Lithium Intercalation into Nanostructured Films Based on Oxides of Tin and Titanium

The lithium intercalation into nanostructured films of mixed tin and titanium oxides is studied. X-ray diffraction and Moessbauer spectroscopy analyses reveal that films consist of a rutile solid solution (Sn, Ti)O2 and an amorphous tin oxide enriched with Sn2+ ions. The films′ specific capacity during the first cathodic polarization in a 1 M lithium imide solution in dioxolane is 200–700 mA h/g, of which nearly one half is the irreversible capacity. During the second cycle, the latter is ∼15% of that in the first cycle. As the films are thin (<1 μm), their capacity does not depend on the current density at 1–80 mA/g. During the electrode cycling, the capacity decreases by 2 mA h/g each cycle. The effective lithium diffusion coefficient, determined by a pulsed galvanostatic method, is ∼ 10–11 cm2/s; it slightly increases with the film lithiation. During the first cycle, the amorphous phase of oxides is reduced to tin metal, the solid solution (Sn, Ti)O2 decomposes, SnO2 disperses to become an x-ray amorphous phase, and TiO2 precipitates as a rutile phase. Lithium reversibly incorporates into the tin metal, yielding Li y Sn, and into a disperse SnO2 phase, yielding Li x SnO2.