Influence of substitution on the structure and electrochemistry of layered manganese oxides
Layered substituted lithium manganese oxides were prepared by ion-exchange of compounds with the nominal composition Na0.7MnO2 or Na0.7Mn0.89M0.11O2, (where M = Fe, Co, Ni, Cu, Zn, Li, or Al) and were characterized structurally and electrochemically. The sodium-containing materials have P2 stacking or are P2/P3 intergrowths, whereas the lithiated analogues have O2 or stacking faulted O2/O3 structures. Compounds with O3 components exhibit higher capacity (or faster intercalation kinetics) than the pure O2 materials. Neither O2 nor, surprisingly, O2/O3 structures converted to spinel upon repeated charging in lithium cells to high voltages, for sixty or more cycles. The results presented herein suggest that it might be possible to design an electrode with an acceptable compromise between the phase stability of the O2 structure and the higher capacity (or better rate capability) of O3 compounds by manipulating the relative amounts and distributions of these two phases in intergrowth structures.