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Wang S.,Institute of New Energy Material Chemistry | Li S.,Institute of New Energy Material Chemistry | Cao Z.,Institute of New Energy Material Chemistry | Yan T.,Institute of New Energy Material Chemistry | Yan T.,Nankai University
Journal of Physical Chemistry C | Year: 2010

The interface structure between room temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM+/PF6 -) and 1-octyl-3-methylimidazolium hexafluorophosphate (OMIM +/PF6 -), and the graphite (0001) surface has been studied by classical molecular dynamic simulations. It is found that the density of IL is much enhanced at the interfacial region and the density oscillation extends to ∼15 Å into the bulk with three layers. The results also demonstrate that the polar groups tend to aggregate forming a polar network, while the nonpolar groups fill up the rest of the vacancy. The imidazolium rings and the side chains preferentially lie flat at the graphite surface with the alkyl side chains of the cations elongated at the interfacial region, and the cations are closer to the graphite surface (ca. 3.6-3.7 Å) than the anions. The surface potential drop across the interface is more profound for OMIM+/PF6 - than for BMIM +/PF6 -, due to relatively larger local density of the anions for OMIM+/PF6 - near the graphite surface. © 2010 American Chemical Society.

Xu Y.,Institute of New Energy Material Chemistry | Ding L.,Hunan City University | Zhong T.,Hunan City University | Han X.,Maple Leaf International School Tianjin TEDA | And 3 more authors.
Journal of Energy Chemistry | Year: 2015

Electrochemical performances of LiCoO2 as a candidate material for supercapacitor are systematically investigated. LiCoO2 nanomaterials are synthesized via hydrothermal reaction with consequent calcination process. And the particle size increases as the calcination temperature rises. LCO-650 sample with the largest particle size displays the maximum capacitances of 817.5 F·g-1 with the most outstanding capacity retention rate of 96.8% after 2000 cycles. It is shown that large particle size is beneficial to the electrochemical and structural stability of LiCoO2 materials. We speculate that the micron-sized waste LiCoO2 materials have great potential for supercapacitor application. It may provide a novel recovered approach for spent LIBs and effectively relieve the burdens on the resource waste and environment pollution. © 2015 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences. Published by Elsevier B.V.

Gao H.,Institute of New Energy Material Chemistry | Gao H.,Nankai University | Jiao L.,Institute of New Energy Material Chemistry | Jiao L.,Nankai University | And 8 more authors.
Electrochimica Acta | Year: 2013

Co-doped LiFe1-xCoxPO4/C (x = 0, 0.005, 0.010, 0.020) composites were synthesized by oxalic acid-assisted sol-gel method and their electrochemical properties had been investigated in detail using galvanostatic charge/discharge, cyclic voltammograms (CVs) and electrochemical impedance spectra (EIS) tests. Co-doping benefited the transportation of Li + and electrochemical conductivity which lead to the excellent high rate capability. The doped LiFe1-xCoxPO4/C with x = 0.010 exhibited the best electrochemical properties, with discharge capacity of 114.8 and 104.2 mAh g-1 at 10 C and 20 C, respectively. © 2013 Elsevier Ltd. All rights reserved.

Cao K.,Institute of New Energy Material Chemistry | Jiao L.,Institute of New Energy Material Chemistry | Liu Y.,Institute of New Energy Material Chemistry | Liu H.,Institute of New Energy Material Chemistry | And 2 more authors.
Advanced Functional Materials | Year: 2015

Although transition metal oxide electrodes have large lithium storage capacity, they often suffer from low rate capability, poor cycling stability, and unclear additional capacity. In this paper, CoO nanowire clusters (NWCs) composed of ultra-small nanoparticles (≈10 nm) directly grown on copper current collector are fabricated and evaluated as an anode of binder-free lithium-ion batteries, which exhibits an ultra-high capacity and good rate capability. At a rate of 1 C (716 mA g-1), a reversible capacity as high as 1516.2 mA h g-1 is obtained, and even when the current density is increased to 5 C, a capacity of 1330.5 mA h g-1 could still be maintained. Importantly, the origins of the additional capacity are investigated in detail, with the results suggesting that pseudocapacitive charge and the higher-oxidation-state products are jointly responsible for the large additional capacity. In addition, nanoreactors for the CoO nanowires are fabricated by coating the CoO nanowires with amorphous silica shells. This hierarchical core-shell CoO@SiO2 NWC electrode achieves an improved cycling stability without degrading the high capacity and good rate capability compared to the uncoated CoO NWCs electrode. © 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.

Yuan S.M.,Institute of New Energy Material Chemistry | Yuan S.M.,Nankai University | Li J.X.,Institute of New Energy Material Chemistry | Li J.X.,Nankai University | And 8 more authors.
ACS Applied Materials and Interfaces | Year: 2011

Fe3O4@C microcapsules were prepared using carbon-coated-FeOOH nanorods as precursors, which were synthesized via two-step hydrothermal reactions. During the subsequent sintering procedure, -FeOOH was reduced to Fe3O4 by carbon, accompanied by the formation of mesopores. In Fe3O4@C microcapsules, mesoporous Fe 3O4 nanorods are coated with amorphorous carbon layers. The Fe3O4/C composites with such special structures demonstrate high specific capacity and good cyclic stability as anode materials in Li test cells. © 2011 American Chemical Society.

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