  Real-time stress evolution in a graphite-based lithium-ion battery
negative-electrode during electrolyte wetting and electrochemical cycling is
measured through wafer-curvature method. Upon electrolyte addition, the
composite electrode rapidly develops compressive stress of the order of 1-2 MPa
due to binder swelling; upon continued exposure, the stress continues to evolve
towards an apparent plateau. During electrochemical intercalation at a slow
rate, the compressive stress increases with the electrode's state-of-charge,
reaching a maximum value of 10 - 12 MPa. There appears to be an approximate
correlation between the rate of stress rise and the staging behavior of the
lithiated graphite. De-intercalation at a slow rate results in a similar linear
decrease in electrode stress. Tensile stress of a few MPa develops at the end
of deintercalation in the first few cycles, after which the electrode remains
under compressive stress only. Although higher peak stresses are seen at high
C-rates, the dependence appears to be relatively weak (up to 5C). These
measurements reveal, for the first time, the nature of stress evolution in
practical lithium-ion-battery electrodes and provide useful data to quantify
the driving force for mechanical damage that accrues in composite electrodes
upon repeated cycling. While the reported results can serve as reference for
calibrating theoretical and computational models to predict electrode stress
and damage evolution, the methodology demonstrated can be used to measure
stresses and characterize fatigue damage in any composite lithium-ion-battery
electrode as well as optimize its microstructure to mitigate stress-related
damage mechanisms.
