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Liu Y.,Jiangsu University | Liu Y.,Postdoctoral Workstation of Chery Automobile Co. | Lv J.,Jiangsu University | Zhu G.,Postdoctoral Workstation of Chery Automobile Co. | And 3 more authors.
Ionics | Year: 2013

Li1.1Ni0.25Mn0.75O2.3 and Li1.5Ni0.25Mn0.75O2.5 have been synthesized by co-precipitation method. The effect of the LiNi0.5Mn1.5O4 spinel structure on physical and electrochemical properties is discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and electrochemical performance tests. The LiNi0.5Mn1.5O4 spinel structure is detected in the XRD pattern, TEM image, first discharge, and CV curves of the Li1.1Ni0.25Mn0.75O2.3 electrode. The rate, cyclic performance, and first coulomb efficiency of Li1.1Ni0.25Mn0.75O2.35 are higher than those of Li1.5Ni0.25Mn0.75O2.5. The first coulomb efficiencies of Li1.1Ni0.25Mn0.75O2.3 and Li1.5Ni0.25Mn0.75O2.5 are 86.2 and 74.7 %, and the capacity retentions are 98.7 and 94.1% after 50 cycles, respectively. EIS results indicate that the charge-transfer reaction resistance of Li1.1Ni0.25Mn0.75O2.3 is lower than that of Li1.5Ni0.25Mn0.75O2.5, which is responsible for the better rate capacity of Li1.1Ni0.25Mn0.75O2.3. © 2013 Springer-Verlag Berlin Heidelberg. Source


Liu Y.,Jiangsu University | Liu Y.,Postdoctoral Workstation of Chery Automobile Co. | Lv J.,Jiangsu University | Liu S.,Postdoctoral Workstation of Chery Automobile Co. | And 2 more authors.
Powder Technology | Year: 2013

Li1.2Ni0.2Mn0.6O2 powders have been synthesized and then treated by ball milling and carbon coating to improve the electrochemical performance. The effect of ball milling and carbon coating on physical and electrochemical properties has been discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), electrochemical impedance spectroscopy (EIS), discharge capacity and rate tests. The first discharge capacity and rate capability exhibit a great improvement for carbon-coated Li1.2Ni0.2Mn0.6O2 than the pristine and ball-milled. The discharge capacities of carbon-coated cathode at 0.1 and 10C are 253 and 130mAhg-1, while those of ball-milled cathode are 228 and 85mAhg-1, and those of pristine Li1.2Ni0.2Mn0.6O2 are only about 219 and 22mAhg-1. The capacity retention of carbon-coated electrode after 50cycles is 97.8%, in compared with those of pristine and ball-milled are 95.3% and 92.8%, respectively. EIS results indicate that the charge transfer resistance (Rct) of pristine electrode has been decreased from 62Ω to 35Ω after ball milling and to 23Ω after carbon coating, and the Rct of pristine Li1.2Ni0.2Mn0.6O2 increased faster than that of carbon-coated sample after cycles. © 2013 Published by Elsevier B.V. Source


Liu Y.,Jiangsu University | Liu Y.,Postdoctoral Workstation of Chery Automobile Co. | Liu S.,Postdoctoral Workstation of Chery Automobile Co. | Wang Y.,Jiangsu University | And 2 more authors.
Journal of Power Sources | Year: 2013

Pristine and MnO2-coated LiNi0.2Li0.2Mn0.6O2 powders have been synthesized in this paper. The effect of MnO2 coating on the physical and electrochemical properties is discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS), discharge, cyclic and rate performance tests. The materials show layered structure before and after coating. The MnO2-coated LiNi0.2Li0.2Mn0.6O2 electrodes show better discharge capacity, first coulomb efficiency, cyclic performance and rate capacity compared with pristine LiNi0.2Li0.2Mn0.6O2. And the LiNi0.2Li0.2Mn0.6O2 coated with MnO2 decomposing from manganese carbonate has the best performance. The first coulomb efficiency is 82.7%. The discharge capacities at 0.1 and 10 C are 253 and 99 mAh g-1, respectively, and it presents no obvious capacity loss after 50 cycles. The discharge and cyclic voltammetry (CV) curves show that the coated MnO2 reacts with Li+ during the charge and discharge cycle, which is responsible for higher discharge capacity after coating. Electrochemical impedance spectroscopy (EIS) results show that the Rct of LiNi0.2Li0.2Mn0.6O2 electrode decreases after coating, which is due to the suppression of the solid electrolyte interfacial (SEI) layer development and is responsible for the better cyclic and rate performance. © 2012 Elsevier B.V. All rights reserved. Source


Liu Y.,Jiangsu University | Liu Y.,Postdoctoral Workstation of Chery Automobile Co. | Wang Y.,Jiangsu University | Liu S.,Postdoctoral Workstation of Chery Automobile Co. | And 3 more authors.
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology) | Year: 2013

Li1.2Ni0.2Mn0.6O2 was synthesized by co-precipitation and high-temperature solid-state reaction. The carbon-coated Li1.2Ni0.2Mn0.6O2 was synthesized by ball-milling and low-temperature pyrogenation. The samples were characterized by XRD, SEM and TEM, respectively. The results show that the samples have layered structure, and the particle size diminishes after coating. The first discharge capacity at 0.1C is increased from 219 mA·h/g to 246 mA·h/g after coating. The discharge capacity at 5.0C is still 125 mA·h/g, while that of pristine is only about 60 mA·h/g. The capacity retaining ratio is increased from 94.7% to 97.8%. The charge transfer resistance is greatly reduced from 62 Ω to 37 Ω after carbon coatimg. Source

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