Three-Dimensional Hierarchical Framework Assembled by Cobblestone-Like CoSe2@C Nanospheres for Ultrastable Sodium-Ion Storage

Stable C-Se-Co interface of CoSe2@N-doped carbon aerogels for efficient sodium storage

The storage characteristics of sodium ions in CoSe2 are intricately linked to the doping species and concentrations of heteroatoms within the carbon matrix. However, a systematic study of the impact of heteroatom doping on the interfacial forces between the carbon matrix and CoSe2 has not been systematically investigated. In this work, CoSe2 nanoparticles coated with different heteroatom doping (N/S) carbon aerogels derived from sodium alginate (SA) were constructed to investigate the influence of dopant atoms on the interfacial forces at the C matrix and CoSe2 interface. The confinement effect of Co-SA-NH2 junction zones facilitates the formation of stable C-Se-Co interface. The higher pyridinic nitrogen can promote the reinforced interfacial connection of CSe bond, further decreasing the interface distance between CoSe2 and N-doped carbon aerogels (NCA) to 3.00 Å, alleviating the interfacial volume expansion to 15 %, thus increasing the sodium ion migration rate and cycling stability. However, the addition of sulfur inhibits the transformation of other nitrogen species into pyridinic nitrogen. Furthermore, sulfur shares the same valence electron configuration as selenium, it replaces selenium in the CSe bond position, thereby reducing the conductivity and stability of the interface. As a consequence, CoSe2@N-doped carbon aerogels (CoSe2@NCA) exhibits the lowest sodium diffusion barrier (1.10 eV) and the highest sodium ion negative adsorption energy (-2.21 eV). As expected, CoSe2@NCA delivers superior long-term cycling performance (519 mAh g-1 at 1.0 A g-1 after 800 cycles) and excellent reversible capacity at high current density (474 mAh g-1 at 5.0 A g-1).

ZnCo Bimetallic Macro-Microporous Metal-Organic Frameworks for Efficient Adsorption of Dyes

The significant threat posed by dye wastewater has driven the development of efficient adsorbents, such as metal organic frameworks (MOFs). Specifically, we explore the synthesis and application of ZnCo-based bimetallic zeolite imidazolate frameworks with a macro-microporous structure (SOM-ZnCo-ZIF), which exhibit enhanced adsorption capacity for dyes due to their large specific surface area and ordered porous arrangement. When SOM-ZnCo-ZIF is immersed in DMA solutions of methylene blue, methyl orange, crystal violet, and rhodamine B, due to its high specific surface area and the synergistic effect of ZnCo bimetallic clusters, SOM-ZnCo-ZIF significantly enhances dye adsorption. Notably, its adsorption capacity for Rhodamine B reaches an impressive 6798.9 mg/g, and within just 1 min, 0.5 g/L of SOM-ZnCo-ZIF can remove over 97% of Rhodamine B from a 60 mg/L solution. Moreover, it maintained a 92.8% dye removal efficiency in ten cycles without regeneration, demonstrating the effective adsorption capacity of SOM-ZnCo-ZIF. Density functional theory calculations have shown that the adsorption energy of ZnCo bimetallic ZIF for Rhodamine B is approximately twice that of a single metal. SOM-ZnCo-ZIF exhibits strong adsorption of Rhodamine B mainly due to its macro-microporous structure, which provides larger pore sizes (∼250 nm) allowing the dye molecules to infiltrate the porous network, and its ability to facilitate π-π stacking interactions between the benzene rings of Rhodamine B and the imidazole rings of the ZIF. Additionally, the interaction is further enhanced by strong coordination bonds and electrostatic interactions between the cationic dye and the negatively charged framework. This work not only proposes an effective adsorbent to remove Rhodamine B but also provides valuable insights for the rational design and synthesis of environmentally sustainable MOF structures.

Fabrication of a Stable and Highly Effective Anode Material for Li-Ion/Na-Ion Batteries Utilizing ZIF-12

Transition metal selenides (TMSs) are receiving considerable interest as improved anode materials for sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs) due to their considerable theoretical capacity and excellent redox reversibility. Herein, ZIF-12 (zeolitic imidazolate framework) structure is used for the synthesis of Cu2Se/Co3Se4@NPC anode material by pyrolysis of ZIF-12/Se mixture. When Cu2Se/Co3Se4@NPC composite is utilized as an anode electrode material in LIB and SIB half cells, the material demonstrates excellent electrochemical performance and remarkable cycle stability with retaining high capacities. In LIB and SIB half cells, the Cu2Se/Co3Se4@NPC anode material shows the ultralong lifespan at 2000 mAg-1, retaining a capacity of 543 mAhg-1 after 750 cycles, and retaining a capacity of 251 mAhg-1 after 200 cycles at 100 mAg-1, respectively. The porous structure of the Cu2Se/Co3Se4@NPC anode material can not only effectively tolerate the volume expansion of the electrode during discharging and charging, but also facilitate the penetration of electrolyte and efficiently prevents the clustering of active particles. In situ X-ray difraction (XRD) analysis results reveal the high potential of Cu2Se/Co3Se4@NPC composite in building efficient LIBs and SIBs due to reversible conversion reactions of Cu2Se/Co3Se4@NPC for lithium-ion and sodium-ion storage.

Synthesis of Iron Sulfide Nanocrystals Encapsulated in Highly Porous Carbon-Coated CNT Microsphere as Anode Materials for Sodium-Ion Batteries

Highly porous carbon materials with a rationally designed pore structure can be utilized as reservoirs for metal or nonmetal components. The use of small-sized metal or metal compound nanoparticles, completely encapsulated by carbon materials, has attracted significant attention as an effective approach to enhancing sodium ion storage properties. These materials have the ability to mitigate structural collapse caused by volume expansion during the charging process, enable short ion transport length, and prevent polysulfide elution. In this study, a concept of highly porous carbon-coated carbon nanotube (CNT) porous microspheres, which serve as excellent reservoir materials is suggested and a porous microsphere is developed by encapsulating iron sulfide nanocrystals within the highly porous carbon-coated CNTs using a sulfidation process. Furthermore, various sulfidation processes to determine the optimal method for achieving complete encapsulation are investigated by comparing the morphologies of diverse iron sulfide-carbon composites. The fully encapsulated structure, combined with the porous carbon, provides ample space to accommodate the significant volume changes during cycling. As a result, the porous iron sulfide-carbon-CNT composite microspheres exhibited outstanding cycling stability (293 mA h g-1 over 600 cycles at 1 A g-1 ) and remarkable rate capability (100 mA h g-1 at 5 A g-1 ).

Trapping Lithium Selenides with Evolving Heterogeneous Interfaces for High-Power Lithium-Ion Capacitors

Transition metal selenides anodes with fast reaction kinetics and high theoretical specific capacity are expected to solve mismatched kinetics between cathode and anode in Li-ion capacitors. However, transition metal selenides face great challenges in the dissolution and shuttle problem of lithium selenides, which is the same as Li-Se batteries. Herein, inspired by the density functional theory calculations, heterogeneous can enhance the adsorption of Li₂ Se relative to single component selenide electrodes, thus inhibiting the dissolution and shuttle effect of Li₂ Se. A heterostructure material (denoted as CoSe₂ /SnSe) with the ability to evolve continuously (CoSe₂ /SnSe→Co/Sn→Co/Li₁₃ Sn₅ ) is successfully designed by employing CoSnO₃ -MOF as a precursor. Impressively, CoSe₂ /SnSe heterostructure material delivers the ultrahigh reversible specific capacity of 510 mAh g^-1 after 1000 cycles at the high current density of 4 A g^-1 . In situ XRD reveals the continuous evolution of the interface based on the transformation and alloying reactions during the charging and discharging process. Visualizations of in situ disassembly experiments demonstrate that the continuously evolving interface inhibits the shuttle of Li₂ Se. This research proposes an innovative approach to inhibit the dissolution and shuttling of discharge intermediates (Li₂ Se) of metal selenides, which is expected to be applied to metal sulfides or Li-Se and Li-S energy storage systems.

Metal-organic framework derived bimetallic selenide embedded in nitrogen-doped carbon hierarchical nanosphere for highly reversible sodium-ion storage

Bimetallic selenides with various valence transitions and high theoretical capacities are extensively studied as anodes for sodium-ion-batteries (SIBs), but their huge volume changes and poor capacity retention limit their practicality. Herein, a facile and controllable strategy using a binary Ni-Co metal-organic framework (MOF) precursors followed by the selenization process, which produced a cobalt nickel selenide/N-doped carbon composite ((CoNi)Se₂/NC) that maintained the hierarchical nanospheres structure. Such a distinctive structure affords both Na⁺ and electron diffusion pathways in the electrochemical reactions as well as high electrical conductivity, thus leading to superior electrochemical performance when the designed composite is utilized as an anode in SIBs. The resulting nanospheres-like (CoNi)Se₂/NC hierarchical structure exhibits a high specific capacity of 526.8 mA h g^-1 at 0.2 A/g over 100 cycles, a stable cycle life with no obvious capacities loss at 1.0 and 3.0 A/g after 500 cycles, and exceptional rate capability of 322.9 mA h g^-1 at 10.0 A/g.

Advances and challenges in metal selenides enabled by nanostructures for electrochemical energy storage applications

The development of nanomaterials and their related electrochemical energy storage (EES) devices can provide solutions for improving the performance and development of existing EES systems owing to their high electronic conductivity and ion transport and abundant embeddable sites. Recent progress has demonstrated that metal selenides are attracting increasing attention in the field of EES because of their unique structures, high theoretical capacities, rich element resources, and high conductivity. However, there are still many challenges in their application in EES, and thus the use of nanoscale metal selenide materials in commercial devices is limited. In this review, we summarize recent advances in the nanostructured design of metal selenides (e.g., zero-, one-, two-, and three-dimensional, and self-supported structures) and present their advantages in terms of EES performance. Moreover, some remarks on the potential challenges and research prospects of nanostructured metal selenides in the field of EES are presented.

Ether-based electrolytes for sodium ion batteries

Sodium-ion batteries (SIBs) are considered to be strong candidates for large-scale energy storage with the benefits of cost-effectiveness and sodium abundance. Reliable electrolytes, as ionic conductors that regulate the electrochemical reaction behavior and the nature of the interface and electrode, are indispensable in the development of advanced SIBs with high Coulombic efficiency, stable cycling performance and high rate capability. Conventional carbonate-based electrolytes encounter numerous obstacles for their wide application in SIBs due to the formation of a dissolvable, continuous-thickening solid electrolyte interface (SEI) layer and inferior stability with electrodes. Comparatively, ether-based electrolytes (EBEs) are emerging in the secondary battery field with fascinating properties to improve the performance of batteries, especially SIBs. Their stable solvation structure enables highly reversible solvent-co-intercalation reactions and the formation of a thin and stable SEI. However, although EBEs can provide more stable cycling and rapid sodiation kinetics in electrodes, benefitting from their favorable electrolyte/electrode interactions such as chemical compatibility and good wettability, their special chemistry is still being investigated and puzzling. In this review, we provide a thorough and comprehensive overview on the developmental history, fundamental characteristics, superiorities and mechanisms of EBEs, together with their advances in other battery systems. Notably, the relation among electrolyte science, interfacial chemistry and electrochemical performance is highlighted, which is of great significance for the in-depth understanding of battery chemistry. Finally, future perspectives and potential directions are proposed to navigate the design and optimization of electrolytes and electrolyte/electrode interfaces for advanced batteries.

Porous Microspheres Comprising CoSe2 Nanorods Coated with N-Doped Graphitic C and Polydopamine-Derived C as Anodes for Long-Lived Na-Ion Batteries

Metal-organic framework-templated nitrogen-doped graphitic carbon (NGC) and polydopamine-derived carbon (PDA-derived C)-double coated one-dimensional CoSe₂ nanorods supported highly porous three-dimensional microspheres are introduced as anodes for excellent Na-ion batteries, particularly with long-lived cycle under carbonate-based electrolyte system. The microspheres uniformly composed of ZIF-67 polyhedrons and polystyrene nanobeads (ϕ = 40 nm) are synthesized using the facile spray pyrolysis technique, followed by the selenization process (P-CoSe₂@NGC NR). Further, the PDA-derived C-coated microspheres are obtained using a solution-based coating approach and the subsequent carbonization process (P-CoSe₂@PDA-C NR). The rational synthesis approach benefited from the synergistic effects of dual carbon coating, resulting in a highly conductive and porous nanostructure that could facilitate rapid diffusion of charge species along with efficient electrolyte infiltration and effectively channelize the volume stress. Consequently, the prepared nanostructure exhibits extraordinary electrochemical performance, particularly the ultra-long cycle life stability. For instance, the advanced anode has a discharge capacity of 291 (1000th cycle, average capacity decay of 0.017%) and 142 mAh g^-1 (5000th cycle, average capacity decay of 0.011%) at a current density of 0.5 and 2.0 A g^-1, respectively.

Carbon-Encapsulated Ni3 Se4 /CoSe2 Heterostructured Nanospheres: Sodium/Potassium-Ion Storage Anode with Prominent Electrochemical Properties

Heterogeneous structures are used as energy storage devices because of their ability to accelerate charge transfer, which greatly contributes to the rate capability of devices. However, the construction of heterostructures with conspicuous electrochemical properties remains a huge challenge. In this study, a design of heterostructured Ni₃ Se₄ /CoSe₂ nanospheres encapsulated by a carbon shell (Ni₃ Se₄ /CoSe₂ @C) synthesized through facile hydrothermal and annealing methods is presented. The Ni₃ Se₄ /CoSe₂ @C exhibits excellent cyclic performance with a capacity of 420 mA h g^-1 at 0.5 A g^-1 after 100 cycles for Na-storage and 330.1 mA h g^-1 at 0.1 A g^-1 after 200 cycles for K-storage. The excellent cyclic performance can be attributed to the carbon coating that maintains the structural stability and enhances electrical conductivity, and significantly, the heterostructures that promote ion/electron transport. The sodium storage mechanism of the Ni₃ Se₄ /CoSe₂ @C is revealed by ex situ X-ray powder diffraction, ex situ high-resolution transmission electron microscopy, and in situ electrochemical impedance spectra analyses. The first principles density functional theory calculation is performed to prove that the heterostructure on the Ni₃ Se₄ /CoSe₂ interface can induce an electric field and thus improve the electrochemical reaction kinetics. This study provides an effective approach for constructing heterostructured composites for high-performance alkaline batteries.

Hydrothermal Preparation and High Electrochemical Performance of NiS Nanospheres as Anode for Lithium-Ion Batteries

Nickel sulfide has been widely studied as an anode material for lithium-ion batteries due to its environmental friendliness, low cost, high conductivity, and high theoretical capacity. A simple hydrothermal method was used to prepare NiS nanospheres materials with the size in the range of 100–500 nm. The NiS nanospheres electrodes exhibited a high reversible capacity of 1402.3 mAh g−1 at 200 mA g−1 after 280 cycles and a strong rate capability of 814.8 mAh g−1 at 0.8 A g−1 and 1130.5 mAh g−1 when back to 0.1 A g−1. Excellent electrochemical properties and the simple preparation method of the NiS nanospheres make it possible to prepare NiS on a large scale as the anode of lithium-ion batteries.

Highly catalytically active CoSe2 supported on nitrogen-doped three dimensional porous carbon as a cathode for high-stability lithium-sulfur battery

Lithium-sulfur batteries, promising secondary energy storage devices, were mainly limited by its unsatisfactory cyclability owing to inefficient reversible conversion of sulfur and lithium sulfide on the cathode during the discharge/charging process. In this study, nitrogen-doped three-dimensional porous carbon material loaded with CoSe 2 nanoparticles (CoSe 2 -PNC) is developed as a cathode for lithium-sulfur battery application. A combination of CoSe 2 and nitrogen-doped porous carbon can efficiently improve the cathode activity and its conductivity, resulting in enhanced redox kinetics of the charge/discharge process. The obtained electrode exhibits a high discharge specific capacity of 1139.6 mAh g -1 at a current density of 0.2 C. After 100 cycles, its capacity remained at 865.7 mAh g -1 corresponding to a capacity retention of 75.97%. In a long-term cycling test, a discharge specific capacity of 546.7 mAh g -1 was observed after 300 cycles performed at a current density of 1 C.

Topological transformation construction of CoSe2/N-doped carbon heterojunction with three-dimensional porous structure for high-performance sodium-ion half/full batteries

Transition metal selenides have been widely used as anode materials for sodium-ion batteries (SIBs) because of their considerable theoretical capacity and good conductivity. Nevertheless, the volume expansion is a serious...

Stabilizing V2O3 in carbon nanofiber flexible films for ultrastable potassium storage

Vanadium oxides, such as V2O3 and VO2, are expected to be potential anode materials for potassium-ion batteries (KIBs) on account of their high theoretical capacity, low price and natural abundance....

Interface-Driven Pseudocapacitance Endowing Sandwiched CoSe2/N-Doped Carbon/TiO2 Microcubes with Ultra-Stable Sodium Storage and Long-Term Cycling Stability

Cobalt diselenide (CoSe₂) has drawn great concern as an anode material for sodium-ion batteries due to its considerable theoretical capacity. Nevertheless, the poor cycling stability and rate performance still impede its practical implantation. Here, CoSe₂/nitrogen-doped carbon-skeleton hybrid microcubes with a TiO₂ layer (denoted as TNC-CoSe₂) are favorably prepared via a facile template-engaged strategy, in which a TiO₂-coated Prussian blue analogue of Co₃[Co(CN)₆]₂ is used as a new precursor accompanied with a selenization procedure. Such structures can concurrently boost ion and electron diffusion kinetics and inhibit the structural degradation during cycling through the close contact between the TiO₂ layer and NC-CoSe₂. Besides, this hybrid structure promotes the superior Na-ion intercalation pseudocapacitance due to the well-designed interfaces. The as-prepared TNC-CoSe₂ microcubes exhibit a superior cycling capability (511 mA h g^-1 at 0.2 A g^-1 after 200 cycles) and long cycling life (456 mA h g^-1 at 6.4 A g^-1 for 6000 cycles with a retention of 92.7%). Coupled with a sodium vanadium fluorophosphate (Na₃V₂(PO₄)₂F₃)@C cathode, this assembled full cell displays a specific capacity of 281 mA h g^-1 at 0.2 A g^-1 for 100 cycles. This work can be potentially used to improve other metal selenide-based anodes for rechargeable batteries.

Core-Shell CoSe2 /WSe2 Heterostructures@Carbon in Porous Carbon Nanosheets as Advanced Anode for Sodium Ion Batteries

Heterojunction, with the advantage of fast charge transfer dynamics, is considered to be an effective strategy to address the low capacity and poor rate capability of anode materials for sodium-ion batteries (SIBs). As well, carbonaceous materials, as a crucial additive, can effectively ameliorate the ion/electron conductivity of integrated composites, realizing the fast ion transport and charge transfer. Here, motivated by the enhancement effect of carbon and heterojunction on conductivity, it is proposed that the CoSe₂ /WSe₂ heterojunction as inner core is coated by carbon outer shell and uniformly embedded in porous carbon nanosheets (denoted as CoSe₂ /WSe₂ @C/CNs), which is used as anode material for SIBs. Combining with density functional theoretical calculations, it is confirmed that the structure of heterojunction can introduce built-in electric-field, which can accelerate the transportation of Na⁺ and improve the conductivity of electrons. Moreover, the introduction of porous carbon nanosheets (CNs) can provide a channel for the transportation of Na⁺ and avoid the volume expansion during Na⁺ insertion and extraction process. As it is expected, CoSe₂ /WSe₂ @C/CNs anode displays ultrastable specific capacity of 501.9 mA h g^-1 at 0.1 A g^-1 over 200 cycles, and ultrahigh rate capacity of 625 mA h g^-1 at 0.1 A g^-1 after 100 cycles.

Bilateral Interfaces in In2Se3-CoIn2-CoSe2 Heterostructures for High-Rate Reversible Sodium Storage

Metal selenides are considered as a group of promising candidates as the anode material for sodium-ion batteries due to their high theoretical capacity. However, the intrinsically low electrical and ionic conductivities as well as huge volume change during the charge-discharge process give rise to an inferior sodium storage capability, which severely hinders their practical application. Herein, we fabricated In₂Se₃/CoSe₂ hollow nanorods composed of In₂Se₃/CoIn₂/CoSe₂ by growing cobalt-based zeolitic imidazolate framework ZIF-67 on the surface of indium-based metal-organic framework MIL-68, followed by in situ gaseous selenization. Because of the CoIn₂ alloy phase in between In₂Se₃ and CoSe₂, a heterostructure consisting of two alloy/selenide interfaces has been successfully constructed, offering synergistically enhanced electrical conductivity, Na diffusion process, and structural stability, in comparison to the single CoIn₂-free interface with only two metal selenides. As expected, this nanoconstruction delivers a high reversible capacity of 297.5 and 205.5 mAh g^-1 at 5 and 10 A g^-1 after 2000 cycles, respectively, and a superior rate performance of 371.6 mAh g^-1 at even 20 A g^-1.

Robust Pseudocapacitive Sodium Cation Intercalation Induced by Cobalt Vacancies at Atomically Thin Co1-x Se2 /Graphene Heterostructure for Sodium-Ion Batteries

Electronic structure engineering on electrode materials could bring in a new mechanism to achieve high energy and high power densities in sodium ion batteries. Herein, we design and create Co vacancies at the interface of atomically thin CoSe₂ /graphene heterostructure and obtain Co_1-x Se₂ /graphene heterostructure electrode materials that facilitate significant Na⁺ intercalation pseudocapacitance. Density functional theory (DFT) calculation suggests that the Na⁺ adsorption energy is dramatically increased, and the Na⁺ diffusion barrier is remarkably reduced due to the introduction of Co vacancy. The optimized electrode delivers a superior capacity of 673.6 mAh g^-1 at 0.1 C, excellent rate capability of 576.5 mAh g^-1 at 2.0 C and ultra-long life up to 2000 cycles. Kinetics analysis indicates that the enhanced Na⁺ storage is mainly attributed to the intercalation pseudocapacitance induced by Co vacancies. This work suggests that the creation of cation vacancy could bestow heterostructured electrode materials with pseudocapacitive Na⁺ intercalation for high-capacity and high-rate energy storage.

Yolk-shell structured CoSe2/C nanospheres as multifunctional anode materials for both full/half sodium-ion and full/half potassium-ion batteries

Transition metal selenides (TMSs) are suitable for SIBs and PIBs owing to their satisfactory theoretical capacity and superior electrical conductivity. However, the large radius of Na+/K+ easily leads to sluggish kinetics and poor conductivity, which hinder the development of SIBs and PIBs. Structure design is an effective method to solve these obstacles. In this study, Co2+ ions combined with glycerol molecules to form self-assembled nanospheres at first, and then they were in situ converted into CoSe2 nanoparticles embedded in a carbon matrix during the selenization process. This structure has three-dimensional ion diffusion channels that can effectively hamper the aggregation of metal compound nanoparticles. Meanwhile, the CoSe2/C of the yolk-shell structure and a large number of pores help alleviate volume expansion and facilitate electrolyte wettability. These structural advantages of CoSe2/C endow it with remarkable electrochemical performances for full/half SIBs and full/half PIBs. The obtained CoSe2/C exhibits superior stability and excellent performance (312.1 mA h g-1 at 4 A g-1 after 1600 cycles) for SIBs. When it is used as an anode material for PIBs, 369.2 mA h g-1 can be retained after 200 cycles at 50 mA g-1 and 248.1 mA h g-1 can be retained after 200 cycles at 500 mA g-1; in addition, CoSe2/C also shows superior rate capacity (186.4 mA h g-1 at 1000 mA g-1). A series of ex situ XRD measurements were adapted to explore the possible conversion mechanism of CoSe2/C as the anode for PIBs. It is worth noting that the full-cell of CoSe2/C//Na3V2(PO4)3@rGO for SIBs and the full-cell of CoSe2/C//PTCDA-450 for PIBs were successfully assembled. The relationship between the structure and performance of CoSe2/C was investigated through density functional theory (DFT).

Constructed Interfacial Oxygen-Bridge Chemical Bonding in Core-Shell Transition Metal Phosphides/Carbon Hybrid Boosting Oxygen Evolution Reaction

A designed structure which CoP nanoparticles (NPs) ingeniously connected with graphene-like carbon layer via in-situ generated interfacial oxygen-bridge chemical bonding was achieved by a mild phosphorization treatment. The results proved that the presence of phosphorus vacancies is a crucial factor enabling formation of Co-O-C bonds. The direct coupling of edge Co of CoP with the oxygen from functional groups on the carbon layer was proposed. As a catalyst for electrocatalytic water splitting, the manufactured Fe₂ O₃ @C@CoP core-shell structure manifested a low overpotential of 230 mV, a low Tafel slope of 55 mV dec^-1 , and long-term stability. Density functional theory calculations verified that the Co-O-C bond played a critical role in decreasing the thermodynamic energy barrier of reaction rate-determining step for the oxygen evolution reaction (OER). This synthetic route might be extended to construct metal-O-C bonds in other transition metal phosphides (or selenides, sulfides)/carbon composites for highly efficient OER catalysts.

Ultrafast and durable Li/Na storage by an iron selenide anode using an elastic hierarchical structure

An exquisite composite consisting of polycystic FeSe/C microspheres encapsulated within a three-dimensional graphene framework was designed and fabricated for fast and durable Li-/Na-storage applications.

Construction of series-wound architectures composed of metal-organic framework-derived hetero-(CoFe)Se2 hollow nanocubes confined into a flexible carbon skeleton as a durable sodium storage anode

Metal chalcogenides with structural pulverization/degradation and intrinsic low electrical conductivity trigger the challenging issues of serious capacity fading and inferior rate capability upon repeated de-/sodiation cycling. Multiple electroactive heterostructures can integrate the inherent advantages of a strong synergistic coupling effect to improve their electrochemical Na+-storage behavior and structural durability, showing robust mechanical features, fast Na+ immigration and abundant active insertion sites at intriguing heterointerfaces. Hence, a series-wound architecture of metal-organic framework (MOF)-derived heterogeneous (CoFe)Se2 hollow nanocubes confined into a one-dimension carbon nanofiber skeleton ((CoFe)Se2@CNS) was successfully developed via a template-assisted liquid phase anion exchange followed by electrospinning and conventional selenization treatment. When examined as an anode for sodium ion batteries, the (CoFe)Se2@CNS electrode exhibits remarkably enhanced electrochemical Na+-storage performance delivering a high sodiation capacity as high as 213.9 mA h g-1 after 3650 cycles at 5 A g-1 with a capacity degradation rate of only 0.0047% per cycle; specifically, it shows tremendous rate performance and ultrastable cycling durability of 194.7 mA h g-1 at a high rate of 8 A g-1 after 5630 cycles. This work can shed light on a fundamental approach for designing heterostructures of multiple electroactive components toward high-performance alkali metal ion batteries.

Building Hierarchical Microcubes Composed of One-Dimensional CoSe2 @Nitrogen-Doped Carbon for Superior Sodium Ion Batteries

Designing and synthesizing highly stable anode materials with high capacity is critical for the practical application of sodium ion batteries (SIBs), however, to date, this remains an insurmountable barrier. The introduction of hierarchical architectures and carbon supports is proving an effective strategy for addressing these challenges. Thus, we have fabricated a hierarchical CoSe₂ @nitrogen-doped carbon (CoSe₂ @NC) microcube composite using the Prussian blue analogue Co₃ [Co(CN)₆ ]₂ as template. The rational combination of the unique hierarchical construction from one to three dimensions and a nitrogen-doped carbon skeleton facilitates sodium ion and electron transport as well as stabilizing the host structure during repeated discharge/charge processes, which contributes to its excellent sodium storage capability. As expected, the as-prepared CoSe₂ @NC composite delivered remarkable reversible capacity and ultralong cycling lifespan even at a high rate of 2.0 A g^-1 (384.3 mA h g^-1 after1800 loops) when serving as the anode material for SIBs. This work shows the great potential of the CoSe₂ -based anode for practical application in SIBs, and the original strategy may be extended to other anode materials.

Golden Bristlegrass-Like Hierarchical Graphene Nanofibers Entangled with N-Doped CNTs Containing CoSe2 Nanocrystals at Each Node as Anodes for High-Rate Sodium-Ion Batteries

Golden bristlegrass-like unique nanostructures comprising reduced graphene oxide (rGO) matrixed nanofibers entangled with bamboo-like N-doped carbon nanotubes (CNTs) containing CoSe₂ nanocrystals at each node (denoted as N-CNT/rGO/CoSe₂ NF) are designed as anodes for high-rate sodium-ion batteries (SIBs). Bamboo-like N-doped CNTs (N-CNTs) are successfully generated on the rGO matrixed nanofiber surface, between rGO sheets and mesopores, and interconnected chemically with homogeneously distributed rGO sheets. The defects in the N-CNTs formed by a simple etching process allow the complete phase conversion of Co into CoSe₂ through the efficient penetration of H₂ Se gas inside the CNT walls. The N-CNTs bridge the vertical defects for electron transfer in the rGO sheet layers and increase the distance between the rGO sheets during cycles. The discharge capacity of N-CNT/rGO/CoSe₂ NF after the 10 000th cycle at an extremely high current density of 10 A g^-1 is 264 mA h g^-1 , and the capacity retention measured at the 100th cycle is 89%. N-CNT/rGO/CoSe₂ NF has final discharge capacities of 395, 363, 328, 304, 283, 263, 246, 223, 197, 171, and 151 mA h g^-1 at current densities of 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 A g^-1 , respectively.

One-Pot Synthesis and High Electrochemical Performance of CuS/Cu1.8S Nanocomposites as Anodes for Lithium-Ion Batteries

CuS and Cu_1.8S have been investigated respectively as anodes of lithium-ion batteries because of their abundant resources, no environment pollution, good electrical conductivity, and a stable discharge voltage plateau. In this work, CuS/Cu_1.8S nanocomposites were firstly prepared simultaneously by the one-pot synthesis method at a relatively higher reaction temperature 200 °C. The CuS/Cu_1.8S nanocomposites anodes exhibited a high initial discharge capacity, an excellent reversible rate capability, and remarkable cycle stability at a high current density, which could be due to the nano-size of the CuS/Cu_1.8S nanocomposites and the assistance of Cu_1.8S. The high electrochemical performance of the CuS/Cu_1.8S nanocomposites indicated that the Cu_xS nanomaterials will be a potential lithium-ion battery anode.

MOF-derived ultrasmall CoSe2 nanoparticles encapsulated by an N-doped carbon matrix and their superior lithium/sodium storage properties

Ultrasmall CoSe₂ nanoparticles encapsulated by an N-doped carbon matrix were prepared by selenizing a novel Co-metal organic framework precursor. The excellent electrochemical performance may be due to the synergistic effect of the N-doped carbon matrix and the ultrasmall CoSe₂.

Cagelike CoSe2@N-Doped Carbon Aerogels with Pseudocapacitive Properties as Advanced Materials for Sodium-Ion Batteries with Excellent Rate Performance and Cyclic Stability

Electrochemical conversion reaction based electrodes offer a high sodium storage capacity in rechargeable batteries by utilizing the variable valence states of transition metals. Thus, transition metal chalcogenides (TMCs) as such materials have been intensively investigated in recent years to explore the possibilities of practical application in rechargeable sodium-ion batteries; however, it is hindered by poor rate performance and a high-cost preparation method. In addition, some issues in regards to conversion reactions remain poorly understood, including incomplete reversible reaction processes, polarization, and hysteresis. Herein, a novel cagelike CoSe₂@N-doped carbon aerogels hybrid composite was designed and prepared by a facile and high-efficiency sol-gel technology. Benefiting from the surface engineering optimization, high charge transfer, and low-energy diffusion barrier, the CoSe₂@N-doped carbon aerogels exhibit a high pseudocapacitive property. Most importantly, the CoSe₂ anode has been carefully investigated at different discharge/charge states by X-ray absorption near edge spectroscopy technologies and density functional theory (DFT) simulations, which deeply reveal the capacity fading mechanism and phase transition behavior.

Synthesis of Porous Ni-Doped CoSe2 /C Nanospheres towards High-Rate and Long-Term Sodium-Ion Half/Full Batteries

Carbon-layer-coated porous Ni-doped CoSe₂ (Ni-CoSe₂ /C) nanospheres have been fabricated by a facile hydrothermal method followed by a new selenization strategy. The porous structure of Ni-CoSe₂ /C is formed by the aggregation of many small particles (20-40 nm), which are not tightly packed together, but are interspersed with gaps. Moreover, the surfaces of these small particles are covered with a thin carbon layer. Ni-CoSe₂ /C delivers superior rate performance (314.0 mA h g^-1 at 20 A g^-1 ), ultra-long cycle life (316.1 mA h g^-1 at 10 A g^-1 after 8000 cycles), and excellent full-cell performance (208.3 mA h g^-1 at 0.5 A g^-1 after 70 cycles) when used as an anode material for half/full sodium-ion batteries. The Na storage mechanism and kinetics have been confirmed by ex situ X-ray diffraction analysis, assessment of capacitance performance, and a galvanostatic intermittent titration technique (GITT). GITT shows that Na⁺ diffusion in the electrode material is a dynamic change process, which is associated with a phase transition during charge and discharge. The excellent electrochemical performance suggests that the porous Ni-CoSe₂ /C nanospheres have great potential to serve as an electrode material for sodium-ion batteries.

Bimetallic organic framework derivation of three-dimensional and heterogeneous metal selenides/carbon composites as advanced anodes for lithium-ion batteries

Heterogeneous structures have been attracting increasing attention in energy storage and conversion applications due to the phase interface and synergistic effect of multiple components. Herein, bimetal organic framework analogues were introduced to construct a Zn/Co bimetallic selenide heterostructure within a 3D-porous N-doped carbon matrix by a NaCl template-assisted lyophilization and annealing process. The cross-linked 3D network can enhance the transport kinetics for both lithium ions and electrons. The stress resulting from the cycling process can be released by interconnected channels in the composite. ZnSe and CoSe₂ experience electrochemical reactions at different potentials, which can buffer volume changes mutually to effectively increase structural stability. Meanwhile, abundant active sites due to the heterostructure enhance pseudocapacitive performance and reaction kinetics, resulting in high specific capacity and good rate performance. As anode materials for lithium-ion batteries, the three-dimensional ZnSe/CoSe₂-C composite exhibits a high reversible capacity of 700 mA h g^-1 after 500 cycles at 1 A g^-1.

In-Situ Fabrication of Bone-Like CoSe2 Nano-Thorn Loaded on Porous Carbon Cloth as a Flexible Electrode for Na-Ion Storage

Sodium-ion batteries (SIBs) based on flexible electrode materials are being investigated recently for improving sluggish kinetics and developing energy density. Transition metal selenides present excellent conductivity and high capacity; nevertheless, their low conductivity and serious volume expansion raise challenging issues of inferior lifespan and capacity fading. Herein, an in-situ construction method through carbonization and selenide synergistic effect is skillfully designed to synthesize a flexible electrode of bone-like CoSe₂ nano-thorn coated on porous carbon cloth. The designed flexible CoSe₂ electrode with stable structural feature displays enhanced Na-ion storage capabilities with good rate performance and outstanding cycling stability. As expected, the designed SIBs with flexible BL-CoSe₂ /PCC electrode display excellent reversible capacity with 360.7 mAh g^-1 after 180 cycles at a current density of 0.1 A g^-1 .

Construction of Bimetallic Selenides Encapsulated in Nitrogen/Sulfur Co-Doped Hollow Carbon Nanospheres for High-Performance Sodium/Potassium-Ion Half/Full Batteries

Metallic selenides have been widely investigated as promising electrode materials for metal-ion batteries based on their relatively high theoretical capacity. However, rapid capacity decay and structural collapse resulting from the larger-sized Na⁺ /K⁺ greatly hamper their application. Herein, a bimetallic selenide (MoSe₂ /CoSe₂ ) encapsulated in nitrogen, sulfur-codoped hollow carbon nanospheres interconnected reduced graphene oxide nanosheets (rGO@MCSe) are successfully designed as advanced anode materials for Na/K-ion batteries. As expected, the significant pseudocapacitive charge storage behavior substantially contributes to superior rate capability. Specifically, it achieves a high reversible specific capacity of 311 mAh g^-1 at 10 A g^-1 in NIBs and 310 mAh g^-1 at 5 A g^-1 in KIBs. A combination of ex situ X-ray diffraction, Raman spectroscopy, and transmission electron microscopy tests reveals the phase transition of rGO@MCSe in NIBs/KIBs. Unexpectedly, they show quite different Na⁺ /K⁺ insertion/extraction reaction mechanisms for both cells, maybe due to more sluggish K⁺ diffusion kinetics than that of Na⁺ . More significantly, it shows excellent energy storage properties in Na/K-ion full cells when coupled with Na₃ V₂ (PO₄ )₂ O₂ F and PTCDA@450 °C cathodes. This work offers an advanced electrode construction guidance for the development of high-performance energy storage devices.

The Progress of Cobalt-Based Anode Materials for Lithium Ion Batteries and Sodium Ion Batteries

Limited by the development of energy storage technology, the utilization ratio of renewable energy is still at a low level. Lithium/sodium ion batteries (LIBs/SIBs) with high-performance electrochemical performances, such as large-scale energy storage, low costs and high security, are expected to improve the above situation. Currently, developing anode materials with better electrochemical performances is the main obstacle to the development of LIBs/SIBs. Recently, a variety of studies have focused on cobalt-based anode materials applied for LIBs/SIBs, owing to their high theoretical specific capacity. This review systematically summarizes the recent status of cobalt-based anode materials in LIBs/SIBs, including Li+/Na+ storage mechanisms, preparation methods, applications and strategies to improve the electrochemical performance of cobalt-based anode materials. Furthermore, the current challenges and prospects are also discussed in this review. Benefitting from these results, cobalt-based materials can be the next-generation anode for LIBs/SIBs.

CoSe2 hollow microspheres with superior oxidase-like activity for ultrasensitive colorimetric biosensing

As one of the transition metal dichalcogenide, CoSe₂ has received much attention because of its superior physicochemical properties. In this work, a self-templated approach was proposed for constructing CoSe₂ hollow microspheres by utilizing ZIF-67 hollow sphere as a template. In the followed selenylation process, selenium vapor reacts with cobalt ion in ZIF-67 to form CoSe₂ microspheres. The obtained CoSe₂ microspheres retain the cavity of the ZIF-67 and massive uniformly dispersed CoSe₂ nanoparticles are embedded throughout carbon walls. The hollow interior and porous structure of CoSe₂ microspheres provide an enhanced surface-volume ratio and short charge/mass transfer distance. The CoSe₂ microspheres show a typical oxidase-like property able to promote 3,3',5,5'-tetramethylbenzidine (TMB) oxidation by dissolved oxygen to produce an intensive color reaction. Reactive oxygen species trials demonstrate that ·OH, ¹O₂ and O₂^•- radicals coexist in the TMB-CoSe₂ system. Based on its inhibitive role, a rapid and ultrasensitive determination of glutathione was reached, showing four orders of magnitude linear range from 0.005 to 10 μM and a limit of detection of 4.62 nM (S/N = 3). The assay has been successfully used to glutathione determination in practical samples.

Fabrication of an anode composed of a N, S co-doped carbon nanotube hollow architecture with CoS2 confined within: toward Li and Na storage

Over the years, transition metal chalcogenides (TMCs) have attracted ample attention from researchers on account of their high theoretical capacity, through which they show great potential for use in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Nevertheless, there are some serious obstacles (particle pulverization and large volume change) still in the way to achieving satisfactory cycling performance and rate property. Here, we report the preparation of a N, S co-doped carbon nanotube hollow architecture confining CoS₂ (CoS₂/NSCNHF) derived from bimetal-organic-frameworks. The rationally designed structure possesses excellent Li⁺/Na⁺ storage performances. Further investigation of the Li⁺/Na⁺ storage behavior indicated the presence of a partial pseudocapacitive contribution, facilitating the fast Li⁺/Na⁺ interaction/extraction process and thus giving it superb electrochemical property. This work may represent an important step forward in the fabrication of MOF-derived hierarchical hybrids combined with a hollow structure and TMCs to help such TMCs achieve their potential in energy storage systems.

Three-Dimensional Hierarchical Flowerlike FeP Wrapped with N-Doped Carbon Possessing Improved Li+ Diffusion Kinetics and Cyclability for Lithium-Ion Batteries

Transition-metal phosphides have a potential application in lithium-ion batteries (LIBs) because of their high theoretical capacities and low cost; nevertheless, they possess dramatic volumetric variation during cycling associated with poor conductivity, limiting their practical applications. Here, a three-dimensional (3D) hierarchical flowerlike FeP coated with nitrogen-doped carbon layer (FeP@N,C hybrid) was constructed through a solvothermal method, followed by a phosphating approach under low temperature. N-doped carbon not only suppresses the volume fluctuation of FeP, but also promotes electron transfer, accompanied by catalyzing the decomposition of Li₃P to improve the reversibility of the FeP@N,C hybrid during cycling processes. In addition, a 3D flowerlike architecture assembled from porous nanosheets is also beneficial for shortening the migration path of ions as well as improving the contact area of electrode with electrolyte, which enhances the reaction kinetics and is proved by both experimental measurement of Li⁺ diffusion coefficient and resistivity, along with the calculation of density functional theory. Consequently, the 3D hierarchical flowerlike FeP@N,C hybrid performs excellent cyclic stability (569 mA h g^-1 at a current density of 500 mA g^-1 for the 300th cycle) and rate performance (331.94 mA h g^-1 at a high current density of 5 A g^-1) for LIBs. Based on above results, the fabrication strategy in this work could offer a thought to design other high-performance metal phosphide hybrids.

Composition Engineering Boosts Voltage Windows for Advanced Sodium-Ion Batteries

Transition-metal selenides have captured sustainable research attention in energy storage and conversion field as promising anodes for sodium-ion batteries. However, for the majority of transition metal selenides, the potential windows have to compress to 0.5-3.0 V for the maintenance of cycling and rate capability, which largely sacrifices the capacity under low voltage and impair energy density for sodium full batteries. Herein, through introducing diverse metal ions, transition-metal selenides consisted of different composition doping (CoM-Se₂@NC, M = Ni, Cu, Zn) are prepared with more stable structures and higher conductivity, which exhibit superior cycling and rate properties than those of CoSe₂@NC even at a wider voltage range for sodium ion batteries. In particular, Zn²⁺ doping demonstrates the most prominent sodium storage performance among series materials, delivering a high capacity of 474 mAh g^-1 after 80 cycles at 500 mA g^-1 and rate capacities of 511.4, 382.7, 372.1, 339.2, 306.8, and 291.4 mAh g^-1 at current densities of 0.1, 0.5, 1.0, 1.4, 1.8, and 2.0 A g^-1, respectively. The composition adjusting strategy based on metal ions doping can optimize electrochemical performances of metal selenides, offer an avenue to expand stable voltage windows, and provide a feasible approach for the construction of high specific energy sodium-ion batteries.

Heterostructured SnS/TiO2@C hollow nanospheres for superior lithium and sodium storage

Tin(ii) sulfide (SnS) is considered to be one of the most promising anode materials for lithium/sodium ion batteries (LIBs/SIBs) due to its high theoretical capacity and low-cost. However, its practical applications are severely impeded by its low electrical conductivity and large volume change upon cycling. Herein, we demonstrate a high-performance SnS/TiO₂ encapsulated by a carbon shell (SnS/TiO₂@C) synthesized by facile coprecipitation and annealing treatment. The exterior carbon coating can not only improve the conductivity, but also effectively relieve volume variation to maintain the structural integrity during cycling. Significantly, the internal SnS/TiO₂ heterostructure formed a built-in electric field to provide favorable driving force for ion transfer. Consequently, the synthesized SnS/TiO₂@C delivered a reversible capacity of 672.4 mA h g^-1 at 0.5 A g^-1 after 100 cycles for lithium storage and 331.2 mA h g^-1 at 0.2 A g^-1 after 200 cycles for sodium storage. Meanwhile, ultra-long lifespans of 3000 cycles at 5.0 A g^-1 with a capacity of 394.5 mA h g^-1 for LIBs and 750 cycles at 5.0 A g^-1 with a capacity of 295 mA h g^-1 for SIBs were achieved. The electrochemical reaction mechanisms of the SnS/TiO₂@C electrode have been investigated by in situ XRD, ex situ XRD, and ex situ HRTEM. Our work may offer further understanding of the hierarchical structure to boost the electrochemical properties of the electrode materials.

Iron-Doping-Induced Phase Transformation in Dual-Carbon-Confined Cobalt Diselenide Enabling Superior Lithium Storage

Transition metal chalcogenides (TMCs) have been investigated as promising anodes for high-performance lithium-ion batteries, but they usually suffer from poor conductivity and large volume variation, thus leading to unsatisfactory performance. Although nanostructure engineering and hybridization with conductive materials have been proposed to address this concern, a better performance toward practical device applications is still highly desired. Herein, we report an iron-doping-induced structural phase transition from pyrite-type (cubic) to marcasite-type (orthorhombic) phases in porous carbon/rGO-coupled CoSe₂. The dual-carbon-confined orthorhombic CoSe₂ ( o-Fe _xCo_{1- x}Se₂@NC@rGO) composites exhibit dramatically enhanced lithium storage performance (920 mAh g^-1 after 1000 cycles at 1.0 A g^-1) over cubic CoSe₂-based composites ( c-CoSe₂@NC@rGO). The combined experimental studies and density functional theory calculations reveal that this doping-induced structural phase transformation strategy could create a favorable electronic structure and ensure a rapid charge transfer. These results demonstrate that the phase-transformation engineering may provide another opportunity in the design of high-performance TMC-based electrodes.

Yolk-Shell-Structured Bismuth@N-Doped Carbon Anode for Lithium-Ion Battery with High Volumetric Capacity

As an anode for lithium-ion batteries, metallic bismuth (Bi) can provide a superb volumetric capacity of 3800 mA h cm^-3, showing perspective value for application. It is a pity that the severe volume swelling during the lithiation process leads to the dramatic deterioration of the cycling performances. To overcome this issue, Bi nanorods encapsulated in N-doped carbon nanotubes (yolk-shell Bi@C-N) are elaborately designed through in situ thermal reduction of Bi₂S₃@polypyrrole nanorods. In comparison with the commercial Bi, the lithium storage capacities of Bi@C-N are significantly enhanced, and it presents a stable volumetric capacity of 1700 mA h cm^-3 over 500 cycles at a high current density of 1.0 A g^-1, nearly 2.2 times that of graphite. The N-doped carbon nanotube and the cavity between the carbon wall and Bi jointly contribute to this superior performance. Especially, the failure mechanism of Bi nanorods and the protective effect of the carbon shell are revealed by ex situ TEM, which illuminates the decreasing tendency in the initial 10-20 cycles and the subsequent stable trend of cyclic performance.

SnS hollow nanofibers as anode materials for sodium-ion batteries with high capacity and ultra-long cycling stability

In this study, a novel anode material of SnS hollow nanofibers (SnS HNFs) was rationally synthesized by a facile process and demonstrated to be a promising anode candidate for sodium-ion batteries.

Constructing Three-Dimensional Porous Carbon Framework Embedded with FeSe2 Nanoparticles as an Anode Material for Rechargeable Batteries

Metal selenides have caused widespread concern due to their high theoretical capacities and appropriate working potential; however, they suffer from large volume variation during cycling and low electrical conductivity, which limit their practical applications. In this article, a three-dimensional (3D) porous carbon framework embedded with homogeneous FeSe₂ nanoparticles (3D porous FeSe₂/C composite) was synthesized by a facile calcined approach, following a selenized method without a template. As the uniformity of FeSe₂ nanoparticles and 3D porous structure are beneficial to accommodate volume stress upon cycling and shorten electrons/ions transport path, associated with carbon as a buffer matrix for increasing conductivity, the 3D porous FeSe₂/C composite displays excellent electrochemical properties with high reversible capacities of 798.4 and 455.0 mA h g^-1 for lithium-ion batteries and sodium-ion batteries, respectively, when the current density is 100 mA g^-1 after 100 cycles. In addition, the as-prepared composite exhibits good cycling stability as compared to bare FeSe₂ nanoparticles. Therefore, the facile synthetic strategy in the current work provides a new perspective in constructing a high-performance anode.

Tailoring hollow microflower-shaped CoSe2 anodes in sodium ion batteries with high cycling stability

Hollow microflower-shaped CoSe2 particles were successfully constructed and further evaluated as an anode material for sodium-ion batteries. It yielded a large discharge capacity of 220 mA h g-1 and ultralong cycle life of 1690 cycles at 1 A g-1. This ultralong cycle life can be attributed to a surface-controlled pseudocapacitive behavior and resulting rapid electron/sodium ion transport.