  Charge lost per unit surface area of a silicon electrode due to the formation
of solid-electrolyte-interphase (SEI) layer during initial lithiation was
quantified, and the species that constitute this layer were identified. Coin
cells made with Si thin-film electrodes were subjected to a combination of
galvanostatic and potentiostatic lithiation and delithiation cycles to
accurately measure the capacity lost to SEI-layer formation. While the planar
geometry of amorphous thin films allows accurate calculation of surface area,
creation of additional surface by cracking was prevented by minimizing the
thickness of the Si film. The cycled electrodes were analyzed with X-ray
photoelectron spectroscopy to characterize the composition of the SEI layer.
The charge lost due to SEI formation measured from coin cell experiments was
found to be in good agreement with the first-cycle capacity loss during the
initial lithiation of a Si (100) crystal with planar geometry. The methodology
presented in this work is expected to provide a useful practical tool for
battery-material developers in estimating the expected capacity loss due to
first cycle SEI-layer formation and in choosing an appropriate particle size
distribution that balances mechanical integrity and the first cycle capacity
loss in large volume expansion electrodes for lithium-ion batteries.
