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1.
Layered Li1+x(Ni0.3Co0.4Mn0.3)O2−δ (x = 0, 0.03 and 0.06) materials were synthesized through the different calcination times using the spray-dried precursor with the molar ratio of Li/Me = 1.25 (Me = transition metals). The physical and electrochemical properties of the lithium excess and the stoichiometric materials were examined using XRD, AAS, BET and galvanostatic electrochemical method. As results, the lithium excess Li1.06(Ni0.3Co0.4Mn0.3)O2−δ could show better electrochemical properties, such as discharge capacity, capacity retention and C rate ability, than those of the stoichiometric Li1.00(Ni0.3Co0.4Mn0.3)O2−δ. In this paper, the effect of excess lithium on the electrochemical properties of Li1+x(Ni0.3Co0.4Mn0.3)O2−δ materials will be discussed based on the experimental results of ex situ X-ray diffraction, transmission electron microscopy (TEM) and galvanostatic intermittent titration technique (GITT) 相似文献
2.
G.T.K. Fey Z.X. Weng J.G. Chen C.Z. Lu T.P. Kumar S.P. Naik A.S.T. Chiang D.C. Lee J.R. Lin 《Journal of Applied Electrochemistry》2004,34(7):715-722
A simple mechano-thermal coating procedure for the production of long-cycling LiCoO2 is described. Preformed nanoparticulate boehmite was used as the coating material. The coating procedure resulted in the
cathode particles covered in a 20-30 nm thick kernel of boehmite, as revealed by TEM examination. XRD studies showed that
the lattice parameter c diminished upon coating, indicating that a substitutional compound of the composition Li
x
Al
y
Co1−y
O2 may have formed upon calcination. SEM images, R-factor values from XRD studies and galvanostatic charge-discharge studies showed that a coating level of 1.0 wt % gave an
optimal performance in capacity and cyclability. SEM images showed that above the 1.0 wt % coating level, the excess boehmite
adhered to the coated cathode particles as sperules. ESCA depth profile analysis showed partial diffusion of aluminum from
the surface to the interior. Galvanostatic cycling studies showed that at a coating level of 1.0 wt %, cyclability improved
three- and twelve-fold for the two commercial LiCoO2 samples tested. Cyclic voltammetry revealed that the hexagonal-monoclinic-hexagonal phase transformations during cycling
were suppressed in the coated cathode materials. 相似文献
3.
Hyung-Wook Ha 《Electrochimica acta》2006,51(16):3297-3302
CeO2-coated LiCoO2 particles were successfully synthesized by a sol-gel coating of CeO2 on the surface of the LiCoO2 powder and subsequent heat treatment at 700 °C for 5 h. The surface-modified and pristine LiCoO2 powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), slow rate cyclic voltammogram (CV), and differential scanning calorimetry (DSC). Cyclic voltammetry curves suggested that the CeO2 coating suppressed the phase transitions. Unlike pristine LiCoO2, the CeO2-coated LiCoO2 cathode exhibited better capacity retention than the pristine LiCoO2 electrode in the higher cutoff voltage. Differential scanning calorimetric data revealed the higher thermal stability of the CeO2-coated LiCoO2 electrode. 相似文献
4.
Seung-Taek MyungShinichi Komaba Naoaki Kumagai Hitoshi YashiroHoon-Taek Chung Tae-Hyung Cho 《Electrochimica acta》2002,47(15):2543-2549
LiNi0.5Mn1.5O4 spinel has been prepared by an emulsion drying method which can intermix cations very homogeneously at the atomic scale. When the emulsion-dried precursor was fired at 750 °C for 24 h, the observed particle of the LiNi0.5Mn1.5O4 was nano-crystallite, being about 50 nm in diameter. The Rietveld refinement result clearly exhibited that the cubic spinel phase was successfully formed without any secondary phases, indicating that Li and transition metal cations occupied the 8a and 16d sites of the Fd3m structure, respectively. Li deintercalation from the spinel framework brings about a shift in the XRD peak toward higher angles and a peak splitting in the composition range δ=0-0.2 in LiδNi0.5Mn1.5O4, implying that the host structure is progressively oxidized from Ni2+ to Ni4+ and accompanied by a two phase reaction. The sample calcined at 750 °C for 24 h showed the best cyclability upon cycling due probably to better crystallinity and a smaller particle size. We suggest that this material can be used as a 4.5 V cathode material for Li-ion battery. 相似文献
5.
Polystyrene/nano-SiO2 composite microspheres (PS/nano-SiO2) with core-shell structure were successfully synthesized in a Pickering emulsion route using nano-SiO2 particles as stabilizers, which were organically modified by methacryloxypropyltrimethoxysilane (MPTMS) which containing a reactive CC bond. The products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier transformation infrared spectrum (FTIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). In addition, bare PS spheres could also be obtained by changing synthetic conditions. It was found that the morphology of the resulting products depends on particle concentration, particle wettability and pH value of particle dispersion. A possible mechanism for the formation of the composites with different morphologies is proposed. 相似文献
6.
George Ting-Kuo Fey P. Muralidharan Cheng-Zhang Lu Yung-Da Cho 《Electrochimica acta》2006,51(23):4850-4858
An enhanced electrochemical performance LiCoO2 cathode was synthesized by coating with various wt.% of La2O3 to the LiCoO2 particle surfaces by a polymeric method, followed by calcination at 923 K for 4 h in air. The surface-coated materials were characterized by XRD, TGA, SEM, TEM, BET and XPS/ESCA techniques. XRD patterns of La2O3-coated LiCoO2 revealed that the coating did not affect the crystal structure, α-NaFeO2, of the cathode material compared to pristine LiCoO2. TEM images showed a compact coating layer on the surface of the core material that had an average thickness of about ∼15 nm. XPS data illustrated that the presence of two different environmental O 1s ions corresponds to the surface-coated La2O3 and core material. The electrochemical performance of the coated materials by galvanostatic cycling studies suggest that 2.0 wt.% coated La2O3 on LiCoO2 improved cycle stability (284 cycles) by a factor of ∼7 times over the pristine LiCoO2 cathode material and also demonstrated excellent cell cycle stability when charged at high voltages (4.4, 4.5 and 4.6 V). Impedance spectroscopy demonstrated that the enhanced performance of the coated materials is attributed to slower impedance growth during the charge-discharge processes. The DSC curve revealed that the exothermic peak corresponding to the release of oxygen at ∼464 K was significantly smaller for the La2O3-coated cathode material and recognized its high thermal stability. 相似文献
7.
Hui Xia 《Electrochimica acta》2007,52(24):7014-7021
LiCoO2 thin films were prepared by pulsed laser deposition (PLD) on Pt/Ti/SiO2/Si (Pt) and Au/MgO/Si (Au) substrates, respectively. Crystal structures and surface morphologies of thin films were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The LiCoO2 thin films deposited on the Pt substrates exhibited a preferred (0 0 3) texture with smooth surfaces while the LiCoO2 thin films deposited on the Au substrates exhibited a preferred (1 0 4) texture with rough surfaces. The electrochemical properties of the LiCoO2 films with different textures were compared with charge-discharge, dQ/dV, and Li diffusion measurements (PITT). Compared with the (1 0 4)-textured LiCoO2 thin films, the (0 0 3)-textured thin films exhibited relatively lower electrochemical activity. However, the advantage of the (1 0 4)-textured film only remained for a small number of cycles due to the relatively faster capacity fade. Li diffusion measurements showed that the Li diffusivity in the (0 0 3)-textured film is one order of magnitude lower than that in the (1 0 4)-textured film. As discussed in this paper, we believe that Li diffusion through grain boundaries is comparable to or even faster than Li diffusion through the grains. 相似文献
8.
E. Minor-Pérez R. Mendoza-Serna J. Méndez-Vivar R. C. Pless D. Quintana-Zavala R. Torres-Robles 《Journal of Porous Materials》2006,13(1):13-19
An experimental strategy was developed to obtain transparent Si-Al-Ti-Ni-Mo and Si-Zr-Ti-Ni-Mo sols via the sol-gel process.
The sol was prepared from Si(OEt)4 (TEOS), Al(OBus)3 (OBus: C2H5CH(CH3)O), Ti(OEt)4 (OEt: OCH2CH3), Zr(OPrn)4 (OPrn: OCH2CH2CH3). In both cases nickel nitrate hexahydrate (Ni(NO3)2 · 6H2O) and ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24 · 4H2O) were the Ni and Mo sources, respectively. The sols were characterized by Fourier Transform Infrared Spectroscopy (FTIR).
Assignments of the simultaneous formation of the Si-O-Al, Si-O-Ti, Si-O-Ni, and Si-O-Zr bonds were done. The sols were polymerized
at room temperature (293 K) to obtain gels, and these were dried at 423 K and calcined at 573, 853 and 893 K in air. The characterization
techniques used were small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and
29Si and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR). The density of the solids was measured following ASTM method
D-4892 and the porosity and surface area were determined by N2 adsorption/desorption isotherms. The corresponding average pore diameters were evaluated using the BJH, HK, and DA methods. 相似文献
9.
Pure-phase and well-crystallized spinel LiMn2O4 powders as cathode materials for lithium-ion batteries were successfully synthesized by a new simple microwave-assisted rheological phase method, which was a timesaving and efficient method. The physical properties of the as-synthesized samples compared with the pristine LiMn2O4 obtained from the rheological phase method were investigated by thermogravimetry analysis (TGA), X-ray diffraction (XRD) and scanning electronic microscope (SEM). The as-prepared powders were used as positive materials for lithium-ion battery, whose charge/discharge properties and cycle performance were examined in detail. The powders resulting from the microwave-assisted rheological phase method were pure, spinel structure LiMn2O4 particles of regular shapes with distribution uniformly, and exhibited promising electrochemical properties for battery. Furthermore, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the reactions of Li-ion insertion into and extraction from LiMn2O4 electrode. 相似文献
10.
11.
Yongjun He 《Powder Technology》2005,155(1):1-4
Nanostructured CeO2 microspheres with an average diameter of 11 μm were prepared by a novel surfactant-free emulsion for the first time. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Brunauer-Emmet-Teller (BET) measurements were used to characterize the products. The images of SEM showed that the CeO2 microspheres consisted of petal-like nanostructures with petal thickness in a range of 60 nm to 100 nm. The BET measurements showed the specific surface area of the CeO2 microspheres exceeded 43 m2/g. The XRD analysis indicated the nanostructured CeO2 microspheres were of cubic lattice. A possible mechanism of an interfacial precipitation reaction with the droplets of solid-stabilized emulsion as templates was proposed. 相似文献
12.
13.
Mixed IrO2-SiO2 oxide films were prepared on titanium substrate by the thermo-decomposition of hexachloroiridate (H2IrCl6) and tetraethoxysilane (TEOS) mixed precursors in organic solvents. The solution chemistry and thermal decomposition kinetics of the mixed precursors were investigated by ultra violet/visible (UV/vis) spectroscopy and thermogravimetry (TGA) and differential thermal analysis (DTA), respectively. The physiochemical characterization of the resulting materials was conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. It is shown from the UV/vis spectra that the electronic absorption intensity of IrCl62− complexes in the precursors decreases in the presence of TEOS, indicating the interaction between these two components. Thermal analysis shows the decomposition reaction of H2IrCl6 is inhibited by TEOS in the low temperature range, but the further oxidation reaction at high temperatures of formed intermediates is independent of the presence of silane component. Physical measurements show a restriction effect of silica on the crystallization and crystal growth processes of IrO2, leading to the formation of finer oxide particles and the porous morphology of the binary oxide films. The porous composite films exhibit high apparent electrocatalytic activity toward the oxygen evolution reaction. In addition, the long-term stability of Ti-supported IrO2 electrodes is found to apparently improve with appropriate amount of SiO2 incorporation, as tested under galvanostatic electrolysis. 相似文献
14.
Choowong ChaisukAnusara Wehatoranawee Sirichai PreampiyawatSirirat Netiphat Artiwan Shotipruk Okorn Mekasuwandumrong 《Ceramics International》2011,37(5):1459-1463
Nanocrystalline TiO2, CeO2 and CeO2-doped TiO2 have been successfully prepared by one-step flame spray pyrolysis (FSP). Resulting powders were characterized with X-ray diffraction (XRD), N2-physisorption, Transmission Electron Microscopy (TEM) and UV-Vis spectrophotometry. The TiO2 and CeO2-doped TiO2 nanopowders were composed of single-crystalline spherical particles with as-prepared primary particle size of 10-13 nm for Ce doping concentrations of 5-50 at%, while square-shape particles with average size around 9 nm were only observed from flame-made CeO2. The adsorption edge of resulting powder was shifted from 388 to 467 nm as the Ce content increased from 0 to 30 at% and there was an optimal Ce content in association with the maximum absorbance. This effect is due to the insertion of Ce3+/4+ in the TiO2 matrix, which generated an n-type impurity band. 相似文献
15.
Hongjian Peng Jiaolian Zhou Ding Tang Yanqing Lai Fangyang Liu Jie Li Yexiang Liu 《Electrochimica acta》2011,56(14):5085
The electrodeposition of Bi2Se3 nanowires on an anodic aluminum oxide template was investigated by cyclic voltammetry in a tartaric acid aqueous solution. The electrochemical behavior of the Bi2Se3 nanowires in the electrolytic solution was also investigated using cyclic voltammetry, and the underpotential deposition mechanism of the Bi2Se3 nanowires was determined. According to the cyclic voltammetric curves, −0.20 V vs. SCE (saturated calomel electrode) was chosen as the deposition potential of the Bi2Se3 nanowires. The ratio of Bi to Se is nearly 2:3, verified by energy-dispersive X-ray spectroscopy and with the addition of surfactant. X-ray diffraction, scanning electron microscopy, selected-area electron diffraction and high-resolution transmission electron microscopy indicate that annealing can improve the crystallinity and chemical composition of Bi2Se3 nanowires. Surfactant can also improve the surface morphology and composition of the Bi2Se3 nanowires. 相似文献
16.
Anatase TiO2 nanowires containing minor TiO2(B) phase were prepared by a hydrothermal chemical reaction followed by the post-heat treatment at 400 °C. The phase structure and morphology were analyzed by X-ray diffraction, Raman scattering, transmission electron microscope, and field-emission scanning electron microscopy. The electrochemical properties were investigated by employing constant current discharge-charge test, cyclic voltammetry, and electrochemical impedance techniques. These nanowires exhibited high rate capacity of 280 mAh g−1 even after 40 cycles, and the coulombic efficiency was approximately 98%, indicating excellent cycling stability and reversibility. The electrochemical impedance spectra showed a stable kinetic process of the electrode reaction. These results indicated that the TiO2 nanowires have promising application for high energy density lithium-ion batteries. 相似文献
17.
Ma Xuedan Guo Daishi Jiang Qizhong Ma Zifeng Ma Zhengfei Ye Weidong Li Chunbo 《Frontiers of Chemical Engineering in China》2007,1(1):45-49
Nanosized solid superacids SO4
2−/TiO2 and S2O8
2−/TiO2, as well as MCM-41-supported SO4
2−/ZrO2, were prepared. Their structures, acidities, and catalytic activities were investigated and compared using XRD, N2 adsorption-desorption, and in situ FTIR-pyridine adsorption, as well as an evaluation reaction with pseudoionone cyclization. The results showed that SO4
2−/TiO2 and S2O8
2−/TiO2 possess not only nanosized particles with diameters < 7.0 nm, a BET surface greater than 140 cm2/g and relatively regular mesostructures with pores around 4.0 nm, but also a pure anatase phase and strong acidity. Different
from the Lewis acid nature of SO4
2−/ZrO2/MCM-41, SO4
2−/TiO2 and S2O8
2−/TiO2 exhibit mainly Bronsted acidities. The strongest Bronsted acid sites were produced on SO4
2−/TiO2 promoted with H2SO4, while Lewis acid sites on S2O8
2−/TiO2 even stronger than those on SO4
2−/ZrO2/MCM-41 were generated when persulfate solution was used as sulfating agent. Because of their distinct acid natures, SO4
2−/TiO2 and S2O8
2−/TiO2 exhibited catalytic activities for the cyclization of pseudoionone that were much higher than that of SO4
2−/ZrO2/MCM-41. It can be concluded that the existence of more Br?nsted acid sites was favorable for proton participation in the
cyclization reaction.
Translated from Journal of Chemical Engineering of Chinese Universities, 2006, 20(2): 239–244 [译自: 高校化学工程学报] 相似文献
18.
Naoaki Kumagai Jung-Min Kim Syo Tsuruta Yoshihiro Kadoma Koichi Ui 《Electrochimica acta》2008,53(16):5287-5293
In our previous report, we have synthesized Li2MnO3-LiCoO2 solid solutions and have investigated electrochemical properties [J.-M. Kim, T. Sho, N. Kumagai, Electrochem. Commun. 9 (2007) 103]. These materials have showed a long charge plateau at above 4.5 V during the first charge, which disappears with the subsequent cycles. This phenomenon is usually observed in Li2MnO3 and Li2MnO3-LiMeO2 system (Me = Ni1/2Mn1/2 [Z. Lu, D.D. MacNeil, J.R. Dahn, Electrochem. Solid State Lett. 4 (2001) 191], Co [K. Numata, C. Sakaki, S. Yamanaka, Solid State Ionics 117 (1999) 257; Y.J. Park, Y.-S. Hong, X. Wu, M.K. Kim, K.S. Ryu, S.H. Chang, J. Electrochem. Soc. 151 (2004) A720], Fe [M. Tabuchi, A. Nakashima, H. Shigemura, K. Ado, H. Kobayashi, H. Sakaebe, H. Kageyama, T. Nakamura, M. Kohzaki, A. Hirano, R. Kanno, J. Electrochem. Soc. 149 (2002) A509], or Cr [B. Ammundsen, J. Paulsen, Adv. Mater. 13 (2001) 943]). In this study, we investigate the relationship between the first lithium extraction process and the electrochemical property of the synthesized Li[Li0.27Co0.2Mn0.53]O2 material. The crystal structure and electrochemical performance of the synthesized Li[Li0.27Co0.20Mn0.53]O2 are modified by the Li+ extraction. 相似文献
19.
Lithium manganese oxide (LiMn2O4) has been synthesized by a spray pyrolysis method from the precursor solution; LiNO3 and Mn(NO3)2·6H2O were stoichiometrically dissolved into distilled water. The synthesized LiMn2O4 particles exhibited a pure cubic spinel structure in the X-ray diffraction (XRD) patterns, however they were spherical hollow spheres for various concentrations of precursor solution. Thus, the as-prepared LiMn2O4 particles were then ground in a mortar and dispersed into distilled water. To make a well dispersed slurry solution, a dispersion agent was also added into the slurry solution. The LiMn2O4 microparticles with a spherical nanostructure were finally prepared by a spray drying method from the slurry solution. The tap density of the LiMn2O4 microparticle prepared by a combination of spray pyrolysis and drying method was larger than that by a conventional spray pyrolysis method.The as-prepared samples were sintered at 750 °C for 1 h in air and used as cathode active materials for lithium batteries. Test experiments in the electrochemical cell Li|1 M LiClO4 in EC:DEC = 1:1|LiMn2O4 demonstrate that the sample prepared by the present method is a promising cathode active material for 4 V lithium-ion batteries at high-charge-discharge and elevated temperature operation. The LiMn2O4 compounds by the combination of spray pyrolysis and drying method are superior to that by the conventional spray pyrolysis method in terms of electrochemical characteristics and tap density. 相似文献
20.
种子乳液聚合法制备纳米SiO_2/苯丙复合乳液 总被引:2,自引:0,他引:2
采用种子乳液聚合工艺,用经硅烷偶联剂改性后的纳米SiO2原位合成了纳米SiO2/苯丙复合乳液。通过正交实验确定了最佳原料配比和聚合工艺条件,并对复合乳液性能进行了分析与表征。结果表明,当功能单体的用量为单体总量的5%、阴离子乳化剂十二烷基硫酸钠(SDS)与非离子乳化剂辛基苯基聚氧乙烯醚(OP-10)质量比为1颐1、复合乳化剂总量3%、纳米SiO2含量为单体总量的1.5%、聚合温度为80℃时,可制备具有良好综合性能的复合乳液,其涂膜耐水性、硬度、附着力等均优于普通苯丙乳液。该复合乳液乳胶粒粒度呈单峰分布,平均粒径为101nm,具有核/壳结构。 相似文献