| Abstract
| - Excess Li located at transition-metal sites significantly improved the structural ordering of both Li and transition-metal sites for Li[(Ni0.5Mn0.5)0.94Li0.06]O2, as confirmed by neutron diffraction, compared to Li[Ni0.5Mn0.5]O2. Such enhancement resulted in the obvious improvement in battery performances, such as capacity, cyclability, and so on. Because of the improved structural stability by the presence of the excess Li in the transition-metal layer, less structural change was observed during the de/-intercalation of Li+ by in situ XRD, especially in the c axis. Furthermore, it brought about the depression of significant exothermic activity and reduced heat generation at a highly delithiated state as confirmed by DSC.
- Layered Li[Ni0.5Mn0.5]O2 (R3̄m space group) was synthesized with controlling the Li/(Ni + Mn) ratioby employing an emulsion drying method, and the effect of Li on the transition-metal layer wasinvestigated. Structural analyses of the final products were done by X-ray diffraction, neutron diffraction,and X-ray absorption near-edge spectroscopy. From the structural studies, we found that an excess amountof Li is located at the transition-metal layer and the presence of Li in the transition metal significantlyimproved structural ordering in the crystal structure. High capacity with good cyclability, faster Li+chemical diffusivity, less changes in the host structure by Li+ de-/intercalation, and higher thermal stabilitywere achieved for the Li-excess Li[(Ni0.5Mn0.5)0.94Li0.06]O2 compound relative to Li[Ni0.5Mn0.5]O2. It isbelieved that such enhanced electrochemical properties are related to the improved physical and structuralproperties of Li-excess Li[(Ni0.5Mn0.5)0.94Li0.06]O2.
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