リチウムイオン電池正極材料LiMn0.5Ni0.5O2の正極特性と結晶・電子構造における置換効果

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We synthesized Li(Mn, M)0.5(Ni, M′)0.5O2 (M = Al, Ti; M′ = Mg) by a conventional solid-state method, and investigated their electrochemical properties, crystal and electronic structures. From X-ray diffraction patterns, it was found that the synthesized samples had a single phase of the layered rock-salt structure. In addition, it was demonstrated by metal composition and valence analyses that the oxygen tended to be deficit slightly in the Al- and Mg-substituted samples. Charge-discharge cycle tests indicated that the samples exhibited different cathode performance depending on substitution; that is, the Ti-substituted samples exhibited better cycle performance than LiMn0.5Ni0.5O2, and Al and Mg substitutions deteriorated the cathode property. In order to study the substitution effects on their crystal structures, the Rietveld analysis using neutron diffractions was carried out. As a result, it was found that the Ti substitution made the structure distortion smaller. This may be one of the reasons why the Ti substitution improved the cathode properties of LiMn0.5Ni0.5O2.