Self-Assembled Porous NiFe2 O4 Floral Microspheres Inlaid on Ultrathin Flake Graphite as Anode Materials for Lithium Ion Batteries

Preparation of rambutan-like Co0.5Ni0.5Fe2O4 as anode for high–performance lithium–ion batteries

NiFe₂O₄ is a kind of promising lithium ion battery (LIB) electrode material, but its commercial applications have been limited due to the electronic insulation property and large volume expansion during the conversion reaction process, which results in rapid capacity decrease and poor cycling stability. We synthesized rambutan-like Co_0.5Ni_0.5Fe₂O₄ using the self-templating solvothermal method. The special structure of Co_0.5Ni_0.5Fe₂O₄ which was formed by the assembly of numerous nanosheets could effectively buffer the volume change during the charging and discharging process. Partial substitution of Ni with Co. in NiFe₂O₄ leads to Co_0.5Ni_0.5Fe₂O₄, the coexisting of both nickel and cobalt components is expected to provide more abundant redox reactions. The specific capacity of the rambutan-like Co_0.5Ni_0.5Fe₂O₄ as an anode material for LIB could reach 963 mA h g⁻¹ at the current density of 500 mA g⁻¹ after 200 cycles, confirming that the as-synthesized material is a promising candidate for LIBs.

NiFe2O4/Ketjen Black Composites as Efficient Membrane Separators to Suppress the Shuttle Effect for Long-Life Lithium-Sulfur Batteries

Lithium-sulfur batteries exhibit great potential as one of the most promising energy storage devices due to their high theoretical energy density and specific capacity. However, the shuttle effect of the soluble polysulfide intermediates could lead to a severe self-discharge effect that hinders the development of lithium-sulfur batteries. In this paper, a battery separator has been prepared based on NiFe₂O₄/Ketjen Black (KB) modification by a simple method to solve the shuttle effect and improve the battery performance. The as-modified separator with the combination of small-size KB and NiFe₂O₄ nanoparticles can effectively use the physical and chemical double-layer adsorption to prevent polysulfide from the shuttle. Moreover, it can give full play to its catalytic effect to improve the conversion efficiency of polysulfide and activate the dead sulfur. The results show that the NiFe₂O₄/KB-modified separator battery still maintains a discharge capacity of 406.27 mAh/g after 1000 stable cycles at a high current density of 1 C. Furthermore, the coulombic efficiency remains at 99%, and the average capacity attenuation per cycle is only 0.051%. This simple and effective method can significantly improve the application capacity of lithium-sulfur batteries.

Preparations of NiFe2O4 Yolk-Shell@C Nanospheres and Their Performances as Anode Materials for Lithium-Ion Batteries

At present, lithium-ion batteries (LIBs) have received widespread attention as substantial energy storage devices; thus, their electrochemical performances must be continuously researched and improved. In this paper, we demonstrate a simple self-template solvothermal method combined with annealing for the synthesis of NiFe2O4 yolk-shell (NFO-YS) and NiFe2O4 solid (NFO-S) nanospheres by controlling the heating rate and coating them with a carbon layer on the surface via high-temperature carbonization of resorcinol and formaldehyde resin. Among them, NFO-YS@C has an obvious yolk-shell structure, with a core-shell spacing of about 60 nm, and the thicknesses of the NiFe2O4 shell and carbon shell are approximately 15 and 30 nm, respectively. The yolk-shell structure can alleviate volume changes and shorten the ion/electron diffusion path, while the carbon shell can improve conductivity. Therefore, NFO-YS@C nanospheres as the anode materials of LIBs show a high initial capacity of 1087.1 mA h g-1 at 100 mA g-1, and the capacity of NFO-YS@C nanospheres impressively remains at 1023.5 mA h g-1 after 200 cycles at 200 mA g-1. The electrochemical performance of NFO-YS@C is significantly beyond NFO-S@C, which proves that the carbon coating and yolk-shell structure have good stability and excellent electron transport ability.

Tunable Metallogels Based on Bifunctional Ligands: Precursor Metallogels, Spinel Oxides, Dye and CO2 Adsorption

A semisolid gel material is a gift of serendipity via various chemical interactions, and metal incorporation (metallogels) imparts diverse functional properties. In this work, we have synthesized four metallogels from tetrapodal and hexapodal carboxylic acid/amide-based low-molecular-weight gelators with Ni(II) and Cu(II) salts. These metallogels can be tuned to be a low-temperature precursor of porous spinel oxides. These xerogels exhibit impressive water soluble dye and carbon dioxide adsorption, which coupled with the tunability and facile synthesis of porous spinel oxides underscores their potential in environmental remediation and energy applications.

Morphology Controllable Synthesis of NiO/NiFe2O4 Hetero-Structures for Ultrafast Lithium-Ion Battery

Rational design of high performance anode material with outstanding rate capability and cycling stability is of great importance for lithium ion batteries (LIBs). Herein, a series of NiO/NiFe₂O₄ hetero-structures with adjustable porosity, particle size, and shell/internal structure have been synthesized via a controllable annealing process. The optimized NiO/NiFe₂O₄ (S-NFO) is hierarchical hollow nanocube that is composed of ~5 nm subunits and high porosity. When being applied as anode for LIBs, the S-NFO exhibits high rate capability and excellent cycle stability, which remains high capacity of 1,052 mAh g^-1 after 300 cycles at 5.0 A g^-1 and even 344 mAh g^-1 after 2,000 cycles at 20 A g^-1. Such impressive electrochemical performance of S-NFO is mainly due to three reasons. One is high porosity of its hierarchical hollow shell, which not only promotes the penetration of electrolyte, but also accommodates the volume change during cycling. Another is the small particle size of its subunits, which can effectively shorten the electron/ion diffusion distance and provide more active sites for Li⁺ storage. Besides, the hetero-interfaces between NiO and NiFe₂O₄ also contribute toitsfast charge transport.

NiFe2O4@ nitrogen-doped carbon hollow spheres with highly efficient and recyclable adsorption of tetracycline

Antibiotics can affect ecosystems and threaten human health; therefore, methods for removing antibiotics have become a popular subject in environmental management and for the protection of human health. Adsorption is considered an effective approach for the removal of antibiotics from water. In this study, NiFe₂O₄@nitrogen-doped carbon hollow spheres (NiFe₂O₄/NCHS) were synthesized via a facile hydrothermal method followed by calcination using NCHS as a hard template. The nanocomposite exhibited high adsorption activity and good recyclability. The nanocomposite was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and nitrogen adsorption–desorption to study its micromorphology, structure, and chemical composition/states. In addition, the factors affecting the adsorption process were systematically investigated, including tetracycline (TC) concentration, solution pH, ionic strength, and temperature. The maximum adsorption capacity for TC was calculated to be 271.739 mg g⁻¹ based on the Langmuir adsorption model, which was higher than various other materials. This study provides an effective method for constructing the NiFe₂O₄/NHCS core–shell structure, which can be applied for the removal of TC from water.

Antibiotics can affect ecosystems and threaten human health; therefore, methods for removing antibiotics have become a popular subject in environmental management and for the protection of human health.