First cycle voltage profiles for Si-CNT anodes are shown in
Figure 1. In Figure 1a, the Si loading is 36% Si w/w,
and the CE is only 58% due to the high surface area of the Si and
CNT current collector. The large voltage plateau that results from
SEI formation during the first cycle lithium insertion is observed at
∼0.8−0.9 V versus Li/Li+. As a result, the lithium insertion capacity
is 2498 mAh/g, whereas the extraction capacity is only 1459 mAh/g.
At a higher Si loading of 69% Si w/w, the surface area of the electrode is
reduced, which improves the CE to 79%.