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1.
Miao Shui   《Applied Surface Science》2003,220(1-4):359-366
The efficacy of the surface treatment of particulate fillers depends on the chemical character of the components, on the method and conditions of the treatment, and on the amount of the treating agent. Here, the ultra-fine calcium carbonate is surface treated with 1, 2, 3 and 4 wt.% polyacrylic acid (PAA) synthesized by ourselves, which has strong ionic interaction and is an efficient surface modifier. The PAA coated filler is submitted to the measurement of the surface bonded amount, bonding efficacy, X-ray photoelectron spectroscopy (XPS) and inverse gas chromatography. Maximum efficacy is expected at the monolayer coverage of the surface, which is about 0.6 wt.% according to the calculation based on the way they are aligned and is basically in agreement with the “substrate overlayer” model based on the mole ratio of C286 and C290 taking no account of the possible underestimation because of the inaccuracy or because of the CHx contamination present originally on the CaCO3. The initial decrease of the mole ratio of C290/O and C290/Ca with the surface bonded PAA may indicate that the bonding interaction between the polymer and the filler surface is the leaving of one molecular carbon dioxide. The IGC measurement shows that there is a considerable surface tension falling in the case of the PAA modified filler compared with the reference. An abnormal high surface energy in the case of filler treated with 4% PAA is observed.  相似文献
2.
A new cathode material for lithium ion battery FeF3?·?0.33H2O/C was synthesized successfully by a simple one-step chemico-mechanical method. It showed a noticeable initial discharge capacity of 233.9 mAh g?1 and corresponding charge capacity of 186.4 mAh g?1. A reversible capacity of ca.157.4 mAh g?1 at 20 mA g?1 can be obtained after 50 charge/discharge cycles. To elucidate the lithium ion transportation in the cathode material, the methods of electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) were applied to obtain the lithium diffusion coefficients of the material. Within the voltage level of 2.05–3.18 V, the method of EIS showed that \( {D}_{{\mathrm{Li}}^{+}} \) varied in the range of 1.2?×?10?13?~?3.6?×?10?14 cm2 s?1 with a maximum of 1.2?×?10?13 cm2 s?1 at 2.5 V. The method of GITT gave a result of 8.1?×?10?14?~?1.2?×?10?15 cm2 s?1. The way and the range of the variation for lithium ion diffusion coefficients measured by the GITT method show close similarity with those obtained by the EIS method. Besides, they both reached their maximum at a voltage level of 2.5 V.  相似文献
3.
Layered lithium ion battery cathode material LiNi1/3Co1/3Mn1/3O2 with uniform particle size of about 6 μm was synthesized by a spray pyrolysis method. Infrared and X-ray diffraction analyses show that the pyrolysis at 1,000 °C for 2 s in the tube furnace eliminates nearly all the organic components but is still not enough for the complete crystallization of LiNi1/3Co1/3Mn1/3O2 materials. Therefore, further annealing at 850 °C is needed. The prepared LiNi1/3Co1/3Mn1/3O2 cathode materials show excellent electrochemical performances. By increasing the C-rates, the cell shows discharge capacities of 159.3, 148.2, 133.7, and 125.7 mAh g?1 at 0.1, 0.2, 0.5, and 1C rates, respectively. Only 2.1 mAh g?1 capacity loss is observed when back to 0.1C rate. Moreover, LiNi1/3Co1/3Mn1/3O2 cathode retains 96, 97.7, 97.1, 94.5, and 97.1 % of its initial discharge capacities after 20 cycles at 0.1, 0.2, 0.5, 1, and back to 0.1C rates, respectively. More than 97 % coulombic efficiencies are observed at all the current densities in 20 cycles.  相似文献
4.
Layered lithium ion battery cathode material LiNi1/3Co1/3Mn1/3O2 with a uniform particle size of about 6 μm was synthesized by a spray pyrolysis method. The lithium ion diffusion kinetics in LiNi1/3Co1/3Mn1/3O2 composite cathode were systematically studied by the ratio of potentio-charge capacity to galvano-charge capacity method, galvanostatic intermittent titration technique, electrochemical impedance spectroscopy, and potential step chronoamperometry methods. The variations of lithium ion diffusion coefficients obtained by the four methods show a close similarity. They vary in the range of 10?8 to 10?10 cm2 s?1, with a maximum at 4.1- to 4.2-V voltage level.  相似文献
5.
Nasicon-type solid electrolyte Li1.3Al0.1Zn0.1Ti1.8P3O12 was prepared by citric acid-assisted acrylamide polymerisation gel method. X-ray diffraction pattern showed that the introduction of Zn2+ in the parent matrix Li1+x Al x Ti2?x P3O12 made it easier to get high-purity rhombohedral structure (space group $ R\overline 3 C $ ) Li1.3Al0.1Zn0.1Ti1.8P3O12 without the evidence of impurity secondary phase. The Li+ kinetics were investigated by complex impedance in bulk pellet and ionic conductivity in battery-type composite cathode, respectively. Grain-interior resistance measured by galvanostatic intermittent titration technique, potential step chronoamperometry, and AC impedance spectroscopy at 20 °C varies in the range 1.2–1.95?×?10?4?S?cm?1, which is in good agreement with that obtained by complex impedance method 1.5?×?10?4?S?cm?1.  相似文献
6.
The LiVPO4F as cathode material for lithium-ion batteries was synthesized through two steps of solid-state reactions and investigated by ex situ Fourier transform infrared (FTIR) spectroscopy for the initial charge and discharge cycle. The characterization of the effect on the structure of the LiVPO4F in the process of lithium-ion insertion/extraction at a molecular level by ex situ FTIR spectroscopy is helpful for the mechanism research for lithium-ion insertion/extraction and the improvement of the performance of lithium-ion batteries. In the process of the initial cycle, new bands of VPO4F appear in the charge and the featured bands of LiVPO4F reappear in the discharge. In this paper, ex situ FTIR spectra indicates that the structure of the LiVPO4F in the process of lithium-ion insertion/extraction is almost not affected, which clearly states that the LiVPO4F possesses stable structure as cathode material. Consequently, the LiVPO4F might be expected as a potential cathode replacement for commercial lithium-ion batteries.  相似文献
7.
A cathode material, 0.5Li2MnO3 0.5LiNi0.5Mn0.5O2, was prepared by citric acid-assisted sol–gel method and its electrochemical performance was investigated. It delivered a charge capacity of 270 mAh g?1 and a discharge capacity of 189 mAh g?1 in the first cycle. With the increase of current density from 14 to 28 mA g?1, the discharge capacity dropped severely to 130 mA g?1. Obviously, the rate capability of the material was inferior to most of the oxide cathode materials. The diffusion coefficient of this material was calculated to be 6.04?×?10?12 cm2 s?1 from the results of cyclic voltammetry measurements. Moreover, diffusion coefficients between 3.13?×?10?12 and 1.22?×?10?10 cm2 s?1 in the voltage range of 3.8–4.7 V were obtained by capacity intermittent titration technique. This, together with the localized Li2MnO3 domains in the crystal structure, may validate the poor rate capability.  相似文献
8.
In this paper, ex situ and in situ devices for Raman observations are designed and compared with each other by using lithium titanate as working electrode. In situ cell is made for Raman spectroscopy based on a confocal microscope Raman spectrometer. The instant evolutions of lithium titanate anode material during cycle can be recorded by in situ Raman in detail. Although the in situ technique is an important method to monitor the structure evolution of lithium titanate, it is difficult to conduct an in situ experiment in most laboratories. Moreover, the existence of electrolyte and surface deposits weakens the Raman signals of sample. Therefore, the structure evolution of Li4Ti5O12 cannot be described accurately. For comparison, air-free ex situ device is a simple and cheap tool to achieve the information from lithiated and delithiated samples. By removing the electrolyte and deposits on the sample with dimethyl carbonate, the ex situ Raman pattern shows higher signal to noise ratio than that of in situ Raman result. As a result, the shift and recovery of ex situ Raman bands confirms that the electrochemical reaction of Li4Ti5O12 with Li in 0.0–2.0 V is not a fully reversible process but a partially reversible process.  相似文献
9.
The thermal stabilities of hard carbon spherule (HCS), artificial graphite (AG), and natural graphite (NG) were investigated by thermo-gravimetric differential scanning calorimetry (TG-DSC). After lithiation, AG shows the lowest onset exothermic temperature. However, all there materials exhibit similar onset temperatures for thermal reactions after ten cycles. It is obvious that the thermal behaviors of solid electrolyte interphase (SEI) film for HCS and AG change gradually with the electrochemical cycling. In contrast, the thermal stability of the surface film on NG is maintained during repeated lithium ion insertion/extraction. Because of their different Li storage behaviors, their thermal reactivities with electrolyte are quite different from each other. Especially for HCS, it shows several successive and different exothermic peaks at the 1st and 11th lithiated states, while both AG and NG display similar thermal reactivity before and after repeated cycles. In summary, it is found that thermal properties of SEI layer and lithium in lithiated carbonaceous materials for all three samples have different impacts on the whole thermal behaviors of electrode.  相似文献
10.
C/FeOF/FeF3 nanocomposite was synthesized by a facile in situ partial oxidation method. High-resolution transmission electron microscopy (HR-TEM) showed a special texture comprised of interpenetrating nanodomains of FeOF and FeF3. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements revealed that the introduction of nanodomain FeOF enhanced both the electronic and ionic conductivity of the composite material. Therefore, the improvement of electron and lithium-ion dynamics resulted in the significant enhancement of the electrochemical performances of the material at ambient temperature. At a current density of 20 mA g−1 within potential range 1.5–4.5 V, the specific capacities of the first ten circles were maintained at about 400 mAh g−1 . This material also exhibited excellent cycling capacity retention capability especially for high C rates. When the current density further increased to 100 and 200 mA g−1, a steady capacity of 80 and 60 mAh g−1 was observed, respectively. Furthermore, nearly no capacity loss was observed for the followed cycles. The discharge platforms based on intercalation and conversion reaction were also heightened by about 0.4 V, which increased the contribution of high voltage capacities. Compared to C/FeF3, C/FeOF/FeF3 is showing more of capacitive behavior, which also contributes to the high specific capacity delivered and is believed to be closely related to the enlarged nanodomain interfaces between two electrochemical active materials. An expansion-cracking-oxidation mechanism was proposed to explain the formation of this interpenetrating nanodomains of FeOF and FeF3.  相似文献
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