The recycling and reuse of graphite from spent lithium-ion batteries (LIBs) are increasingly important for resource sustainability, however, the mechanisms governing graphite reusability remain unclear, particularly for natural graphite (NG) and synthetic graphite (SG). In this study, graphite electrode composites were recovered from cycled cylindrical LIBs, and their structural evolution and electrochemical performance were compared systematically. The NG exhibited significant particle cracking during electrode fabrication and cycling, resulting in increased specific surface area and exposure of new basal planes. This led to the expansion of the electrochemically active interface, which enabled the material to maintain a discharge capacity of approximately 350 mAh g−1 despite a slight decrease in the initial coulombic efficiency. In contrast, the SG showed limited particle cracking but accumulated lithium-containing compounds and surface residues that covered the particle surfaces and suppressed the active interface. Consequently, SG exhibited increased charge-transfer resistance and significant capacity fading. These results demonstrate that the reusability of graphite electrodes is fundamentally governed by how cycling-induced structural evolution modifies the effective reaction interface, which is expanded in NG but suppressed in SG, thereby highlighting the need for mechanism-based recycling strategies.
Hideaki Oka (Thu,) studied this question.