Valorization of waste graphite in spent lithium-ion batteries to graphene via modified mechanical exfoliation and the mechanism exploration

Abstract

In the electrodes of spent lithium-ion batteries, graphite, due to its layered structure and crystalline composition, presents significant recyclable value, yet it has not been fully utilized. This study proposes a modified mechanical exfoliation method (MEM), which employs leaching-drying pretreatment to transform waste graphite into two-dimensional graphene. Three drying methods were evaluated, among which freeze drying was found to be the most conducive for exfoliation. Pneumatic drying, being basic and simple, did not exhibit any special effects that benefit exfoliation. XRD results showed that leaching restores the lamellar structure of graphite, with peak intensity ( × 105) increasing from 6.5 to 8.9–10.1. XPS analysis revealed that vacuum roasting drying leads to dehydration condensation of hydroxyl groups between layers, resulting in the obtained graphite having the best dehydration effect and the lowest oxygen content, at only 1.89%, but this enhances interlayer forces, which is counterproductive for exfoliation. In contrast, freeze drying, through the volumetric expansion caused by the freezing of water, disrupts the interlayer forces, achieving an interlayer spacing of 337.5 nm, which facilitates the exfoliation of graphene. This was confirmed by TEM results. This method effectively overcomes the problem of impurity contamination in waste graphite, providing a new approach for the high-value utilization and green recycling of graphite in spent lithium batteries.