  Composite cathode coatings made of a high energy density layered oxide
(Li1.2Ni0.15Mn0.55Co0.1O2, theoretical capacity ~377 mAh/g), polyvinylidene
fluoride (PVdF) binder, and electron-conduction additives, were bonded to an
elastic substrate. An electrochemical cell, built by pairing the cathode with a
capacity-matched graphite anode, was electrochemically cycled and the real-time
average stress evolution in the cathode coating was measured using a
substrate-curvature technique. Features in the stress evolution profile showed
correlations with phase changes in the oxide, thus yielding data complementary
to in situ XRD studies on this material. The stress evolution showed a complex
variation with lithium concentration suggesting that the volume changes
associated with phase transformations in the oxide are not monotonically
varying functions of lithium concentration. The peak tensile stress in the
cathode during oxide delithiation was approximately 1.5 MPa and the peak
compressive stress during oxide lithiation was about 6 MPa. Stress evolution in
the anode coating was also measured separately using the same technique. The
measured stresses are used to estimate the internal pressures that develop in a
cylindrical lithium-ion cell with jelly-roll electrodes.
