Polysulfide-Scission Reagents for the Suppression of the Shuttle Effect in Lithium-Sulfur Batteries

Enhanced Polysulfide Conversion and Shuttle Suppression in Lithium-Sulfur Batteries via Fe-Phytate Modified Sulfur Cathode

The practical application of lithium-sulfur (Li-S) batteries is severely impeded by poor cycling performance arising from sluggish redox kinetics and the shuttle effect of polysulfides. In this work, novel transition metal phytates are pioneered to functionalize conductive carbon to address these key limitations. Among a series of phytates evaluated, the Fe-Phytate-modified carbon (Fe-PA@CB) demonstrates superior specific capacity and rate performance. The unique molecular-level Fe-PA coating ensures uniform dispersion and increased active site, leveraging optimized adsorption and enhanced catalytic properties. Consequently, the activation energy for polysulfide conversion is significantly reduced, and polarization potential is minimized. The Fe-PA@CB electrode demonstrates significantly improved cycling stability, retaining 61% of the initial capacity after 500 cycles, compared to 40% retention by a conventional carbon-based cathode. This work not only provides a practical solution for enhancing the electrochemical performance of Li-S batteries but also offers valuable insights into material design and mechanistic understanding, paving the way for the development of next-generation energy storage systems.

A Dual-Functional Sulfur-Rich Copolymers for Stable Anchoring and Enhanced Conversion of Polysulfide in Lithium-Sulfur Batteries

Sulfur-rich copolymers have gained a great deal of attention as promising cathode materials in Li-S batteries due to their low cost and naturally uniform sulfur dispersion. However, the poor electrical conductivity and shuttle effect cause rapid capacity decay and low sulfur utilization especially under high sulfur loading and low electrolyte/sulfur ratio. Herein, the Fe1-xS/C dispersed and Se-containing sulfur-rich copolymer (FSP) was synthesized by one-pot reaction of ferrocene, trithiocyanuric acid with SexSy. In such process, the trithiocyanuric acid reacts with SexSy to form Se-containing sulfur-rich copolymers. Simultaneously, ferrocene reacts with sulfur to form highly dispersed Fe1-xS/C within sulfur-rich copolymers. The covalent chemical binding of sulfur in the FSP effectively suppress the shuttle effect of polysulfides by chemical binding. Meanwhile, the Se improves the conductivity of FSP, which enhances the reaction kinetics. Moreover, the highly dispersed Fe1-xS/C in the FSP is able to effectively catalyze polysulfide conversion and inhibit the shuttle effect. As a result, the optimized FSP electrode exhibits a high capacity of 1330 mAh g-1 at 0.2 C. Even under high sulfur loading (4.08 mg cm-2) and low E/S ratio (6 μL mg-1), the FSP cathode demonstrates a remarkable capacity of 734.7 mAh g-1 at 0.2 C.

Strategically Engineered Metal Cluster-Rare Earth Oxide Heterojunction Catalyst for High-Performance Lean Electrolyte Lithium-Sulfur Batteries

Developing high-energy-density lithium-sulfur batteries faces serious polysulfide shuttle effects and sluggish conversion kinetics, often necessitating the excessive use of electrolytes, which in turn adversely affects battery performance. Our study introduces a meticulously designed electrocatalyst, Cu-CeO2-x@N/C, to enhance lean-electrolyte lithium-sulfur battery performance. This catalyst, featuring in situ synthesized Cu clusters, regulates oxygen vacancies in CeO2 and forms Cu-CeO2-x heterojunctions, thereby diminishing sulfur conversion barriers and hastening reaction kinetics through the generation of S32-/S3*- intermediates. Besides, the three-dimensional conductive networks, composed of Cu and nitrogen-doped carbon matrices with high electrolyte affinity, effectively confine sparse electrolytes proximal to the catalyst locations, thereby facilitating rapid transport of Li+/electron to the active sites. As a result, the 1% Cu-CeO2-x@N/C cell demonstrated robust performance, achieving an initial discharge capacity of 793.2 mAh/g at 5 C over 500 cycles and maintaining a capacity of 719.9 mAh/g at 0.3 C with an electrolyte-to-sulfur ratio of 5 μL mg-1 and a high sulfur loading of 5.4 mg cm-2 after 60 cycles. These findings highlight the catalyst design for high-performance lean-electrolyte lithium-sulfur batteries, further paving the way for their commercialization.

Synergistic Regulation of Bidirectional Conversion of LiPSs and Li2S Using Anthraquinone as a Redox Mediator

Lithium-sulfur (Li-S) batteries are strong contenders as energy storage options in the next-generation, primarily because of their potential for delivering high energy densities. Nonetheless, their widespread commercialization faces several obstacles, including sluggish sulfur redox kinetics, the insulating properties of the Li2S discharge product, and significant reaction energy barriers. In this work, anthraquinone (AQ) was introduced as a redox mediator and incorporated onto Co-doped carbon materials through π-π interactions. The results showed that synergistic effect between AQ and Co atoms facilitated the bidirectional conversion of lithium polysulfides (LiPSs) and Li2S. During charging, AQ lowered the reaction energy barrier for Li2S oxidation and thereby enhanced the reversibility of sulfur redox reactions. Density functional theory (DFT) calculations showed that AQ-Li2Sx exhibits a lower energy for the lowest unoccupied molecular orbital (LUMO) and a higher energy for the highest occupied molecular orbital (HOMO). Experimental results demonstrated that an impressive initial discharge specific capacity of 1290 mAh g-1 was achieved by the fabricated S@AQ/Co-N-C electrode at 0.1 C. After 600 cycles at 1 C, it retained 64% of this capacity and exhibited a minimal 0.06% capacity decay rate per cycle.

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.

Flash Joule Heating: A Promising Method for Preparing Heterostructure Catalysts to Inhibit Polysulfide Shuttling in Li-S Batteries

The "shuttle effect" issue severely hinders the practical application of lithium-sulfur (Li-S) batteries, which is primarily caused by the significant accumulation of lithium polysulfides in the electrolyte. Designing effective catalysts is highly desired for enhancing polysulfide conversion to address the above issue. Here, the one-step flash-Joule-heating route is employed to synthesize a W-W2C heterostructure on the graphene substrate (W-W2C/G) as a catalytic interlayer for this purpose. Theoretical calculations reveal that the work function difference between W (5.08 eV) and W2C (6.31 eV) induces an internal electric field at the heterostructure interface, accelerating the movement of electrons and ions, thus promoting the sulfur reduction reaction (SRR) process. The high catalytic activity is also confirmed by the reduced activation energy and suppressed polysulfide shuttling by in situ Raman analyses. With the W-W2C/G interlayer, the Li-S batteries exhibit an outstanding rate performance (665 mAh g-1 at 5.0 C) and cycle steadily with a low decay rate of 0.06% over 1000 cycles at a high rate of 3.0 C. Moreover, a high areal capacity of 10.9 mAh cm-2 (1381.4 mAh g-1) is obtained with a high area sulfur loading of 7.9 mg cm-2 but a low electrolyte/sulfur ratio of 9.0 µL mg-1.

Strategy to Simultaneously Manipulate Direct Zn Nucleation and Hydrogen Evolution via Surface Modifier Hydrolysis for High-Performance Zn-Ion Batteries

The demand for safer batteries is growing rapidly due to fire incidents in electronic devices that use Li-ion batteries. Zn-ion batteries are among the most promising candidates to replace Li-ion batteries because they use a water-based electrolyte and are not explosive. However, Zn-ion batteries suffer from persistent corrosion and dendritic crystal formation during the charge-discharge process, which decrease their reversibility and hinder their commercial usage. Extensive research has been conducted to address these issues, but there are significant limitations due to high process and time costs. In this study, the modulation of the Zn-electrolyte interface to overcome these challenges is attempted using acetamide-derived thioacetamide (TAA), a surface modifier used in electroplating. TAA undergoes hydrolysis in an aqueous solution and produces weakly acidic byproducts and sulfide ions. These species are adsorbed onto the Zn metal surface, which induces uniform Zn2+ deposition, facilitates the formation of a stable interfacial layer, and inhibits side reactions due to the reduced water activity. Consequently, the symmetric cell with TAA achieves a low polarization of 50 mV and stable cycling for 700 h at 1 mA cm-2. Additionally, a Zn|V6O13 full cell exhibits electrochemical reversibility, maintaining a capacity retention of 64% over 300 cycles. Therefore, this study offers useful insights into the development of a simple manufacturing process to ensure the competitiveness of Zn-ion batteries for practical applications using functional electrolyte additives.

Development of Electrolytes under Lean Condition in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries stand out as one of the promising candidates for next-generation electrochemical energy storage technologies. A key requirement to realize high-specific-energy Li-S batteries is to implement low amount of electrolyte, often characterized by the electrolyte/sulfur (E/S) ratio. Low E/S ratio aggravates the known challenges for Li-S batteries and introduces new ones originated from the high concentration of polysulfides in limited electrolyte reservoir. In this review, the connections between the fundamental properties of electrolytes and the electrochemical/chemical reactions in Li-S batteries under lean electrolyte condition are elucidated. The emphasis is on how the solvating properties of the electrolyte affect the fate of polysulfides. Built upon the mechanistic analysis, different strategies to design lean electrolytes to improve the overall process of Li-S reactions and Li anode protection are discussed.

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.

Hydroxylated Multi-Walled Carbon Nanotubes Covalently Modified with Tris(hydroxypropyl) Phosphine as a Functional Interlayer for Advanced Lithium-Sulfur Batteries

We have successfully constructed a new type of intercalation membrane material by covalently grafting organic tris(hydroxypropyl)phosphine (THPP) molecules onto hydroxylated multi-walled carbon nanotubes (CNT-OH) as a functional interlayer for the advanced LSBs. The as-assembled interlayer has been demonstrated to be responsible for the fast conversion kinetics of polysulfides, the inhibition of polysulfide shuttle effect, as well as the formation of a stable solid electrolyte interphase(SEI) layer. By means of spectroscopic and electrochemical analysis, we further found THPP plays a key role in accelerating the conversion of polysulfides into low-ordered lithium sulfides and suppressing the loss of polysulfides, thus rendering the as-designed lithium-sulfur battery in this work a high capacity, excellent rate performance and long-term stability. Even at low temperatures, the capacity decay rate was only 0.036 % per cycle for 1700 cycles.

In Situ Synthesis of Organopolysulfides Enabling Spatial and Kinetic Co-Mediation of Sulfur Chemistry

Li-S batteries have been regarded as one of the most promising alternatives of the next-generation Li batteries. However, the dissolution and shuttling of lithium polysulfides lead to low cycle stability and low Coulombic efficiency, which intensively hinder the practical application of Li-S batteries. Herein, we propose a strategy to simultaneously promote the redox kinetics and inhibit the shuttle of lithium polysulfides, through in situ synthesis of insoluble organopolysulfides by adding a special additive. Attractively, the thus-formed insoluble organopolysulfides in the form of nanoparticle aggregates are also capable of adsorbing unconverted lithium polysulfides and hence effectively spatially suppress the shuttle effect. Furthermore, the organopolysulfides served as active redox mediators, showing faster redox kinetics of S chemistry than that of lithium polysulfides. As a result, the Li-S batteries showed impressive capacity, improved rate performance, and long cycling stability even under lean-electrolyte and high sulfur loading conditions.

Customized Structure Design and Functional Mechanism Analysis of Carbon Spheres for Advanced Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are attracting much attention due to their high theoretical energy density and are considered to be the predominant competitors for next-generation energy storage systems. The practical commercial application of LSBs is mainly hindered by the severe "shuttle effect" of the lithium polysulfides (LiPSs) and the serious damage of lithium dendrites. Various carbon materials with different characteristics have played an important role in overcoming the above-mentioned problems. Carbon spheres (CSs) are extensively explored to enhance the performance of LSBs owing to their superior structures. The review presents the state-of-the-art advances of CSs for advanced high-energy LSBs, including their preparation strategies and applications in inhibiting the "shuttle effect" of the LiPSs and protecting lithium anodes. The unique restriction effect of CSs on LiPSs is explained from three working mechanisms: physical confinement, chemical interaction, and catalytic conversion. From the perspective of interfacial engineering and 3D structure designing, the protective effect of CSs on the lithium anode is also analyzed. Not only does this review article contain a summary of CSs in LSBs, but also future directions and prospects are discussed. The systematic discussions and suggested directions can enlighten thoughts in the reasonable design of CSs for LSBs in near future.

Constructing Heterogeneous Structure in Metal-Organic Framework-Derived Hierarchical Sulfur Hosts for Capturing Polysulfides and Promoting Conversion Kinetics

Lithium-sulfur batteries (LSBs) are still severely blocked by the shuttle of polysulfides (LiPSs), resulting in low sulfur utilization and decreased lifetime. The optimal design of hosts with tailored porous structures and catalytic sites is expected to address this issue. Herein, a Bi/Bi₂O₃ heterostructure within the metal-organic framework (MOF)-derived sulfur host with a hierarchical structure was elaborated for both serving as sulfur hosts and promoting the redox reaction kinetics of LiPSs. The shuttle effects of LiPSs can be mitigated by the dual functional Bi/Bi₂O₃ heterostructure enriched in the outer layer of CAU-17-derived carbonic rods, i.e., the effective redox conversion of LiPSs can be realized at the Bi/Bi₂O₃ heterointerface by the adsorption of LiPSs over Bi₂O₃ and subsequently catalytic conversion over Bi. Benefiting from these merits, the fabricated LSBs realized a significantly optimized performance, including a high discharge capacity of 740.8 mAh g^-1 after 1000 cycles with an ultralow decay rate of 0.022% per cycle at 1 C, a high areal capacity of 6.6 mAh cm^-2 after 100 cycles with a sulfur loading of 8.1 mg cm^-2, and good performance in pouch cells as well.

Progress and Prospect of Organic Electrocatalysts in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries featured by ultra-high energy density and cost-efficiency are considered the most promising candidate for the next-generation energy storage system. However, their pragmatic applications confront several non-negligible drawbacks that mainly originate from the reaction and transformation of sulfur intermediates. Grasping and catalyzing these sulfur species motivated the research topics in this field. In this regard, carbon dopants with metal/metal-free atoms together with transition-metal complex, as traditional lithium polysulfide (LiPS) propellers, exhibited significant electrochemical performance promotions. Nevertheless, only the surface atoms of these host-accelerators can possibly be used as active sites. In sharp contrast, organic materials with a tunable structure and composition can be dispersed as individual molecules on the surface of substrates that may be more efficient electrocatalysts. The well-defined molecular structures also contribute to elucidate the involved surface-binding mechanisms. Inspired by these perceptions, organic electrocatalysts have achieved a great progress in recent decades. This review focuses on the organic electrocatalysts used in each part of Li-S batteries and discusses the structure-activity relationship between the introduced organic molecules and LiPSs. Ultimately, the future developments and prospects of organic electrocatalysts in Li-S batteries are also discussed.

A special core-shell ZnS-CNTs/S@NH cathode constructed to elevate electrochemical performances of lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are regarded as promising candidates for next-generation electrochemical energy storage systems due to their low cost and high energy density. However, the insulative sulfur, the volume expansion and high soluble polysulfides are three roots impeding their practical applications, and consequently bring challenges of low sulfur utilization, poor cyclic stability and sluggish redox kinetics. Herein, a special core-shell ZnS-CNTs/S@Ni(OH)₂ (labeled as ZnS-CNTs/S@NH) cathode has been designed to overcome above obstacles and elevate the electrochemical performance. The ZnS-CNTs/S@NH cathode is synthesized via a facile step-by-step strategy, in which ZnS-decorated CNTs was used as a framework to load sulfur and followed with a ultrathin Ni(OH)₂ (NH) layer encapsulation. The ZnS-CNT core combines merits of CNT network and polar ZnS quantum dots (QDs), accommodating the volume change, offering efficient pathways for fast electron/ion transport, and anchoring polysulfides through polar interactions. The outer Ni(OH)₂ shell physically confines the active material and meanwhile provides plenty of catalytic sites for effective polysulfide chemisorption. Benefiting from these merits, the ZnS-CNTs/S@NH cathode exhibits excellent cell performances in comparison with ZnS-CNTs/S and CNTs/S. Its discharge capacity at different C-rates is optimal in the three cathodes, which decreases from 1037.0 mAh g^-1 at 0.1 C to 646.1 mAh g^-1 at 2.0 C. Its cyclic capacity also manifests the slowest reduction from 861.1 to 760.1 mAh g^-1 after 150 cycles at 0.5 C, showing a high retention (88.3%) and a tiny average fading rate (0.078%). The strategy in this work provides a feasible approach to design and construct core-shell cathode materials for realizing practically usable Li-S batteries.

Red phosphorus embedded in TiO2/C nanofibers to enhance the potassium-ion storage performance

TiO₂-red phosphorus/C nanofibers (TiO₂-RP/CN) have been synthesized via electrospinning and then annealed with red phosphorus sublimation. Benefiting from the high electronic/ionic conductivity and robust stability of the unique structure, the TiO₂-RP/CN show high reversible capacities, as well as an outstanding cycling ability. In K half cells, the capacity decay of the TiO₂-RP/CN electrode mainly occurs in the first few cycles, and at 0.05 A g^-1 it delivers a high specific capacity of 257.8 mA h g^-1 after 500 cycles. K full cells were fabricated; these are well-matched with PTCDA (perylene-3,4,9,10-tetracarboxylic dianhydride) and also exhibited a good electrochemical performance (62 mA h g^-1 after 100 cycles). Therefore, the TiO₂-RP/CN are potential anode materials for use in K-ion batteries.

Recent advances in cathode engineering to enable reversible room-temperature aluminium-sulfur batteries

The rigorous requirements, such as high abundance, cost-effectiveness, and increased storage capacities, pose severe challenges to the existing Li-ion batteries' long-term sustainability. Room-temperature aluminum-sulfur (Al-S) chemistry, in particular, is gaining importance due to its high theoretical energy density (1700 W h kg-1). Al-S battery technology is one of the emerging metal-sulfur candidates that can surpass current Li-ion chemistries. When coupled with sulfur, aluminum metal brings a cheap and energy-rich option to existing battery technologies. Owing to the unique virtues of the Al-S battery, it has garnered increasing interest among scientific communities. Al-S chemistry has been investigated for quite some time, yet the cell performance remained in its infancy, which poses a challenge to this technology's viability. Besides stabilizing the Al metal anode, the most important challenge in the practical development of Al-S batteries is the development of a suitable sulfur cathode material. Owing to the complexity of this multivalent system, numerous factors have been taken into account, but the best sulfur cathode is yet to be identified. A detailed exploration of sulfur cathodes and their implications on the battery performance are discussed in this mini-review article. We present a detailed picture of cathode materials that may serve as the reference guide for developing more practical cathode materials. Also, fundamental principles and challenges encountered in the development of the sulfur cathodes are highlighted. Through the knowledge disseminated in this mini-review, the development in the multivalent post-Li-ion battery can be accelerated. A glimpse of the future outlook on the Al-S battery system with different potential solutions is also discussed.

Interaction Mechanisms between Lithium Polysulfides/Sulfide and Small Organic Molecules

Lithium polysulfides (LiPSs)/sulfide are essential in secondary lithium batteries. In this work, we used density functional theory computational methods to obtain the law of constraining lithium polysulfides/sulfide by the affinitive interactions at the electronic level. The proton transfer, the orientation of polysulfides, the electron affinity, and the acid dissociation constant of small organic molecules were examined to elucidate the lithium polysulfides/sulfide binding mechanism with functional groups. The carboxyl groups exhibited a strong ability to dissolve the low-order polysulfides via proton transfer, although this type of group is highly unstable. In comparison, 1,2-diaminopropane with adjacent amino groups can strongly anchor the high-order polysulfides. The electrostatic attractions between lithium-ion and the electron-rich groups and their number and location dominated the binding energetics. Also, the entropy contribution to the binding should be considered. The information gained from these results can serve as a criterion for the selection of co-solvent for the electrolyte or postmodified functional groups for decorating the cathode in the lithium-sulfur system.

Hydrogen-substituted graphdiyne/graphene as an sp/sp2 hybridized carbon interlayer for lithium-sulfur batteries

To overcome the shuttle effect in lithium-sulfur (Li-S) batteries, an sp/sp2 hybridized all-carbon interlayer by coating graphene (Gra) and hydrogen-substituted graphdiyne (HsGDY) with a specific surface area as high as 2184 m2 g-1 on a cathode is designed and prepared. The two-dimensional network and rich pore structure of HsGDY can enable the fast physical adsorption of lithium polysulfides (LiPSs). In situ Raman spectroscopy and ex situ X-ray photoelectron spectroscopy (XPS) combined with density functional theory (DFT) computations confirm that the acetylenic bonds in HsGDY can trap the Li+ of LiPSs owing to the strong adsorption of Li+ by acetylenic active sites. The strong physical adsorption and chemical anchoring of LiPSs by the HsGDY materials promote the conversion reaction of LiPSs to further mitigate the shuttling problem. As a result, Li-S batteries integrated with the all-carbon interlayers exhibit excellent cycling stability during long-term cycling with an attenuation rate of 0.089% per cycle at 1 C over 500 cycles.

Flexible pore structure modulation enables durable sulfur carrier for advanced lithium–sulfur batteries

The immobilization of polysulfide by carbon matrix via synergism can restrict the shuttle effect and extend the cycle life of Li–S batteries.

A Review of Functional Separators for Lithium Metal Battery Applications

Lithium metal batteries are considered “rough diamonds” in electrochemical energy storage systems. Li-metal anodes have the versatile advantages of high theoretical capacity, low density, and low reaction potential, making them feasible candidates for next-generation battery applications. However, unsolved problems, such as dendritic growths, high reactivity of Li-metal, low Coulombic efficiency, and safety hazards, still exist and hamper the improvement of cell performance and reliability. The use of functional separators is one of the technologies that can contribute to solving these problems. Recently, functional separators have been actively studied and developed. In this paper, we summarize trends in the research on separators and predict future prospects.

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

The lithium-sulfur (Li-S) battery is regarded as a promising high-energy-density battery system, in which the dissolution-precipitation redox reactions of the S cathode are critical. However, soluble Li polysulfides (LiPSs), as the indispensable intermediates, easily diffuse to the Li anode and react with the Li metal severely, thus depleting the active materials and inducing the rapid failure of the battery, especially under practical conditions. Herein, an organosulfur-containing solid electrolyte interphase (SEI) is tailored for the stabilizaiton of the Li anode in Li-S batteries by employing 3,5-bis(trifluoromethyl)thiophenol as an electrolyte additive. The organosulfur-containing SEI protects the Li anode from the detrimental reactions with LiPSs and decreases its corrosion. Under practical conditions with a high-loading S cathode (4.5 mg_S cm^-2 ), a low electrolyte/S ratio (5.0 µL mg_S ^-1 ), and an ultrathin Li anode (50 µm), a Li-S battery delivers 82 cycles with an organosulfur-containing SEI in comparison to 42 cycles with a routine SEI. This work provokes the vital insights into the role of the organic components of SEI in the protection of the Li anode in practical Li-S batteries.

Single-atom Catalytic Materials for Lean-electrolyte Ultrastable Lithium-Sulfur Batteries

Lithium-sulfur batteries with high energy capacity are promising candidates for advanced energy storage. However, their applications are impeded by shuttling of soluble polysulfides and sluggish conversion kinetics with inferior rate performance and short cycling life. Here, single-atom materials are designed to accelerate polysulfide conversion for Li-S batteries. Nitrogen sites in the structure not only anchor polysulfides to alleviate the shuttle effect but also enable high loading of single-atom irons. Density functional theory calculations indicate that single-atom sites reduce the energy barrier of electrochemical reactions and thus improve the rate and cycling performances of batteries. The coin battery shows impressive energy storage properties, including a high reversible capacity of 1379 mAh g^-1 at 0.1 C and a high rate capacity of 704 mAh g^-1 at 5 C. The ratio of electrolyte dosage/energy density is as low as 5.5 g Ah^1-. It exhibits excellent cycling performance with a capacity retention of 90% even after 200 cycles at 0.2 C.

Water-Based Dual-Cross-Linked Polymer Binders for High-Energy-Density Lithium-Sulfur Batteries

High-mass-loading electrodes with long-term stability have long been a great challenge for lithium-sulfur batteries (LSBs), since the conventional binders are unable to cope with the shuttling of lithium polysulfides and the structural damage in an electrode. Here, a novel water-based polymer, polyphosphate acid cross-linked chitosan ethylamide carbamide (PACEC), is developed as a binder to construct high-energy-density sulfur cathode and flexible LSBs. With a dual-cross-linked network, the PACEC shows excellent affinity with lithium polysulfides to relieve the shuttle effect and robust mechanical properties to stabilize the electrode. The sulfur cathode based on PACEC demonstrates a high sulfur loading of 14.8 mg cm^-2, the areal initial capacity of 17.5 mAh cm^-2, and Coulombic efficiency of 99.3%, while the amount of electrolyte is strictly limited to 6 μL mg^-1. More importantly, a robust pouch cell with an area of 6 cm² and only 177% oversized lithium can successfully integrate the energy density of 6.5 mAh cm^-2 with the cycling retention per cycle of 99.74% during 270 cycles and flexibility at a curvature of 3 mm. This study provides inspirations for the design of eco-friendly polymer binders and paving new ways for the development of LSBs.

Dual-Regulation Strategy to Improve Anchoring and Conversion of Polysulfides in Lithium-Sulfur Batteries

The sluggish reaction kinetics at the cathode/electrolyte interface of lithium-sulfur (Li-S) batteries limits their commercialization. Herein, we show that a dual-regulation system of iron phthalocyanine (FePc) and octafluoronaphthalene (OFN) decorated on graphene (Gh), denoted as Gh/FePc+OFN, accelerates the interfacial reaction kinetics of lithium polysulfides (LiPSs). Multiple in situ spectroscopy techniques and ex situ X-ray photoelectron spectroscopy combined with density functional theory calculations demonstrate that FePc acts as an efficient anchor and scissor for the LiPSs through Fe···S coordination, mainly facilitating their liquid-liquid transformation, whereas OFN enables Li-bond interaction with the LiPSs, accelerating the kinetics of the liquid-solid nucleation and growth of Li₂S. This dual-regulation system promotes the smooth conversion reaction of sulfur, thereby improving the battery performance. A Gh/FePc+OFN-based Li-S cathode delivered an ultrahigh initial capacity of 1604 mAh g^-1 at 0.2 C, with an ultralow capacity decay rate of 0.055% per cycle at 1 C over 1000 cycles.

Tellurium: A High-Volumetric-Capacity Potassium-Ion Battery Electrode Material

Currently, exploring high-volumetric-capacity electrode materials that allow for reversible (de-)insertion of large-size K⁺ ions remains challenging. Tellurium (Te) is a promising alternative electrode for storage of K⁺ ions due to its high volumetric capacity, confirmed in lithium-/sodium-ion batteries, and the intrinsic good electronic conductivity. However, the charge storage capability and mechanism of Te in potassium-ion batteries (KIBs) have not been unveiled until now. Here, a novel K-Te battery is constructed, and the K⁺ -ion storage mechanism of Te is revealed to be a two-electron conversion-type reaction of 2K + Te ↔ K₂ Te, resulting in a high theoretical volumetric capacity of 2619 mAh cm^-3 . Consequently, the rationally fabricated tellurium/porous carbon electrodes deliver an ultrahigh reversible volumetric capacity of 2493.13 mAh cm^-3 at 0.5 C (based on Te), a high-rate capacity of 783.13 mAh cm^-3 at 15 C, and superior long-term cycling stability for 1000 cycles at 5 C. This excellent electrochemical performance proves the feasibility of utilizing Te as a high-volumetric-capacity active material for storage of K⁺ ions and will advance the practical application of KIBs.

Electrode Degradation in Lithium-Ion Batteries

Although Li-ion batteries have emerged as the battery of choice for electric vehicles and large-scale smart grids, significant research efforts are devoted to identifying materials that offer higher energy density, longer cycle life, lower cost, and/or improved safety compared to those of conventional Li-ion batteries based on intercalation electrodes. By moving beyond intercalation chemistry, gravimetric capacities that are 2-5 times higher than that of conventional intercalation materials (e.g., LiCoO₂ and graphite) can be achieved. The transition to higher-capacity electrode materials in commercial applications is complicated by several factors. This Review highlights the developments of electrode materials and characterization tools for rechargeable lithium-ion batteries, with a focus on the structural and electrochemical degradation mechanisms that plague these systems.

Abundant Defects-Induced Interfaces Enabling Effective Anchoring for Polysulfides and Enhanced Kinetics in Lean Electrolyte Lithium-Sulfur Batteries

In response to the concept of "compact energy storage", research on electrolyte dosage dwindling is definitely efficient owing to present electrolyte usage up to 70 wt % in a cell. While less electrolyte usage leads to slow reaction kinetics. Herein, a heterojunction, MoP/MoS₂ core with much defects and vacancies coated by porous carbon shell, is synthesized. Besides, the small particle size of MoP/MoS₂@C facilitates a close packing to form a dense and porous modified layer on PP-based (F-PP) separator. The heterojunction with defects exposes abundant interfaces and assures an adequate local electrolyte availability and an improved electrolyte affinity that are beneficial for Li⁺ transfer. When using F-PP separator, Li-S cell performs well in the lean electrolyte. Apart from a high discharging capacity of 517.1 mAh g^-1 at 5 C in E/S = 10 (only half benchmark dosage), the cell realizes a favorable stability at C/2 over 500 cycles even in E/S = 7 (0.065% decay per cycle), demonstrating an effective polysulfides (PS) shuttling relief and reversibility of PS-relating chemical conversion. All these enhanced electrochemical behaviors in lean electrolyte result from a three-in-one strategy realized by defects-included MoP/MoS₂@C heterojunction, including incorporating the lithiuphilic and sulfophilic sites for PS confinement and electrocatalysis triggered by abundant S vacancies and Lewis and Brønsted acid sites.

VO2(p)-V2C(MXene) Grid Structure as a Lithium Polysulfide Catalytic Host for High-Performance Li-S Battery

Extensive efforts have been devoted to improving the cycling stability and reversibility of lithium-sulfur batteries. However, unsolved challenges and difficulties still remain in suppressing the shuttle effect, improving the conductivity and structural stability of sulfur cathodes. Here, we report a three-dimensional (3D) grid heterostructure VO₂(p) (paramontroseite-VO₂) nanorod cluster growing on the surface of two-dimensional V₂C (MXene) nanosheets as a high-performance catalytic host for sulfur cathodes. The results of first-principles calculation demonstrate that VO₂(p) nanorods can synergize with V₂C to enhance the adsorption capacity of host for lithium polysulfides in this host structure and reduce the redox reaction barrier in the conversion of polysulfides to short-chain sulfides. In addition, the high specific surface area and structural stability of the host material can increase the redox reaction kinetics and cyclic reversibility of the electrode. The VO₂(p)-V₂C/S cathode exhibits outstanding electrochemical performance and excellent reversible discharge capacity (1250 mAh·g^-1 at 0.2C), long-term cycling stability (69.1% retention at 2C after 500 cycles), and high sulfur loading cycling capacity (initial areal capacity of 9.3 mAh·cm^-2 at 0.2C for 200 cycles). Our research provides a valuable reference for the design of high-performance cathode structures with high sulfur loading.

Stabilization of Li-Se Batteries by Wearing PAN Protective Clothing

Lithium-selenium (Li-Se) batteries have recently attracted more and more attentions as new secondary battery systems due to the similarity but better performances than lithium-sulfur (Li-S) batteries. However, the dissolution of selenium in electrolytes results in low selenium utilization, concentration polarization, inferior capacities, and unstable cycling performances. Herein, 46.58 wt% of selenium is loaded on carbon cloths through the calcination process, which were directly used as self-supporting cathodes. Carbonized polyacrylonitrile (PAN) nanofiber membranes produced by electrospinning are worn as the protective clothing between the cathode and separator to avoid the loss and dissolution of selenium. The stabilization of Li-Se batteries was enhanced by introducing two interlayers, as expected, they exhibit a stable reversible average capacity of 590 mA h g^-1 during 1000 cycles at a current density of 0.5 C (1 C = 675 mA g^-1). No polyselenide formation is found during charging/discharging, and the effects of the introduced PAN interlayers on improving the stability and reducing the polarization of the assembled Li-Se batteries are confirmed by mechanistic characterizations. These regulated Li-Se batteries present great application potential in the future, and the design idea can also be promoted to explore other energy storage systems.

Titanium silicalite as a radical-redox mediator for high-energy-density lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are receiving intense interest owing to their high energy densities, cost effectiveness, and the natural abundance of sulfur. However, practical applications are still limited by rapid capacity decay caused by multielectron redox reactions and complex phase transformations. Here, we include commercially available titanium silicalite-1 (TS-1) in carbon/sulfur cathodes, to introduce strong chemical interactions between the lithium polysulfides (LiPS) and TS-1 in a working Li-S battery. In situ UV-visible spectroscopy together with other experimental results confirm that incorporation of TS-1 mediators enables direct conversion between S₈^2- and S₃*^- radicals during the discharge process, which effectively promotes the kinetic behaviors of soluble LiPS and regulates uniform nucleation and growth of solid sulfide precipitates. These features give our TS-1 engineered sulfur cathode an ultrahigh initial capacity of 1459 mA h g^-1 at 0.1C. Moreover, the system has an impressively high areal capacity (3.84 mA h cm^-2) and long cycling stability with a high sulfur loading of 4.9 mg cm^-2. This novel and low-cost fabrication procedure is readily scalable and provides a promising avenue for potential industrial applications.

Two-dimensional boron nitride as a sulfur fixer for high performance rechargeable aluminum-sulfur batteries

Aluminum-ion batteries (AIBs) are regarded as promising candidates for post-lithium-ion batteries due to their lack of flammability and electrochemical performance comparable to other metal-ion batteries. The lack of suitable cathode materials, however, has hindered the development of high-performing AIBs. Sulfur is a cost-efficient material, having distinguished electrochemical properties, and is considered an attractive cathode material for AIBs. Several pioneering reports have shown that aluminum-sulfur batteries (ASBs) exhibit superior electrochemical capacity over other cathode materials for AIBs. However, a rapid decay in the capacity is a huge barrier for their practical applications. Here, we have demonstrated systematically for the first time that the two-dimensional layered materials (e.g. MoS2, WS2, and BN) can serve as fixers of S and sulfide compounds during repeated charge/discharge processes; BN/S/C displays the highest capacity of 532 mAh g-1 (at a current density of 100 mA g-1) compared with the current state-of-the-art cathode material for AIBs. Further, we could improve the life-span of ASBs to an unprecedented 300 cycles with a high Coulombic efficiency of 94.3%; discharge plateaus at ~1.15 V vs. AlCl4-/Al was clearly observed during repeated charge/discharge cycling. We believe that this work opens up a new method for achieving high-performing ASBs.