Abstract
The O1 phase transition is suppressed by Ni migration to tetrahedral sites in NiO2.
Highlights
Ni-enriched layered materials are utilized as positive electrode materials of high-energy Li-ion batteries
Because electrode reversibility is gradually lost for stoichiometric LiNiO2 after continuous cycles, Ni ions are partially substituted by other metal ions (Co, Mn, Al etc.)
For fully charged NiO2, Ni ions migrate from original octahedral sites in NiO2 slabs to face-sharing tetrahedral sites in Li layers, by which the O3 to O1 phase transition is suppresed
Summary
Electrode kinetics are deteriorated because of the Ni occupation in Li layers, and the accumulation of Ni ions at tetrahedral sites results in the loss of reversible capacities in the high voltage region. This finding opens a new way to design high-capacity Ni-enriched electrode materials, leading to the development of high-energy Li-ion batteries. The O1 phase transition is, allowed only for a fully delithiated phase, or a small number of Li ions is probably found at neighboring tetrahedral sites, which share edges with the CoO6 octahedra This observation was rst evidenced in 1996 by Amatucci et al using an in situ X-ray diffraction (XRD) study.[4] O1-type CoO2 is isostructural with CdI2 with space group P3m1. Thermal instability of NiO2 is another practical issue as an electrode material.[9,10]
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