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

Metal Coordination Complex Derived Fe7S8 Particles Embedded in N-doped Carbon Framework with Regulated Porous Structure Enabling High-Rate and Durable Sodium Storage

Iron sulfides with high theoretical capacity confront the challenges of low rate capability and severe capacity fading for sodium storage, which are mainly caused by poor electron/ion transport kinetics and drastic volume fluctuations during cycling. Herein, to mitigate these obstacles, a multi-step synthetic tactic involving solvothermal, carbonization, and subsequent sulfurization is put forward for the construction of wire-like structure by confining Fe7S8 particles in porous N-doped carbon framework (denoted as Fe7S8/PNC) using zinc iron nitrilotriacetate as template. By partially substituting Fe3+ with Zn2+ in the metal coordination complex, the porous structure of coordination complex derived carbon framework can be regulated through pore structure engineering of Zn nanodroplets. The desired porous and robust core/shell structure can not only afford favorable electron/Na+ transport paths and additional active sites for Na+ storage, but also provide reinforced structural integrity of interior Fe7S8 particles by retarding the pulverization and buffering the mechanical stress against volume fluctuations. As anode for sodium-ion batteries, the optimal Fe7S8/PNC delivers a high reversible capacity (743 mAh g-1 at 0.1 A g-1), superior rate capability (553 mAh g-1 at 10 A g-1), and long-term cycling stability (602 mAh g-1 at 5 A g-1 with 98.5% retention after 1000 cycles).

In Situ Construction of (NiCo)3Se4 Nanobeads Embedded in N-Doped Carbon 3D Interconnected Networks for Enhanced Sodium Storage

Transition metal selenides, boasting remarkable specific capacity, have emerged as a promising electrode material. However, the substantial volume fluctuations during sodium ion insertion and extraction result in inadequate cyclic stability and rate performance, impeding their practical utility. Here, we synthesized N-doped carbon three-dimensional (3D) interconnected networks encapsulating (NiCo)3Se4 nanoparticles, denoted as ((NiCo)3Se4/N-C), exhibiting a bead-like structure and carbon confinement through electrospinning and subsequent thermal treatment. The N-doped carbon 3D interconnected networks possess high porosity and ample volume buffering capacity, enhance conductivity, shorten ion diffusion paths, and mitigate mechanical stress induced by volume changes during cycling. The uniformly distributed (NiCo)3Se4 nanoparticles, featuring a stable structure, demonstrate rapid electrochemical kinetics and numerous available active sites. The distinctive structure and composition of the optimized (NiCo)3Se4/N-C material showcase a high specific capacity (656.2 mAh g-1 at 0.1 A g-1) and an outstanding rate capability. A kinetic analysis confirms that (NiCo)3Se4/N-C stimulates the pseudocapacitive Na+ storage mechanism with capacitance contributing up to 89.2% of the total capacity. This unique structure design and doping approach provide new insights into the design of electrode materials for high-performance batteries.

Efficient Sodium Storage in Cu1.96S@NC Anode Achieved by Robust S─C Bonds and Current Collector Self-Induced Forming Cu2S Quantum Dots

Transition metal sulfides are investigation hotspots of anode material for sodium-ion batteries (SIBs) due to their structural diversity and high storage capacity. However, they are still plagued by inevitable volume expansion during sodiation/desodiation and an unclear energy storage mechanism. Herein, a one-step sulfidation-carbonization strategy is proposed for in situ confined growth of Cu1.96S nanoparticles in nitrogen-doped carbon (Cu1.96S@NC) using octahedral metal-organic framework (Cu-BTC) as a precursor and investigate the driving effect of Cu current collector on its sodium storage. The generation of S─C bonds in Cu1.96S@NC avoids the volume change and structural collapse of Cu1.96S nanoparticles during the cycling process and improves the adsorption and transport capacity of the material for Na+. More exciting, the Cu species in the Cu current collector are self-induced forming Cu2S quantum dots to enter the original anode material during the initial few charging and discharging cycles, which unique small-size effect and abundant edge-active sites enhance the energy storage capacity of Cu1.96S. Thus, the Cu1.96S@NC exhibits a superior first discharge capacity of 608.56 mAh g-1 at 0.2 A g-1 with an initial Coulomb efficiency (ICE) of 75.4%, as well as provides excellent rate performance and long cycle durability up to 2000 cycles.

Tailoring Stress-Relieved Structure for SnSe Toward High Performance Potassium Ion Batteries

Metal chalcogenides as an ideal family of anode materials demonstrate a high theoretical specific capacity for potassium ion batteries (PIBs), but the huge volume variance and poor cyclic stability hinder their practical applications. In this study, a design of a stress self-adaptive structure with ultrafine SnSe nanoparticles embedded in carbon nanofiber (SnSe@CNF) via the electrospinning technology is presented. Such an architecture delivers a record high specific capacity (272 mAh g-1 at 50 mA g-1) and high-rate performance (125 mAh g-1 at 1 A g-1) as a PIB anode. It is decoded that the fundamental understanding for this great performance is that the ultrafine SnSe particles enhance the full utilization of the active material and achieve stress relief as the stored strain energy from cycling is insufficient to drive crack propagation and thus alleviates the intrinsic chemo-mechanical degradation of metal chalcogenides.

Ni-CoSe2 heterojunction coated by N-doped carbon for modified separators of high-performance Li-sulfur batteries

Functional separators modified by transition metal compounds have been proven to be effective in suppressing the shuttle effect of polysulfides and accelerating sluggish electrode dynamics in lithium-sulfur batteries (LSBs). However, the behaviors of heterojunctions composed of transition metals and their compounds in LSBs are still rarely studied. Herein, we report a novel Ni-CoSe2 heterostructure coated with nitrogen-doped carbon. Compared to homogeneous cobalt diselenide, it exhibits much stronger adsorption and catalytic conversion abilities towards polysulfides. With the modified separators, the lithium-sulfur batteries exhibit significantly improved capacity retention and reduced polarization during cycling.

Construction of Sugar-Gourd-Shaped Carbon Nanofibers Embedded with Heterostructured Zinc-Cobalt Selenide Nanocages for Superior Potassium-Ion Storage

Transition metal selenides are considered as promising anode materials for potassium-ion batteries (PIBs) due to their high theoretical capacities. However, their applications are limited by low conductivity and large volume expansion. Herein, sugar-gourd-shaped carbon nanofibers embedded with heterostructured ZnCo-Se nanocages are prepared via a facile template-engaged method combined with electrospinning and selenization process. In this hierarchical ZnCo-Se@NC/CNF, abundant phase boundaries of CoSe2/ZnSe heterostructure can promote interfacial electron transfer and chemical reactivity. The interior porous ZnCo-Se@NC nanocage structure relieves volume expansion and maintains structural integrity during K+ intercalation and deintercalation. The exterior spinning carbon nanofibers connect the granular nanocages in series, which prevents the agglomeration, shortens the electron transport distance and enhances the reaction kinetics. As a self-supporting anode material, ZnCo-Se@NC/CNF delivers a high capacity (362 mA h g-1 at 0.1 A g-1 after 100 cycles) with long-term stability (95.9% capacity retention after 1000 cycles) and shows superior reaction kinetics with high-rate K-storage. Energy level analysis and DFT calculations illustrate heterostructure facilitates the adsorption of K+ and interfacial electron transfer. The K+ storage mechanism is revealed by ex situ XRD and EIS analyses. This work opens a novel avenue in designing high-performance heterostructured anode materials with ingenious structure for PIBs.

Coral-like CoSe2@N-doped carbon with a high initial coulombic efficiency as advanced anode materials for Na-ion batteries

Na-ion batteries (NIBs) have attracted great interest as a possible technology for grid-scale energy storage for the past few years owing to the wide distribution, low cost and environmental friendliness of sodium resources and similar chemical mechanisms to those of established Li-ion batteries (LIBs). Nonetheless, the implementation of NIBs is seriously hindered because of their low rate capability and cycling stability. This is mainly because the large ionic size of Na+ can reduce the structural stability and cause sluggish reaction kinetics of electrode materials. Herein, three-dimensional nanoarchitectured coral-like CoSe2@N-doped carbon (CL-CoSe2@NC) was synthesized through solvothermal and selenizing techniques. As a result, CL-CoSe2@NC for NIBs at 2 A g-1 exhibits an ultrahigh specific capacity of 345.4 mA h g-1 after 2800 cycles and a superhigh initial coulombic efficiency (ICE) of 93.1%. Ex situ XRD, HRTEM, SAED and XPS were executed to study the crystal structure evolution between Na and CoSe2 during sodiation/de-sodiation processes. The aforementioned results indicate that the improved sodium storage property of CL-CoSe2@NC could be attributed to better electrode kinetics and a stable SEI film because of the 3D nanoarchitecture and the existence of the NC layer.

Design and Construction of Carbon-Coated Fe3 O4 /Cr2 O3 Heterostructures Nanoparticles as High-Performance Anodes for Lithium Storage

Transition metal oxides, highly motivated anodes for lithium-ion batteries due to high theoretical capacity, typically afflict by inferior conductivity and significant volume variation. Architecting heterogeneous structures with distinctive interfacial features can effectively regulate the electronic structure to favor electrochemical properties. Herein, an engineered carbon-coated nanosized Fe3 O4 /Cr2 O3 heterostructure with multiple interfaces is synthesized by a facile sol-gel method and subsequent heat treatment. Such ingenious components and structural design deliver rapid Li+ migration and facilitate charge transfer at the heterogeneous interface. Simultaneously, the strong coupling synergistic interactions between Fe3 O4 , Cr2 O3 , and carbon layers establish multiple interface structures and built-in electric fields, which accelerate ion/electron transport and effectively eliminate volume expansion. As a result, the multi-interface heterostructure, as a lithium-ion battery anode, exhibits superior cycling stability maintaining a reversible capacity of 651.2 mAh g-1 for 600 cycles at 2 C. The density functionaltheory calculations not only unravel the electronic structure of the modulation but also illustrate favorable lithium-ion adsorption kinetics. This multi-interface heterostructure strategy offers a pathway for the development of advanced alkali metal-ion batteries.

Resolving Deactivation of Low-Spin Fe Sites by Redistributing Electron Density toward High-Energy Sodium Storage

Prussian blue (PB) has been an emerging class of cathode material for sodium-ion batteries due to its low cost and high theoretical capacity. However, their working voltage and capacity are substantially restricted due to the deactivation of low-spin Fe sites. Herein, we demonstrate a universal strategy to activate the low-spin Fe sites of PB by hybridizing them with the π-π conjugated electronic conductors. The redistribution of electron density between π-π conjugated conductors and PB effectively promotes the participation of low-spin Fe sites in sodium storage. Consequently, the low-spin Fe-induced plateau is greatly aroused, resulting in a high specific capacity of 148.4 mAh g-1 and remarkable energy density of 444.2 Wh kg-1. In addition, the excellent structural stability enables superior cycling stability over 2500 cycles and outstanding rate performance. The work will provide fundamental insight into activating the low-spin Fe sites of PB for advanced battery technologies.

In-situ-grown multidimensional Cu-doped Co1-xS2@MoS2 on N-doped carbon nanofibers as anode materials for high-performance alkali metal ion batteries

Transition metal sulfides with the high theoretical capacity and low cost have been considered as advanced anode candidate for alkali metal ion batteries, but suffered from unsatisfactory electrical conductivity and huge volume expansion. Herein, a multidimensional structure Cu-doped Co1-xS2@MoS2 in-situ-grown on N-doped carbon nanofibers (denoted as Cu-Co1-xS2@MoS2 NCNFs) have been elaborately constructed for the first time. The bimetallic zeolitic imidazolate framework CuCo-ZIFs were encapsulated in the one-dimensional (1D) NCNFs through an electrospinning route and then on which the two-dimensional (2D) MoS2 nanosheets were in-situ grown via a hydrothermal process. The architecture of 1D NCNFs can effectively shorten ion diffusion path and enhance electrical conductivity. Besides, the formed heterointerface between MOF-derived binary metal sulfides and MoS2 can provide extra active centers and accelerate reaction kinetics, which guarantee a superior reversibility. As expected, the resulting Cu-Co1-xS2@MoS2 NCNFs electrode delivers excellent specific capacity of Na-ion batteries (845.6 mAh/g at 0.1 A/g), Li-ion batteries (1145.7 mAh/g at 0.1 A/g), and K-ion batteries (474.3 mAh/g at 0.1 A/g). Therefore, this innovative design strategy will bring a meaningful prospect for developing high-performance multi-component metal sulfides electrode for alkali metal ion batteries.

Unveiling the Nature of Superior Sodium Storage in the CoSe2/rGO Nanocomposite

Sodium-ion batteries (SIBs) are considered the most promising alternatives to lithium-ion batteries (LIBs) due to the abundant availability of sodium and their cost-effectiveness. Transition metal selenides (TMSes) are considered promising anodes for SIBs due to their economic efficiency and high theoretical capacity. Nevertheless, overcoming the challenges of sluggish reaction kinetics and severe structural damage is crucial to improving cycle life and rate capability. Herein, a simple microwave hydrothermal process was used to synthesize a nanocomposite of CoSe2 nanoparticles uniformly anchored on reduced graphene oxide nanosheets (CoSe2/rGO). The influences of rGO on the structure and electrochemical performance and Na+ diffusion kinetics are investigated through a series of characterization and electrochemical tests. The resulting CoSe2/rGO nanocomposite exhibits a remarkable initial specific capacity of 544 mAh g-1 at 0.5 A g-1, impressive rate capability (368 mAh g-1 at 20 A g-1), and excellent cycle life and maintains 348 mAh g-1 at 5 A g-1 over 1200 cycles. In addition, the in situ electrochemical impedance spectroscopy (EIS), ex situ X-ray diffraction (XRD), and transmission electron microscopy (TEM) tests are selected to further investigate the sodium storage mechanism.

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

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

Unlocking Deep and Fast Potassium-Ion Storage through Phosphorus Heterostructure

Potassium-ion battery represents a promising alternative of conventional lithium-ion batteries in sustainable and grid-scale energy storage. Among various anode materials, elemental phosphorus (P) has been actively pursued owing to the ideal natural abundance, theoretical capacity, and electrode potential. However, the sluggish redox kinetics of elemental P has hindered fast and deep potassiation process toward the formation of final potassiation product (K3 P), which leads to inferior reversible capacity and rate performance. Here, it is shown that rational design on black/red P heterostructure can significantly improve K-ion adsorption, injection and immigration, thus for the first time unlocking K3 P as the reversible potassiation product for elemental P anodes. Density functional theory calculations reveal the fast adsorption and diffusion kinetics of K-ion at the heterostructure interface, which delivers a highly reversible specific capacity of 923 mAh g-1 at 0.05 A g-1 , excellent rate capability (335 mAh g-1 at 1 A g-1 ), and cycling performance (83.3% capacity retention at 0.8 A g-1 after 300 cycles). These results can unlock other sluggish and irreversible battery chemistries toward sustainable and high-performing energy storage.

Three-Dimensional (3D) Ordered Macroporous Bimetallic (Mn,Fe) Selenide/Carbon Composite with Heterojunction Interface for High-Performance Sodium Ion Batteries

Transition-metal selenides have captured significant research attention as anode materials for sodium ion batteries (SIBs) due to their high theoretical specific capacities and excellent electronic conductivity. However, volumetric expansion and inferior cycle life still hinder their practical application. Herein, a three-dimensional (3D) ordered macroporous bimetallic (Mn,Fe) selenide modified by a carbon layer (denoted as 3DOM-MnFeSex@C) composite containing a heterojunction interface is fabricated through selenizing a 3D ordered macroporous Mn-based Prussian Blue analogue single crystal. The 3DOM-MnFeSex@C exhibits hierarchically porous architecture with enhanced mass-transfer efficiency; MnSe and FeSe2 particles are encapsulated into macroporous carbon framework, which can significantly promote the electronic conductivity and maintain the structural integrity. The density functional theory calculation indicates that the heterojunction interface between MnSe and FeSe2 has been successfully engineered so that Na+ can be readily adsorbed and rapidly converted, thus promoting the reaction kinetics and extending the cyclic life. As expected, the 3DOM-MnFeSex@C composite delivers excellent rate performance (277.6 mA h g-1 at 10 A g-1), and prolonged cycling life (191.6 mA h g-1 even after 1000 cycles at 2 A g-1) as a sodium storage anode. The sodium storage mechanism of the composite was further investigated by in situ X-ray diffraction and ex situ high-resolution transmission electron microscopy characterization techniques.

ZIF-67-derived Co/CoSe ultrafine nanocrystal Schottky heterojunction decorated hollow carbon nanospheres as new-type anodes for potassium-ion batteries

Metal-organic frameworks (MOFs) have the advantages of controllable chemical properties, rich pore structures and reaction sites and are expected to be high-performance anode materials for the next generation of potassium-ion batteries (PIBs). However, due to the large radius of potassium ions, the pure MOF crystal structure is prone to collapse during ion insertion and processing, so its electrochemical performance is quite limited. In this work, a hollow carbon sphere-supported MOF-derived Co/CoSe heterojunction anode material for potassium-ion batteries was developed by a hydrothermal method. The anode has high potassium storage capacity (461.9 mA h/g after 200 cycles at 1 A/g), excellent cycling stability and superior rate performance. It is worth noting that the potassium ion storage capacity of the anode material shows a gradual upward trend with the charge-discharge cycle, which is 145.9 mA h/g after 3000 cycles at a current density of 10 A/g. This work demonstrates that MOF-derived CoSe anodes with high capacity and low cost may be promising candidates for the introduction of potassium ion storage.

Enhanced Interfacial Magnetization is Responsible for the Negative Capacity Fading of Cobalt Ditelluride Anodes for Lithium Storage

In lithium-ion batteries (LIBs), the stabilized capacities of transition metal compound anodes usually exhibit higher values than their theoretical values due to the interfacial charge storage, the formation of reversible electrolyte-derived surface layer, or interfacial magnetization. But the effectively utilizing the mechanisms to achieve novel anodes is rarely explored. Herein, a novel nanosized cobalt ditelluride (CoTe₂ ) anodes with ultra-high capacity and long term stability is reported. Electrochemical tests show that the lithium storage capacity of the best sample reaches 1194.7 mA h g^-1 after 150 cycles at 0.12 A g^-1 , which increases by 57.8% compared to that after 20 cycles. In addition, the sample offers capacities of 546.6 and 492.1 mA h g^-1 at 0.6 and 1.8 A g^-1 , respectively. During cycles, CoTe₂ particles (average size 20 nm) are gradually pulverized into the smaller nanoparticles (<3 nm), making the magnetization more fully due to the larger contact area of Co/Li₂ Te interface, yielding an increased capacity. The negative capacity fading is observed, and verified by ex situ structural characterizations and in situ electrochemical measurements. The proposed strategy can be further extended to obtain other high-performance ferromagnetic metal based electrodes for energy storage applications.

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

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

Oxygen vacancy-mediated amorphous GeOx assisted polysulfide redox kinetics for room-temperature sodium-sulfur batteries

The practical applications of room-temperature sodium-sulfur (RT Na-S) batteries have been greatly hindered by the natural sluggish reaction kinetics of sulfur and the shuttle effect of sodium polysulfide (NaPSs). Herein, oxygen vacancy (OV)-mediated amorphous GeOx/nitrogen doped carbon (donated as GeOx/NC) composites were well designed as sulfur hosts for RT Na-S batteries. Experimental and density functional theory studies show that the introduction of oxygen vacancies on GeOx/NC can effectively immobilize polysulfides and accelerate the redox kinetics of polysulfides. Meanwhile, the micro-and mesoporous framework, acting as a reactor for storing active S, is conducive to alleviating the expansion of S during the charging/discharging process. Consequently, the S@GeOx/NC cathode affords a reversible capacity of 1017 mA h g-1 at 0.1 A g-1 after 100 cycles, outstanding rate capability of 333 mA h g-1 at 10.0 A g-1 and long lifespan cyclability of 385 mAh g-1 at 1 A g-1 after 1200 cycles. This work furnishes a new way for the rational design of metal oxides with oxygen vacancies and boosts the application for RT Na-S batteries.

Electrochemical performance of CoSe2 with mixed phases decorated with N-doped rGO in potassium-ion batteries

Potassium-ion batteries (PIBs) have received much attention as next-generation energy storage systems because of their abundance, low cost, and slightly lower standard redox potential than lithium-ion batteries (LIBs). Nevertheless, they still face great challenges in the design of the best electrode materials for applications. Herein, we have successfully synthesized nano-sized CoSe₂ encapsulated by N-doped reduced graphene oxide (denoted as CoSe₂@N-rGO) by a direct one-step hydrothermal method, including both orthorhombic and cubic CoSe₂ phases. The CoSe₂@N-rGO anodes exhibit a high reversible capacity of 599.3 mA h g⁻¹ at 0.05 A g⁻¹ in the initial cycle, and in particular, they also exhibit a cycling stability of 421 mA h g⁻¹ after 100 cycles at 0.2 A g⁻¹. Density functional theory (DFT) calculations show that CoSe₂ with N-doped carbon can greatly accelerate electron transfer and enhance the rate performance. In addition, the intrinsic causes of the higher electrochemical performance of orthorhombic CoSe₂ than that of cubic CoSe₂ are also discussed.

Potassium-ion batteries (PIBs) have received much attention as next-generation energy storage systems because of their abundance, low cost, and slightly lower standard redox potential than lithium-ion batteries (LIBs).