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Liu W.,CAS Beijing National Laboratory for Molecular | Wang M.,CAS Beijing National Laboratory for Molecular | Gao X.L.,Pulead Technology Industry Co. | Zhang W.,CAS Beijing National Laboratory for Molecular | And 3 more authors.
Journal of Alloys and Compounds | Year: 2012

The high-temperature cycling stability at a high cutoff voltage of LiNi 0.5Co 0.2Mn 0.3O 2 was improved by TiO 2 coating. The mechanism of enhancement was elucidated by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses. TiO 2 coating formed a uniform layer on the surface of LiNi 0.5Co 0.2Mn 0.3O 2 particles without changing the crystal structure. Electrochemical tests indicated that TiO 2 coating can improve the lithium ion intercalation stability at 328 K and at a high cutoff voltage of 4.4 V. The 1.0% TiO 2-coated LiNi 0.5Co 0.2Mn 0.3O 2 discharged 149.2 mAh g -1 after 100 cycles at 0.5C, and maintained 92.1% of the initial discharge capacity. By contrast, the bare sample discharged only 87.7 mAh g -1 with 48.2% capacity retention. ICP-AES results proved that the TiO 2 coating layer can reduce the dissolution of transition metal ions from LiNi 0.5Co 0.2Mn 0.3O 2. EIS and XPS confirmed that the improved cycling stability can be attributed to the suppression of the reaction between cathode and electrolyte in lithium-ion batteries. © 2012 Elsevier B.V. All rights reserved. Source

Gu Y.-J.,Shandong University of Science and Technology | Zhang Q.-G.,Shandong University of Science and Technology | Zhang Q.-G.,Pulead Technology Industry Co. | Chen Y.-B.,Shandong University of Science and Technology | And 10 more authors.
Journal of Alloys and Compounds | Year: 2015

Layered Li1+ xNi0.5Co0.2Mn0.3O2 (x = 0, 0.02, 0.04, 0.06, 0.08) materials were synthesized using the co-precipitation method. Rietveld refinements measurements reveal that the concentration of Ni2+-3b ions decreases from 0.06 to 0.043, with x changing from 0.02 to 0.08. The initial coulombic efficiency improves with the increase in the content of Li-excess because the content of Ni at the 3b site decreases with the increase of Li-excess in the samples from 0 to 0.08. The analysis indicates that Li1.08Ni0.5Co0.2Mn0.3O2 exhibits the largest diffusivity value due to the dependence of the diffusion coefficient of lithium ions on the content of Ni in the 3b sites. © 2015 Published by Elsevier B.V. Source

Yang X.,Beijing Institute of Technology | Yang X.,Peking University | Mi Y.,Peking University | Zhang W.,Pulead Technology Industry Co. | And 2 more authors.
Journal of Power Sources | Year: 2015

A ferrocene-assisted calcination process (FACP) has been applied during the preparation of LiFe0.6Mn0.4PO4/C cathode material. Ferrocene works as a promoter to improve the quality of the coated carbon layers. The influence of ferrocene on the property of carbon layers and electrochemical performance of LiFe0.6Mn0.4PO4/C has been investigated systematically. The LiFe0.6Mn0.4PO4/C with FACP presents more uniformly and tightly coated carbon layers with higher graphitization degree than the sample without FACP. High-quality carbon layers can greatly enhance the electrochemical performance of cathode materials. The LiFe0.6Mn0.4PO4/C with FACP behaves higher discharge capacities (163.6 and 120.7 mAh g-1 at 0.2C and 20C, respectively) than the LiFe0.6Mn0.4PO4/C without FACP (158.4 and 111.5 mAh g-1 at the same rates). Furthermore, the LiFe0.6Mn0.4PO4/C with FACP exhibits excellent cycling performance even at 60°C, still delivering capacity retention above 96% after 100 cycles at 3C, while the retention of the controlled sample is only 70% after 75 cycles. The cycling performance of the LiFe0.6Mn0.4PO4/C with FACP at high temperature is largely improved. © 2014 Elsevier B.V. All rights reserved. Source

Wang Z.-P.,Beijing Institute of Technology | Liu W.,CAS Beijing National Laboratory for Molecular | Wang Y.,Beijing Research Institute of Chemical Defense | Zhao C.-S.,Pulead Technology Industry Co. | And 4 more authors.
Wuli Huaxue Xuebao/ Acta Physico - Chimica Sinica | Year: 2012

Mg and Ti ions co-doped (Li 0.98Mg 0.01)(Fe 0.98Ti 0.01)PO 4/C cathode material for lithium-ion batteries was prepared by a solid-state method under N 2 atmosphere. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and galvanostatic charge-discharge test. Results indicated that Mg and Ti ions co-doping remarkably improved the electrochemical performance of LiFePO 4, including rate capacity, temperature behavior, and cycling stability. Discharge capacities of 154.7 and 146.9 mAh·g -1 were obtained at the rates of 0.2C and 1C for half-cell tests, respectively. For 60 Ah full-cell tests, 100% of 1C capacity was maintained even at 3C rate, 89.7% and 63.1% of initial capacity at room temperature were retained at 0 and -20 °C, respectively. 89% capacity retention remained after 2000 cycles at room temperature, presenting excellent cycle stability. This investigation suggests that the present co-doping material and the resulting battery possess large discharge capacity and excellent cycling performance, making it applicable in electric vehicle (EV)/hybrid electric vehicle (HEV) and energy storage systems on a large scale. © Editorial office of Acta Physico-Chimica Sinica. Source

Zhang W.,Peking University | Wan W.,Peking University | Zhou H.,Peking University | Chen J.,Pulead Technology Industry Co. | And 2 more authors.
Journal of Power Sources | Year: 2013

Magnetite (Fe 3O 4)/expanded graphite (EG) composite material is prepared through the oxidation progress of ferrocene-graphite intercalation compound in acetone solution. The reactions occur in this system and lead to in-situ synthesis of the composite with nanosized magnetite and expanded graphite. Due to the lithium insertion/extraction experiment, the Fe 3O 4/EG composite material shows high reversible capacities (ca. 720 mA h g -1 at 120 mA g -1 charge current) and excellent rate performances (ca. 630 mA h g -1 at 600 mA g -1, 420 mA h g -1 at 6000 mA g -1 and 360 mA h g -1 at 9000 mA g -1charge current). Owning to the strong interaction between Fe 3O 4 and EG from in-situ synthesis, it is demonstrated that these properties of this novel Fe 3O 4/EG composite material will be an idea candidate for the negative electrode material of high-current lithium ion battery. © 2012 Elsevier B.V. All rights reserved. Source

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