Lithium-ion conductors of the system LiCo1-xFexO2, preparation and structural investigation

Layered structure oxides of the system NaCo1-xFexO2 were prepared for 0 less than or equal to x less than or equal to 1 by solid-state reaction. Vegard-like behavior was proved for these compounds by X-ray analysis, indicating mixed transition metal layers and sodium layers without cation disorder. By ion-exchange of these compounds in a molten eutectic mixture of LiCI and LiNO3 at 260 degreesC the system LiCo1-xFexO2 was prepared for the whole composition range and characterized by chemical analysis, X-ray diffraction and FTIR spectroscopy. Atomic absorption spectroscopy showed almost complete ion-exchange from sodium to lithium. The members of this system are shown to crystallize, as the sodium compounds, in the rhombohedral space group R(3) over bar m (alpha -NaFeO2-type). X-ray diffraction, considerations based on the intensity ratio R-101 = I-101/I-104 and Rietveld refinement give evidence for increasing cation disorder with increasing iron content, that reaches the value of LiFeO2 (4.5%) already at an iron content of x = 0.4. (C) 2001 Academic Press.