Lithium Intercalation into Layered LiMnO2

Recently Armstrong and Bruce ' reported a layered modification of lithium manganese oxide, LiMnO7, isostructural with LiCoO2. LiMnO1 obtained by ion exchange from ct-NaMnO1 synthesized in air is characterized by x-ray diffraction and by electrochemical insertion and extraction of lithium in a series of voltage ranges between 1.5 and 4.5 V relative to a lithium electrode. During cycling, voltage plateaus at 3.0 and 4.0 V vs. Li develop, indicating that the material is con-verted from its original layered structure to a spinel structure. This finding is confirmed by x-ray diffraction. Contrary to expectations based on thermodynamics, insertion of larger amounts of lithium leads to a more complete conversion. We suggest that a relatively high mobility of manganese leaves Li and Mn randomly distributed in the close-packed oxygen lattice after a deep discharge. This isotropic Mn distribution can relatively easily relax to the Mn distribution character-istic of spinels whereas the anisotropic distribution characteristic of layered structures is not reformed when excess lithi-um is extracted. Infroduction With the introduction of the lithium-ion battery con-cept, the "voltage " (potential relative to a lithium elec-trode) of electrode materials has become an importan