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Hu X.,Sichuan Normal University | Hu X.,Zhongke Laifang Power Science and Technology Co. | Lin Z.,Food and Beverage | Yang K.,CAS Chengdu Institute of Organic Chemistry | And 2 more authors.
Journal of Physical Chemistry A | Year: 2011

The kinetics of one-step solid-state reaction of Li 4Ti 5O 12/C in a dynamic nitrogen atmosphere was first studied by means of thermogravimetric-differential thermal analysis technique at five different heating rates. According to the double equal-double steps method, the Li 4Ti 5O 12/C solid-state reaction mechanism could be properly described as the Jander equation, which was a three-dimensional diffusion with spherical symmetry, and the reaction mechanism functions were listed as follows: f(α) ≥ 3/ 2(1 - α) 2/3[1 - (1 - α) 1/3] -1, G(α) ≥ [1 - (1 - α) 1/3] 2. In FWO method, average activation energy, frequency factor, and reaction order were 284.40 kJ mol -1, 2.51×10 18 min -1, and 1.01, respectively. However, the corresponding values in FRL method were 271.70 kJ mol -1, 1.00×10 17 min -1, and 0.96, respectively. Moreover, the values of enthalpy of activation, Gibbs free energy of activation, and entropy of activation at the peak temperature were 272.06 kJ mol -1, 240.16 kJ mol -1, and 44.24 J mol -1 K -1, respectively. © 2011 American Chemical Society. Source


Yang K.,CAS Chengdu Institute of Organic Chemistry | Yang K.,University of Chinese Academy of Sciences | Lin Z.,CAS Chengdu Institute of Organic Chemistry | Lin Z.,University of Chinese Academy of Sciences | And 6 more authors.
Electrochimica Acta | Year: 2011

A LiFePO4/C composite was successfully prepared by a polymer-pyrolysis-reduction method, using FePO4·2H 2O and lithium polyacrylate (PAALi) as raw materials. The structure of the LiFePO4/C composites was investigated by X-ray diffraction (XRD). The micromorphology of the precursor and LiFePO4/C powders was observed using scanning electron microscopy (SEM), and the in situ coating of carbon on the particles was observed by transmission electron microscopy (TEM). Furthermore, the electrochemical properties were evaluated by cyclic voltammograms (CVs), electrochemical impedance spectra (EIS) and constant current charge/discharge cycling tests. The results showed that the sample synthesized at 700 °C had the best electrochemical performance, exhibiting initial discharge capacities of 157, 139 and 109 mAh g-1 at rates of 0.1, 1 and 5 C, respectively. Moreover, the sample presented excellent capacity retention as there was no significant capacity fade after 50 cycles. © 2011 Elsevier Ltd. All rights reserved. Source


Yang K.,CAS Chengdu Institute of Organic Chemistry | Yang K.,University of Chinese Academy of Sciences | Deng Z.,CAS Chengdu Institute of Organic Chemistry | Deng Z.,University of Chinese Academy of Sciences | And 3 more authors.
Journal of Power Sources | Year: 2012

Olivine LiFePO 4 and LiFePO 4/C are successfully prepared by a simple solid-state reaction using FePO 4·2H 2O, lithium oxalate and glucose (bare LiFePO 4 without adding glucose) as raw materials. The structure of the LiFePO 4 and LiFePO 4/C is investigated by X-ray diffraction (XRD). The micromorphology of LiFePO 4 and LiFePO 4/C is observed using scanning electron microscopy (SEM) and BET, and the in situ coating of carbon on the particles is observed by transmission electron microscopy (TEM) and Raman spectrum. Furthermore, the electrochemical properties are evaluated by cyclic voltammograms (CVs), electrochemical impedance spectra (EIS) and constant current charge/discharge cycling tests. The results show that carbon coated LiFePO 4 can deliver better battery performance than the bare LiFePO 4. It exhibits initial discharge capacities of 162, 142 and 112 mA h g -1 at rates of 0.1, 1 and 10 C, respectively, and it presents excellent capacity retention as there is tiny capacity fade after 100 cycles. Moreover, the reductive mechanism of using lithium carboxylic acid to synthesize LiFePO 4 is firstly mentioned. © 2011 Elsevier B.V. Source


Hu X.,Sichuan Normal University | Hu X.,Zhongke Laifang Power Science and Technology Co. | Lin Z.,CAS Chengdu Institute of Organic Chemistry | Lin Z.,University of Chinese Academy of Sciences | And 7 more authors.
Journal of Alloys and Compounds | Year: 2010

Spinel Li4Ti5O12/C was synthesized by one-step solid-state reaction route using lithium polyacrylate (PAALi) as lithium and carbon sources, and TiO2 as titanium source. The characteristics of Li4Ti5O12/C composites were determined by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and thermogravimetric-differential thermal analysis methods. Their electrochemical performances were investigated by cyclic voltammograms, constant current charge-discharge and rate charge-discharge. It was found that molecular weight of polyacrylic acid (PAA), heating rate and sintering duration directly affected the physical and electrochemical performances of Li 4Ti5O12/C composites. The Li4Ti 5O12/C composites with the optimized electrochemical performances were obtained in the following conditions, i.e., PAA with the molecular weight of 10,000, heating rate of 20 °C min-1 and sintering duration of 8 h. At charge-discharge rate of 4 C and 8 C, the optimized sample showed discharge capacities of 148.4 and 142.4 mAh g -1, with capacity retention of 94.48 and 90.53% after 50 cycles, respectively. Even at 20 C, its discharge capacity was 116.0 mAh g-1 with capacity retention of 87.61% after 50 cycles. © 2010 Elsevier B.V. All rights reserved. Source


Lin Z.,CAS Chengdu Institute of Organic Chemistry | Lin Z.,University of Chinese Academy of Sciences | Hu X.,Sichuan Normal University | Huai Y.,CAS Chengdu Institute of Organic Chemistry | And 9 more authors.
Solid State Ionics | Year: 2010

Li4Ti5O12/C anode material was simply obtained via a modified one-step solid-state reaction route using the original materials of lithium polyacrylate (PAALi) as lithium and carbon sources, and TiO2 as titanium source. The physical characteristics of the Li4Ti5O12/C composite were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. The particle size of Li4Ti5O12 in the composite was about 200 nm. The electrochemical properties were evaluated by electrochemical impedance spectra and constant current charge/discharge cycling. It was demonstrated that the as-prepared Li4Ti5O12/C composite presented excellent high-rate characteristics and cycleabilities. The initial specific capacity of the composite was 130.0 mA h g- 1 at 8.60 mA cm- 2, and excellent cycle performance was still maintained with the current density increase. Moreover, it was proved that the electric conductivity and cycle performance of Li4Ti5O12 were effectively enhanced due to the uniformly dispersed pyrolytic carbon in the Li4Ti5O12 particles. © 2010 Elsevier B.V. All rights reserved. Source

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