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Politano R.,Brazilian Nuclear Energy Research Institute (IPEN) | Politano R.,Materials Science and Technology Center
Journal of Physics: Conference Series | Year: 2013

Modelling on Plasma and gas nitriding of austenitic and low alloy steels have strong influence of interfacial-nanoescale phenomena. Gamma prime and epsilon nitrogen-iron phases evolution during the nitriding process wasn't found explicitly simulated on literature. On present work we simulated nitrind process on low alloy steels-with their precipitation phenomena and nitrides moving interfaces-using diffusional models plus cellular automata. Surface effects and heterogeneities and local transition phenomena considered on our models show that some experimental results considered "errors" on literature are predicted by our simulations. In present work parameters like diffusion coefficient and surface conditions and gradient of nitrogen concentrations between different phases was measured. © Published under licence by IOP Publishing Ltd.

Liu J.,Northeast Normal University | Liu J.,Materials Science and Technology Center | Liu F.,Sinopec | Yang G.,Northeast Normal University | And 4 more authors.
Electrochimica Acta | Year: 2010

A simple and effective method has been developed to synthesize a nano-sized LiFePO4/PAS (polyacenic semiconductor) composite. The LiFePO4 particles coated and connected by PAS are uniformly distributed in the range of 50-80 nm. The electronic conductivity of this material is as high as 1.2 × 10-1 S/cm due to the conductive network of PAS. In comparison with the micro-LiFePO4/PAS, the nano-LiFePO4/PAS exhibits much better rate performance. At the 12-min charge-discharge rate, the power and energy densities of the nano-LiFePO4/PAS are shown as 2063 W/kg and 412 Wh/kg, which are much higher than those of the micro-LiFePO4/PAS (1600 W/kg and 320 Wh/kg). It is especially notable that the nano-LiFePO4/PAS cathode without adding Super P shows similar electrochemical behaviors with the cathode adding Super P at all C-rates. Thus, such cathode without adding Super P will enlarge both the volume energy density and weight energy density of batteries. In addition, this cathode exhibits an excellent long-term cyclability, retaining over 95.4% of its original discharge capacity beyond 500 cycles at 0.2C rate. These favorable electrochemical performances should be attributed to its nanometric particle size and the high electronic conductivity. © 2009 Elsevier Ltd. All rights reserved.

Yu Z.,Northeast Normal University | Yu Z.,Materials Science and Technology Center | Zhang X.,Heilongjiang University | Yang G.,Kunming University of Science and Technology | And 8 more authors.
Electrochimica Acta | Year: 2011

Li4Ti4.9V0.1O12 nanometric powders were synthesized via a facile solid-state reaction method under inert atmosphere. XRD analyses demonstrated that the V-ions successfully entered the structure of cubic spinel-type Li4Ti5O12 (LTO), reduced the lattice parameter and no impurities appeared. Compared with the pristine LTO, the electronic conductivity of Li4Ti 4.9V0.1O12 powders is as high as 2.9 × 10-1 S cm-1, which should be attributed to the transformation of some Ti3+ from Ti4+ induced by the efficient V-ions doping and the deficient oxygen condition. Meanwhile, the results of XPS and EDS further proved the coexistence of V5+ and Ti3+ ions. This mixed Ti4+/Ti3+ ions can remarkably improve its cycle stability at high discharge-charge rates because of the enhancement of the electronic conductivity. The images of SEM showed that Li4Ti4.9V0.1O12 powders have smaller particles and narrower particle size distribution under 330 nm. And EIS indicates that Li4Ti4.9V0.1O12 has a faster lithium-ion diffusivity than LTO. Between 1.0 and 2.5 V, the electrochemical performance, especially at high rates, is excellent. The discharge capacities are as high as 166 mAh g-1 at 0.5C and 117.3 mAh g-1 at 5C. At the rate of 2C, it exhibits a long-term cyclability, retaining over 97.9% of its initial discharge capacity beyond 1713 cycles. These outstanding electrochemical performances should be ascribed to its nanometric particle size and high conductivity (both electron and lithium ion). Therefore, the as-prepared material is promising for such extensive applications as plug-in hybrid electric vehicles and electric vehicles. © 2011 Elsevier Ltd.

Zhang X.,Northeast Normal University | Zhang X.,Materials Science and Technology Center | Liu J.,Northeast Normal University | Liu J.,Materials Science and Technology Center | And 11 more authors.
Electrochimica Acta | Year: 2010

A simple and effective method, ethylene glycol-assisted co-precipitation method, has been employed to synthesize LiNi0.5Mn1.5O4 spinel. As a chelating agent, ethylene glycol can realize the homogenous distributions of metal ions at the atomic scale and prevent the growth of LiNi0.5Mn1.5O4 particles. XRD reveals that the prepared material is a pure-phase cubic spinel structure (Fd3m) without any impurities. SEM images show that it has an agglomerate structure with the primary particle size of less than 100 nm. Electrochemical tests demonstrate that the as-prepared LiNi0.5Mn1.5O4 possesses high capacity and excellent rate capability. At 0.1 C rate, it shows a discharge capacity of 137 mAh g-1 which is about 93.4% of the theoretical capacity (146.7 mAh g-1). At the high rate of 5 C, it can still deliver a discharge capacity of 117 mAh g-1 with excellent capacity retention rate of more than 95% after 50 cycles. These results show that the as-prepared LiNi0.5Mn1.5O4 is a promising cathode material for high power Li-ion batteries. © 2009 Elsevier Ltd. All rights reserved.

Liu J.,Northeast Normal University | Liu J.,Materials Science and Technology Center | Liu J.,Shandong University | Yang G.,Northeast Normal University | And 6 more authors.
Journal of Power Sources | Year: 2012

For the first time, a LiFePO4/C core-shell nanocomposite has been synthesized using a nano-FePO4/polythiophene (PTh) as an iron source. With this method, the PTh is in situ polymerized to restrain the growth of FePO4 particles, and the typical size of FePO4/PTh particles is in the range of 20-50 nm. The optimized LiFePO4/C nanocomposite is synthesized at 750 °C using 40% citric acid. The prepared LiFePO4 particles show a typical size of 50-100 nm and they are fully coated by carbon of 2-4 nm thickness. The LiFePO4/C core-shell nanocomposite gives an improved high electronic conductivity and a good electrochemical behavior at high rates. Thus, this novel method is an effective and facile strategy to improve the rate performance of the LiFePO4 cathode. © 2011 Elsevier B.V. All rights reserved.

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