Confining ZnS/SnS2 Ultrathin Heterostructured Nanosheets in Hollow N-Doped Carbon Nanocubes as Novel Sulfur Host for Advanced Li-S Batteries

Enhancing the performance of a lithium-sulfur battery with spatially confined mesoporous nanoreactors in sulfurized polyacrylonitrile cathodes

Sulfurized polyacrylonitrile (SPAN), which is recognized as a promising cathode material for lithium-sulfur batteries (Li-SBs), effectively mitigates the shuttle effect resulting from polysulfide dissolution. However, conventional SPAN cathodes typically exhibit sulfur loadings below 40 wt%. While encapsulation of sulfur within pores via a solid electrolyte interface addresses the low sulfur loading issue, the suboptimal kinetics of the solid-solid reactions hinder effective utilization of sulfur within the pores. In this work, Me-SeSPAN/SeS fibrous membranes were successfully synthesized through electrospinning and molten salt-assisted pyrolysis of ZIF-8, which resulted in the formation of spatially confined interconnected mesoporous nanoreactors. These nanoreactors function as supplementary storage spaces, loading and constraining the size of internal active material clusters. The fibrous membranes facilitate Li+ movement through pore spaces and promote adsorption of the discharge product Li2S on the pore walls via the spatial confinement effect. Based on density functional theory (DFT) calculations, this process guarantees a supply of electrons and Li+ to the active material, thereby enabling continuous electron transfer during redox reactions. The optimized Me-SeSPAN/SeS electrode, featuring a sulfur and selenium loading of 70 wt%, demonstrates exceptional cycling stability in both coin and pouch cells. This study presents an effective strategy for enhancing the kinetics of active materials encapsulated in SPAN cathodes.

Enhancing Lithium-Sulfur Battery Performance with MXene: Specialized Structures and Innovative Designs

Established in 1962, lithium-sulfur (Li-S) batteries boast a longer history than commonly utilized lithium-ion batteries counterparts such as LiCoO2 (LCO) and LiFePO4 (LFP) series, yet they have been slow to achieve commercialization. This delay, significantly impacting loading capacity and cycle life, stems from the long-criticized low conductivity of the cathode and its byproducts, alongside challenges related to the shuttle effect, and volume expansion. Strategies to improve the electrochemical performance of Li-S batteries involve improving the conductivity of the sulfur cathode, employing an adamantane framework as the sulfur host, and incorporating catalysts to promote the transformation of lithium polysulfides (LiPSs). 2D MXene and its derived materials can achieve almost all of the above functions due to their numerous active sites, external groups, and ease of synthesis and modification. This review comprehensively summarizes the functionalization advantages of MXene-based materials in Li-S batteries, including high-speed ionic conduction, structural diversity, shuttle effect inhibition, dendrite suppression, and catalytic activity from fundamental principles to practical applications. The classification of usage methods is also discussed. Finally, leveraging the research progress of MXene, the potential and prospects for its novel application in the Li-S field are proposed.

Organic Electrolyte Additive: Dual Functions Toward Fast Sulfur Conversion and Stable Li Deposition for Advanced Li-S Batteries

Lithium-sulfur (Li-S) battery is of great potential for the next generation energy storage device due to the high specific capacity energy density. However, the sluggish kinetics of S redox and the dendrite Li growth are the main challenges to hinder its commercial application. Herein, an organic electrolyte additive, i.e., benzyl chloride (BzCl), is applied as the remedy to address the two issues. In detail, BzCl can split into Bz· radical to react with the polysulfides, forming a Bz-S-Bz intermediate, which changes the conversion path of S and improves the kinetics by accelerating the S splitting. Meanwhile, a tight and robust solid electrolyte interphase (SEI) rich in inorganic ingredients namely LiCl, LiF, and Li2O, is formed on the surface of Li metal, accelerating the ion conductivity and blocking the decomposition of the solvent and lithium polysulfides. Therefore, the Li-S battery with BzCl as the additive remains high capacity of 693.2 mAh g-1 after 220 cycles at 0.5 C with a low decay rate of 0.11%. This work provides a novel strategy to boost the electrochemical performances in both cathode and anode and gives a guide on the electrolyte design toward high-performance Li-S batteries.

Toward robust lithium-sulfur batteries via advancing Li2S deposition

Lithium-sulfur batteries (LSBs) with two typical platforms during discharge are prone to the formation of soluble lithium polysulfides (LiPS), leading to a decrease in the cycling life of the battery. Under practical working conditions, the transformation of S8 into Li2S is cross-executed rather than a stepwise reaction, where the liquid LiPS to solid Li2S conversion can occur at a high state of charge (SOC) to maintain the current requirement. Therefore, advancing Li2S deposition can effectively reduce the accumulation of LiPSs and ultimately improve the reaction kinetics. Herein, a "butterfly material" GeS2-MoS2/rGO is used as a sulfur host. Rich catalytic heterointerfaces can be obtained via the abundant S-S bonds formed between GeS2 and MoS2. MoS2 (left wing) can enhance LiPS adsorption, while the lattice-matching nature of Fdd2 GeS2 (right wing) and Fm3̄m Li2S can induce multiple nucleation and regulate the 3D growth of Li2S. Li2S deposition can be advanced to occur at 80% SOC, thereby effectively inhibiting the accumulation of soluble LiPSs. Attributed to the synergistic effect of catalytic and lattice-matching properties, robust coin and pouch LSBs can be achieved.

Dual-Confinement Effect of Nanocages@Nanotubes Suppresses Polysulfide Shuttle Effect for High-Performance Lithium-Sulfur Batteries

The shuttle effect of lithium polysulfides (LiPSs) severely hinders the development and commercialization of lithium-sulfur batteries, and the design of high-conductive carbon fiber-host material has become a key solution to suppress the shuttle effect. In this work, a unique Co/CoN-carbon nanocages@TiO2-carbon nanotubes structure (NC@TiO2-CNTs) is constructed using an electrospinning and nitriding process. Lithium-sulfur batteries using NC@TiO2-CNTs as cathode host materials exhibit high sulfur utilization (1527 mAh g-1 at 0.2 C) and can still maintain a discharge capacity of 663 mAh g-1 at a high current density of 5 C, and the capacity loss is only 0.056% per cycle during 500 cycles at 1 C. It is worth noting that even under extreme conditions (sulfur-loading = 90%, surface-loading = 5.0 mg cm-2 (S), and E/S = 6.63 µL mg-1), the lithium-sulfur batteries can still provide a reversible capacity of 4 mAh cm-2. Throughdensity functional theory calculations, it has been found that the Co/CoN heterostructures can adsorb and catalyze LiPSs conversion effectively. Simultaneously, the TiO2 can adsorb LiPSs and transfer Li+ selectively, achieving dual confinement for the shuttle effect of LiPSs (nanocages and nanotubes). The new findings provide a new performance enhancement strategy for the commercialization of lithium-sulfur batteries.

Metal-Redox Bicatalysis Batteries for Energy Storage and Chemical Production

New types of electrochemical energy conversion and storage devices based on redox electrocatalytic reactions possess great potential in renewable energy to maximize energy utilization and balance environmental issues. The typical device is the metal-redox bicatalysis battery, where the cathode is redox bifunctional catalyst (named as redox bicatalyst) with gas, solid, liquid as active reactants while anode is metal, driven by cathodic redox electrocatalytic reactions during charge/discharge processes, which promotes the energy storage and chemical production. In this system, the metal anode, redox-bicatalyst cathode, electrolytes, and the redox electrochemical reactions can be modified and adjusted to achieve the optimal energy conversion and utilization. Therefore, the deep understanding of the electrochemical system is conducive to designing new devices to meet the demand among various applications, including energy storage and conversion. In this review, the authors clarify the fundamentals and design principles of the rechargeable/reversible metal-redox bicatalysis batteries and how each part affects the devices in energy conversion and chemical production. The authors summarize the electrocatalytic reduction/oxidation reactions, the reported systems relied on redox reactions, and the corresponding redox bicatalysts. Finally, a perspective of the key challenges and the possible new types of metal-redox bicatalysis batteries for efficient energy utilization and chemical production are given.

Modulating d-Band Electronic Structures of Molybdenum Disulfide via p/n Doping to Boost Polysulfide Conversion in Lithium-Sulfur Batteries

Polysulfide shuttle effect and sluggish sulfur reaction kinetics severely impede the cycling stability and sulfur utilization of lithium-sulfur (Li-S) batteries. Modulating d-band electronic structures of molybdenum disulfide electrocatalysts via p/n doping is promising to boost polysulfide conversion and suppress polysulfide migration in lithium-sulfur batteries. Herein, p-type V-doped MoS2 (V-MoS2 ) and n-type Mn-doped MoS2 (Mn-MoS2 ) catalysts are well-designed. Experimental results and theoretical analyses reveal that both of them significantly increase the binding energy of polysulfides on the catalysts' surface and accelerate the sluggish conversion kinetics of sulfur species. Particularly, the p-type V-MoS2 catalyst exhibits a more obvious bidirectional catalytic effect. Electronic structure analysis further demonstrates that the superior anchoring and electrocatalytic activities are originated from the upward shift of the d-band center and the optimized electronic structure induced by duplex metal coupling. As a result, the Li-S batteries with V-MoS2 modified separator exhibit a high initial capacity of 1607.2 mAh g-1 at 0.2 C and excellent rate and cycling performance. Moreover, even at a high sulfur loading of 6.84 mg cm-2 , a favorable initial areal capacity of 8.98 mAh cm-2 is achieved at 0.1 C. This work may bring widespread attention to atomic engineering in catalyst design for high-performance Li-S batteries.

The Dual-Site Adsorption and High Redox Activity Enabled by Hybrid Organic-Inorganic Vanadyl Ethylene Glycolate for High-Rate and Long-Durability Lithium-Sulfur Batteries

Transition metal oxides (TMOs) have attracted considerable attention owing to their strong anchoring ability and natural abundance. However, their single-site adsorption toward sulfur (S) species significantly lowers the possibility of S species reacting with Li⁺ in the electrolyte and increases the reaction barrier. This study investigates molecular modification by coupling the TMO structure with Li⁺ conductive polymer ligands, and vanadyl ethylene glycolate (VEG) is successfully synthesized by introducing organic ligands into the VO_x crystal structure. In addition to the strong interaction between the VO_x and lithium polysulfides via the V-S bond, the groups in the VEG polymer ligands can reversibly couple/decouple with Li⁺ in the electrolyte. Such dual-site adsorption enables a smooth dynamic adsorption-diffusion process. Accordingly, the VEG-based Li-S cells exhibit excellent rate reversibility, cyclic stability, and a long cycle life without the addition of conducting agents. Encouragingly, the VEG-based cells also exhibit close and excellent capacity decays of 0.081%, 0.078%, and 0.095% at 0, 25, and 50 °C (1 C for 200 cycles), respectively. This work provides a novel approach for developing advanced catalysts that can realize Li-S batteries with long-term durability, fast charge-discharge properties, and applications in a wide temperature range.

Synergistically Designed Dual Interfaces to Enhance the Electrochemical Performance of MoO2 /MoS2 in Na- and Li-Ion Batteries

It is indispensable to develop and design high capacity, high rate performance, long cycling life, and low-cost electrodes materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Herein, MoO₂ /MoS₂ /C, with dual heterogeneous interfaces, is designed to induce a built-in electric field, which has been proved by experiments and theoretical calculation can accelerate electrochemical reaction kinetics and generate interfacial interactions to strengthen structural stability. The carbon foam serves as a conductive frame to assist the movement of electrons/ions, as well as forms heterogeneous interfaces with MoO₂ /MoS₂ through CS and CO bonds, maintaining structural integrity and enhancing electronic transport. Thanks to these unique characteristics, the MoO₂ /MoS₂ /C renders a significantly enhanced electrochemical performance (324 mAh g^-1 at 1 A g^-1 after 1000 cycles for SIB and 500 mAh g^-1 at 1 A g^-1 after 500 cycles for LIBs). The current work presents a simple, useful and cost-effective route to design high-quality electrodes via interfacial engineering.

Nucleophilic ring-opening of thiocyclic carbonates: A scheme to prepare sulfhydryl-rich binders for high-performance lithium-sulfur batteries

Problems such as cathode collapse caused by volume change and shuttle effect of lithium polysulfides (LiPSs) limit the commercialization of Lithium-Sulfur (Li-S). Herein, we developed a sulfhydryl-containing multifunctional binder prepared by the nucleophilic ring-opening reaction of thiocyclic carbonates with amino groups. The binders (CNP-T and CNP-F) form sulfur-containing polymers with sulfur through the wet-slurry process, thereby effectively suppressing the shuttle effect. The abundant polar functional groups (e.g., -NH₂, -CS(NH)-) in CNP-T and CNP-F can effectively adsorb LiPSs to weaken the shuttle effect, which is confirmed by both density functional theory (DFT) and experimental results. At the same time, their own hyperbranched network structure can also limit the volume change of the sulfur cathode. Therefore, the Li-S battery exhibits an initial specific capacity of 924.02 mAh/g and a decay rate of 0.033% when cycled at 1C for 500 cycles.

Anchoring polysulfides via a CoS2/NC@1T MoS2 modified separator for high-performance lithium–sulfur batteries

CoS2/NC@1T MoS2 synthesized by a one-step hydrothermal method forms a unique hierarchical configuration with simultaneous internal and external modifications. A lithium–sulfur battery with a CoS2/NC@1T MoS2-PP separator shows superior cycling performance.

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

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

Multifunctional Atomic Molybdenum on Graphene with Distinctive Coordination to Solve Li and S Electrochemistry

The improvement of lithium-sulfur batteries is still impeded by notorious shuttling effect and sluggish kinetics on the S cathode, and rampant Li dendrite formation on the Li anode makes it worse. Herein, a type of single-atom dispersed Mo on nitrogen-doped graphene (Mo/NG) with a distinctive Mo-N₂ O₂ -C coordination structure first serving as a multifunctional material is designed by a structure-oriented strategy to solve Li and S electrochemistry. Mo/NG with superior intrinsic properties endowed by the unique coordination configuration adsorbs soluble polysulfides and promotes bidirectional conversion of LiPSs at the cathode side. Meanwhile, the suitable binding strength of Mo/NG with lithium ions endows it with an attractive lithiophilic feature. Specifically, Mo/NG is able to work as the adaptor to redistribute lithium ions on the interface of separator and homogenize the lithium ion flux. Due to the suitable binding ability with Li⁺ , it does not interfere with the diffusion of lithium ions across and provides tunnels exclusive to lithium ions to generate fast and homogeneous flux. Ascribed to such unique multifunctionality, Li-S batteries assembled with Mo/NG exhibit excellent electrochemical performance including long cycling stability over 1000 cycles and high areal capacities under high sulfur mass loading.