Structural characterization for the chemically Li+ ion extracted LiyCoO2, LiyCo0.95Ga0.05O2, and LiyCo0.9Ga0.1O2 compounds Original Research Article

Chemical Li ion extraction processes have been carried out for pristine LiCoO2, LiCo0.95Ga0.05O2, and LiCo0.9Ga0.1O2 compounds by swirling them in 0.35 M H2SO4 solution. It is confirmed from XRD patterns that the compounds maintain the two-dimensional framework with pristine-type structure even after the acid treatment up to 12 h. The Ga-substituted compounds keep Li ions for longer time on the acid treatment rather than the LiCoO2. The average oxidation state of Co ions increases with the Li+ ion extraction time up to 3.45+. The local structure refinements for the chemically Li+ ion extracted compounds have been investigated by Co K-edge X-ray absorption spectroscopy. The extraction causes the increase of Debye–Waller (DW) factor or static disorder around the Co ion. The DW factor of the Co–Co bond pair less increases with the extraction time for the LiyCo0.95Ga0.05O2, and LiyCo0.9Ga0.1O2 compounds than that for the LiCoO2. The Ga-substituted compounds are more stable against acid treatments than the LiCoO2, since more basic Ga3+ ion retards the structural distortion of the CoO6 octahedra against the Li ion extraction.