In Situ Transmission Electron Microsopy of Oxide Shell-Induced Pore Formation in (De)lithiated Silicon Nanowires

Silicon
(Si) nanowires with a silicon oxide (SiOx) shell undergoing lithiation and delithiation
were examined by in situ transmission electron microscopy (TEM). Large
pores formed in the nanowires during the delithiation cycle. We found
that the oxide shell constrains the expansion of the Si nanowires
during lithitation and then induces pore formation in the nanowires.
We propose that the SiOx shell prevents the vacancies that result from the loss of lithium
from escaping the Si core, leading to pore nucleation and growth.
It is also possible that the difference in mechanical properties of
the expanding and contracting Si nanowire and SiOx shell contribute to the observed pore formation.
This in situ study reaffirms the need to directly observe structural
changes that occur during cycling in battery materials, especially
when modified by coatings.