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.
It is important to note that >90−95% of this capacity comes from
the Si rather than the CNT current collector.9 At a higher Si loading
of 69% Si w/w (7.2 mAh/cm2), the surface area of the electrode is
reduced,8 which improves the CE to 79%. Although a large
improvement in CE can be achieved by increasing the Si loading, an
80% CE is still low compared to state-of-the-art materials that have
CE values >90%.