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Li Y.,Central South University | Wang X.,Central South University | Ming X.,Citic Dameng Mining Industries Ltd | Xu C.,Central South University | And 4 more authors.
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology) | Year: 2013

Li4Ti5O12 precursor was synthesized by a wet chemical method in aqueous media using amorphous hydrated TiO2, which was prepared by hydrolysis method from TiCl4 aqueous solution. The effects of calcining temperature on the phase composition, morphology and electrochemical property of the products were investigated. The physical and electrochemical performances of Li4Ti5O12 were characterized by thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscope (SEM) and constant current discharge-charge measurement. The results indicate that the Li4Ti5O12 products synthesized by the wet chemical method followed by heat treatment at 750°C and 800°C have a good spinel structure. The sample calcined at 750°C for 6 h has a uniform particle size distribution, regular morphology, and shows the best electrochemical performance. The tests show that the as-prepared Li4Ti5O12 delivers the initial discharge specific capacity of 175.0 mA·h/g at 0.1C current rate in the voltage range of 1.0-2.5 V, and its discharge capacity reduces to 167.5 mA·h/g at 0.5C. The capacity decays to 163.0 mA·h/g after 60 cycles, and remains 97.3% of its initial specific capacity at 0.5C rate. Source

Wang L.,Taiyuan University of Technology | Chen J.,Taiyuan University of Technology | Hao J.-J.,Taiyuan University of Technology | Hao J.-J.,Shanxi Engineering Vocational Technology College | And 3 more authors.
Guocheng Gongcheng Xuebao/The Chinese Journal of Process Engineering | Year: 2013

Medium and low-carbon ferrochrome powder containing CaO was obtained by fast solid-phase decarburization of high-carbon ferrochrome powder with CaCO3 by microwave heating. High-carbon ferrochrome powder with calcium carbonate was decarburized at 900, 1000, 1100, 1200°C for 60 min. The carbon content of decarburized material was measured. The microstructure and phase composition of this new metallurgical material were studied by metallography, electron probe and XRD phase analyzers, the carbon content and phases change during the solid-phase decarburization were also analyzed. The results show that carbon content of high-carbon ferrochrome powder was 5.06%, 2.24%, 1.71% and 1.39% at 900, 1000, 1100 and 1200°C. Compared with original carbon content of 8.16%, it was obviously reduced during the decarburization, carbon-rich carbide phase (Cr, Fe)7C3 changed gradually to metal-rich carbide phase (Cr, Fe)23C6 and ferrochrome ferrite phase CrFe; Coarse grain structure (Cr, Fe)7C3 changed to honeycomb dissolution structure (Cr, Fe)23C6 and granular encroach structure CrFe. Chromium oxides in the decarburized material were mainly Cr2O3, CaCr2O4 and CaCr2O7. Generally, the optimum conditions of solid phase decarburization were decarburization temperature of 1100°C and 60 min heating. Source

Kong L.,Central South University | Kong L.,Citic Dameng Mining Industries Ltd | Li Y.-J.,Central South University | Li Y.-J.,Citic Dameng Mining Industries Ltd | And 3 more authors.
Wuji Cailiao Xuebao/Journal of Inorganic Materials | Year: 2013

Spinel Li1.035Mn1.965O4 and Al-doped Li1.035Al0.035Mn1.930O4 cathode materials were synthesized by a simple wet-chemical technique and heat treatment. The structure and the morphology of the two samples were investigated by powder X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The XRD patterns show that both of the two samples exhibit a well-defined spinel structure. The TEM result demonstrates that the Li1.035Al0.035Mn1.930O4 powder possesses a good crystalline state. The galvanostatic charge/discharge tests indicate that the Li1.035Al0.035Mn1.930O4 material delivers an excellent cycling ability and a nice rate capability, maintaining 96.4% of its initial capacity after 100 charge-discharge cycles at 0.5C and keeping 79.6% of the reversible capacity at 0.5C discharge rate when discharges at 4C rate. Source

Li L.,Central South University | Li Y.,Central South University | Li Y.,Citic Dameng Mining Industries Ltd | Xu C.,Central South University | And 7 more authors.
Hydrometallurgy | Year: 2014

The potential-pH diagrams for lithium-titanium-water system at temperatures of 333.15, 363.15, 393.15 and 453.15 K and ion activities of 0.01, 0.1 and 1 of the dissolved species were constructed to predict the predominant areas of lithium-titanium composite oxides in the Li-Ti-H2O system. Empirical functions were applied to estimate the thermodynamic data, which are unavailable in the literature. The presented Eh-pH diagrams show that temperature and ion activity have significant effects upon the stable regions of various species considered in Li-Ti-H2O system. With an increase in temperature, or ion activity, the dominant regions of Li2TiO3(hc), Li 4Ti5O12(hc) and Li4TiO 4(hc) shift towards lower pH zones. Also, the predominant areas of Li4Ti5O12(hc) and Li2TiO 3(hc) shrink, while that of Li4TiO4(hc) enlarges. This demonstrates that the production of Li4Ti 5O12 and Li2TiO3 is thermodynamically feasible by a wet process. Experiments were subsequently performed in light of the constructed potential-pH diagrams. The results indicated that the potential-pH diagrams are consistent with experiment. Therefore, the preparation of Li4Ti5O12 and Li2TiO3 in aqueous solution is feasible and the process can be controlled in practice. © 2013 Elsevier B.V. Source

Kong L.,Central South University | Kong L.,Citic Dameng Mining Industries Ltd | Li Y.-J.,Central South University | Li Y.-J.,Citic Dameng Mining Industries Ltd | And 5 more authors.
Journal of Central South University | Year: 2014

A simple hydrothermal process followed by heat treatment was applied to the preparation of spinel Li1.05Mn1.95O4. In this process, electrolytic manganese dioxide (EMD) and LiOH·H2O were used as starting materials. The physiochemical properties of the synthesized samples were investigated by thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray diffractometry (XRD), and scanning electronic microscopy (SEM). The results show that the hydrothermally synthesized precursor is an essential amorphous. The precursor can be easily transferred to spinel powders with a homogeneous structure and a regularly-shaped morphology by heat treatment. Li1.05Mn1.95O4 powder obtained by heat treating the precursor at 430°C for 12 h and then calcining at 800°C for 12 h shows an excellent cycling performance with an initial charge capacity of 118.2 mA·h·g-1 obtained at 0.5C rate and 93.8% of its original value retained after 100 cycles. © 2014 Central South University Press and Springer-Verlag Berlin Heidelberg. Source

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