Heterogeneous Structured Bi2S3/MoS2@NC Nanoclusters: Exploring the Superior Rate Performance in Sodium/Potassium Ion Batteries

Modulation of Surface/Interface States in Bi2S3/VS4 Heterostructure With CN Layer for High-Performance Sodium-Ion Batteries: Enhanced Built-in Electric Field and Polysulfide Capture

Metal sulfides are promising materials for sodium-ion batteries (SIBs) owing to unique structures and high theoretical capacity. However, issues like poor conductivity, large volume changes, and polysulfide dissolution limit practical application. This study introduces a novel Christmas tree-like heterostructure composed of Bi2S3 and VS4 encapsulated in nitrogen-doped carbon shell (Bi2S3/VS4@CN), synthesized by sulfurizing dopamine-coated BiVO4 precursor. The in situ synthesis ensures excellent lattice matching between Bi2S3 and VS4, minimizing interface states and enhancing effective built-in electric field. This design accelerates electrochemical reaction kinetics; moreover, it promotes progressive reaction that mitigates structural fragmentation, suppresses degradation, and prevents polysulfide dissolution and shuttle. Additionally, the CN shell effectively passivates the surface states of Bi2S3 and VS4 nanostructures, lowering surface barrier and improving overall conductivity. As a result, Bi2S3/VS4@CN-based half-SIBs demonstrate remarkable long-cycle stability, maintaining 387.1 mAh g-1 after 1600 cycles at 2 A g-1, and excellent rate performance with 376.3 mAh g-1 at 5 A g-1. Full-SIBs using Na3V2(PO4)3//Bi2S3/VS4@CN exhibit outstanding cycling stability, retaining 117.2 mAh g-1 after 200 cycles at 1 A g-1, along with 218 Wh kg-1 high energy density at 145.3 W kg-1. This work highlights the potential of heterostructures in advancing metal sulfide-based SIBs for high-performance energy storage.

Nitrogen and Sulfur-Codoped Carbon Nanotube-Encapsulated Co9S8 Nanoparticles for Efficient Lithium/Potassium Storage

Carbon materials stand out as anode materials in both lithium-ion batteries and potassium-ion batteries as they are capable of sustaining stable electrochemical cycles, yet limited reversible capacities hinder their further development for practical applications. In this work, carbon materials are rationally designed to integrate with metal sulfides, resulting in a structure of metal-catalyzed nitrogen and sulfur-codoped carbon nanotube-encapsulated Co9S8 nanoparticles. Synthesized by sequential chemical vapor deposition and a sulfidation process, this hybrid structure exhibits high capacities for lithium and potassium storage while maintaining long cycling stability. As a lithium-ion/potassium-ion battery anode, the hybrid delivers a reversible specific capacity (808/429 mA h g-1 at 0.1 A g-1), great rate performance (437/145 mA h g-1 at 10 A g-1), and excellent cyclability. Furthermore, a lithium-ion/potassium-ion hybrid capacitor utilizing this anode can attain substantial energy density and elevated power density (89 W h kg-1/136 W h kg-1 at 4750 W kg-1/1280 W kg-1) simultaneously. Detailed kinetic analyses show that the excellent electrochemical performance originates from a synergistic effect of Co9S8 and functional carbon at a certain ratio. This work may provide useful insights for the application of carbon-based anodes that chemically integrated with metal sulfides for electrochemical energy storage.

Advanced Bismuth-Based Anode Materials for Efficient Potassium Storage: Structural Features, Storage Mechanisms and Modification Strategies

Potassium-ion batteries (PIBs) are considered as a promising energy storage system owing to its abundant potassium resources. As an important part of the battery composition, anode materials play a vital role in the future development of PIBs. Bismuth-based anode materials demonstrate great potential for storing potassium ions (K+) due to their layered structure, high theoretical capacity based on the alloying reaction mechanism, and safe operating voltage. However, the large radius of K+ inevitably induces severe volume expansion in depotassiation/potassiation, and the sluggish kinetics of K+ insertion/extraction limits its further development. Herein, we summarize the strategies used to improve the potassium storage properties of various types of materials and introduce recent advances in the design and fabrication of favorable structural features of bismuth-based materials. Firstly, this review analyzes the structure, working mechanism and advantages and disadvantages of various types of materials for potassium storage. Then, based on this, the manuscript focuses on summarizing modification strategies including structural and morphological design, compositing with other materials, and electrolyte optimization, and elucidating the advantages of various modifications in enhancing the potassium storage performance. Finally, we outline the current challenges of bismuth-based materials in PIBs and put forward some prospects to be verified.

Realizing Ultrahigh Cycle Life Anode for Sodium-Ion Batteries through Heterostructure Design and Introducing Electro Active Polymer Coating

Bi2S3 has attracted increasing attention in sodium-ion batteries (SIBs) for its high theoretical capacity and low discharge platform. However, the sodium storage performance of Bi2S3 is limited by poor electrical conductivity and volume expansion during cycling. Herein, we report a special polypyrrole (PPy)-coated MoS2/Bi2S3 (MBS@PPy) heterostructure composite obtained by hydrothermal reaction as an anode material for SIB. As a result, the MBS@PPy composites demonstrate exceptional electrochemical performance in SIB, exhibiting a high capacity of 361.1 mA h g-1 at 10 A g-1 and showcasing remarkable rate performance. Even under a high current density of 35 A g-1, the specific capacity remains stable at 280 mA h g-1 after 2,000 cycles. Furthermore, a successfully assembled Na3V2(PO4)3//MBS@PPy sodium-ion full cell can achieve an impressive specific capacity of approximately 400 mA h g-1 after 300 cycles at 0.5 A g-1. In MBS@PPy composites, the polypyridine coating not only improves the interfacial conductivity of nanorods but also effectively inhibits the agglomeration between nanorods due to large volume changes. The MoS2 heterostructure further inhibits the coarsening of the internal structure, improves electron transport and reaction kinetics, and increases the rate capability of the material. This work provides an effective strategy to develop energy storage materials with superior electrochemical properties.

Olivine-Type Fe2GeX4 (X = S, Se, and Te): A Novel Class of Anode Materials for Exceptional Sodium Storage Performance

The introduction of abundant metals to form ternary germanium-based chalcogenides can dilute the high price and effectively buffer the volume variation of germanium. Herein, olivine-structured Fe2GeX4 (X = S, Se, and Te) are synthesized by a chemical vapor transport method to compare their sodium storage properties. A series of in situ and ex situ measurements validate a combined intercalation-conversion-alloying reaction mechanism of Fe2GeX4. Fe2GeS4 exhibits a high capacity of 477.9 mA h g-1 after 2660 cycles at 8 A g-1, and excellent rate capability. Furthermore, the Na3V2(PO4)3//Fe2GeS4 full cell delivers a capacity of 375.5 mA h g-1 at 0.5 A g-1, which is more than three times that of commercial hard carbon, with a high initial Coulombic efficiency of 93.23%. Capacity-contribution and kinetic analyses reveal that the alloying reaction significantly contributes to the overall capacity and serves as the rate-determining step within the reaction for both Fe2GeS4 and Fe2GeSe4. Upon reaching a specific cycle threshold, the assessment of the kinetic properties of Fe2GeX4 primarily relies on the ion diffusion process that occurs during charging. This work demonstrates that Fe2GeX4 possesses promising practical potential to outperform hard carbon, offering valuable insights and impetus for the advancement of ternary germanium-based anodes.

Synergy Between Surface Confinement and Heterointerfacial Regulations with Fast Electron/Ion Migration in InSe-PPy for Sodium-Ion Storage

Layered indium selenide (InSe) is a new 2D semiconductor material with high carrier mobility, widely adjustable bandgap, and high ductility. However, its ion storage behavior and related electrochemical reaction mechanism are rarely reported. In this study, InSe nanoflakes encapsulated in conductive polypyrrole (InSe@PPy) are designed in consideration of restraining the severe volume change in the electrochemical reaction and increasing conductivity via in situ chemical oxidation polymerization. Density functional theory calculations demonstrate that the construction of heterostructure can generate an internal electric field to accelerate electron transfer via additional driving forces, offering synergistically enhanced structural stability, electrical conductivity, and Na+ diffusion process. The resulting InSe@PPy composite shows outstanding electrochemical performance in the sodium ion batteries system, achieving a high reversible capacity of 336.4 mA h g-1 after 500 cycles at 1 A g-1 and a long-term cyclic stability with capacity of 274.4 mA h g-1 after 2800 cycles at 5 A g-1 . In particular, the investigation of capacity fluctuation within the first cycling reveals the alternating significance of intercalation and conversion reactions and evanescent alloying reaction. The combined reaction mechanism of insertion, conversion, and alloying of InSe@PPy is revealed by in situ X-ray diffraction, ex situ electrochemical impedance spectroscopy, and transmission electron microscopy.

Ultrahigh initial coulombic efficiency for deep sodium storage enabled by carbon-free vanadium-doping MoS2 hierarchical nanostructure

Molybdenum disulfide (MoS2) has garnered attention as a promising anode material for sodium-ion batteries due to its high theoretical capacity and unique lamellar texture. Nevertheless, unmodified MoS2 suffers from inferior electrical conductivity, poor reaction reversibility, and suboptimal cycle life upon repeated sodiation/desodiation. In this study, a novel carbon-free V-heteroatom doping MoS2 composite (abbr. VMS) with hierarchical laurustinus-like structure was synthesized by a facile one-step hydrothermal process. Specifically, the rational doping of V-atoms can effectively modulate the intrinsic electronic structure of pure MoS2, resulting in enhanced Na-ion diffusion rate, improved reaction kinetics and reduced activation energy compared to bare MoS2. Additionally, the hierarchical structure of the VMS composite, with sufficient spacing, effectively mitigates mechanical stress and ensures the integrity of active materials. Consequently, the prepared VMS composite possesses exceptional reaction reversibility (average ICE value of 92 %) and remarkable capacity retention (92.1 % after 450 cycles at 10 A/g). These findings contribute valuable insights into the development of advanced MoS2-based anode for sodium ion batteries.

Hetero-structural and hetero-interfacial engineering of MXene@Bi2S3/Mo7S8 hybrid for advanced sodium/potassium-ion batteries

Herein, heterogeneous bimetallic sulfides Bi2S3/Mo7S8 nanoparticles anchored on MXene (Ti3C2Tx) nanosheets (MXene@Bi2S3/Mo7S8) were prepared through a solvothermal process and subsequent chemical vapor deposition process. Benefiting from the heterogeneous structure between Bi2S3 and Mo7S8 and the high conductivity of the Ti3C2Tx nanosheets, the Na+ diffusion barrier and charge transfer resistance of this electrode are effectively decreased. Simultaneously, the hierarchical architectures of Bi2S3/Mo7S8 and Ti3C2Tx not only effectively inhibit the re-stacking of MXene and the agglomeration of bimetallic sulfides nanoparticles, but also dramatically relieve the volume expansion during the periodic charge/discharge processes. As a result, the MXene@Bi2S3/Mo7S8 heterostructure demonstrated remarkable rate capability (474.9 mAh/g at 5.0 A/g) and outstanding cycling stability (427.3 mAh/g after 1400 cycles at 1.0 A/g) for sodium ion battery. The Na+ storage mechanism and the multiple-step phase transition in the heterostructures are further clarified by the ex-situ XRD and XPS characterizations. This study paves a new way to design and exploit conversion/alloying type anodes of sodium ion batteries with hierarchical heterogeneous architecture and high-performance electrochemical properties.

Soft-Rigid Heterostructures with Functional Cation Vacancies for Fast-Charging and High-Capacity Sodium Storage

Optimizing charge transfer and alleviating volume expansion in electrode materials are critical to maximize electrochemical performance for energy-storage systems. Herein, an atomically thin soft-rigid Co9 S8 @MoS2 core-shell heterostructure with dual cation vacancies at the atomic interface is constructed as a promising anode for high-performance sodium-ion batteries. The dual cation vacancies involving VCo and VMo in the heterostructure and the soft MoS2 shell afford ionic pathways for rapid charge transfer, as well as the rigid Co9 S8 core acting as the dominant active component and resisting structural deformation during charge-discharge. Electrochemical testing and theoretical calculations demonstrate both excellent Na+ -transfer kinetics and pseudocapacitive behavior. Consequently, the soft-rigid heterostructure delivers extraordinary sodium-storage performance (389.7 mA h g-1 after 500 cycles at 5.0 A g-1 ), superior to those of the single-phase counterparts: the assembled Na3 V2 (PO4 )3 ||d-Co9 S8 @MoS2 /S-Gr full cell achieves an energy density of 235.5 Wh kg-1 at 0.5 C. This finding opens up a unique strategy of soft-rigid heterostructure and broadens the horizons of material design in energy storage and conversion.

Layer-Structured Anisotropic Metal Chalcogenides: Recent Advances in Synthesis, Modulation, and Applications

The unique electronic and catalytic properties emerging from low symmetry anisotropic (1D and 2D) metal chalcogenides (MCs) have generated tremendous interest for use in next generation electronics, optoelectronics, electrochemical energy storage devices, and chemical sensing devices. Despite many proof-of-concept demonstrations so far, the full potential of anisotropic chalcogenides has yet to be investigated. This article provides a comprehensive overview of the recent progress made in the synthesis, mechanistic understanding, property modulation strategies, and applications of the anisotropic chalcogenides. It begins with an introduction to the basic crystal structures, and then the unique physical and chemical properties of 1D and 2D MCs. Controlled synthetic routes for anisotropic MC crystals are summarized with example advances in the solution-phase synthesis, vapor-phase synthesis, and exfoliation. Several important approaches to modulate dimensions, phases, compositions, defects, and heterostructures of anisotropic MCs are discussed. Recent significant advances in applications are highlighted for electronics, optoelectronic devices, catalysts, batteries, supercapacitors, sensing platforms, and thermoelectric devices. The article ends with prospects for future opportunities and challenges to be addressed in the academic research and practical engineering of anisotropic MCs.

Recent Development Strategies for Bismuth-Driven Materials in Sustainable Energy Systems and Environmental Restoration

Bismuth(Bi)-based materials have gained considerable attention in recent decades for use in a diverse range of sustainable energy and environmental applications due to their low toxicity and eco-friendliness. Bi materials are widely employed in electrochemical energy storage and conversion devices, exhibiting excellent catalytic and non-catalytic performance, as well as CO₂ /N₂ reduction and water treatment systems. A variety of Bi materials, including its oxides, chalcogenides, oxyhalides, bismuthates, and other composites, have been developed for understanding their physicochemical properties. In this review, a comprehensive overview of the properties of individual Bi material systems and their use in a range of applications is provided. This review highlights the implementation of novel strategies to modify Bi materials based on morphological and facet control, doping/defect inclusion, and composite/heterojunction formation. The factors affecting the development of different classes of Bi materials and how their control differs between individual Bi compounds are also described. In particular, the development process for these material systems, their mass production, and related challenges are considered. Thus, the key components in Bi compounds are compared in terms of their properties, design, and applications. Finally, the future potential and challenges associated with Bi complexes are presented as a pathway for new innovations.

Nickel sulfide/nickel phosphide heterostructures anchored on porous carbon nanosheets with rapid electron/ion transport dynamics for sodium-ion half/full batteries

Nickel-based materials have been extensively deemed as promising anodes for sodium-ion batteries (SIBs) owing to their superior capacity. Unfortunately, the rational design of electrodes as well as long-term cycling performance remains a thorny challenge due to the huge irreversible volume change during the charge/discharge process. Herein, the heterostructured ultrafine nickel sulfide/nickel phosphide (NiS/Ni₂P) nanoparticles closely attached to the interconnected porous carbon sheets (NiS/Ni₂P@C) are designed by facile hydrothermal and annealing methods. The NiS/Ni₂P heterostructure promotes ion/electron transport, thus accelerating the electrochemical reaction kinetics benefited from the built-in electric field effect. Moreover, the interconnected porous carbon sheets offer rapid electron migration and excellent electronic conductivity, while releasing the volume variance during Na⁺ intercalation and deintercalation, guaranteeing superior structural stability. As expected, the NiS/Ni₂P@C electrode exhibits a high reversible specific capacity of 344 mAh g^-1 at 0.1 A g^-1 and great rate stability. Significantly, the implementation of NiS/Ni₂P@C//Na₃(VPO₄)₂F₃ SIB full cell configuration exhibits relatively satisfactory cycle performance, which suggests its widely practical application. This research will develop an effective method for constructing heterostructured hybrids for electrochemical energy storage.

Defective Bi2S3 Anchored on CuS/C as an Ultrafast and Long-Life Anode for Sodium-Ion Storage

Due to the high electrical conductivity and abundant redox active sites, bimetal sulfides are highly competitive anode materials for sodium storage with long-life and high-rate. Herein, a heterostructured metal sulfide (Bi₂S₃-CuS) with a carbon-based support is prepared by calcination and ion exchange methods. The synergistic effects of the heterostructure and defective structure provide facile diffusion channels, fast Na⁺ migration, and plentiful active sites for Na⁺, which reflect in the impressive electrochemical performance with a high reversible capacity of 592.2 mA h g^-1 after 1000 cycles at 8 A g^-1. Furthermore, the Na-ion full batteries exhibit an ultra-long cycling performance with a value of 216 mA h g^-1 after 4000 cycles at 10 A g^-1. Interestingly, the defective structure of Bi₂S₃ remains after cycling. Kinetic analyses and density functional theoretical calculations clarified that the heterointerfacial structure, especially on the interface containing sulfur defects in Bi₂S₃ of Bi₂S₃-CuS, could induce feasible ion adsorption and promote ion transfer, which lays the foundation for achieving ultrafast sodiation kinetics.

Rich Self-Generated Phase Boundaries of Heterostructured VS4 /Bi2 S3 @C Nanorods for Long Lifespan Sodium-Ion Batteries

Rationally designing on sundry multiphase compounds has come into the spotlight for sodium-ion batteries (SIBs) due to enhanced structural stability and improved electrochemical performances. Nevertheless, there is still a lack of thorough understanding of the reaction mechanism of high-active phase boundaries existing between multiphase compounds. Here, a VS₄ /Bi₂ S₃ @C composite anode for SIBs with rich phase boundaries in heterostructure is successfully synthesized. In situ X-ray diffraction analyses demonstrate a multistep redox mechanism in the heterostructures and ex situ transmission electron microscopy results confirm that tremendous self-generated phase boundaries are obtained and well-maintained during cycling, dramatically leading to stable reaction interfaces and better structural integrity. Combining experimental and theoretical results, a self-built-in electric field forming between phase boundaries acts as a dominate driving force for Na⁺ transport kinetics. Benefiting from the fast reaction kinetics of phase boundaries, the heterojunction provides an efficient approach to avoid abnormal voltage failure. As expected, the VS₄ /Bi₂ S₃ @C heterostructure displays superior sodium storage performances, especially an excellent long-term cycling stability (379.0 mAh g^-1 after 1800 cycles at a current density up to 2 A g^-1 ). This work confirms a critical role of phase boundaries on superior reversibility and structural stability, and provides a strategy for analogous conversion/alloying-type anodes.

Electrochemically Controllable Synthesis of Low-Valence Titanium Sulfides for Advanced Sodium Ion Batteries with Ultralong Cycle Life in a Wide Potential Window

Low-valence titanium sulfides (LVTS) have metal-like electrical conductivities and a strong polysulfide binding abilities, which are promising anodes for sodium ion batteries with high capacities and long cycle lifes. However, it is difficult for traditional synthesis methods to synthesize LVTS without impurities. The electric field regulation method possesses the advantages of flexibility and high efficiency, achieving accurate control of the metal reduction process by adjusting the electrolysis potential and reaction time. In this work, we synthesized a series of LVTS (TiS and Ti₂S) using electric field control methods and investigated their electrochemical behaviors as sodium storage anodes for the first time. Compared with traditional TiS₂, LVTS display remarkable Na storage properties under the condition of complete electrochemical conversion at 0.005-3 V. Especially for TiS, it demonstrates a high capacity of 409 mAh g^-1 at 1 A g^-1 and inspiring cyclic stability over 6000 cycles. The large number of vacancies in the crystal structure can chemically anchor polysulfides and alleviate their dissolution in the electrolyte, resulting in superior long-term cyclic stability. The high intrinsic conductivity of LVTS is in favor of rapid transfer of electrons and promotes the fast conversion of polysulfides to sodium sulfides, thus realizing high reversible capacities. Moreover, with its fast Na⁺ transport kinetics, the as-prepared TiS demonstrates an impressive rate performance of 321 mAh g^-1 at 15 A g^-1. Overall, the electric field regulation method is flexible and efficient, which provides a new route for the preparation of high-performance electrode materials. Moreover, nonstoichiometric metal compounds possess abundant active sites and rapid electron transport kinetics, which provide a new choice for promising sodium storage materials in large-scale energy storage applications.

Flat-Zigzag Interface Design of Chalcogenide Heterostructure toward Ultralow Volume Expansion for High-Performance Potassium Storage

Heterostructure construction of layered metal chalcogenides can boost their alkali-metal storage performance, where the charge transfer kinetics can be promoted by the built-in electric fields. However, these heterostructures usually undergo interface separation due to severe layer expansion, especially for large-size potassium accommodation, resulting in the deconstruction of heterostructures and battery performance fading. Herein, first a stable interface design strategy where two metal chalcogenides with totally different layer-morphologies are stacked to form large K⁺ transport channels, rendering ultralow interlayer expansion, is presented. As a proof of concept, the flat-zigzag MoS₂ /Bi₂ S₃ heterostructures stacked with zigzag-morphology Bi₂ S₃ and flat-morphology MoS₂ present an ultralow expansion ratio (1.98%) versus MoS₂ (9.66%) and Bi₂ S₃ (9.61%), which deliver an ultrahigh potassium storage capacity of above 600 mAh g^-1 and capacity retention of 76% after 500 cycles, together with the built-in electric field of heterostructures. Once the heterostructures are used as an anode for potassium-based dual-ion batteries (K-DIBs), it achieves a superior full-cell capacity of ≈166 mAh g^-1 with a capacity retention of 71% after 400 cycles, which is an outstanding performance among the reported K-DIBs. This proposed interface stacking strategy may offer a new way toward stable heterostructure design for metal ions storage and transport applications.

Fundamental Understanding and Research Progress on the Interfacial Behaviors for Potassium-Ion Battery Anode

Potassium-ion batteries (PIBs) exhibit a considerable application prospect for energy storage systems due to their low cost, high operating voltage, and superior ionic conductivity. As a vital configuration in PIBs, the two-phase interface, which refers to K-ion diffusion from the electrolyte to the electrode surface (solid-liquid interface) and K-ion migration between different particles (solid-solid interface), deeply determines the diffusion/reaction kinetics and structural stability, thus significantly affecting the rate performance and cyclability. However, researches on two-phase interface are still in its infancy and need further attentions. This review first starts from the fundamental understanding of solid-liquid and solid-solid interfaces to in-depth analyzing the effect mechanism of different improvement strategies on them, such as optimization of electrolyte and binders, heterostructure design, modulation of interlayer spacing, etc. Afterward, the research progress of these improvement strategies is summarized comprehensively. Finally, the major challenges are proposed, and the corresponding solving strategies are presented. This review is expected to give an insight into the importance of two-phase interface on diffusion/reaction kinetics, and provides a guidance for developing other advanced anodes in PIBs.

Coupling of Metallic VSe2 and Conductive Polypyrrole for Boosted Sodium-Ion Storage by Reinforced Conductivity Within and Outside

Although transitional metal dichalcogenides have been regarded as appealing electrodes for sodium/potassium-ion batteries (SIBs/PIBs) owing to their high theoretical capacity, it is a key challenge to realize dichalcogenide anodes with long-period cycling performance and high-rate capability because of their poor conductivity and large volumetric change. Herein, polypyrrole-encapsulated VSe₂ nanoplates (VSe₂@PPy) were prepared by the selenization of VOOH hollow nanospheres and subsequent in situ polymerization and coating by pyrrole. Benefiting from the inherent metallicity of VSe₂, the improvement in the conductivity and the structural protection provided by the PPy layer, the VSe₂@PPy nanoplates exhibited enhanced sodium/potassium-storage performances, delivering a superior rate capability with a capacity of 260.0 mA h g^-1 at 10 A g^-1 in SIBs and 148.6 mA h g^-1 at 5 A g^-1 in PIBs, as well as revealing an ultrastability in cycling of 324.6 mA h g^-1 after 2800 cycles at 4 A g^-1 in SIBs. Moreover, the insertion and conversion mechanisms of VSe₂@PPy in SIBs with intermediates of Na_0.6VSe₂, NaVSe₂, and VSe were elucidated by in situ/ex situ X-ray diffraction combined with ex situ transmission electron microscopy observation and in situ potentio-electrochemical impedance spectroscopy during the sodiation and desodiation processes. Density functional theory calculations show that the strong coupling between VSe₂ and PPy not only causes it to have a stronger total density of states and a built-in electric field, leading to an increased electrical conductivity, but also effectively decreases the ion diffusion barrier.

Encapsulation of BiOCl nanoparticles in N-doped carbon nanotubes as a highly efficient anode for potassium ion batteries

With gradually increasing cost and shrinking crustal abundance for lithium ion batteries (LIBs), it is necessary to develop potassium ion batteries (PIBs) and explore suitable electrode materials for advanced PIBs. In this work, nanoscale BiOCl nanoparticles encapsulated in N-doped carbon nanotubes (BiOCl@N-CNTs) are designed and used as the anode material for K ion storage. The BiOCl@N-CNT composite is composed of BiOCl nanoparticles (≈ 5 nm) and N-doped carbon nanotubes. The ultralsmall BiOCl nanoparticles offer excellent electrochemical activity for K ion storage and short ion diffusion path for rapid reaction kinetics, while the outer layer of N-CNTs can effectively improve the conductivity and provide space to accommodate volume expansion. Due to this synergistic effect of small size and a highly conductive skeleton, the BiOCl@N-CNT composite delivers good rate capability and long-term cycling stability when evaluated as an anode for PIBs. The special structure of embedding ultrasmall active materials with high performance in highly conductive N-CNTs represents an effective way of improving the activity of the electrode material, facilitating ion/charge transfer, and alleviating volume change towards excellent energy storage technology.

Structure Engineering of BiSbSx Nanocrystals Embedded within Sulfurized Polyacrylonitrile Fibers for High Performance of Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are regarded as promising candidates in next-generation energy storage technology; however, the electrode materials in PIBs are usually restricted by the shortcomings of large volume expansion and poor cycling stability stemming from a high resistance towards diffusion and insertion of large-sized K ions. In this study, BiSbS_x nanocrystals are rationally integrated with sulfurized polyacrylonitrile (SPAN) fibres through electrospinning technology with an annealing process. Such a unique structure, in which BiSbS_x nanocrystals are embedded inside the SPAN fibre, affords multiple binding sites and a short diffusion length for K⁺ to realize fast kinetics. In addition, the molecular structure of SPAN features robust chemical interactions for stationary diffluent discharge products. Thus, the electrode demonstrates a superior potassium storage performance with an excellent reversible capacity of 790 mAh g^-1 (at 0.1 A g^-1 after 50 cycles) and 472 mAh g^-1 (at 1 A g^-1 after 2000 cycles). It's one of the best performances for metal dichalcogenides anodes for PIBs to date. The unusual performance of the BiSbS_x @SPAN composite is attributed to the synergistic effects of the judicious nanostructure engineering of BiSbS_x nanocrystals as well as the chemical interaction and confinement of SPAN fibers.

The Multicomponent Synergistic Effect of Sandwich Structure Hierarchical Nanofibers for Enhanced Sodium Storage

Constructing hierarchical micro/nanostructures as anodes for sodium ion batteries is an important approach for exploiting efficient energy storage devices. Herein, sandwich structure hierarchical nanofibers composed of hollow carbon fibers as the substrate, and MoS₂ as the interlayer with Co and/or ZnS nanoparticles anchoring in carbon skeletons as the outer shell (carbon nanofiber/MoS₂ /Co-ZnS⊂NC) are prepared via a multistep reaction strategy. Profiting from the unique hierarchical structure, abundant migration channels of Na⁺ , and multicomponent synergistic effects, the rapid diffusion kinetics are ensured and the utilization of active materials is maximized. The coaxial structure can evenly disperse volumetric strain, making structural stability guaranteed. Hierarchical nanofibers deliver a high reversible capacity of 352.3 mAh g^-1 at 5.0 A g^-1 over 3000 cycles. A discharge capacity of 182.5 mAh g^-1 is retained even after 10 000 cycles at 10.0 A g^-1 as well as a high rate capacity of 202.0 mAh g^-1 up to 30 A g^-1 . The optimal atomic ratio of Co element is further verified by the kinetic analysis. The full-cells assembled with Na₃ V₂ (PO₄ )₃ cathode provide a high capacity of 179.2 mAh g^-1 at 1.0 A g^-1 for 500 cycles. Combining in situ and ex situ characterizations and theoretical calculations, possible sodium storage mechanisms and the origin of superior electrochemical properties are revealed.

Bismuth-based mixed-anion compounds for anode materials in rechargeable batteries

A facile solvothermal synthesis approach for chemical composition control in ternary Bi-S-I systems is reported by simply controlling the sulfide concentration. We demonstrate the application of these bismuth-based ternary mixed-anion compounds as high capacity anode materials in rechargeable batteries. Cells utilising Bi₁₃S₁₈I₂ achieved an initial capacity value of 807 mA h g^-1, while those with BiSI/Bi₁₃S₁₈I₂ a value of 1087 mA h g^-1 in lithium-ion battery systems.

Constructing Heterostructured Bimetallic Selenides on an N-Doped Carbon Nanoframework as Anodes for Ultrastable Na-Ion Batteries

Transition-metal selenides have been recognized as a class of promising anode materials for sodium-ion batteries (SIBs) on account of their high capacity. Nevertheless, the sluggish conversion kinetics and rapid capacity decay caused by insufficient conductivity and volume change restrain their applications. Herein, hollow heterostructured bimetallic selenides embedded in an N-doped carbon nanoframework (H-CoSe₂/ZnSe@NC) were prepared via a facile template-engaged method. Benefiting from the rich defect at the phase boundary of the CoSe₂/ZnSe heterostructure, pre-reserved cavity, and enhanced structure rigidity, the abovementioned issues are resolved at once, and the accelerated charge transportation kinetics traced by spectroscopy techniques and theoretical calculations certify the interface effect in the capacity release. In addition, ex situ X-ray photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy all confirm the high-reversible electrochemical conversion mechanism in H-CoSe₂/ZnSe@NC. Together with a reasonable structural architecture and the highly reversible conversion reaction, H-CoSe₂/ZnSe@NC displays a prominent rate capacity (244.8 mA h g^-1 at 10 A g^-1) as well as an ultralong lifespan (10,000 cycles at 10 A g^-1), highlighting the significance of structure control in fabricating high-performance anodes for SIBs.

Rod-like Ni0.5Co0.5C2O4·2H2O in-situ formed on rGO by an interface induced engineering: Extraordinary rate and cycle performance as an anode in lithium-ion and sodium-ion half/full cells

Transition metal oxalates have attracted wide attention due to the characteristics of the conversion reaction as anode materials in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), However, there are huge volume expansion and sluggish circulation dynamics during the reversible Li⁺ and Na⁺ insertion/extraction process, which would lead to unsatisfactory reversible capacity and stability. In order to solve these problems, a rod-like structure Ni_0.5Co_0.5C₂O₄·2H₂O is in-situ formed on the reduced graphene oxide layer (Ni_0.5Co_0.5C₂O₄·2H₂O/rGO) in a glycol-water mixture medium via an interface induced engineering strategy. Benefitting from the synergistic cooperation of nano-diameter rod-like structure and high conductive rGO networks, the experimental results show that the prepared Ni_0.5Co_0.5C₂O₄·2H₂O/rGO electrode has predominant rate performance and ultra-long cycle stability. For the LIBs, it not only exhibits an ultrahigh reversible capacity (1179.9 mA h g^-1 at 0.5 A g^-1 after 300 cycles), but also presents outstanding rate and cycling performance (646.5 mA h g^-1 at 5 A g^-1 after 1200 cycles). Besides, the Ni_0.5Co_0.5C₂O₄·2H₂O/rGO electrode displays remarkable sodium storage capacity of 221.6 mA h g^-1 after 100 cycles at 0.5 A g^-1. Further, the extraordinary electrochemical capability of Ni_0.5Co_0.5C₂O₄·2H₂O/rGO active material is also reflected in two full-cells, assembled using commercial LiCoO₂ as cathode for LIBs and commercial Na₃V₂(PO₄)₃ as cathode for SIBs, both of which can show wonderful specific capacity and cycling stability. It is found in in-situ Raman experiments that the reversible changes of oxalate peaks are monitored in a charge/discharge process, which is scientific evidence for the transform reaction mechanism of metal oxalates in LIBs. These findings not only provide important ideas for studying the charge/discharge storage mechanism but also give scientific basis for the design of high-performance electrode materials.

Facile Preparation of MoS2 Nanocomposites for Efficient Potassium-Ion Batteries by Grinding-Promoted Intercalation Exfoliation

Efficient exfoliations of bulk molybdenum disulfide (MoS₂ ) into few-layered nanosheets in pure phase are highly attractive because of the promising applications of the resulted 2D materials in diversified optoelectronic devices. Here, a new exfoliation method is presented to prepare semiconductive 2D hexagonal phase (2H phase) MoS₂ -cellulose nanocrystal (CNC) nanocomposites using grinding-promoted intercalation exfoliation (GPIE). This method with facile grinding of the bulk MoS₂ and CNC powder followed by conventional liquid-phase exfoliation in water can not only efficiently exfoliate 2H-MoS₂ nanosheets, but also produce the 2H-MoS₂ /CNC 2D nanocomposites simultaneously. Interestingly, the intercalated CNC sandwiched in MoS₂ nanosheets increases the interlayer spacing of 2H-MoS₂ , providing perfect conditions to accommodate the large-sized ions. Therefore, these nanocomposites are good anode materials of potassium-ion batteries (KIBs), showing a high reversible capacity of 203 mAh g^-1 at 200 mA g^-1 after 300 cycles, a good reversible capacity of 114 mAh g^-1 at 500 mA g^-1 , and a low decay of 0.02% per cycle over 1500 cycles. With these impressive KIB performances, this efficient GPIE method will open up a new avenue to prepare pure-phase MoS₂ and promising 2D nanocomposites for high-performance device applications.

Controllable synthesis of CoFe2Se4/NiCo2Se4 hybrid nanotubes with heterointerfaces and improved oxygen evolution reaction performance

The rational construction of heterointerfaces in hollow nanohybrids is considered as a promising and challenging approach for enhancing their electrocatalytic performance. Herein, we demonstrate the synthesis of CoFe₂Se₄/NiCo₂Se₄ hybrid nanotubes (CFSe/NCSe HNTs) with open ends and abundant heterointerfaces. The CFSe/NCSe HNT hybrid nanotubes are obtained by using NiCo₂-aspartic acid nanofibres (NiCo-Asp NFs) as the templates which can be converted to the CFSe/NCSe HNTs via proton etching, three metal coprecipitation, Kirkendall effect and anion-exchange reaction. The CFSe/NCSe HNTs may function as the oxygen evolution reaction (OER) electrocatalysts, and they exhibit a low overpotential of 224 mV at a current density of 10 mA cm^-2 and outstanding stability with only 1.4% current density change even after 15 h, superior to those of the reported single-component counterparts. The obtained density of states and differential charge density confirm the existence of a heterointerface which can induce the accumulation of electrons at the interface of CFSe-NCSe and consequently increase the carrier density and electrical conductivity of the CFSe/NCSe HNTs. This research provides a new avenue for the fabrication of hollow nanohybrids with heterointerfaces.