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1.
Core–shell LiFePO 4/C composite was synthesized via a sol–gel method and doped by fluorine to improve its electrochemical performance. Structural
characterization shows that F − ions were successfully introduced into the LiFePO 4 matrix. Transmission electron microscopy verifies that F-doped LiFePO 4/C composite was composed of nanosized particles with a ~3 nm thick carbon shell coating on the surface. As a cathode material
for lithium-ion batteries, the F-doped LiFePO 4/C nanocomposite delivers a discharge capacity of 162 mAh/g at 0.1 C rate. Moreover, the material also shows good high-rate
capability, with discharge capacities reaching 113 and 78 mAh/g at 10 and 40 C current rates, respectively. When cycled at
20 C, the cell retains 86% of its initial discharge capacity after 400 cycles, demonstrating excellent high-rate cycling performance. 相似文献
2.
Lithium iron phosphate (LiFePO4) cathode materials were synthesized by the solvothermal method with the assistance of different surfactants. The influences of polyethylene glycol 2000 (PEG 2000), polyvinylpyrrolidone (PVP), and cetyltrimethyl ammonium bromide (CTAB) on the microstructure and electrochemical performance of LiFePO4 were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), electrochemical impedance spectroscopy (EIS), and charge/discharge measurements. The particle size of the LiFePO4 synthesized with the assistance of PEG was uniform and showed a flat rhombohedron-like shape. The initial discharge specific capacity is up to 122.80 mAh/g with an initial coulombic efficiency of 95.50% at 0.1C. LiFePO4 synthesized with PVP-assisted presents a porous structure with an initial discharge specific capacity of 91.01 mAh/g. LiFePO4 synthesized with CTAB-assisted shows a flower-like morphology with an initial discharge specific capacity of 100.44 mAh/g. Though the initial discharge capacities of the LiFePO4 materials prepared with the assistance of CTAB and PVP are lower than those of the LiFePO4 prepared without the assistance of surfactant, the two materials exhibited excellent cyclic stability at 0.1C. 相似文献
3.
Olivine-type LiFePO 4 composite materials for cathode material of the lithium-ion batteries were synthesized by using a sol-gel method and were
coated by a chemical deposition of silver particles. As-obtained LiFePO 4/C-Ag (2.1 wt.%) composites were characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD),
conductivity measurements, cyclic voltammetry, as well as galvanostatic measurements. The results revealed that the discharge
capacity of the LiFePO 4/C-Ag electrode is 136.6 mAh/g, which is 7.6% higher than that of uncoated LiFePO 4/C electrode (126.9 mAh/g). The LiFePO 4/C coated by silver nanoparticles enhances the electrode conductivity and specific capacity at high discharge rates. The improved
capacity at high discharge rates may be attributed to increased electrode conductivity and the synergistic effect on electron
and Li + transport after silver incorporation. 相似文献
4.
The olivine-typed cathode materials of LiFePO 4were prepared via solid-state reaction under argon atmosphere and co-doped by manganese and fluorine to improve their electrochemical
performances. The crystal structure, morphology, and electrochemical properties of the prepared samples were investigated
using X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy,
cyclic voltammetry, and charge–discharge cycle measurements. The result showed that the electrochemical performance of LiFePO 4 had been improved dramatically by Mn–F co-doping. The initial discharge capacity of LiFe 0.99Mn 0.01 (PO 4) 2.99/3F 0.01/C samples reached 140.2 mAh/g at 1C rate and only had a small amount of fading in 50 cycles. 相似文献
5.
A facile chemical polymerization method was applied to prepare LiFePO 4/C-PPy composite using Fe(III)tosylate as oxidant. The as-prepared LiFePO 4/C-PPy sample with PPy content of approximately 4 wt% showed great rate capability with a discharge capacity of 115 mAh/g at 20C. High temperate cycling performance of the LiFePO 4/C-PPy sample was compared with bare LiFePO 4/C at 5C charge–discharge rate at 55 °C. The LiFePO 4/C-PPy cathode showed superior cycling stability with an initial capacity of 155 mAh/g. Ninety percentage of this initial capacity was retained after 300 cycles, compared to 40% of that of bare LiFePO 4/C. The LiFePO 4/C-PPy electrode showed stable discharge plateau voltage of 3.35–3.25 V vs. Li +/Li during long term cycling. The superior performance of the LiFePO 4/C-PPy electrode was due to the enhanced electrical conductivity, negligible iron dissolution and alleviated electrode cracking contributed by PPy coating. 相似文献
6.
Olivine LiFePO 4/C cathode materials for lithium ion batteries were synthesized using monodisperse polystyrene (PS) nano-spheres and other
carbon sources. The structure, morphology, and electrochemical performance of LiFePO 4/C were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge–discharge tests,
electrochemical impedance spectroscopy (EIS) measurements, and Raman spectroscopy measurements. The results demonstrated that
LiFePO 4/C materials have an ordered olivine-type structure with small particle sizes. Electrochemical analyses showed that the LiFePO 4/C cathode material synthesized from 7 wt.% PS nano-spheres delivers an initial discharge capacity of 167 mAh g -1 (very close to the theoretical capacity of 170 mAh g -1) at 0.1 C rate cycled between 2.5 and 4.1 V with excellent capacity retention after 50 cycles. According to Raman spectroscopy
and EIS analysis, this composite had a lower I
D/ I
G, sp
3/ sp
2 peak ratio, charge transfer resistance, and a higher exchange current density, indicating an improved electrochemical performance,
due to the increased proportion of graphite-like carbon formed during pyrolysis of PS nano-spheres, containing functionalized
aromatic groups. 相似文献
7.
Nanocrystalline LiFePO 4 and LiFe 0.97Sn 0.03PO 4 cathode materials were synthesized by an inorganic-based sol–gel route. The physicochemical properties of samples were characterized
by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and
elemental mapping. The doping effect of Sn on the electrochemical performance of LiFePO 4 cathode material was extensively investigated. The results showed that the doping of tin was beneficial to refine the particle
size, increase the electrical conductivity, and facilitate the lithium-ion diffusion, which contributed to the improvement
of the electrochemical properties of LiFePO 4, especially the high-rate charge/discharge performance. At the low discharge rate of 0.5 C, the LiFe 0.97Sn 0.03PO 4 sample delivered a specific capacity of 158 mAh g −1, as compared with 147 mAh g −1 of the pristine LiFePO 4. At higher C-rate, the doping sample exhibited more excellent discharge performance. LiFe 0.97Sn 0.03PO 4 delivered specific capacity of 146 and 128 mAh g −1 at 5 C and 10 C, respectively, in comparison with 119 and 107 mAh g −1 for LiFePO 4. Moreover, the doping of Sn did not influence the cycle capability, even at 10 C. 相似文献
8.
A fast and convenient sol–gel route was developed to synthesize LiFePO 4/C composite cathode material, and the sol–gel process can be finished in less than an hour. Polyethyleneglycol (PEG), d-fructose, 1-hexadecanol, and cinnamic acid were firstly introduced to non-aqueous sol–gel system as structure modifiers and
carbon sources. The samples were characterized by X-ray powder diffraction, field emission scanning electron microscopy, and
elemental analysis measurements. Electrochemical performances of LiFePO 4/C composite cathode materials were characterized by galvanostatic charge/discharge and AC impedance measurements. The material
obtained using compound additives of PEG and d-fructose presented good electrochemical performance with a specific capacity of 157.7 mAh g −1 at discharge rate 0.2 C, and the discharge capacity remained about 153.6 mAh g −1 after 50 cycles. The results indicated that the improved electrochemical performance originated mainly from the microporous
network structure, well crystalline particles, and the increased electronic conductivity by proper carbon coating (3.11%). 相似文献
9.
Nano-crystalline LiFePO 4 and LiMg 0.05Fe 0.95PO 4 cathode materials were synthesized by sol–gel method in argon atmosphere using succinic acid as a chelating agent. Physico-chemical
characterizations were done by thermogravimetric and differential thermal analysis, X-ray diffraction, scanning electron microscopy,
transmittance electron microscopy, and Raman spectroscopy. Electrochemical behavior of the cathode materials were analyzed
using cyclic voltammetry, and galvanostatic charge/discharge cycling studies were employed to characterize the reaction of
lithium-ion insertion into and extraction from virginal and magnesium-doped LiFePO 4, in the voltage range 2.5 to 4.5 V (Vs Li/Li +) using 1 M LiPF 6 with 1:1 ratio of ethylene carbonate and dimethyl carbonate as electrolytes. LiMg 0.05Fe 0.95PO 4 exhibits initial charge and discharge capacities of 159 and 141 mAh/g at 0.2 C rate respectively, as compared to 121 and
107 mAh/g of pristine LiFePO 4. Furthermore, LiMg 0.05Fe 0.95PO 4 has retained more than 89% of the capacity even after 60 cycles. Hence, LiMg 0.05Fe 0.95PO 4 is a promising cathode material for rechargeable lithium-ion batteries. 相似文献
10.
Three kinds of LiFePO 4 materials, mixed with carbon (as LiFePO 4/C), doped with Ti (as Li 0.99Ti 0.01FePO 4), and treated both ways (as Li 0.99Ti 0.01FePO 4/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 LiFePO 4 could be increased by carbon coating and Ti-doping methods. Among the materials, Li 0.99Ti 0.01FePO 4/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 Li 0.99Ti 0.01FePO 4/C composite developed here can be used as the cathode material for lithium ion batteries. 相似文献
11.
Nanosized lithium iron phosphate (LiFePO 4) and transition metal oxide (MO, where M is Cu, Ni, Mn, Co, and Fe) particles are synthesized continuously in supercritical water at 25?C30?MPa and 400??C under various conditions for active material application in lithium secondary ion batteries. The properties of the nanoparticles, including crystallinity, particle size, surface area, and electrochemical performance, are characterized in detail. The discharge capacity of LiFePO 4 was enhanced up to 140?mAh/g using a simple carbon coating method. The LiFePO 4 particles prepared using supercritical hydrothermal synthesis (SHS) deliver the reversible and stable capacity at a current density of 0.1?C rate during ten cycles. The initial discharge capacity of the MO is in the range of 800?C1,100?mAh/g, values much higher than that of graphite. However, rapid capacity fading is observed after the first few cycles. The continuous SHS can be a promising method to produce nanosized cathode and anode materials. 相似文献
12.
The V 2O 3-C dual-layer coated LiFePO 4 cathode materials with excellent rate capability and cycling stability were prepared by carbothermic reduction of V 2O 5. X-ray powder diffraction, elemental analyzer, high resolution transmission electron microscopy and Raman spectra revealed that the V 2O 3 phase co-existed with carbon in the coating layer of LiFePO 4 particles and the carbon content reduced without graphitization degree changing after the carbothermic reduction of V 2O 5. The electrochemical measurement results indicated that small amounts of V 2O 3 improved rate capability and cycling stability at elevated temperature of LiFePO 4/C cathode materials. The V 2O 3-C dual-layer coated LiFePO 4 composite with 1wt% vanadium oxide delivered an initial specific capacity of 167 mAh/g at 0.2 C and 129 mAh/g at 5 C as well as excellent cycling stability. Even at elevated temperature of 55 oC, the specific capacity of 151 mAh/g was achieved at 1 C without capacity fading after 100 cycles. 相似文献
13.
The low-temperature performance of LiFePO 4/C cathode in a quaternary carbonate-based electrolyte (1.0 M LiPF 6/EC+DMC+DEC+EMC (1:1:1:3, v/v)) was studied. The discharge capacities of the LiFePO 4/C cathode were about 134.5 mAh/g (20 °C), 114 mAh/g (0 °C), 90 mAh/g (−20 °C) and 69 mAh/g (−40 °C) using a 1C charge–discharge rate. Cyclic voltammetry measurements show obviously sluggish of the lithium insertion–extraction process of the LiFePO 4/C cathode as the operation temperature falls below −20 °C. Electrochemical impedance analyses demonstrate that the sluggish of charge-transfer reaction on the electrolyte/LiFePO 4/C interface and the decrease of lithium diffusion capability in the bulk LiFePO 4 was the main performance limiting factors at low-temperature. 相似文献
14.
The yeast cells are adopted as a template and cementation agent to prepare LiFePO 4/C with high surface area by co-precipitation and microwave processing. The electrochemical properties of the resultant products
are investigated. The synthesized LiFePO 4/C is characterized by means of X-ray diffraction, transmission electron microscopy (TEM), Brunauer–Emmett–Teller method,
and battery test instrument. The LiFePO 4/C particles with average size of 35-100 nm coated by porous carbon are observed by TEM. The LiFePO 4/C, with the specific surface area of 98.3 m 2/g, exhibits initial discharge specific capacity of 147 mAh/g and good cycle ability. The yeast cells as a template are used
to synthesize the precursor LiFePO 4/cells compounds. In microwave heating process, the use of yeast cells as reducing matter and cementation agent results in
the enhancement of the electrochemical properties. 相似文献
15.
High performance PPy/PEG-LiFePO 4 nanocomposites as cathode materials were synthesized by solvothermal method and simple chemical oxidative polymerization of pyrrole (Py) monomer on the surface of LiFePO 4 particles. The samples were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectrometry (XPS) and charge-discharge tests. PPyPEG hybrid layers decrease particle to particle contact resistance while the impedance measurements confirmed that the coating of PPy-PEG significantly decreases the charge transfer resistance of the electrode material. The initial discharge capacities of this sample at C/5 and 1C are 150 and 128 mAh/g, respectively. The results show that PPy/PEGLiFePO 4 composites are more effective than bare LiFePO 4 as cathode material. 相似文献
16.
Na + doped sample Li 0.95Na 0.05FePO 4/C was prepared through solid state method. Structure characterization shows Na + is successfully introduced into the LiFePO 4 matrix. Scanning electron microscopy shows the particle size mainly ranges in 1~3 μm. X-ray diffraction Rietveld refinement demonstrates lattice distortion with an increased cell volume. As one cathode material, it has a discharge capacity of 150 mAh/g at 0.1 C rate. The material exhibits a capacity of 109 and 107 mAh/g at 5 and 7.5 C respectively. When cycled at 1 and 5 C, the material retains 84% (after 1000 cycles) and 86% (after 350 cycles) of the initial discharge capacity respectively indicating excellent structure stability and cycling perfor-mance. Na +doping enhances the electrochemical activity especially the cycle performance effectively. 相似文献
17.
A novel network composite cathode was prepared by mixing LiFePO 4 particles with multiwalled carbon nanotubes for high rate capability. LiFePO 4 particles were connected by multiwalled carbon nanotubes to form a three-dimensional network wiring. The web structure can improve electron transport and electrochemical activity effectively. The initial discharge capacity was improved to be 155 mA h/g at C/10 rate (0.05 mA/cm 2) and 146 mA h/g at 1C rate. The comparative investigation on MWCNTs and acetylene black as a conducting additive in LiFePO 4 proved that MWCNTs addition was an effective way to increase rate capability and cycle efficiency. 相似文献
18.
This paper describes systematic studies on the effect of polyethylene glycol (PEG) molecular weight on the crystal structure
and particularly the electrochemical performance of LiV 3O 8. Scanning electron microscopy results indicate that after the decomposition of PEG, the structure of resultant products exhibits
differences in morphology (shape, particle size, and specific surface area). The electrochemical results show that LiV 3O 8 cathode material treated by PEG (mean molecular weight of 10,000) has greater initial discharge capacity and better cyclic
stability than other materials treated with PEG of different molecular weight. Its initial discharge capacity is 282.1 mAh
g −1 and maintains 222.2 mAh/g after 50 cycles in 0.5 C rates (150 mA g −1). 相似文献
19.
In this work, we studied LiFePO 4 particles coated with thin films of highly conductive polypyrrole (PPy) and their electrochemical performance in cathode
layers of lithium cells. Carbon-free LiFePO 4 particles were synthesized by a solvothermal method. Besides this, a part of the experiments were carried out on commercial
carbon-coated LiFePO 4 for comparison. Polypyrrole coated LiFePO 4 particles (PPy-LiFePO 4) were obtained by a straightforward oxidative polymerization of dissolved pyrrole on LiFePO 4 particles dispersed in water. The use of polyethylene glycol (PEG) as an additive during the polymerization was decisive
to achieve high electronic conductivities in the final cathode layers. The carbon-free and carbon-coated LiFePO 4 particles were prepared with PPy and with PPy/PEG coating. The obtained PPy-LiFePO 4 and PPy/PEG-LiFePO 4 powders were characterized by SEM, EIS, cyclic voltammetry, and galvanostatic charge/discharge measurements in lithium-ion
cells with lithium metal as counter and reference electrode. Carbon-free LiFePO 4 coated with PPy/PEG hybrid films exhibited very good electrode kinetics and a stable discharge capacity of 156 mAh/g at a
rate of C/10. Impedance measurements showed that the PPy/PEG coating decreases the charge-transfer resistance of the corresponding
LiFePO 4 cathode material very effectively, which was attributed to a favorable mixed ionic and electronic conductivity of the PPy/PEG
coatings. 相似文献
20.
Using the cheap raw materials lithium carbonate, iron phosphate, and carbon, LiFePO 4/C composite can be obtained from the carbothermal reduction method. X-ray diffraction (XRD) and scanning electronic microscope (SEM) observations were used to investigate the structure and morphology of LiFePO 4/C. The LiFePO 4 particles were coated by smaller carbon particles. LiFePO 4/C obtained at 750 °C presents good electrochemical performance with an initial discharge capacity of 133 mAh/g, capacity retention of 128 mAh/g after 20 cycles, and a diffusion coefficient of lithium ions in the LiFePO 4/C of 8.80?×?10 ?13 cm 2/s, which is just a little lower than that of LiFePO 4/C obtained from the solid-state reaction (9.20?×?10 ?13 cm 2/s) by using FeC 2O 4 as a precursor. 相似文献
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