鉄置換Li<sub>2</sub>MnO<sub>3 </sub>系正極材料の合成と充放電特性に及ぼすチタン置換効果

Abstract

Fe- or Fe and Ti-substituted Li2MnO3 positive electrode material (FM or FMT sample) with monoclinic Li2MnO3 type structure (C2/m) was synthesized using coprecipitation-hydrothermal-calcination. Both materials exhibited high specific capacity greater than 200 mAh/g against a Li metal negative electrode at moderate current density of 40 mA/g between 2.0 and 4.8 V using stepwise charging. The cycle performance for the FMT sample (Li1+x(Fe0.2Ti0.2Mn0.6)1−xO2, 0 < x< 1/3) using a graphite negative electrode was better than that for the FM sample (Li1+x(Fe0.2Mn0.8)1−xO2, 0<x<1/3), indicating that partial substitution of Ti4+ for Mn4+ ion is effective for improving cycle performance under the practical lithium-ion cell configuration. The results presented above demonstrate that an Fe-substituted Li2MnO3 based positive electrode material can become an attractive candidate as an inexpensive constituent material for a large-scale lithium-ion battery by selecting suitable additional elements such as Ti and electrochemical charge conditions for activation.