Abstract

In the effort to mitigate climate change, the transition from traditional petroleum-based engines to electric motors has accelerated the adoption of lithium-ion batteries (LIBs). Although this trend has contributed to reducing greenhouse gas emissions, it has also introduced new challenges. The rapid growth in LIB production has led to stockpiles of end-of-life or scrap batteries, raising concerns about secondary pollution and resource scarcity.

Battery recycling has emerged as a promising avenue to address these concerns. It would allow for the reduction of waste while also recovering valuable minerals such as cobalt, nickel, and lithium. Despite its appeal, current recycling practices face economic and environmental hurdles. Pyrometallurgical processes require high energy input and produce significant greenhouse gases due to binder and electrolyte vaporization, as well as graphite burning. On the other hand, hydrometallurgical pathways rely on large quantities of solvents, generating large volumes of effluent. One culprit for these issues is graphite. Although graphite has limited financial value in recycling streams, its presence destabilizes temperature gradients in pyrometallurgical furnaces, causes process hotspots, releases carbon dioxide, and reduces leaching efficiency in hydrometallurgical circuits. These downstream complications increase processing costs and environmental emissions.

My research introduces an innovative approach to selectively remove a portion of the graphite from industrial black mass using electrostatic charging and separation. Recycled battery feedstock undergoes contact electrification through a pneumatic conveying line due to particle-particle and particle-wall contacts. The charged particles are conveyed to a cyclone, which dissipates their kinetic energy, allowing them to free-fall into an electrostatic separator. Due to graphite’s conductive nature, it dissipates charge through the conductive conveying line. In contrast, insulating metal oxides retain their acquired charges. This charge discrepancy allows for the partial separation of graphite, thereby enhancing the quality of the feedstock. Results from preliminary testing will be presented for synthetic and real waste battery material to demonstrate the separation performance efficiency of the new proposed technique.

The implications of this work are both environmental and economic. The removal of graphite in the pyrometallurgical pathway allows for a less energy intensive process, less greenhouse gas production, and a more stable process. The hydrometallurgical process, it allows for a lower leaching time, enhancing process throughput and minimizing process waste.