Electrochimica Acta
A carbon coated Li3V2(PO4)(3) cathode material for lithium ion batteries was synthesized by a sol-gel method using V2O5, H2O2, NH4H2PO4, LiOH and citric acid as starting materials, and its physicochemical properties were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), transmission electron microscope (TEM), and electrochemical methods. The sample prepared displays a monoclinic structure with a space group of P2(1)/n, and its surface is covered with a rough and porous carbon layer. In the voltage range of 3.0-4.3 V, the Li3V2(PO4)(3) electrode displays a large reversible capacity, good rate capability and excellent cyclic stability at both 25 and 55 degrees C. The largest reversible capacity of 130 mAh g(-1) was obtained at 0.1C and 55 degrees C, nearly equivalent to the reversible cycling of two lithium ions per Li3V2(PO4)(3) formula unit (133 mAh g(-1)). It was found that the increase in total carbon content can improve the discharge performance of the Li3V2-(PO4)(3) electrode. In the voltage range of 3.0-4.8 V, the extraction and reinsertion of the third lithium ion in the carbon coated Li3V2(PO4)(3) host are almost reversible, exhibiting a reversible capacity of 177 mAh g(-1) and good cyclic performance. The reasons for the excellent electrochemical performance of the carbon coated Li3V2(PO4)(3) cathode material were also discussed. (c) 2007 Elsevier Ltd. All rights reserved.
关键词:
Li3V2(PO4)(3);sol-gel method;carbon surface layer;electrochemical;performance;lithium-ion batteries;carbothermal reduction method;state synthesis;routine;vanadium fluorophosphate;electrode materials;phosphates;lifepo4;li3fe2(po4)(3);composites;insertion
Chinese Journal of Inorganic Chemistry
A carbon-coated Li3V2(PO4)(3) Composite cathode material was synthesized by a sol-gel method using V2O5, LIOH center dot H2O, H2O2, NH4H2PO4 and citric acid as starting materials. Properties of the prepared composite material were investigated using XPS, XRD, SEM, Raman spectroscopy, TEM, and various electrochemical techniques. The relationship among structure, calcination temperature, electronic conductivity and the electrochemical performance of samples was also studied. The sample obtained had a monoclinic structure with a space group of P2(1)/n and a rough and porous carbon surface layer. The electronic conductivity of the carbon-coated Li3V2(PO4)3 samples synthesized at 800 degrees C was about a factor of similar to 10(4) higher than that of carbon-free Li3V2(PO4)(3) prepared by solid-state hydrogen reducing reaction. The results show that the carbon-coated Li3V2(PO4)(3) is superior in the electrochemical performance to the carbon-free sample. In the voltage range of 3.0 similar to 4.3 V, the carbon-coated Li3V2(PO4)(3) synthesized at 800 degrees C displays large reversible capacities (128 mAh center dot g(-1) at 0.1C and 109 mAh center dot g(-1) at 2C, respectively) and excellent cyclic stability. The reason for the excellent electrochemical performance of the carbon coated Li3V2(PO4)(3) is discussed.
关键词:
Li3V2(PO4)(3);sol-gel method;carbon-coated;lithium-ion batteries;state synthesis routine;electrochemical performance;high-capacity;lifepo4;pyrolysis;precursor;surface;xps;fe
Communications in Theoretical Physics
Ground state energies for shallow states of donor impurities at certain idealized defective isotropic semiconductor surfaces are calculated variationally for GaAs surfaces with electrons confined within the semiconductor. Calculations show that impurity states with donor ions located at parts projecting out of surfaces have lower ground state energies than those with ions located at parts sunk into surfaces.
关键词:
si;ge
Journal of Alloys and Compounds
The formation of impurity Li(x)Ni(1-x)O when synthesizing spinel LiNi(0.5)Mn(1.5)O(4) using solid state reaction method, and its influence on the electrochemical properties of product LiNi(0.5)Mn(1.5)O(4) were studied. The secondary phase LixNi(1-x)O emerges at high temperature due to oxygen deficiency for LiNi(0.5)Mn(1.5)O(4) and partial reduction of Mn(4+) to Mn(3+) in LiNi(0.5)Mn(1.5)O(4). Annealing process can diminish oxygen deficiency and inhibit impurity Li(x)Ni(1-x)O. The impurity reduces the specific capacity of product, but it does not have obvious negative effect on cycle performance of product. The capacity of LiNi(0.5)Mn(1.5)O(4) that contains Li(x)Ni(1-x)O can deliver about 120 mAhg(-1). (C) 2011 Elsevier B.V. All rights reserved.
关键词:
Lithium ion batteries;LiNi(0.5)Mn(1.5)O(4);Impurity Li(x)Ni(1-x)O;Electrochemical properties;lithium batteries;rate capability;spinel;performance
Gang JI
,
Shishen YAN
,
Yanxue CHEN
,
Qiang CAO
,
Wei XIA
,
Yihua LIU
,
Liangmo MEI
,
Ze ZHANG
,
null
材料科学技术（英文）
2×(FeNi/CoZnO)/ZnO/(CoZnO/Co) ×2 spin-injection devices were prepared by sputtering and photo-lithography. In the devices, two composite magnetic layers 2×(FeNi/CoZnO) and (CoZnO/Co) ×2 with different coercivities were used to fabricate the ZnO-based semiconductor spin valve. Since the CoZnO ferromagnetic semiconductor layers touched the ZnO space layer directly, the significant spin injection from CoZnO into ZnO was observed by measuring the magnetoresistance of the spin-injection devices. The magnetoresistance reduced linearly with increasing temperature, from 1.12% at 90 K to 0.35% at room temperature.
关键词:
Spin injection
,
磁电阻
,
铁磁性半导体
Physical Review B
Longitudinal electron transport is investigated for a long-period semiconductor superlattice in the presence of a magnetic field applied along the growth direction of the superlattice. It is shown that the longitudinal magnetoresistance exhibits a complicated dependence on the magnetic-field strength. In contrast with the conventional Shubnikov-de Haas oscillations, the magnetoresistance shows periodic oscillations only in the region of low reciprocal magnetic field.
关键词:
magnetoresistance
