Investigation of the Nanocrystal CoS2 Embedded in 3D Honeycomb-like Graphitic Carbon with a Synergistic Effect for High-Performance Lithium Sulfur Batteries

Integrating CoP/Co heterojunction into nitrogen-doped carbon polyhedrons as electrocatalysts to promote polysulfides conversion in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have garnered extensive research interest as one of the most promising energy storage devices due to their ultra-high theoretical energy density. However, the sluggish reaction kinetics, abominable shuttling effect and inferior cycling stability severely restrict its practical application. Herein, a multifunctional CoP/Co@NC/CNT heterostructure host material was elaborately designed and synthesized by integrating CoP/Co heterojunction, N-doped carbon hollow polyhedrons (NC) and carbon nanotubes (CNTs). Specifically, the CoP/Co heterojunction can reconfigure the local electronic structure, resulting in a synergistic effect that enhances adsorption capacity and catalytic activity compared to CoP and Co alone. Furthermore, the CNTs-grafted NC not only provides multi-dimensional pathways for rapid electron transport and ion diffusion, but also physically restricts the diffusion of polysulfides during charge-discharge processes. Owing to these advantages, the battery assembled with the CoP/Co@NC/CNT/S cathode yields an impressive discharge specific capacity of 1479.9 mAh g-1 at 0.1C, and excellent capacity retention of 793.7 mAh g-1 over 500 cycles at 2C (∼85.5 % of initial capacity). The rational integration of multifunctional heterostructures could provide an effective strategy for designing high-efficiency nanocomposite electrocatalysts to promote sulfur redox kinetics in Li-S batteries.

In situ self-reconstructed hierarchical bimetallic oxyhydroxide nanosheets of metallic sulfides for high-efficiency electrochemical water splitting

The advancement of economically efficient electrocatalysts for alkaline water oxidation based on transition metals is essential for hydrogen production through water electrolysis. In this investigation, a straightforward one-step solvent method was utilized to spontaneously cultivate bimetallic sulfide S-FeCo1 : 1/NIF on the surface of a nickel-iron foam (NIF). Capitalizing on the synergistic impact between the bimetallic constituents and the highly active species formed through electrochemical restructuring, S-FeCo1 : 1/NIF exhibited remarkable oxygen evolution reaction (OER) performance, requiring only a 310 mV overpotential based on 500 mA cm-2 current density. Furthermore, it exhibited stable operation at 200 mA cm-2 for 275 h. Simultaneously, the catalyst demonstrated excellent hydrogen evolution reaction (HER) and overall water-splitting capabilities. It only requires an overpotential of 191 mV and a potential of 1.81 V to drive current densities of 100 and 50 mA cm-2. Density functional theory (DFT) calculations were also employed to validate the impact of the bimetallic synergistic effect on the catalytic activity of sulfides. The results indicate that the coupling between bimetallic components effectively reduces the energy barrier required for the rate-determining step in water oxidation, enhancing the stability and activity of bimetallic sulfides. The exploration of bimetallic coupling to improve the OER performance holds theoretical significance in the rational design of advanced electrocatalysts.

A Wearable Electrochemical Biosensor Utilizing Functionalized Ti3C2Tx MXene for the Real-Time Monitoring of Uric Acid Metabolite

Wearable, noninvasive sensors enable the continuous monitoring of metabolites in sweat and provide clinical information related to an individual's health and disease states. Uric acid (UA) is a key indicator highly associated with gout, hyperuricaemia, hypertension, kidney disease, and Lesch-Nyhan syndrome. However, the detection of UA levels typically relies on invasive blood tests. Therefore, developing a wearable device for noninvasive monitoring of UA concentrations in sweat could facilitate real-time personalized disease prevention. Here, we introduce 1,3,6,8-pyrene tetrasulfonic acid sodium salt (PyTS) as a bifunctional molecule functionalized with Ti3C2Tx via π-π conjugation to design nonenzymatic wearable sensors for sensitive and selective detection of UA concentration in human sweat. PyTS@Ti3C2Tx provides many oxidation-reduction active groups to enhance the electrocatalytic ability of the UA oxidation reaction. The PyTS@Ti3C2Tx-based electrochemical sensor demonstrates highly sensitive detection of UA in the concentration range of 5 μM-100 μM, exhibiting a lower detection limit of 0.48 μM compared to the uricase-based sensor (0.84 μM). In volunteers, the PyTS@Ti3C2Tx-based wearable sensor is integrated with flexible microfluidic sweat sampling and wireless electronics to enable real-time monitoring of UA levels during aerobic exercise. Simultaneously, it allows for comparison of blood UA levels via a commercial UA analyzer. Herein, this study provides a promising electrocatalyst strategy for nonenzymatic electrochemical UA sensor, enabling noninvasive real-time monitoring of UA levels in human sweat and personalized disease prevention.

Hollow Structure Co1-xS/3D-Ti3C2Tx MXene Composite for Separator Modification of Lithium-Sulfur Batteries

The commercial application of lithium-sulfur (Li-S) batteries has faced obstacles, including challenges related to low sulfur utilization, structural degradation resulting from electrode volume expansion, and migration of polysulfide lithium (LiPSs). Herein, Co1-xS/3D-Ti3C2Tx composites with three-dimensional (3D) multilayered structures are used as separator modification materials for Li-S batteries to solve these problems. The multilevel layered structure of Co1-xS/3D-Ti3C2Tx establishes an efficient electron and Li+ transfer path, alleviates the volume change during the battery charge-discharge process, and enhances the stability of the structure. In addition, the battery assembled with the modified separator shows excellent discharge capacity and cycle stability at 0.5 C and could maintain a high discharge capacity after 500 cycles. This work provides a method for designing highly dispersed metal sulfide nanoparticles on MXenes and extends the application of MXenes-based composites in electrochemical energy storage.

Highly Reversible Lithium-Ion Battery with Excellent Rate Performance and Cycle Stability Based on a Ti3C2/CoS2 Composite Anode

Transition metal sulfide (TMS) CoS2 is considered an ideal anode material for new-generation lithium-ion batteries (LIBs) because of its high specific capacity, high electrochemical activity, and low cost. However, CoS2 is prone to volume expansion and structural collapse when it participates in the internal conversion reaction of the battery, which limits its practical application. After analyzing the failure mechanism of CoS2 as the anode material of LIBs, the concept of nanoengineered materials is introduced here. CoS2 particles are nanosized and stabilized by constructing a composite structure on an alkali-treated two-dimensional Ti3C2 Mxene conductive network. Both experiments and theoretical calculations show that special Ti-O-Co bonds are formed at the interface of the Ti3C2/CoS2 composite through oxygen-containing functional groups. Ti-O-Co bonding with adjustable electronic characteristics can effectively promote the utilization rate of anode materials, electronic conductivity, and ionic diffusivity and thus enhance the redox reaction kinetics of the device. When the Ti3C2/CoS2 composite is used as the anode material for LIBs, it still provides a high specific capacity of 405.8 mAh g-1 after 100 cycles at 0.1 A g-1. After running for 1000 cycles at a high current of 1 A g-1, the capacity retention is still close to 100%. Also, high cycle stability under the condition of highly active material loading (10.58 mg cm-2) and low electrolyte/active material ratio (10 μL mg-1) is achieved. This work provides a new idea for the development of commercial LIBs as anode materials.

Enhancement of Organic Oxygen Atoms on Metal Cobalt for Sulfur Adsorption and Catalytic Polysulfide Conversion

Metals and their compounds effectively suppress the polysulfide shuttle effect on the cathodes of a lithium-sulfur (Li-S) battery by chemisorbing polysulfides and catalyzing their conversion. However, S fixation on currently available cathode materials is below the requirements of large-scale practical application of this battery type. In this study, perylenequinone was utilized to improve polysulfide chemisorption and conversion on cobalt (Co)-containing Li-S battery cathodes. According to IGMH analysis, the binding energies of DPD and carbon materials as well as polysulfide adsorption were significantly enhanced in the presence of Co. According to in situ Fourier transform infrared spectroscopy, the hydroxyl and carbonyl groups in perylenequinone are able to form O-Li bonds with Li₂S_n, facilitating chemisorption and catalytic conversion of polysulfides on metallic Co. The newly prepared cathode material demonstrated superior rate and cycling performances in the Li-S battery. It exhibited an initial discharge capacity of 780 mAh g^-1 at 1 C and a minimum capacity decay rate of only 0.041% over 800 cycles. Even with a high S loading, the cathode material maintained an impressive capacity retention rate of 73% after 120 cycles at 0.2 C.

MultiElement-Doped Ni-Based Disulfide Enhances the Specific Capacity of Thermal Batteries by High Thermal Stability

With the high theoretical capacity and the ability of large current discharge, NiS₂ has been expected as a new cathode material for thermal batteries. However, its lower decomposition temperature (∼500 °C) restricts its application on thermal batteries because of the high operating temperature of thermal batteries (500-600 °C). In this case, Cr, Fe, Co, and Cu multielement-doped NiS₂ (NiS₂-d) has been successfully prepared by low-temperature solid-phase sintering. Owing to the effect of high entropy, the multielement doping improved the thermodynamic system stability of NiS₂, and the decomposition temperature (2NiS₂ → 2NiS + S₂) increased from 482 to 610 °C. Interestingly, doping also reduces the particle size of NiS₂, resulting in defects on the surface of NiS₂ particles and improving the conductivity of NiS₂.The actual discharge capacity of NiS₂ enhanced significantly from 516 to 643 mA h g^-1 at 500 °C, with a current density of 100 mA cm^-2 and a cut-off voltage of 1.5 V. This is due to a more complete release of the first discharge reaction (NiS₂ + 2Li⁺ + 2e^- → NiS + Li₂S) as the decomposition temperature rises. The enhancement of conductivity, meanwhile, lessens polarization during the discharge process, raises the voltage of the NiS₂ discharge platform, and improves the stability of the NiS₂ later discharge platform. Additionally, the smaller particle size enables improved contact between the cathode and the electrolyte interface, allowing electrolyte ions to quickly come into touch with the NiS₂ surface. These results show that the discharge performance of NiS₂ at high temperatures could be effectively improved by multielement doping. It provides a new method for improving the stability of a metal sulfide and its application at high-temperature discharge.

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.

Multi-Dimensional Composite Frame as Bifunctional Catalytic Medium for Ultra-Fast Charging Lithium-Sulfur Battery

The shuttle effect of soluble lithium polysulfides (LiPSs) between electrodes and slow reaction kinetics lead to extreme inefficiency and poor high current cycling stability, which limits the commercial application of Li-S batteries. Herein, the multi-dimensional composite frame has been proposed as the modified separator (MCCoS/PP) of Li-S battery, which is composed of CoS₂ nanoparticles on alkali-treated MXene nanosheets and carbon nanotubes. Both experiments and theoretical calculations show that bifunctional catalytic activity can be achieved on the MCCoS/PP separator. It can not only promote the liquid-solid conversion in the reduction process, but also accelerate the decomposition of insoluble Li₂S in the oxidation process. In addition, LiPSs shuttle effect has been inhibited without a decrease in lithium-ion transference numbers. Simultaneously, the MCCoS/PP separator with good LiPSs adsorption capability arouses redistribution and fixing of active substances, which is also beneficial to the rate performance and cycling stability. The Li-S batteries with the MCCoS/PP separator have a specific capacity of 368.6 mAh g^-1 at 20C, and the capacity decay per cycle is only 0.033% in 1000 cycles at 7C. Also, high area capacity (6.34 mAh cm^-2) with a high sulfur loading (7.7 mg cm^-2) and a low electrolyte/sulfur ratio (7.5 μL mg^-1) is achieved.

CuCo2S4 Nanoparticles Embedded in Carbon Nanotube Networks as Sulfur Hosts for High Performance Lithium-Sulfur Batteries

Rational design of sulfur hosts for lithium-sulfur (Li-S) batteries is essential to address the shuttle effect and accelerate reaction kinetics. Herein, the composites of bimetallic sulfide CuCo₂S₄ loaded on carbon nanotubes (CNTs) are prepared by hydrothermal method. By regulating the loading of CuCo₂S₄ nanoparticles, it is found that when Cu²⁺ and CNT are prepared in a 10:1 ratio, the CuCo₂S₄ nanoparticles loaded on the CNT are relatively uniformly distributed, avoiding the occurrence of agglomeration, which improves the electrical conductivity and number of active sites. Through a series of electrochemical performance tests, the S/CuCo₂S₄-1/CNT presents a discharge specific capacity of 1021 mAh g^-1 at 0.2 C after 100 cycles, showing good cycling stability. Even at 1 C, the S/CuCo₂S₄-1/CNT cathode delivers a discharge capacity of 627 mAh g^-1 after 500 cycles. This study offers a promising strategy for the design of bimetallic sulfide-based sulfur hosts in Li-S batteries.

Understanding the interactions between lithium polysulfides and anchoring materials in advanced lithium-sulfur batteries using density functional theory

Lithium-sulfur batteries (LSBs) are promising energy storage devices because of their high theoretical capacity and energy density. However, the "shuttle" effect in lithium polysulfides (LiPSs) is an unresolved issue that can hinder their practical commercial application. Research on LSBs has focused on finding appropriate materials that suppress this effect by efficiently anchoring the LiPSs intermediates. Quantum chemical computations are a useful tool for understanding the mechanistic details of chemical interaction involving LiPSs, and they can also offer strategies for the rational design of LiPSs anchoring materials. In this perspective, we highlight computational and theoretical work performed on this topic. This includes elucidating and characterizing the adsorption mechanisms, and the dominant types of interactions, and summarizing the binding energies of LiPSs on anchoring materials. We also give examples and discuss the potential of descriptors and machine learning approaches to predict the adsorption strength and reactivity of materials. We believe that both approaches will become indispensable in modelling future LSBs.

Harnessing Heteropolar Lithium Polysulfides by Amphoteric Polymer Binder for Facile Manufacturing of Practical Li-S Batteries

Enabling efficient and durable charge storage under high sulfur loading and lean electrolyte remains a paramount challenge for Li-S battery technology to truly demonstrate its commercial viability. This work reports an amphoteric polymer binder, whose negatively and positively charged moieties allow for coregulation of both lithium cations and heteropolar lithium polysulfides through multiple intermolecular interactions. These interactions and the physical properties lead to simultaneously improved Li⁺ transport, polysulfide adsorption and catalysis, cathode robustness and anode stability. Therefore, this multifunctional binder endows Li-S batteries with compelling overall performances even under rigorous conditions. At low sulfur loading and copious electrolyte, the cell shows a low capacity-fading rate of 0.056% cycle-1 upon 700 cycles. At sulfur loading of 6.8 mg cm^-2 and low E/S of 6 µL mg^-1 , the cell still delivers stable areal capacities between 4.2 and 4.8 mAh cm^-2 in 50 cycles without obvious decay at 0.2 C. The commercial feasibility of this work is further manifested by its zero added weight, low material cost, and ease of manufacturing and scale-up. The efficacy and simplicity of this work symbolize an example of lab-scale battery research aiming at improved technology and manufacturing readiness level.

Boosting polysulfides immobilization and conversion through CoS2 catalytic sites loaded carbon fiber for robust lithium sulfur batteries

The practical applications of lithium sulfur battery is impeded by the lithium polysulfide shuttling and sluggish redox kinetics. To address the issues, herein, a multifunctional host is developed by the combination of nitrogen, phosphorus co-doped carbon fiber (NPCF) and CoS₂ towards boost the soluble polysulfides adsorption and transformation. Benefiting from the NPCF originated from biomass cattail fibers, a high conductive network is provided, and shuttle effect is reduced due to the strong chemical interaction between abundant heteroatom polar sites and lithium polysulfides. Moreover, the electrocatalytic CoS₂ on the carbon skeleton facilitate lithium polysulfides conversion and lithium sulfide deposition based on the density functional theory calculations and experiments. The efficient lithium polysulfides entrapment and subsequent electrocatalytic conversion improve dynamic stability during cycling, especially for rate capability. With these advantageous features, the electrode with NPCF/CoS₂ host can deliver a good rate capability (903 and 782 mAh g^-1 at 1C and 2C, respectively) and stable cycling performance with an ultra-low capacity decay of 0.014% per cycle at 1C. Notably, the cell can achieve a high areal capacity of 4.96 mA h cm^-2 under an elevated sulfur loading of 5.0 mg cm^-2. Overall, the improvement on the electrochemical performance ascertains the validity of the design strategy based on synergy engineering, which is a highly suitable approach for energy storage and conversion application.

N-doped three-dimensional needle-like CoS2 bridge connection Co3O4 core-shell structure as high-efficiency room temperature NO2 gas sensor

The N-doped three-dimensional (3D) needle bridge connection core-shell structure N-CoS₂@Co₃O₄ synthesized in this work was prepared by simple hydrothermal and high-temperature vulcanization methods. The optimized N-CoS₂@Co₃O₄^-2 composite response to NO₂ is 62.3-100 ppm, a response time of 1.3 s, the recovery time of 17.98 s, the detection limit of 5 ppb and stability of as long as 10 weeks at room temperature (RT). Its excellent NO₂ sensing performance is attributed to the unique porous and bridge connection core-shell structure of the N-CoS₂@Co₃O₄^-2 with high specific surface area, interconnected internal channels, abundant exposed S edge active sites, and high catalytic performance promoted by N-doping. This simple manufacturing method of high-performance sensing materials paves the way for the design of N-doped bridge connection core-shell structures.

Co4 N-Decorated 3D Wood-Derived Carbon Host Enables Enhanced Cathodic Electrocatalysis and Homogeneous Lithium Deposition for Lithium-Sulfur Full Cells

The sluggish kinetics of sulfur conversion in the cathode and the nonuniform deposition of lithium metal at the anode result in severe capacity decay and poor cycle life for lithium-sulfur (Li-S) batteries. Resolving these deficiencies is the most direct route toward achieving practical cells of this chemistry. Herein, a vertically aligned wood-derived carbon plate decorated with Co₄ N nanoparticles host (Co₄ N/WCP) is proposed that can serve as a host for both the sulfur cathode and the metallic lithium anode. This Co₄ N/WCP electrode host drastically enhances the reaction kinetics in the sulfur cathode and homogenizes the electric field at the anode for the uniform lithium plating. Density functional theory calculations confirm the experimental observations that Co₄ N/WCP provides a lower energy barrier for the polysulfide redox reaction in the cathode and a low adsorption energy for lithium deposition at the anode. Employing the Co₄ N/WCP host at both electrodes in a S@Co₄ N/WCP||Li@Co₄ N/WCP full cell delivers a specific capacity of 807.9 mAh g^-1 after 500 cycles at a 1 C rate. Additional experiments are performed with high areal sulfur loading of 4 mg cm^-2 to demonstrate the viability of this strategy for producing practical Li-S cells.

Multisize CoS2 Particles Intercalated/Coated-Montmorillonite as Efficient Sulfur Host for High-Performance Lithium-Sulfur Batteries

The chemisorption and catalysis of lithium polysulfides (LiPSs) are effective strategies to suppress the shuttle effect in lithium-sulfur (Li-S) batteries. Herein, multisize CoS₂ particles intercalated/coated-montmorillonite (MMT) as an efficient sulfur host is synthesized. As expected, the obtained S/CoS₂ @MMT cathode achieves an absorption-catalysis synergistic effect through the polar MMT aluminosilicate sheets and the well-dispersed nano-micron CoS₂ particles. Furthermore, efficient interlamellar ion pathways and interconnected conductive network are constructed within the composite host due to the intercalation/coating of CoS₂ in/on MMT. Therefore, the S/CoS₂ @MMT cathode achieves an outstanding rate performance up to 5C (∼548 mAh g^-1 ) and a high cycling stability with low capacity decay of 0.063 and 0.067 % per cycle for 500 cycles at 1C and 2C, respectively. With a higher sulfur loading of 4.0 mg cm^-2 , the cathode still delivers satisfactory rate and cycling performance. It shows that the CoS₂ @MMT host has great application prospects in Li-S batteries.

Metal-based electrocatalysts for room-temperature Na-S batteries

Room-temperature sodium-sulfur (RT Na-S) batteries have recently captured intensive research attention from the community and are regarded as one of promising next-generation energy storage devices since they not only integrate the advantages in high abundance and low commercial cost of elemental Na/S but also exhibit exceptionally high theoretical capacity and energy density. Whereas, the notorious shuttle effect of soluble intermediates and sluggish kinetics remain two main obstacles for RT Na-S batteries to step into new developmental stage. Recently, impressive advancements of metal-based electrocatalysts have offered a viable solution to stabilize S cathodes and unlocked new opportunities for RT Na-S batteries. Here, we underline the recent progress on metal-based electrocatalysts for RT Na-S batteries for the first time by shedding light on this emerging but promising field. The involved metal-based electrocatalysts include metals, metal oxides, metal sulfides, metal carbides, and other metal-based catalytic species. Our emphasis is focused on the discussion of design, fabrication, and properties of these electrocatalysts as well as interactions between electrocatalysts and sodium polysulfides. Otherwise, some potential electrocatalysts for RT Na-S batteries are pointed out as well. At last, perspectives for the future development of RT Na-S batteries with S cathode electrocatalysts are offered.

Metastable marcasite NiSe2 nanodendrites on carbon fiber clothes to suppress polysulfide shuttling for high-performance lithium-sulfur batteries

The incorporation of catalytic components is a promising strategy to promote redox reaction kinetics and suppress polysulfide shuttling for high-performance lithium-sulfur batteries (LSBs). In this work, metastable marcasite NiSe₂ nanodendrites grown on carbon fiber clothes (m-NiSe₂/CFC) were synthesized to improve chemical adsorption and electrocatalytic activity towards lithium polysulfides. The multifunctional m-NiSe₂/CFC film was utilized as both the interlayer and the three-dimensional (3D) current collector in LSBs. In comparison with the stable pyrite NiSe₂ nanodendrite-covered CFC (p-NiSe₂/CFC) counterpart, the m-NiSe₂/CFC film exhibits even stronger chemisorption, higher catalytic activity and faster reaction kinetics, thereby resulting in significantly improved lithium storage performance. The Al@S/rGO@m-NiSe₂/CFC cell has a high reversible capacity of 1646 mA h g^-1 at 0.2C, a high Q_L/Q_H ratio of 3.00 at 0.2C, a high rate capability of 900 mA h g^-1 at 4C, and an outstanding cyclic stability exhibiting a low capacity decay of 0.028% per cycle for 600 cycles at 4C. Moreover, a symmetrically sandwiched cathode of m-NiSe₂/CFC@S/rGO@m-NiSe₂/CFC was designed for high sulfur loading LSBs (4.5 mg cm^-2) with superior electrochemical performance of 3.73 mA h cm^-2 after 100 cycles at 1C rate. Our work opens up a new opportunity to enhance the electrochemical performance of LSBs by phase engineering of NiSe₂ catalysts in sandwiched structural cathodes.

Porous Cobalt Sulfide Selenium Nanorods for Electrochemical Hydrogen Evolution

A key process in electrochemical energy technology is hydrogen evolution reaction (HER). However, its electrochemical properties mainly depend on the catalytic activity of the material itself. Therefore, it is important to find efficient electrocatalysts to realize clean hydrogen production. As a typical kind of catalytic materials, transition metal dichalcogenides (TMCs) play important roles in the field of energy catalysis. As a representative of TMCs, cobalt disulfide (CoS₂), recently has raised much research interest owing to its abundant reserves, environmental friendliness, and excellent electrochemical stability. Meanwhile, given the fact that doping is one of the effective methods to improve the electrochemical catalytic property, various means of doping have been researched. Here, we report for the first time that porous-like Se-CoS_2-x (or Se:CoS_2-x ) nanorod can be facilely synthesized via a controllable two-step strategy. It is demonstrated that doping Se can greatly improve the catalytic performance of CoS₂ electrode. The electrode can obtain a current density of 10 mA cm^-2 at overpotential of only ∼260 mV. And the current changes with the applied bias voltage in an obvious stepped pattern, in the chronopotential (CP) curve of Se-CoS_2-x , indicating its outstanding mass transfer property and mechanical stability.

Sandwiched Cathodes Assembled from CoS2 -Modified Carbon Clothes for High-Performance Lithium-Sulfur Batteries

Structural design of advanced cathodes is a promising strategy to suppress the shuttle effect for lithium-sulfur batteries (LSBs). In this work, the carbon cloth covered with CoS2 nanoparticles (CC-CoS2 ) is prepared to function as both three-dimensional (3D) current collector and physicochemical barrier to retard migration of soluble lithium polysulfides. On the one hand, the CC-CoS2 film works as a robust 3D current collector and host with high conductivity, high sulfur loading, and high capability of capturing polysulfides. On the other hand, the 3D porous CC-CoS2 film serves as a multifunctional interlayer that exhibits efficient physical blocking, strong chemisorption, and fast catalytic redox reaction kinetics toward soluble polysulfides. Consequently, the Al@S/AB@CC-CoS2 cell with a sulfur loading of 1.2 mg cm-2 exhibits a high rate capability (≈823 mAh g-1 at 4 C) and delivers excellent capacity retention (a decay of ≈0.021% per cycle for 1000 cycles at 4 C). Moreover, the sandwiched cathode of CC-CoS2 @S/AB@CC-CoS2 is designed for high sulfur loading LSBs. The CC-CoS2 @S/AB@CC-CoS2 cells with sulfur loadings of 4.2 and 6.1 mg cm-2 deliver high reversible capacities of 1106 and 885 mAh g-1 , respectively, after 100 cycles at 0.2 C. The outstanding electrochemical performance is attributed to the sandwiched structure with active catalytic component.

Comparative study on supercapacitive and oxygen evolution reaction applications of hollow nanostructured cobalt sulfides

Due to the diversity of sulfur valence in cobalt-based sulfides, it is difficult to control the crystal phase and composition of the products during synthesis. Herein, a one-pot hydrothermal method is reported to self-assemble the cobalt sulfides (CoS₂, Co₉S₈and Co₃S₄) with hollow nanostructures. The whole preparation process is simple and mild, avoiding high temperature calcination. The performances of the three kinds of cobalt sulfide in superior supercapacitors and electrocatalytic oxygen evolution performance applications follow the order of CoS₂ > Co₉S₈ > Co₃S₄. Further analysis demonstrates that the performance difference in these cobalt sulfides may be attributed to three factors: the presence ofS22-,the coordination environment of Co and the presence of continuous network of Co-Co bonds. The distinctive electrochemical performance of CoS₂and Co₉S₈may help us to better understand the excellent electrochemical activity of metal polysulfides and metal sulfides after doping or alloying. Therefore, this work may provide a reference in understanding and designing the electrode materials for highly efficient applications in the fields of energy storage and conversion.

Ammonia-free fabrication of ultrafine vanadium nitride nanoparticles as interfacial mediators for promoting electrochemical behaviors of lithium-sulfur batteries

Transition metal nitrides are promising mediators for improving the electrochemical performance of lithium-sulfur (Li-S) batteries, but the synthesis of ultrafine and durable nanoparticles in the absence of ammonia gas is still a great challenge. Herein, we reported a new method for the fabrication of ultrafine vanadium nitride (VN) nanoparticles uniformly embedded into N-doped porous carbon using a main-chain imidazolium-based ionic polymer (ImIP) containing metavanadate anions as a precursor. ImIP not only serves as sole carbon and nitrogen sources, but also effectively inhibits the aggregation and coalescence of VN nanoparticles during pyrolysis. Benefiting from the ultrafine particle size, high polarity and good electrocatalytic effects of VN, both redox kinetics of sulfur species and chemical adsorbability toward polysulfides are greatly expedited. The resultant electrode exhibits superior cycling stability with a low average capacity decay rate of 0.035% for 1200 cycles at a high rate of 5 C. This work develops a facile ammonia-free approach to fabricate ultrafine VN nanoparticles for improving electrochemical behaviors of Li-S batteries.

Improved Redox Reaction of Lithium Polysulfides on the Interfacial Boundary of Polar CoC2 O4 as a Polysulfide Catenator for a High-Capacity Lithium-Sulfur Battery

The performance of cobalt oxalate as an electrocatalyst in a lithium-sulfur battery (LSB) is improved owing to the suitable adsorbent properties of sulfur. The adsorption mechanism is elucidated by UV/Vis spectroscopy and surface analysis through X-ray photoelectron spectroscopy. Li₂ S₆ is converted into thiosulfate and polythionate by a catenation reaction on the interfacial boundary of CoC₂ O₄ contacted with carbon. Following this, the active polythionate and short-chained liquid lithium polysulfides (LiPS) bound to the cobalt surface are further reduced as CoC₂ O₄ reduces the overpotential to facilitate the LiPS redox reaction, leading to high specific capacity, lower self-discharge rate, and stable long-term cycling performance.

Theoretical investigation on lithium polysulfide adsorption and conversion for high-performance Li-S batteries

Lithium-sulfur (Li-S) batteries have shown great application prospects as next-generation energy storage systems due to their high theoretical capacity and high energy density. However, the practical application of Li-S batteries is still hindered by several challenges, such as their sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs). To date, significant research has been focused on the confinement adsorption and catalytic conversion of LiPSs using theoretical or/and experimental methods. Among them, theoretical calculations are highly attractive to observe complex LiPS conversion reactions, which facilitate the rational design of S mediators for high-performance Li-S batteries. In this review, we summarize and discuss the recent advances in the adsorption and conversion of LiPSs from the viewpoint of theoretical calculations. Moreover, a set of theoretical principles to guide the screening of suitable host materials for Li-S batteries is presented and discussed. Finally, some personal insights about the future challenges and the focus of research in this field are presented, which will push a milestone step toward high-efficiency and long-life Li-S batteries.

Cobalt disulfide supported on porous carbon foam as a high performance hydrogen evolution reaction catalyst

An excellent cobalt disulfide–carbon foam composite catalyst was synthesized by a hydrothermal method for the electrochemical hydrogen evolution reaction (HER).

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

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

Tuning the Band Structure of MoS2 via Co9S8@MoS2 Core-Shell Structure to Boost Catalytic Activity for Lithium-Sulfur Batteries

The introduction of a dual-functional interlayer into lithium-sulfur batteries (LSBs) provides many opportunities for restraining the "shuttle effect" and enhancing sluggish sulfur conversion kinetics. Tuning the band structure of the metal sulfide provides an opportunity to enhance its catalytic activity, which plays an important role in suppressing the "shuttle effect" of lithium polysulfides (LiPSs) in LSBs. Here were present a Co₉S₈@MoS₂ core-shell heterostructure anchored to a carbon nanofiber (Co₉S₈@MoS₂/CNF), developed as an interlayer for suppressing the shuttle effect of LiPSs. The fabricated composite heterostructure is determined to be an effective alternative material that combines the synergistic relationship between chemisorption and electrochemical catalysis. We find that the band structure of the MoS₂ shell can be effectively tuned by the Co₉S₈ core and that the Co₉S₈@MoS₂/CNF can capture the LiPSs, providing excellent catalytic ability to convert LiPSs into Li₂S₂, with subsequent transformation from Li₂S₂ to Li₂S. Importantly, high capacities of 1002 and 986 mAh g^-1 can be retained after 50 cycles with high-sulfur loadings of 6 and 10 mg cm^-2. Our results highlight the design of an atomic-scale heterostructure as a multifunctional interlayer providing a synergistic relationship between adsorption and catalysis. The net result is an effective retardation of the shuttling of LiPSs and an enhancement of the electrochemical redox reactions of LiPSs. This work shows great promise toward the development of practical applications of LSBs.

Novel Hoberman Sphere Design for Interlaced Mn3O4@CNT Architecture with Atomic Layer Deposition-Coated TiO2 Overlayer as Advanced Anodes in Li-Ion Battery

The Hoberman sphere is a stable and stretchable spatial structure with a unique design concept, which can be taken as the ideal prototype of the internal mechanical/conductive skeleton for the anode with large volume change. Herein, Mn₃O₄ nanoparticles are interlaced with a Hoberman sphere-like interconnected carbon nanotube (CNT) network via a facile self-assembly strategy in which Mn₃O₄ can "locally expand" in the CNT network, limit the volume expansion to the interior space, and maintain a stable outer surface of the hybrid particle. Furthermore, an ultrathin uniform ALD-coated TiO₂ shell is adopted to stabilize the solid electrolyte interphase (SEI), provide high electron conductivity and lithium ion (Li⁺) diffusivity with lithiated Li_xTiO₂, and enhance the reaction kinetics of the Mn₃O₄ by an "electron-density enhancement effect". With this design, the Mn₃O₄@CNT/TiO₂ exhibits a high capacity of 1064 mAh g^-1 at 0.1 A g^-1, a stable cycling stability over 200 cycles, a superior rate capability, and a commercial-level areal capacity of 4.9 mAh cm^-2. In this way, a novel electrode design strategy is achieved by the Hoberman sphere-like CNT design along with the in situ porous formation, which can not only achieve a high-performance anode for LIBs but also can be widely adapted in a variety of advanced electrode materials for alkali metal ion batteries.

Promoting Reversible Redox Kinetics by Separator Architectures Based on CoS2 /HPGC Interlayer as Efficient Polysulfide-Trapping Shield for Li-S Batteries

Main obstacles from the shuttle effect and slow conversion rate of soluble polysulfide compromise the sulfur utilization and cycling life for lithium sulfur (Li-S) batteries. In pursuit of a practically viable high performance Li-S battery, a separator configuration (CoS₂ /HPGC/interlayer) as efficient polysulfide trapping barrier is reported. This configuration endows great advantages, particularly enhanced conductivity, promoted polysulfide trapping capability, accelerated sulfur electrochemistry, when using the functional interlayer for Li-S cells. Attributed to the above merits, such cell shows excellent cyclability, with a capacity of 846 mAh g^-1 after 250 cycles corresponding to a high capacity retention of 80.2% at 0.2 C, and 519 mAh g^-1 after 500 cycles at 1C (1C = 1675 mA g^-1 ). In addition, the optimized separator exhibits a high initial areal capacity of 4.293 mAh cm^-2 at 0.1C. Moreover, with CoS₂ /HPGC/interlayer, the sulfur cell enables a low self-discharge rate with a very high capacity retention of 97.1%. This work presents a structural engineering of the separator toward suppressing the dissolution of soluble Li₂ Sn moieties and simultaneously promoting the sulfur conversion kinetics, thus achieving durable and high capacity Li-S batteries.

Nanoengineering to achieve high efficiency practical lithium-sulfur batteries

Rapidly increasing markets for electric vehicles (EVs), energy storage for backup support systems and high-power portable electronics demand batteries with higher energy densities and longer cycle lives. Among the various electrochemical energy storage systems, lithium-sulfur (Li-S) batteries have the potential to become the next generation rechargeable batteries because of their high specific energy at low cost. However, the development of practical Li-S batteries for commercial products has been challenged by several obstacles, including unstable cycle life and low sulfur utilization. Only a few studies have considered the importance of low electrolyte and high sulfur loading to improve the overall energy densities of Li-S cells. This article reviews the recent developments of Li-S batteries that can meet the benchmarks of practical parameters and exceed the practical energy density of lithium-ion batteries (LIBs) including areal sulfur loading of at least 4 mg cm^-2, electrolyte to sulfur ratio of less than 10 μL mg^-1, and high cycling stability of over 300 cycles. This review presents the advancements in each component in Li-S batteries, including the enhancement of the electrochemical properties of sulfur cathodes, lithium anodes, or electrolytes. Also identified are several important strategies of nanoengineering and how they address the practical limitations of Li-S batteries to compete against LIBs. Additionally, perspectives on fundamentals, technology, and materials are provided for the development of Li-S batteries based on nanomaterials and nanoengineering so that they can enter the market of high energy density rechargeable storage systems.

A one-pot synthesis of hetero-Co9S8–NiS sheets on graphene to boost lithium–sulfur battery performance

Graphene decorated with hetero-Co₉S₈–NiS sheets have abundant active sites, which can efficiently catalyze the electrochemical conversion of lithium polysulfides in Li–S battery.