Large-scale Ni-MOF derived Ni3S2 nanocrystals embedded in N-doped porous carbon nanoparticles for high-rate Na+ storage

Metal-Organic Framework-Based Materials for Advanced Sodium Storage: Development and Anticipation

As a pioneering battery technology, even though sodium-ion batteries (SIBs) are safe, non-flammable, and capable of exhibiting better temperature endurance performance than lithium-ion batteries (LIBs), because of lower energy density and larger ionic size, they are not amicable for large-scale applications. Generally, the electrochemical storage performance of a secondary battery can be improved by monitoring the composition and morphology of electrode materials. Because more is the intricacy of a nanostructured composite electrode material, more electrochemical storage applications would be expected. Despite the conventional methods suitable for practical production, the synthesis of metal-organic frameworks (MOFs) would offer enormous opportunities for next-generation battery applications by delicately systematizing the structure and composition at the molecular level to store sodium ions with larger sizes compared with lithium ions. Here, the review comprehensively discusses the progress of nanostructured MOFs and their derivatives applied as negative and positive electrode materials for effective sodium storage in SIBs. The commercialization goal has prompted the development of MOFs and their derivatives as electrode materials, before which the synthesis and mechanism for MOF-based SIB electrodes with improved sodium storage performance are systematically discussed. Finally, the existing challenges, possible perspectives, and future opportunities will be anticipated.

Synergistic γ-In2 Se3 @rGO Nanocomposites with Beneficial Crystal Transformation Behavior for High-Performance Sodium-Ion Batteries

Crystal transformation of metal compound cathodes during charge/discharge processes in alkali metal-ion batteries usually generates profound impact on structural stability and electrochemical performance, while the theme in anode materials, which always occurs and completes during the first redox cycle, is rarely explored probably due to the fast transformation dynamics. Herein, for the first time, a unique crystal transformation behavior with slow dynamics in anode of sodium-ion batteries (SIBs) is reported, which further promotes electrochemical performance. Specifically, irreversible γ → β crystal transformation of In2 Se3 is observed, induced by the persistent size degradation of In2 Se3 particles during repeated sodiation/desodiation, supported by a series of ex situ characterizations, such as HRTEM, XRD, and XPS of γ-In2 Se3 /reduced graphene oxide (γ-In2 Se3 @rGO) nanocomposite. The hybrid electrode shows ultrahigh long-term cycling stability (378 mA h g-1 at 1.0 A g-1 after 1000 cycles) and excellent rate capability (272 mA h g-1 at 20.0 A g-1 ). Full battery with Na3 V2 (PO4 )3 cathode also manifests superior performance, promising β-In2 Se3 dominated electrode materials in high-power and long-life SIBs. The first-principle calculations suggest the crystal transformation enhances electric conductivity of β-In2 Se3 and facilitates its accessibility to sodium. In combination with the synergistic effect between rGO matrix, substantially enhanced electrochemical performance is realized.

A NiS2/C composite as an innovative anode material for sodium-ion batteries: ex situ XANES and EXAFS studies to investigate the sodium storage mechanism

The successful deployment of sodium-ion batteries (SIBs) requires high-performance sustainable and cost-effective anode materials having a high current density. In this regard, sodium disulphide (NiS2) has been prepared as a composite with activated carbon (C) using a facile hydrothermal synthesis route in the past. The X-ray diffraction pattern of the as-prepared NiS2/C composite material shows well-defined diffraction peaks of NiS2. Most carbonaceous materials are amorphous, and the Brunauer-Emmett-Teller (BET) study shows that the surface area is close to 148 m2 g-1. At a current density of 50 mA g-1, the NiS2/C composite exhibits a high capacity of 480 mA h g-1 during the initial cycle, which subsequently decreases to 333 mA h g-1 after the completion of the 100th cycle. The NiS2/C composite electrode provides an exceptional rate capability by delivering a capacity of 270 mA h g-1 at a high current density of 2000 mA g-1, suggesting the suitability of the NiS2/C composite for SIBs. Ex situ X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses at the Ni K-edge have been used to examine the type of chemical bonding present in the anode and also how it changes during electrochemical redox cycling. The understanding of the sodium storage mechanism is improved by the favorable results, which also offer insights for developing high-performance electrode materials for rechargeable SIBs.

Noncrystalline Carbon Anodes for Advanced Sodium-Ion Storage

Developing an anode with excellent rate performance, long-cycle stability, high coulombic efficiency, and high specific capacity is one of the key research directions of sodium-ion batteries. Among all the anode materials, noncrystalline carbon (NCC) has great possibilities according to its supreme performance and low cost, but with the complexity and variability of the structure. With the in-depth study of the sodium storage behaviors of NCC in recent years, three modes of interlayer intercalation, clustering into micropores, and adsorption are reported and summarized. Although the storage mechanism has gradually become more evident, the complex behavior of the ions at different voltage regions, especially in the low-voltage (plateau) region, still remains controversial. It is essential to understand further the relationship between ions and NCC structure during energy storage processes. Based on the summary of previous works, this article has reviewed the storage mechanism of sodium ions in NCC and evaluated the structure-behavior relationship between sodium-ion storage and the carbon structure.

Hard Carbons as Anodes in Sodium-Ion Batteries: Sodium Storage Mechanism and Optimization Strategies

Sodium-ion batteries (SIBs) are regarded as promising alternatives to lithium-ion batteries (LIBs) in the field of energy, especially in large-scale energy storage systems. Tremendous effort has been put into the electrode research of SIBs, and hard carbon (HC) stands out among the anode materials due to its advantages in cost, resource, industrial processes, and safety. However, different from the application of graphite in LIBs, HC, as a disordered carbon material, leaves more to be completely comprehended about its sodium storage mechanism, and there is still plenty of room for improvement in its capacity, rate performance and cycling performance. This paper reviews the research reports on HC materials in recent years, especially the research process of the sodium storage mechanism and the modification and optimization of HC materials. Finally, the review summarizes the sterling achievements and the challenges on the basis of recent progress, as well as the prospects on the development of HC anode materials in SIBs.

Silica and nitrogen-doped carbon co-coated lithium manganese iron phosphate microspheres as cathode materials for lithium batteries

Lithium manganese iron phosphate (LiMn1-xFexPO4, LMFP) combines the advantages of LiFePO4 and LiMnPO4. However, low electronic conductivity and sluggish lithium ion diffusion of the LMFP cathode limits its commercial application. In this work, the LMFP microspheres were co-coated by silica and N-doped carbon for the improvement of electronic and ionic conductivity of LMFP. The hydrolysis of tetraethyl orthosilicate and the polymerization of dopamine can be mutually promoted in one reaction system to realize the simultaneous precipitation of Si and C species on the LMFP surfaces without the addition of acid–base catalysts or buffering agents. After high-temperature treatment in argon, the silica and N-doped carbon co-coated LMFP microspheres were obtained with improved cycling stability (84.4% of capacity retention for 300 cycles at 1 C) and enhanced rate performance (80.0 mAh g−1 at 5 C). Therefore, this work shows a facile and common method for the composite coating of cathode materials.

Superstructure MOF as a framework to composite MoS2 with rGO for Li/Na-ion battery storage with high-performance and stability

Metal sulfides, one kind of electrode material with very high theoretical capacity, have been widely studied for use in lithium and sodium ion batteries. However, there are some problems hindering their applications in electrodes, such as low conductivity and volume expansion. The MOF introduces metals with different coordination strengths into an existing MOF structure, which improves the performance of the electrode to a certain extent. In this paper, Fe/Zn bimetallic MOF rod-like superstructure was prepared based on Ostwald theory. Accompanied by sulfuration, the MOF was effectively combined with MoS₂ and GO, and the objective materials Fe₇S₈-C/ZnS-C@MoS₂/rGO composites were successfully prepared. The MOF material provides a good frame and an efficient electron transport path, while the robust rGO wall effectively inhibits the pulverization of materials during the lithium/sodium intercalation/escalation courses. This particular material exhibited excellent cycling and rate capability performance when used in Li/Na-ion batteries. When used in Li-batteries, the electrode material delivered a specific capacity of 1598.3 mA h g^-1 at 0.1 A g^-1 and remained at 1196.7 mA h g^-1 even after about 100 cycles and further exhibited a specific capacity of 368.68 mA h g^-1 at the current rate of 5 A g^-1 even after 1000 cycles, respectively. As for sodium batteries, these electrode materials exhibited an initial reversible capacity of 1053.6 mA h g^-1 at 0.1 A g^-1 and the reversible capacity was still as high as 592.2 mA h g^-1 after 200 cycles. It is perhaps that this composite material with its particular architecture and composition is greatly beneficial for electron transfer and Li/Na ion diffusion. In the repeated physicochemical/nutrifying process, the appropriate distance between adjacent MOFs is of great help in preventing volume changes and thus improving the electrochemical performance.

Heterojunction-Promoted Sodium Ion Storage of Bimetallic Selenides Encapsulated in a Carbon Sheath with Boosted Ion Diffusion and Stable Structure

Although metallic chalcogenides are deemed as attractive sodium anode materials recently, the electrochemical performance is severely confined by the liability of structural collapse and sluggish ion diffusion kinetics. Herein a composite of carbon-encapsulated bimetallic selenides MoSe₂-Sb₂Se₃ was prepared by a hydrothermal method on the basis of abundant reaction sites, high activity, an extra built-in electric field generated from heterointerfaces, and synergistic effects between the different components. Equally important, the carbon coating is effective to support the structural stability by restraining the vast volumetric variation to achieve the purpose of improving the cycling performance. The density functional theory calculation results indicate that the band gap is narrowed and that the work function is decreased on the interface of the MoSe₂-Sb₂Se₃ heterojunction, leading to an additional driving force stemming from the introduction of the built-in electric field and the formation of the Sb-Se (Se from MoSe₂) bond. Therefore, the resultant composite presents increased reaction kinetics and good electrochemical properties by acquiring a capacity of 376.0 mA h g^-1 over 580 cycles at 2.0 A g^-1 for the half-cell and 276 mA h g^-1 over 750 cycles at 2 A g^-1 for the full-cell. This work highlights bimetallic selenides with facilitated ion transferability with high performance.

MoO42--mediated engineering of Na3V2(PO4)3 as advanced cathode materials for sodium-ion batteries

Sodium vanadium phosphate [Na₃V₂(PO₄)₃] with high voltage platform, low cost and environment friendliness has been considered as one of the most promising candidates as cathodes for high-performance sodium-ion batteries. However, the sodium storage property of Na₃V₂(PO₄)₃ is limited because of its low electronic conductivity and poor kinetic performance. Herein, MoO₄^2--doped Na_(3+2x)V₂(PO₄)_(3-x)MoO_4(x) [NVP-MoO₄ (x), x = 0, 0.05, 0.10, 0.15] have been developed and prepared by a feasible solid-state reaction. The optimal NVP-MoO₄ (0.10) delivers a high initial capacity of 108.9 mA h g^-1 and presents an excellent capacity retention of 91.5% at 1 C after 150 cycles. In addition, the NVP-MoO₄ (0.10) shows a good rate capability, delivering a relatively high capacity of 84.2 mA h g^-1 at 50 C. The results of sodium storage measurement and density of states calculation indicate that MoO₄^2- doping can significantly enhance the structural stability, promote the kinetics behavior and boost the electronic conductivity of the materials. In-situ XRD test reveals that the electrochemical reaction of the NVP-MoO₄ (0.10) exhibits a highly reversible phase transition process. This work provides a new insight for the design of advanced cathodes for high-performance sodium-ion batteries by the strategy of unique anion doping.

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.

Hierarchical microstructure constructed with graphitic carbon-coated Ni3S2 nanoparticles anchored on N-doped mesoporous carbon nanoflakes for optimized sodium storage

A hierarchical microstructure constructed with graphitic-carbon-coated Ni₃S₂ nanoparticles anchored on N-doped mesoporous carbon nanoflakes was fabricated using a nickel-based micro-nano structure as a precursor and polydopamine as a carbon source. By optimizing the microstructure, the obtained Ni₃S₂/carbon composite compounded with the thickest carbon nanoflakes delivers ultrafast and stable Na-ion storage performance, and can maintain a reversible charge capacity of 372 mA h g^-1 at a current density of 5 A g^-1 over 250 cycles, and 316 mA h g^-1 even at a current density of 20 A g^-1 for 2000 cycles. These remarkable electrochemical properties can be attributed to its hierarchical microstructure of graphitic-carbon-coated Ni₃S₂ particles and N-doped mesoporous carbon nanoflakes, which provide easy accessibility to the electrolyte, fast electron transport and Na⁺ diffusion, and even relieve the strain caused by the volume expansion upon cycling.

Constructing electronic interconnected bimetallic selenide-filled porous carbon nanosheets for stable and highly efficient sodium-ion half/full batteries

Owing to their large theoretical capacity and relatively high electronic conductivity, transition metal selenides have been investigated as potential anodes for energy storage applications. On the other hand, the quick capacity decline induced by volume expansion during cycling and unconnected conducting network of the transition metal selenide-based electrode severely limit their employment in sodium-ion batteries (SIBs). Herein, a simple solvent ultrasonic technique and pyrolysis selenation process were used to make a porous N-doped carbon nanosheet-supported FeSe₂/CoSe₂ electrode. The electrochemical kinetics could be improved, and the stress generated by volume expansion could be efficiently adjusted by exquisitely constructed boundary of the FeSe₂/CoSe₂-CN electrode. As expected, the FeSe₂/CoSe₂-CN porous nanosheets exhibited a high Na⁺ storage capacity of 350 mA h g^-1 (10 A g^-1, 1000 cycles). Kinetic studies were conducted to explore the Na⁺ storage mechanism of FeSe₂/CoSe₂-CN. The as-constructed full sodium-ion batteries, when combined with Na₃V₂(PO₄)₂O₂F, have a phenomenal energy density (109 W h kg^-1), encouraging the exploration of energy-related components with the high-energy density properties.

[Co3(μ3-O)]-Based Metal-Organic Frameworks as Advanced Anode Materials in K- and Na-Ion Batteries

A new metal-organic framework {(Me₂NH₂)₂[Co₃(μ₃-O)(btb)₂(py)(H₂O)]·(DMF)₂(H₂O)₂}_n (Cobtbpy) was solvothermal synthesized (H₃btb = 1,3,5-tri(4-carboxylphenyl)benzene, py = pyridine, DMF = N,N-dimethylformamide). Cobtbpy shows a (3,6)-connected rtl 3D network with a point symbol of (4·6²)₂(4²·6¹⁰·8³) based on the [Co₃(μ₃-O)] clusters. The obtained Cobtbpy has stable, accessible, dense active sites and can be applied in the potassium- and sodium-ion batteries. Through mixing with single-walled carbon nanotubes, the prepared composite anode material Cobtbpy-0.9 achieved a high reversible capability, delivering 416 mAh/g in the potassium-ion batteries and 379 mAh/g in the sodium-ion batteries at 0.05 A/g. The outstanding properties of Cobtbpy-0.9 in the batteries demonstrated that this MOFs-based carbon composite is a highly desirable electrode material candidate for high-performance potassium- and sodium-ion batteries.

High-rate transition metal-based cathode materials for battery-supercapacitor hybrid devices

With the rapid development of portable electronic devices, electric vehicles and large-scale grid energy storage devices, there is a need to enhance the specific energy density and specific power density of related electrochemical devices to meet the fast-growing requirements of energy storage. Battery-supercapacitor hybrid devices (BSHDs), combining the high-energy-density feature of batteries and the high-power-density properties of supercapacitors, have attracted mass attention in terms of energy storage. However, the electrochemical performances of cathode materials for BSHDs are severely limited by poor electrical conductivity and ion transport kinetics. As the rich redox reactions induced by transition metal compounds are able to offer high specific capacity, they are an ideal choice of cathode materials. Therefore, this paper reviews the currently advanced progress of transition metal compound-based cathodes with high-rate performance in BSHDs. We discuss some efficient strategies of enhancing the rate performance of transition metal compounds, including developing intrinsic electrode materials with high conductivity and fast ion transport; modifying materials, such as inserting defects and doping; building composite structures and 3D nano-array structures; interfacial engineering and catalytic effects. Finally, some suggestions are proposed for the potential development of cathodes for BSHDs, which may provide a reference for significant progress in the future.

Iron Phosphide Confined in Carbon Nanofibers as a Free-Standing Flexible Anode for High-Performance Lithium-Ion Batteries

Iron phosphide with high specific capacity has emerged as an appealing candidate for next-generation lithium-ion battery anodes. However, iron phosphide could undergo conversion reactions and generally suffer from a rapid capacity degradation upon cycling due to its structure pulverization. Chemomechanical breakdown of iron phosphide due to its rigidity has been a challenge to fully realizing its electrochemical performance. To address this challenge, we report here on an enticing opportunity: a flexible, free-standing iron phosphide anode with Fe₂P nanoparticles confined in carbon nanofibers may overcome existing challenges. For the synthesis, we introduce a facile electrospinning strategy that enables in situ formation of Fe₂P within a carbon matrix. Such a carbon matrix can effectively minimize the structure change of Fe₂P particles and protect them from pulverization, allowing the electrodes to retain a free-standing structure after long-term cycling. The produced electrodes showed excellent electrochemical performance in lithium-ion half and full cells, as well as in flexible pouch cells. These results demonstrate the successful development of iron phosphide materials toward high capacity, light weight, and flexible energy storage.

Waste utilization of crab shell: 3D hierarchical porous carbon towards high-performance Na/Li storage

Waste into wealth: an advanced anode material with a unique 3D porous structure derived from discarded crab shells.

Chemical Vapor Deposition-Assisted Fabrication of Self-Assembled Co/MnO@C Composite Nanofibers as Advanced Anode Materials for High-Capacity Li-Ion Batteries

Constructing the nanostructure of transition metal oxides for high energy density lithium-ion batteries has been widely studied recently. Prompted by the idea that the transition metal can serve as a catalyzer influence on the reversibility of solid-electrolyte interphase films, Co/MnO@C composite nanofibers were designed by electrospinning and chemical vapor deposition methods. The Co/MnO@C electrode showed superior electrochemical performance with a large capacity increase for the first 400 cycles and a high rate performance of 1345 mA h g^-1 at 1000 mA g^-1. There was no obvious decay of capacity over the whole 1000 cycles, demonstrating the excellent cycling stability of the samples. The new design and synthesis of the anodic materials may offer a prototype for high-performance and strong-stability batteries.