  An in situ study of deformation, fracture, and fatigue behavior of silicon as
a lithium-ion battery electrode material is presented. Thin films (100-200 nm)
of silicon are cycled in a half-cell configuration with lithium metal foil as
counter/reference electrode, with 1M lithium hexafluorophosphate in ethylene
carbonate, diethylene carbonate, dimethyl carbonate solution (1:1:1, wt.%) as
electrolyte. Stress evolution in the Si thin-film electrodes during
electrochemical lithiation and delithiation is measured by monitoring the
substrate curvature using the multi-beam optical sensing method. The stress
measurements have been corrected for contributions from residual stress arising
from sputter-deposition. An indirect method for estimating the potential errors
due to formation of the solid-electrolyte-interphase layer and surface charge
on the stress measurements was presented. The films undergo extensive inelastic
deformation during lithiation and delithiation. The peak compressive stress
during lithiation was 1.48 GPa. The stress data along with the electron
microscopy observations are used to estimate an upper bound fracture resistance
of lithiated Si, which is approximately 9-11 J/m^2. Fracture initiation and
crack density evolution as a function of cycle number is also reported.
