Riveting Dislocation Motion: The Inspiring Role of Oxygen Vacancies in the Structural Stability of Ni-Rich Cathode Materials.

Abstract

In Ni-rich cathode materials, dislocation can be generated at the surface of primary grains because of the accumulation of stress fields. The migration of dislocation into grains, accelerating the annihilation of reverse dislocation as well as oxygen loss, is considered as the principal origin of crack nucleation, phase transformation, and consequent fast capacity decay. Thus, reducing the dislocation would be effective for improving cathode stability. Here, we report the inspiring role of oxygen vacancies in blocking and anchoring the dislocation. Specifically, a large number of oxygen vacancies can assemble to form dense dislocation layers at the surface of grains. Thanks to the dislocation interaction mechanism, preformed dense dislocation at the surface can effectively rivet the newly developed dislocation during cycling. Ex situ transmission electron microscopy analysis indicates that the intragranular cracks and phase transformation were hindered by the riveted effect, which in turn improved the structural and cycling stability of the Ni-rich cathode. Overall, this work provides novel crystallographic design and understanding of the enhanced mechanical strength of Ni-rich cathode materials.