The Effect of Internal Stress and Oxygen Non-Stoichiometry on Phase Transformations in Battery Cathodes

In battery electrode materials, phase transformations during Li insertion and removal generally lead to volume changes.  These can lead to localized stresses that contribute directly to the degradation of the active material.  We have employed thin V₂O₅ films as model cathode materials, to systematically investigate relationships between stress, phase transformations, and degradation.  To directly probe the impact of stress, processing conditions were controlled to vary the initial stress state over a wide range (while maintaining similar grain structures).  All of these investigations employed precise in situ stress measurements, along with x-ray diffraction and detailed electron microscopy studies.  The experimental data was then compared to a  thermodynamic model that takes into account the impact of initial and lithiation induced stresses.  The experiments and analysis reveal that stress in the electrode can significantly alter the voltage plateaus associated with two phase equillibria.