Alloyed BiSb Nanoparticles Confined in Tremella-Like Carbon Microspheres for Ultralong-Life Potassium Ion Batteries

Recent Advances in Electrocatalytic C-N Coupling for Urea Synthesis

Urea, one of the most widely used nitrogen-containing fertilizers globally, is essential for sustainable agriculture. Improving its production is crucial for meeting the increasing demand for fertilizers. Electrocatalytic co-reduction of CO₂ and nitrogenous compounds (NO₂-/NO₃-) has emerged as a promising strategy for green and energy-efficient urea synthesis. However, challenges such as slow reaction kinetics and complex multi-step electron transfers have hindered the development of efficient urea synthesis methods. This review explores recent advances in the electrocatalytic C-N coupling process, focusing on bimetallic catalysts, metal oxide/hydroxide catalysts, and carbon-based catalysts. The review also discusses the future prospects of designing effective catalysts for electrocatalytic C-N coupling to improve urea synthesis.

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.

Bismuth nanoparticles embedded in carbon fibers as flexible and free-standing anodes for efficient sodium ion batteries

Metallic bismuth is a promising anode electrode material for sodium ion batteries due to its high theoretical specific capacity. However, the formation of Na3Bi during the reaction process brings about significant volume changes and structural collapse of the electrode, resulting in the destruction of structures and a decrease in the cycling stability of sodium ion batteries. In this study, bismuth nanoparticles embedded in carbon fibers (Bi/CF) through a facile approach of electrospinning and calcination. Bi nanoparticles with diameters of approximately 20 nm were homogeneously dispersed in the carbon fibers, as confirmed by relevant morphological and structural features. The carbon fiber substrate can serve as a flexible and free-standing electrode, forming a conductive network to accelerate electron transport and ion diffusion. In light of this, Bi/CF anodes exhibit a high reversible capacity (376.6 mA h g-1 at 0.1 A g-1) and long-term cycle stability (only attenuates 0.12% in each cycle after 2000 times). This work provides a convenient and effective strategy for the synthesis of flexible and free-standing anodes for high-performance sodium ion batteries.

Stable Long-Persistent Luminescence from Self-Activated CaSb2O6 Induced by Intrinsic Defects

Long-persistent luminescence (LPL) materials have attracted intensive attention due to their fascinating emission after excitation. However, current LPL materials typically depend on external doping to introduce traps or emitting centers, resulting in a complex synthesis and controllability. For the first time, we develop another category of undoped LPL materials based on antimonate CaSb2O6, which exhibits blue LPL for over 8000 s. Both experimental and theoretical evidence indicate that excitons are trapped by intrinsic oxygen vacancies. Then, they are detrapped and recombine through singlet and triplet emission of Sb3+ to form LPL. Moreover, CaSb2O6 maintains approximately 100% of its initial LPL performance and structural integrity even after being treated under 1000 °C, UV irradiation, and extreme conditions (pH = 1 or 13). This study highlights the significant potential of antimonates as robust and versatile luminescent materials.

Chloride-Ion-Enriched Solid Electrolyte Interphase with Rapid Na+ Migration toward High-Performance Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have emerged as potential alternatives to lithium-ion batteries (LIBs), particularly for large-scale applications. Alloy-type anode materials for sodium-ion batteries are esteemed as prospective candidate materials for sodium-ion anodes, owing to their elevated theoretical capacity, heightened utilization efficiency, and minimal production of insulating byproducts. However, the severe volume changes and sluggish ion diffusion kinetics can lead to irreversible particle fragmentation and reaggregation phenomena, ultimately resulting in electrode degradation. Additionally, repetitive volume changes can cause an unstable solid electrolyte interphase (SEI). This study presents the synthesis of chloride-ion-modulated bimetallic SnSb/C nanoparticle anode materials, highlighting the following advantages: (i) Designing a bimetallic SnSb alloy structure serves to buffer the structural stresses generated during sodium insertion/extraction processes, effectively mitigating particle fracture phenomena induced by electrode material expansion/contraction. (ii) Nanostructuring both alloy materials enables the full utilization of active materials and shortens diffusion pathways, thereby significantly enhancing the diffusion rate of sodium ions. (iii) Introducing a carbonaceous matrix serves to alleviate self-agglomeration phenomena of the material during charge/discharge cycles, enhancing the material's conductivity and structural stability. (iv) Utilizing chloride-ion interface modification to achieve a chloride-rich solid-electrolyte interphase (SEI) enhances battery performance.

Encapsulating Bi Nanoparticles in Reduced Graphene Oxide with Strong Interfacial Bonding toward Advanced Potassium Storage

Bismuth (Bi) is regarded as a promising anode material for potassium ion batteries (PIBs) due to its high theoretical capacity, but the huge volume expansion during potassiation and intrinsic low conductivity cause poor cycle stability and rate capability. Herein, a unique Bi nanoparticles/reduced graphene oxide (rGO) composite is fabricated by anchoring the Bi nanoparticles over the rGO substrate through a ball-milling and thermal reduction process. As depicted by the in-depth XPS analysis, strong interfacial Bi-C bonding can be formed between Bi and rGO, which is beneficial for alleviating the huge volume expansion of Bi during potassiation, restraining the aggregation of Bi nanoparticles and promoting the interfacial charge transfer. Theoretical calculation reveals the positive effect of rGO to enhance the potassium adsorption capability and interfacial electron transfer as well as reduce the diffusion energy barrier in the Bi/rGO composite. Thereby, the Bi/rGO composite exhibits excellent potassium storage performances in terms of high capacity (384.8 mAh g-1 at 50 mA g-1), excellent cycling stability (197.7 mAh g-1 after 1000 cycles at 500 mA g-1 with no capacity decay) and superior rate capability (55.6 mAh g-1 at 2 A g-1), demonstrating its great potential as an anode material for PIBs.

3D Dense Encapsulated Architecture of 2D Bi Nanosheets Enabling Potassium-Ion Storage with Superior Volumetric and Areal Capacities

2D alloy-based anodes show promise in potassium-ion batteries (PIBs). Nevertheless, their low tap density and huge volume expansion cause insufficient volumetric capacity and cycling stability. Herein, a 3D highly dense encapsulated architecture of 2D-Bi nanosheets (HD-Bi@G) with conducive elastic networks and 3D compact encapsulation structure of 2D nano-sheets are developed. As expected, HD-Bi@G anode exhibits a considerable volumetric capacity of 1032.2 mAh cm-3, stable long-life span with 75% retention after 2000 cycles, superior rate capability of 271.0 mAh g-1 at 104 C, and high areal capacity of 7.94 mAh cm-2 (loading: 24.2 mg cm-2) in PIBs. The superior volumetric and areal performance mechanisms are revealed through systematic kinetic investigations, ex situ characterization techniques, and theorical calculation. The 3D high-conductivity elastic network with dense encapsulated 2D-Bi architecture effectively relieves the volume expansion and pulverization of Bi nanosheets, maintains internal 2D structure with fast kinetics, and overcome sluggish ionic/electronic diffusion obstacle of ultra-thick, dense electrodes. The uniquely encapsulated 2D-nanosheet structure greatly reduces K+ diffusion energy barrier and accelerates K+ diffusion kinetics. These findings validate a feasible approach to fabricate 3D dense encapsulated architectures of 2D-alloy nanosheets with conductive elastic networks, enabling the design of ultra-thick, dense electrodes for high-volumetric-energy-density energy storage.

Thermodynamic Origin-Based In Situ Electrochemical Construction of Reversible p-n Heterojunctions for Optimal Stability in Potassium Ion Storage

Heterojunctions in electrode materials offer diverse improvements during the cycling process of energy storage devices, such as volume change buffering, accelerated ion/electron transfer, and better electrode structure integrity, however, obtaining optimal heterostructures with nanoscale domains remains challenging within constrained materials. A novel in situ electrochemical method is introduced to develop a reversible CuSe/PSe p-n heterojunction (CPS-h) from Cu3PSe4 as starting material, targeting maximum stability in potassium ion storage. The CPS-h formation is thermodynamically favorable, characterized by its superior reversibility, minimized diffusion barriers, and enhanced conversion post K+ interaction. Within CPS-h, the synergy of the intrinsic electric field and P-Se bonds enhance electrode stability, effectively countering the Se shuttling phenomenon. The specific orientation between CuSe and PSe leads to a 35° lattice mismatch generates large space at the interface, promoting efficient K ion migration. The Mott-Schottky analysis validates the consistent reversibility of CPS-h, underlining its electrochemical reliability. Notably, CPS-h demonstrates a negligible 0.005% capacity reduction over 10,000 half-cell cycles and remains stable through 2,000 and 4,000 cycles in full cells and hybrid capacitors, respectively. This study emphasizes the pivotal role of electrochemical dynamics in formulating highly stable p-n heterojunctions, representing a significant advancement in potassium-ion battery (PIB) electrode engineering.

Novel Ultra-Stable 2D SbBi Alloy Structure with Precise Regulation Ratio Enables Long-Stable Potassium/Lithium-Ion Storage

The inferior cycling stabilities or low capacities of 2D Sb or Bi limit their applications in high-capacity and long-stability potassium/lithium-ion batteries (PIBs/LIBs). Therefore, integrating the synergy of high-capacity Sb and high-stability Bi to fabricate 2D binary alloys is an intriguing and challenging endeavor. Herein, a series of novel 2D binary SbBi alloys with different atomic ratios are fabricated using a simple one-step co-replacement method. Among these fabricated alloys, the 2D-Sb0.6 Bi0.4 anode exhibits high-capacity and ultra-stable potassium and lithium storage performance. Particularly, the 2D-Sb0.6 Bi0.4 anode has a high-stability capacity of 381.1 mAh g-1 after 500 cycles at 0.2 A g-1 (≈87.8% retention) and an ultra-long-cycling stability of 1000 cycles (0.037% decay per cycle) at 1.0 A g-1 in PIBs. Besides, the superior lithium and potassium storage mechanism is revealed by kinetic analysis, in-situ/ex-situ characterization techniques, and theoretical calculations. This mainly originates from the ultra-stable structure and synergistic interaction within the 2D-binary alloy, which significantly alleviates the volume expansion, enhances K+ adsorption energy, and decreases the K+ diffusion energy barrier compared to individual 2D-Bi or 2D-Sb. This study verifies a new scalable design strategy for creating 2D binary (even ternary) alloys, offering valuable insights into their fundamental mechanisms in rechargeable batteries.

Bismuth-Antimony Alloy Nanoparticles Embedded in 3D Hierarchical Porous Carbon Skeleton Film for Superior Sodium Storage

A composite film that features bismuth-antimony alloy nanoparticles uniformly embedded in a 3D hierarchical porous carbon skeleton is synthesized by the polyacrylonitrile-spreading method. The dissolved polystyrene is used as a soft template. The average diameter of the bismuth-antimony alloy nanoparticles is ~34.5 nm. The content of the Bi-Sb alloy has an impact on the electrochemical performance of the composite film. When the content of the bismuth-antimony alloy is 45.27%, the reversible capacity and cycling stability of the composite film are the best. Importantly, the composite film outperforms the bismuth-antimony alloy nanoparticles embedded in dense carbon film and the cube carbon nanobox in terms of specific capacity, cycling stability, and rate capability. The composite film can provide a discharge capacity of 322 mAh g-1 after 500 cycles at 0.5 A g-1, 292 mAh g-1 after 500 cycles at 1 A g-1, and 185 mAh g-1 after 2000 cycles at 10 A g-1. The carbon film prepared by the spreading method presents a unique integrated composite structure that significantly improves the structural stability and electronic conductivity of Bi-Sb alloy nanoparticles. The 3D hierarchical porous carbon skeleton structure further enhances electrolyte accessibility, promotes Na+ transport, increases reaction kinetics, and buffers internal stress.

Achieving Stable and Ultrafast Potassium Storage of Antimony Anode via Dual Confinement of MXene@Carbon Framework

Antimony-based anode materials are recognized for their high potassium storage capacities and appropriate operating potentials. However, the large volume expansion of Sb during the potassiation/depotassiation process, which results in a quick capacity decay, severely limits its practical application in potassium-ion batteries (PIBs). Here, a carbon-coated Sb/MXene heterostructure composite (CSM) is synthesized by adsorption of Sb3+ on MXene nanosheets via Sb-O-Ti bonds followed by carbothermic reduction to construct dual-confined MXene@carbon conductive framework capable of withstanding high volume expansion of Sb and conducive to enabling accelerated electron transfer kinetics. The CSM composite, particularly CSM-700, when configured as an anode for PIBs, realized high capacity (484.4 mAh g-1 at 0.1 A g-1 ), an ultra-stable cycling performance with a high reversible capacity of 435.9 mAh g-1 at 0.1 A g-1 after 100 cycles corresponding to a capacity retention rate of 90.0%, and superior rate performance of 323.0 mAh g-1 at 1 A g-1 . The proposed strategy offers a simple route to construct high-performance Sb-based anodes for advanced PIBs.

Unveiling the Nature of Ultrastable Potassium Storage in Bi0.48Sb1.52Se3 Composite

The conversion and alloying-type anodes for potassium-ion batteries (PIBs) have drawn attention. However, it is still a challenge to relieve the huge volume expansion/electrode pulverization. Herein, we synthesized a composite material comprising Bi_0.48Sb_1.52Se₃ nanoparticles uniformly dispersed in carbon nanofibers (Bi_0.48Sb_1.52Se₃@C). Benefiting from the synergistic effects of the high electronic conductivity of Bi_0.48Sb_1.52Se₃ and the mechanical confinement of the carbon fiber that buffers the large chemomechanical stress, the Bi_0.48Sb_1.52Se₃@C//K half cells deliver a high reversible capacity (491.4 mAh g^-1, 100 cycles at 100 mA g^-1) and an extraordinary cyclability (80% capacity retention, 1000 cycles at 1000 mA g^-1). Furthermore, the Bi_0.48Sb_1.52Se₃@C-based PIB full cells achieve a high energy density of 230 Wh kg^-1. In situ transmission electron microscopy (TEM) reveals an intercalation, conversion, and alloying three-step reaction mechanism and a reversible amorphous transient phase. More impressively, the nanofiber electrode can almost return to its original diameter after the potassiation and depotassiation reaction, indicating a highly reversible volume change process, which is distinct from the other conversion type electrodes. This work reveals the stable potassium storage mechanisms of Bi_0.48Sb_1.52Se₃@C composite material, which provides an effective strategy to enable conversion/alloying-type anodes for high performance PIBs for energy storage applications.

Understanding the Highly Reversible Potassium Storage of Hollow Ternary (Bi-Sb)2S3@N-C Nanocube

Metal sulfide anodes have aroused much attention in potassium ion batteries (PIBs) owing to their high theoretical capacities, but the sluggish kinetics and inferior cycling performance caused by severe volumetric change and particle pulverization greatly hinder their further development. Herein, robust hollow structure design together with phase structure engineering endow (Bi-Sb)₂S₃@N-C anode with superior (de)potassiation kinetics and excellent electrochemical performances in PIBs. Specifically, in situ X-ray diffraction combined with density functional theory calculations and ex situ X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy (TEM) analyses indicated a fresh reaction mechanism of (Bi-Sb)₂S₃ anode with a distinctive multistep (de)potassiation route along (003) plane of (Bi,Sb) alloy thanks to the Bi-Sb phase regulation in (Bi-Sb)₂S₃ anode, ensuring it with superior reaction kinetics. Moreover, in situ TEM characterization revealed the advantages of the hollow nanostructure with carbon shell, facilitating fast ion transport kinetics and high tolerance of volume change as well as enabling the structural integrity of electrode material during (de)potassiation. As a result, the (Bi-Sb)₂S₃ hollow nanocube with N-doped carbon shell ((Bi-Sb)₂S₃@N-C) delivers a high initial Coulombic efficiency of 66.3%, a great rate performance of 289 mAh g^-1 at 2.0 A g^-1, and an ultralong cycling life (89% retention after 220 cycles at 0.1 A g^-1 and 85% retention after 1600 cycles at 2.0 A g^-1) in PIBs. Furthermore, the full cell of (Bi-Sb)₂S₃@N-C//PTCDA affords a high reversible capacity of 281 mA h g^-1 at 1.0 A g^-1 after 300 cycles. This work combines structural design and in situ techniques, proving a successful nanostructure engineering strategy to rationalize alloy-type electrode materials for PIBs.

Electrochemical Self-Healing Nanocrystal Electrodes for Ultrastable Potassium-Ion Storage

The unique properties of self-healing materials hold great potential in battery systems, which can exhibit excellent deformability and return to its original shape after cycling. Herein, a Cu₃ BiS₃ anode material with self-healing mechanisms is proposed for use in ultrastable potassium-ion battery (PIB) and potassium-ion hybrid capacitor (PIHC). Different from the binder design, Cu₃ BiS₃ anode can exhibit the dual advantages of phase and morphological reversibility, further remaining original property after potassiation/depotassiation and exhibiting ultrastable cycling performance. The reversible electrochemical reconstruction during the continuous charge/discharge processes is beneficial to maintain the structure and function of the material. Furthermore, the conversion reactions during the charge and discharge process produce two advantages: i) suppressing the shuttle effect due to the formation of the heterostructure interface between Cu (111) and Bi (012); ii) Cu can avoid the agglomeration of Bi nanoparticles (NPs), further improving the electrochemical performance and long-cycle stability of the Cu₃ BiS₃ electrode. As a result, the Cu₃ BiS₃ electrode not only exhibits a long cycle life in half cells, but also 2000 cycles and 12000 cycles in PIB and PIHC full cells, respectively.

Bismuth nanoparticles embedded in a carbon skeleton as an anode for high power density potassium-ion batteries

Bismuth is a promising anode for potassium-ion batteries (PIBs) due to its suitable redox potential, large theoretical capacity, and superior electronic conductivity. Herein, we report a Bi@C (Bi nanoparticles uniformly embedded in a carbon skeleton) composite anode which delivers a superior rate performance of 244.3 mA h g-1 at 10.0 A g-1 and a reversible capacity of 255.6 mA h g-1 after 200 cycles in an optimized ether-based electrolyte. The outstanding electrochemical performance results from its robust structural design with fast reaction kinetics, which are confirmed by both experimental characterization studies and first-principles calculations. The reversible potassium storage mechanism of the Bi@C composite was also investigated by in situ X-ray diffraction. In addition, the full PIB cell assembled with a Bi@C composite anode and nickel-based Prussian blue analogue cathode exhibits high discharge voltage (3.18 V), remarkable power density (>10 kW kg-1), and an excellent capacity retention of 87.8% after 100 cycles. The results demonstrate that the PIBs with Bi anodes are promising candidates for power-type energy storage devices.

Boosting Interfacial Ion Transfer in Potassium-Ion Batteries via Synergy Between Nanostructured Bi@NC Bulk Anode and Electrolyte

Using high-capacity alloy-type anodes can greatly advance potassium-ion batteries (PIBs). However, the primary limits are unstable solid electrolyte interphase (SEI) and tough interfacial ion transfer associated with large-size K⁺ during electrochemical (de)alloy reactions. Here, we achieve excellent energy storage performance of PIBs via the synergy between a nanostructured Bi@N-doped carbon (Bi@NC) bulk anode and a KPF₆-dimethoxyethane (DME) electrolyte. The Bi@NC material with a high tap density of 3.81 g cm^-3 is prepared by simply pyrolyzing a commercial Bi salt yet affords a favorable nano/microstructure consisting of Bi nanograins confined in 3D ultrathin N-doped carbon shells, facilitating electron/ion transport and structural integrity. Detailed impedance spectroscopy investigation unveils that K⁺ transport through SEI at the Bi@NC anode, rather than the desolvation of K⁺, dominates the interfacial K⁺ transfer. More importantly, spectroscopic and microscopic characterizations provide clear evidence that the interplay between Bi@NC anode and optimized KPF₆-DME electrolyte can produce a unique SEI layer containing Bi³⁺-solvent complex that enables the activation energy of interfacial K⁺ transfer as low as 25.9 kJ mol^-1, thereby ultrafast charge transfer at Bi@NC. Consequently, the Bi@NC anode in half cells achieves exceptional rate capability (206 mAh g^-1 or 784 mAh cm^-3 at 120C) accompanied by high specific capacity (331 mAh g^-1 or 1261 mAh cm^-3) and long cycle life (running 1400 cycles at 15C with a tiny capacity fading rate of 0.013% per cycle). Moreover, the Bi@NC anode and KPF₆-DME electrolyte are also compatible with a potassium Prussian blue cathode and assembled full PIBs achieve stable cyclability (87.3% capacity retention after 100 cycles at 2.5C) and excellent rate performance (65.1% capacity retention upon increasing rates from 1 to 20C).

Amorphous Tellurium-Embedded Hierarchical Porous Carbon Nanofibers as High-Rate and Long-Life Electrodes for Potassium-Ion Batteries

Tellurium (Te) is a promising electrode active material for potassium-ion batteries due to its intrinsic electrical conductivity and ultra-high theoretical volumetric capacity. Nevertheless, Te-based electrodes usually exhibit low capacity at high rates and poor cycling stability caused by the large volume expansion and severe polytellurides dissolution. Herein, hierarchical porous carbon nanofibers (HPCNFs) film is utilized as a multifunctional Te substrate. The free-standing Te@HPCNFs electrode renders an outstanding K-ion storage performance with a high-rate capacity of 1294.4 mAh cm^-3 (207.1 mAh g^-1 _Te ) at 14C and ultra-long lifespan for 4500 cycles at 7C, and K-ion full batteries coupled with KSn alloy anode also exhibit good cyclability. Such a superior performance benefits from the space confinement of HPCNFs to load amorphous Te in the micropores for accommodating the volume change, where the interconnected conductive frameworks and residual hierarchical pores enable fast ion/electron diffusion kinetics. In situ UV-vis absorption spectra confirm that the detachment of polytellurides and K₂ Te from the electrode is effectively suppressed, and ex situ X-ray photoelectron spectroscopy analysis reveals the conversion of Te into K₅ Te₃ and K₂ Te. This work presents the significance of porous structure design of carbon matrix to construct high performance Te electrodes, which will be instructive for chalcogens-based energy-storage materials.

Highly Dispersed Antimony-Bismuth Alloy Encapsulated in Carbon Nanofibers for Ultrastable K-Ion Batteries

Antimony-based alloys have appealed to an ever-increasing interest for potassium ion storage due to their high theoretical capacity and safe voltage. However, sluggish kinetics and the large radius of K⁺ lead to limited rate performance and severe capacity fading. In this Letter, highly dispersed antimony-bismuth alloy nanoparticles confined in carbon fibers are fabricated through an electrospinning technology followed by heat treatment. The BiSb nanoparticles are uniformly confined into the carbon fibers, which facilitate rapid electron transport and inhibit the volume change during cycling owing to the synergistic effect of the BiSb alloy and carbon confinement engineering. Furthermore, the effect of a potassium bis(fluorosulfonyl)imide (KFSI) electrolyte with different concentrations has been investigated. Theoretical calculation demonstrates that the incorporation of Bi metal is favorable for potassium adsorption. The combination of delicate nanofiber morphology and electrolyte chemistry endows the fiber composite with an improved reversible capacity of 274.4 mAh g^-1, promising rate capability, and cycling stability upon 500 cycles.

Bean Pod-Like SbSn/N-Doped Carbon Fibers toward a Binder Free, Free-Standing, and High-Performance Anode for Sodium-Ion Batteries

Bimetallic SbSn alloy stands out among the anode materials for sodium-ion batteries (SIBs) because of its high theoretical specific capacity (752 mAh g^-1 ) and good electrical conductivity. However, the major challenge is the large volume change during cycling processes, bringing about rapid capacity decay. Herein, to cope with this issue, through electrostatic spinning and high temperature calcination reduction, the unique bean pod-like free-standing membrane is designed initially, filling SbSn dots into integrated carbon matrix including hollow carbon spheres and nitrogen-doped carbon fibers (B-SbSn/NCFs). Significantly, the synergistic carbon matrix not only improves the conductivity and flexibility, but provides enough buffer space to alleviate the large volume change of metal particles. More importantly, the B-SbSn/NCFs free-standing membrane can be directly used as the anode without polymer binder and conductive agent, which improves the energy density and reaction kinetics. Satisfyingly, the free-standing BSbSn/NCFs membrane anode shows excellent electrochemical performance in SIB. The specific capacity of the membrane electrode can maintain 486.9 mAh g^-1 and the coulombic efficiency is close to 100% after 400 cycles at 100 mA g^-1 . Furthermore, the full cell based on B-SbSn/NCFs anode also exhibits the good electrochemical performance.

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.

Metal-organic framework-derived nitrogen-doped carbon-confined CoSe2 anchored on multiwalled carbon nanotube networks as an anode for high-rate sodium-ion batteries

Metal selenides, as potential alternative candidates for sodium storage, have promising applicability due to their high theoretical specific capacity. However, their huge volume change and sluggish electrode kinetics during sodium ion uptake and release processes can result in insufficient cycling life and inferior rate performance, hindering their practical application. Herein, nitrogen (N)-doped carbon-confined cobalt selenide anchored on multiwalled carbon nanotube networks (denoted as CoSe₂@NC/MWCNTs) was designed and successfully built through a selenization process with ZIF-67 MOF as the template. The existence of the interconnected MWCNT network plays a crucial role in not only enhancing the electronic conductivity and ion/electron-transfer efficiency but also ensuring structural stability. Consequently, the optimized CoSe₂@NC/MWCNTs composite delivers a high reversible capacity of 479.6 mA h g^-1 at a current rate of 0.2 A g^-1, accompanied by a 92.0% capacity retention over 100 cycles and a predominant rate performance of 227.4 mA h g^-1 even under 20 A g^-1 when examined as the anode in Na-ion batteries. Moreover, the kinetic behaviors were confirmed using CV profiles at various rates, as well as the galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS). Besides, the HRTEM images clearly reveal the sodium-ion storage mechanism of the CoSe₂ hybrid. These results make CoSe₂@NC/MWCNTs a prospective anode material in advanced sodium-ion batteries.

Confining MoSe2 Nanosheets into N-Doped Hollow Porous Carbon Microspheres for Fast-Charged and Long-Life Potassium-Ion Storage

The potassium-ion battery (PIB) is the most promising alternative to a lithium-ion battery (LIB). Exploitation of a suitable electrode material is crucial to promote the development of PIBs. The MoSe₂ material has attracted much attention due to its high theoretical capacity, unique layered structure, and good conductivity. However, the potassium storage property of MoSe₂ has been suffering from structural fragmentation and sluggish reaction kinetic caused by large potassium ions upon insertion/extraction, which needs to be further improved. Herein, the MoSe₂ nanosheets are confined into N-doped hollow porous carbon microspheres (MoSe₂@N-HCS) by spray drying and high-temperature selenization. It delivers a superior rate performance of 113.7 mAh g^-1 at 10 A g^-1 and remains at a high capacity of 158.3 mAh g^-1 at 2 A g^-1 even after 16 700 cycles for PIBs. The excellent electrochemical performance can be attributed to unique structure, N-doping, and robust chemical bonds. The storage mechanism of MoSe₂ for potassium ions was explored. The outstanding properties of MoSe₂@N-HCS make it a promising anode material for PIBs.

Bi@C Nanospheres with the Unique Petaloid Core-Shell Structure Anchored on Porous Graphene Nanosheets as an Anode for Stable Sodium- and Potassium-Ion Batteries

Bismuth (Bi) has emerged as a prospective candidate as Na-ion and potassium-ion battery anodes because of its unique advantages of low cost, high theoretical gravimetric capacity (386 mAh g^-1), and superior volumetric capacity (3800 mAh cm^-3). However, the low electronic conductivity and the huge volume expansion of Bi during the alloying/dealloying reactions are extremely detrimental to cycling stability, which seriously hinder its practical application. To overcome these issues, we propose a rational design: Bi@C nanospheres with the unique petaloid core-shell structure are synthesized in one step for the first time and then combined with different contents of graphene (GR) nanosheets to form the composites Bi@C@GR. The Bi@C nanospheres with a core-shell structure are beneficial to shortening the transmission path of electrons/ions and reducing the risk from structural rupture of the particles during cycling. In addition, the combination of Bi@C nanospheres and porous GR could greatly improve the conductivity and prevent the aggregation of particles, which is conducive to better cycling stability and rate performance. Consequently, Bi@C@GR-2 presents a superior reversible capacity for sodium storage (300 mAh g^-1 over 80 cycles) and potassium storage (200 mAh g^-1 over 70 cycles) at 0.1 A g^-1. Furthermore, in situ electrochemical impedance spectroscopy and ex situ transmission electron microscopy are carried out to analyze and reflect the kinetic reaction mechanism and the phase change of the Bi@C@GR-2 electrode during the charge/discharge processes.