In-situ Conversion of Graphite into Graphene Quantum Dots (GQDs) towards Upcycling of Spent Lithium-ion Batteries

Abstract

The rapid growth of lithium-ion batteries (LIBs) has created critical environmental and resource management challenges, particularly due to the underutilization of spent graphite (SG) anodes. Herein, we develop a defect-activated upcycling strategy that transforms SG into high-value spent graphene quantum dots (SGQDs) by harnessing its electrochemical cycling-induced multiscale defects. These native imperfections, such as lattice vacancies, interlayer expansion, and SEI residues, serve as reactive sites that promote uniform exfoliation and oxidation during the modified Hummers process. This facilitates the production of spent graphene oxide (SGO) with enhanced oxidation degree and effective retention of defect structures. Subsequent hydrothermal treatment yields ultrasmall SGQDs with high crystallinity, excitation-independent emission, and superior fluorescence quantum yield and lifetime, outperforming counterparts derived from pristine commercial graphite. Notably, the SGQDs exhibit excellent environmental tolerance, including strong salt/pH stability, and demonstrate high sensitivity and selectivity toward metal ions such as Al³⁺ and Fe³⁺. A comprehensive life cycle analysis (LCA) confirms that this upcycling approach reduces energy and greenhouse gas emissions by over 70% while generating substantial economic value. This study introduces a scalable, defect-guided conversion pathway for spent graphite, offering new insights into defect engineering and enabling sustainable, high-performance nanomaterial production from battery waste.