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Xuanye Y.,Hunan University | Xuanye Y.,Hunan Provincial Key Laboratory of Spray Deposition Technology and Application | Hongge Y.,Hunan University | Hongge Y.,Hunan Provincial Key Laboratory of Spray Deposition Technology and Application | And 6 more authors.
Solid State Ionics | Year: 2016

Ultrafine LiCoO2 powders with the layered rock-salt structure are successfully synthesized by enhanced thermal decomposition of carbonate precursors followed by double calcining. The mean size of the primary nanoparticles is about 500 nm with a narrow size distribution and is close to roundness with smooth surface. The LiCoO2 powders are also characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The lattice parameters of the synthesized LiCoO2 powders are the same as those of the corresponding powders formed by conventional high temperature solid-state synthesis processing. The double-calcining heating method can improve the crystalline perfection and produce the high temperature phase. The mechanism of solid-state reaction is also discussed. The electrochemical properties of as-formed ultrafine-sized LiCoO2 is examined and the maximum discharge capacities are 166.7 mAh/g, 160 mAh/g and 140 mAh/g at 0.2C, 0.5C and 1C, respectively. After 50 cycle performance, it is with a capacity retention of 88.84%, 88.10% and 72.90%, respectively. © 2016 Elsevier B.V. All rights reserved.

Wei J.,Hunan University | Wei J.,Jiangling Motors Co. | Chen J.,Hunan University | Chen J.,Hunan Provincial Key Laboratory of Spray Deposition Technology and Application | And 8 more authors.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2014

Microstructures, tensile properties and creep resistances of seven kinds of sub-rapidly solidified Mg-Zn-Sn-Al-Ca alloys were studied. Results show that as for the Mg-xZn-ySn-2Al-0.2Ca (x+y=9, x/y=2, 1 and 0.5, in mass%) alloys, the highest UTS and YTS at RT are obtained with the Zn/Sn mass ratio of 1. The YTS at 150℃ increases but that at 200℃ decreases with the increase of Zn/Sn mass ratio. It is possibly ascribed to the elevated-temperature strengthening of Mg2Sn particles since the alloy with the lower Zn/Sn mass ratio contains a higher amount of Mg2Sn and a lower fraction of Zn-containing phases. As for the Mg-4.5Zn-4.5Sn-2Al-zCa (z=0, 0.2, 0.4 and 0.6) alloys, UTS and YTS increase at first and then decrease with the increase of Ca content at both RT and 200℃. The strength peaks occur at 0.2% Ca and 0.4% Ca, respectively. Both the initial strain and the steady creep rate decrease with the increase of Ca content below 0.4% Ca at 200℃ under the compression stress of 55 MPa. Minor Ca addition can improve the RT and elevated temperature strength and enhance the compressive creep resistance of the Mg-4.5Zn-4.5Sn-2Al alloy, but reduce the elevated-temperature plasticity. In addition, it also has an obvious influence on the tensile fracture mode, which changes from cleavage to quasi-cleavage at RT and from ductile to quasi-cleavage at 200℃ with the increasing of Ca addition. Copyright © 2014, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.

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