Cobalt oxide-carbon nanosheet nanoarchitecture as an anode for high-performance lithium-ion battery

Structural Defects on Graphene Generated by Deposition of CoO: Effect of Electronic Coupling of Graphene

Understanding the interactions in hybrid systems based on graphene and functional oxides is crucial to the applicability of graphene in real devices. Here, we present a study of the structural defects occurring on graphene during the early stages of the growth of CoO, tailored by the electronic coupling between graphene and the substrate in which it is supported: as received pristine graphene on polycrystalline copper (coupled), cleaned in ultra-high vacuum conditions to remove oxygen contamination, and graphene transferred to SiO2/Si substrates (decoupled). The CoO growth was performed at room temperature by thermal evaporation of metallic Co under a molecular oxygen atmosphere, and the early stages of the growth were investigated. On the decoupled G/SiO2/Si samples, with an initial low crystalline quality of graphene, the formation of a CoO wetting layer is observed, identifying the Stranski-Krastanov growth mode. In contrast, on coupled G/Cu samples, the Volmer-Weber growth mechanism is observed. In both sets of samples, the oxidation of graphene is low during the early stages of growth, increasing for the larger coverages. Furthermore, structural defects are developed in the graphene lattice on both substrates during the growth of CoO, which is significantly higher on decoupled G/SiO2/Si samples mainly for higher CoO coverages. When approaching the full coverage on both substrates, the CoO islands coalesce to form a continuous CoO layer with strip-like structures with diameters ranging between 70 and 150 nm.

A Review of Cobalt-Containing Nanomaterials, Carbon Nanomaterials and Their Composites in Preparation Methods and Application

With the increasing demand for sustainable and green energy, electric energy storage technologies have received enough attention and extensive research. Among them, Li-ion batteries (LIBs) are widely used because of their excellent performance, but in practical applications, the electrochemical performance of electrode materials is not satisfactory. Carbon-based materials with high chemical stability, strong conductivity, high specific surface area, and good capacity retention are traditional anode materials in electrochemical energy storage devices, while cobalt-based nano-materials have been widely used in LIBs anodes because of their high theoretical specific capacity. This paper gives a systematic summary of the state of research of cobalt-containing nanomaterials, carbon nanomaterials, and their composites in LIBs anodes. Moreover, the preparation methods of electrode materials and measures to improve electrochemical performance are also summarized. The electrochemical performance of anode materials can be significantly improved by compounding carbon nanomaterials with cobalt nanomaterials. Composite materials have better electrical conductivity, as well as higher cycle ability and reversibility than single materials, and the synergistic effect between them can explain this phenomenon. In addition, the electrochemical performance of materials can be significantly improved by adjusting the microstructure of materials (especially preparing them into porous structures). Among the different microscopic morphologies of materials, porous structure can provide more positions for chimerism of lithium ions, shorten the diffusion distance between electrons and ions, and thus promote the transfer of lithium ions and the diffusion of electrolytes.

Urchin-like Co3O4 anchored on reduced graphene oxide with enhanced performance for peroxymonosulfate activation in ibuprofen degradation

Urchin-like Co₃O₄ anchored on reduced graphene oxide was easily prepared with hydrothermal reaction by using a cheap and green agent. First, the surface morphology and physicochemical properties of Co₃O₄-rGO were characterized. Compared with Co₃O₄, Co₃O₄-rGO possessed excellent activity in peroxymonosulfate (PMS) activation for ibuprofen (IBU) degradation. Then, the influences of Co₃O₄-rGO dosage, IBU concentration, PMS concentration and pH on IBU and TOC removal were investigated, respectively. Furthermore, both ·OH and SO₄^•- were identified to be the main active species, and SO₄^•- made the predominant contribution. In addition, residual PMS and SO₄^•- quantification demonstrated that Co₃O₄-rGO could activate PMS more effectively, and produce more SO₄^•-. The mechanistic study revealed that the valence state conversion of Co²⁺/Co³⁺ was the critical PMS activation mechanism. Moreover, the enhanced activity of Co₃O₄-rGO is accounted for the combination of multiple unique characteristics, including excellent electronic transmission (Co²⁺ to Co³⁺, Co²⁺ to PMS), more active sites, and chemical bonds between Co₃O₄ and rGO. 13 degradation products were determined and possible degradation routes were proposed based on the results of LC-MS/MS. Finally, the Co₃O₄-rGO/PMS system also exhibited satisfactory removal of IBU in real water matrices.

Machine Learning enabled High-Throughput Screening of Inorganic Solid Electrolytes for Regulating Dendritic Growth in Lithium Metal Anodes

The Li-S secondary battery system has gained popularity owing to their advantage of higher specific energy compared to the Li ion battery. However, it suffers majorly due to the Li...

Utilization of Interfacial Charge Storage toward Ultra-high Capacity: Li2SO4 Sealed Micron Sized Iron Oxides as Anode for Lithium Batteries

The interfacial charge storage is derived from spin-polarized electrons stored on the surface of iron metal nanoparticles, and reasonable utilization can achieve a capacity far beyond the traditional conversion mechanism. Generally, iron oxide is easy to crack, pulverize, and fall off due to its poor conductivity and large volume change during cycling, and causes serious side reactions with the electrolyte. Herein, this pulverization phenomenon was intentionally utilized to in situ form nano-sized iron particles and create a large number of Fe/Li₂O interfaces. Specifically, a Li⁺ conductor like Li₂SO₄ was utilized to seal micron sized iron oxides and also work as an aggregation barrier. Thus, the in situ formed nanoparticles were separated from the electrolyte and could provide huge capacity through interfacial charge storage. Therefore, the specific capacity of this unique composite continues to rise upon activation cycling and finally reaches 1708 mA h g^-1, which is more than twice its theoretical capacity based on the conversion mechanism. The gradually increasing interfacial charge storage capacity was also directly confirmed by X-ray photoelectron spectroscopy tests. This novel strategy provides new opportunities for the design and commercialization of advanced energy storage systems.

Electrochemical detection of hydrocortisone using green-synthesized cobalt oxide nanoparticles with nafion-modified glassy carbon electrode

Developing highly sensitive and selective sensors is important for the detection of steroid hormones. Electrochemical sensors are of great interest in this regard. Also utilization of bio-derived substances as an electrode material is environment friendly. In this study, we used green-synthesized cobalt oxide nanoparticles (CoO NPs) along with nafion (Naf) on a glassy carbon electrode to detect hydrocortisone (HC) by voltammetry. Electron microscopy, X-ray diffraction, Raman spectroscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy were used to characterize the CoO NPs prepared using Nigella sativa seeds extract. Cyclic voltammetry and differential pulse voltammetry was utilized for the detection of HC. Only one reduction peak at -0.5 V was observed in the presence of HC in 0.1 M sodium hydroxide, indicating an irreversible electrode process. The Naf-CoO NPs enhanced the active surface area of the glassy carbon electrode (GCE) that resulted in a good response for detecting HC with two linear ranges: 0.001-1 μM and 1-9 μM. In comparison to other published electrochemical sensors, the current sensor displayed a low limit of detection of 0.49 nM, as well as remarkable stability and reproducibility. The sensor exhibited credibility for the sensing of HC in pharmaceutical injections and blood serum samples with recovery percentages ranging from 97.7% to 102.5%. The electrochemical sensor has proved to be valuable for HC detection.

A Comprehensive Review of Li-Ion Battery Materials and Their Recycling Techniques

In the context of constant growth in the utilization of the Li-ion batteries, there was a great surge in the quest for electrode materials and predominant usage that lead to the retiring of Li-ion batteries. This review focuses on the recent advances in the anode and cathode materials for the next-generation Li-ion batteries. To achieve higher power and energy demands of Li-ion batteries in future energy storage applications, the selection of the electrode materials plays a crucial role. The electrode materials, such as carbon-based, semiconductor/metal, metal oxides/nitrides/phosphides/sulfides, determine appreciable properties of Li-ion batteries such as greater specific surface area, a minimal distance of diffusion, and higher conductivity. Various classifications of the anode materials such as the intercalation/de- intercalation, alloy/de-alloy, and various conversion materials are illustrated lucidly. Further, the cathode materials, such as nickel-rich LiNixCoyMnzO2 (NCM), were discussed. NCM members such as NCM 333, NCM 523 that enabled to advance for NCM622 and NCM81are reported. The nanostructured materials bridged the gap in the realization of next-generation Li-ion batteries. Li-ion batteries’ electrode nanostructure synthesis, performance, and reaction mechanisms were considered with great concern. The serious effects of Li-ion batteries disposal need to be cut significantly to reduce the detrimental effect on the environment. Hence, the recycling of spent Li-ion batteries has gained much attention in recent years. Various recycling techniques and their effect on the electroactive materials are illustrated. The key areas covered in this review are anode and cathode materials and recent advances along with their recycling techniques. In light of crucial points covered in this review, it constitutes a suitable reference for engineers, researchers, and designers in energy storage applications.

Construction of Co3O4 three-dimensional mesoporous framework structures from zeolitic imidazolate framework-67 with enhanced lithium storage properties

High-porosity mesoporous framework structures are attractive for electrochemical energy storage and other applications. Herein we demonstrate a novel synthesis strategy to make zeolitic imidazolate framework-67 oxidize to a Co₃O₄ three-dimensional mesoporous framework structure. This strategy relies on the oxygen-limitation effect of the closed nanocage and the affinity effect of polyvinylpyrrolidone towards zeolitic imidazolate framework-67. Several TiO₂ nanospheres, as the unique structure junctions, are uniformly embedded within the Co₃O₄ framework to enhance the framework strength. The TiO₂/hydrous titania polyhedron nanocage, as the protecting shell, further encapsulates the Co₃O₄ framework, forming a perfect capsule-type hybrid. As anode materials for lithium-ion batteries, TiO₂@Co₃O₄ framework capsules show superior lithium storage performance with high reversible capacity, stable cycling life and good rate capability. A reversible capacity of 1042 mAh g^-1 can be delivered after 200 cycles at a current density of 300 mA g^-1. The average discharge capacity over 200 cycles reaches 926 mAh g^-1. This demonstrates the superiority of this material structure and its great potential as an anode for high-performance lithium-ion batteries. This work indicates a new strategy to take advantage of metal-organic frameworks to synthesize their mesoporous framework derivatives.

Three-dimensional porous Co3O4-CoO@GO composite combined with N-doped carbon for superior lithium storage

Transition metal oxides (TMOs) as anode materials have potential for lithium-ion batteries (LIBs). However, the poor rate capacity and cycle stability restrict its application. Herein, we demonstrate a facile one-step hydrothermal method to construct a three-dimensional porous conductive network structure, which consists of thin-layered graphene, ultrafine Co₃O₄-CoO nanoparticles and nitrogen-doped carbon. This unique structure can effectively prevent particle agglomeration and cracking caused by volume expansion, provide fast passage for lithium ion/electron transport during cycling and improve the electrical conductivity of the electrode. Moreover, the electrochemical kinetic analysis proves that this is a process dominated by pseudocapacitive behavior. Consequently, the N-C@Co₃O₄-CoO@GO hybrid electrode delivers an ultrahigh capacity of 1 273.1 mA h g^-1 at 0.1 A g^-1 and superior rate performance (725.1 mA h g^-1 at 5 A g^-1). Additionally, it exhibits a high reversible cycling capacity of 787.4 mA h g^-1 at 1 A g^-1 over 600 cycles and even maintains excellent cycling stability for a ultra-long cycles at 5 A g^-1. This work provides a feasible strategy for fabricating the N-C@Co₃O₄-CoO@GO composite as a promising high-performance TMOs anode for LIBs.

Co3O4-nanoparticle-entrapped nitrogen and boron codoped mesoporous carbon as an efficient electrocatalyst for hydrogen evolution

Co₃O₄-nanoparticle-entrapped nitrogen and boron codoped mesoporous carbon was synthesized via the molten salt method. Melamine formaldehyde resin (MF resin) was used as the nitrogen and carbon precursor, and boric acid was utilized as the boron precursor. Furthermore, cobalt chloride was used as the cobalt precursor and the template for the formation of mesopores, which could also be removed and partly recovered by acid washing. The characterization results revealed that the as-obtained samples possessed mesoporous structures, with high cobalt, boron, and nitrogen content values. For the sample of Co_0.65B_0.3NC₈₀₀, the atomic content values of Co, N, and B are 2.3%, 8.87%, and 8.67%, respectively. Moreover, the carbonation temperature and the amount of salt template could both affect the mesoporous structures of the final samples and then affect the electrocatalytic activities for the hydrogen evolution reaction (HER). When the carbonation temperature was 800 °C, the sample of Co_0.65B_0.3NC₈₀₀ showed superior performance for the HER under basic conditions, with high current density, low overpotential, and good stability.

Graphene Liquid Cell Electron Microscopy of Initial Lithiation in Co3O4 Nanoparticles

As it governs the overall performance of lithium-ion batteries, understanding the reaction pathway of lithiation is highly desired. For Co₃O₄ nanoparticles as anode material, here, we report an initial conversion reaction pathway during lithiation. Using graphene liquid cell electron microscopy (GLC-EM), we reveal a CoO phase of the initial conversion product as well as morphological dynamics during Co₃O₄ lithiation. In accordance with the in situ TEM observation, we confirmed that the Co₃O₄ to CoO conversion is a thermodynamically favorable process by calculating the theoretical average voltage based on density functional theory. Our observation will provide a useful insight into the oxide electrode that undergoes conversion reaction.

Coral-Like Yolk-Shell-Structured Nickel Oxide/Carbon Composite Microspheres for High-Performance Li-Ion Storage Anodes

In this study, coral-like yolk-shell-structured NiO/C composite microspheres (denoted as CYS-NiO/C) were prepared using spray pyrolysis. The unique yolk-shell structure was characterized, and the formation mechanism of the structure was proposed. Both the phase separation of the polyvinylpyrrolidone and polystyrene (PS) colloidal solution and the decomposition of the size-controlled PS nanobeads in the droplet played crucial roles in the formation of the unique coral-like yolk-shell structure. The CYS-NiO/C microspheres delivered a reversible discharge capacity of 991 mAh g^-1 after 500 cycles at the current density of 1.0 A g^-1. The discharge capacity of the CYS-NiO/C microspheres after the 1000th cycle at the current density of 2.0 A g^-1 was 635 mAh g^-1, and the capacity retention measured from the second cycle was 91%. The final discharge capacities of the CYS-NiO/C microspheres at the current densities of 0.5, 1.5, 3.0, 5.0, 7.0, and 10.0 A g^-1 were 753, 648, 560, 490, 440, and 389 mAh g^-1, respectively. The synergetic effect of the coral-like yolk-shell structure with well-defined interconnected mesopores and highly conductive carbon resulted in the excellent Li⁺-ion storage properties of the CYS-NiO/C microspheres.

Electrochemical exploration of the effects of calcination temperature of a mesoporous zinc vanadate anode material on the performance of Na-ion batteries

As transition metal oxides are attractive candidates for energy storage applications, the spinel-structure of mesoporous ZnV₂O₄ as a potential novel anode for Na-ion storage and the synergetic effects of calcination temperature were studied.

"Electron-Sharing" Mechanism Promotes Co@Co3O4/CNTs Composite as the High-Capacity Anode Material of Lithium-Ion Battery

Hybridization of nanostructured cobalt oxides with carbon nanotubes (CNTs) is considered to be an operative approach to harvest high-performance anode material for lithium-ion batteries (LIBs). On the other hand, there are numerous related works, most of which adopted a "post-combination" strategy, which is not only complicated but also ecologically unpromising for using toxic acid for surface modification of CNTs. Herein, we productively fabricate Co@Co₃O₄/CNTs nanocomposite with excellent conductivity through arc discharge following low-temperature oxidation in air. As the anode material for LIBs, this nanocomposite shows an exceedingly high reversible capacity of 820 mA h g^-1 at a current density of 0.2 A g^-1 after 250 cycles, much higher than its theoretical capacity. The rate performance of the material is also outstanding, with a capacity of 760 mA h g^-1 after 350 cycles at 1 A g^-1 (103% of the initial capacity) and 529 mA h g^-1 after 600 cycles at 2 A g^-1. X-ray photoelectron spectroscopy tests are accomplished to disclose the true cause of extra capacity. And for the first time, we propose an "electron-sharing" storage mode, where extra electrons and Li⁺ can separate and be stored at the interface of cobalt metal/Li₂O. This not only gives a reasonable revelation for this unusual capacity exceeding the theoretical value but also directs the capacitor-like electrochemical behavior extra capacity.

Electrochemical properties of novel FeV2O4 as an anode for Na-ion batteries

Spinel based transition metal oxide – FeV₂O₄ is applied as a novel anode for sodium-ion battery. The electrochemical tests indicate that FeV₂O₄ is generally controlled by pseudo-capacitive process. Using cost-effective and eco-friendly aqueous based binders, Sodium-Carboxymethylcellulose/Styrene butadiene rubber, a highly stable capacity of ~97 mAh∙g⁻¹ is obtained after 200 cycles. This is attributed to the strong hydrogen bonding of carboxyl and hydroxyl groups indicating superior binding with the active material and current collector which is confirmed by the ex-situ cross-section images of the electrode. Meanwhile, only ~27 mAh∙g⁻¹ is provided by the electrode using poly(vinylidene difluoride) due to severe detachment of the electrode material from the Cu foil after 200 cycles. The obtained results provide an insight into the possible applications of FeV₂O₄ as an anode material and the use of water-based binders to obtain highly stable electrochemical tests for sodium-ion battery.

Biocarbon-templated synthesis of porous Ni–Co-O nanocomposites for room-temperature NH3 sensors

Mesoporous nickel–cobalt oxide (Ni–Co-O) nanocomposites were fabricated using a mesoporous biocarbon material (BCM), resulting from hemp stem, as a template.

Cationically Substituted Bi0.7Fe0.3OCl Nanosheets as Li Ion Battery Anodes

Cation substitution of Bi³⁺ with Fe³⁺ in BiOCl leads to the formation of ionically layered Bi_0.7Fe_0.3OCl nanosheets. The synthesis follows a hydrolysis route using bismuth(III) nitrate and iron(III) chloride, followed by postannealing at 500 °C. Room temperature electrical conductivity improves from 6.11 × 10^-8 S/m for BiOCl to 6.80 × 10^-7 S/m for Bi_0.7Fe_0.3OCl. Correspondingly, the activation energy for electrical conduction reduces from 862 meV for pure BiOCl to 310 meV for Bi_0.7Fe_0.3OCl. These data suggest improved charge mobility in Bi_0.7Fe_0.3OCl nanosheets. Density functional theory calculations confirm this behavior by predicting a high density of states near the Fermi level for Bi_0.7Fe_0.3OCl. The improvement in electrical conductivity is exploited in the electrochemical performance of Bi_0.7Fe_0.3OCl nanosheets. The insertion capacity of Li⁺ ions shows an increase of 2.5×, from 215 mAh·.g^-1 for undoped BiOCl to 542 mAh·g^-1 for Bi_0.7Fe_0.3OCl after 50 cycles at a current density of 50 mA·g^-1. Thus, the direct substitution of Bi³⁺ sites with Fe³⁺ in BiOCl results in nanosheets of an ionically layered ternary semiconductor compound which is attractive for Li ion battery anode applications.

Two-dimensional porous Co3O4nanosheets for high-performance lithium ion batteries

2D porous Co₃O₄nanosheets are synthesizedviaa self-sacrificing template method. When applied as an anode for LIBs, the as-obtained 2D porous Co₃O₄nanosheets exhibit a high discharge specific capacity, good cycling stability, and high rate capability.

A facile electrospinning and electrospraying synchronization technique for preparation of high performance MnO/C@rGO composite anodes for lithium storage

A facile electrospinning and electrospraying synchronization technique is used to assemble 1D nanowires with 2D graphene sheets to build as 3D MnO/C@rGO composite thin film. The raw material MnO₂powder was recovered from spent Zn/MnO₂batteries.

A hybrid composite catalyst of Fe3O4 nanoparticles-based carbon for electrochemical reduction of oxygen

We report an Fe₃O₄ nanoparticles-based carbon catalyst with good electrical conductivity, abundant active sites and efficient catalytic ORR activity.

A 3D Nanostructure Based on Transition-Metal Phosphide Decorated Heteroatom-Doped Mesoporous Nanospheres Interconnected with Graphene: Synthesis and Applications

A novel three-dimensional nanostructure based on cobalt phosphide nanoparticles (Co₂P NPs) and heteroatom-doped mesoporous carbon spheres interconnected with graphene (3D PZM@Co₂P@RGO) was facilely synthesized for the first time, and it was used for enhancing the flame retardancy and toxicity suppression of epoxy resins (EP) via a synergistic effect. Herein, the cross-linked polyphosphazene hollow spheres (PZM) were used as templates for the fabrication of 3D architecture. The 3D architecture based on Co₂P-decorated heteroatom-doped carbon sphere and reduced graphene oxide was prepared via a carbonization procedure followed by a hydrothermal self-assembly strategy. The as-prepared material exhibits excellent catalytic activity with regard to the combustion process. Notably, inclusion of incorporating PZM@Co₂P@RGO resulted in a dramatic reduction of the fire hazards of EP, such as a 47.9% maximum decrease in peak heat release rate and a 29.2% maximum decrease in total heat release, lower toxic CO yield, and formation of high-graphitized protective char layer. In addition, the mechanism for flame retardancy and toxicity suppression was proposed. It is reasonable to know that the improved flame-retardant performance for EP nanocomposites is attributed to tripartite cooperative effect from respective components (Co₂P NPs and RGO) plus the heteroatom-doped carbon spheres.

High-Capacity and Self-Stabilized Manganese Carbonate Microspheres as Anode Material for Lithium-Ion Batteries

Manganese carbonate (MnCO3) is an attractive anode material with high capacity based on conversion reaction for lithium-ion batteries (LIBs), but its application is mainly hindered by poor cycling performance. Building nanostructures/porous structures and nanocomposites has been demonstrated as an effective strategy to buffer the volume changes and maintain the electrode integrity for long-term cycling. It is widely believed that microsized MnCO3 is not suitable for use as anode material for LIBs because of its poor conductivity and the absence of nanostructure. Herein, different from previous reports, spherical MnCO3 with the mean diameters of 6.9 μm (MnCO3-B), 4.0 μm (MnCO3-M), and 2.6 μm (MnCO3-S) were prepared via controllable precipitation and utilized as anode materials for LIBs. It is interesting that the as-prepared MnCO3 microspheres demonstrate both high capacity and excellent cycling performance comparable to their reported nanosized counterparts. MnCO3-B, MnCO3-M, and MnCO3-S deliver reversible specific capacities of 487.3, 573.9, and 656.8 mA h g(-1) after 100 cycles, respectively. All the MnCO3 microspheres show capacity retention more than 90% after the initial stage. The advantages of MnCO3 microspheres were investigated via constant-current charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The results indicate that there should be substantial structure transformation from microsized particle to self-stabilized nanostructured matrix for MnCO3 at the initial charge/discharge stage. The evolution of EIS during charge/discharge clearly indicates the formation and stabilization of the nanostructured matrix. The self-stabilized porous matrix maintains the electrode structure to deliver excellent cycling performance, and contributes extra capacity beyond conversion reaction.

Rational Design of Graphene-Reinforced MnO Nanowires with Enhanced Electrochemical Performance for Li-Ion Batteries

Recently, transition metal oxides (TMOs) mixed with carbon materials have attracted attention as lithium-ion battery (LIB) anode materials. However, the aggregation issue in TMOs hinders the development of an ideal encapsulation structure with carbon materials. In this paper, we report graphene reinforced MnO nanowires with enhanced electrochemical performance as an anode in LIB. The graphene nanosheets (GNs)/MnO feature was confirmed by transmission electron microscopy, X-ray diffraction, Raman scattering, and X-ray photoelectron spectroscopy. The GNs/MnO nanowires delivered a highly stable discharge capacity of ∼815 mAh g(-1) at a current density of 100 mA g(-1) after 200 cycles, which is 1.5 times higher than that of pure MnO nanowires. This GNs/MnO structure with a specific capacity of ∼995 mAh g(-1) at a current density of 50 mA g(-1) also exhibited excellent Li storage properties. The superior cycling and high rate capability were attributed to the intimate incorporation between the MnO and GNs. The structure of the GNs/MnO nanowires effectively accommodated the volume change of the MnO nanowires and prevented structure collapse during cycling.

Porous Fe3O4-NCs-in-Carbon Nanofoils as High-Rate and High-Capacity Anode Materials for Lithium-Ion Batteries from Na-Citrate-Mediated Growth of Super-Thin Fe-Ethylene Glycolate Nanosheets

Porous Fe3O4/C composite nanofoils, characterized by a thickness of ∼20 nm and with ∼8 nm open pores and ∼5 nm Fe3O4 nanoparticles embedded in the carbon matrix, were prepared for the first time using Na-citrate to mediate the growth of hexagonal Fe-ethylene glycolate nanosheets and subsequently annealing them at 350 °C in N2. It has been found that the Fe-ethylene glycolate nanosheets can be effectively slimmed by increasing the concentration of Na-citrate, and the microstructures of Fe3O4/C nanocomposites may be tailored by the annealing temperature. When tested as the anode materials in LIBs, the Fe3O4/C nanofoils obtained after annealing at 350 °C were found to exhibit superior electrochemical performance due to its optimal microstructure, featured by a reversible capacity of 1314.4 mAh g(-1) at 0.4 A g(-1) over 100 cycles, 1034.2 mAh g(-1) at 1 A g(-1), and 686.4 mAh g(-1) at 5 A g(-1) after 500 cycles, whereas the annealing treatments at 450 and 550 °C render the Fe3O4/C nanocomposites with the inferior electrochemical performances as a result of shrinking porous microstructures and coarsening of Fe3O4 nanoparticles in the carbon matrix. With a particle-size control model proposed herein, the cycle discharging behaviors of the Fe3O4/C nanocomposites with different microstructures are well explained from the perspective of the local confinement of Fe3O4 nanoparticles inside the carbon matrix and their evolution in size and composite microstructure during the charge/discharge cycling.

Hollow Nanobarrels of α-Fe2O3 on Reduced Graphene Oxide as High-Performance Anode for Lithium-Ion Batteries

Alpha-phase iron oxide nanoparticles (α-NPs), α-iron oxide hollow nanobarrels (α-HNBs), and α-HNBs on reduced graphene oxide (α-HNBs/RGO) for Li-ion batteries (LIBs) were synthesized by a time-efficient microwave method to improve the low electrical conductivity of iron oxide and exploit the porous structure of RGO, which prevents the volume expansion of α-Fe2O3 during the insertion/extraction. On the other hand, α-HNBs (∼200 nm in diameter, ∼360 nm in length) provide a short diffusion path for Li ions and accommodate the strain generated by the volume change. The α-HNBs/RGO hybrid structure was synthesized by a one-step microwave-assisted hydrothermal method to bond α-HNBs with RGO. The as-prepared α-HNBs/RGO electrode exhibited a superior reversible capacity of 1279 mA h g(-1) at 0.5 C after the first cycle; such a capacity was nearly recovered after numerous cycles (2nd to 100th cycle, 95%). The long-term cyclability of α-HNBs/RGO shows 478 mA h g(-1) after 1000 cycles. Moreover, the α-HNBs/RGO electrode shows a high rate capacity of 403 mA h g(-1) even at 10 C. The α-HNBs/RGO exhibited a better electrochemical performance that could be attributed to the absence of nanoparticle agglomeration and RGO restacking, which provided a buffer effect against the volume expansion, promoted electrical conductivity and high structural integrity.

Coupled cobalt oxide/hollow carbon sphere as an efficient electrocatalyst for the oxygen reduction reaction

Nanosized Co₃O₄ and the hollow carbon sphere has been deliberately coupled to be as an non-precious efficient catalyst for oxygen reduction reaction by a facile one-pot method.

Graphene-coated mesoporous Co3O4 fibers as an efficient anode material for Li-ion batteries

The graphene-coating porous cobalt oxide fibers (Co₃O₄@G) were synthesized using coordination polymers as precursors through calcination and subsequent self-assembly process. The obtained materials exhibit good electrochemical performances.

Dopant-induced shape evolution of polyhedral magnetite nanocrystals and their morphology/component-dependent high-rate electrochemical performance for lithium-ion batteries

Mn doped Fe₃O₄ polyhedrons are shown to have component-related morphology evolution and crystal plane-dependent electrochemical performance when used as high-rate anode materials for LIBs.

Synthesis of NiO Nanofibers Composed of Hollow Nanospheres with Controlled Sizes by the Nanoscale Kirkendall Diffusion Process and Their Electrochemical Properties

NiO nanofibers composed of hollow NiO nanospheres with different sizes were prepared by electrospinning method. The mean size of the hollow NiO nanospheres was determined by the mean size of the Ni nanocrystals of the Ni-C composite nanofibers formed as an intermediate product. Porous-structured NiO nanofibers were also prepared as a comparison sample by direct oxidation of the electrospun nanofibers. The discharge capacities of the nanofibers composed of hollow nanospheres reduced at 300, 500, and 700 °C for the 250th cycle were 707, 655, and 261 mA h g(-1), respectively. However, the discharge capacity of the porous-structured NiO nanofibers for the 250th cycle was low as 206 mA h g(-1). The nanofibers composed of hollow nanospheres had good structural stability during cycling.

Rational synthesis of Ni nanoparticle-embedded porous graphitic carbon nanosheets with enhanced lithium storage properties

Carbon-based materials have recently received increased attention as very promising anode materials for rechargeable lithium-ion batteries (LIBs) because of their non-toxicity, low cost, and excellent performances. Nanostructure engineering has been demonstrated as an effective approach to improve the electrochemical performance of electrode materials. Here, we present a facile and scalable synthesis of two-dimensional (2D) porous graphitic carbon nanosheets embedded by numerous homogeneously dispersed Ni nanoparticles. With both structural and compositional advantages, the as-synthesized nanohybrid manifests a very stable high reversible capacity of 740 mA h g(-1) after 100 cycles at a current density of 100 mA g(-1), and also excellent rate capability and cycling stability. We believe that the synthetic strategy outlined here can be extended to other rationally designed anode materials with high performances in LIBs.