Quantification of single crystallinity in single crystal cathodes for lithium-ion batteries

Abstract

Ni-rich single crystal cathodes (SCCs) are promising candidates for next-generation lithium-ion battery cathode materials. Their micron-sized particles, resembling single crystals, offer potential solutions to structural degradation in conventional Ni-rich cathodes prone to intergranular cracking. Consequently, the level of single crystallization within SCC particles, highly sensitive to synthesis conditions, plays a pivotal role in determining their performance. However, the absence of a quantitative measure for single crystallinity poses a challenge in establishing correlations between SCC performance and their structural characteristics. We introduce an innovative method for quantifying SCC single crystallinity using 4D-STEM-ASTAR in transmission electron microscopy (TEM), which attains sub-degree angular and nanometer spatial resolutions. Our approach utilizes thousands of 3D orientation data points within an SCC particle to assess its overall orientation bias toward specific points. We achieve this by dividing a 3D inverse pole figure into meshes with constant angular distances and determining the pole proportion of the densest mesh while progressively refining mesh size. This yields single crystallinity as a percentile of reasonable magnitude. Importantly, statistical analysis validates its effectiveness in assessing SCC single crystallinity across samples synthesized at various temperatures, revealing significant structural insights. This robust method can be used as a measure for evaluating single crystallinity, which has not been established thus far.