A Novel Ion-exchange Method for the Synthesis of Nano-SnO/micro-C Hybrid Structure as High Capacity Anode Material in Lithium Ion Batteries

A novel and simple ion-exchange method was developed for the synthesis of nano-SnO/micro-C hybrid structure. The structure of the as prepared nano-SnO/micro-C was directly revealed by scanning electron microscopy（SEM） and transmission electron microscopy（TEM）.SnO particles with the size about 25 nm were well confined in amorphous carbon microparticles.Carbon matrix in micrometer scale not only acts as a protective buffer for the SnO nanoparticles during the battery cycling processes,but also avoids the shortcomings of nanostructures, such as low tap density and potential safety threats.Electrochemical behaviors of the nano-SnO/micro-C were tested as anode material in lithium ion batteries.The initial reversible capacity is 508 mA h g^-1,and the reversible capacity after 60 cycles is 511 mA h g^-1,indicating good capacity retention ability.     

非整比锂锰尖晶石的合成与电化学性质

A nonstoichiometric spinel phase (Li1.1Mn2.1O4 y) was synthesized using reheological phase reaction method. It was characterized by XRD and XPS techniques. The particle size and shape of the expected compounds were observed by transmission electron microscopy technique. The composition of new spinel phase was checked by ICP. The electrochemical properties of the spinel phase (Li1.1Mn2.1O4 y) were also investigated. The results showed that the Li1.1Mn2.1O4 y behaved excellent recharge ability to compare with stoichiometric LiMn2O4. The initial discharge capacity of the battery was 126mAh/g when current density was 1mA/cm^2 over voltage range of 4.4 to 3.0V. It dropped slowly during 60 cycles. After 100 cycles, the discharge capacity was retained at 117mAh/g (about 93% of initial discharge capacity) when the metallic lithium was the anode. The outstanding electrochemical properties of Li1.1Mn2.1O4 y make it possible to be used as a promising cathode material. The novel synthesis method provides a simple and effective route for inorganic material synthesis.     

Novel porous starfish-like Co<Subscript>3</Subscript>O<Subscript>4</Subscript>@nitrogen-doped carbon as an advanced anode for lithium-ion batteries

A Co-based metal-organic framework (Co-MOF) with a unique three-dimensional starfish-like nanostructure was successfully synthesized using a simple ultrasonic method.After subsequent carbonization and oxidation,a nanocomposite of nitrogen-doped carbon with a Co3O4 coating (Co3O4@N-C) with a porous starfish-like nanostructure was obtained.The final hybrid exhibited excellent lithium storage performance when evaluated as an anode material in a lithiumion battery.A remarkable and stable discharge capacity of 795 mAh·g-1 was maintained at 0.5 A·g-1 after 300 cycles.Excellent rate capability was also obtained.In addition,a full Co3O4@N-C/LiFePO4 battery displayed stable capacity retention of 95％ after 100 cycles.This excellent lithium storage performance is attributed to the unique porous starfish-like structure,which effectively buffers the volume expansion that occurs during Li+ insertion/deinsertion.Meanwhile,the nitrogendoped carbon coating enhances the electrical conductivity and provides a buffer layer to accommodate the volume change and accelerate the formation of a stable solid electrolyte interface layer.     

Hierarchical porous metal ferrite ball-in-ball hollow spheres: General synthesis,formation mechanism,and high performance as anode materials for Li-ion batteries

High yields of CoFe204, NiFe204 and CdFe204 hierarchical porous ball-in-ball hollow spheres have been achieved using hydrothermal synthesis followed by calcination. The mechanism of formation is shown to involve an in situ carbonaceous-template process. Hierarchical porous CoFe2O4 hollow spheres with different numbers of shells can be obtained by altering the synthesis conditions. The electrochemical properties of the resulting CoFe2O4 electrodes have been compared, using different binders. The as-obtained CoFe2O4 and NiFe2O4 have relatively high reversible discharge capacity and good rate retention performance which make them promising materials for use as anode materials in lithium ion batteries.     

A Novel Method to Improve the Electrochemical Performance of LiMn_2O_4 Cathode Active Material by CaCO_3 Surface Coating

Spinel LiMn2O4 was synthesized by glycine-nitrate method and coated with CaCO3 in order to enhance the electrochemical performance at room temperature (250C) and 550C. The uncoated and CaCO3-coated LiMn2O4 materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. XRD and SEM results indicated that CaCO3 particles encapsulated the surface of the LiMn2O4 without causing any structural change. The charge-discharge tests showed that the specific discharge capacity fade of pristine electrode at 25 and 550C were 25.5% and 52%, respectively. However, surface modified cathode shows 7.4% and 29.5% loss compared to initial specific discharge capacity at 70th cycle for 25 and 550C, respectively. The improvement of electrochemical performance is attributed to suppression of Mn2+ dissolution into electrolyte via CaCO3 layer.     

Electrochemical Performance of Surface-Modified LiMn2O4 Prepared by a Melting Impregnation Method

The surface of as-prepared LiMn2O4 was modified with ZnO, Al2O3, CoO and LiCoO2 using a simple nitrate melting impregnation method. Transmission electron microscopy （TEM） studies indicated that oxide nano- particles in the range of 10～50 nm are coated on the surface of the spinel. The surface modified samples show better capacity retention than the unmodified LiMn2O4 spinel at both room temperature and 55℃. Among these samples, the ZnO-modified LiMn2O4 shows the best combination of a high capacity and a low capacity fading rate of 0.036% per cycle at room temperature and 0.064% per cycle at 55℃. The improvement for surface modified LiMn2O4 can be attributed to the inhibition of Mn dissolution and O losses on the surface.     

Preparation and electrochemical characterization of ultrathin WO<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>/C nanosheets as anode materials in lithium ion batteries

Ultrathin two-dimensional (2D) nanomaterials offer unique advantages compared to their counterparts in other dimensionalities.O-vacancies in such materials allow rapid electron diffusion.Carbon doping often improves the electric conductivity.Considering these merits,the WO3-x/C ultrathin 2D nanomaterial is expected to exhibit excellent electrochemical performance in Li-ion batteries.Here,ultrathin WO3-x/C nanosheets were prepared via an acid-assisted one-pot process.The as-prepared WO3-x/C ultrathin nanosheets showed good electrochemical performance,with an initial discharge capacity of 1,866 mA·h·g-1 at a current density of 200 mA·g-1.After 100 cycles,the discharge and charge capacities were 662 and 661 mA·h·g-1,respectively.The reversible capacity of the WO3-x/C ultrathin nanosheets exceeded those of WO3 and WO3-x nanosheets.The electrochemical testing results demonstrated that WO3-x/C ultrathin nanosheets are promising alternative anode materials for Li-ion batteries.     

Carbon–Iron Microfibrous Material Produced by Thermal Treatment of Self-rolled Poly(4-vinyl pyridine) Films Loaded by Fe_2O_3 Particles

Ensembles of freeze-dried self-rolled polymer micro-scrolls are explored as template media for producing carbon–iron based composites with fibrous morphology. Polymer fibres impregnated with furfuryl alcohol and loaded with Fe2O3 particles, were thermally treated under inert atmosphere at 700 °C and subsequently analysed by scanning and transmission electron microscopy, X-ray diffraction,thermogravimetric analysis, and nitrogen adsorption. The resulting material has a micro-fibrous morphology and is basically composed of metallic Fe0 and FeO particles, i.e., more than 98 wt% of the carbon/iron-based composite mass. These particles are held together by amorphous porous carbon foam obtained by in-situ carbonization of the polymer/Fe2O3 composite with evacuation of carbon from the system via COx gases released by carbo-reduction of Fe2O3. The material has significant activity in the reaction of catalytic decomposition of hydrogen peroxide in water solutions.     

Porous CuO nanowires as the anode of rechargeable Na-ion batteries

We report the preparation of porous CuO nanowires that are composed of nanoparticles （-50 nm） via a simple decomposition of a Cu（OH）2 precursor and their application as the anode materials of rechargeable Na-ion batteries. The as-prepared porous CuO nanowires exhibit a Brunauer-Emmett-Teller （BET） surface area of 13.05 m^2.g^-1, which is six times larger than that of bulk CuO （2.16 m^2.g^-1）. The anode of porous CuO nanowires showed discharge capacities of 640 mA.h.g^-1 in the first cycle and 303 mA.h.g^-1 after 50 cycles at 50 mA.g^-1 The high capacity is attributed to porous nanostructure which facilitates fast Na-intercalation kinetics. The mechanism of electrochemical Na-storage based on conversion reactions has been studied through cyclic voltammetry, X-ray diffraction （XRD）, Raman spectroscopy, and high resolution transmission electron microscopy （HRTEM）. It is demonstrated that in the discharge process, Na＋ions first insert into CuO to form a CuⅡ1-x CuⅠ x O1-x/2solid and a Na2O matrix then CuⅡ1-xCu Ⅰ xO1-x/2 reacts with Na＋ to produce Cu2O, and finally Cu2O decompose into Cu nanoparticles enclosed in a Na2O matrix. During the charge process, Cu nanopartides are first oxidized to generate Cu2O and then converted back to CuO. This result contributes to the design and mechanistic analysis of high-performance anodes for rechargeable Na-ion batteries.     

Rationally designed carbon-coated Fe304 coaxial nanotubes with hierarchical porosity as high-rate anodes for lithium ion batteries

Fe3O4 is a promising high-capacity anode material for lithium ion batteries, but challenges including short cycle life and low rate capability hinder its widespread implementation. In this work, a well-defined tubular structure constructed by carbon-coated Fe3O4 has been successfully fabricated with hierarchically porous structure, high surface area, and suitable thickness of carbon layer. Such purposely designed hybrid nanostructures have an enhanced electronic/ionic conductivity, stable electrode/electrolyte interface, and physical buffering effect arising from the nanoscale combination of carbon with Fe3O4, as well as the hollow, aligned and hierarchically porous architectures. When used as an anode material for a lithium-ion half cell, the carbon-coated hierarchical Fe3O4 nanotubes showed excellent cycling performance with a specific capacity of 1,020 mAh.g^-1 at 200 mA.g^-1 after 150 cycles, a capacity retention of ca. 103%. Even at a higher current density of 1,000 mA·g^-1, a capacity of 840 mAh·g^-1 is retained after 300 cycles with no capacity loss. In particular, a superior rate capability can be obtained with a stable capacity of 355 mAh.g^-1 at 8,000 mA·g^-1. The encouraging results indicate that hierarchically tubular hybrid nanostructures can have important implications for the development of high-rate electrodes for future rechargeable lithium ion batteries （LIBs）.     

Synthesis and electrochemical properties of Co3O4 nanofibers as anode materials for lithium-ion batteries

Co₃O₄ nanofibers as anode materials for lithium-ion batteries were prepared from sol precursors by using electrospinning. The morphology, structure and electrochemical properties of Co₃O₄ nanofibers were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and charge-discharge experiments. The results show that Co₃O₄ nanofibers possessed typical spinel structure with average diameter of 200 nm. The initial capacity of Co₃O₄ nanofibers was 1336 mAhg^− 1 and the capacity reached 604 mAhg^− 1 up to 40 cycles. It was suggested that the high reversible capacity could be ascribed to the high surface area offered by the nanofibers' structure.     

A Study of the Effect of Nanometer Fe3O4 Addition on the Properties of Silicone Oil-based Magnetorheological Fluids

With the aim to improve the performance of magnetorheological fluids (MRFs) for mechanical transmission system, a process to prepare silicone oil-based MRFs with the addition of nanometer Fe₃O₄ particles is presented and five MRFs samples with different mass fraction of nanometer Fe₃O₄ particles have been prepared. The experimental materials, the preparation process, and test methods are elaborated. Moreover, the microstructures of soft magnetic carbonyl iron particles, nanometer Fe₃O₄ particles, and carbonyl iron/nano-sized Fe₃O₄ composites have been characterized via scanning electron microscope (SEM). Finally, test experiments of sedimentation stability, zero field viscosity, and shear yield stress have been carried out. The experimental results show that adding a certain amount of nanometer Fe₃O₄ particles (4 and 6 wt%) into MRFs can improve the performance of MRFs.     

Li-storage and cycling properties of spinel,CdFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as an anode for lithium ion batteries

Cadmium ferrite, CdFe₂O₄, is synthesized by urea combustion method followed by calcination at 900°C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) techniques. The Li-storage and cycling behaviour are examined by galvanostatic cycling, cyclic voltammetry (CV) and impedance spectroscopy in the voltage range, 0·005–3·0 V vs Li at room temperature. CdFe₂O₄ shows a first cycle reversible capacity of 870 (± 10) mAhg⁻¹ at 0·07C-rate, but the capacity degrades at 4 mAhg⁻¹ per cycle and retains only 680 (± 10) mAhg⁻¹ after 50 cycles. Heat-treated electrode of CdFe₂O₄ (300°C; 12 h, Ar) shows a significantly improved cycling performance under the above cycling conditions and a stable capacity of 810 (± 10) mAhg⁻¹ corresponding to 8·7 moles of Li per mole of CdFe₂O₄ (vs theoretical, 9·0 moles of Li) is maintained up to 60 cycles, with a coulombic efficiency, 96–98%. Rate capability of heat-treated CdFe₂O₄ is also good: reversible capacities of 650 (± 10) and 450 (± 10) mAhg⁻¹ at 0·5 C and 1·4 C (1 C = 840 mAg⁻¹) are observed, respectively. The reasons for the improved cycling performance are discussed. From the CV data in 2–15 cycles, the average discharge potential is measured to be ∼0·9 V, whereas the charge potential is ∼2·1 V. Based on the galvanostatic and CV data, ex situ-XRD, -TEM and -SAED studies, a reaction mechanism is proposed. The impedance parameters as a function of voltage during the 1st cycle have been evaluated and interpreted. Dedicated to Prof. C N R Rao on his 75th birthday, and his contributions to science for the past 56 years     

Structure and electrochemical performance of Fe3O4/graphene nanocomposite as anode material for lithium-ion batteries

Using hydrothermal method, Fe₃O₄/graphene nanocomposite is prepared by synthesizing Fe₃O₄ particles in graphene. The synthesized Fe₃O₄ is nano-sized sphere particles (100–200 nm) and uniformly distributed on the planes of graphene. Fe₃O₄/graphene nanocomposite as anode material for lithium ion batteries shows high reversible specific capacity of 771 mAh g⁻¹ at 50th cycle and good rate capability. The excellent electrochemical performance of the nanocomposite can be attributed to the high surface area and good electronic conductivity of graphene. Due to the high surface area, graphene can prevent Fe₃O₄ nanoparticles from aggregating and provide enough space to buffer the volume change during the Li insertion/extraction processes in Fe₃O₄ nanoparticles.     

Microstructure and properties of in situ nanostructured ceramic matrix composite coating prepared by plasma spraying

In situ nanostructured ceramic matrix composite coating toughened by metallic phase was fabricated by reactive plasma spraying micro-sized Al–Fe₂O₃ composite powders. The microstructure of the composite coating was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, respectively. The adhesive strength, microhardness, toughness, and wear resistance of the composite coating were explored. The results indicated that the composite coating exhibited dense microstructure with a lot of spherical α-Fe and γ-Al₂O₃ nano-sized grains embedded within the equiaxed and columnar FeAl₂O₄ nano-grains matrix. The adhesive strength, toughness, and wear resistance of the composite coating were significantly enhanced despite its lower microhardness compared with the micro-sized Al₂O₃ coating, which were attributed to the inclusion of ductile metallic phase Fe in the composite coating and the nanostructure of the composite coating.     

Hydrothermal synthesis of Fe3O4 nanoparticles and its application in lithium ion battery

Well dispersed Fe₃O₄ nanoparticles with a mean diameter of about 160 nm were synthesized by a simple hydrothermal method in the presence of sodium sulfate. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectrum, and Fourier transform infrared spectra (FTIR). Electrochemical properties of the nanostructured Fe₃O₄ as cathode electrodes of lithium ion battery were studied by conventional charge/discharge tests, showing a high initial discharge capacity of 1267 mA h g^− 1 at a current density of 0.1 mA cm^− 2.     

Preparation and characterisation of PPy/NanoGs/Fe3O4 conductive and magnetic nanocomposites

Nanocomposites composed of polypyrrole (PPy), graphite nanosheets (NanoGs), magnetite (Fe₃O₄) nanoparticles, have been successfully synthesised with a two-step process. First, we prepared NanoGs/Fe₃O₄ powder via wet chemical co-precipitation method. Next, pyrrole was polymerised in the suspension of NanoGs/Fe₃O₄ and then PPy/NanoGs/Fe₃O₄ nanocomposites were produced. The products were characterised by Fourier-transform infrared spectroscopy, Transmission electron microscopy, Thermogravimetric, conductivity and magnetisation analysis. The result showed that the conductivity of the PPy/NanoGs/Fe₃O₄ composites, compared with pure PPy, increased dramatically. And the saturation magnetisation of nanocomposites increased with the increase of the volume fraction of the Fe₃O₄ particles. In addition, according to the thermal gravimetric analysis, compared with PPy, nanocomposites exhibited enhanced thermal stability due to the introduction of NanoGs/Fe₃O_4. The PPy/NanoGs/Fe₃O₄ composites show potential applications in electric–magnetic shield materials.     

Preparation of Fe3O4/PVA nanofibers via combining in-situ composite with electrospinning

A novel approach, combining in-situ composite method with electrospinning, was used to prepare high magnetic Fe₃O₄/poly(vinyl alcohol) (PVA) composite nanofibers. Fe₃O₄ magnetic fluids were synthesized by chemical co-precipitation method in the presence of 6 wt.% PVA aqueous solution. PVA was used as stabilizer and polymeric matrix. The resulting Fe₃O₄/PVA composite nanofibers were characterized with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffractometer (XRD), respectively. These composite fibers showed a uniform and continuous morphology, with the Fe₃O₄ nanoparticles embedded in the fibers. Magnetization test confirmed that the composite fiber showed a high saturated magnetization (M_s = 2.42 emµ·g^-1) although only 4 wt.% content.     

Fe3O4 magnetic nanoparticles synthesis from tailings by ultrasonic chemical co-precipitation

The aim of this study is to develop a new method for the preparation of high-value, environmentally friendly products from tailings. Magnetic Fe₃O₄ nano-powder was synthesized by ultrasonic-assisted chemical co-precipitation utilizing high purity iron separated from iron ore tailings by acidic leaching method. Magnetite particles with 15 nm average diameter were characterized by X-ray diffraction, field-emission scanning electron microscopy and vibrating sample magnetometer. Surfactant influence on particles shape and size was investigated. Fe₃O₄ nanoparticles coated with C₁₂H₂₅OSO₃Na exhibit better dispersion and uniform size. The product consisted of ferrous ferrite (Fe3O4) nanosized cubic particles with a high level of crystallinity and exhibit super-paramagnetism based on magnetization curves lacking hysteresis.     

Dechlorination of 3,3′,4,4′-tetrachlorobiphenyl in aqueous solution by hybrid Fe0/Fe3O4 nanoparticle system

The kinetics and efficiency of 3,3′,4,4′-tetrachlorobiphenyl (PCB77) degradation in aqueous solution by hybrid Fe⁰/Fe₃O₄ nanoparticle system were investigated. The results showed that nano-sized Fe⁰ and Fe₃O₄ could efficiently degrade PCB77, and the residual rate of PCB77 by nano-sized Fe⁰ and Fe₃O₄ were 67.70% ± 0.42% and 82.26% ± 2.96%, respectively after 240 min of reaction (for 5 mg·L^?1 PCB77 and 5 g·L^?1 nanoparticles). The combined use of nanoscale Fe⁰ and Fe₃O₄ could enhance the degradation of PCB77. The dose ratios of nano-sized Fe⁰ and Fe₃O₄ significantly affected the PCB77 degradation rate. At Fe⁰/Fe₃O₄ ratios of 1:0.1, 1:0.2 and 1:1, the residual rates of PCB77 were 6.46%, 10.23% and 38.20%, respectively. The PCB77 degradation efficiency was also greatly affected by solution pH, and was maximised at pH 6.8. The degradation of PCB77 by Fe⁰/Fe₃O₄ nanoparticle was a dechlorination process, and the chlorion concentration increased with the decreasing residual rate of PCB77 accordingly. Fe₃O₄ provided Fe²⁺ and Fe³⁺ for enhancing the PCB77 degradation by nanoscale Fe⁰, suggesting a synergy between Fe⁰ and Fe₃O₄.