リチウムイオン電池正極材料LiMn_0.5Ni_0.5O₂の正極特性と結晶・電子構造における置換効果

抄録

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 LiMn_0.5Ni_0.5O₂, 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 LiMn_0.5Ni_0.5O₂.