Nitrogen-Doped Yolk-Shell-Structured CoSe/C Dodecahedra for High-Performance Sodium Ion Batteries

Synthesis and Electrochemical Performance of ZnSe Electrospinning Nanofibers as an Anode Material for Lithium Ion and Sodium Ion Batteries

ZnSe nitrogen-doped carbon composite nanofibers (ZnSe@N-CNFs) were derived as anode materials from selenization of electrospinning nanofibers. Electron microscopy shows that ZnSe nanoparticles are distributed in electrospinning nanofibers after selenization. Electrochemistry tests were carried out and the results show the one-dimensional carbon composite nanofibers reveal a great structural stability and electrochemistry performance by the enhanced synergistic effect with ZnSe. Even at a current density of 2 A g-1, the as-prepared electrodes can still reach up to 701.7 mA h g-1 after 600 cycles in lithium-ion batteries and 368.9 mA h g-1 after 200 cycles in sodium-ion batteries, respectively. ZnSe@N-CNFs with long cycle life and high capacity at high current density implies its promising future for the next generation application of energy storage.

Sulfur-Doped Mesoporous Carbon Nitride with an Ordered Porous Structure for Sodium-Ion Batteries

Mesoporous carbon nitride (MCN) with well-ordered porous structures is a promising anode material for secondary ion batteries owing to their unique physico- and electrochemical properties. However, the practical application of these MCNs in sodium-ion batteries (SIBs) is still limited because of their confined interlayer distance, which results in restricted accommodation of Na ions inside the lattice. Here, we report on the synthesis of highly ordered sulfur-doped MCN (S-MCN) through a hard template approach by employing dithiooxamide (DTO) as a single molecular precursor containing carbon, nitrogen, and sulfur elements. The interlayer distance of carbon nitride is significantly expanded upon the introduction of larger S ions on the MCN lattice, which enables high capability of Na ion accommodation. We also demonstrate through the first-principles density functional theory calculation that the present S-MCN is highly optimized not only for the chemical structure but also for uptaking abundant Na ions with high adsorption energy. The specific discharge capacity of SIBs appears to be remarkably enhanced for S-MCN (304.2 mA h g^-1) compared to the nonporous S-CN (167.9 mA h g^-1) and g-C₃N₄ (5.4 mA h g^-1), highlighting the pivotal roles of the highly ordered mesoporous structure and S-doping in enhancing the electrochemical functionality of carbon nitride as an anode material for SIBs.

Phase-Tunable Synthesis of Ultrathin Layered Tetragonal CoSe and Nonlayered Hexagonal CoSe Nanoplates

Multiple structural phases in transition metal dichalcogenides have attracted considerable recent interest for their tunable chemical and electronic properties. Herein, a chemical vapor deposition route to ultrathin CoSe nanoplates with tunable structure phases is reported. By precisely tailoring the growth temperature, ultrathin 2D layered tetragonal CoSe nanoplates and nonlayered hexagonal CoSe nanoplates can be selectively prepared as square or hexagonal geometries, with thickness as thin as 2.3 and 3.7 nm, respectively. X-ray diffraction, transmission electron microscopy, and selected area electron diffraction studies show that both types of nanoplates are high-quality single crystals. Electrical transport studies reveal that both the tetragonal and hexagonal CoSe nanoplates show strong thickness-tunable electrical properties and excellent breakdown current density. The 2D hexagonal CoSe nanoplates display metallic behavior with an excellent conductivity up to 6.6 × 10⁵ S m^-1 and an extraordinary breakdown current density up to 3.9 × 10⁷ A cm^-2 , while the square tetragonal nanoplates show considerably lower conductivity up to 8.2 × 10⁴ S m^-1 with angle-dependent magnetoresistance and weak antilocalization effect at lower field. This study offers a tunable material system for exploring multiphase 2D materials and their potential applications for electronic and magnetoelectronic devices.

Solvothermally Doping NiS2 Nanoparticles on Carbon with Ferric Ions for Efficient Oxygen Evolution Catalysis

Exploring efficient non-precious metal based electrocatalysts for the oxygen evolution reaction (OER) is a prerequisite to implement the widespread application of a water electrolyzer and metal-air batteries. Herein, Fe-doped NiS2 nanoparticles on a carbon matrix (Fe-NiS2/C) are facilely prepared via a two-step solvothermal process, where Ni-containing metal organic frameworks (Ni-MOFs) are vulcanized in situ and carbonized by a solvothermal method to form abundant NiS2 nanoparticles homogeneously distributed on a carbon matrix (NiS2/C), followed by doping with ferric ions via a similar solvothermal treatment. The resulting Fe-NiS2/C nanoparticle composites show a rougher surface than the NiS2/C parent, likely due to the formation of more structural defects after ferric ion doping, which maximizes the exposure of active sites. Moreover, ferric ion doping can also regulate the surface electronic state to reduce the activation energy barrier for OER on NiS2/C sample. With these merits, the best sample Fe-NiS2/C-30 only requires a potential of +1.486 V (vs. RHE) to reach an OER current density of 10 mA cm−2 and can retain 96.85% of its initial current after continuous working for about 10 h in 1.0 M KOH aqueous solution, along with a small Tafel slope of 45.66 mV/dec, outperforming a commercial RuO2 catalyst. The results in this work enrich the method to tailor the catalytic activity of transition metal sulfides for electrochemical energy technologies.

Applications of MxSey (M = Fe, Co, Ni) and Their Composites in Electrochemical Energy Storage and Conversion

Transition-metal selenides (M_xSe_y, M = Fe, Co, Ni) and their composites exhibit good storage capacities for sodium and lithium ions and occupy a unique position in research on sodium-ion and lithium-ion batteries. M_xSe_y and their composites are used as active materials to improve catalytic activity. However, low electrical conductivity, poor cycle stability, and low rate performance severely limit their applications. This review provides a comprehensive introduction to and understanding of the current research progress of M_xSe_y and their composites. Moreover, this review proposes a broader research platform for these materials, including various bioelectrocatalytic performance tests, lithium-sulfur batteries, and fuel cells. The synthesis method and related mechanisms of M_xSe_y and their composites are reviewed, and the effects of material morphologies on their electrochemical performance are discussed. The advantages and disadvantages of M_xSe_y and their composites as well as possible strategies for improving the storage and conversion of electrochemical energy are also summarized.

Electrolytes and Electrolyte/Electrode Interfaces in Sodium-Ion Batteries: From Scientific Research to Practical Application

Sodium-ion batteries (SIBs) have drawn considerable interest as power-storage devices owing to the wide abundance of their constituents and low cost. To realize a high performance-price ratio, the cathode and anode materials must be optimized. As essential components of SIBs, electrolytes should have wide electrochemical windows, high thermal stability, and exceptional ionic conductivity. Therefore, improved electrolytes, based on various materials and compositions, are developed to meet the practical demands of SIBs, including organic electrolytes, ionic liquids, aqueous, solid electrolytes, and hybrid electrolytes. Although mature organic electrolytes are currently used in production, aqueous and solid electrolytes show advantages for future applications, as discussed here in detail. Current efforts in modifying electrolytes to optimize their interfacial compatibility with electrodes, leading to longer battery lifetimes and greater safety, are described. The advanced characterization techniques used to investigate the properties of electrolytes and interfaces are introduced, and the reaction processes and degradation mechanisms of SIBs are revealed. Furthermore, the practical prospects of SIBs promoted by high-quality electrolytes appropriately matched with electrodes are predicted and directions for developing next-generation SIBs are suggested.

Necklace-like Si@C nanofibers as robust anode materials for high performance lithium ion batteries

Silicon is believed to be a promising anode material for lithium ion batteries because of its highest theoretical capacity and low discharge potential. However, severe pulverization and capacity fading caused by huge volume change during cycling limits its practical application. In this work, necklace-like N-doped carbon wrapped mesoporous Si nanofibers (NL-Si@C) network has been synthesized via electrospinning method followed by magnesiothermic reduction reaction process to suppress these issues. The mesoporous Si nanospheres are wrapped with N-doped carbon shells network to form yolk-shell structure. Interestingly, the distance of adjacent Si@C nanospheres can be controllably adjusted by different addition amounts of SiO₂ nanospheres. When used as an anode material for lithium ion batteries, the NL-Si@C-0.5 exhibits best cycling stability and rate capability. The excellent electrochemical performances can be ascribed to the necklace-like network structure and N-doped carbon layers, which can ensure fast ions and electrons transportation, facilitate the electrolyte penetration and provide finite voids to allow large volume expansion of inner Si nanoparticles. Moreover, the protective carbon layers are also beneficial to the formation of stable solid electrolyte interface film.

Unraveling the Impact of Ether and Carbonate Electrolytes on the Solid-Electrolyte Interface and the Electrochemical Performances of ZnSe@C Core-Shell Composites as Anodes of Lithium-Ion Batteries

The recognition of the solid electrolyte interface (SEI) between the electrode materials and electrolyte is limiting the selection of electrode materials, electrolytes, and further the electrochemical performance of batteries. Herein, we report ZnSe@C core-shell nanocomposites derived from ZIF-8 as anode materials of lithium-ion batteries, the electrochemical performances, and SEI films formed on ZnSe@C in both ether and carbonate electrolytes. It is found that ZnSe@C delivers a reversible capacity of 617.1 mA h·g^-1 after 800 cycles at 1 A·g^-1 in the ether electrolyte, much higher than that in the carbonate electrolyte. Both ex situ X-ray diffraction and X-ray photoelectron spectroscopies reveal that stable SEI films are formed on ZnSe@C in the ether electrolyte while selenium is involved in the formation of SEI films and further dissolved into the carbonate electrolyte because of the concurrent decomposition of electrolytes and insertion of Li⁺ into ZnSe, which differentiates between the cycling performances of ZnSe@C composites in ether and carbonate electrolytes.

A Salt-Templated Strategy toward Hollow Iron Selenides-Graphitic Carbon Composite Microspheres with Interconnected Multicavities as High-Performance Anode Materials for Sodium-Ion Batteries

In this work, a facile salt-templated approach is developed for the preparation of hollow FeSe₂ /graphitic carbon composite microspheres as sodium-ion battery anodes; these are composed of interconnected multicavities and an enclosed surface in-plane embedded with uniform hollow FeSe₂ nanoparticles. As the precursor, Fe₂ O₃ /carbon microspheres containing NaCl nanocrystals are obtained using one-pot ultrasonic spray pyrolysis in which inexpensive NaCl and dextrin are used as a porogen and carbon source, respectively, enabling mass production of the composites. During post-treatment, Fe₂ O₃ nanoparticles in the composites transform into hollow FeSe₂ nanospheres via the Kirkendall effect. These rational structures provide numerous conductive channels to facilitate ion/electron transport and enhance the capacitive contribution. Moreover, the synergistic effect between the hollow cavities within FeSe₂ and the outstanding mechanical strength of the porous carbon matrix can effectively accommodate the large volume changes during cycling. Correspondingly, the composite microsphere exhibits high discharge capacity of 510 mA h g^-1 after 200 cycles at 0.2 A g^-1 with capacity retention of 88% when calculated from the second cycle. Even at a high current density of 5.0 A g^-1 , a high discharge capacity of 417 mA h g^-1 can be achieved.

In situ TEM and half cell investigation of sodium storage in hexagonal FeSe nanoparticles

A hexagonal FeSe anode for sodium-ion batteries shows desirable electrochemical performance with an irreversible phase transition from the hexagonal to tetragonal phase.

Enhanced activity of selenocyanate-containing transition metal chalcogenides supported by nitrogen-doped carbon materials for the oxygen reduction reaction

The SeCN⁻ containing transition metal chalcogenides supported by nitrogen-doped carbon catalyzes the ORR activity.

High-Performance P2-Na0.70Mn0.80Co0.15Zr0.05O2 Cathode for Sodium-Ion Batteries

Room-temperature sodium-ion batteries (NIBs) using a manganese-based layered cathode have been considered promising candidates for grid-scale energy storage applications. However, manganese-based materials suffer from serious Jahn-Teller distortion, phase transition, and unstable interface, resulting in severe structure degradation, sluggish sodium diffusion kinetics, and poor cycle, respectively. Herein, we demonstrate a Zr-doped Na_0.70Mn_0.80Co_0.15Zr_0.05O₂ material with much improved specific capacity and rate capability compared with Zr-free Na_0.70Mn_0.85Co_0.15O₂ when used as cathode materials for NIBs. The material delivers a reversible capacity of 173 mA h g^-1 at 0.1 C rate, corresponding to approximately 72% of the theoretical capacity (239 mA h g^-1) based on a single-electron redox process, and a capacity retention of 88% after 50 cycles was obtained. Additionally, a homogenous solid-state interphase (SEI) film was revealed directly by high-resolution transmission electron microscopy in Zr-doped material after battery cycling. Electrochemical impedance spectroscopy proves that the formation of SEI films provides the Zr-doped material with special chemical/electrochemical stability. These results here give clear evidence of the utility of Zr-doping to improve the surface and environmental stability, sodium diffusion kinetics, and electrochemical performance of P2-type layered structure, promising advanced sodium-ion batteries with higher energy density, higher surface stability, and longer cycle life compared with the commonly used magnesiumdoping method in electrode materials.

CoSe2 Nanoparticles Encapsulated by N-Doped Carbon Framework Intertwined with Carbon Nanotubes: High-Performance Dual-Role Anode Materials for Both Li- and Na-Ion Batteries

It is of fundamental and technological significance to develop dual-role anode materials for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) with high performance. Here, a composite material based on CoSe2 nanoparticles encapsulated in N-doped carbon framework intertwined with carbon nanotubes (CoSe2@N-CF/CNTs) is prepared successfully from cobalt-based zeolitic imidazolate framework (ZIF-67). As anode materials for LIBs, CoSe2@N-CF/CNTs composites deliver a reversible capacity of 428 mAh g-1 even after 500 cycles at a current density of 1 A g-1 with almost 100% Coulombic efficiency. The charge and discharge mechanisms of CoSe2 are characterized using ex situ X-ray diffraction and Raman analysis, from which the lithiation products of CoSe2 are found to be Li x CoSe2 and Li2Se, which are further converted to CoSe2 upon delithiation. The CoSe2@N-CF/CNTs composites also demonstrate excellent electrochemical performance as anode materials for SIBs with a carbonate-based electrolyte, with specific capacities of 606 and 501 mAh g-1 at 0.1 and 1 A g-1 in the 100th cycle. The electrochemical performance of the anode materials is further studied by pseudocapacitance and galvanostatic intermittent titration technique (GITT) measurements. This work may be exploited for the rational design and development of dual-role anode materials for both Li- and Na-ion batteries.

Nanoflower-like N-doped C/CoS2 as high-performance anode materials for Na-ion batteries

Novel nanoflower-like N-doped C/CoS2 spheres assembled from 2D wrinkled CoS2 nanosheets were synthesized through a facile one-pot solvothermal method followed by sulfurization. Ascribed to the optimized 3D nanostructure and rational surface engineering, the unique hierarchical structure of the nanoflower-like C/CoS2 composites showed an excellent sodium ion storage capacity accompanied by high specific capacity, superior rate performance and long-term cycling stability. Specifically, the conductive interconnected wrinkled nanosheets create a number of mesoporous structures and thus can greatly release the mechanical stress caused by Na+ insertion/extraction. Besides, it was observed from the experiments that many extra defect vacancies and Na+ storage sites are introduced by the nitrogen doping process. It was also observed that the crosslinked 2D nanosheets can effectively reduce the diffusion lengths of sodium ions and electrons, resulting in an outstanding rate performance (>700 mA h g-1 at 1 A g-1 and 458 mA h g-1 at even 10 A g-1) and extraordinary cycling stability (698 mA h g-1 at 1 A g-1 after 500 cycles). The results provide a facile approach to fabricate promising anode materials for high-performance sodium-ion batteries (SIBs).

Determination of the antioxidant propyl gallate in meat by using a screen-printed electrode modified with CoSe2 nanoparticles and reduced graphene oxide

A voltammetric sensor is described for the quantitation of propyl gallate (PG). A screen-printed carbon electrode (SPCE) was modified with reduced graphene sheets that were decorated with cobalt diselenide nanoparticles (CoSe₂@rGO). The material was hydrothermally prepared and characterized by several spectroscopic techniques. The modified SPCE displays excellent electrocatalytic ability towards PG. Differential pulse voltammetry, with a peak voltage at 0.34 V (vs. Ag/AgCl) has a sensitivity of 12.84 μA·μM^-1·cm^-2 and a detection limit as low as 16 nM. The method is reproducible, selective, and practical. This method was applied to the determination of PG in spiked meat samples, and the result showed an adequate recovery. Graphical abstract Schematic of a new method for fast and sensitive electrochemical determination of the food additive propyl gallate in meat.

Double-Morphology CoS2 Anchored on N-Doped Multichannel Carbon Nanofibers as High-Performance Anode Materials for Na-Ion Batteries

Na-ion batteries (NIBs) have attracted increasing attention given the fact that sodium is relatively more plentiful and affordable than lithium for sustainable and large-scale energy storage systems. However, the shortage of electrode materials with outstanding comprehensive properties has limited the practical implementations of NIBs. Among all the discovered anode materials, transition-metal sulfide has been proven as one of the most competitive and promising ones due to its excellent redox reversibility and relatively high theoretical capacity. In this study, double-morphology N-doped CoS₂/multichannel carbon nanofibers composites (CoS₂/MCNFs) are precisely designed, which overcome common issues such as the poor cycling life and inferior rate performance of CoS₂ electrodes. The conductive 3D interconnected multichannel nanostructure of CoS₂/MCNFs provides efficient buffer zones for the release of mechanical stresses from Na⁺ ions intercalation/deintercalation. The synergy of the diverse structural features enables a robust frame and a rapid electrochemical reaction in CoS₂/MCNFs anode, resulting in an impressive long-term cycling life of 900 cycles with a capacity of 620 mAh g^-1 at 1 A g^-1 (86.4% theoretical capacity) and a surprisingly high-power output. The proposed design in this study provides a rational and novel thought for fabricating electrode materials.

Encapsulation of CoS x Nanocrystals into N/S Co-Doped Honeycomb-Like 3D Porous Carbon for High-Performance Lithium Storage

A honeycomb-like 3D N/S co-doped porous carbon-coated cobalt sulfide (CoS, Co9S8, and Co1-x S) composite (CS@PC) is successfully prepared using polyacrylonitrile (PAN) as the nitrogen-containing carbon source through a facile solvothermal method and subsequent in situ conversion. As an anode for lithium-ion batteries (LIBs), the CS@PC composite exhibits excellent electrochemical performance, including high reversible capacity, good rate capability, and cyclic stability. The composite electrode delivers specific capacities of 781.2 and 466.0 mAh g-1 at 0.1 and 5 A g-1, respectively. When cycled at a current density of 1 A g-1, it displays a high reversible capacity of 717.0 mAh g-1 after 500 cycles. The ability to provide this level of performance is attributed to the unique 3D multi-level porous architecture with large electrode-electrolyte contact area, bicontinuous electron/ion transport pathways, and attractive structure stability. Such micro-/nanoscale design and engineering strategies may also be used to explore other nanocomposites to boost their energy storage performance.

Metal Organic Framework Derived Materials: Progress and Prospects for the Energy Conversion and Storage

Exploring new materials with high efficiency and durability is the major requirement in the field of sustainable energy conversion and storage systems. Numerous techniques have been developed in last three decades to enhance the efficiency of the catalyst systems, control over the composition, structure, surface area, pore size, and moreover morphology of the particles. In this respect, metal organic framework (MOF) derived catalysts are emerged as the finest materials with tunable properties and activities for the energy conversion and storage. Recently, several nano- or microstructures of metal oxides, chalcogenides, phosphides, nitrides, carbides, alloys, carbon materials, or their hybrids are explored for the electrochemical energy conversion like oxygen evolution, hydrogen evolution, oxygen reduction, or battery materials. Interest on the efficient energy storage system is also growing looking at the practical applications. Though, several reviews are available on the synthesis and application of MOF and MOF derived materials, their applications for the electrochemical energy conversion and storage is totally a new field of research and developed recently. This review focuses on the systematic design of the materials from MOF and control over their inherent properties to enhance the electrochemical performances.

Hierarchically Porous Fe2 CoSe4 Binary-Metal Selenide for Extraordinary Rate Performance and Durable Anode of Sodium-Ion Batteries

Owing to high energy capacities, transition metal chalcogenides have drawn significant research attention as the promising electrode materials for sodium-ion batteries (SIBs). However, limited cycle life and inferior rate capabilities still hinder their practical application. Improvement of the intrinsic conductivity by smart choice of elemental combination along with carbon coupling of the nanostructures may result in excellence of rate capability and prolonged cycling stability. Herein, a hierarchically porous binary transition metal selenide (Fe2 CoSe4 , termed as FCSe) nanomaterial with improved intrinsic conductivity was prepared through an exclusive methodology. The hierarchically porous structure, intimate nanoparticle-carbon matrix contact, and better intrinsic conductivity result in extraordinary electrochemical performance through their synergistic effect. The synthesized FCSe exhibits excellent rate capability (816.3 mA h g-1 at 0.5 A g-1 and 400.2 mA h g-1 at 32 A g-1 ), extended cycle life (350 mA h g-1 even after 5000 cycles at 4 A g-1 ), and adequately high energy capacity (614.5 mA h g-1 at 1 A g-1 after 100 cycles) as anode material for SIBs. When further combined with lab-made Na3 V2 (PO4 )3 /C cathode in Na-ion full cells, FCSe presents reasonably high and stable specific capacity.

Construction of Bimetallic ZIF-Derived Co-Ni LDHs on the Surfaces of GO or CNTs with a Recyclable Method: Toward Reduced Toxicity of Gaseous Thermal Decomposition Products of Unsaturated Polyester Resin

This work proposed an idea of recycling in preparing Co-Ni layered double hydroxide (LDH)-derived flame retardants. A novel and feasible method was developed to synthesize CO-Ni LDH-decorated graphene oxide (GO) and carbon nanotubes (CNTs), by sacrificing bimetal zeolitic imidazolate frameworks (ZIFs). Organic ligands that departed from ZIFs were recyclable and can be reused to synthesize ZIFs. ZIFs, as transitional objects, in situ synthesized on the surfaces of GO or CNTs directly suppressed the re-stacking of the carbides and facilitated the preparation of GO@LDHs and CNTs@LDHs. As-prepared hybrids catalytically reduced toxic CO yield during the thermal decomposition of unsaturated polyester resin (UPR). What is more, the release behaviors of aromatic compounds were also suppressed during the pyrolysis process of UPR composites. The addition of GO@LDHs and CNTs@LDHs obviously inhibited the heat release and smoke emission behaviors of the UPR matrix during combustion. Mechanical properties of the UPR matrix also improved by inclusion of the carbides derivatives. This work paved a feasible method to prepare well-dispersed carbides@Co-Ni LDH nanocomposites with a more environmentally friendly method.

MOF-Templated N-Doped Carbon-Coated CoSe2 Nanorods Supported on Porous CNT Microspheres with Excellent Sodium-Ion Storage and Electrocatalytic Properties

Three-dimensional (3D) porous microspheres composed of CoSe₂@N-doped carbon nanorod-deposited carbon nanotube (CNT) building blocks (CoSe₂@NC-NR/CNT) can be successfully synthesized using CNT/Co-based metal-organic framework (ZIF-67) porous microspheres as a precursor. This strategy involves the homogeneous coating of ZIF-67 polyhedrons onto porous CNT microspheres prepared by spray pyrolysis and further selenization of the composites under an Ar/H₂ atmosphere. During the selenization process, the ZIF-67 polyhedrons on the CNT backbone are transformed into N-doped carbon-coated CoSe₂ nanorods by a directional recrystallization process, resulting in a homogeneous deposition of CoSe₂@NC nanorods on the porous CNT microspheres. Such a unique structure of CoSe₂@NC-NR/CNT microspheres facilitates the transport of ions, electrons, and mass and provides a conductive pathway for electrons during electrochemical reactions. Correspondingly, the composite exhibits a superior dual functionality as both an electrocatalyst for the hydrogen evolution reaction (HER) and an electrode for sodium-ion batteries (SIBs). The CoSe₂@NC-NR/CNT microspheres exhibit a small Tafel slope (49.8 mV dec^-1) and a superior stability for HER. Furthermore, the composite delivers a high discharge capacity of 555 mA h g^-1 after 100 cycles at a current density of 0.2 A g^-1 and a good rate capability for SIBs.

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

Sodium-ion batteries (SIBs), as the promising commercial energy system, are restricted by their sluggish kinetics and low sodium-ion storage. Metal selenide possesses good conductivity and capacity but still suffers from the stacked problem and volume expansion. Significantly, CoSe₂/C is successfully prepared with the assistance of citric acid as both a chelating agent and carbon precursor, displaying that cobblestone-like nanospheres with the radii (<25 nm) distribute uniformly in the carbon matrix. It is expected that the established Co-O-C bonds enhance the stability of the structure with faster ion shuttling. With the available electrolyte (NaCF₃SO₃/diethylene glycol dimethyl ether) in a potential window range from 0.5 to 3.0 V, the as-obtained sample shows the ultralong lifespan at 4.5 A g^-1, retaining a capacity of 345 mA h g^-1 after 10 000 cycles. From the detailed kinetic analysis, it is clear that the surface-controlled electrochemical behavior mainly contributes to the excellent large-current cycling stability and Na storage capacity. The ex situ results support that the crystal and morphological structure remains stable. This work is anticipated to enhance the in-depth understanding of the CoSe₂/C anode and supply a facile manner to obtain electrode materials for SIBs.

The State and Challenges of Anode Materials Based on Conversion Reactions for Sodium Storage

Sodium-ion batteries (SIBs) have huge potential for applications in large-scale energy storage systems due to their low cost and abundant sources. It is essential to develop new electrode materials for SIBs with high performance in terms of energy density, cycle life, and cost. Metal binary compounds that operate through conversion reactions hold promise as advanced anode materials for sodium storage. This Review highlights the storage mechanisms and advantages of conversion-type anode materials and summarizes their recent development. Although conversion-type anode materials have high theoretical capacities and abundant varieties, they suffer from multiple challenging obstacles to realize commercial applications, such as low reversible capacity, large voltage hysteresis, low initial coulombic efficiency, large volume changes, and low cycling stability. These key challenges are analyzed in this Review, together with emerging strategies to overcome them, including nanostructure and surface engineering, electrolyte optimization, and battery configuration designs. This Review provides pertinent insights into the prospects and challenges for conversion-type anode materials, and will inspire their further study.

Formation of Hierarchical Cu-Doped CoSe2 Microboxes via Sequential Ion Exchange for High-Performance Sodium-Ion Batteries

Electrode materials based on electrochemical conversion reactions have received considerable interest for high capacity anodes of sodium-ion batteries. However, their practical application is greatly hindered by the poor rate capability and rapid capacity fading. Tuning the structure at nanoscale and increasing the conductivity of these anode materials are two effective strategies to address these issues. Herein, a two-step ion-exchange method is developed to synthesize hierarchical Cu-doped CoSe₂ microboxes assembled by ultrathin nanosheets using Co-Co Prussian blue analogue microcubes as the starting material. Benefitting from the structural and compositional advantages, these Cu-doped CoSe₂ microboxes with improved conductivity exhibit enhanced sodium storage properties in terms of good rate capability and excellent cycling performance.

Tuning Pseudocapacitance via C-S Bonding in WS2 Nanorods Anchored on N,S Codoped Graphene for High-Power Lithium Batteries

Pseudocapacitance plays an important role in high-power lithium-ion batteries (LIBs). However, it is still lack of effective methods to tailor the pseudocapacitance contribution in electrode materials for LIBs. Herein, pseudocapacitance tuned by the strength of C-S bonding has been rendered in WS₂ nanorods anchored on the N,S codoped three-dimensional graphene hybrid (WS₂@N,S-3DG) for the first time. The pseudocapacitive contributions in the charge storage can be enhanced effectively with the increased strength of C-S bonding. As expected, the enhanced extrinsic pseudocapacitance makes WS₂@N,S-3DG a fascinating electrode material for high-power LIBs, with a high reversible capacity of 509 mA h g^-1 over 500 cycles at a current density as high as 2 A g^-1. These encouraging results of pseudocapacitance tailored by chemical bonding provide new opportunities for designing advanced electrode materials.

Tailoring yolk–shell FeP@carbon nanoboxes with engineered void space for pseudocapacitance-boosted lithium storage

A unique yolk–shell FeP@C nanobox is synthesized by an etching-in-box combined with a phosphidation-in-box approach, manifesting remarkable pseudocapacitance-boosted lithium ion storage properties.

Metal-Organic Framework-Derived Materials for Sodium Energy Storage

Recently, sodium-ion batteries (SIBs) are extensively explored and are regarded as one of the most promising alternatives to lithium-ion batteries for electrochemical energy conversion and storage, owing to the abundant raw material resources, low cost, and similar electrochemical behavior of elemental sodium compared to lithium. Metal-organic frameworks (MOFs) have attracted enormous attention due to their high surface areas, tunable structures, and diverse applications in drug delivery, gas storage, and catalysis. Recently, there has been an escalating interest in exploiting MOF-derived materials as anodes for sodium energy storage due to their fast mass transport resulting from their highly porous structures and relatively simple preparation methods originating from in situ thermal treatment processes. In this Review, the recent progress of the sodium-ion storage performances of MOF-derived materials, including MOF-derived porous carbons, metal oxides, metal oxide/carbon nanocomposites, and other materials (e.g., metal phosphides, metal sulfides, and metal selenides), as SIB anodes is systematically and completely presented and discussed. Moreover, the current challenges and perspectives of MOF-derived materials in electrochemical energy storage are discussed.

Self-assembled Mn-doped MoS2 hollow nanotubes with significantly enhanced sodium storage for high-performance sodium-ion batteries

Mn-Doped MoS₂ hollow nanotubes as an anode exhibit an enhanced fast sodium ion transport capability and superb electrochemical properties in sodium-ion batteries.

Synchronous synthesis of Kirkendall effect induced hollow FeSe2/C nanospheres as anodes for high performance sodium ion batteries

Facilely synthesized Kirkendall effect induced hollow FeSe₂/C nanospheres exhibit excellent electrochemical performance as an anode for sodium ion batteries.

A Review: Enhanced Anodes of Li/Na-Ion Batteries Based on Yolk-Shell Structured Nanomaterials

Lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) have received much attention in energy storage system. In particular, among the great efforts on enhancing the performance of LIBs and SIBs, yolk-shell (YS) structured materials have emerged as a promising strategy toward improving lithium and sodium storage. YS structures possess unique interior void space, large surface area and short diffusion distance, which can solve the problems of volume expansion and aggregation of anode materials, thus enhancing the performance of LIBs and SIBs. In this review, we present a brief overview of recent advances in the novel YS structures of spheres, polyhedrons and rods with controllable morphology and compositions. Enhanced electrochemical performance of LIBs and SIBs based on these novel YS structured anode materials was discussed in detail.

Selenium Encapsulated into Metal-Organic Frameworks Derived N-Doped Porous Carbon Polyhedrons as Cathode for Na-Se Batteries

The substitution of Se for S as cathode for rechargeable batteries, which confine selenium in porous carbon, attracts much attention as a potential area of research for energy storage systems. To date, there are no reports about metal-organic frameworks (MOFs) to use for Na-Se batteries. Herein, MOFs-derived nitrogen-doped porous carbon polyhedrons (NPCPs) have been obtained via facile synthesis and annealing treatment. Se is encapsulated into the mesopores of carbon polyhedrons homogeneously by melt-diffusion process to form Se/NPCPs composite, using as cathode for advanced Na-Se batteries. Se/NPCPs cathode exhibits excellent rate capabilities of 351.6 and 307.8 at 0.5C and 2C, respectively, along with good cycling performance with high Coulombic efficiency of 99.7% and slow decay rate of 0.05% per cycle after 1000 cycles at 2C, which result from the NPCPs having a unique porous structure to accommodate volumetric expansion of Se during discharge-charge processes. Nitrogen doping could enhance the electrical conductivity of carbon matrix and facilitate rapid charge transfer.

CoS2 Nanoparticles Wrapping on Flexible Freestanding Multichannel Carbon Nanofibers with High Performance for Na-Ion Batteries

Exploration for stable and high-powered electrode materials is significant due to the growing demand for energy storage and also challengeable to the development and application of Na-ion batteries (NIBs). Among all promising electrode materials for NIBs, transition-mental sulfides have been identified as potential candidates owing to their distinct physics-chemistry characteristics. In this work, CoS₂ nanomaterials anchored into multichannel carbon nanofibers (MCNFs), synthesized via a facile solvothermal method with a sulfidation process, are studied as flexible free-standing electrode materials for NIBs. CoS₂ nanoparticles uniformly distributed in the vertical and horizontal multichannel networks. Such nanoarchitecture can not only support space for volume expansion of CoS₂ during discharge/charge process, but also facilitate ion/electron transport along the interfaces. In particular, the CoS₂@MCNF electrode delivers an impressively high specific capacity (537.5 mAh g^-1 at 0.1 A g^-1), extraordinarily long-term cycling stability (315.7 mAh g^-1 at at 1 A g^-1 after 1000 cycles), and excellent rate capacity (537.5 mAh g^-1 at 0.1 A g^-1 and 201.9 mAh g^-1 at 10 A g^-1) for sodium storage. Free-standing CoS₂@MCNF composites with mechanical flexibility provide a promising electrode material for high-powered NIBs and flexible cells.

ZnS-Sb2S3@C Core-Double Shell Polyhedron Structure Derived from Metal-Organic Framework as Anodes for High Performance Sodium Ion Batteries

Taking advantage of zeolitic imidazolate framework (ZIF-8), ZnS-Sb₂S₃@C core-double shell polyhedron structure is synthesized through a sulfurization reaction between Zn²⁺ dissociated from ZIF-8 and S^2- from thioacetamide (TAA), and subsequently a metal cation exchange process between Zn²⁺ and Sb³⁺, in which carbon layer is introduced from polymeric resorcinol-formaldehyde to prevent the collapse of the polyhedron. The polyhedron composite with a ZnS inner-core and Sb₂S₃/C double-shell as anode for sodium ion batteries (SIBs) shows us a significantly improved electrochemical performance with stable cycle stability, high Coulombic efficiency and specific capacity. Peculiarly, introducing a carbon shell not only acts as an important protective layer to form a rigid construction and accommodate the volume changes, but also improves the electronic conductivity to optimize the stable cycle performance and the excellent rate property. The architecture composed of ZnS inner core and a complex Sb₂S₃/C shell not only facilitates the facile electrolyte infiltration to reduce the Na-ion diffusion length to improve the electrochemical reaction kinetics, but also prevents the structure pulverization caused by Na-ion insertion/extraction. This approach to prepare metal sulfides based on MOFs can be further extended to design other nanostructured systems for high performance energy storage devices.