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)O-2 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 similar to15% of that in the first cycle. As the films are thin (<1 mum), 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 similar to 10-11 cm(2)/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)O-2 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 LiySn, and into a disperse SnO2 phase, yielding LixSnO2.