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Structural and electrochemical properties of as positive electrode materials for lithium batteries were investigated. The materials were prepared via a coprecipatation process. From X-ray diffraction studies, it was found that the synthesized materials were crystallized into an layered structure . With increasing Co and Mn content in , the corresponding lattices were slightly contracted. X-ray absorption near edge spectra of also showed that the oxidation state of Ni is changed from to when tetravalent Mn is present in oxide . From Rietveld refinements of powder X-ray diffraction data, it was found that further increase in Co and Mn content also resulted in reduced cation mixing between and in Li layers. Electrochemical properties and thermal stability were also affected by the physical properties. When tetravalent Mn appeared in the structure, the corresponding cyclability was greatly improved compared to that of . Furthermore, thermal stability at highly delithiated state was also significantly enhanced by the existence of electrochemically inactive tetravalent Mn in the oxide matrix.
Lee et al. (Mon,) studied this question.