LiFePO4/graphene composites have been prepared by using tailoring graphene oxide (GO) nanosheets as precursors. The structure and electrochemical properties of the composites were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman microscopy, and a variety of electrochemical testing techniques. The decrease in graphene size reduces the contact resistance between activated materials, and enhances the lithium-ion transport in LiFePO4/graphene composites. With low weight fractions of small-size graphene sheets, the composites show better electrochemical performance than those with large size graphene sheets. 相似文献
Exploring soft-chemistry synthesis of Fe-based battery cathode materials, we have optimized combustion synthesis as an ultra-rapid approach to produce Na2FePO4F fluorophosphate cathode. It yields nanoscale, carbon-coated target product by annealing (at 600 °C) for just 1 min. The purity of the material crystallizing in the orthorhombic structure was confirmed by powder X-ray diffraction pattern and XPS analysis, while the morphology was studied by scanning electron microscopy. The as-synthesized material exhibits good electrochemical performance delivering a first discharge capacity of more than 70 mAh/g at C/10 rate versus both Li+/Li and Na+/Na, hence acting as an efficient host for both Li-ion and Na-ion insertion. Combustion synthesis can be employed as an economic route for synthesis and rapid screening of various phosphate-based insertion materials. 相似文献
A novel approach has been made to tailor Niobium pentoxide (Nb2O5) as a coating material on the surface of lithium iron phosphate (LiFePO4) via a facile polyol technique. The coating content was optimized at 1 wt%. The superficial coating demonstrated superior discharge capacity than the pristine LiFePO4. However, increasing the coating content further would result in a capacity loss. This may be due to the electrochemical inactiveness that increases with the content of the coating material, and 1 wt% of Nb2O5-coated LiFePO4 sample exhibits initial discharge capacity of 163 mAh g?1 at a current of 0.1 C and retains a stable discharge capacity of 143 mAh g?1 up to 400 cycles at 1 C rate with a coulombic efficiency of 98%.
In this work, highly activated graphene oxide/multiwalled carbon nanotube/Fe3O4 ternary nanocomposite adsorbent was prepared from a simple hydrothermal route by using ferrous sulfate as precursor. For this purpose, the graphene oxide/multiwalled carbon nanotube architectures were formed through the π-π attractions between them, followed by attaching Fe3O4 nanoparticles onto their surface. The structure and composition of as-prepared ternary nanocomposite were characterized by XRD, FTIR, XPS, SEM, TEM, Raman, TGA, and BET. It was found that the resultant porous graphene oxide/multiwalled carbon nanotube/Fe3O4 ternary nanocomposite with large surface area could effectively prevent the π-π stacking interactions between graphene oxide nanosheets and greatly improve sorption sites on the surfaces. Thus, owing to the unique ternary nanocomposite architecture and synergistic effect among various components, as-prepared ternary nanocomposite exhibited high separation efficiency when they were used to remove the Cu (II) and methylene blue from aqueous solutions. Furthermore, the adsorption isotherms of ternary nanocomposite structures for Cu (II) and methylene blue removal fitted the Langmuir isotherm model. This work demonstrated that the graphene oxide/multiwalled carbon nanotube/Fe3O4 ternary nanocomposite was promising as an efficient adsorbent for heavy metal ions and organic dye removal from wastewater in low concentration. 相似文献
Carbon-coated ZnFe2O4 spheres with sizes of ~110–180 nm anchored on graphene nanosheets (ZF@C/G) are successfully prepared and applied as anode materials for lithium ion batteries (LIBs). The obtained ZF@C/G presents an initial discharge capacity of 1235 mAh g?1 and maintains a reversible capacity of 775 mAh g?1 after 150 cycles at a current density of 500 mA g?1. After being tested at 2 A g?1 for 700 cycles, the capacity still retains 617 mAh g?1. The enhanced electrochemical performances can be attributed to the synergetic role of graphene and uniform carbon coating (~3–6 nm), which can inhibit the volume expansion, prevent the pulverization/aggregation upon prolonged cycling, and facilitate the electron transfer between carbon-coated ZnFe2O4 spheres. The electrochemical results suggest that the synthesized ZF@C/G nanostructures are promising electrode materials for high-performance lithium ion batteries.
Preparing spherical particles with carbon additive is considered as one effective way to improve both high rate performance
and tap density of Li4Ti5O12 and LiFePO4 materials. Spherical Li4Ti5O12/C and LiFePO4/C composites are prepared by spray-drying–solid-state reaction method and controlled crystallization–carbothermal reduction
method, respectively. The X-ray diffraction characterization, scanning electron microscope, Brunauer–Emmett–Teller, alternating
current impedance analyzing, tap density testing, and electrochemical property measurements are investigated. After hybridizing
carbon with a proper quantity, the crystal grain size of active materials is remarkably decreased and the electrochemical
properties are obviously improved. The Li4Ti5O12/C and LiFePO4/C composites prepared in this work are spherical. The tap density and the specific surface area are as high as 1.71 g cm−3 and 8.26 m2 g−1 for spherical Li4Ti5O12/C, which are 1.35 g cm−3 and 18.86 m2 g−1 for spherical LiFePO4/C powders. Between 1.0 and 3.0 V versus Li, the reversible specific capacity of the Li4Ti5O12/C is more than 150 mAh g−1 at 1.0-C rate. Between 2.5 and 4.2 V versus Li, the reversible capacity of the LiFePO4/C is close to 140 mAh g−1 at 1.0-C rate. 相似文献
The olivine-type LiFePO4/C cathode materials were prepared via carbothermal reduction method using cheap Fe2O3 as raw material and different contents of glucose as the reducing agent and carbon source. Their structural and morphological
properties were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope, and particle
size distribution analysis. The results demonstrated that when the content of the carbon precursor of glucose was 16 wt.%,
the synthesized powder had good crystalline and exhibited homogeneous and narrow particle size distribution. Even and thin
coating carbon film was formed on the surface of LiFePO4 particles during the pyrolysis of glucose, resulting in the enhancement of the electronic conductivity. Electrochemical tests
showed that the discharge capacity first increased and then decreased with the increase of glucose content. The optimal sample
synthesized using 16 wt.% glucose as carbon source exhibited the highest discharge capacity of 142 mAh g−1 at 0.1C rate with the capacity retention rate of 90.4% and 118 mAh g−1 at 0.5C rate. 相似文献
LiFePO4-positive electrode material was successfully synthesized by a solid-state method, and the effect of storage temperatures
on kinetics of lithium-ion insertion for LiFePO4-positive electrode material was investigated by electrochemical impedance spectroscopy. The charge-transfer resistance of
LiFePO4 electrode decreases with increasing the storage temperatures. This suggests that it has a high electrochemical activity at
high temperature. The diffusion coefficient of lithium ion is greatly increased with increasing the storage temperatures,
indicating that the kinetics of Li+ and electron transfer into the electrodes were much fast at high storage temperature. 相似文献
Cobalt-ferrite (CoFe2O4) nanoparticles (CFNPs) are obtained using direct plasmachemical synthesis in the plasma of a low-pressure arc discharge. The formation of the CFNPs with an average size of 9 nm and a narrow granulometric composition is established employing the methods of X-ray structure analysis and transmission microscopy. The CFNP behavior upon high-temperature annealing is analyzed. The CFNP functional groups are determined using the infrared Fourier spectrum. The results of the X-ray energy dispersion confirm the correspondence of the ratio of the number of atoms of each material to the nominal stoichiometry. The basic magnetic properties of the obtained and annealed samples are investigated at room temperature using the vibrating spectrum magnetometry (VSM). 相似文献
We describe in this paper the synthesis and the characterization of Li4Ti5O12-reduced graphene oxide (LTO-RGO) composite and demonstrate their use as hybrid supercapacitor, which is consist of an LTO negative electrode and activate carbon (AC) positive electrode. The LTO-RGO composites were synthesized using a simple, one-step process, in which lithium sources and titanium sources were dissolved in a graphene oxide (GO) suspension and then thermal treated in N2. The lithium-ion battery with LTO-RGO composite anode electrode revealed higher discharge capacity (167 mAh g?1 at 0.2 C) and better capacity retention (67%) than the one with pure LTO. Meanwhile, compared with the AC//LTO supercapacitor, the AC//LTO-RGO hybrid supercapacitor exhibits higher energy density and power density. Results show that the LTO-RGO composite is a very promising anode material for hybrid supercapacitor. 相似文献
In this work, the commercial carbon paper was firstly peeled in K2CO3 solution and then was further treated in a KNO3 solution to form functional exfoliation graphene (FEG) on the commercial carbon paper. The FEG/carbon paper was characterized by Raman spectra and scanning electron microscopy, confirming that some typical layered fold graphenes were successfully peeled off and stood on the carbon paper matrix. Then, Fe3O4 nanoparticles (NPs) were grown on the surface of FEG/carbon paper and the as-prepared Fe3O4 NPs/FEG/carbon paper was directly used as supercapacitor electrode. The specific capacitance of Fe3O4 NPs/FEG/carbon paper was about 316.07 F g?1 at a current density of 1 A g?1. Furthermore, the FEG/carbon papers were also functionalized by benzene carboxylic acid to form FFEG/carbon papers, and then the Fe3O4 NPs were grown on the surface of FFEG/carbon paper. The specific capacitance of Fe3O4 NPs/FFEG/carbon paper was 470 F g?1 at a current density of 1 A g?1, superior to some previous reported results. This work might provide a new strategy to prepare various nanostructures on FFEG/carbon papers for future applications. 相似文献
Carbon-coated olivine-structured LiFePO4/C composites are synthesized via an efficient and low-cost carbothermal reduction method using Fe2O3 as iron source at a relative low temperature (600 °C). The effects of two kinds of carbon sources, inorganic (acetylene black) and organic (sucrose), on the structures, morphologies, and lithium storage properties of LiFePO4/C are evaluated in details. The particle size and distribution of the carbon-coated LiFePO4 from sucrose (LiFePO4/SUC) are more uniform than that obtained from acetylene black (LiFePO4/AB). Moreover, the LiFePO4/SUC nanocomposite shows superior electrochemical properties such as high discharge capacity of 156 mAh g?1 at 0.1 C, excellent cyclic stability, and rate capability (78 mAh g?1 at 20 C), as compared to LiFePO4/AB. Cyclic voltammetric test discloses that the Li-ion diffusion, the reversibility of lithium extraction/insertion, and electrical conductivity are significantly improved in LiFePO4/SUC composite. It is believed that olivine-structured LiFePO4 decorated with carbon from organic carbon source (sucrose) using Fe2O3 is a promising cathode for high-power lithium-ion batteries. 相似文献
A new functionalized ionic liquid (IL) based on cyclic quaternary ammonium cations with ester group and bis(trifluoromethanesulfonyl)imide ([TFSI]?) anion, namely, N-methyl-N-methoxycarbonylpiperidinium bis(trifluoromethanesulfonyl)imide ([MMOCPip][TFSI]), was synthesized and characterized. Physical and electrochemical properties, including Li-ion transference number, ionic conductivity, and electrochemical stability, were investigated. The electrochemical window of [MMOCPip][TFSI] was 6 V, which was wide enough to be used as a common electrolyte material. The Li-ion transference number of this IL electrolyte containing 0.1 M LiTFSI was 0.56. The half-cell tests indicated that the [MMOCPip][TFSI] obviously improved the cyclability of a Li/LiFePO4 cell. For the Li/LiFePO4 half-cells, after 20 cycles at room temperature at 0.1 C, the discharge capacity was 109.7 mAh g?1 with 98.7% capacity retention in the [MMOCPip][TFSI]/0.1 M LiTFSI electrolyte. The good electrochemical performance demonstrated that the [MMOCPip][TFSI] could be used as electrolyte for lithium-ion batteries. 相似文献
The olivine-type LiFe1-xYxPO4/C (x?=?0, 0.01, 0.02, 0.03, 0.04, 0.05) products were prepared through liquid-phase precipitation reaction combined with the high-temperature solid-state method. The structure, morphology, and electrochemical performance of the samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), energy-dispersive spectroscopy (EDS), galvanostatic charge-discharge, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). We found that the small amount of Y3+ ion-doped can keep the microstructure of LiFePO4, modify the particle morphology, decrease charge transfer resistance, and enhance exchange current density, thus enhance the electrochemical performance of the LiFePO4/C. However, the large doping content of Y3+ ion cannot be completely doped into LiFePO4 lattice, but existing partly in the form of YPO4. The electrochemical performance of LiFePO4/C was restricted owing to YPO4. Among all the doped samples, LiFe0.98Y0.02PO4/C showed the best electrochemical performance. The LiFe0.98Y0.02PO4/C sample exhibited the initial discharge capacity of 166.7, 155.8, 148.2, 139.8, and 121.1 mAh g?1 at a rate of 0.2, 0.5, 1, 2, and 5 C, respectively. And, the discharge capacity of the material was 119.6 mAh g?1 after 100 cycles at 5 C rates. 相似文献
Bi4Ti3O12 (BIT) nanoparticles with a narrow average particle size distribution in the range of 11–46 nm was synthesized via a metal-organic polymeric precursor process. The crystallite size and lattice parameter of BIT were determined by XRD analysis. At annealing temperatures >550 °C, the orthorhombic BIT compound with lattice parameters a = 5.4489 Å, b = 5.4147 Å, and c = 32.8362 Å was formed while at lower annealing temperatures orthorhombicity was absent. Reaction proceeded via the formation of an intermediate phase at 500 °C with a stoichiometry close to Bi2Ti2O7. The particle size and the agglomerates of the primary particles have been confirmed by FESEM and TEM. The decomposition of the polymeric gel was ascertained in order to evaluate the crystallization process from TG-DSC analysis. Raman spectroscopy was used to investigate the lattice dynamics in BIT nanoparticles. In addition, investigation of the dependence of the visible emission band around the blue–green color emission on annealing temperatures and grain sizes showed that the effect of grain size plays important roles, and that oxygen vacancies may act as the radiative centers responsible for the observed visible emission band. 相似文献
Single-crystal Fe3O4 nanoparticles with uniform size and relatively better monodispersity have been successfully synthesized via a facile room temperature coprecipitation route in the present of poly(vinyl pyrrolidone) (PVP). This method does not require high temperature, expensive and toxic starting materials, complicated procedure and toxic organic solvents. The magnetic properties of as-prepared samples were recorded on a superconducting quantum interference device magnetometer. Its blocking temperature is 140 K. The hysteresis loops of single-crystal Fe3O4 nanoparticles at 300 K and 10 K show the transition from superparamagnetic to ferromagnetic behavior. And the maintenance of high saturation magnetization ascribes to the single-crystalline nature of these Fe3O4 nanoparticles. PACS 75.50.K; 75.70.C 相似文献
A facile and efficient one-pot method for the synthesis of well-dispersed hollow CuFe2O4 nanoparticles (H-CuFe2O4 NPs) in the presence of cellulose nanocrystals (CNC) as the support was described. Based on the one-pot solvothermal condition control, magnetic H-CuFe2O4 NPs were in-situ grown on the CNC surface uniformly. TEM images indicated good dispersity of H-CuFe2O4 NPs with uniform size of 300 nm. The catalytic activity of H-CuFe2O4/CNC was tested in the catalytic reduction of 4-nitrophenol (4-NP) in aqueous solution. Compared with most CNC-based ferrite catalysts, H-CuFe2O4/CNC catalyst exhibited an excellent catalytic activity toward the reduction of 4-NP. The catalytic performance of H-CuFe2O4/CNC catalyst was remarkably enhanced with the rate constant of 3.24 s?1 g?1, which was higher than H-CuFe2O4 NPs (0.50 s?1 g?1). The high catalytic activity was attributed to the introduction of CNC and the special hollow mesostructure of H-CuFe2O4 NPs. In addition, the H-CuFe2O4/CNC catalyst promised good conversion efficiency without significant decrease even after 10 cycles, confirming relatively high stability. Because of its environmental sustainability and magnetic separability, H-CuFe2O4/CNC catalyst was shown to indicate that the ferrite nanoparticles supported on CNC were acted as a promising catalyst and exhibited potential applications in numerous ferrite based catalytic reactions.
High discharge capacity and long life cycles of electrodes fabricated from various LiFePO4 powders have been used to select samples for detailed structural studies. In some samples, the presence of ferromagnetic Fe3P crystallites was revealed by the synchrotron X-ray diffraction analysis, with the integral intensity ratio of the peaks Fe3P (231) and LiFePO4 (112) equal to ~1/12. Small-angle polarized neutron scattering (SAPNS) detected the presence of magnetic nuclear contrasting regions with size of 17 ± 1 nm. The average diameter of LiFePO4 crystallites is 230 nm, and Fe3P crystallites were found as 17 × 54 nm2 plates. The high quality of these samples was provided by their manufacturer via synthesis of the Fe3P impurity phase. It can be stated that the set of studies, developed in the study, is helpful in a search for new effective impurity phases and in optimization of their parameters. 相似文献
Pristine LiFePO4 (LFP) and carbon-coated LiFePO4 (LFP/C) are synthesized by sol-gel process using citric acid as a carbon precursor. LFP/C is prepared with three different stoichiometric ratios of metal ions and citric acid, namely 1:0.5, 1:1, and 1:2. Prepared LFP and LFP/C powder samples are characterized by X-ray diffractometer, field emission scanning electron microscope, transmission electron microscope, and Raman spectrophotometer. Electrochemical performances of pristine and carbon-coated LFP are investigated by charge-discharge and cyclic voltammetry technique. The results show that LFP/C (1:1) with an optimum thickness of 4.2 nm and higher graphitic carbon coating has the highest discharge capacity of 148.2 mA h g?1 at 0.1 C rate and 113.1 mA h g?1 at a high rate of 5 C among all four samples prepared. The sample LFP/C (1:1) shows 96% capacity retention after 300 cycles at 1 C rate. The decrease in discharge capacity (141.4and 105.9 mA h g?1 at 0.1 and 5 C, respectively) is observed for the sample LFP/C (1:2). Whereas, pristine LFP shows the lowest discharge capacity of 111.1 mA h g?1 at 0.1 C and capacity was decreased very fast and work only up to 147 cycles. Moreover, cyclic voltammetry has also revealed the lowest polarization of 0.19 V for LFP/C (1:1) and the highest 0.4 V for pristine LFP. 相似文献
A facile room-temperature synthesis has been developed to prepare colloidal Mn3O4 and γ-Fe2O3 nanoparticles (5 to 25 nm) by an ultrasonic-assisted method in the absence of any additional nucleation and surfactant. The
morphology of the as-prepared samples was observed by transmission electron microscopy. High-resolution transmission electron
microscopy observations revealed that the as-synthesized nanoparticles were single crystals. The magnetic properties of the
samples were investigated with a superconducting quantum interference device magnetometer. The possible formation process
has been proposed. 相似文献