High-Throughput Analysis of Recycled Battery Graphite Using Electron Microscopy

With the push towards an electrified grid, there has been a sharp increase in the number spent lithium-ion batteries. Specifically, earlier generation electric vehicles (EVs) are being improved upon and replaced by newer generation EVs with higher performing batteries. This highlights the need to develop environmentally friendly and low-cost methods to recycle battery materials and feed them back into a circular energy economy. Among these materials, graphite is a key component for anodes. Although it has been historically viewed as a waste product for end-of-life batteries due to its low cost, the massive scale increase in energy storage requirements has created a need to circularize every component of battery materials. Due to leaps in graphite optimization since the dawn of batteries, the morphology of graphite in early generation batteries does not resemble state of the art anodes, as spheroidized particles are replacing early-generation flake-like particles.

This project seeks to optimize the graphite upcycling process by developing methods to convert spent flake-like graphite particles into high performing spheroidized graphite anodes at scale. Advanced microscopic techniques are used to analyze reclaimed battery anode graphite that has been through a series of mechanical tuning processes. High throughput scanning electron microscopy (SEM) imaging is used to capture large sample sizes of particles and extract data about their external properties, while focused-ion beam milling is used to capture data about internal particle properties. These properties are assessed for thousands of particles per sample using a machine-learning program that segments and analyzes SEM images. It is found that a broad range of recycling conditions were able to produce graphite particles with variable size distributions, circularity distributions, and morphological properties that can be compared to optimized spheroidized graphite to further tune recycling processes. The study of internal particle characteristics further revealed the mechanism by which graphite is spheroidized to be the flakes folding in on themselves to form a larger ball. Finally, characteristics within each sample were compared to reveal that particle size is linked to particle circularity, with smaller particles skewing towards greater circularity. In future work, properties of particle size, circularity, and porosity in upcycled graphite can then be linked to cell performance to better inform recycling processes.