Progress and Prospect of Bimetallic Oxides for Sodium-Ion Batteries: Synthesis, Mechanism, and Optimization Strategy

Sodium-ion batteries (SIBs) are considered as an alternative to and even replacement of lithium-ion batteries in the near future in order to address the energy crisis and scarcity of lithium resources due to the wide distribution and abundance of sodium resources on the earth. The exploration and development of high-performance anode materials are critical to the practical applications of advanced SIBs. Among various anode materials, bimetallic oxides (BMOs) have attracted special research attention because of their abundance, easy access, rich redox reactions, enhanced capacity and satisfactory cycling stability. Although many BMO anode materials have been reported as anode materials in SIBs, very limited studies summarized the progress and prospect of BMOs in practical applications of SIBs. In this review, recent progress and challenges of BMO anode materials for SIBs have been comprehensively summarized and discussed. First, the preparation methods and sodium storage mechanisms of BMOs are discussed. Then, the challenges, optimization strategies, and sodium storage performance of BMO anode materials have been reviewed and summarized. Finally, the prospects and future research directions of BMOs in SIBs have been proposed. This review aims to provide insight into the efficient design and optimization of BMO anode materials for high-performance SIBs.

Molten salt synthesis of disordered spinel CoFe2O4 with improved electrochemical performance for sodium-ion batteries

Sodium-ion (Na-ion) batteries are currently being investigated as an attractive substitute for lithium-ion (Li-ion) batteries in large energy storage systems because of the more abundant and less expensive supply of Na than Li. However, the reversible capacity of Na-ions is limited because Na possesses a large ionic radius and has a higher standard electrode potential than that of Li, making it challenging to obtain electrode materials that are capable of storing large quantities of Na-ions. This study investigates the potential of CoFe2O4 synthesised via the molten salt method as an anode for Na-ion batteries. The obtained phase structure, morphology and charge and discharge properties of CoFe2O4 are thoroughly assessed. The synthesised CoFe2O4 has an octahedron morphology, with a particle size in the range of 1.1-3.6 μm and a crystallite size of ∼26 nm. Moreover, the CoFe2O4 (M800) electrodes can deliver a high discharge capacity of 839 mA h g-1 in the first cycle at a current density of 0.1 A g-1, reasonable cyclability of 98 mA h g-1 after 100 cycles and coulombic efficiency of ∼99%. The improved electrochemical performances of CoFe2O4 can be due to Na-ion-pathway shortening, wherein the homogeneity and small size of CoFe2O4 particles may enhance the Na-ion transportation. Therefore, this simple synthetic approach using molten salt favours the Na-ion diffusion and electron transport to a great extent and maximises the utilisation of CoFe2O4 as a potential anode material for Na-ion batteries.

Metal-organic frameworks as a good platform for the fabrication of multi-metal nanomaterials: design strategies, electrocatalytic applications and prospective

MOF-derived multi-metal nanomaterials are attracting numerous attentions in widespread applications such as catalysis, sensors, energy storage and conversion, and environmental remediation. Compared to the monometallic counterparts, the presence of foreign metal is expected to bring new physicochemical properties, thus exhibiting synergistic effect for enhanced performance. MOFs have been proved as a good platform for the fabrication of polymetallic nanomaterials with requisite features. Herein, various design strategies related to constructing multi-metallic nanomaterials from MOFs are summarized for the first time, involving metal nodal substitution, seed epitaxial growth, ion-exchange strategy, guest species encapsulation, solution impregnation and combination with extraneous substrate. Afterwards, the recent advances of multi-metallic nanomaterials for electrocatalytic applications, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), are systematically discussed. Finally, a personal outlook on the future trends and challenges are also presented with hope to enlighten deeper understanding and new thoughts for the development of multi-metal nanomaterials from MOFs.

3D Ultralight Hollow NiCo Compound@MXene Composites for Tunable and High-Efficient Microwave Absorption

The 3D hollow hierarchical architectures tend to be designed for inhibiting stack of MXene flakes to obtain satisfactory lightweight, high-efficient and broadband absorbers. Herein, the hollow NiCo compound@MXene networks were prepared by etching the ZIF 67 template and subsequently anchoring the Ti₃C₂T_x nanosheets through electrostatic self-assembly. The electromagnetic parameters and microwave absorption property can be distinctly or slightly regulated by adjusting the filler loading and decoration of Ti₃C₂T_x nanoflakes. Based on the synergistic effects of multi-components and special well-constructed structure, NiCo layered double hydroxides@Ti₃C₂T_x (LDHT-9) absorber remarkably achieves unexpected effective absorption bandwidth (EAB) of 6.72 GHz with a thickness of 2.10 mm, covering the entire Ku-band. After calcination, transition metal oxide@Ti₃C₂T_x (TMOT-21) absorber near the percolation threshold possesses minimum reflection loss (RL_min) value of - 67.22 dB at 1.70 mm within a filler loading of only 5 wt%. This work enlightens a simple strategy for constructing MXene-based composites to achieve high-efficient microwave absorbents with lightweight and tunable EAB.

Surfactant-Assisted Growth of a Conversion-Type Binary Metal Oxide-Based Composite Electrode for Boosting the Reversible Lithium Storage

High-performance anode materials play a crucial role in paving the development of next-generation lithium-ion batteries (LIBs). NiCo₂O₄, as a typical binary metal oxide, has been extensively demonstrated to possess higher capacity and electrochemical activity compared with a monometal oxide such as NiO or Co₃O₄. However, the advances in the application of LIBs are usually limited by the relatively low electrical conductivity and large volume change during repeated charging/discharging processes. Herein, a NiCo₂O₄@carbon nanotube (CNT) composite electrode with advanced architecture is developed through a facile surfactant-assisted synthetic strategy. The introduced polyvinyl pyrrolidone can greatly facilitate the heterogeneous nucleation and growth of the NiCo precursor on CNTs and thus benefit the uniform transformation to a well-confined NiCo₂O₄@CNT composite. The CNTs combined with NiCo₂O₄ tightly act as both a conductive network for enhancing the ion/electron transfer and a support for mitigating the volume expansion of NiCo₂O₄. As a result, the NiCo₂O₄@CNT electrode exhibits a high initial capacity of 830.3 mA h g^-1 and a good cycling stability of 608.1 mA h g^-1 after 300 cycles at 2000 mA g^-1.

Recent progress on metal–organic framework-derived materials for sodium-ion battery anodes

Recent progress on MOF-derived materials, including carbon and metal oxides/sulfides/selenides/phosphides, as anode materials for sodium-ion batteries is summarized.

Binder-free C@NiCo2O4 on Ni foam with ultra-stable pseudocapacitive lithium ion storage

Carbon-coated nickel cobaltate on nickel foam (C@NCO@NF) with stable pseudocapacitive lithium storage capacity was prepared via a two-step strategy. NiCo hydroxide was initially grown on Ni foam via electrodeposition. Subsequent glucose soaking and annealing converted the intermediate into C@NCO@NF. Carbon coating could significantly improve the cycling stability and rate performance of the binder-free anode. The C@NCO@NF electrode could stably deliver a reversible capacity of 513 mAh · g^-1 after 500 cycles at a current density of 500 mA · g^-1. It could even stably cycle at a high current density of 5000 mA · g^-1 for 3000 cycles, with a reversible capacity of 115 mAh · g^-1. Kinetic analysis revealed that surface-controlled pseudocapacitance plays a dominant role in the lithium ion storage. Improved electrochemical performance is attributed to the synergetic effect of pseudocapacitance and carbon coating.

Synthesis of Sea Urchin-Like NiCo2O4 via Charge-Driven Self-Assembly Strategy for High-Performance Lithium-Ion Batteries

In this study, hydrothermal synthesis of sea urchin-like NiCo₂O₄ was successfully demonstrated by a versatile charge-driven self-assembly strategy using positively charged poly(diallydimethylammonium chloride) (PDDA) molecules. Physical characterizations implied that sea urchin-like microspheres of ~ 2.5 μm in size were formed by self-assembly of numerous nanoneedles with a typical dimension of ~ 100 nm in diameter. Electrochemical performance study confirmed that sea urchin-like NiCo₂O₄ exhibited high reversible capacity of 663 mAh g^-1 after 100 cycles at current density of 100 mA g^-1. Rate capability indicated that average capacities of 1085, 1048, 926, 642, 261, and 86 mAh g^-1 could be achieved at 100, 200, 500, 1000, 2000, and 3000 mA g^-1, respectively. The excellent electrochemical performances were ascribed to the unique micro/nanostructure of sea urchin-like NiCo₂O₄, tailored by positively charged PDDA molecules. The proposed strategy has great potentials in the development of binary transition metal oxides with micro/nanostructures for electrochemical energy storage applications.

Designed formation of Co3O4@NiCo2O4 sheets-in-cage nanostructure as high-performance anode material for lithium-ion batteries

Structural and compositional control of functional nanoparticles is considered to be an efficient way to obtain enhanced chemical and physical properties. A unique Co3O4@NiCo2O4 sheets-in-cage nanostructure is fabricated via a facile conversion reaction, involving subsequent hydrolysis and annealing treatment. Such hollow nanoparticles provide an excellent property for Li storage.

Surface phosphation of 3D mesoporous NiCo2O4 nanowire arrays as bifunctional anodes for lithium and sodium ion batteries

A novel surface phosphate strategy was adopted to dramatically improve the charge transport, ion diffusion, electroactive sites, and cycle stability of mesoporous NiCo2O4 nanowire arrays (NWAs), drastically boosting their electrochemical properties. Consequently, the as-prepared phosphated NiCo2O4 NWA (P-NiCo2O4 NWA) electrode achieved excellent energy storage performance as a bifunctional anode material for both lithium ion batteries (LIBs) and sodium ion batteries (SIBs). When evaluated as an anode for LIBs, this P-NiCo2O4 NWA electrode showed a high reversible capacity up to 1156 mA h g-1 for 1500 cycles at 200 mA g-1 without appreciable capacity attenuation, while in SIBs, the electrode could also deliver an admirable initial capacity as high as 687 mA h g-1 and maintained 83.5% of this after 500 cycles at the same current density. Most important, when the current density increased from 100 to 1000 mA g-1, the capacity retention was about 63% in LIBs and 54% in SIBs. This work may shed light on the engineering of efficient electrodes for multifunctional flexible energy storage device applications.

Electrodeposited binder-free NiCo2O4@carbon nanofiber as a high performance anode for lithium ion batteries

Binder-free nickel cobaltite on a carbon nanofiber (NiCo₂O₄@CNF) anode for lithium ion batteries was prepared via a two-step procedure of electrospinning and electrodeposition. The CNF was obtained by annealing electrospun poly-acrylonitrile (PAN) in nitrogen (N₂). The NiCo₂O₄ nanostructures were then grown on the CNF by electrodeposition, followed by annealing in air. Experimental results showed that vertically aligned NiCo₂O₄ nanosheets had uniformly grown on the surface of the CNF, forming an interconnected network. The NiCo₂O₄@CNF possessed considerable lithium storage capacity and cycling stability. It exhibited a high reversible capacity of 778 mAhg^-1 after 300 cycles at a current density of 0.25 C (1 C = 890 mAg^-1) with an average capacity loss rate of 0.05% per cycle. The NiCo₂O₄@CNF had considerable rate capacities, delivering a capacity of 350 mAhg^-1 at a current density of 2.0 C. The outstanding electrochemical performance can be mainly attributed to the following: (1) The nanoscale structure of NiCo₂O₄ could not only shorten the diffusion path of lithium ions and electrons but also increase the specific surface area, providing more active sites for electrochemical reactions. (2) The CNF with considerable mechanical strength and electrical conductivity could function as an anchor for the NiCo₂O₄ nanostructure and ensure an efficient electron transfer. (3) The porous structure resulted in a high specific surface area and an effective buffer for the volume changes during the repeated charge-discharge processes. Compared with a conventional hydrothermal method, electrodeposition could significantly simplify the preparation of NiCo₂O₄, with a shorter preparation period and lower energy consumption. This work provides an alternative strategy to obtain a high performance anode for lithium ion batteries.

Facile preparation of monodisperse NiCo2O4 porous microcubes as a high capacity anode material for lithium ion batteries

Monodisperse NiCo₂O₄ porous microcubes were used as anode materials for lithium-ion batteries, and they exhibit outstanding rate capability and cycling stability.

Microwave-Assisted Synthesis of NiCo2O4 Double-Shelled Hollow Spheres for High-Performance Sodium Ion Batteries

The ternary transitional metal oxide NiCo₂O₄ is a promising anode material for sodium ion batteries due to its high theoretical capacity and superior electrical conductivity. However, its sodium storage capability is severely limited by the sluggish sodiation/desodiation reaction kinetics. Herein, NiCo₂O₄ double-shelled hollow spheres were synthesized via a microwave-assisted, fast solvothermal synthetic procedure in a mixture of isopropanol and glycerol, followed by annealing. Isopropanol played a vital role in the precipitation of nickel and cobalt, and the shrinkage of the glycerol quasi-emulsion under heat treatment was responsible for the formation of the double-shelled nanostructure. The as-synthesized product was tested as an anode material in a sodium ion battery, was found to exhibit a high reversible specific capacity of 511 mAh g^-1 at 100 mA g^-1, and deliver high capacity retention after 100 cycles.

Templating synthesis of Fe2O3 hollow spheres modified with Ag nanoparticles as superior anode for lithium ion batteries

Ag-Fe₂O₃ hollow spheres are synthesized by using Ag@C core-shell matrix as sacrificial templates. The morphologies and structures of the as-prepared samples are characterized by scanning electron microscopy, X-ray powder diffraction energy dispersive, transmission electron microscopy and high resolution transmission electron microscopy. In contrast to Fe₂O₃ hollow spheres, Ag-Fe₂O₃ hollow spheres exhibit much higher electrochemical performances. The Ag-Fe₂O₃ composites exhibit an initial discharge capacity of 1030.9 mA h g^-1 and retain a high capacity of 953.2 mA h g^-1 at a current density of 100 mA g^-1 after 200 cycles. Furthermore, Ag-Fe₂O₃ electrode can maintain a stable capacity of 678 mA h g^-1 at 1 A g^-1 after 250 cycles. Rate performance of Ag-Fe₂O₃ electrode exhibits a high capacity of 650.8 mA h g^-1 even at 5 A g^-1. These excellent performances can be attributed to the decoration of Ag particles which will enhance conductivity and accelerate electrochemical reaction kinetics. Moreover, the hollow structure and the constructing particles with nanosize will benefit to accommodate huge volume change and stabilize the structure.

Recent Progress in Metal-Organic Frameworks and Their Derived Nanostructures for Energy and Environmental Applications

Metal-organic frameworks (MOFs), as a very promising category of porous materials, have attracted increasing interest from research communities due to their extremely high surface areas, diverse nanostructures, and unique properties. In recent years, there is a growing body of evidence to indicate that MOFs can function as ideal templates to prepare various nanostructured materials for energy and environmental cleaning applications. Recent progress in the design and synthesis of MOFs and MOF-derived nanomaterials for particular applications in lithium-ion batteries, sodium-ion batteries, supercapacitors, dye-sensitized solar cells, and heavy-metal-ion detection and removal is reviewed herein. In addition, the remaining major challenges in the above fields are discussed and some perspectives for future research efforts in the development of MOFs are also provided.

Custom designed ZnMn2O4/nitrogen doped graphene composite anode validated for sodium ion battery application

pH control synthesised ZnMn₂O₄ nanoparticles embedded in nitrogen doped graphene sheets demonstrate themselves to be a potential anode for sodium-ion batteries.

Hierarchically porous CoNiO2nanosheet array films with superior sodium storage performance

The hierarchically porous CoNiO₂nanosheet array film preparedviaa low-temperature solvothermal method manifests superior sodium storage performance.