Three kinds of LiFePO4 materials, mixed with carbon (as LiFePO4/C), doped with Ti (as Li0.99Ti0.01FePO4), and treated both ways (as Li0.99Ti0.01FePO4/C composite), were synthesized via ball milling by solid-state reaction method. The crystal structure and electrochemical
behavior of the materials were investigated using X-ray diffraction, SEM, TEM, cyclic voltammetry, and charge/discharge cycle
measurements. It was found that the electrochemical behavior of LiFePO4 could be increased by carbon coating and Ti-doping methods. Among the materials, Li0.99Ti0.01FePO4/C composite presents the best electrochemical behavior, with an initial discharge capacity of 154.5 mAh/g at a discharge
rate of 0.2 C, and long charge/discharge cycle life. After 120 cycles, its capacity remains at 92% of the initial capacity.
The Li0.99Ti0.01FePO4/C composite developed here can be used as the cathode material for lithium ion batteries. 相似文献
LiFePO4/C composite cathode material is prepared by ball milling with the assistance of EDTA chelation with using water as the media
of ball mill procedure. FePO4 and LiOH are used as starting materials; a certain amount of glucose is used as carbon sources and reduction agent. The structure
and morphology of the composite are characterized by X-ray diffraction and scanning electron microscopy. Cyclic voltammetry,
AC impedance measurements, and galvanostatic charge–discharge and cycling performances are used to characterize its electrochemical
properties. The results indicate that the performances of composites prepared by chelation-assisted method are much better
than common ball milling method which using alcohol or acetone as the media of ball mill procedure. The stable discharge capacity
of the prepared composite is 150 and 105 mAh g−1 at 1 and 10 C rate, respectively. 相似文献
The macroporous Li3V2(PO4)3/C composite was synthesized by oxalic acid-assisted carbon thermal reaction, and the common Li3V2(PO4)3/C composite was also prepared for comparison. These samples were characterized by X-ray diffraction (XRD), scanning electron
microscope (SEM), and electrochemical performance tests. Based on XRD and SEM results, the sample has monoclinic structure
and macroporous morphology when oxalic acid is introduced. Electrochemical tests show that the macroporous Li3V2(PO4)3/C sample has a high initial discharge capacity (130 mAh g−1 at 0.1 C) and a reversible discharge capacity of 124.9 mAh g−1 over 20 cycles. Moreover, the discharge capacity of the sample is still 91.5 mAh g−1, even at a high rate of 2 C, which is better than that of the sample with common morphology. The improvement in electrochemical
performance should be attributed to its improved lithium ion diffusion coefficient for the macroporous morphology, which was
verfied by cyclic voltammetry and electrochemical impedance spectroscopy. 相似文献
Carbon coated Li1 + xFePO4 (x = 0, 0.01, 0.02, 0.03, 0.04) and doped compositions Li1.03Fe0.99Ti0.01PO4 have been synthesized by thermal reduction method in this paper. The results showed that increasing the content in Li1 + xFePO4 result in better electrochemical properties and cyclic performances until x = 0.03, which had similar change law with the particle size of samples; and the initial discharge capacity and cycle life
of Li1.03Fe0.9Ti0.01PO4 was better than other samples under 1 C rate. When the Li1.03Fe0.99Ti0.01PO4/C sample cycled before 60 times, this sample exhibited a trend of increased capacity, and reached the highest discharging
rate capacity of 156 mA h g−1 at 60 cycles. The electrochemical performances of LiFePO4 compositions synthesized by thermal reduction method, to some extent, can be improved by Li excess content and Ti doping. 相似文献
The effect of fluorine doping on the electrochemical performance of LiFePO4/C cathode material is investigated. The stoichiometric proportion of LiFe(PO4)1−xF3x/C (x = 0.01, 0.05, 0.1, 0.2) materials was synthesized by a solid-state carbothermal reduction route at 650 °C using NH4F as dopant. X-ray diffraction, scanning electron microscope, energy-dispersive X-ray, and X-ray photoelectron spectroscopy
analyses demonstrate that fluorine can be incorporated into LiFePO4/C without altering the olivine structure, but slightly changing the lattice parameters and having little effect on the particle
sizes. However, heavy fluorine doping can bring in impurities. Fluorine doping in LiFePO4/C results in good reversible capacity and rate capability. LiFe(PO4)0.95 F0.15/C exhibits highest initial capacity and best rate performance. Its discharge capacities at 0.1 and 5 C rates are 156.1 and
119.1 mAh g−1, respectively. LiFe(PO4)0.95 F0.15/C also presents an obviously better cycle life than the other samples. We attribute the improvement of the electrochemical
performance to the smaller charge transfer resistance (Rct) and influence of fluorine on the PO43− polyanion in LiFePO4/C. 相似文献
Olivine-type LiFePO4 is a very promising polyanion-type cathode material for lithium-ion batteries. In this work, LiFePO4 with high specificity capacity is obtained from a novel precursor NH4FePO4·H2O via microwave processing. The grains grow up in the duration of sintering until they reach the decomposition temperature.
The apparent conductivity of the samples rises rapidly with the irradiation time and influences the electrochemical performance
of the material greatly at high current density. As a result, the LiFePO4 cathode material obtained with a sintering time of 15 min has good electrochemical performance. Between 2.5 and 4.2 V versus
Li, a reversible capacity is as high as 156 mAh g−1 at 0.05 C. 相似文献
LiVPO4F/C composites with better electrochemical performance were prepared by calcination of LiF and amorphous vanadium phosphorus
oxide (VPO) intermediate synthesized by a sol–gel method using H3PO4, V2O5 and citric acid as raw materials. The properties of LiVPO4F/C composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests.
The analysis of XRD patterns and Fourier transform infrared spectra (FTIR) reveal that VPO intermediate prepared by sol–gel
method is amorphous and VPO4 may exist in VPO intermediate. The compositions of LiVPO4F/C composites are related to the calcination temperature for preparation of amorphous VPO/C intermediate and LiVPO4F/C composite prepared by VPO/C synthesized at 700°C consists of a single crystal phase of LiVPO4F. The electrochemical tests show that LiVPO4F/C composite prepared by VPO/C synthesized at 700°C exhibits higher discharge capacity and excellent cycle performance. This
LiVPO4F/C composite displays discharge capacity of 133 mAh g−1 at 0.5 C (78 mA g−1) and remains capacity retention of 96.8% after 30 cycles, even at a high rate of 5 C, the composite exhibits high discharge
capacity of 115 mAh g−1 and capacity retention of 97% after 100 cycles. 相似文献
Large-scale Li1+xV3O8 nanobelts were successfully fabricated using filter paper as deposition substrate through a simple surface sol–gel method.
The nanobelts were as long as tens of micrometers with widths of 0.4–1.0 μm and thickness of 50–100 nm. The nanobelts were
characterized by X-ray diffration (XRD), Fourier infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission
electron microscopy (TEM). The formation mechanism of the nanobelts was investigated, showing that the morphology of the nanobelts
is mainly determined by the calcination temperature. Electrochemical properties of the Li1+xV3O8 nanobelts were characterized by charge–discharge experiments, and the results demonstrate that the Li1+xV3O8 nanobelts exhibit a high discharge capacity (278 mAh g−1) and excellent cycling stability. 相似文献
Among the various positive electrode materials investigated for Li-ion batteries, spinel LiMn2O4 is one of the most important materials. Small particles of the active materials facilitate high-rate capability due to large
surface to mass ratio and small diffusion path length. The present work involves the synthesis of submicron size particles
of LiMn2O4 in a quaternary microemulsion medium. The precursor obtained from the reaction is heated at different temperatures in the
range from 400 to 900 °C. The samples heated at 800 and 900 °C are found to possess pure spinel phase with particle size <200 nm,
as evidenced from XRD, SEM, and TEM studies. The electrochemical characterization studies provide discharge capacity values
of about 100 mAh g−1 at C/5 rate, and there is a moderate decrease in capacity by increasing the rate of charge–discharge cycling. Studies also
include charge–discharge cycling and ac impedance studies in temperature range from −10 to 40 °C. Impedance data are analyzed
with the help of an equivalent circuit and a nonlinear least squares fitting program. From temperature dependence of charge-transfer
resistance, a value of 0.62 eV is obtained for the activation energy of Mn3+/Mn4+ redox process, which accompanies the intercalation/deintercalation of the Li+ ion in LiMn2O4. 相似文献
Molybdenum trioxide (MoO3) has attracted considerable attention due to their typical two-dimensional layered structure consisting of double layers
of edge- and vertex-sharing MoO6 octahedral being weakly held together by van der Waals bonds. These MoO3 nanostructures and their polymer composites are currently drawing interest for the potential applications of Li batteries,
supercapacitors, and other electrochemical as well as electrochromic display devices. In this paper, we report the synthesis
of MoO3 nanobelts and polyethylene glycol (PEG) surfactant MoO3 nanobelts by hydrothermal method. Structure and morphology of the samples were investigated by X-ray diffraction, Fourier
transform spectroscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The pure MoO3 nanobelts show an initial specific capacity of 275 mAh g−1, whereas the 0.5 mol% PEG surfactant MoO3 nanobelts show 307 mAh g−1 at constant current density of 30.7 mA g−1 with the 1.0–3.0 V vs. Li/Li+ potential range. It was found that PEG surfactant MoO3 nanobelts show not only a high initial specific capacity but also show better cyclic performance compared with that of pure
MoO3 nanobelts. The PEG surfactant MoO3 nanobelts show stability and improvement of the specific capacity due to decreasing the length, width, and thickness of the
nanobelts by surface reaction. Electrochemical impedance spectroscopy reveals that the PEG surfactant MoO3 nanobelts exhibit low electrode resistance compared with pure MoO3 nanobelts. 相似文献
Compound Zn2SnO4 was synthesized by a hydrothermal method in which SnCl4 · 5H2O, ZnCl2 and N2H4 · H2O were used as reactants. Composite Zn2SnO4/C was then synthesized through a carbothermic reduction process using the as-prepared Zn2SnO4 and glucose as reactants. Comparing to the pure Zn2SnO4, some improved electrochemical properties were obtained for composite Zn2SnO4/C. When doped with 15% glucose, the composite Zn2SnO4/C showed the best electrochemical performance. Its first discharge capacity was about 1500 mA h g−1, with a capacity retain of 500 mA h g−1 in the 40th cycle at a constant current density of 100 mA/g in the voltage range of 0.05–3.0 V. There were also some differences
displayed in their cyclic voltammogram. 相似文献
Nano-structured spinel Li2Mn4O9 powder was prepared via a combustion method with hydrated lithium acetate (LiAc·2H2O), manganese acetate (MnAc2·4H2O), and oxalic acid (C2H2O4·2H2O) as raw materials, followed by calcination of the precursor at 300 °C. The sample was characterized by X-ray diffraction,
scanning electron microscope, and energy-dispersive X-ray spectroscopy techniques. Electrochemical performance of the nano-Li2Mn4O9 material was studied using cyclic voltammetry, ac impedance, and galvanostatic charge/discharge methods in 2 mol L−1 LiNO3 aqueous electrolyte. The results indicated that the nano-Li2Mn4O9 material exhibited excellent electrochemical performance in terms of specific capacity, cycle life, and charge/discharge
stability, as evidenced by the charge/discharge results. For example, specific capacitance of the single Li2Mn4O9 electrode reached 407 F g−1 at the scan rates of 5 mV s−1. The capacitor, which is composed of activated carbon negative electrode and Li2Mn4O9 positive electrode, also exhibits an excellent cycling performance in potential range of 0–1.6 V and keeps over 98% of the
maximum capacitance even after 4,000 cycles. 相似文献
Li1 − xKxFePO4/C (x = 0, 0.03, 0.05, and 0.07) composites were synthesized at 700 °C in an argon atmosphere by carbon thermal reduction method.
Based on X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analysis, the composite was
ultrafine sphere-like particles with 100–300 nm size, and the lattice structure of LiFePO4 was not destroyed by K doping, while the lattice volume was enlarged. The electrochemical properties were investigated by
four-point probe conductivity measurements, galvanostatic charge and discharge tests, cyclic voltammetry and electrochemical
impedance spectroscopy. The results indicated that the capacity performance at high rate and cyclic stability were improved
by doping an appropriate amount of K, which might be ascribed to the fact that the doped K ion expands Li ion diffusion pathway.
Among the doped materials, the Li0.97K0.03FePO4/C samples exhibited the best electrochemical activity, with the initial discharge capacity of 153.7 mAh g−1 at 0.1 C and the capacity retention rate of about 92% after 50 cycles at above 1 C, 11% higher than undoped sample. Remarkably,
it still showed good cycle retention at a high current rate of 10 C. 相似文献
A porous, hollow, microspherical composite of Li2MnO3 and LiMn1/3Co1/3Ni1/3O2 (composition: Li1.2Mn0.53Ni0.13Co0.13O2) was prepared using hollow MnO2 as the sacrificial template. The resulting composite was found to be mesoporous; its pores were about 20 nm in diameter. It also delivered a reversible discharge capacity value of 220 mAh g?1 at a specific current of 25 mA g?1 with excellent cycling stability and a high rate capability. A discharge capacity of 100 mAh g?1 was obtained for this composite at a specific current of 1000 mA g?1. The high rate capability of this hollow microspherical composite can be attributed to its porous nature.
Homogeneous manganocolumbite (MnNb2O6) was synthesized from Nb2O5 and MnO oxides. Powder sample was orthorhombic with unit cell parameters: α = 0.5766 nm, b = 1.4439 nm, c = 0.5085 nm and V = 0.4234 nm3. Heat capacity over the temperature range of 313–1253 K was measured in an inert atmosphere with combined thermogravimetry
and calorimetry using NETZSCH STA 449C Jupiter thermoanalyzer. Melting point was 1767 ± 3 K, enthalpy of melting was 144 ± 4 kJ mol−1. Experimental heat capacity of MnNb2O6 is fitted to polynomial Cpm = 221.46 + 3.03 · 10−3T + −39.79 · 105T−2 + 40.59 · 10−6T2. 相似文献
Li4Ti5O12/Li2TiO3 composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li4Ti5O12/Li2TiO3 composite nanofibers exhibit initial discharge capacity of 216.07 mAh g?1 at 0.1 C, rate capability of 151 mAh g?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g?1 after 1000 cycles at 20 C. Compared with pure Li4Ti5O12 nanofibers and Li2TiO3 nanofibers, Li4Ti5O12/Li2TiO3 composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li2TiO3 which could strengthen the structure stability of the hosted materials and has fast Li+-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li4Ti5O12 anodes for lithium rechargeable batteries. 相似文献
Yttrium-doped lithium manganese oxide (LiMn0.98Y0.02O2) was prepared by ion exchange of lithium for sodium in NaMn0.98Y0.02O2 precursors obtained by using rheological phase reaction method. This material had small particle size, which was composed of grain size of about 100 nm. Especially, LiMn0.98Y0.02O2 delivered the initial discharge capacity of about 191 mA h g−1 at room temperature when cycled between 2.0 and 4.4 V vs Li/Li+. Moreover, it showed an excellent cycling behavior, its specific capacity remained above 173 mA h g−1 after 20 cycles, and the material did not transform into spinel structure during the electrochemical cycling according to the cyclic voltammograms and X-ray powder diffraction. The electrochemical results revealed that the doping of Y3+ improved the performance of LiMnO2 considerably. 相似文献
Electrical conductivity in the monoclinic Li2TiO3, cubic Li1.33Ti1.67O4, and in their mixture has been studied by impedance spectroscopy in the temperature range 20–730 °C. Li2TiO3 shows low lithium ion conductivity, σ300≈10–6 S/cm at 300 °C, whereas Li1.33Ti1.67O4 has 3×10–8 at 20 °C and 3×10–4 S/cm at 300 °C. Structural properties are used to discuss the observed conductivity features. The conductivity dependences
on temperature in the coordinates of 1000/T versus loge(σT) are not linear, as the conductivity mechanism changes. Extrinsic and intrinsic conductivity regions are observed. The change
in the conductivity mechanism in Li2TiO3 at around 500–600 °C is observed and considered as an effect of the first-order phase transition, not reported before. Formation
of solid solutions of Li2–xTi1+xO3 above 900 °C significantly increases the conductivity. Irradiation by high-energy (5 MeV) electrons causes defects and the
conductivity in Li2TiO3 increases exponentially. A dose of 144 MGy yields an increase in conductivity of about 100 times at room temperature.
Electronic Publication 相似文献
The heat capacity and the enthalpy increments of strontium metaniobate SrNb2O6 were measured by the relaxation method (2-276 K), micro DSC calorimetry (260-320 K) and drop calorimetry (723-1472 K). Temperature
dependence of the molar heat capacity in the form Cpm=(200.47±5.51)+(0.02937±0.0760)T-(3.4728±0.3115)·106/T2 J K−1 mol−1 (298-1500 K) was derived by the least-squares method from the experimental data. Furthermore, the standard molar entropy
at 298.15 K Sm0 (298.15 K)=173.88±0.39 J K−1 mol−1 was evaluated from the low temperature heat capacity measurements. The standard enthalpy of formation ΔfH0 (298.15 K)=-2826.78 kJ mol−1 was derived from total energies obtained by full potential LAPW electronic structure calculations within density functional
theory. 相似文献
Lithium iron phospho-olivine cathode material with optimized lithium amount for lithium-ion batteries was successfully prepared from low cost Fe2O3 as raw materials by thermal reduction method. The as-obtained material showed a reversible discharge capacity of 153.8 mAh g–1 in the voltage window of 2.0–4.2 V at half-cell level. The pouch-typed cells with prepared Li1.05FePO4 were assembled to investigate electrochemical performance at level of full-cell. The results show that the assembled pouch-typed full-cells present better rate capability and cycle life. The low-cost approach reported here firstly sheds light on application of mass production of olivinestructured LiFePO4 at level of full-cell. 相似文献