Ion-exchange properties of P2-NaxMnO2:: evidence of the retention of the layer structure based on chemical reactivity data and electrochemical measurements of lithium cells

The ion-exchange properties of two P2-type layered NaxMnO2 bronzes (x = 0.6, 0.75) with a differential microstructure were studied in LiCF3SO3 solutions in acetonitrile under ambient conditions. Na+ ions are readily exchanged with Li+, but the reaction causes a significant loss of crystallinity that results in some amorphization. The feasibility of the process increases with increasing structural disorder in the parent compound; conversion, however, is incomplete. The ability of the exchanged material to intercalate water in the air is consistent with the formation of an Li-Mn-O compound that retains the layered framework. Also, the electrochemical data obtained for this material as cathode in lithium cells are consistent with retention of the layer structure and exclude a potential spinet transition due to the ion-exchange reaction. However, the cycling properties of cells made from these layered compounds are quite modest, probably because of the strong structural disorder induced by the lithium reaction. (C) 2003 Elsevier Inc. All rights reserved.