Stress Evolution in Lithium-ion Composite Electrodes during Electrochemical Cycling and Resulting Internal Pressures on the Cell Casing

摘要

Composite cathode coatings made of a high energy density layered oxide(Li1.2Ni0.15Mn0.55Co0.1O2, theoretical capacity ~377 mAh/g), polyvinylidenefluoride (PVdF) binder, and electron-conduction additives, were bonded to anelastic substrate. An electrochemical cell, built by pairing the cathode with acapacity-matched graphite anode, was electrochemically cycled and the real-timeaverage stress evolution in the cathode coating was measured using asubstrate-curvature technique. Features in the stress evolution profile showedcorrelations with phase changes in the oxide, thus yielding data complementaryto in situ XRD studies on this material. The stress evolution showed a complexvariation with lithium concentration suggesting that the volume changesassociated with phase transformations in the oxide are not monotonicallyvarying functions of lithium concentration. The peak tensile stress in thecathode during oxide delithiation was approximately 1.5 MPa and the peakcompressive stress during oxide lithiation was about 6 MPa. Stress evolution inthe anode coating was also measured separately using the same technique. Themeasured stresses are used to estimate the internal pressures that develop in acylindrical lithium-ion cell with jelly-roll electrodes.