High-value utilization of graphite electrodes in spent lithium-ion batteries: From 3D waste graphite to 2D graphene oxide

• SEI film, electrolyte and binders remain on the surface of waste graphite. • Li 2 CO 3 and CuO have invaded the crystal structure of waste graphite. • Modified Hummers method can remove impurities without secondary pollution. • Graphite in spent LIBs can be prepared directly into 2D graphene oxide. The graphite electrodes of spent lithium-ion batteries (LIBs) have a good crystalline composition and layered structure, and the recovery potential is promising. However, the internal and external surfaces of the waste graphite are often polluted with various organic and inorganic impurities, which seriously restrict its high-value utilization. Herein, the microstructure and surface analysis of waste graphite at variable scales were carried out systematically to reveal the types and occurrence status of impurities and their influence on the preparation of graphene oxide (GO) using a modified Hummers method. The results show that the graphite surface contaminants are polyvinylidene fluoride binder, LiPF 6 electrolyte and LiF residue from the solid electrolyte interface, while residual lithium (Li 2 CO 3 ) and CuO were found to have invaded the crystal structure of graphite. Fortunately, the modified Hummers method can effectively remove these complicated associated impurities and prevent their re-contamination on the GO surface. More importantly, the modified Hummers method can not only destroy the longitudinal molecular bonds between graphite layers, but also splice them horizontally to form 2D GO, which is verified by high-resolution transmission electron microscope (HR-TEM) images. This paper provides theoretical support and practical guidance for the high-value utilization of waste graphite in spent LIBs.