BiSb@Bi2O3/SbOx encapsulated in porous carbon as anode materials for sodium/potassium-ion batteries with a high pseudocapacitive contribution

Synergistic Effect of Anionic-Tuning and Architecture Engineering in BiPO4@C Anode for Durable and Fast Potassium Storage

Bismuth-based materials that adhere to the alloy/dealloy reaction mechanism are regarded as highly promising anode materials for potassium-ion batteries due to their high volume-specific capacity and moderate reaction potentials. However, their commercial viability has been limited by the effects of structural collapse due to volume distortion and impeded electron conduction, resulting in rapid capacity decline. In this work, a carbon-coated nanosized BiPO4 rod (BiPO4@C) was designed and fabricated to overcome the aforementioned challenges through the architecture engineering and anionic-tuning strategy. In particular, the nanosized nanorods significantly reduce the volume expansion; the incorporation of the bulk and open-skeleton anion PO43- serves to mitigate the considerable volume distortion and generates the high ionic conductivity product (K3PO4) to ameliorate the poor ionic transport due to the structural deformation. The elaborated BiPO4 rods exhibit high specific capacity (310.3 mAh g-1, at 500 mA g-1), excellent cycling stability (over 700 cycles at 500 mA g-1) and superior rate performance (137.8 mAh g-1, at 1000 mA g-1). Systematic ex-situ XRD and TEM, as well as kinetic tests, have revealed the "conversion-multistep alloying" reaction process and the "battery-capacitance dual-mode" potassium storage mechanism. Moreover, the thick electrodes showed excellent specific capacity and rate performance, demonstrating their significant application potential in the next generation of SIBs.

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.

Self-hybridization structures of BiOBr0.5Cl0.5: An ultra-high capacity anode material for half/full potassium-ion batteries

Potassium-ion batteries (PIBs) are gaining attention among emerging technologies for their cost-effectiveness and the abundance of resources they utilize. Within this context, bismuth oxyhalides (BiOX) have emerged as exceptional candidates for anode materials in PIBs due to their unique structural and superior electrochemical properties. However, challenges such as structural instability and low electronic conductivity remain to be addressed. In this study, a flower-like BiOBr0.5Cl0.5/rGO composite anode material was synthesized, demonstrating outstanding K+ storage performance. The self-hybridized structure enhances ion adsorption and diffusion, which in turn improves charge and discharge efficiency as well as long-term stability. In situ X-ray diffraction (XRD) tests confirmed the gradual release and alloying potassium storage mechanism of Bi metal, which occurs through the intermediate KxBiOBr0.5Cl0.5 phase within the BiOBr0.5Cl0.5 anode. This composite exhibited a high specific capacity of 246.4 mAh/g at 50 A/g and maintained excellent capacity retention after 2400 cycles at 5 A/g. Additionally, in full battery tests, it showed good rate performance and long cycle life, maintaining a discharge specific capacity of 119.6 mAh/g at a high current density of 10 A/g. Comprehensive characterizations revealed insights into the structural, electrochemical, and kinetic properties, advancing high-performance PIBs.

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.

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.

Bismuth-Antimony Alloy Embedded in Carbon Matrix for Ultra-Stable Sodium Storage

Alloy-type anodes are the most promising candidates for sodium-ion batteries (SIBs) due to their impressive Na storage capacity and suitable voltage platform. However, the implementation of alloy-type anodes is significantly hindered by their huge volume expansion during the alloying/dealloying processes, which leads to their pulverization and detachment from current collectors for active materials and the unsatisfactory cycling performance. In this work, bimetallic Bi-Sb solid solutions in a porous carbon matrix are synthesized by a pyrolysis method as anode material for SIBs. Adjustable alloy composition, the introduction of porous carbon matrix, and nanosized bimetallic particles effectively suppress the volume change during cycling and accelerate the electrons/ions transport kinetics. The optimized Bi₁Sb₁@C electrode exhibits an excellent electrochemical performance with an ultralong cycle life (167.2 mAh g^-1 at 1 A g^-1 over 8000 cycles). In situ X-ray diffraction investigation is conducted to reveal the reversible and synchronous sodium storage pathway of the Bi₁Sb₁@C electrode: (Bi,Sb) Na(Bi,Sb) Na₃(Bi,Sb). Furthermore, online electrochemical mass spectrometry unveils the evolution of gas products of the Bi₁Sb₁@C electrode during the cell operation.

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.

Sn-, Sb- and Bi-Based Anodes for Potassium Ion Battery

Owing to the abundant resources of potassium resources, potassium ion batteries (PIBs) hold great potential in various energy storage devices. However, the poor lifespan of PIBs anodes limit their merchant applications. The exploitation of anode materials with high performance is one of the critical factors to the development of PIBs. Metallic Sn-, Sb-, and Bi-based materials, show promising future thanks to their high theoretical capacities and safe working voltage. However, the rapid capacity decay caused by the large K⁺ is still a pivotal challenge. In this review, recent progresses on alloying anodes were summarized. Schemes, such as ultra-small nanoparticles, hetero-element doping, and electrolyte optimization are effective strategies to improve their electrochemical properties. This review provides an outlook on the nanostructures and their synthesis methods for the alloying-type materials, and will stimulate their intensive study for practical application in the near future.

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.

Heterostructured Bi2O3@rGO Anode for Electrochemical Sodium Storage

Bismuth oxide (Bi2O3) is an auspicious anode material for sodium-ion batteries owing to its high theoretical capacity and abundant Bi resources. However, the poor electronic conductivity and huge volume expansion of Bi2O3 during cycling lead to the low coulombic efficiency and unstable cycling stability. Aiming to suppress these issues, we use highly conductive reduced graphene oxide (rGO) as a continuous skeleton to fabricate a Bi2O3@rGO heterostructure. It exhibits high reversibility and stability for electrochemical sodium storage by delivering a reversible capacity of 161 mAh g−1 after 100 cycles at 50 mA g−1, which completely outperforms Bi2O3 (43 mAh g−1). In addition, the coulombic efficiency of the heterostructure stabilizes at >90% upon only 3 cycles. The results can be attributed to the dual function of rGO in supporting Bi2O3 nanoparticles and providing conductive pathways to fasten electron transport.

Implantation of Fe7S8 nanocrystals into hollow carbon nanospheres for efficient potassium storage

As a desirable candidate for lithium-ion batteries, potassium-ion batteries (PIBs) have aroused great interest because of their low cost and high power and energy densities. However, the insertion/extraction of K⁺ with a large radius (1.38 Å) usually bring about the destruction of the electrode materials. Here, ultrafine Fe₇S₈ nanocrystals are successfully implanted into hollow carbon nanospheres (Fe₇S₈@HCSs) via a facile solvothermal method and subsequent novel low-temperature sulfurization, which avoid the aggregation of Fe₇S₈ nanoparticles produced during high-temperature sulfidation. The ultrafine Fe₇S₈ nanoparticles and hollow carbon spheres can not only buffer the severe expansion/shrinkage of electrode materials caused by the repeated insertion/extraction of K⁺, but also provide additional accessible pathways for the high-rate K⁺ transmission. When tested as an anode material for PIBs, Fe₇S₈@HCSs achieve impressive K⁺ storage capacity of 523.2 mAh g^-1 at 0.1 A g^-1 after 100 cycles and remarkable rate capacity of 176.3 mAh g^-1 at 5 A g^-1. Further, assembling this anode with a K₂NiFe(CN)₆ cathode yields stable cycling performance, revealing its great potential for large-scale energy storage applications.

In-situ growth of Cu(2-methylimidazole imidazole)2 on Cu2O polyhedrons for high-performance potassium-ion batteries

In this work, Cu₂O/Cu(2-MeIm)₂ core-shell structure was designed and used as an anode for potassium-ion batteries. The Cu₂O core not only ensured a high energy density through surface redox reactions, but also served as a copper-ion reservoir to keep the stability of skeleton structure of Cu(2-MeIm)₂ shell during electrochemical process. The Cu(2-MeIm)₂ shell, in turn, not only provided high power through rapid K⁺ adsorption/desorption, but also acted as an artificial solid electrolyte interphase layer and accommodated volumetric change during K⁺ intercalation/de-intercalation. The as-designed composite material was studied by X-ray diffraction, thermo gravimetric, Fourier transform infrared, nitrogen adsorption-desorption, X-ray photoelectron spectroscopic and electron microscopic characterizations. As an anode for potassium-ion batteries, it was galvanostatically discharged and charged to study its electrochemical properties, such as Coulombic efficiency, capacity retention and rate performance, and cyclic voltammetry curves were also tested to reveal its K-storage mechanism.

Facile in-situ synthesis of heazlewoodite on nitrogen-doped reduced graphene oxide for enhanced sodium storage

Nickel sulfide based anode materials, featuring rich types, high specific capacities and favorable conversion kinetics, have been proved to be promisingly applied in high-performance sodium-ion batteries (SIBs). Unfortunately, the poor electronic/ionic conductivity, together with the structure change induced degraded capacity upon cycling, restricts their further development. In this work, heazlewoodite nanoparticles decorated on nitrogen doped reduced graphene oxide (Ni₃S₂/NrGO) were fabricated via a facile combined approach with freeze-drying and subsequent in-situ sulfidation. In the obtained hybrid structure, the synergistic effect between Ni₃S₂ and NrGO endows the composite with highly conductive pathways, thus accelerating the charge transfer. Benefitting from the buffering matrix offered by NrGO as well as the tight combination between Ni₃S₂ and NrGO, this novel Ni₃S₂/NrGO demonstrates satisfying sodium storage performance, with a stable reversible capacity of 299.2 mAh g^-1 up to 100 cycles (0.1 A g^-1) and a high initial Coulombic efficiency of 76.8%. Importantly, the rational structure design and synthesis method, as well as the insights on the improved electrochemical performance reported in this work, should be helpful for the development of new-type host materials with high performance for SIBs.

Efficient photocatalytic degradation of doxycycline by coupling α-Bi2O3/g-C3N4 composite and H2O2 under visible light

Antibiotic pollutants have posed a huge threat to the ecological environment and human health. In this work, α-Bi₂O₃/g-C₃N₄ composite was prepared and coupled with H₂O₂ for the rapid and efficient degradation of doxycycline (DOX) in water under visible light irradiation. The composite exhibited enhanced photocatalytic activity and 80.5% of DOX could be degraded in 120 min. The addition of H₂O₂ significantly improved the degradation efficiency of DOX under visible light, resulting in 79.0% of it degraded within 30 min, and the degradation rate constant of DOX was 3.6 times than that without H₂O₂. On the one hand, the Z-scheme heterojunction of α-Bi₂O₃/g-C₃N₄ promoted the separation rate of photogenerated electron-hole pairs, thereby enhancing the photocatalytic activity of the composite. On the other hand, the improvement of photocatalytic efficiency also benefited from the extra hydroxyl radicals generated by the reaction of photogenerated electrons with H₂O₂ in the photocatalytic system. Free radicals trapping experiments and electron spin resonance tests proved that played prominent role in the degradation process. After adding H₂O₂, OH also became important active species. Cyclic degradation experiments demonstrated the recyclability of the composite photocatalyst in DOX elimination applications. This work provides an efficient, clean, and recyclable purification strategy for removing antibiotic contaminants from water.

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

Bismuth-antimony alloy is considered as a promising potassium ion battery anode because of its combination of the high theoretical capacity of antimony and the excellent rate capacity of bismuth. However, the large volume change and sluggish reaction kinetic upon cycling have triggered severe capacity fading and poor rate performance. Herein, a nanoconfined BiSb in tremella-like carbon microspheres (BiSb@TCS) are delicately designed to address these issues. As-prepared BiSb@TCS renders an outstanding potassium-storage performance with a reversible capacity of 181 mAh g^-1 after ultralong 5700 cycles at a current density of 2 A g^-1 , and an excellent rate capacity of 119.3 mAh g^-1 at 6 A g^-1 . Such a superior performance can be ascribed to the delicate microstructure. The self-assembled carbon microspheres can strengthen integral structure and effectively accommodate the volume expansion of BiSb nanoparticles, and 2D carbon nanowalls in carbon microspheres can provide fast ion/electron diffusion dynamic. Theoretical calculation also suggests a thermodynamic feasibility of alloyed BiSb nanoparticles for storing potassium ion. Such a work shows that BiSb@TCS possesses a great potential to be a high-performance anode of potassium ion batteries. The rational designing of multiscaled structure would be instructive to the exploitation of other energy-storage materials.

Rational design of MoSe2 nanosheet-coated MOF-derived N-doped porous carbon polyhedron for potassium storage

For potassium-ion battery (PIB), it remains a huge challenge to develop an appropriate anode material to compensate the large radius of K⁺. MoSe₂ shows great potential for efficient K⁺ insertion/extraction due to its unique lamellar structures with an interlayer spacing of 6.46 Å. However, pure MoSe₂ has low electronic conductivity and agglomerates during long-term cycling. In the present work, MoSe₂ nanosheets were fabricated on the N-doped porous carbon polyhedron (NPCP). The obtained product was designated as NPCP@MoSe₂ and functioned as anode materials for PIBs. NPCP@MoSe₂ displayed a promising reversible capacity (325 mAh/g at 100 mA/g after 80 cycles), long-term cycling performance (128 mAh/g at 500 mA/g after 800 cycles), and superior rate property at 5000 mA/g. The enhanced electrochemical performance of NPCP@MoSe₂ could be attributed to the rational design of hybrid structures. Notably, the hollow NPCP provide a large contact area for the interactions among the electrolytes and electro-active materials as well as partly buffer the volume expansion. The synergistic effects between MoSe₂ and NPCP could mitigate the agglomeration of MoSe₂ nanosheets. Besides, the uniformly doping N elements enhanced the conductivity of the carbon matrix, and the N-group also provided potential binding active sites for K-ion accommodation. This work paves the ideas for the design of novel anode materials with high specific capacity, good cycling stability and outstanding rate capability for PIBs.

Encapsulating V2O3 Nanoparticles in Hierarchical Porous Carbon Nanosheets via C-O-V Bonds for Fast and Durable Potassium-Ion Storage

Vanadium oxide (V₂O₃) has been considered as a promising anode material for potassium-ion batteries (PIBs), but challenging as well for the low electron/ion conductivity and poor structural stability. To tackle these issues, herein, a novel sheetlike hybrid nanoarchitecture constructed by uniformly encapsulating V₂O₃ nanoparticles in amorphous carbon nanosheets (V₂O₃@C) with the generation of C-O-V bonding is presented. Such a subtle architecture effectively facilitates the infiltration of electrolyte, relieves the mechanical strain, and reduces the potassium-ion diffusion distance during the repetitive charging/discharging processes. The generated C-O-V bonding not only accelerated charge transfer across the carbon-V₂O₃ interface but also strengthened the structural stability. Benefiting from the synergistic effects, the as-prepared V₂O₃@C nanosheets display fast and durable potassium storage behaviors with a reversible capacity of 116.6 mAh g^-1 delivered at 5 A g^-1, and a specific capacity of 147.9 mAh g^-1 retained after 1800 cycles at a high current density of 2 A g^-1. Moreover, the insertion/extraction mechanism of V₂O₃@C nanosheets in potassium-ion storage is systematically demonstrated by electrochemical analysis and ex situ technologies. This study will shed light on the fabricating of other metal oxides anodes for high-performance PIBs and beyond.

Unveiling Intrinsic Potassium Storage Behaviors of Hierarchical Nano Bi@N-Doped Carbon Nanocages Framework via In Situ Characterizations

Metallic bismuth has drawn attention as a promising alloying anode for advanced potassium ion batteries (PIBs). However, serious volume expansion/electrode pulverization and sluggish kinetics always lead to its inferior cycling and rate properties for practical applications. Therefore, advanced Bi-based anodes via structural/compositional optimization and sur-/interface design are needed. Herein, we develop a bottom-up avenue to fabricate nanoscale Bi encapsulated in a 3D N-doped carbon nanocages (Bi@N-CNCs) framework with a void space by using a novel Bi-based metal-organic framework as the precursor. With elaborate regulation in annealing temperatures, the optimized Bi@N-CNCs electrode exhibits large reversible capacities and long-duration cyclic stability at high rates when evaluated as competitive anodes for PIBs. Insights into the intrinsic K⁺ -storage processes of the Bi@N-CNCs anode are put forward from comprehensive in situ characterizations.