Systematic evaluation of degradation in waste graphite induced by spent battery recycling processes: Effects of mechanical crushing and thermal treatment

Abstract

As demand for lithium-ion batteries (LIBs) continues to grow, efficient recycling of end-of-life batteries is essential for sustainable resource recovery. While current industrial efforts focus on cathode materials, graphite-despite comprising up to 20 wt% of battery mass-is often neglected due to its low market value and regeneration challenges. However, rising global demand and strategic importance of graphite underscore the need to recycle and reuse this critical material. Yet, the effects of common recycling processes on graphite's structure and performance remain poorly understood. This study systematically evaluates the individual impacts of mechanical milling and air-based thermal treatment on commercial artificial graphite (AG). Ball milling induces crystallite fragmentation, amorphization, and loss of lithium staging behavior, resulting in severe electrochemical degradation. In contrast, thermal treatment up to 800 degrees C preserves bulk crystallinity and staging characteristics but causes surface etching and permanent carbon loss as CO2. These effects are validated by comparing with spent graphite obtained from industrial LFP battery black mass, revealing similar degradation features. High-temperature annealing at 1500 degrees C under inert atmosphere partially restores graphitic order and performance. This work offers valuable insights into degradation pathways of graphite in recycling and high-lights strategies for its effective regeneration.