Stability of the monoclinic and orthorhombic phases of LiMnO2 with temperature, oxygen partial pressure, and Al doping

The monoclinic and orthorhombic ordered-rocksalt polymorphs of LiMnO2 are o f interest as high-capacity cathode materials for rechargeable Li batteries . The relative stability of the monoclinic and orthorhombic phases has been studied as a function of firing temperature, oxygen partial pressure, and Al doping. Control of temperature and oxygen partial pressure is crucial in order to obtain the LiAlyMn1-yO2 phases while minimizing impurity phases s uch as LiMn2O4, Li2MnO3, and Mn3O4. The solid solubility of Al in LiMnO2 ha s been determined to reach a maximum of 5-7% at 950 degrees C and P-O2 = 10 (-7) atm. The existence of a maximum in Al solid solubility is attributed t o the competing stability of gamma-LiAlO2 at higher temperatures. A phase s tability mechanism for the monoclinic phase upon Al-doping is proposed. (C) 2000 Elsevier Science B.V. All rights reserved.