CoSe2 nanoparticles anchored on porous carbon network structure for efficient Na-ion storage

Nickel telluride nanoparticles@hollow porous carbon sphere confined within carbon fibers for fast stable sodium storage

For sodium-ion batteries, nickel telluride (NiTe2) is an excellent anode material. However, significant volume changes and slow kinetics compromise its structural stability and its capacity for high-current reactions. To increase sodium storage performance, NiTe2 nanoparticles are synthesized in situ within hollow porous carbon spheres (NiTe2@HPCS) through a "drop-dry" process, vacuum-assisted adsorption, and vapor tellurization. Then, a large number of NiTe2@HPCS particles are densely encapsulated in carbon fibers (CFs) via electrospinning and carbonization (NiTe2@HPCS/CF). In coin-type half cells, NiTe2@HPCS/CF exhibits a high and stable capacity of 432 mAh g-1 after 500 cycles at 1.0 A g-1. When half cells are operated at 5.0 and 10.0 A g-1, the lifespan reaches 1000 cycles and the capacities sustain at 332 and 195 mAh g-1. The cycled electrode materials preserve the intact composite structure, demonstrating remarkable robustness. Kinetic investigation affirms swift electron and Na+ conduction within NiTe2@HPCS/CF. Furthermore, in Na3V2(PO4)3//NiTe2@HPCS/CF full cells, NiTe2@HPCS/CF also exhibits favorable cycling stability. At 1.0 and 5.0 A g-1 after 300 and 500 cycles, reversible capacities reach 299 and 172 mAh g-1, respectively. The outstanding performance is associated with the unique dual carbon encapsulation structure: HPCSs effectively confine NiTe2 nanoparticles, maintaining their high electrochemical activity and promoting the sodiation/de-sodiation reactions. CFs further reinforce structural stability and electron conduction of NiTe2.

Carbon Nanotube Intertwined Nano-Nested Heterojunction Cubes with Double Shell Layers FeSe2-CoSe2@NC for Efficient Lithium/Sodium Ion Storage Anode

Transition metal selenides (TMSes) have been extensively researched as anode materials of lithium/sodium-ion batteries (LIBs/SIBs). However, the serious volume expansion, unsatisfying initial coulombic efficiency (ICE), and ion diffusion extremely limited their further application. Therefore, nanostructure design and construction of heterogeneous structures can effectively alleviate the above problems. Herein, elaborately designed carbon nanotube-intertwined nano-nested heterojunction cubes, FeSe2-CoSe2@NC (FeSe2-CoSe2@NC/CNT), with unique double shell layers, are successfully prepared. Electrochemical tests and theoretical calculations show that the construction of double transition metal selenide heterostructures and CNTs inter-transfer networks promotes ion transport kinetics. Furthermore, the double-layer nested cubic structure contributes to alleviating the volume expansion over charging/discharging. Thanks to these merits, the FeSe2-CoSe2@NC/CNT composite exhibits enhanced Li+ storage capacity (1479.7 mAh g-1 after 500 cycles at a high current density of 2 A g-1), and outstanding rate capabilities. When used in SIB, the capacity is maintained at 300.1 mAh g-1 for 500 cycles at 1 A g-1. In addition, the FeSe2-CoSe2@NC/CNT as anode in the full cell displays a nice reversible capacity of 100.1 mAh g-1 at 0.5 C cycling for 115 cycles, demonstrating vast potential for feasible synthesis, superior performance, and efficient lithium/sodium ion storage anodes.

Yolk-shell SnSe2@NC nanocubes: synergistic interior void and spatial confinement for superior sodium-ion battery anodes

Rationally designed nanostructured electrode materials, especially yolk-shell metal selenide@void@C architectures, are gaining prominence as potential anode candidates for sodium-ion batteries (SIBs) due to their exceptional sodium-ion storage capabilities. In this work, we propose a template-assisted carbon coating route to fabricate nitrogen-doped carbon nanocubes encapsulating SnSe2 nanoparticles, forming a yolk-shell structure with an internal void space (SnSe2@NC), resulting in a high-performance anode for SIBs. The yolk-shell architecture, with SnSe2 nanoparticles embedded within a nitrogen-doped carbon shell, significantly boosts structural integrity and sodium storage performance. The SnSe2@NC electrode delivers a high reversible capacity of 368.9 mA h g-1 after 50 cycles at 0.5 A g-1 and an impressive capacity retention of 324.2 mA h g-1 at 5 A g-1 after 1000 cycles. Electrochemical analyses reveal that the enhanced performance is attributed to the improved Na-ion diffusion kinetics, reduced charge-transfer resistance, and the structural stability conferred by the nitrogen-doped carbon shell and the internal void space. The yolk-shell SnSe2@NC nanocubes demonstrate superior electrochemical properties, representing a potential strategy for the development of advanced SIB anode materials.

Tannic acid etching construction of hollow heterogeneous CoSe2-FeSe2@nitrogen-doped carbon rhombic dodecahedron for high-performance sodium storage

Metal selenides are very promising anode materials for sodium ion batteries (SIBs) due to their rich redox behaviors, low cost, high theoretical capacity, and environmentally benign. However, the poor cycle performance and rate capability greatly hinder their widespread applications. In this paper, we have proposed a tannic acid etching zeolitic imidazolate framework-67 (ZIF-67)-derived selenide strategy to construct hollow heterogeneous CoSe2-FeSe2@N-doped carbon rhombic dodecahedron (CoSe2-FeSe2@NC) as anode for high-performance SIBs. The special microstructural characteristics with hollow rhombic dodecahedron can reduce the Na+/electron migration path and alleviate the volume variations during cycling. The NC can improve conductivity and reduce volume effects during cycling. What's more, the built-in electric fields (BIEF) at the CoSe2-FeSe2 heterointerfaces can modulate the electronic structure and accelerate the kinetics of ionic diffusion, resulting in the improvement electrochemical properties. When applied as anodes for SIBs, the CoSe2-FeSe2@NC can deliver a remarkable electrochemical performance in terms of sodium storage capacity (648.5 mAh g-1 at 0.2 A/g), initial coulombic efficiency (82.0 %), cycle performance (92.6 % capacity retention after 100 cycles), and rate capability of 450.6 mAh g-1 after 1000 cycles at a high rate of 1 A/g. The kinetic analysis indicates that the discharging-charging process of CoSe2-FeSe2@NC is ascribed to both capacitive behavior and controlled diffusion.

Synergetic interface engineering and space-confined effect in CoSe2@Ti3C2Tx heterostructure for high power and long life sodium ion capacitors

The intriguing characteristics of two-dimensional (2D) heterostructures stem from their unique interfaces, which can improve ion storage capability and rate performance. However, there are still challenges in increasing the proportion of heterogeneous interfaces in materials and understanding the complex interaction mechanisms at these interfaces. Here, we have successfully synthesized confined CoSe2 within the interlayer space of Ti3C2Tx through a simple solvothermal method, resulting in the formation of a superlattice-like heterostructures of CoSe2@Ti3C2Tx. Both density functional theory (DFT) calculations and experimental results show that compared with CoSe2 and Ti3C2Tx, CoSe2@Ti3C2Tx can significantly improve adsorption of Na+ ions, while maintaining low volume expansion and high Na+ ions migration rate. The heterostructure formed by MXene and CoSe2 is a Schottky heterostructure, and its interfacial charge transfer induces a built-in electric field that promotes rapid ion transport. When CoSe2@Ti3C2Tx was used as an anode material, it exhibits a high specific capacity of up to 600.1 mAh/g and an excellent rate performance of 206.3 mAh/g at 20 A/g. By utilizing CoSe2@Ti3C2Tx as the anode and activated carbon (AC) as the cathode, the sodium-ion capacitor of CoSe2@Ti3C2Tx//AC exhibits excellent energy and power density (125.0 Wh kg-1 and 22.5 kW kg-1 at 300.0 W kg-1 and 37.5 Wh kg-1, respectively), as well as a long service life (86.3 % capacity retention over 15,300 cycles at 5 A/g), demonstrating its potential for practical applications.

Electron-Spin Regulation Driving Heterointerface Electron Distribution and Phase Transition toward Ultrafast and Durable Sodium Storage

Phase engineering is an effective strategy for modulating the electronic structure and electron transfer mobility of cobalt selenide (CoSe2) with remarkable sodium storage. Nevertheless, it remains challenging to improve fast-charging and cycling performance. Herein, a heterointerface coupling induces phase transformation from cubic CoSe2 to orthorhombic CoSe2 accompanied by the formation of MoSe2 to construct a CoSe2/MoSe2 heterostructure decorated with N-doped carbon layer on a 3D graphene foam (CoSe2/MoSe2@NC/GF). The incorporated Mo cations in the bridged o-CoSe2/MoSe2 not only act an electron donor to regulate charge-spin configurations with more active electronic states but also trigger the upshift of d/p band centers and a decreased ∆d-p band center gap, which greatly enhances ion adsorption capability and lowers the ion diffusion barrier. As expected, the CoSe2/MoSe2@NC/GF anode demonstrates a high-rate capability of 447 mAh g-1 at 2 A g-1 and an excellent cyclability of 298 mAh g-1 at 1 A g-1 over 1000 cycles. The work deepens the understanding of the elaborate construction of heterostructured electrodes for high-performance SIBs.

Hollow Porous Co0.85Se/ZnSe@MXene Anode with Multilevel Built-in Electric Fields for High-Performance Sodium Ion Capacitors

Sodium ion capacitors (SICs) are promising candidates in energy storage for their remarkable power and energy density. However, the inherent disparity in dynamic behavior between the sluggish battery-type anodes and the rapid capacitor-type cathodes constrained their performance. To address this, we fabricated a hollow porous Co0.85Se/ZnSe@MXene anode featuring multiheterostructure, utilizing facile etching and electrostatic self-assembly strategies. The hollow porous structure and multiple heterointerfaces stabilize the anode by mitigating the volume changes. Density functional theory (DFT) calculations further revealed that induced multilevel built-in electric fields facilitate the formation of rapid ion diffusion pathways and reduce the Na+ adsorption energy, thereby boosting Na+/electron transport kinetics. The fabricated TA-Co0.85Se/ZnSe@MXene anode demonstrates outstanding long-term cycling stability of 406 mA h g-1 after 1000 cycles at 1 A g-1, with an ultrahigh rate performance of 288 mA h g-1 at 10 A g-1. When paired with the active carbon (AC) cathode, the SICs deliver extraordinary energy/power densities of 144 W h kg-1 and 12000 W kg-1, maintaining over 80% capacity retention at 1 A g-1 after 10000 cycles. This innovative strategy of engineering multiheterostructured anode with the induced multilevel built-in electric fields holds significant promise for advancing high-energy and high-power energy storage systems.

Heterostructured MnSe/FeSe nanorods encapsulated by carbon with enhanced Na+ diffusion as anode materials for sodium-ion batteries

The natural abundance of sodium has fostered the development of sodium-ion batteries for large-scale energy storage. However, the low capacity of the anodes hinders their future application. Herein, carbon-encapsulated MnSe-FeSe nanorods (MnSe-FeSe@C) have been fabricated by the in-situ transformation from polydopamine-coated MnO(OH)-Fe2O3. The heterostructure constructed by MnSe and FeSe nanocrystals induces the formation of built-in electric fields, accelerating electron transfer and ion diffusion, thereby improving reaction kinetics. In addition, carbon enclosure can buffer the volumetric stress and enhance the electrical conductivity. These aspects cooperatively endow the anode with superior cycling stability and distinguished rate performance. Specifically, the discharge capacity of MnSe-FeSe@C reaches 414.3 mA h g-1 at 0.1 A g-1 and 388.8 mA h g-1 even at a high current density of 5.0 A g-1. In addition, it still retains a high reversible capacity of 449.2 mA h g-1 after 700 long cycles at 1.0 A g-1. Further, the ab initio calculation has been employed to authenticate the existence of the built-in electric field by Bader charge, indicating that 0.24 electrons in MnSe were transferred to FeSe. The in-situ XRD has been used to evaluate the phase transition during the charging/discharging process, revealing the sodium ion storage mechanism. The construction of heterostructure material paves a new way to design performance-enhanced anode materials for sodium-ion batteries.

MoS2 spheres covered with a few layers of MXene as a high-performance anode for sodium-ion batteries

As a kind of anode material with high theoretical sodium storage capacity for sodium-ion batteries (SIBs), MoS2 has been widely studied. However, its low conductivity and large volume change hamper its application in SIBs. Herein, MoS2 microspheres were first synthesized through the sulfidation of molybdenyl acetylacetonate via a solvothermal method and then successfully covered with a few layers of MXene nanosheets using the electrostatic assembly method. The ratio of MoS2 to MXene was also investigated. The obtained MXene@MoS2 composite has a large specific surface area due to its porous and non-stacked structure, which benefits the enhancement of ion and electron diffusion kinetics in SIBs. Therefore, the MXene@MoS2 composite has a specific capacity of 257.8 mA h g-1 after 1000 cycles at a current density of 1 A g-1 with a capacity retention of 95.7% and excellent rate performance (220.8 mA h g-1 at 5 A g-1).

Few-layer MoS2 promotes SnO2@C nano-composites for high performance sodium ion batteries

Due to its abundance, high theoretical capacity, and environmental benefits, tin dioxide (SnO2) shows great potential as an anode material in sodium-ion batteries (SIBs). However, the inadequate electrical conductivity and significant volume fluctuations during the Na+ insertion/extraction process are major limitations to its practical application. Herein, few-layered MoS2@SnO2@C (FMSC) composites with hierarchical nanostructures were prepared through a two-step hydrothermal method. As expected, the electrochemical tests show that the FMSC exhibits superior electrochemical properties, such as an outstanding rate capability of 288.9 mA h g-1 at a current density of 2 A g-1, a high reversible capacity of 415.9 mA h g-1 after 50 cycles at a current density of 0.1 A g-1, and remarkable cycling stability of 158.4 mA h g-1 after 4400 cycles at a current density of 5 A g-1, as an anode material for SIBs. The exceptional performance can be attributed to the presence of a thin layer of MoS2, which enhances surface electrochemical reactions and provides a flexible structure.

Transition Metal Selenide-Based Anodes for Advanced Sodium-Ion Batteries: Electronic Structure Manipulation and Heterojunction Construction Aspect

In recent years, sodium-ion batteries (SIBs) have gained a foothold in specific applications related to lithium-ion batteries, thanks to continuous breakthroughs and innovations in materials by researchers. Commercial graphite anodes suffer from small interlayer spacing (0.334 nm), limited specific capacity (200 mAh g-1), and low discharge voltage (<0.1 V), making them inefficient for high-performance operation in SIBs. Hence, the current research focus is on seeking negative electrode materials that are compatible with the operation of SIBs. Many studies have been reported on the modification of transition metal selenides as anodes in SIBs, mainly targeting the issue of poor cycling life attributed to the volume expansion of the material during sodium-ion extraction and insertion processes. However, the intrinsic electronic structure of transition metal selenides also influences electron transport and sodium-ion diffusion. Therefore, modulating their electronic structure can fundamentally improve the electron affinity of transition metal selenides, thereby enhancing their rate performance in SIBs. This work provides a comprehensive review of recent strategies focusing on the modulation of electronic structures and the construction of heterogeneous structures for transition metal selenides. These strategies effectively enhance their performance metrics as electrodes in SIBs, including fast charging, stability, and first-cycle coulombic efficiency, thereby facilitating the development of high-performance SIBs.

Facilitating Rapid Na+ Storage through MoWSe/C Heterostructure Construction and Synergistic Electrolyte Matching Strategy

The realization of sodium-ion devices with high-power density and long-cycle capability is challenging due to the difficulties of carrier diffusion and electrode fragmentation in transition metal selenide anodes. Herein, a Mo/W-based metal-organic framework is constructed by a one-step method through rational selection, after which MoWSe/C heterostructures with large angles are synthesized by a facile selenization/carbonization strategy. Through physical characterization and theoretical calculations, the synthesized MoWSe/C electrode delivers obvious structural advantages and excellent electrochemical performance in an ethylene glycol dimethyl ether electrolyte. Furthermore, the electrochemical vehicle mechanism of ions in the electrolyte is systematically revealed through comparative analyses. Resultantly, ether-based electrolytes advantageously construct stable solid electrolyte interfaces and avoid electrolyte decomposition. Based on the above benefits, the Na half-cell assembled with MoWSe/C electrodes demonstrated excellent rate capability and a high specific capacity of 347.3 mA h g-1 even after cycling 2000 cycles at 10 A g-1. Meanwhile, the constructed sodium-ion capacitor maintains ∼80% capacity retention after 11,000 ultralong cycles at a high-power density of 3800 W kg-1. The findings can broaden the mechanistic understanding of conversion anodes in different electrolytes and provide a reference for the structural design of anodes with high capacity, fast kinetics, and long-cycle stability.

Review of Transition Metal Chalcogenides and Halides as Electrode Materials for Thermal Batteries and Secondary Energy Storage Systems

Transition metal chalcogenides and halides (TMCs and TMHs) have been extensively used and reported as electrode materials in diverse primary and secondary batteries. This review summarizes the suitability of TMCs and TMHs as electrode materials focusing on thermal batteries (utilized for defense applications) and energy storage systems like mono- and multivalent rechargeable batteries. The report also identifies the specific physicochemical properties that need to be achieved for the same materials to be employed as cathode materials in thermal batteries and anode materials in monovalent rechargeable systems. For example, thermal stability of the materials plays a crucial role in delivering the performance of the thermal battery system, whereas the electrical conductivity and layered structure of similar materials play a vital role in enhancing the electrochemical performance of the mono- and multivalent rechargeable batteries. It can be summarized that nonlayered CoS2, FeS2, NiS2, and WS2 were found to be ideal as cathode materials for thermal batteries primarily due to their better thermal stability, whereas the layered structures of these materials with a coating of carbon allotrope (CNT, graphene, rGO) were found to be suitable as anode materials for monovalent alkali metal ion rechargeable batteries. On the other hand, vanadium, titanium, molybdenum, tin, and antimony based chalcogenides were found to be suitable as cathode materials for multivalent rechargeable batteries due to the high oxidation state of cathode materials which resists the stronger field produced during the interaction of di- and trivalent ions with the cathode material facilitating higher energy density with minimal structural and volume changes at a high rate of discharge.

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.

In-situ synthesis of porous Na3V2(PO4)3 with stable VOC bridge bonding by hard template method

Low electronic conductivity and poor properties at high rate have hindered the application of Na3V2(PO4)3 (NVP). Herein, a facile synthesis of NVP with porous carbon skeleton is proposed. Specifically, Na2CO3 and glucose, acting as hard templates, are introduced to the precursors after initial firing stage, and Na2CO3 particles are removed by flushing after the final heatment. Due to the thermal conductivity of Na2CO3, the secondary addition of glucose can generate distinctive graphitized porous carbon skeleton, which bonds well with the amorphous carbon coating to construct stable and conductive network. The porous construction can alleviate the stress and strain caused by the current impact through deformation. Furthermore, ex-situ EIS reveals the highly conductive carbon skeleton can significantly reduce the surface resistance and result in an increase of effective voltage to promote the de-intercalation of Na+. Moreover, the ex-situ X-ray photoelectron spectroscopy (XPS) at different potentials confirms the stabilized existence of VOC bonds. Benefiting from the unique carbon skeleton, the PC-NVP releases capacity of 116.9 mAh g-1 at 0.1C. Even at 120C, PC-NVP still exhibits a high capacity of 84.7 mAh g-1, retaining a value of 41.3 mAh g-1 after 16,000 cycles, corresponding to a low decay rate of 0.0032% per cycle.

A self-sacrificing template strategy: In-situ construction of bimetallic MOF-derived self-supported CuCoSe nanosheet arrays for high-performance supercapacitors

Transition metal selenides (TMSs) are viewed as a prospective high-capacity electrode material for asymmetric supercapacitors (ASCs). However, the inability to expose sufficient active sites due to the limitation of the area involved in the electrochemical reaction severely limits their inherent supercapacitive properties. Herein, a self-sacrificing template strategy is developed to prepare self-supported CuCoSe (CuCoSe@rGO-NF) nanosheet arrays by in situ construction of copper-cobalt bimetallic organic framework (CuCo-MOF) on rGO-modified nickel foam (rGO-NF) and rational design of Se2- exchange process. Nanosheet arrays with high specific surface area are considered to be ideal platforms for accelerating electrolyte penetration and exposing rich electrochemical active sites. As a result, the CuCoSe@rGO-NF electrode delivers a high specific capacitance of 1521.6 F/g at 1 A/g, good rate performance and an excellent capacitance retention of 99.5% after 6000 cycles. The assembled ASC device has a high energy density of 19.8 Wh kg-1 at 750 W kg-1 and an ideal capacitance retention of 86.2% after 6000 cycles. This proposed strategy offers a viable strategy for designing and constructing electrode materials with superior energy storage performance.