期刊
JOURNAL OF THE ELECTROCHEMICAL SOCIETY
卷 155, 期 4, 页码 A282-A291出版社
ELECTROCHEMICAL SOC INC
DOI: 10.1149/1.2832650
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资金
- EPSRC [EP/G005001/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/G005001/1] Funding Source: researchfish
Crystal structure and oxygen stoichiometry in LiMn1.5Ni0.5O4-delta, a potential lithium-battery cathode, vary with temperature, as observed in samples quenched from different temperatures and by in situ diffraction and thermogravimetry techniques. When prepared in high O-2 pressure, this cation-ordered spinel is oxygen-stoichiometric, delta = 0, space group P4(3)32. Upon heating between 650 and 680 C, increasing oxygen deficiency occurs exclusively in MnO6 octahedra and Mn-O-Mn bonds, which induces a volume increase of the 12d octahedra, a reduction of Mn as shown by X-ray absorption near-edge structure, equalization of Mn-O and Ni-O bond lengths, and disordering of Mn, Ni on octahedral sites. Hence, the transformation to space group Fd (3) over barm, shown by Rietveld refinement of variable-temperature neutron diffraction data, is a direct consequence of oxygen loss from the structure. On further oxygen loss, a second phase transformation occurs to give a cation-deficient cubic rock salt phase, delta similar to 0.65, at 950 degrees C, which loses more oxygen at higher temperatures until, at 1100 degrees C, the material is essentially a stoichiometric, single-phase cation-disordered rock salt, space group Fm (3) over barm. A second spinel phase persists in small amounts from 950 to 1100 degrees C. Differences in electrochemical behavior depend on sample preparation and correlate with the oxygen content of LiMn1.5Ni0.5O4-delta when used as a cathode in Li test cells. (c) 2008 The Electrochemical Society.
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