Recycling of Spent Graphite Anode Materials from Lithium-Ion Batteries

The global transition toward renewable energy and electric vehicles has triggered exponential growth in lithium-ion batteries (LIBs), resulting in a surge of retired batteries. As the predominant anode material in LIBs, graphite accounts for a significant mass proportion of batteries. However, improper disposal of spent graphite (S-Gr) through incineration or landfilling poses severe environmental risks, including particulate emissions and toxic residue release. Recycling S-Gr is critical to alleviating resource shortages, reducing production costs of high-purity graphite (which requires energy-intensive graphitization processes at 2500–3000 ℃), and achieving sustainable development goals. This review focuses on the failure mechanisms, recycling strategies, and reuse pathways of S-Gr, providing key insights for advancing closed-loop battery ecosystems.

The degradation of graphite anodes during LIB cycling originates from multiscale failure mechanisms. Deterioration of the solid electrolyte interphase (SEI) caused by chemical decomposition, mechanical stress, and thermal instability leads to irreversible lithium loss and capacity fade. Concurrently, lithium dendrite growth on graphite surfaces increases internal short-circuit risks, while repeated Li⁺ intercalation/deintercalation induces microcracks and structural collapse of graphite layers. These coupled mechanisms initiate a vicious cycle of performance degradation, highlighting the necessity for tailored recycling approaches.

Current recycling technologies focus on efficient separation and purification of S-Gr. Physical methods (e.g., flotation and sieving) achieve preliminary separation but suffer from impurity retention (purity <73.56%). Innovative techniques such as Fenton reagent-assisted flotation and pyrolysis-ultrasonic synergy enhance recovery efficiency, but face scalability challenges. Hydrometallurgical processes utilizing HCl, H₂SO₄, or organic acids (e.g., citric acid) effectively leach impurities like Li, Al, and Fe but generate corrosive waste. Pyrometallurgical approaches (e.g., inert atmosphere calcination and catalytic graphitization) restore graphite crystallinity but demand high energy consumption (>2600 ℃) and emit hazardous gases. Hybrid strategies combining hydrometallurgical treatment with high-temperature annealing emerge as promising solutions.

Regenerated S-Gr demonstrates versatility in energy storage and functional applications. For secondary batteries, carbon-modified S-Gr via rapid thermal shock or phenolic resin coating exhibits superior performance in LIBs. In sodium/potassium-ion batteries, defect-engineered S-Gr shows enhanced kinetics and stability. Beyond energy storage, S-Gr can be transformed into high-value materials. Advanced applications include graphene production through lithium-intercalation exfoliation and catalytic composites for environmental remediation.

Despite progress, critical challenges persist. The heterogeneity of S-Gr sources (natural, synthetic, or composite graphite) complicates standardized recycling. High costs, toxic emissions (e.g., fluorine), and intensive energy-consuming steps hinder process scalability. Future directions should prioritize intelligent sorting systems, AI-driven process optimization, and green alternatives like bioleaching. Integrating ultrasound, microwave, or electrochemical technologies could streamline processes and reduce energy consumption. Expanding S-Gr applications (e.g., flexible electronics, CO₂ capture, and defect-engineered catalysts) requires interdisciplinary innovation. Addressing these issues will accelerate commercialization of S-Gr recycling technologies, promote sustainable battery ecosystems, and advance global carbon neutrality goals.