第一原理計算を用いたLiイオン電池用正極捕物質LiNi_(0.5)Mn_(0.5)O_2の脱Liに伴う電子構造への影響

摘要

Liイオン電池正極材料では充放電に伴いLiが挿入・脱離し，このLiの移動に伴って結晶構造が変化することが知られているり～7）。LiNio．5Mno．502についてはin－Situによる放射光Ⅹ線を用いたⅩ線回折1）～3），Ⅹ線吸収4)～5．x線光電子分光6），ex－situ血による中性子を用いた測定7）もなされている。%We investigated changes of crystal, electronic structure according to delithiation by using first-principle calculation. The structure with Li vacancy near Ni at Li site, I.e. cation mixing was more stable than other structures. It suggests that Li de-intercalates from near cation mixing at first. From electron density distributions, it was found that covalent bond of M-O (M = Ni, Mn) was increased by delithiation and it seemed that such a change relaxed the structure destabilization according to delithiation. It is also indicated that increase of Ni-O_6 octahedra distortion attributes to asymmetric Ni-O covalent bonds which was induced by formation of Li vacancy. Density of states of Ni at Li site didn't change so much, and thus Ni redox reaction occurred only at normal transition metal site.