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Zhang X.,Peking University | Zhang X.,University Pierre and Marie Curie | Jiang W.J.,CITIC Guoan Co. | Mauger A.,University Pierre and Marie Curie | And 3 more authors.
Journal of Power Sources | Year: 2010

Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 layered materials were synthesized by the co-precipitation method with different Li/M molar ratios (M = Ni + Mn + Co). Elemental titration evaluated by inductively coupled plasma spectrometry (ICP), structural properties studied by X-ray diffraction (XRD), Rietveld analysis of XRD data, scanning electron microscopy (SEM) and magnetic measurements carried out by superconducting quantum interference devices (SQUID) showed the well-defined α-NaFeO2 structure with cationic distribution close to the nominal formula. The Li/Ni cation mixing on the 3b Wyckoff site of the interlayer space was consistent with the structural model [Li1-yNiy]3b[Lix+yNi(1-x)/3-yMn(1-x)/3Co(1-x)/3]3aO2 (x = 0.02, 0.04) and was very small. Both Rietveld refinements and magnetic measurements revealed a concentration of Ni2+-3b ions lower than 2%; moreover, for the optimized sample synthesized at Li/M = 1.10, only 1.43% of nickel ions were located into the Li sublattice. Electrochemical properties were investigated by galvanostatic charge-discharge cycling. Data obtained with Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 reflected the high degree of sample optimization. An initial discharge capacity of 150 mAh g-1 was delivered at 1 C-rate in the cut-off voltage of 3.0-4.3 V. More than 95% of its initial capacity was retained after 30 cycles at 1 C-rate. Finally, it is demonstrated that a cation mixing below 2% is considered as the threshold for which the electrochemical performance does not change for Li1+x(Ni1/3Mn1/3Co1/3)1-xO2. © 2009 Elsevier B.V. All rights reserved.

Zhang D.,CAS Beijing National Laboratory for Molecular | Yan H.,CAS Beijing National Laboratory for Molecular | Zhu Z.,CAS Beijing National Laboratory for Molecular | Zhang H.,CITIC Guoan Co. | And 2 more authors.
Journal of Power Sources | Year: 2011

The electrochemical stability of lithium bis(oxatlato) borate (LiBOB) containing solid polymer electrolyte has been evaluated both by inert electrode and real cathodes. Enhanced intrinsic anodic stability and decreased interface impedance, are obtained by addition of nano-sized MgO to PEO20-LiBOB. It is also found that the LiBOB-containing SPEs exhibit prominent kinetic stability between 3.0 and 4.5 V. For cells using SPEs as the separators, good cycling performance is obtained for real 4 V class cathodes material LiNi 1/3Co1/3Mn1/3O2 and LiCoO 2. The LiPEO20-LiBOBLiNi1/3Co 1/3Mn1/3O2 cell takes an initial capacity of 156.8 mAh g-1, with retention of 142.5 mAh g-1 after 20 cycles at 0.2C-rate. The cell also works well up to 1C-rate. The addition of nano-sized MgO into PEO20-LiBOB readily reduces the irreversible capacity per cycle, both for LiNi1/3Co1/3Mn 1/3O2 and LiCoO2 cathodes. In addition, the critical role of LiBOB in obtaining kinetic stability and passivating ability towards cathodes are specially discussed. © 2011 Elsevier B.V. All rights reserved.

Huang J.,Tsinghua University | Zhang J.,Tsinghua University | Li Z.,Tsinghua University | Song S.,CITIC Guoan Co. | Wu N.,CITIC Guoan Co.
Electrochimica Acta | Year: 2014

The electrochemical impedance spectroscopy (EIS) of a lithium-ion battery is usually measured at open-circuit state under a constant state-of-charge (SOC). In this way, the differences between charge and discharge cannot be distinguished, because they both occur in one cycle of the alternating current. To explore the differences, in this study, we propose a new implementation method measuring the dynamic EIS (DEIS) of a LiMn2O4/Li half-cell (0.8 mAh) in the galvanostatic mode while the cell is under charging or discharging at a series of direct currents (DC). The results show the charge transfer resistance, Rct, decreases with the increased DC. Also, Rct during charging is usually smaller than that during discharging. The dependency of Rct on the DC can be explained according to the Butler-Volmer equation. The difference in Rct between charge and discharge, ΔRct, is ascribed to a significant surface concentration variation caused by the DC. © 2014 Elsevier Ltd.

Zhang X.,University Pierre and Marie Curie | Zhang X.,Peking University | Jiang W.J.,CITIC Guoan Co. | Zhu X.P.,CITIC Guoan Co. | And 3 more authors.
Journal of Power Sources | Year: 2011

LiNi1/3Mn1/3Co1/3O2 compound was successfully synthesized by the co-precipitation method. The effect of H2O on LiNi1/3Mn1/3Co1/3O 2 in humid atmosphere was investigated by structural, magnetic and electrochemical analysis, and Raman spectroscopy. The consequence is that immersion of LiNi1/3Mn1/3Co1/3O2 to H2O and exposure of LiNi1/3Mn1/3Co 1/3O2 to humid atmosphere (ambient atmosphere, 20 °C, 50% relative humidity) led to a rapid attack that manifests itself by the delithiation of the surface layer of the particles and the concomitant formation of LiOH and Li2 CO3 at the surface. This aging process occurred during the first few minutes, then it is saturated, and the thickness of the surface layer at saturation is 10 nm. After aging, an initial discharge capacity of 139 mAh/g was delivered at 1C-rate in the cut-off voltage of 3.0-4.3 V. About 95% of its initial capacity was retained after 30 cycles. © 2011 Elsevier B.V.

Wu N.,University of Science and Technology Beijing | Wu N.,CITIC Guoan Co. | Yang D.,CITIC Guoan Co. | Liu J.,CITIC Guoan Co. | Tian W.,University of Science and Technology Beijing
Electrochimica Acta | Year: 2012

This paper describes the capacity fade of LiMn 2O 4/graphite batteries under different external conditions. The discharge capacity and the cycling performance of the batteries were investigated. Compared with batteries cycled under constant-temperature (25 °C) conditions, LiMn 2O 4/graphite batteries cycled under alternating temperatures and with vibration (referred to as operating-mode conditions) faded more rapidly. The reasons for the accelerated capacity fade of LiMn 2O 4/graphite batteries under operating-mode conditions were investigated using XRD, SEM, DSC, EDS, ICP and AC impedance. Compared with batteries cycled under constant-temperature conditions, the crystallinity of LiMn 2O 4 in batteries cycled under operating-mode conditions was poor, and the lattice parameter and the amount of dissolved Mn increased, which resulted in an accelerated capacity fade under operating-mode conditions. With an increased number of cycles, the thermal stability of the anode surface membrane decreased, whereas the anode surface membrane was severely damaged by the alternating temperature and vibrations. This damage led to the surface membrane being repaired more rapidly and the formation of grains with a mushroom-like morphology on the anode surface. As a result, the impedance increased more rapidly, and the capacity fade accelerated. © 2011 Elsevier Ltd.

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