Synthesis and electrochemical characteristics of Li0.7[Ni0.05Mn0.95]O2 as a positive materials for rechargeable lithium batteries.

Abstract

The presently commercialized lithium-ion batteries use layer structured LiCoO2 cathodes. Because of the high cost and toxicity of cobalt, an intensive search for new cathode materials has been underway in recent years. One of the most attractive cathode materials is the spinel LiMn2O4 and its derivatives due to their low cost, abundance, and nontoxicity. However, the spinel LiMn2O4 and its derivatives demonstrate smaller discharge capacity than layer structured materials and a slow capacity loss at elevated temperature in the range of 50 ∼ 80℃. Therefore, many research groups have been studied to prepare layered LiMnO2 with the O3 (α-NaFeO2) structure as LiCoO2 and LiNiO2. Direct synthesis of O3 LiMnO2 is not possible because the nonlayered structures LiMn2O4 (spinel), LiMnO2 (orthorhombic), or Li2MnO3 (rock salt) are more stable at high temperature. In this study, layered Na0.7[Ni0.05Mn0.95]O2 compounds were synthesized by a sol-gel method using glycolic acid as a chelating agent at the low temperature condition. Na0.7[Ni0.05Mn0.95]O2 precursors were used to prepare layered lithium manganese oxides by ion exchange for Na by Li using LiBr in hexanol. Powder X-ray diffraction shows the layered Li0.7[Ni0.05Mn0.95]O2 has an O3 type structure. It exhibits a large reversible capacity of approximately 190 mAh/g in the 2.4 ∼ 4.5 V range. Li0.7[Ni0.05Mn0.95]O2 powders undergo transformation to spinel during cycling.