Determination of the chemical diffusion coefficient of Li-ions in carbon-rich silicon oxycarbide anodes by electro-analytical methods

The diffusion coefficient of Li-ions (DLi+) within carbon-rich silicon-oxycarbide ceramic anodes of specific chemical composition SiO0.95C3.72 is determined by potentiostatic and galvanostatic intermittent titration technique (PITT, GITT) and electrochemical impedance spectroscopy (EIS). The estimated values for DLi+ range between 10−9 and 10−11 cm2 s−1, dependent on the applied method. The observed variation of DLi+ is in a comparable range as reported for disordered carbons, well reflecting the Li-ion storage in the segregated free carbon phase in the amount of about 43 wt-% within the SiOC microstructure. However, in contrast to graphite and disordered carbons, the diffusion coefficient of lithium within carbon-rich SiOC is less potential dependent. This feature is discussed with respect to the particular morphology of the free carbon phase.