548.5 mAh g^-1 and a reversible capacity of 1306.9 mAh g^-1 after 200 cycles. The Li-S pouch cell with 1,4-BDT and 2.8 g of sulfur exhibits an initial capacity of 2640 mAh and a capacity retention rate of 84.2% after 26 cycles at a C/10 rate. This work demonstrates that organodithiol compounds can be used as functional electrolyte additives and provides a new direction to design materials for advanced Li-S batteries.

Selective Permeable Lithium-Ion Channels on Lithium Metal for Practical Lithium-Sulfur Pouch Cells

Lithium metal batteries are considered a promising candidate for high-energy-density energy storage. However, the strong reducibility and high reactivity of lithium lead to low Coulombic efficiency when contacting oxidants, such as lithium polysulfide caused by the serious "shuttle effect" in lithium-sulfur batteries. Herein we design selectively permeable lithium-ion channels on lithium metal surface, which allow lithium ions to pass through by electrochemical overpotential, while the polysulfides are effectively blocked due to the much larger steric hindrance than lithium ions. The selective permeation of lithium ions through the channels is further elucidated by the molecular simulation and visualization experiment. Consequently, a prolonged cycle life of 75 cycles and high Coulombic efficiency of 99 % are achieved in a practical Li-S pouch cell with limited amounts of lithium and electrolyte, confirming the unique role the selective ion permeation plays in protecting highly reactive alkali metal anodes in working batteries.

A Natural Polymer Captor for Immobilizing Polysulfide/Polyselenide in Working Li-SeS2 Batteries

SeS₂ has become a promising cathode material owing to its enhanced electrical conductivity over sulfur and higher theoretical specific capacity than selenium; however, the working Li-SeS₂ batteries have to face the practical challenges from the severe shuttling of soluble dual intermediates of polysulfide and polyselenide, especially in high-SeS₂-loading cathodes. Herein, a natural organic polymer, Nicandra physaloides pectin (NPP), is proposed to serve as an effective polysulfide/polyselenide captor to address the shuttling issues. Informed by theoretical calculations, NPP is competent to provide a Lewis base-based strong binding interaction with polysulfides/polyselenides via forming lithium bonds, and it can be homogeneously deposited onto a three-dimensional double-carbon conductive scaffold to finally constitute a polysulfide/polyselenide-immobilizing interlayer. Operando spectroscopy analysis validates the enhanced polysulfide/polyselenide trapping and high conversion efficiency on the constructed interlayer, hence bestowing the Li-SeS₂ cells with ultrahigh rate capability (448 mAh g^-1 at 10 A g^-1), durable cycling lifespan (≈ 0.037% capacity attenuation rate per cycle), and high areal capacity (> 6.5 mAh cm^-2) at high SeS₂ loading of 15.4 mg cm^-2. Importantly, pouch cells assembled with this interlayer exhibit excellent flexibility, decent rate capability with relatively low electrolyte-to-capacity ratio, and stable cycling life even under a low electrolyte condition, promising a low-cost, viable design protocol toward practical Li-SeS₂ batteries.

In situ Construction of Robust Biphasic Surface Layers on Lithium Metal for Lithium-Sulfide Batteries with Long Cycle Life

Lithium-sulfur (Li-S) batteries have potential in high energy density battery systems. However, intermediates of lithium polysulfides (LiPSs) can easily shuttle to the Li anode and react with Li metal to deplete the active materials and cause rapid failure of the battery. A facile solution pretreatment method for Li anodes involving a solution of metal fluorides/dimethylsulfoxide was developed to construct robust biphasic surface layers (BSLs) in situ. The BSLs consist of lithiophilic alloy (Li_x M) and LiF phases on Li metal, which inhibit the shuttle effect and increase the cycle life of Li-S batteries. The BSLs allow Li⁺ transport and they inhibit dendrite growth and shield the Li anodes from corrosive reaction with LiPSs. Li-S batteries containing BSLs-Li anodes demonstrate excellent cycling over 1000 cycles at 1 C and simultaneously maintain a high coulombic efficiency of 98.2 %. Based on our experimental and theoretical results, we propose a strategy for inhibition of the shuttle effect that produces high stability Li-S batteries.

Fe2O3/rGO/CNT composite sulfur hosts with physical and chemical dual-encapsulation for high performance lithium–sulfur batteries

A sulfur host material of a Fe2O3/rGO/CNT fluffy composite with Fe2O3 and CNTs being dispersed between the rGO interlayers has been prepared by a hydrothermal reaction. The initial specific capacity of Fe2O3/rGO/CNT/S at 2C is 899 mA h g−1.