Meaning
Two dimensional interruptions in the periodic arrangement of atoms within a crystal lattice represent this structural feature. Presence of planar defects like grain boundaries or stacking faults alters the mechanical and electrical properties of a material. These boundaries act as sites for energy storage or chemical reactivity.
In battery materials, they can influence the path of ion migration.
Structural Integrity
Mechanical strength of a material is often determined by the density and type of internal interfaces. While planar defects can strengthen an alloy by pinning dislocations, they may also serve as initiation points for cracks. The energy associated with these interfaces governs the grain growth during thermal processing.
Ionic Barrier
Resistance to the movement of charge carriers often increases at the junction between two crystal orientations. High concentrations of planar defects in a cathode particle can impede the diffusion of lithium. This resistance leads to localized heating and potential degradation of the surrounding electrolyte.
Engineering the microstructure to minimize these barriers improves the rate performance of the cell. High resolution electron microscopy allows for the direct observation of these boundaries.
Lattice Distortion
Misalignment of atomic planes creates strain fields that extend into the surrounding crystal. Such planar defects can accommodate impurities or dopants that stabilize the structure against phase transitions. These lattice strains directly influence the capacity retention of the battery material during long term cycling.
