  We report real-time average stress measurements on composite silicon
electrodes made with two different binders [Carboxymethyl cellulose (CMC), and
polyvinylidene fluoride (PVDF)] during electrochemical lithiation and
delithiation. During galvanostatic lithiation at very slow rates, the stress in
a CMC-based electrode becomes compressive and increases to 70 MPa, where it
reaches a plateau and increases slowly thereafter with capacity. The PVDF-based
electrode exhibits similar behavior, although with lower peak compressive
stress of about 12 MPa. These initial experiments indicate that the stress
evolution in a Si composite electrode depends strongly on the mechanical
properties of the binder. Stress data obtained from a series of
lithiation/delithiation cycles suggests plasticity induced irreversible shape
changes in contacting Si particles, and as a result, the stress response of the
system during any given lithiation/delithiation cycle depends on the cycling
history of the electrode. While these results constitute the first in-situ
stress measurements on composite Si electrodes during electrochemical cycling,
the diagnostic technique described herein can be used to assess the mechanical
response of a composite electrode made with other active material/binder
combinations.
