Investigation on Crystal and Electronic Structures of 0.5Li₂MnO₃-0.5LiMn_xNi_xCo_(1−2x)O₂ (x = 1/3, 5/12) Samples Heat-Treated under Vacuum Reducing Conditions

Abstract

We prepared two 0.5Li₂MnO₃-0.5LiMn_xNi_xCo_(1−2x)O₂ (x = 1/3, 5/12) samples using the solution method, followed by heat treatment under vacuum reducing conditions. ICP and average-valence analyses clarified that the amounts of lithium and oxygen were decreased by reductive heat treatments. Results of a cycle performance test showed that the heat-treated samples exhibited a high discharge capacity, although the voltage regions contributing to the improvements depended on the metal composition, i.e., 3.3 and 3.8 V for x = 1/3 and x = 5/12, respectively. In order to discuss the crystal structure, a Rietveld analysis by neutron diffraction was carried out. A localized model in which Mn occupied the 4g site and Li occupied the 2b site in the Li₂MnO₃-type structure (S.G.; C2/m) resulted in good fitting.