Raman investigation on thin-film electrodes of a-C:Li

Amorphous carbon films, deposited via radio frequency magnetron sputtering, have been electrochemically intercalated with lithium to study their possible application as anodes for rechargeable Li microbatteries. Various concentrations of intercalated lithium have been obtained by using galvanostatic and potentiostatic methods. After preliminary examinations by optical microscopy and by optical absorption measurement, a comparative Raman spectroscopy characterization of the films has been performed with excitation wavelengths ranging from 676.4 to 457.9 nm, to follow resonance effects. A study is made on the Raman spectral shape and its excitation wavelength dependence for the film samples with different Li concentrations. A moderate graphitization process of a-C films after intercalation results from this analysis, The Raman spectral changes induced by Li insertion ion not reverse after further de-intercalation cycles, and this fact is discussed in connection to the observed electrochemical reversibility of the a-C:Li electrodes.