Synthesis of orthorhombic LiMnO2 by solid-phase reaction under steam atmosphere and a study of its heat and acid-treated phases

Low crystalline orthorhombic LiMnO2 (o-LiMnO2) samples were synthesized by reacting either gamma-MnOOH or Mn2O3 with LiOH . H2O in the solid phase under steam atmosphere at 120degreesC. In the closed system, the vapor arising from LiOH . H2O may strengthen the reactivity of LiOH at the surface of MnOOH or Mn2O3 particles, which may enable slow diffusion of Li+ ions forming LiMnO2. These samples were compared with crystalline o-LiMnO2 prepared by a solid-state reaction method at 700degreesC in nitrogen gas. The powder X-ray diffraction patterns of low crystalline samples after heating at 400degreesC in air revealed the formation of a single phase of cubic Li1.6Mn1.6O4, but the crystalline sample revealed a mixed phase of o-LiMnO2 and LiMn2O4 after heating at 400degreesC in air. The Li+/H+ exchange in the Li1.6Mn1.6O4 sample progressed topotactically, while maintaining the crystal structure and morphology of the precursor. But heat-treated crystalline o-LiMnO2 showed a disproportionation reaction with dissolution of Mn2+ ions. (C) 2002 Elsevier Science (USA). All rights reserved.