Three-dimensional P-doped carbon skeleton with built-in Ni2P nanospheres as efficient polysulfides barrier for high-performance lithium-sulfur batteries

Active MXene-Based Electrode Interface Chemistry for High Performance Li-S Battery: Design Strategies and Prospects

Lithium-sulfur (Li-S) battery with high capacity and energy density is a promising next-generation energy storage device. However, the shuttle effect of polysulfides causes the low utilization of sulfur and the side reactions at the electrode interface. The electrode/electrolyte interface determines the chemical activity of electrode and electrochemical reversibility as well as the cycling stability of battery. Therefore, the ideal electrode interface in Li-S battery depends on the sulfur loading, the fast ion diffusion, the effective utilization of active intermediates, and the uniform deposition of lithium ion on anode. MXene with two dimension layer structure, good conductivity, and abundant terminal groups can serve as the active interface carrier layer to load sulfur, anchor polysulfides, and accelerate ion transfer. This review summarizes three strategies of active MXene-based electrode interfaces including sulfur host interface, functional separator interface, and lithium anode interface based on the electrochemical principles and challenges of Li-S battery. In addition, the interfacial regulation and application of MXene-based materials focus on the electrochemical activity and reversibility of polysulfides in electrochemical process are also presented. Finally, the further prospective and challenges of MXene in Li-S battery are also discussed.

Polysulfide-mediating properties of nickel phosphide carbon composite nanofibers as free-standing interlayers for lithium-sulfur batteries

Issues such as the polysulfide shuttle effect and sulfur loss challenge the development of high-energy-density lithium-sulfur batteries. To address these limitations, a tailored approach is introduced using nickel phosphide carbon composite nanofibers (Ni x P/C) with controlled surface oxidation layers. These nanofibers feature a hierarchical structure that leverages the benefits of nickel phosphide nanoparticles and a carbonaceous matrix to enable efficient sulfur encapsulation and suppress polysulfide diffusion. Comprehensive characterization and electrochemical testing reveal that Ni x P/C, when employed as interlayers in a cell with a bio-waste-derived carbon-based sulfur cathode, significantly enhance electrochemical performance by increasing charge-discharge capacities and reducing charge-transfer resistance. Post-mortem analyses further show effective polysulfide trapping and conversion on the cathode side, preventing their shuttle to the anode, which results in a remarkable cycle stability of up to 200 cycles at 2C with a high discharge capacity of about 800 mA h g-1. These findings confirm the potential of Ni x P/C to improve lithium-sulfur battery technologies and demonstrate their applicability in diverse lithium-sulfur cell configurations.

In Situ Phosphorization for Constructing Ni5P2-Ni Heterostructure Derived from Bimetallic MOF for Li-S Batteries

Heterostructured materials commonly consist of bifunctions due to the different ingredients. For host material in the sulfur cathode of lithium-sulfur (Li-S) batteries, the chemical adsorption and catalytic activity for lithium polysulfides (LiPS) are important. This work obtains a Ni5P2-Ni nanoparticle (Ni5P2-NiNPs) heterostructure through a confined self-reduction method followed by an in situ phosphorization process using Al/Ni-MOF as precursors. The Ni5P2-Ni heterostructure not only has strong chemical adsorption, but also can effectively catalyze LiPS conversion. Furthermore, the synthetic route can keep Ni5P2-NiNPs inside of the nanocomposites, which have structural stability, high conductivity, and efficient adsorption/catalysis in LiPS conversion. These advantages make the assembled Li-S battery deliver a reversible specific capacity of 619.7 mAh g- 1 at 0.5 C after 200 cycles. The in situ ultraviolet-visible technique proves the catalytic effect of Ni5P2-Ni heterostructure on LiPS conversion during the discharge process.

Establishing Transition Metal Phosphides as Effective Sulfur Hosts in Lithium-Sulfur Batteries through the Triple Effect of "Confinement-Adsorption-Catalysis"

Structurally optimized transition metal phosphides are identified as a promising avenue for the commercialization of lithium-sulfur (Li-S) batteries. In this study, a CoP nanoparticle-doped hollow ordered mesoporous carbon sphere (CoP-OMCS) is developed as a S host with a "Confinement-Adsorption-Catalysis" triple effect for Li-S batteries. The Li-S batteries with CoP-OMCS/S cathode demonstrate excellent performance, delivering a discharge capacity of 1148 mAh g-1 at 0.5 C and good cycling stability with a low long-cycle capacity decay rate of 0.059% per cycle. Even at a high current density of 2 C after 200 cycles, a high specific discharge capacity of 524 mAh g-1 is maintained. Moreover, a reversible areal capacity of 6.56 mAh cm-2 is achieved after 100 cycles at 0.2 C, despite a high S loading of 6.8 mg cm-2 . Density functional theory (DFT) calculations show that CoP exhibits enhanced adsorption capacity for sulfur-containing substances. Additionally, the optimized electronic structure of CoP significantly reduces the energy barrier during the conversion of Li2 S4 (L) to Li2 S2 (S). In summary, this work provides a promising approach to optimize transition metal phosphide materials structurally and design cathodes for Li-S batteries.

Regulating Electrochemical Kinetics of CoP by Incorporating Oxygen on Surface for High-Performance Li-S Batteries

Lithium-sulfur (Li-S) batteries are widely studied because of their high theoretical specific capacity and environmental friendliness. However, the further development of Li-S batteries is hindered by the shuttle effect of lithium polysulfides (LiPSs) and the sluggish redox kinetics. Since the adsorption and catalytic conversion of LiPSs mainly occur on the surface of the electrocatalyst, regulating the surface structure of electrocatalysts is an advisable strategy to solve the obstacles in Li-S batteries. Herein, CoP nanoparticles with high oxygen content on surface embedded in hollow carbon nanocages (C/O-CoP) is employed to functionalize the separators and the effect of the surface oxygen content of CoP on the electrochemical performance is systematically explored. Increasing the oxygen content on CoP surface can enhance the chemical adsorption to lithium polysulfides and accelerate the redox conversions kinetics of polysulfides. The cell with C/O-CoP modified separator can achieve the capacity of 1033 mAh g-1 and maintain 749 mAh g-1 after 200 cycles at 2 C. Moreover, DFT calculations are used to reveal the enhancement mechanism of oxygen content on surface of CoP in Li-S chemistry. This work offers a new insight into developing high-performance Li-S batteries from the perspective of surface engineering.

Polar Electrocatalysts for Preventing Polysulfide Migration and Accelerating Redox Kinetics in Room-Temperature Sodium-Sulfur Batteries

Due to the high theoretical energy density, low cost, and rich abundance of sodium and sulfur, room-temperature sodium-sulfur (RT Na-S) batteries are investigated as the promising energy storage system. However, the inherent insulation of the S₈ , the dissolution and shuttle of the intermediate sodium polysulfides (NaPSs), and especially the sluggish conversion kinetics, restrict the commercial application of the RT Na-S batteries. To address these issues, various catalysts are developed to immobilize the soluble NaPSs and accelerate the conversion kinetics. Among them, the polar catalysts display impressive performance. Polar catalysts not only can significantly accelerate (or alter) the redox process, but also can adsorb polar NaPSs through polar-polar interaction because of their intrinsic polarity, thus inhibiting the notorious shuttle effect. Herein, the recent advances in the electrocatalytic effect of polar catalysts on the manipulation of S speciation pathways in RT Na-S batteries are reviewed. Furthermore, challenges and research directions to realize rapid and reversible sulfur conversion are put forward to promote the practical application of RT Na-S batteries.

Synthesis of the Ni2P-Co Mott-Schottky Junction as an Electrocatalyst to Boost Sulfur Conversion Kinetics and Application in Separator Modification in Li-S Batteries

To overcome the shuttling effect and sluggish conversion kinetics of polysulfides, a large number of catalysts have been designed for lithium-sulfur (Li-S) batteries. Herein, a Mott-Schottky junction catalyst composed of Co nanoparticles and Ni₂P was designed to improve polysulfide kinetics. Our investigations reveal the rearrangement of charges at the Schottky junction interface and the construction of the built-in electric field are crucial for lowering the activation energy of the dissolved Li₂S_n reduction and Li₂S nucleation reaction. Furthermore, a series of experimental and electrochemical tests were performed to demonstrate that the Schottky catalytic effect enhanced the synergistic catalytic effect. With a Ni₂P-Co@CNT catalyst, the battery exhibits an initial specific capacity of 874 mAh g^-1 at a rate of 4.0 C, and the decay rate per cycle is 0.049% in 700 cycles. Meanwhile, the battery shows 0.118% decay rate per cycle at 0.5 C in 100 cycles at a high sulfur loading of 10 mg cm^-2. The Schottky heterojunction structure proposed here has been shown to have a good catalytic effect on the reduction of Li₂S_n and nucleation of Li₂S, which provides a profound guidance for efficient and rational catalyst design.

Carbon Coated Metal-Based Composite Electrode Materials for Lithium Sulfur Batteries: A Review

Lithium-sulfur battery is one of the most promising secondary battery systems due to their high energy density and low material cost. During the past decade, great progress has been achieved in promoting the performances of Li-S batteries by addressing the challenges at the laboratory-level model systems. With growing attention paid to the application of Li-S batteries, new challenges at practical cell scales emerge as the bottleneck. However, challenges remain for the commercialization of lithium-sulfur batteries. The current review mainly focused on metal-based catalysts decorated-carbon materials for enhanced lithium sulfur battery performance. Firstly, the synthesis methods of various carbon-sulfur composites are discussed, as well as the influence of different material structures on the electrochemical performance. Secondly, a variety of catalysts, including metal atoms, metal oxides, sulfides, phosphides, nitrides, and carbide-decorated carbon nanomaterials, are systematically introduced to determine how lithium can be enhanced by suppressing polysulfides and promoting redox conversion reactions. Also, analyzed the multi-step electrochemical reaction mechanism of the battery during the charging and discharging process, and provide a feasible path for the practical application of high energy density lithium-sulfur batteries.

Two-in-one template-assisted construction of hollow phosphide nanotubes for electrochemical energy storage

In this work, the template-assisted method was used to develop novel Ni2P@PANI hollow nanotubes as a positive electrode material for supercapacitors by using prepared polyaniline (PANI) nanotubes as precursors, and...

Multifunctional Metal Phosphides as Superior Host Materials for Advanced Lithium-Sulfur Batteries

For the past few years, a new generation of energy storage systems with large theoretical specific capacity has been urgently needed because of the rapid development of society. Lithium-sulfur (Li-S) batteries are regarded as one of the most promising candidates for novel battery systems, since their resurgence at the end of the 20th century Li-S batteries have attracted ever more attention, attributed to their notably high theoretical energy density of 2600 W h kg^-1 , which is almost five times larger than that of commercial lithium-ion batteries (LIBs). One of the determining factors in Li-S batteries is how to design/prepare the sulfur cathode. For the sulfur host, the major technical challenge is avoiding the shuttling effect that is caused by soluble polysulfides during the reaction. In past decades, though the sulfur cathode has developed greatly, there are still some enormous challenges to be conquered, such as low utilization of S, rapid decay of capacity, and poor cycle life. This article spotlights the recent progress and foremost findings in improving the performance of Li-S batteries by employing multifunctional metal phosphides as host materials. The current state of development of the sulfur electrode of Li-S batteries is summarized by emphasizing the relationship between the essential properties of metal phosphide-based hybrid nanomaterials, the chemical reaction with lithium polysulfides and the latter's influence on electrochemical performance. Finally, trends in the development and practical application of Li-S batteries are also pointed out.

Achieving Fast and Durable Lithium Storage through Amorphous FeP Nanoparticles Encapsulated in Ultrathin 3D P-Doped Porous Carbon Nanosheets

Conversion-type transition-metal phosphide anode materials with high theoretical capacity usually suffer from low-rate capability and severe capacity decay, which are mainly caused by their inferior electronic conductivities and large volumetric variations together with the poor reversibility of discharge product (Li₃P), impeding their practical applications. Herein, guided by density functional theory calculations, these obstacles are simultaneously mitigated by confining amorphous FeP nanoparticles into ultrathin 3D interconnected P-doped porous carbon nanosheets (denoted as FeP@CNs) via a facile approach, forming an intriguing 3D flake-CNs-like configuration. As an anode for lithium-ion batteries (LIBs), the resulting FeP@CNs electrode not only reaches a high reversible capacity (837 mA h g^-1 after 300 cycles at 0.2 A g^-1) and an exceptional rate capability (403 mA h g^-1 at 16 A g^-1) but also exhibits extraordinary durability (2500 cycles, 563 mA h g^-1 at 4 A g^-1, 98% capacity retention). By combining DFT calculations, in situ transmission electron microscopy, and a suite of ex situ microscopic and spectroscopic techniques, we show that the superior performances of FeP@CNs anode originate from its prominent structural and compositional merits, which render fast electron/ion-transport kinetics and abundant active sites (amorphous FeP nanoparticles and structural defects in P-doped CNs) for charge storage, promote the reversibility of conversion reactions, and buffer the volume variations while preventing pulverization/aggregation of FeP during cycling, thus enabling a high rate and highly durable lithium storage. Furthermore, a full cell composed of the prelithiated FeP@CNs anode and commercial LiFePO₄ cathode exhibits impressive rate performance while maintaining superior cycling stability. This work fundamentally and experimentally presents a facile and effective structural engineering strategy for markedly improving the performance of conversion-type anodes for advanced LIBs.

A multifunctional separator based on scandium oxide nanocrystal decorated carbon nanotubes for high performance lithium-sulfur batteries

Rare earths (REs) and their oxides have aroused worldwide interest because of their unusual and remarkable properties, which mainly stem from the unique 4f orbital of REs. Research on their potential applications in electrochemical energy storage devices is just budding, and needs bold and active exploration. Here, a multifunctional Sc₂O₃@CNT-coated separator was developed and introduced into the Li-S battery system, simply by coating a thin and lightweight capping layer of a synthesized composite of Sc₂O₃ nanocrystal decorated carbon nanotubes (Sc₂O₃@CNTs) over one side of a commercial separator. The Li-S battery based on the Sc₂O₃@CNT-coated separator possesses very important properties, including high capacity, superior cycling stability, impressive rate performance, favorable anti-self-discharge capabilities, and greatly mitigated anode corrosion. Theoretical computation and experimental results demonstrate that such outstanding electrochemical properties originate from the synergy of CNTs and Sc₂O₃, which enables the Sc₂O₃@CNT-coated separator to achieve an optimal balance of multiple functions: (1) physically blocking polysulfide migration and acting as an upper current collector, (2) chemically anchoring polysulfide species, and (3) catalytically promoting the conversion of sulfur species into Li₂S₂/Li₂S. This work first applies Sc₂O₃ to Li-S batteries, and the encouraging results show great potential of rare earth oxides for producing high-performance energy storage devices.

3D hierarchical rose-like Ni2P@rGO assembled from interconnected nanoflakes as anode for lithium ion batteries

In recent years, anode materials of transition metal phosphates (TMPs) for lithium ion batteries have drawn a vast amount of attention, due to their high theoretical capacity and comparatively low intercalation potentials vs. Li/Li⁺.