Yvan Teddy Chegang Kwebou, PhD
Y T. Chegang Kwebou1, K.E. Waters1, O. Kokkilic1
1Department of Mining and Materials Engineering - McGill University, Montreal, Quebec, Canada
Graphite, a critical material for lithium-ion battery (LIB) anodes, is often overlooked in recycling processes and typically downcycled as a reductant in metallurgical slag, where its economic potential is underutilized. However, with proper dismantling to separate the anode from cathode components, spent graphite can be recycled into high-purity material suitable for reuse in battery applications. This study presents a comprehensive three-stage recycling process designed to recover and regenerate high-purity graphite, emphasizing its economic and environmental value.
The first stage involves physical separation, leveraging shaking table stratification and Falcon centrifugal concentration to remove mechanically adherent metallic impurities, primarily copper and aluminum, as well as other contaminants from battery casing materials. These processes efficiently isolate graphite-rich fractions, significantly reducing the metallic impurity load before subsequent treatment.
The second stage employs phosphoric acid (H₃PO₄) leaching to dissolve residual metallic and ionic impurities embedded within the graphite structure. Key impurities targeted include lithium ions intercalated within the graphite lattice (derived from cathode precursors), fluorine ions from the electrolyte and solid electrolyte interface (SEI) layer, and other embedded ions. The mechanism involves protonation and complexation, whereby H₃PO₄ dissociates into H₂PO₄⁻, HPO₄²⁻, and PO₄³⁻ ions, which disrupt metal-carbon bonds and stabilize impurities in soluble phosphate complexes. Advanced characterization techniques such as ICP-OES, XRD, SEM-EDS, and XPS confirmed the significant reduction of impurity levels to below 0.1 ppm after leaching.
The final stage, graphitization, restores the crystalline structure of the graphite. Initial analysis revealed a disordered graphitic structure with increased d-spacing, indicative of structural degradation. High-temperature heat treatment reordered the lattice, reducing d-spacing to 0.335 nm, characteristic of high-purity graphite. These structural improvements were verified using XRD and Raman spectroscopy, which demonstrated reduced defect intensity and enhanced graphitic crystallinity.
This multi-step process not only recovers graphite with purity levels exceeding 99.8% but also enhances its structural and electrochemical properties, making it suitable for LIB applications. By integrating physical separation, selective chemical leaching, and thermal graphitization, the study showcases a scalable and environmentally sustainable pathway for recycling graphite. This approach highlights the untapped potential of graphite recovery, reducing dependency on virgin materials and supporting the transition to a circular economy for critical battery components