Efficient Polysulfide Redox Enabled by Lattice-Distorted Ni3Fe Intermetallic Electrocatalyst-Modified Separator for Lithium-Sulfur Batteries

Favorable Moderate Adsorption of Polysulfide on FeNi3 Intermetallic Compound Accelerating Conversion Kinetics for Advanced Lithium-Sulfur Batteries

Sluggish conversion kinetics of polysulfides during discharge and the severe shuttle effect significantly hinder the practical application of lithium-sulfur (Li-S) batteries. In this work, the lattice engineering strategy of Fe hybridization is employed to manipulate the bulk phase spacing of FeNi3 (space group Pm3m) intermetallic compounds to adjust the 3d electronic structure, optimizing the adsorption of polysulfides, thereby accelerating the catalytic conversion. As a result, FeNi2.25@OC achieves favorable moderate adsorption toward polysulfides. Due to the larger number of electrons occupying the lowest occupied molecular orbital of Li2S4, the S-S bonds are weakened and broken. Temperature-dependent experiments confirm that FeNi2.25@OC exhibits the lowest activation energy and can effectively accelerate the catalytic conversion of polysulfides. The Li-S cell assembled with FeNi2.25@OC modified PP separator delivers a high initial discharge specific capacity of 1219.5 mAh g-1 at 0.2 C. Even at a high sulfur loading of 6.06 mg cm-2 and lean electrolyte conditions (6 µL mg-1), it can cycle stably for 60 cycles.

Boron dopant- and nitrogen defect-decorated C3N5 porous nanostructure as an efficient sulfur host for lithium-sulfur batteries

Active site implantation and morphology manipulation are efficient protocols for boosting the electrochemical performance of carbon nitrides. As a promising sulfur host for lithium-sulfur batteries (LSBs), in this study, C3N5 porous nanostructure incorporated with both boron (B) atoms and nitrogen (N) defects was constructed (denoted as ND-B-C3N5) using a two-step strategy, i.e., pyrolysis of the mixture of 3-amino-1,2, 4-triazole and boric acid to obtain B-doped C3N5 porous nanostructure and then KOH etching under hydrothermal condition to generate N defects. The doped B atoms in the C3N5 porous nanostructure are in the form of B-N bonds and grafted B-O bonds. N defects are primarily created at the CN-C positions of the triazine unit, leaving behind some N vacancies and cyano groups. Benefiting from the involvement of B dopants and N defects, the optimized ND-B-C3N5-12 sample exhibits ameliorative conductivity, mass transport, lithium polysulfides (LiPSs) adsorption ability, diffusion of Li+ ions, Li2S deposition capacity, sulfur redox polarization, and a reversible solid-solid sulfur redox process. Consequently, the ND-B-C3N5-12/S cathode delivers accelerated redox performance of polysulfides for LSBs, revealing capacities of 1091 ± 44 and 753 ± 20 mAh/g at 0.2C for the initial and 300th cycles, respectively. The ND-B-C3N5-12/S cathode is also endowed with desired sulfur redox activity and stability at 2C for 1000 cycles, holding an initial discharging capacity of 788 ± 24 mAh/g and a low decay rate of 0.05 % per cycle.

Porous FeNi Prussian blue cubes derived carbon-based phosphides as superior sulfur hosts for high-performance lithium-sulfur batteries

In contrast to lithium-ion batteries, lithium-sulfur batteries have higher theoretical energy density and lower cost, so they would become competitive in the practical application. However, the shuttle effect of polysulfides and slow oxidation-reduction kinetics can degrade their electrochemical performance and cycle life. In this work, we have first developed the porous FeNi Prussian blue cubes as precursors. The calcination in different atmospheres was employed to make precursors convert into common pyrolysis products or novel carbon-based phosphides, and sulfides, labeled as FeNiP/A-C, FeNiP/A-P, and FeNiP/A-S. When these products serve as host materials in the sulfur cathode, the electrochemical performance of lithium-sulfur batteries is in the order of S@FeNiP/A-P > S@FeNiP/A-S > S@FeNiP/A-C. Specifically, the initial discharge capacity of S@FeNiP/A-P can reach 679.1 mAh g-1at 1 C, and the capacity would maintain 594.6 mAh g-1after 300 cycles. That is because the combination of carbon-based porous structure and numerous well-dispersed Ni2P/Fe2P active sites contribute FeNiP/A-P to obtain larger lithium-ion diffusion, lower resistance, stronger chemisorption, and more excellent catalytic effect than other samples. This work may deliver that metal-organic framework-derived carbon-based phosphides are more suitable to serve as sulfur hosts than carbon-based sulfides or common pyrolysis products for enhancing Li-S batteries' performance.

Nickel and nickel oxide nanoparticle-embedded functional carbon nanofibers for lithium sulfur batteries

Lithium-sulfur (Li-S) batteries are attracting tremendous attention owing to their critical advantages, such as high theoretical capacity of sulfur, cost-effectiveness, and environment-friendliness. Nevertheless, the vast commercialisation of Li-S batteries is severely hindered by sharp capacity decay upon operation and shortened cycle life because of the insulating nature of sulfur along with the solubility of intermediate redox products, lithium polysulfides (LiPSs), in electrolytes. This work proposes the use of multifunctional Ni/NiO-embedded carbon nanofibers (Ni/NiO@CNFs) synthesized by an electrospinning technique with the corresponding heat treatment as promising free-standing current collectors to enhance the kinetics of LiPS redox reactions and to provide prolonged cyclability by utilizing more efficient active materials. The electrochemical performance of the Li-S batteries with Ni/NiO@CNFs with ∼2.0 mg cm-2 sulfur loading at 0.5 and 1.0C current densities delivered initial specific capacities of 1335.1 mA h g-1 and 1190.4 mA h g-1, retrieving high-capacity retention of 77% and 70% after 100 and 200 cycles, respectively. The outcomes of this work disclose the beneficial auxiliary effect of metal and metal oxide nanoparticle embedment onto carbon nanofiber mats as being attractively suited up to achieve high-performance Li-S batteries.

Porous Ni3Fe intermetallic compounds as efficient and stable catalysts for the hydrogen evolution reaction in alkaline solutions

It is crucial to develop cost-effective novel non-noble metal catalysts with high activity and durability for large-scale industrial hydrogen production via water splitting. Here, based on a facile powder metallurgy method, Ni3Fe intermetallic electrodes with porous structures and controllable phases have been designed and fabricated by sintering mixed Ni and Fe powders under an Ar atmosphere. The effects of sintering temperature on the morphology, porous structure and phase composition of the intermetallic were studied. The resultant Ni3Fe-900 intermetallic electrode exhibits promising HER activity in alkaline electrolytes with an overpotential of 112 mV to drive a current density of 10 mA cm-2. Additionally, the Ni3Fe-900 intermetallic electrode shows good alkali corrosion resistance and stability in the HER process at a current density as high as 500 mA cm-2 for 24 h with no significant changes of the surface morphology, porous structure and phases. The efficient HER performance of the Ni3Fe-900 electrode is attributed to the unique intrinsic activity of the intermetallic electrode, increased accessible active sites originating from the porous structure and accelerated charge transfer. This work provides new insights into the design of electrocatalysts for industrial large-scale hydrogen production by water splitting.

Application of Inorganic Quantum Dots in Advanced Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have emerged as one of the most attractive alternatives for post-lithium-ion battery energy storage systems, owing to their ultrahigh theoretical energy density. However, the large-scale application of Li-S batteries remains enormously problematic because of the poor cycling life and safety problems, induced by the low conductivity , severe shuttling effect, poor reaction kinetics, and lithium dendrite formation. In recent studies, catalytic techniques are reported to promote the commercial application of Li-S batteries. Compared with the conventional catalytic sites on host materials, quantum dots (QDs) with ultrafine particle size (<10 nm) can provide large accessible surface area and strong polarity to restrict the shuttling effect, excellent catalytic effect to enhance the kinetics of redox reactions, as well as abundant lithiophilic nucleation sites to regulate Li deposition. In this review, the intrinsic hurdles of S conversion and Li stripping/plating reactions are first summarized. More importantly, a comprehensive overview is provided of inorganic QDs, in improving the efficiency and stability of Li-S batteries, with the strategies including composition optimization, defect and morphological engineering, design of heterostructures, and so forth. Finally, the prospects and challenges of QDs in Li-S batteries are discussed.

MOF-Derived Hollow Carbon Supported Nickel-Cobalt Alloy Catalysts Driving Fast Polysulfide Conversion for Lithium-Sulfur Batteries

Transition-metal compounds can be used as electrocatalysts to expedite polysulfide conversion effectively in lithium-sulfur batteries. However, insufficient conductivity and tedious preparation process still limit their practical applications. In this work, NiCo alloy nanoparticles embedded in hollow carbon spheres (NiCo@HCS) are fabricated via a facile, template-free strategy from the NiCo-metal-organic framework (MOF) precursor and used as electrocatalysts for separator modification. NiCo@HCS can not only improve the adsorption capacity of polysulfides by d-band deviation to the Fermi level but also reduce the energy barrier in the process of catalytic polysulfide conversion. Due to favorable three-dimensional (3-D) morphology, improved adsorption, and promoted kinetics of NiCo@HCS, the battery containing the NiCo@HCS-modified separator gives a starting capacity of 1377 mAh g^-1 at 0.2C, which is retained by 72% over 500 charge/discharge operations at 1.0C current density. Moreover, the battery's start capacity reaches 1180 mAh g^-1 (5.9 mAh cm^-2) with a high sulfur content of 5.0 mg cm^-1 at 0.2C.

Coordinating Interface Polymerization with Micelle Mediated Assembly Towards Two-Dimensional Mesoporous Carbon/CoNi for Advanced Lithium-Sulfur Battery

Lithium-sulfur battery has attracted significant attention by virtues of their high theoretical energy density, natural abundance, and environmental friendliness. However, the notorious shuttle effect of polysulfides intermediates severely hinders its practical application. Herein, a novel 2D mesoporous N-doped carbon nanosheet with confined bimetallic CoNi nanoparticles sandwiched graphene (mNC-CoNi@rGO) is successfully fabricated through a coordinating interface polymerization and micelle mediated co-assembly strategy. mNC-CoNi@rGO serves as a robust host material that endows lithium-sulfur batteries with a high reversible capacity of 1115 mAh g^-1 at 0.2 C after 100 cycles, superior rate capability, and excellent cycling stability with 679.2 mAh g^-1 capacity retention over 700 cycles at 1 C. With sulfur contents of up to 5.0 mg cm^-2 , the area capacity remains to be 5.1 mAh cm^-2 after 100 cycles at 0.2 C. The remarkable performance is further resolved via a series of experimental characterizations combined with density functional theory calculations. These results reveal that the ordered mesoporous N-doped carbon-encapsulated graphene framework acts as the ion/electron transport highway with excellent electrical conductivity, while bimetallic CoNi nanoparticles enhance the polysulfides adsorption and catalytic conversion that simultaneously accelerate the multiphase sulfur/polysulfides/sulfides conversion and inhibit the polysulfides shuttle.

Regeneration of Activated Sludge into SiO2-Decorated Heteroatom-Doped Porous Carbon as Advanced Electrodes for Li-S Batteries

The regeneration of harmful activated sludge into an energy source is an important strategy for municipal sludge treatment and recycling. Herein, SiO₂-modified N,S auto-doped porous carbon (NSC@SiO₂) with high conductivity (70 S m^-1) is successfully obtained through a simple calcination method of the activated sludge from wastewater treatment. Further, P-doped NSC@SiO₂ (NSPC@SiO₂) is designed to achieve a higher surface area (891 m² g^-1 vs 624 m² g^-1), a larger pore volume (0.87 cm³ g^-1 vs 0.08 cm³ g^-1), and more carbon defects. Due to its special structure, NSPC@SiO₂ is used as a sulfur host of lithium-sulfur batteries. The results of polysulfide adsorption experiments, S 2p X-ray photoelectron spectra (XPS), Li₂S nucleation experiments, polysulfide symmetric cells, measurement of the galvanostatic intermittent titration (GITT), polarization voltage difference, lithium-ion diffusion rate, and Tafel slope verified that NSPC@SiO₂ greatly improved the adsorption capacity of polysulfides, lowered the barrier to Li₂S formation and the internal resistances of cells, and accelerated Li⁺ ion diffusion and the reaction kinetics of polysulfide conversion, resulting in the excellent performance of polysulfide capture and superior rate performance and cyclic stability. By comparing NSPC@SiO₂ with NSC@SiO₂, a higher initial capacity (1377 mAh g^-1 vs 1150 mAh g^-1 at 0.1C), better rate capacity (912 mAh g^-1 vs 719 mAh g^-1 at 2C), and low capacity decay (0.094% per cycle within 200 cycles) are obtained. Our work provides direction for the treatment, disposal, and resource utilization of activated sludge.

Catalytic effects of Ni nanoparticles encapsulated in few-layer N-doped graphene and supported by N-doped graphitic carbon in Li–S batteries†

Although lithium–sulfur batteries possess the highest theoretical capacity and lowest cost among all known rechargeable batteries, their commercialization is still hampered by the intrinsic disadvantages of low conductivity of sulfur and polysulfide shuttle effect, which is most critical. Considerable research efforts have been dedicated to solving these difficulties for every part of Li–S batteries. Separator modification with metal electrocatalysts is a promising approach to overcome the major part of these disadvantages. This work focuses on the development of Ni nanoparticles encapsulated in a few-layer nitrogen-doped graphene supported by nitrogen-doped graphitic carbon (Ni@NGC) with different metal loadings as separator modifications. The effect of metal loading on the Li–S electrochemical reaction kinetics and performance of Li–S batteries was investigated. Controlling the Ni loading allowed for the modulation of the surface area-to-metal content ratio, which influenced the reaction kinetics and cycling performance of Li–S cells. Among the separators with different Ni loadings, the one with 9 wt% Ni exhibited the most efficient acceleration of the polysulfide redox reaction and minimized the polysulfide shuttling effect. Batteries with this separator retained 77.2% capacity after 200 cycles at 0.5C, with a high sulfur loading of ∼4.0 mg cm⁻², while a bare separator showed 51.3% capacity retention after 200 cycles under the same conditions. This work reveals that there is a vast utility space for carbon-encapsulated Ni nanoparticles in electrochemical energy storage devices with optimal selection and rational design.

Ni@NGC with different contents of Ni coated onto the surface of commercial separators effectively suppresses the polysulfide shuttle effect and enhances the electrochemical reaction kinetics and overall performance of a Li–S battery.

In Situ Constructing a Stable Solid Electrolyte Interface by Multifunctional Electrolyte Additive to Stabilize Lithium Metal Anodes for Li-S Batteries

Lithium (Li) metal is considered to be the most promising anode due to the ultrahigh capacity and extremely low electrochemical potential. The tricky thing is that the growth of dendritic Li brings huge safety hazards to Li metal batteries. Herein, we demonstrate cerium nitrate as a multifunctional electrolyte additive to form a stable solid electrolyte interface on the metallic Li anode surface for durable Li-S batteries. The presence of Ce³⁺ helps to modulate the electroplating/stripping of Li and inhibits the growth of dendritic Li. An excellent cycle life exceeding 1400 h at the current density of 1 mA cm^-2 can be realized in symmetric Li||Li cells. In addition, the in situ formed robust solid-electrolyte interface (SEI) layer containing cerium sulfide on the Li anode surface conduces to weaken the reducibility of Li and regulate the electrochemical dissolution/deposition reaction on the Li anode. Surprisingly, by virtue of cerium nitrate additive with a low concentration of 0.03 M, the Li-S batteries can afford a capacity of 553 mA h g^-1 at 5 C and a long cycle life at 1 C with a high capacity retention of 70.4%. Therefore, this study provides a novel idea to realize a uniform and dendrite-free Li anode for practical Li-S batteries.

Bimetal CoNi Active Sites on Mesoporous Carbon Nanosheets to Kinetically Boost Lithium-Sulfur Batteries

In order to solve the problem that soluble polysulfide intermediates diffuse between cathode and anode during charging and discharging, which leads to rapid attenuation of battery cycle life, the separator modification materials come into people's sight. Herein, a mesoporous carbon-supported cobalt-nickel bimetal composite (CoNi@MPC) is synthesized and directly coated on the original separator to serve as a secondary collector for lithium-sulfur batteries. CoNi@MPC exhibits multiple Co-Ni active sites, able to catalyze the reactions of soluble polysulfides, specifically accelerating the generation and decomposition of insoluble Li₂ S in lithiation and delithiation process testified by the electrochemical results and density functional theory calculation. Relying on the bifunctionality of CoNi@MPC composite, the shuttle effect of lithium polysulfides can be effectively alleviated. Moreover, porous carbon as the conductive scaffold favors the improvement of electronic conductivity. Benefiting from the above advantages, the cell with CoNi@MPC separator indicates significantly enhanced electrochemical performances with excellent cycling life over 500 cycles and superior rate capabilities.

An in-situ electrodeposited cobalt selenide promotor for polysulfide management targeted stable Lithium-Sulfur batteries

Lithium-sulfur batteries (LSBs) have attracted much attention due to their high theoretical specific capacity, energy density and low cost. However, the commercial application of LSBs is hindered due to the lithium polysulfide (LiPS) shuttle as well as the sluggish reaction kinetics. Herein, cobalt selenide (Co_0.85Se) nanowire arrays have been constructed on a carbon-modified separator by an in-situ electrodeposition technique without any other post-treatments such as coating with other ancillary materials. The introduced three-dimensional (3D) conductive carbon layer comprising of carbon nanotube (CNT) and acetylene black (AB) not only serves as the effective support for Co_0.85Se (CS) but also builds a hierarchical structure to promote the e^- transfer. The as-obtained CS-CNT/AB presents a strong anchoring effect on LiPSs and high electrocatalytic activity for sulfur reaction kinetics. As a result, the LSBs inserted with electrodeposition-enabled CS modified separator exhibit an outstanding rate capability (1560.4 mAh g^-1 at 0.1 C) and relatively low capacity decay of only 0.068% per cycle over 500 cycles at 2.0 C. This study provides a promising strategy to realize the rational construction of high-efficiency and long-life LSBs.

To Promote the Catalytic Conversion of Polysulfides Using Ni-B Alloy Nanoparticles on Carbon Nanotube Microspheres under High Sulfur Loading and a Lean Electrolyte

Despite their high theoretical energy density, the application of lithium-sulfur batteries is seriously hindered by the polysulfide shuttle and sluggish kinetics, especially with high sulfur loading and under low electrolyte usage. Herein, to facilitate the conversion of lithium polysulfides, nickel-boron (Ni-B) alloy nanoparticles, dispersed uniformly on carbon nanotube microspheres (CNTMs), are used as sulfur hosts for lithium-sulfur batteries. It is demonstrated that Ni-B alloy nanoparticles can not only anchor polysulfides through Ni-S and B-S interactions but also exhibit high electrocatalytic capability toward the conversion of intermediate polysulfide species. In addition, the intertwined CNT microspheres provide an additional conductive scaffold in response to the fast electrochemical redox. The enhanced redox kinetics is beneficial to improve the specific capacity and cycling stability of the sulfur cathode, based on the fast conversion of lithium polysulfides and effective deposition of the final sulfide products. Conclusively, the S/Ni-B/CNTM composite delivers a high specific capacity (1112.7 mAh g_s^-1) along with good cycle performance under both high sulfur loading (8.3 mg cm^-2) and a lean electrolyte (3 μL mg_s^-1). Consequently, this study opens up a path to design new sulfur hosts toward lithium-sulfur batteries.

Fe-cation Doping in NiSe2 as an Effective Method of Electronic Structure Modulation towards High-Performance Lithium-Sulfur Batteries

The commercialization of Li-S batteries is hindered by the shuttling of lithium polysulfides (LiPSs), the sluggish sulfur redox kinetics as well as the low sulfur utilization during charge/discharge processes. Herein, a free-standing cathode material was developed, based on Fe-doped NiSe₂ nanosheets grown on activated carbon cloth substrates (Fe-NiSe₂ /ACC) for high-performance Li-S batteries. Fe-doping in NiSe₂ plays a key role in the electronic structure modulation of NiSe₂ , enabling improved charge transfer with the adsorbed LiPSs molecules, stronger interactions with the active sulfur species and higher electrical conductivity. Effective promotion of the sulfur redox kinetics and enhanced sulfur utilization were achieved under high areal sulfur loadings. The stronger interactions with LiPSs together with the unique 3D structure of Fe-NiSe₂ /ACC also induced the transformation of Li₂ S₂ /Li₂ S growth from conventional 2D films to 3D particles, significantly eliminating the barriers of solid nucleation and growth during the phase transition of liquid LiPSs to solid Li₂ S₂ /Li₂ S. With a high sulfur loading of 9.9 mg cm^-2 , the Fe-NiSe₂ /ACC cathode enabled a high area capacity of 9.14 mAh cm^-2 with a low average decay of 0.11 % per cycle over 200 cycles at 0.1 C.

Catalytic separators with Co–N–C nanoreactors for high-performance lithium–sulfur batteries

An atomically dispersed supported metal catalyst with a Co–N₄ structure on active carbon (Co–N–C/AC) is prepared and introduced to modify the separators of Li–S batteries.