Correlative Microscopy-Based Approach for Analyzing Microscopic Impurities in Carbon Black for Lithium-Ion Battery Applications

Abstract

A novel method based on correlative microscopy for analyzing metal-rich particulate impurities randomly distributed in large volumes of carbon black powder is described here. Approximately 5 g of carbon black of tap density of 0.075 g cm−3 was used. The powder was encapsulated in epoxy and a combination of 3D X-ray computed tomography (X-CT), laser/ion beam milling and energy dispersive X-ray spectroscopy (EDS) was used to locate and analyze particles of interest. The locations of impurities were identified using X-CT and a focused ion beam (FIB) system with ion and laser beam milling capabilities was then used to analyze regions of interest in the encapsulated sample. The use of a nanosecond pulsed laser for milling allowed for enhanced material removal rates of up to 3 × 105 μm3 s−1. Finally, scanning electron microscopy (SEM) and EDS were used to image and analyze the composition of the exposed particles. This correlative workflow is shown to be capable of providing detailed spatial, morphological and compositional information about large metal-rich impurities in a carbon black product or a device with carbon black as additives, which may be used for identifying the source of impurities or predicting failure modes in the device.