Three-Dimensionally Hierarchical Ni/Ni3S2/S Cathode for Lithium-Sulfur Battery

Synergistic Interaction of Strongly Polar Zinc Selenide and Highly Conductive Carbon Nanoframeworks Accelerates Redox Kinetics of Polysulfides

Lithium-sulfur batteries (LSBs) have become strong competitors in secondary battery systems because of their superior theoretical capacity and energy density. However, due to the serious shuttle effect of soluble long-chain lithium polysulfides (LiPSs) and the slow solid-solid reaction kinetics, LSBs face some specific challenges, such as a short cycle life and low rate performance. The introduction of selenide/carbon composites derived from zeolite imidazolate frameworks (ZIFs) into separator coatings is a direct and effective solution to the aforementioned problems. Here, a zinc selenide/carbon catalyst material (ZnSe@C) was constructed and employed to modify commercial polypropylene (PP) separators to accelerate the conversion of intermediates. The highly polar ZnSe effectively fixes the active material on the cathode side by transferring electrons between elements with LiPSs and improves the utilization rate of sulfur. Concurrently, the highly conductive carbon nanoskeleton generated following the pyrolysis of ZIF-8 ensures the rapid transfer of charges during the catalytic reaction. The prepared ZnSe@C has a large specific surface area (250.07 m2 g-1) and mesoporous ratio (78.03%), which not only enhances adsorption and catalysis but also promotes the penetration of the electrolyte and the transport of Li+. Based on this, ZnSe@C/PP separator cells exhibit a low average capacity decay rate of 0.051% per cycle after 500 cycles at 1 C.

Selecting non-metal doped FeS2 as efficient sulfur cathode host for enhanced Li-S redox chemistry

Lithium-sulfur batteries (LSBs) are considered as the development direction of the new generation energy storage system due to their high energy density and low cost. The slow redox kinetics of sulfur and the shuttle effect of lithium polysulfide (LiPS) are considered to be the main obstacles to the practical application of LSBs. Transition-metal sulfide as the cathode host can improve the Li-S redox chemistry. However, there has been no investigation of the application of FeS2 host in Li-S redox chemistry. Applying the first-principles calculations, we investigated the formation energy, band gap, Li+ diffusion, adsorption energy, catalytic performance and Li2 S decomposition barrier of FeAx S2-x (A=N, P, O, Se; x=0, 0.125, 0.25, 0.375) to explore the Li-S redox chemistry and finally select excellent host material. FeA0.25 S1.75 (A=P, Se) has a low Li+ diffusion barrier and superior electronic conductivity. FeO0.25 S1.75 is more favorable for LiPS adsorption, followed by FeP0.25 S1.75 . FeP0.25 S1.75 (001) shows a low overpotential for the Li-S redox chemistry. In summary, FeP0.25 S1.75 has more application potential in LSBs due to its physical and chemical properties, followed by FeSe0.25 S1.75 . This work provides theoretical guidance for the design and selection of the sulfur cathode host materials in LSBs.

Synergistic modulation in a triphasic Ni5P4-Ni2P@Ni3S2 system manifests remarkable overall water splitting

The potential for water splitting electrocatalysts with high efficiency paves the way for a sustainable future in hydrogen energy. However, this task is challenging due to the sluggish kinetics of the oxygen evolution reaction (OER), which has a significant impact on the hydrogen evolution reaction (HER). Herein multi-heterointerface of Ni5P4-Ni2P@Ni3S2 was fabricated by a two-step synthesis procedure that consist the development of Ni5P4-Ni2P nanosheets over nickel foam followed by the electrodeposition of Ni3S2. The HR-TEM analysis shows that the Ni5P4-Ni2P@Ni3S2 nanosheets array provide numerous well-exposed diverse heterointerfaces. The electrochemical investigations conducted on the Ni5P4-Ni2P@Ni3S2 nanosheets for complete water splitting indicate that they possess an overpotential of 73 mV and 230 mV in HER and OER respectively, enabling them to generate a current density of 10 and 50 mA cm-2. The nanosheets also demonstrate Tafel slope values of 95 mV dec-1 and 83 mV dec-1 for HER and OER, respectively. The HER stability of the catalyst was conducted for 45 h using chronoamperometric technique under a current density of 20 mA cm-1, while the stability test for OER was carried out at current densities of 100 and 200 mA cm-1 for 100 h each. Furthermore, in the overall water splitting, the catalyst exhibits a cell voltage of 1.47 V@10 mA cm-2 and displayed a stability operation for 100 h at a current density of 150 mA cm-1.

Watermelon Flesh-Like Ni3 S2 @C Composite Separator with Polysulfide Shuttle Inhibition for High-Performance Lithium-Sulfur Batteries

The shuttle effect limits the practical application of lithium-sulfur (Li-S) batteries with high specific capacity and cheap price. Herein, a three-dimensional carbon substrate containing Ni₃ S₂ nanoparticles is created to modify the separator. The in situ optical visualization battery proves that the material can realize the rapid conversion of Li₂ S₆ . Moreover, the impact of lithium-ion diffusion on the reactions in the cell is investigated, and the mechanism of Ni₃ S₂ @C in the cell is proposed based on the "adsorption-diffusion-conversion" mechanism. The "adsorption-diffusion-conversion" process of polysulfide is carried out on the surface of the composite separator, showing positive effects on the inhibition of polysulfide shuttle and the promotion of conversion. The separator is modified to improve sulfur utilization and reduce dead sulfur accumulation through a strategy of chemical immobilization and physical blocking. This helps to bridge the existing gaps of Li-S batteries.

Self-Supporting Multicomponent Hierarchical Network Aerogel as Sulfur Anchoring-Catalytic Medium for Highly Stable Lithium-Sulfur Battery

The low utilization rate of active materials, shuttle effect of lithium polysulfides (LiPSs), and slow reaction kinetics lead to the extremely low efficiency and poor high current cycle stability of lithium sulfur batteries (Li-S batteries). In this paper, a self-supporting multicomponent hierarchical network aerogel is proposed as the modified cathode (S/GO@MX@VS₄ ). It consists of graphene (GO) and MXene nanosheets (MX) loaded with VS₄ nanoparticles. The experimental results and first-principles calculations show that the GO@MX@VS₄ aerogel has strong adsorption and reversible conversion effects on LiPSs. It can not only inhibit the shuttle effect and improve the utilization rate of active substances by keeping the chain crystal structure of VS₄ , but also promote the reversibility and kinetics of the reaction by accelerating the liquid-solid transformation in the reduction process and the decomposition of insoluble Li₂ S in the oxidation process. The GO@MX@VS₄ aerogel modified cathode with a multicomponent synergy exhibits the capacity ratios (Q₁ /Q₂ ) at different discharge stages is close to the theoretical value (1:2.8), and the capacity decay per cycle is 0.019% in 1200 cycles at 5C. Also, a high areal capacity of 6.90 mAh cm^-2 is provided even at high sulfur loading (7.39 mg cm^-2 ) and low electrolyte/sulfur ratio (E/S, 8.0 µL mg^-1 ).

Constructing NiCo2Se4/NiCoS4 heterostructures for high-performance rechargeable aluminum battery cathodes

An aluminum battery based on the NiCo2Se4/NiCoS4 cathode delivers a capacity of 112 mA h g−1 after 195 cycles. The charge–discharge principle of the NiCo2Se4/NiCoS4 cathode is the Al3+ intercalation and valence state transition of the Ni, Co, and S elements.

Dual-role Magnesium Aluminate Ceramic Film as an Advanced Separator and Polysulfide Trapper in Li-S battery: Experimental and DFT investigations

Developing an advanced separator that could stop the polysulfide shuttling remains a work-in-progress in the Li-S battery domain. Most of the work reported so far concentrates on functionalizing the commercial...

Lithium-Sulfur Battery Cathode Design: Tailoring Metal-Based Nanostructures for Robust Polysulfide Adsorption and Catalytic Conversion

Lithium-sulfur (Li-S) batteries have a high specific energy capacity and density of 1675 mAh g^-1 and 2670 Wh kg^-1 , respectively, rendering them among the most promising successors for lithium-ion batteries. However, there are myriads of obstacles in the practical application and commercialization of Li-S batteries, including the low conductivity of sulfur and its discharge products (Li₂ S/Li₂ S₂ ), volume expansion of sulfur electrode, and the polysulfide shuttle effect. Hence, immense attention has been devoted to rectifying these issues, of which the application of metal-based compounds (i.e., transition metal, metal phosphides, sulfides, oxides, carbides, nitrides, phosphosulfides, MXenes, hydroxides, and metal-organic frameworks) as sulfur hosts is profiled as a fascinating strategy to hinder the polysulfide shuttle effect stemming from the polar-polar interactions between the metal compounds and polysulfides. This review encompasses the fundamental electrochemical principles of Li-S batteries and insights into the interactions between the metal-based compounds and the polysulfides, with emphasis on the intimate structure-activity relationship corroborated with theoretical calculations. Additionally, the integration of conductive carbon-based materials to ameliorate the existing adsorptive abilities of the metal-based compound is systematically discussed. Lastly, the challenges and prospects toward the smart design of catalysts for the future development of practical Li-S batteries are presented.

Metal-Based Electrocatalysts for High-Performance Lithium-Sulfur Batteries: A Review

The lithium-sulfur (Li-S) redox battery system is considered to be the most promising next-generation energy storage technology due to its high theoretical specific capacity (1673 mAh g−1), high energy density (2600 Wh kg−1), low cost, and the environmentally friendly nature of sulfur. Though this system is deemed to be the next-generation energy storage device for portable electronics and electric vehicles, its poor cycle life, low coulombic efficiency and low rate capability limit it from practical applications. These performance barriers were linked to several issues like polysulfide (LiPS) shuttle, inherent low conductivity of charge/discharge end products, and poor redox kinetics. Here, we review the recent developments made to alleviate these problems through an electrocatalysis approach, which is considered to be an effective strategy not only to trap the LiPS but also to accelerate their conversion reactions kinetics. Herein, the influence of different chemical interactions between the LiPS and the catalyst surfaces and their effect on the conversion of liquid LiPS to solid end products are reviewed. Finally, we also discussed the challenges and perspectives for designing cathode architectures to enable high sulfur loading along with the capability to rapidly convert the LiPS.

Coupling a Sponge Metal Fibers Skeleton with In Situ Surface Engineering to Achieve Advanced Electrodes for Flexible Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are regarded as promising next-generation energy storage systems, however, the uncontrollable dendrite formation and serious polysulfide shuttling severely hinder their commercial success. Herein, a powerful 3D sponge nickel (SN) skeleton plus in situ surface engineering strategy, to address these issues synergistically, is reported, and a high-performance flexible LSB device is constructed. Specifically, the rationally designed spray-quenched lithium metal on the SN matrix (solid electrolyte interface (SEI)@Li/SN), as dendrite inhibitor, combines the merits of the 3D lithiophilic SN skeleton and the in situ formed SEI layer derived from the spray-quenching process, and thereby exhibits a steady overpotential within 75 mV for 1500 h at 5 mA cm^-2 /10 mA h cm^-2 . Meanwhile, in situ surface sulfurization of the SN skeleton hybridizing with the carbon/sulfur composite (SC@Ni₃ S₂ /SN) serves as efficient lithium polysulfide adsorbent to catalyze the overall reaction kinetics. COMSOL Multiphysics simulations and density functional theory calculations are further conducted to explore the underlying mechanisms. As a proof of concept, the well-designed SEI@Li/SN||SC@Ni₃ S₂ /SN full cell shows excellent electrochemical performance with a negative/positive ratio in capacity of ≈2 and capacity retention of 99.82% at 1 C under mechanical deformation. The novel design principles of these materials and electrodes successfully shed new light on the development of flexible LSBs.

Crepe Cake Structured Layered Double Hydroxide/Sulfur/Graphene as a Positive Electrode Material for Li-S Batteries

Solving the polysulfide shuttle problem is one of the core challenges for the industrialization of lithium-sulfur batteries. In this work, a triphasic composite of LDH/sulfur/rGO (LDH: layered double hydroxide, rGO: reduced graphene oxide) with a crepe cake like structure is designed and fabricated as a positive electrode material for lithium-sulfur batteries. Sulfur nanoparticles are embedded in the interlayer space of the composite and thus are well protected physically via three-dimensional wrapping and chemically via strong interaction of LDH nanoflakes with lithium polysulfides, such as ionic bonds and S···H hydrogen bonds. In addition, the flexible lamellar structure of the composite with soft graphene layers can tolerate the volume expansion of sulfur during lithiation as well as facilitate ionic permeability and electron transport, which is favorable for the redox reactions of polysulfide. The present work sheds light on the future development and industrialization of lithium-sulfur batteries.

Probing the Extent of Polysulfide Confinement Using a CoNi2S4 Additive Inside a Sulfur Cathode of a Na/Li-Sulfur Rechargeable Battery

The extent of confinement of soluble metal polysulfides inside a sulfur cathode strongly determines the performance of metal-sulfur rechargeable batteries. This challenge has been largely tackled by loading sulfur inside various conducting porous scaffolds. However, this approach has not proven to be fully effective because of poor chemical interaction between the scaffold and polysulfides. Here, we demonstrate an excellent strategy of using a sulfide additive in the sulfur cathode, viz., cobalt nickel sulfide (CoNi₂S₄), to efficiently trap the soluble polysulfides inside the sulfur cathode. In situ Raman and ex situ UV-vis spectroscopies clearly reveal higher retention of polysulfides inside CoNi₂S₄/S compared to bare sulfur and carbon-sulfur mixture cathodes. Against sodium, the CoNi₂S₄/S assembly showed remarkable cyclability both as a function of current density (at room temperature) and temperature (at constant current density). The versatility of CoNi₂S₄ is further proven by the exemplary cyclability at various current densities at room temperature against lithium.

Self-supported molybdenum doping Ni3S2 nanoneedles as efficient bifunctional catalysts for overall water splitting

The as-obtained grass-like Ni₃S₂/NF-3 nanoneedle electrode exhibited superior electrocatalytic performance and extraordinary durability for the OER, the HER, and overall water splitting.

Programmed Design of a Lithium-Sulfur Battery Cathode by Integrating Functional Units

Sulfur is considered to be one of the most promising cathode materials due to its high theoretical specific capacity and low cost. However, the insulating nature of sulfur and notorious "shuttle effect" of lithium polysulfides (LiPSs) lead to severe loss of active sulfur, poor redox kinetics, and rapid capacity fade. Herein, a hierarchical electrode design is proposed to address these issues synchronously, which integrates multiple building blocks with specialized functions into an ensemble to construct a self-supported versatile cathode for lithium-sulfur batteries. Nickel foam acts as a robust conductive scaffold. The heteroatom-doped host carbon with desired lithiophilicity and electronic conductivity serving as a reservoir for loading sulfur can trap LiPSs and promote electron transfer to interfacial adsorbed LiPSs and Ni3S2 sites. The sulfurized carbon nanofiber forest can facilitate the Li-ion and electron transport and retard the LiPSs diffusion as a barrier layer. Sulfiphilic Ni3S2 acts as both a chemical anchor with strong adsorption affinity to LiPSs and an efficient electrocatalyst for accelerating kinetics for redox conversion reactions. Synergistically, all functional units promote the lithium ion coupled electron transfer for binding and redox conversion of LiPSs, resulting in high reversible capacities, remarkable cycle stability, and excellent rate capability.

2D Free-Standing Nitrogen-Doped Ni-Ni3 S2 @Carbon Nanoplates Derived from Metal-Organic Frameworks for Enhanced Oxygen Evolution Reaction

2D metal-organic frameworks (2D MOFs) are promising templates for the fabrication of carbon supported 2D metal/metal sulfide nanocomposites. Herein, controllable synthesis of a newly developed 2D Ni-based MOF nanoplates in well-defined rectangle morphology is first realized via a pyridine-assisted bottom-up solvothermal treatment of NiSO₄ and 4,4'-bipyridine. The thickness of the MOF nanoplates can be controlled to below 20 nm, while the lateral size can be tuned in a wide range with different amounts of pyridine. Subsequent pyrolysis treatment converts the MOF nanoplates into 2D free-standing nitrogen-doped Ni-Ni₃ S₂ @carbon nanoplates. The obtained Ni-Ni₃ S₂ nanoparticles encapsulated in the N-doped carbon matrix exhibits high electrocatalytic activity in oxygen evolution reaction. A low overpotential of 284.7 mV at a current density of 10 mA cm^-2 is achieved in alkaline solution, which is among the best reported performance of substrate-free nickel sulfides based nanomaterials.

Three-Dimensionally Porous Li-Ion and Li-S Battery Cathodes: A Mini Review for Preparation Methods and Energy-Storage Performance

Among many types of batteries, Li-ion and Li-S batteries have been of great interest because of their high energy density, low self-discharge, and non-memory effect, among other aspects. Emerging applications require batteries with higher performance factors, such as capacity and cycling life, which have motivated many research efforts on constructing high-performance anode and cathode materials. Herein, recent research about cathode materials are particularly focused on. Low electron and ion conductivities and poor electrode stability remain great challenges. Three-dimensional (3D) porous nanostructures commonly exhibit unique properties, such as good Li⁺ ion diffusion, short electron transfer pathway, robust mechanical strength, and sufficient space for volume change accommodation during charge/discharge, which make them promising for high-performance cathodes in batteries. A comprehensive summary about some cutting-edge investigations of Li-ion and Li-S battery cathodes is presented. As demonstrative examples, LiCoO₂, LiMn₂O₄, LiFePO₄, V₂O₅, and LiNi_1−x−yCo_xMn_yO₂ in pristine and modified forms with a 3D porous structure for Li-ion batteries are introduced, with a particular focus on their preparation methods. Additionally, S loaded on 3D scaffolds for Li-S batteries is discussed. In addition, the main challenges and potential directions for next generation cathodes have been indicated, which would be beneficial to researchers and engineers developing high-performance electrodes for advanced secondary batteries.

Chemical vapor deposition growth of carbon nanotube confined nickel sulfides from porous electrospun carbon nanofibers and their superior lithium storage properties

Multidimensional architecture design is a promising strategy to explore unique physicochemical characteristics by synergistically integrating different structural and compositional materials. Herein, we report the facile synthesis of a novel dendritic hybrid architecture, where carbon nanotubes (CNTs) with nickel sulfide nanoparticles encapsulated inside are epitaxially grown out of the porous electrospun N-doped carbon nanofibers (CNFs) (denoted as CNT@NS@CNFs) through a combined strategy of electrospinning and chemical vapor deposition (CVD). The adopted thiophene (C₄H₄S) not only serves as a carbon source for the growth of CNTs but also as a sulfur source for the sulfurization of Ni particles and S-doping into carbon matrices. When examined as an anode material for lithium-ion batteries (LIBs), the dendritic CNT@NS@CNFs display superior lithium storage properties including good cycle stability and high rate capability, delivering a high reversible capacity of 630 mA h g^-1 at 100 mA g^-1 after 200 cycles and 277 mA h g^-1 at a high rate of 1000 mA g^-1. These outstanding electrochemical properties can be attributed to the novel hybrid architecture, in which the encapsulation of nickel sulfide nanoparticles within the CNT/CNFs not only efficiently buffers the volume changes upon lithiation/delithiation, but also facilitates charge transfer and electrolyte diffusion owing to the highly conductive networks with open frame structures.

Novel Non-Carbon Sulfur Hosts Based on Strong Chemisorption for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered as promising candidates for energy storage systems owing to their high theoretical capacity and high energy density. The application of Li-S batteries is hindered by several obstacles, however, including the shuttle effect, poor electrical conductivity, and the severe volume expansion of sulfur. The traditional method is to integrate sulfur with carbon materials. But the interaction between polysulfide intermediates and carbon is only weak physical adsorption, which easily leads to the escape of species from the framework (shuttle effect) of the material causing capacity loss. Recently, however, there has been a trend for the introduction of novel non-carbon materials as sulfur hosts based on the strong chemisorption. This review highlights recent research progress on novel non-carbon sulfur hosts based on strong chemisorption, in Li-S batteries. In comparison with carbon-based sulfur hosts, most non-carbon sulfur hosts have been demonstrated to be polar host materials that could efficiently adsorb polysulfide via strong chemisorption, mitigating their dissolution. The intrinsic mechanism associated with the role of non-carbon-based host materials in improving the performance of Li-S batteries is discussed.

Cobalt-Doped Vanadium Nitride Yolk-Shell Nanospheres @ Carbon with Physical and Chemical Synergistic Effects for Advanced Li-S Batteries

Lithium-sulfur (Li-S) battery has been attracting increasing attention because of its high energy density and the presence of abundance of sulfur. However, its commercialization is still restricted owing to the low conductivity of sulfur, large volume expansion, and a severe polysulfide-shuttle effect. To address these problems, here, we have reported for the first time a simple template-free solvothermal method combined with a subsequent calcination method to prepare cobalt-doped vanadium nitride (VN) yolk-shell nanospheres, encapsulated in a thin layer of a nitrogen-doped carbon (Co-VN@C) composite as an ideal sulfur host. Benefiting from the unique structural advantages and the synergistic effect of conductive VN, cobalt, and nitrogen-doped carbon (NC), the obtained composite could not only facilitate the kinetics of polysulfide conversion as a functional catalyst but also physically confine and chemically absorb the polysulfides effectively. With these advantages, the batteries present a high initial discharge capacity of 1379.2 mAh g^-1 at 0.1 C (1 C is defined as 1675 mA g^-1), good rate performance, and excellent cycling performances (∼715 mAh g^-1 at 0.5 C after 200 cycles and ∼600 mAh g^-1 at 1 C after 300 cycles, respectively), even with a high areal sulfur loading of 4.07 mg cm^-2 (∼830 mAh g^-1 at 0.2 C after 100 cycles). These results demonstrate that the rationally designed multifunctional sulfur host material Co-VN@C has great potential for application in Li-S batteries.