Atomic-Scale Characterization of Microscale Battery Particles Enabled by a High Throughput Focused Ion Beam Milling Technique

The cathode materials in lithium-ion batteries (LIBs) require improvements to address issues such as surface degradation, short circuiting, and the formation of dendrites. One such method for addressing these issues is using surface coatings. Coatings can be sought to improve the durability of cathode materials, but the characterization of the uniformity and stability of the coating is important to assess the performance and lifetime of these materials. For microscale particles there are, however, challenges associated with characterizing their surface modifications by transmission electron microscopy (TEM) techniques due to the size of these particles. Often, techniques such as focused ion beam (FIB) assisted lift-out can be used to prepare thin cross-sections to enable TEM analysis, but these techniques are very time consuming and have a relatively low throughput. The work outlined herein demonstrates a FIB technique with a direct support of microscale cathode materials on a TEM grid that increases sample throughput and reduces the processing time by 60 to 80% (i.e., from >5 h to ~1.5 h). The demonstrated workflow incorporates an air-liquid particle assembly followed by direct particle transfer to a TEM grid, FIB milling and subsequent TEM analysis, which was illustrated with lithium nickel cobalt aluminum oxide particles and lithium manganese nickel oxide particles. These TEM analyses included mapping the elemental composition of cross-sections of the microscale particles using energy dispersive X-ray spectroscopy. The methods developed in this study can be extended to high throughput characterization of additional LIB cathode materials (e.g., new compositions, coating, end of life studies), as well as to other microparticles and their coatings as prepared for a variety of applications.