Degradation Phenomena in Silicon/Graphite Electrodes with Varying Silicon Content

The degradation phenomena of Silicon/Graphite electrodes and the effect of FEC as electrolyte additive was investigated through galvanostatic cycling, XPS analyses and SEM cross section analyses. To understand the direct influence of silicon on the electrode degradation, the silicon amount was varied between 0%–30%. By evaluating the cycling performance and the accumulated capacity loss of the different Si/Gr electrodes (cycled with and without 10 vol-% of FEC), we see that the capacity decay can be distinguished into two phenomena, where one is independent of the Si/Gr ratio while the other one depends on the Si content. As expected, adding FEC improves the cell performance and minimizes the capacity decay. Combing our XPS data and SEM cross section analyses on cycled electrodes, this improvement stems from a thin and flexible SEI including poly(vinyl carbonate) that helps maintaining the overall electrode integrity as we observe less electrode fractures and less pronounced thickness increase. Si/Gr electrodes with 10 and 20% Si content showed very similar accumulated irreversible capacity losses over 100 cycles indicating that with 10 % FEC as electrolyte additive, also higher Si contents could be feasible for future high energy density anodes.