Failure characterization and regeneration mechanisms of spent graphite anodes from lithium-ion batteries.

The large-scale application of lithium-ion batteries has generated a massive volume of decommissioned batteries, creating urgent demand for the efficient recycling and reuse of key electrode materials. Compared to cathode materials, graphite anodes occupy a higher mass percentage in batteries, yet they are rarely recycled due to low added value, inconsistent regeneration performance, and high energy consumption.

Traditional methods for regenerating spent graphite primarily include acid leaching, high-temperature heat treatment, and catalytic graphitization. While these methods can remove surface residues, improve crystallinity, and restore electrochemical performance to some extent, they all rely on bulk structural repair and lack targeted regulation for the deep structural defects formed during cycling.

The performance degradation of spent graphite does not stem solely from surface SEI residue, inorganic impurities, or a decline in the degree of graphitization. The long-term lithium-ion intercalation and deintercalation processes induce local stress accumulation, C–C bond distortion, and carbon skeleton reconstruction, which generate topological defects such as carbon vacancies and quasi-sp³-C.

These defects disrupt the intra-layer conjugated structure of graphite, hindering electron transport and reversible lithium-ion intercalation/deintercalation, making them a critical limiting factor in the upcycling and regeneration of spent graphite. Therefore, identifying the atomic-scale failure characteristics of spent graphite and establishing a defect-selective repair method represents a key scientific challenge for achieving its high-value regeneration.

To address these issues, the research team led by professors Yang Guorui, Ding Shujiang, and Xi Kai from Xi'an Jiaotong University (XJTU) focused on the atomic-scale defect structures of spent graphite. They identified carbon vacancies and quasi-sp³-C topological defects as key signatures of structural degradation and proposed a synergistic regeneration strategy coupling electrothermal fields with molten salt catalysis.

In this approach, a CoCl2 molten salt provides an excellent interface contact and catalytic environment. The electrothermal coupling field generated by flash Joule heating enhances the interaction between cobalt and the defect sites, achieving precise defect targeting and boosting charge transfer.

This causes electrons to inject from the Co–3d orbitals into the π* antibonding orbitals of the quasi-sp³-C, triggering bond cleavage. At the same time, electromigration and thermal driving forces work in tandem to promote the migration of carbon atoms toward the defects, reconstructing them into sp²-C.

Consequently, this method achieves second-scale topological defect conversion and upcycling regeneration, while delivering beneficial outcomes such as impurity removal, residual stress relief, and easy recovery of transition metals.

The regenerated graphite exhibits outstanding electrochemical performance, delivering a stable specific discharge capacity of 388 mAh g^-1 at a current density of 0.1 A g^-1. Even at a higher current density of 1 A g^-1, it maintains a capacity of 320 mAh g^-1 and cycles stably for 1,000 cycles.

Compared with traditional calcination regeneration methods, this technique reduces costs, energy consumption, and pollutant emissions by more than 77 percent, demonstrating significant economic and environmental advantages.

The research findings have been published in the internationally renowned journal Angewandte Chemie International Edition under the title Electrothermal Coupling Enables Defect-Targeted Topological Repair for Rapid Graphite Upcycling.