Ionic-Liquid-Assisted Synthesis of FeSe-MnSe Heterointerfaces with Abundant Se Vacancies Embedded in N,B Co-Doped Hollow Carbon Microspheres for Accelerating the Sulfur Reduction Reaction

Zinc Tellurium with Anionic Vacancies Anchored on Ordered Macroporous Carbon Skeleton Enabling Accelerated Polysulfide Conversion for Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) showcase great promise for large-scale energy storage systems, however, their practical commercialization is seriously hindered by the sluggish redox reaction kinetics and detrimental shuttle effect of soluble polysulfides. Herein, small ZnTe1- x nanoparticles with anionic vacancies firmly anchored on 3D ordered macroporous N-doped carbon skeleton (3DOM-ZnTe1- x@NC) are elaborately constructed as a high-efficiency electrocatalyst for LSBs. The ordered macroporous carbon skeleton not only greatly increases the external surface area to expose sufficient active sites but also facilitates the electrolyte penetration. Additionally, the experimental studies combined with theoretical calculations confirm the presence of Te vacancies optimizes the electronic structure to enhance the intrinsic catalytic activity and chemical absorption. Consequently, LSBs assembled with the 3DOM-ZnTe1- x@NC modified separators exhibit high specific discharge capacity, as well as superior rate performance and good long-term cycling stability. Even under a high sulfur loading of 6.5 mg cm-2 and lean electrolyte, an impressive areal capacity of 5.28 mAh cm-2 is achieved at 0.1 C after 100 cycles. More significantly, the 3DOM-ZnTe1- x@NC based pouch cells are also fabricated to demonstrate its potential for practical applications. This work highlights that the rational combination of 3DOM architecture and vacancy engineering is important for designing advanced Li-S electrocatalysts.

Multifunctional TiN-MXene-Co@CNTs Networks as Sulfur/Lithium Host for High-Areal-Capacity Lithium-Sulfur Batteries

The inevitable shuttling and slow redox kinetics of lithium polysulfides (LiPSs) as well as the uncontrolled growth of Li dendrites have strongly limited the practical applications of lithium-sulfur batteries (LSBs). To address these issues, we have innovatively constructed the carbon nanotubes (CNTs) encapsulated Co nanoparticles in situ grown on TiN-MXene nanosheets, denoted as TiN-MXene-Co@CNTs, which could serve simultaneously as both sulfur/Li host to kill "three birds with one stone" to (1) efficiently capture soluble LiPSs and expedite their redox conversion, (2) accelerate nucleation/decomposition of solid Li2S, and (3) induce homogeneous Li deposition. Benefiting from the synergistic effects, the TiN-MXene-Co@CNTs/S cathode with a sulfur loading of 2.5 mg cm-2 could show a high reversible specific capacity of 1129.1 mAh g-1 after 100 cycles at 0.1 C, and ultralong cycle life over 1000 cycles at 1.0 C. More importantly, it even achieves a high areal capacity of 6.3 mAh cm-2 after 50 cycles under a sulfur loading as high as 8.9 mg cm-2 and a low E/S ratio of 5.0 μL mg-1. Besides, TiN-MXene-Co@CNTs as Li host could deliver a stable Li plating/striping behavior over 1000 h.

Encasing Few-Layer MoS2 within 2D Ordered Cubic Graphitic Cages to Smooth Trapping-Conversion of Lithium Polysulfides for Dendrite-Free Lithium-Sulfur Batteries

The industrialization of lithium-sulfur (Li-S) batteries faces challenges due to the shuttling effect of lithium polysulfides (LiPSs) and the growth of lithium dendrites. To address these issues, a simple and scalable method is proposed to synthesize 2D membranes comprising a single layer of cubic graphitic cages encased with few-layer, curved MoS2. The distinctive 2D architecture is achieved by confining the epitaxial growth of MoS2 within the open cages of a 2D-ordered mesoporous graphitic framework (MGF), resulting in MoS2@MGF heterostructures with abundant sulfur vacancies. The experimental and theoretical studies establish that these MoS2@MGF membranes can act as a multifunctional interlayer in Li-S batteries to boost their comprehensive performance. The inclusion of the MoS2@MGF interlayer facilitates the trapping and conversion kinetics of LiPSs, preventing their shuttling effect, while simultaneously promoting uniform lithium deposition to inhibit dendrite growth. As a result, Li-S batteries with the MoS2@MGF interlayer exhibit high electrochemical performance even under high sulfur loading and lean electrolyte conditions. This work highlights the potential of designing advanced MoS2-encased heterostructures as interlayers, offering a viable solution to the current limitations plaguing Li-S batteries.

Oxygen-vacancy-reinforced perovskites promoting polysulfide conversion for lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are considered to be one of the most promising energy storage systems because of the ultrahigh energy density. However, their shuttle effect and slow redox kinetics seriously hinder the development of LSBs. To solve these issues, the perovskite La1-xSrxMnO3-δ (x = 0-0.5) with different oxygen vacancy concentrations were prepared by a facile liquid-phase synthesis and followed by the thermal annealing. The La1-xSrxMnO3-δ can not only anchor lithium polysulfides (LiPSs), but also catalyze the conversion of LiPSs. The detailed kinetic analysis and density functional theory calculations reveal that the optimal level of oxygen vacancies can effectively increase the binding energy between perovskites and LiPSs, and effectively promote the LiPS conversion kinetics. The S/La0.6Sr0.4MnO3-δ cathode with a moderate oxygen vacancy concentration exhibits high rate performance and ultrahigh capacity retention of 93.2% after 150 cycles at 0.1 C, which provides a potential for practical applications of LSBs. This work reveals the application of perovskite materials in the development of advanced LSBs.

Linearly Interlinked Fe-Nx-Fe Single Atoms Catalyze High-Rate Sodium-Sulfur Batteries

Linearly interlinked single atoms offer unprecedented physiochemical properties, but their synthesis for practical applications still poses significant challenges. Herein, linearly interlinked iron single-atom catalysts that are loaded onto interconnected carbon channels as cathodic sulfur hosts for room-temperature sodium-sulfur batteries are presented. The interlinked iron single-atom exhibits unique metallic iron bonds that facilitate the transfer of electrons to the sulfur cathode, thereby accelerating the reaction kinetics. Additionally, the columnated and interlinked carbon channels ensure rapid Na+ diffusion kinetics to support high-rate battery reactions. By combining the iron atomic chains and the topological carbon channels, the resulting sulfur cathodes demonstrate effective high-rate conversion performance while maintaining excellent stability. Remarkably, even after 5000 cycles at a current density of 10 A g-1, the Na-S battery retains a capacity of 325 mAh g-1. This work can open a new avenue in the design of catalysts and carbon ionic channels, paving the way to achieve sustainable and high-performance energy devices.

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.

Undercoordination Chemistry of Sulfur Electrocatalyst in Lithium-Sulfur Batteries

Undercoordination chemistry is an effective strategy to modulate the geometry-governed electronic structure and thereby regulate the activity of sulfur electrocatalysts. Efficient sulfur electrocatalysis is requisite to overcome the sluggish kinetics in lithium-sulfur (Li-S) batteries aroused by multi-electron transfer and multi-phase conversions. Recent advances unveil the great promise of undercoordination chemistry in facilitating and stabilizing sulfur electrochemistry, yet a related review with systematicness and perspectives is still missing. Herein, it is carefully combed through the recent progress of undercoordination chemistry in sulfur electrocatalysis. The typical material structures and operational strategies are elaborated, while the underlying working mechanism is also detailly introduced and generalized into polysulfide adsorption behaviors, polysulfide conversion kinetics, electron/ion transport, and dynamic reconstruction. Moreover, perspectives on the future development of undercoordination chemistry are further proposed.

Unveiling the Synergy of Architecture and Anion Vacancy on Bi2Te3-x@NPCNFs for Fast and Stable Potassium Ion Storage

Large volume strain and slow kinetics are the main obstacles to the application of high-specific-capacity alloy-type metal tellurides in potassium-ion storage systems. Herein, Bi2Te3-x nanocrystals with abundant Te-vacancies embedded in nitrogen-doped porous carbon nanofibers (Bi2Te3-x@NPCNFs) are proposed to address these challenges. In particular, a hierarchical porous fiber structure can be achieved by the polyvinylpyrrolidone-etching method and is conducive to increasing the Te-vacancy concentration. The unique porous structure together with defect engineering modulates the potassium storage mechanism of Bi2Te3, suppresses structural distortion, and accelerates K+ diffusion capacity. The meticulously designed Bi2Te3-x@NPCNFs electrode exhibits ultrastable cycling stability (over 3500 stable cycles at 1.0 A g-1 with a capacity degradation of only 0.01% per cycle) and outstanding rate capability (109.5 mAh g-1 at 2.0 A g-1). Furthermore, the systematic ex situ characterization confirms that the Bi2Te3-x@NPCNFs electrode undergoes an "intercalation-conversion-step alloying" mechanism for potassium storage. Kinetic analysis and density functional theory calculations reveal the excellent pseudocapacitive performance, attractive K+ adsorption, and fast K+ diffusion ability of the Bi2Te3-x@NPCNFs electrode, which is essential for fast potassium-ion storage. Impressively, the assembled Bi2Te3-x@NPCNFs//activated-carbon potassium-ion hybrid capacitors achieve considerable energy/power density (energy density up to 112 Wh kg-1 at a power density of 1000 W kg-1) and excellent cycling stability (1600 cycles at 10.0 A g-1), indicating their potential practical applications.

Metal-injection and interface density engineering induced nickel diselenide with rapid kinetics for high-energy sodium storage

The key to the innovation of sodium-ion batteries (SIBs) is to find efficient sodium-storage electrode. Here, metal Mo doping of NiSe2 is proposed by modified electrospinning strategy followed by in situ conversion process. The Mo-NiSe2 anchoring on hollow carbon nanofibers (HCNFs) would make full use of the multi-channel HCNFs in the inner layer and the active sites of Mo-NiSe2 in the outer layer, which plays an important role in buffering the volume stress of Na+ (de)insertion and reducing the adsorption energy barrier of Na+. Innovatively, it is proposed to jointly regulate the SIBs performance of NiSe2 by both metal atom doping and interface effects, thereby adjusting the sodium ion adsorption barrier of NiSe2. The Mo-NiSe2@HCNFs exhibits remarkable performance in SIBs, demonstrating a high specific capacity of 396 mAh/g after 100 cycles at 1 A/g. Moreover, it maintains outstanding cycling stability, retaining 77.6 % of its capacity (211 mAh/g) even after 1000 cycles at 10 A/g. This comprehensive electrochemical performances are due to the structural stability and outstanding electronic conductance of the Mo-NiSe2@HCNFs, as evidenced by the diffusion analysis and ex situ charge-discharge process characterization. Furthermore, coupled with the Na3V2(PO4)2O2F cathodes, the full cell also achieves a high energy density of 123 Wh kg-1. The theoretical calculation of the hypervalent Mo doing further proves the benefit of its Na+ adsorption and denser conduction band distribution. This study provides a reference for the construction of transition metal selenide via doping and interface engineering in sodium storage.

Applications, prospects and challenges of metal borides in lithium sulfur batteries

Although the lithium-sulfur (Li-S) battery has a theoretical capacity of up to 1675 mA h g-1, its practical application is limited owing to some problems, such as the shuttle effect of soluble lithium polysulfides (LiPSs) and the growth of Li dendrites. It has been verified that some transition metal compounds exhibit strong polarity, good chemical adsorption and high electrocatalytic activities, which are beneficial for the rapid conversion of intermediate product in order to effectively inhibit the "shuttle effect". Remarkably, being different from other metal compounds, it is a significant characteristic that both metal and boron atoms of transition metal borides (TMBs) can bind to LiPSs, which have shown great potential in recent years. Here, for the first time, almost all existing studies on TMBs employed in Li-S cells are comprehensively summarized. We firstly clarify special structures and electronic features of metal borides to show their great potential, and then existing strategies to improve the electrochemical properties of TMBs are summarized and discussed in the focus sections, such as carbon-matrix construction, morphology control, heteroatomic doping, heterostructure formation, phase engineering, preparation techniques. Finally, the remaining challenges and perspectives are proposed to point out a direction for realizing high-energy and long-life Li-S batteries.

Multimodal Engineering of Catalytic Interfaces Confers Multi-Site Metal-Organic Framework for Internal Preconcentration and Accelerating Redox Kinetics in Lithium-Sulfur Batteries

The development of highly efficient catalysts to address the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) in lithium-sulfur batteries (LSBs) remains a formidable challenge. In this study, a series of multi-site catalytic metal-organic frameworks (MSC-MOFs) were elaborated through multimodal molecular engineering to regulate both the reactant diffusion and catalysis processes. MSC-MOFs were crafted with nanocages featuring collaborative specific adsorption/catalytic interfaces formed by exposed mixed-valence metal sites and surrounding adsorption sites. This design facilitates internal preconcentration, a coadsorption mechanism, and continuous efficient catalytic conversion toward polysulfides concurrently. Leveraging these attributes, LSBs with an MSC-MOF-Ti catalytic interlayer demonstrated a 62 % improvement in discharge capacity and cycling stability. This resulted in achieving a high areal capacity (11.57 mAh cm-2 ) at a high sulfur loading (9.32 mg cm-2 ) under lean electrolyte conditions, along with a pouch cell exhibiting an ultra-high gravimetric energy density of 350.8 Wh kg-1 . Lastly, this work introduces a universal strategy for the development of a new class of efficient catalytic MOFs, promoting SRR and suppressing the shuttle effect at the molecular level. The findings shed light on the design of advanced porous catalytic materials for application in high-energy LSBs.

Boosting Manganese Selenide Anode for Superior Sodium-Ion Storage via Triggering α → β Phase Transition

Sodium-ion batteries (SIBs) have been extensively studied owing to the abundance and low-price of Na resources. However, the infeasibility of graphite and silicon electrodes in sodium-ion storage makes it urgent to develop high-performance anode materials. Herein, α-MnSe nanorods derived from δ-MnO2 (δ-α-MnSe) are constructed as anodes for SIBs. It is verified that α-MnSe will be transferred into β-MnSe after the initial Na-ion insertion/extraction, and δ-α-MnSe undergoes typical conversion mechanism using a Mn-ion for charge compensation in the subsequent charge-discharge process. First-principles calculations support that Na-ion migration in defect-free α-MnSe can drive the lattice distortion to phase transition (alpha → beta) in thermodynamics and dynamics. The formed β-MnSe with robust lattice structure and small Na-ion diffusion barrier boosts great structure stability and electrochemical kinetics. Hence, the δ-α-MnSe electrode contributes excellent rate capability and superior cyclic stability with long lifespan over 1000 cycles and low decay rate of 0.0267% per cycle. Na-ion full batteries with a high energy density of 281.2 Wh·kg-1 and outstanding cyclability demonstrate the applicability of δ-α-MnSe anode.

Synthesis, characterization, and application of N-CNT/1-(2-Hydroxyethyl)-3-methylimidazolium dicyanamide as a green nanocatalyst for the sulfur removal from light oils

Adsorptive desulfurization of light fuels is sustainable due to its ambient operation and reusability of exhausted adsorbents. In this study, 1-(2-hydroxyethyl)-3-methylimidazolium dicyanamide [HEMIM][DCA] IL was synthesized and utilized to modify N-doped carbon nanotubes (CNTs) to produce N-CNT/[HEMIM][DCA] as a green hybrid adsorbent. The adsorbent was characterized using XRD, FE-SEM, FTIR, BET, and TGA. It was indicated that the N-CNT treatment with [HEMIM][DCA] IL resulted in decreased crystallinity with the cubic and rod-shaped morphology and harsh surfaces and curved edges. The absence of shifts or variations in FTIR peaks of starting materials and N-CNT/[HEMIM][DCA] suggested that neither component was affected by chemical interactions. The adsorption capacity of N-CNT and N-CNT/[HEMIM][DCA] was 54.3 mg/g and for 83.6 mg/g for 50 ppm BT, respectively. Saturated with BT, the adsorbent's performance was decreased at high BT concentrations. The adsorption isotherms provided an understanding of interactions of BT with sorbent surface which follows the Langmuir model for N-CNT/[HEMIM][DCA] and N-CNT. The kinetics of BT adsorption on N-CNT/[HEMIM][DCA] was fitted with second-order kinetic model with the decreased adsorption ratio over time due to pore saturation. 25 % reduction of the adsorption capacity was obtained after two recycling cycles of the adsorbent (62.5 mg/g). N-CNT/[HEMIM][DCA] showed good recyclability and potential as a promising BT adsorbent.

Unraveling the Coupling Effect between Cathode and Anode toward Practical Lithium-Sulfur Batteries

The localized reaction heterogeneity of the sulfur cathode and the uneven Li deposition on the Li anode are intractable issues for lithium-sulfur (Li-S) batteries under practical operation. Despite impressive progress in separately optimizing the sulfur cathode or Li anode, a comprehensive understanding of the highly coupled relationship between the cathode and anode is still lacking. In this work, inspired by the Butler-Volmer equation, a binary descriptor (IBD ) assisting the rational structural design of sulfur cathode by simultaneously considering the mass-transport index (Imass ) and the charge-transfer index (Icharge ) is identified, and subsequently the relationship between IBD and the morphological evolution of Li anode is established. Guided by the IBD , a scalable electrode providing interpenetrated flow channels for efficient mass/charge transfer, full utilization of active sulfur, and mechanically elastic support for aggressive electrochemical reactions under practical conditions is reported. These characteristics induce a homogenous distribution of local current densities and reduced reaction heterogeneity on both sides of the cathode and anode. Impressive energy density of 318 Wh kg-1 and 473 Wh L-1 in an Ah-level pouch cell can be achieved by the design concept. This work offers a promising paradigm for unlocking the interaction between cathode and anode and designing high-energy practical Li-S batteries.

Band Structure Engineering and Orbital Orientation Control Constructing Dual Active Sites for Efficient Sulfur Redox Reaction

The kinetics difference among multistep electrochemical processes leads to the accumulation of soluble polysulfides and thus shuttle effect in lithium-sulfur (Li-S) batteries. While the interaction between catalysts and representative species has been reported, the root of the kinetics difference, interaction change among redox reactions, remains unclear, which significantly impedes the catalysts design for Li-S batteries. Here, this work deciphers the interaction change among electrocatalytic sulfur reactions, using tungsten disulfide (WS2 ) a model system to demonstrate the efficiency of modifying electrocatalytic selectivity via dual-coordination design. Band structure engineering and orbital orientation control are combined to guide the design of WS2 with boron dopants and sulfur vacancies (B-WS2- x ), accurately modulating interaction with lithium and sulfur sites in polysulfide species for relatively higher interaction with short-chain polysulfides. The modified interaction trend is experimentally confirmed by distinguishing the kinetics of each electrochemical reaction step, indicating the effectiveness of the designed strategy. An Ah-level pouch cell with B-WS2- x delivers a gravimetric energy density of up to 417.6 Wh kg-1 with a low electrolyte/sulfur ratio of 3.6 µL mg-1 and negative/positive ratio of 1.2. This work presents a dual-coordination strategy for advancing evolutionarily catalytic activity, offering a rational strategy to develop effective catalysts for practical Li-S batteries.

Structural regulation enabled stable hollow molybdenum diselenide nanosheet anode for ultrahigh energy density sodium ion pouch cell

For the continued use of sodium-ion batteries (SIBs), which require matching anode materials, it is crucial to create high energy density energy storage devices. Here, hollow nanoboxes shaped carbon supported sulfur-doped MoSe2 nanosheets (S-MoSe2@NC) are fabricated by in situ growth and heterodoping strategy. This ensures that the MoSe2 nanosheets are tightly anchored to the nanoboxes carbon, and the structure can effectively buffer the volume stress caused by sodium ion (de)intercalation, as well as providing abundant ion/electron migration transportations. As anode for SIBs, the S-MoSe2@NC shows a higher rate capability and excellent cycling stability (431.1 mAh/g after 1100 cycles at 10 A/g). This excellent cycle life and high rate ability are due to the structural stability and outstanding electronic conductance with reduced band gap of the S-MoSe2@NC, as evidenced by the diffusion analysis and theoretical calculation. In order to promote the application of SIBs, the S-MoSe2@NC and NaNi1/3Fe1/3Mn1/3O2 were assembled into a pouch cell, and the test found that besides the excellent cycle rate performance, the ultrahigh energy density of 256 Wh kg-1 and flexible characteristics can be achieved. This study has proven that building a structure with a rock-steady foundation and quick ion migration may efficiently control sodium storage and pave the way for novel applications of high-performance transition metal dichalcogenides in sodium storage.

Binary Transition-Metal Sulfides/MXene Synergistically Promote Polysulfide Adsorption and Conversion in Lithium-Sulfur Batteries

Currently, severe shuttle effects and sluggish conversion kinetics are the main obstacles to the advancement of lithium-sulfur (Li-S) batteries. Modification of the battery separator by a catalyst is a promising approach to tackle these problems, but simultaneously obtaining rich catalytic active sites, high conductivity, and remarkable stability remains a great challenge. Herein, a flower-like MXene/MoS2/SnS@C heterostructure as the functional intercalation of Li-S batteries was prepared for accelerating the synergistic adsorption-electrocatalysis of sulfur conversion. The MXene skeleton constructs a three-dimensional conductive network that anchors polysulfides and enhances charge transfer. Meanwhile, the MoS2/SnS has rich active sites for accelerating polysulfide conversion, leading to excellent electrochemical performances. A battery with MXene/MoS2/SnS@C displays an extraordinary capacity of 836.1 mAh g-1 over 200 cycles at 0.5C and demonstrates a remarkable cycling stability with a capacity attenuation of approximately 0.051% per cycle during 1000 cycles at 2C. When the sulfur loading reaches 5.1 mg cm-2, the capacity still maintains 722.4 mAh g-1 over 50 cycles. This research proposes a novel strategy to design stable catalysts for Li-S batteries with an extended lifespan.

Enhancing Sulfur Redox Conversion of Active Iron Sites by Modulation of Electronic Density for Advanced Lithium-Sulfur Battery

Despite lithium-sulfur (Li-S) batteries possessing ultrahigh energy density as great promising energy storage devices, the suppressing shuttle effect and improving sulfur redox reaction (SROR) are vital for their practical application. Developing high-activity electrocatalysts for enhancing the SROR kinetics is a major challenge for the application of Li-S batteries. Herein, single-molecule iron phthalocyanine species are anchored on the N and P dual-doped porous carbon nanosheets (Fe-NPPC) via axial Fe-N coordination to optimize the electronic structure of active centers. The Fe-NPPC can promote the catalytic conversion of polysulfides by modulation of the electronic density in active moieties, endowing the Li-S battery with a high reversible capacity of 1023 mAh g-1 at 1 C as well as an ultralow capacity decay of 0.035% per cycle over 1500 cycles. Even with a high sulfur loading of 7.1 mg cm-2 , the Li-S battery delivers a high areal capacity of 4.8 mAh cm-2 after 150 cycles at 0.2 C. With further increasing the sulfur loading to 9.2 mg cm-2 , an excellent areal capacity of up to 9.3 mAh cm-2 is obtained at 0.1 C.

Dual-Defect Engineering of Bidirectional Catalyst for High-Performing Lithium-Sulfur Batteries

Practical applications of lithium-sulfur (Li-S) batteries have been hindered by sluggish reaction kinetics and severe capacity decay during charge-discharge cycling due to the notorious shuttle effect of polysulfide and the unfavored deposition and dissolution of Li2 S. Herein, to address these issues, a double-defect engineering strategy is developed for preparing Co-doped FeP catalyst containing P vacancies on MXene, which effectively improves the bidirectional redox of Li2 S. Mechanism analysis indicates that P vacancy accelerates Li2 S nucleation via increased unsaturated sites, and Co doping generates local electric field to reduce the reaction energy barrier and accelerate Li2 S dissolution. MXene provides highly conductive channels for electron transport, and effectively captures polysulfide. The double-defect catalyst enables an impressive reversible specific capacity of 1297.9 mAh g-1 at 0.2 C, and excellent rate capability of 726.5 mAh g-1 at 4 C. Remarkably, it demonstrates excellent cycling stability with capacity retention of 533.3 mAh g-1 after 500 cycles at 2 C. The results can unlock the double-defect engineering of vacancy induction and heteroatomic doping towards practical Li-S batteries.

Elucidating the Volcanic-Type Catalytic Behavior in Lithium-Sulfur Batteries via Defect Engineering

Defects are generally considered to be effective and flexible in the catalytic reactions of lithium-sulfur batteries. However, the influence of the defect concentration on catalysis remains ambiguous. In this work, molybdenum sulfide with different sulfur vacancy concentrations is comprehensively modulated, showing that the defect level and the adsorption-catalytic performance result in a volcano relationship. Moreover, density functional theory and in situ experiments reveal that the optimal level of sulfur defects can effectively increase the binding energy between molybdenum sulfide and lithium polysulfides (LiPSs), lower the energy barrier of the LiPS conversion reaction, and promote the kinetics of Li2S bidirectional catalytic reaction. The lower bidirectional catalytic performance incited by excessive or deficient sulfur defects is mainly due to the deformed geometrical structures and reduced adsorption of key LiPSs on the catalyst surface. This work underscores the imperative of controlling the defect content and provides a potential approach to the commercialization of lithium-sulfur batteries.

Oxygen Vacancies in Bismuth Tantalum Oxide to Anchor Polysulfide and Accelerate the Sulfur Evolution Reaction in Lithium-Sulfur Batteries

The shuttling effect of soluble lithium polysulfides (LiPSs) and the sluggish conversion kinetics of polysulfides into insoluble Li₂S₂/Li₂S severely hinders the practical application of Li-S batteries. Advanced catalysts can capture and accelerate the liquid-solid conversion of polysulfides. Herein, we try to make use of bismuth tantalum oxide with oxygen vacancies as an electrocatalyst to catalyze the conversion of LiPSs by reducing the sulfur reduction reaction (SRR) nucleation energy barrier. Oxygen vacancies in Bi₄TaO₇ nanoparticles alter the electron band structure to improve instinct electronic conductivity and catalytic activity. In addition, the defective surface could provide unsaturated bonds around the vacancies to enhance the chemisorption capability with LiPSs. Hence, a multidimensional carbon (super P/CNT/Graphene) standing sulfur cathode is prepared by coating oxygen vacancies Bi₄TaO_7-x nanoparticles, in which the multidimensional carbon (MC) with micropores structure can host sulfur and provide a fast electron/ion pathway, while the outer-coated oxygen vacancies with Bi₄TaO_7-x with improved electronic conductivity and strong affinities for polysulfides can work as an adsorptive and conductive protective layer to achieve the physical restriction and chemical immobilization of lithium polysulfides as well as speed up their catalytic conversion. Benefiting from the synergistic effects of different components, the S/C@Bi₃TaO_7-x coin cell cathode shows superior cycling and rate performance. Even under a high level of sulfur loading of 9.6 mg cm^-2, a relatively high initial areal capacity of 10.20 mAh cm^-2 and a specific energy density of 300 Wh kg^-1 are achieved with a low electrolyte/sulfur ratio of 3.3 µL mg^-1. Combined with experimental results and theoretical calculations, the mechanism by which the Bi₄TaO₇ with oxygen vacancies promotes the kinetics of polysulfide conversion reactions has been revealed. The design of the multiple confined cathode structure provides physical and chemical adsorption, fast charge transfer, and catalytic conversion for polysulfides.