High-Energy-Density, Long-Life Lithium-Sulfur Batteries with Practically Necessary Parameters Enabled by Low-Cost Fe-Ni Nanoalloy Catalysts

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.

Vacancies-Induced Delocalized States Cobalt Phosphide for Binder-Free Anode Toward Stable and High-Rate Sodium-Ion Batteries

Metal phosphides with easy synthesis, controllable morphology, and high capacity are considered as potential anodes for sodium-ion batteries (SIBs). However, the inherent shortcomings of metal phosphating materials, such as conductivity, kinetics, volume strain, etc are not satisfactory, which hinders their large-scale application. Here, a CoP@carbon nanofibers-composite containing rich Co─N─C heterointerface and phosphorus vacancies grown on carbon cloth (CoP1-x@MEC) is synthesized as SIB anode to accomplish extraordinary capacity and ultra-long cycle life. The hybrid composite nanoreactor effectively impregnates defective CoP as active reaction center while offering Co─N─C layer to buffer the volume expansion during charge-discharge process. These vast active interfaces, favored electrolyte infiltration, and a well-structured ion-electron transport network synergistically improve Na+ storage and electrode kinetics. By virtue of these superiorities, CoP1-x@MEC binder-free anode delivers superb SIBs performance including a high areal capacity (2.47 mAh cm-2@0.2 mA cm-2), high rate capability (0.443 mAh cm-2@6 mA cm-2), and long cycling stability (300 cycles without decay), thus holding great promise for inexpensive binder-free anode-based SIBs for practical applications.

Strong aggregation-induced electrochemiluminescence of pyrene-coordination metal-organic frameworks coupled with zero-valent iron as novel accelerator for ultrasensitive immunoassay

Polycyclic aromatic hydrocarbons (PAHs) are excellent alternative luminophores for electrochemiluminescence (ECL) immunoassays. However, they are inevitably limited by the aggregation-caused quenching effect. In this study, aimed at eliminating the aggregation quenching of PAHs, luminescent metal-organic frameworks (MOFs) with 1,3,6,8-tetra(4-carboxybenzene)pyrene (H4TBAPy) as the ligand were exploited as a novel nano-emitter for the construction of ECL immunoassays. The luminophore exhibits efficient aggregation-induced emission enhancement, good acid-base resistance property and unusual ECL reactivity. In addition, the simultaneous use of potassium persulfate and hydrogen peroxide as dual co-reactants resulted in a synergistic enhancement of the cathodic ECL efficiency. The use of magnetic iron-nickel alloys as the multifunctional sensing platform can further enhance the ECL activity, and its enriched zero-valent iron as a co-reactant accelerator effectively drives ECL analytical performance. Profiting from the excellent characteristics, signal-on ECL immunoassays have been constructed. With carcinoembryonic antigen as the model analysis target, a detection limit of 0.63 pg/mL was obtained within the linear range of 1 pg/mL to 50 ng/mL, accompanied by excellent analytical performance. This report opens a new window for the rational design of efficient ECL illuminators, and the proposed ECL immunoassays may find promising applications in the detection of disease markers.

Synergistic Electrocatalysis and Spatial Nanoconfinement to Accelerate Sulfur Conversion Kinetics in Aqueous Zn-S Battery

Aqueous zinc batteries based on the conversion-type sulfur cathodes are promising in energy storage system due to the high theoretical energy density, low cost, and good safety. However, the multi-electron solid-state intermediate conversion reaction of sulfur cathodes generally possess sluggish kinetics, which leads to lower discharge voltage and inefficient sulfur utilization, thus suppressing the practical energy density. Herein, sulfur nanoparticles derived from metal-organic frameworks confined in situ within electrospun fibers derived sulfur and nitrogen co-doped carbon nanofibers (S@S,N-CNF) composite, which possesses yolk-shell S@C nanostructure, is fabricated through successive sulfidation, pyrolysis, and sulfide oxidation processes, and served as a high-performance cathode material for Zn-S battery. The S and N dopants on carbon can collectively catalyse sulfur reduction reaction (SRR) by lowering energy barrier and accelerating kinetics to increase discharge voltage and specific capacity. Meanwhile, the yolk-shell S@C structure with spatially confined S nanoparticle yolks is beneficial to improve charge transfer and lower activation energy, thus further expediting SRR kinetics. Furthermore, extensive density functional theory (DFT) calculations reveal that S and N dual-doping can thermodynamically and dynamically reduce the energy barrier of rate-determining step (i.e., the transformation of *ZnS4 into *ZnS2) for the overall SRR, thereby significantly accelerating SRR kinetics.

Diminishing Self-Discharge of High-Loading Li-S Batteries with Oxygen-Rich Biomass Carbon Interlayers

Lithium-sulfur batteries (Li-S) have possessed gratifying development in the past decade due to their high theoretical energy density. However, the severe polysulfide shuttling provokes undesirable self-discharge effect, leading to low energy efficiency in Li-S batteries. Herein, an interlayer composed of oxygen-rich carbon nanosheets (OCN) derived from bagasse is elaborated to suppress the shuttle effect and reduce the resultant self-discharge effect. The OCN interlayer is able to physically block the shuttling behavior of polysulfides and its oxygen-rich functional groups can strongly interact with polysulfides via O-S bonds to chemically immobilize mobile polysulfides. The self-discharge test for seven days further shows that the self-discahrge rate is diminished by impressive 93 %. As a result, Li-S batteries with the OCN interlayer achieve an ultrahigh discharge specific capacity of 710 mAh g-1 at a high mass loading of 7.18 mg. The work provides a facile method for designing functional interlayers and opens a new avenue for realizing Li-S batteries with high energy efficiency.

Electrochemical Restructuring Driven Catalytic Cycle of Bi-Based Heterojunctions for High-Performance Lithium-Sulfur Batteries

Restructuring is an important phenomenon in catalytic reactions. Conversion-type materials with suitable redox potential may undergo in situ electrochemically driven restructurings and induce highly active catalytic sites in a working lithium-sulfur battery. Herein, driven by the electrochemical conversion reaction of BiVO4, a reversible catalytic cycle of Bi/amorphous Li3VO4 (a-Li3VO4) and Bi2S3/a-Li3VO4 heterojunctions is constructed, which targets the oxidation of Li2S and the conversion of polysulfide, respectively. The heterostructures and electrochemically driven size confinement provide abundant sites for shuttle restraining and sulfur conversion. Especially, the p-block Bi and Bi2S3 could dramatically reduce the conversion energy barriers of Li2S and polysulfide by virtue of the p-p orbital hybridization, promoting bidirectional reactions of the sulfur cathode. As a result, the corresponding sulfur cathode possesses a high reversible capacity of 7.5 mAh cm-2 after 120 cycles under a high sulfur loading of 10.3 mg cm-2 with a current density of 0.38 mA cm-2. This study furnishes a feasible scheme to obtain highly effective catalysts for bidirectional sulfur redox by utilizing the electrochemically induced restructuring.

Surface-Phosphided Metal Oxide Microspheres as Catalytic Host of Sulfur to Enhance the Performance of Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are one of the most promising high-energy density secondary batteries due to their high theoretical energy density of 2600 Wh kg-1. However, the sluggish kinetics and severe "shuttle effect" of polysulfides are the well-known barriers that hinder their practical applications. A carefully designed catalytic host of sulfur may be an effective strategy that not only accelerates the conversion of polysulfides but also limit their dissolution to mitigate the "shuttle effect." Herein, in situ surface-phosphided Ni0.96Co0.03Mn0.01O (p-NCMO) oxide microspheres are prepared via gas-phase phosphidation as a catalytic host of sulfur. The as-prepared unique heterostructured microspheres, with enriched surface-coated metal phosphide, exhibit superior synergistic effect of catalytic conversion and absorption of the otherwise soluble intermediate polysulfides. Correspondingly, the sulfur cathode exhibits excellent electrochemical performance, including a high initial discharge capacity (1162 mAh gs-1 at 0.1C), long cycling stability (491 mAh gs-1 after 1000 cycles at 1C), and excellent rate performance (565 mAh gs-1 at 5C). Importantly, the newly prepared sulfur cathode shows a high areal capacity of 4.0 mAh cm-2 and long cycle stability under harsh conditions (high sulfur loading of 5.3 mg cm-2 and lean electrolyte/sulfur ratio of 5.8 μL mg-1). This work proposes an effective strategy to develop the catalytic hosts of sulfur for achieving high-performance Li-S batteries via surface phosphidation.

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.

Selective Reduction of Multivariate Metal-Organic Frameworks for Advanced Electrocatalytic Cathodes in High Areal Capacity and Long-Life Lithium-Sulfur Batteries

Lithium-sulfur batteries hold great promise as next-generation high-energy-density batteries. However, their performance has been limited by the low cycling stability and sulfur utilization. Herein, we demonstrate that a selective reduction of the multivariate metal-organic framework, MTV-MOF-74 (Co, Ni, Fe), transforms the framework into a porous carbon decorated with bimetallic CoNi alloy and Fe3O4 nanoparticles capable of entrapping soluble lithium polysulfides while synergistically facilitating their rapid conversion into Li2S. Electrochemical studies on coin cells containing 89 wt % sulfur loading revealed a reversible capacity of 1439.8 mA h g-1 at 0.05 C and prolonged cycling stability for 1000 cycles at 1 C/1060.2 mA h g-1 with a decay rate of 0.018% per cycle. At a high areal sulfur loading of 6.9 mg cm-2 and lean electrolyte/sulfur ratio (4.5 μL:1.0 mg), the battery based on the 89S@CoNiFe3O4/PC cathode provides a high areal capacity of 6.7 mA h cm-2. The battery exhibits an outstanding power density of 849 W kg-1 at 5 C and delivers a specific energy of 216 W h kg-1 at 2 C, corresponding to a specific power of 433 W kg-1. Density functional theory shows that the observed results are due to the strong interaction between the CoNi alloy and Fe3O4, facilitated by charge transfer between the polysulfides and the substrate.

A Catalytic Electrolyte Additive Modulating Molecular Orbital Energy Levels of Lithium Polysulfides for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have ultrahigh theoretical specific capacity, but the practical application is hindered by the severe shuttle effect and the sluggish redox kinetics of the intermediate lithium polysulfides (LiPSs). Effectively enhancing the conversion kinetics of LiPSs is essential for addressing these issues. Herein, the redox kinetics of LiPSs are effectively improved by introducing 6-azauracil (6-AU) molecules to the organic electrolyte to modulate the molecular orbital energy level of LiPSs. The 6-AU as a soluble catalyst can form complexes with LiPSs via Li-O bonds. These complexes are liable to transform because of the elevated HOMO and the reduced LUMO energy levels as compared to the dissociative LiPSs, resulting in small energy gaps (Egap) and exhibiting stronger redox activity. Benefiting from the rapid conversion kinetics, the shuttling effect of LiPSs is alleviated to a great extent, so that sulfur utilization is improved and the lithium electrode is protected. In addition, the introduction of 6-AU modulates the deposition behavior of Li2S and eases the coverage of the cathode surface by the insulating Li2S layer. The Li-S battery containing 6-AU provides superior capacity retention of 853 mAh g-1 after 150 cycles at 0.2 C and shows remarkable high-rate performance and retains a specific discharge capacity of 855 mAh g-1 at 5 C. This study accelerates the kinetics of Li-S batteries by tuning the HOMO and LUMO energy levels of LiPSs, which opens an avenue for designing functional electrolyte additives.

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

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

Boosting Lean Electrolyte Lithium-Sulfur Battery Performance with Transition Metals: A Comprehensive Review

Lithium-sulfur (Li-S) batteries have received widespread attention, and lean electrolyte Li-S batteries have attracted additional interest because of their higher energy densities. This review systematically analyzes the effect of the electrolyte-to-sulfur (E/S) ratios on battery energy density and the challenges for sulfur reduction reactions (SRR) under lean electrolyte conditions. Accordingly, we review the use of various polar transition metal sulfur hosts as corresponding solutions to facilitate SRR kinetics at low E/S ratios (< 10 µL mg-1), and the strengths and limitations of different transition metal compounds are presented and discussed from a fundamental perspective. Subsequently, three promising strategies for sulfur hosts that act as anchors and catalysts are proposed to boost lean electrolyte Li-S battery performance. Finally, an outlook is provided to guide future research on high energy density Li-S batteries.

Self-Templated Formation of Carbon Nanotubes Interpenetrating Ordered Microporous Carbon Nanospheres for High-Performance Li-S Batteries

Lithium-sulfur (Li-S) batteries are known as a prospective new generation of battery systems owing to their high energy density, low cost, non-toxicity, and environmental friendliness. Nevertheless, several issues remain in the practical application of Li-S batteries, such as low sulfur usage, poor rate performance, and poor cycle stability. Ordered microporous carbon materials and carbon nanotubes (CNTs) can effectively limit the diffusion of polysulfides (LiPSs) and have high electrical conductivity, respectively. Here, inspired by the evaporation of zinc at high temperatures, we constructed CNTs interpenetrating ordered microporous carbon nanospheres (CNTs/OMC NSs) by high-temperature calcination and used them as a sulfur host material. With the benefit from the excellent electrical conductivity of CNTs and OMC achieving uniform sulfur dispersion and effectively limiting LiPS dissolution, the S@CNTs/OMC NS cathodes show outstanding cycling stability (initial discharge capacity of 879 mAh g^-1 at 0.5 C, maintained at 629 mAh g^-1 for 500 cycles) and excellent rate performance (521 mAh g^-1 at 5.0 C). Furthermore, the current study can serve as a significant reference for the synthesis of CNTs that interpenetrate various materials.

Firmly interlocked Janus-type metallic Ni3Sn2S2-carbon nanotube heterostructure suppresses polysulfide dissolution and Sn aggregation

Ternary transition-metal tin chalcogenides, with their diverse compositions, abundant constituents, high theoretical capacities, acceptable working potentials, excellent conductivities, and synergistic active/inactive multi-components, hold promise as anode materials for metal-ion batteries. However, abnormal aggregation of Sn nanocrystals and the shuttling of intermediate polysulfides during electrochemical tests detrimentally affect the reversibility of redox reactions and lead to rapid capacity fading within a limited number of cycles. In this study, we present the development of a robust Janus-type metallic Ni₃Sn₂S₂-carbon nanotube (NSSC) heterostructured anode for Li-ion batteries (LIBs). The synergistic effects of Ni₃Sn₂S₂ nanoparticles and a carbon network successfully generate abundant heterointerfaces with steady chemical bridges, thereby enhancing ion and electron transport, preventing the aggregation of Ni and Sn nanoparticles, mitigating the oxidation and shuttling of polysulfides, facilitating the reforming of Ni₃Sn₂S₂ nanocrystals during delithiation, creating a uniform solid-electrolyte interphase (SEI) layer, protecting the mechanical integrity of electrode materials, and ultimately enabling highly reversible lithium storage. Consequently, the NSSC hybrid exhibits an excellent initial Coulombic efficiency (ICE > 83 %) and superb cyclic performance (1218 mAh/g after 500 cycles at 0.2 A/g and 752 mAh/g after 1050 cycles at 1 A/g). This research provides practical solutions for the intrinsic challenges associated with multi-component alloying and conversion-type electrode materials in next-generation metal-ion batteries.

Ultrathin Carbon-Shell-Encapsulated Cobalt Nanoparticles with Balanced Activity and Stability for Lithium-Sulfur Batteries

High-performance metal-based catalysts are pursued to improve the sluggish reaction kinetics in lithium-sulfur batteries. However, it is challenging to achieve high catalytic activity and stability simultaneously due to the inevitable passivation of the highly active metal nanoparticles by lithium polysulfides (LiPSs). Herein, we show a design with well-balanced activity and stability to solve the above problem, that is, the cobalt (Co) nanoparticles (NPs) encapsulated with ultrathin carbon shells prepared by the one-step pyrolysis of ZIF-67. With an ultrathin carbon coating (∼1 nm), the direct exposure of Co NPs to LiPSs is avoided, but it allows the fast electron transfer from the highly active Co NPs to LiPSs for their conversion to the solid products, ensuring the efficient suppression of shuttling in long cycling. As a result, the sulfur cathode with such a catalyst exhibited good cycling stability (0.073% capacity fading over 500 cycles) and high sulfur utilization (638 mAh g^-1 after 180 cycles under a high sulfur mass loading of 7.37 mg cm^-2 and a low electrolyte/sulfur ratio of 5 μL mg^-1). This work provides insights into the rational design of a protection layer on a metal-based catalyst to engineer both high catalytic activity and stability toward high-energy and long-life Li-S batteries.

Realizing anti-self-discharged lithium-sulfur batteries by using hierarchical porous carbon nanofibers embedded with Fe/Ni-N catalytic sites

Lithium-sulfur (Li-S) batteries are featured with high gravimetric energy density, yet their commercial application is significantly deteriorated with the severe self-discharging resulted from the polysulfides shuttle and sluggish electrochemical kinetics. Here, a hierarchical porous carbon nanofibers implanted with Fe/Ni-N (denoted as Fe-Ni-HPCNF) catalytic sites are prepared and used as a kinetics booster toward anti-self-discharged Li-S batteries. In this design, the Fe-Ni-HPCNF possesses interconnected porous skeleton and abundant exposed active sites, enabling fast Li-ion conduction, excellent shuttle inhibition and catalytic ability for polysulfides' conversion. Combined with these advantages, this cell with the Fe-Ni-HPCNF equipped separator exhibits an ultralow self-discharged rate of 4.9% after resting for one week. Moreover, the modified batteries deliver a superior rate performance (783.3 mAh g^-1 at 4.0 C) and an outstanding cycling life (over 700 cycles with 0.057% attenuation rate at 1.0 C). This work may guide the advanced design of anti-self-discharged Li-S batteries.

Interface Engineering Toward Expedited Li2 S Deposition in Lithium-Sulfur Batteries: A Critical Review

Lithium-sulfur batteries (LSBs) with superior energy density are among the most promising candidates of next-generation energy storage techniques. As the key step contributing to 75% of the overall capacity, Li₂ S deposition remains a formidable challenge for LSBs applications because of its sluggish kinetics. The severe kinetic issue originates from the huge interfacial impedances, indicative of the interface-dominated nature of Li₂ S deposition. Accordingly, increasing efforts have been devoted to interface engineering for efficient Li₂ S deposition, which has attained inspiring success to date. However, a systematic overview and in-depth understanding of this critical field are still absent. In this review, the principles of interface-controlled Li₂ S precipitation are presented, clarifying the pivotal roles of electrolyte-substrate and electrolyte-Li₂ S interfaces in regulating Li₂ S depositing behavior. For the optimization of the electrolyte-substrate interface, efforts on the design of substrates including metal compounds, functionalized carbons, and organic compounds are systematically summarized. Regarding the regulation of electrolyte-Li₂ S interface, the progress of applying polysulfides catholytes, redox mediators, and high-donicity/polarity electrolytes is overviewed in detail. Finally, the challenges and possible solutions aiming at optimizing Li₂ S deposition are given for further development of practical LSBs. This review would inspire more insightful works and, more importantly, may enlighten other electrochemical areas concerning heterogeneous deposition processes.

Dilute Alloying to Implant Activation Centers in Nitride Electrocatalysts for Lithium-Sulfur Batteries

Dilute alloying is an effective strategy to tune properties of solid catalysts but is rarely leveraged in complex reactions beyond small molecule conversion. In this work, dilute dopants are demonstrated to serve as activating centers to construct multiatom catalytic domains in metal nitride electrocatalysts for lithium-sulfur (Li-S) batteries, of which the sulfur cathode suffers from sluggish and complex conversion reactions. With titanium nitride (TiN) as a model system, the dilute cobalt alloying is shown to greatly improve the reaction kinetics while inducing negligible catalyst reconstruction. Compared to the pristine TiN, the dilute nitride alloy catalyst enables onefold increase in the high rate (2.0 C) capacities of Li-S batteries, as well as an impressively low cyclic decay rate of 0.17% at a sulfur loading of 4.0 mg_S cm^-2 . This work opens up new opportunities toward the rational design of Li-S electrocatalysts by dilute alloying and also enlightens the understandings of complex domain-catalyzed reactions in energy applications.

Oxygen vacancies in open-hollow microcapsule enable accelerated kinetics for stable Li-S battery

The fast development of lithium-sulfur (Li-S) batteries is catching more attention to improve cycling stability and kinetics. Herein, a hierarchical porous Ni/NiO/C microsphere (NIONC) with openings assembled by ultrathin nanosheets is introduced to solve the poor conductivity, shuttle effect, and slow electrochemical kinetics of Li-S batteries. The structure of NIONC open-hollow microcapsules combines several advantageous properties for the improvement of electrochemical performances. Primarily, a well-developed hollow structure and openings can perform as containers and doors for sulfur immobilization. Therefore, the confinement effect to sulfur species is obtained by this hollow sphere. Secondly, the nanosheets with oxygen vacancies and Ni active sites provide abundant active sites for the chemical absorption of polysulfides. Based on the open structure and oxygen vacancies of Ni/NiO, both the physical absorption and chemical immobilization of sulfur are realized, with high stability and fast kinetics. The S-injected NIONC (NIONC/S) cathode exhibits outstanding rate performance at 5 A g-1 with a high capability of 794 mAh g-1 and excellent long-cycle performance of 653 mAh g-1 after 300 cycles at 1 A g-1. We proposed a simple and controllable route to fabricate sulfur hosts by structure and composition adjustment, which will inspire the commercial application of Li-S batteries.

Catalytic Effects of Electrodes and Electrolytes in Metal-Sulfur Batteries: Progress and Prospective

Metal-sulfur (M-S) batteries are promising energy-storage devices due to their advantages such as large energy density and the low cost of the raw materials. However, M-S batteries suffer from many drawbacks. Endowing the electrodes and electrolytes with the proper catalytic activity is crucial to improve the electrochemical properties of M-S batteries. With regard to the S cathodes, advanced electrode materials with enhanced electrocatalytic effects can capture polysulfides and accelerate electrochemical conversion and, as for the metal anodes, the proper electrode materials can provide active sites for metal deposition to reduce the deposition potential barrier and control the electroplating or stripping process. Moreover, an advanced electrolyte with desirable design can catalyze electrochemical reactions on the cathode and anode in high-performance M-S batteries. In this review, recent progress pertaining to the design of advanced electrode materials and electrolytes with the proper catalytic effects is summarized. The current progress of S cathodes and metal anodes in different types of M-S batteries are discussed and future development directions are described. The objective is to provide a comprehensive review on the current state-of-the-art S cathodes and metal anodes in M-S batteries and research guidance for future development of this important class of batteries.

TinO2n-1/MXene Hierarchical Bifunctional Catalyst Anchored on Graphene Aerogel toward Flexible and High-Energy Li-S Batteries

The development of lithium-sulfur (Li-S) batteries with high-energy density, flexibility, and safety is very appealing for emerging implantable devices, biomonitoring, and roll-up displays. Nevertheless, the poor cycling stability and flexibility of the existing sulfur cathodes, flammable liquid electrolytes, and extremely reactive lithium anodes raise serious battery performance degradation and safety issues. Herein, a metallic 1T MoS₂ and rich oxygen vacancies Ti_nO_2n-1/MXene hierarchical bifunctional catalyst (Mo-Ti/Mx) anchored on a reduced graphene oxide-cellulose nanofiber (GN) host (Mo-Ti/Mx-GN) was proposed to address the above challenges. By applying a directional freezing process, the hierarchical architecture of a flexible GN scaffold composed of waved multiarch morphology with long-range alignment is achieved. The synergetic effects of 1T MoS₂ and Ti_nO_2n-1/MXene are beneficial to suppress the shuttling behavior of lithium polysulfides (LiPSs), expedite the redox kinetics of sulfur species, and promote the electrocatalytic reduction of LiPSs to Li₂S. The electrode demonstrates improved electrochemical properties with high sulfur-mass loading (8.4 mg_s cm^-2) and lean electrolyte (7.6 μL mg_s^-1) operation. We also explored the feasibility of producing pouch cells with such flexible electrodes, gel polymer electrolytes, and a robust lithium anode, which exhibited reversible energy storage and output, wide temperature adaptability, and good safety against rigorous strikes, implying the potential for practical applications.

Kinetic Acceleration of Lithium Polysulfide Conversion via a Copper-Iridium Alloying Catalytic Strategy in Li-S Batteries

To solve the shuttle effect of soluble lithium polysulfides (LiPSs), a porous N-doped carbon-supported copper-iridium alloy catalyst composite (CuIr/NC) has been synthesized and served as a modified cathode sulfur host for lithium-sulfur batteries (LSBs). The metal-organic framework-derived calcined carbon frameworks build efficient conductive channels for fast ion/electron transport. Furthermore, alloying noble metals Ir with thiophilic metal Cu provides abundant active sites to effectively capture LiPSs and accelerate the catalytic conversion process, originating from modulating the surface electronic structure of the metal Cu by introducing Ir atoms to affect the 3d-orbital distribution. All of the above are strongly supported by a range of characterization studies and density functional theory calculations. Benefiting from the above advantages, the LSBs generally show satisfactory cycling performance. Apart from exhibiting a terrific initial specific capacity of 1288 mA h g^-1 at 0.2 C, they can also keep long-term cycling stability under a high current density up to 5 C together with a slow specific capacity decay ratio (0.033%) per cycle after 1000 cycles. In addition, it is worth mentioning that a high areal capacity (4.7 mA h cm^-2) with a low E/S ratio (6.2 μL mg^-1) could still be accomplished at higher sulfur loading (4.3 mg cm^-2).

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.

Theoretical and Experimental Understanding of Metal Single-Atom Electrocatalysts for Accelerating the Electrochemical Reaction of Lithium-Sulfur Batteries

Metal single-atom materials have attracted tremendous attention in the research field of lithium-sulfur (Li-S) batteries because they can effectively improve the reaction kinetics of sulfur cathodes. However, it is still difficult to determine the best metal single-atom catalyst for Li-S batteries, due to the lack of a unified measurement and evaluation method. Herein, a series of metal single-atom- and nitrogen-doped graphene materials (M-NG, M = Fe, Co, Ni, Ir, Ru) have been prepared as the catalysts for promoting the reaction kinetics of the sulfur reduction reaction process. Using rotating disk electrode measurements and density functional theory-based theoretical calculations, Ni-NG was screened out to be the best catalyst. It is found that Ni-NG materials can provide a kinetically favorable pathway for the reversible conversion of polysulfide conversion, thus increasing the utilization of sulfur. By coating the Ni-NG materials on the separator as a multifunctional interlayer, a commercially available sulfur cathode presents a stable specific capacity of 701.8 mAh g^-1 at a current rate of 0.5C over 400 cycles. Even with a high sulfur loading of 3.8 mg cm^-2, a high areal capacity of 4.58 mAh cm^-2 can be achieved. This work will provide a fundamental understanding of efficient single-atom catalyst materials for Li-S batteries.

Poly(ionic liquid) Nanovesicle-Templated Carbon Nanocapsules Functionalized with Uniform Iron Nitride Nanoparticles as Catalytic Sulfur Host for Li-S Batteries

Poly(ionic liquid)s (PIL) are common precursors for heteroatom-doped carbon materials. Despite a relatively higher carbonization yield, the PIL-to-carbon conversion process faces challenges in preserving morphological and structural motifs on the nanoscale. Assisted by a thin polydopamine coating route and ion exchange, imidazolium-based PIL nanovesicles were successfully applied in morphology-maintaining carbonization to prepare carbon composite nanocapsules. Extending this strategy further to their composites, we demonstrate the synthesis of carbon composite nanocapsules functionalized with iron nitride nanoparticles of an ultrafine, uniform size of 3-5 nm (termed "Fe_xN@C"). Due to its unique nanostructure, the sulfur-loaded Fe_xN@C electrode was tested to efficiently mitigate the notorious shuttle effect of lithium polysulfides (LiPSs) in Li-S batteries. The cavity of the carbon nanocapsules was spotted to better the loading content of sulfur. The well-dispersed iron nitride nanoparticles effectively catalyze the conversion of LiPSs to Li₂S, owing to their high electronic conductivity and strong binding power to LiPSs. Benefiting from this well-crafted composite nanostructure, the constructed Fe_xN@C/S cathode demonstrated a fairly high discharge capacity of 1085 mAh g^-1 at 0.5 C initially, and a remaining value of 930 mAh g^-1 after 200 cycles. In addition, it exhibits an excellent rate capability with a high initial discharge capacity of 889.8 mAh g^-1 at 2 C. This facile PIL-to-nanocarbon synthetic approach is applicable for the exquisite design of complex hybrid carbon nanostructures with potential use in electrochemical energy storage and conversion.

FeCo/Fe3C-cross-linked N-doped carbon via synergistic confinement and efficient catalyst to enable high-performance Li-S batteries

Lithium-sulfur batteries (LSB) with high specific energy capacity and low material costs promise to be the next generation of energy storage devices. However, their commercialization is holding back by the poor cycling stability and fast capacity fading resulting from the shuttle effect and slow redox reaction. In this work, the FeCo/Fe₃C-CNC composite was prepared by anchoring FeCo/Fe₃C nanoparticles onto the crosslinked N-doped Carbon (CNC). The results showed that the addition of Co element improved the electrochemical activity of Co-Fe alloy through tuning the electronic structure of Fe atoms. The carbon nanotubes (CNTs) grown around Co-Fe alloy and Fe₃C nanoparticles exhibited a strong affinity to polysulfide species and superior catalytic capability as nano-reactors. The N-doping CNTs/carbon sheets (CS) facilitated the formation of Li₂S compound by promoting the Li⁺ ions transport while hindering the polysulfide shuttle effect. Hence, the issues of slow redox reactions and loss of polysulfide species were effectively rectified. As a result, the composite cathode FeCo/Fe₃C-CNC-based LSB delivered a good specific capacity of 1401 mAh g^-1 at 0.1C, and a low apacity fading rate of 0.029% per cycle at 1C. Besides, the structural stability of the FeCo/Fe₃C-CNC composite confirms its potential for the deployment in LSB applications.

Large-Scale Li-Ion Battery Research and Application in Mining Industry

The lithium-ion battery (LIB) has the advantages of high energy density, low self-discharge rate, long cycle life, fast charging rate and low maintenance costs. It is one of the most widely used chemical energy storage devices at present. However, the safety of LIB is the main factor that restricts its commercial scalable application, specifically in hazardous environments such as underground coal mines. When a LIB is operating under mechanical and electrical abuse such as extrusion, impact, overcharge and overheating, it will trigger thermal runaway and subsequently cause fire or even an explosion. According to the relevant requirements in IEC60079, the explosion-proof protection of LIB can be adapted to the working environment of high dust and explosive gas environments such as in the mining face of coal production. This paper presents an overview of the LIB-relevant technology, thermal runaway, safety and applications in the general mining industry with implications to establish a theoretical and technical basis for the application of high-capacity LIBs in the industry. These then promote intelligent, safe and efficient production not only for the coal mine industry but also for non-coal applications.

Recent Advances and Strategies toward Polysulfides Shuttle Inhibition for High-Performance Li-S Batteries

Lithium-sulfur (Li-S) batteries are regarded as the most promising next-generation energy storage systems due to their high energy density and cost-effectiveness. However, their practical applications are seriously hindered by several inevitable drawbacks, especially the shuttle effects of soluble lithium polysulfides (LiPSs) which lead to rapid capacity decay and short cycling lifespan. This review specifically concentrates on the shuttle path of LiPSs and their interaction with the corresponding cell components along the moving way, systematically retrospect the recent advances and strategies toward polysulfides diffusion suppression. Overall, the strategies for the shuttle effect inhibition can be classified into four parts, including capturing the LiPSs in the sulfur cathode, reducing the dissolution in electrolytes, blocking the shuttle channels by functional separators, and preventing the chemical reaction between LiPSs and Li metal anode. Herein, the fundamental aspect of Li-S batteries is introduced first to give an in-deep understanding of the generation and shuttle effect of LiPSs. Then, the corresponding strategies toward LiPSs shuttle inhibition along the diffusion path are discussed step by step. Finally, general conclusions and perspectives for future research on shuttle issues and practical application of Li-S batteries are proposed.

PPy-constructed core–shell structures from MOFs for confining lithium polysulfides

Core–shell structured MIL-96-Al composites are prepared through a melt-diffusion method followed by a water-phase polymerization process. The composites can strongly confine lithium polysulfides in a cathode.

Stable Dendrite-Free Sodium-Sulfur Batteries Enabled by a Localized High-Concentration Electrolyte

Ambient-temperature sodium-sulfur batteries are an appealing, sustainable, and low-cost alternative to lithium-ion batteries due to their high material abundance and specific energy of 1274 W h kg^-1. However, their viability is hampered by Na polysulfide (NaPS) shuttling, Na loss due to side reactions with the electrolyte, and dendrite formation. Here, we demonstrate that a solid-electrolyte interphase rich in inorganic components can be realized at both the sulfur cathode and the Na anode by tweaking the solvation structure of the electrolyte. This transforms the sulfur redox process from conventional dissolution-precipitation chemistry into a quasi-solid-state reaction, which eliminates NaPS shuttling and facilitates dendrite-free Na-metal plating and stripping. With the solvated ionic liquid electrolyte structure, a high initial capacity of 922 mA h g^-1 with a capacity fade of as low as 0.10% per cycle over 300 cycles was achieved. The scalability of this approach to pouch cells with practically necessary parameters demonstrates its potential for practical viability.

Fast polysulfide catalytic conversion and self-repairing ability for high loading lithium-sulfur batteries using a permselective coating layer modified separator

Li-S batteries are considered as one of the most promising battery systems because of their large theoretical capacity and high energy density. However, the "shuttle effect" of soluble polysulfides and sluggish electrochemical redox kinetics of Li-S batteries could cause a broken electrode structure and poor electrochemical performance. Herein, a high-performance and stable Li-S battery has been demonstrated by employing organo-polysulfide chain modified acetylene black (ABPS) as the coating layer on the separator. In addition to the traditional advantages of fast electron transport and polysulfide-interception ability of the carbon coating layer, the grafted organo-polysulfide chain endows the ABPS coating layer with permselectivity for lithium ion against polysulfides, electrocatalytic ability for the sluggish redox kinetics and self-repairing ability for the broken electrode. Hence, the battery prepared using an ABPS-coated separator delivers the best cycling performance (970 mA h g^-1 at 0.2 C after 100 cycles) and rate performance (805 mA h g^-1 at 2 C) as compared to the cells using acetylene black (AB)-coated or Celgard separators. Moreover, the Li-S battery prepared using an ABPS-coated separator exhibits a stable cycling performance at 1 C over 500 cycles with a low degradation of 0.04% per cycle, and a high coulombic efficiency (near 100%). Furthermore, as the sulfur loading was increased to 6.8 mg cm^-2, the Li-S battery using the ABPS-coated separator still could deliver a high areal capacity of 6.03 mA h cm^-2 with a low electrolyte/sulfur ratio (E/S = 4, μL_electrolyte mg_S^-1) after 170 cycles. Significantly, ABPS is an effective coating layer material for improving and stabilizing Li-S batteries.