COMPARISON OF THE LAYERED TO SPINEL-LIKE PHASE TRANSITION IN Li_(0.5)MO_2 (M = Mn, Co AND Ni) CATHODES

摘要

Li_(0.5)MO_2 (M = Mn, Co, Ni, Ni_(1-y)Co_y and Ni_(1-y)Mn_y) compositions have been synthesized by chemically extracting lithium with the oxidizing agent sodium perdisulfate from the corresponding LiMO_2 oxides. The ease of transformation of the Li_(0.5)MO_2 compositions thus obtained to cubic spinel-like phases has been investigated systematically by heating them at various temperatures. The Li_(0.5)MnO_2 compositions obtained from both the monoclinic layered and orthorhombic LiMnO_2 transform easily to spinel-like phases at ambient temperatures during the process of lithium extraction. The Li_(0.5)NiO_2 composition needs some heat (T≈150℃) to transform to a cubic spinel-like phase while the Li_(0.5)CoO_2 composition obtained from conventional layered LiCoO_2 does not transform to spinel-like phase even under heat (T≈200℃). The differences among the three systems are explained on the basis of crystal field stabilization energy. Additionally, cationic substitutions for the transition metal ions are found to suppress the formation of spinel-like phase.