Low-temperature molten salt ion regeneration strategy towards green and efficient spent graphite recycling†

Recovering electrode materials from spent lithium-ion batteries (LIBs) is increasingly valued for resource conservation and environmental protection. Graphite is the dominant anode material for commercial LIBs. However, the spent graphite (SG) is often discarded or incinerated due to its low economic value, complexity of separation, and structural damage by extended use. This study demonstrates a green and efficient method to regenerate spent graphite by a molten salt ion-assisted thermal treatment in air atmosphere, from which a MSG sample can be obtained. During the thermal treatment, residual metal ions from the SG are substantially removed due to the rapid ion migration process, atomic-level mixing and high solubility in the molten salt environment. Meanwhile, structural imperfections in the sp³-hybridized carbons of graphite and the attached amorphous carbons are repaired by the low temperature oxidation process. Interestingly, abundant nanochannels and CO bonds are introduced, which facilitate the intercalation/deintercalation process of Li⁺ and provide increased active sites for lithium storage. Thus, the MSG sample demonstrated a significant improvement as an anode material for LIBs compared with commercial graphite (CG) and conventionally processed graphite (CPG). A high discharge capacity of up to 427.1 mA h g⁻¹ at 0.1 C could be delivered for the MSG sample, representing an increment of 141.4 mA h g⁻¹ compared with SG. Even at 2.0 C, a reversible capacity of 200.2 mA h g⁻¹ after 1000 cycles can be achieved for the MSG. This work offers a green and feasible approach for recycling SG materials, alleviating resource pressure and environmental hazards while being suitable for industrial applications.