Dual-Role Phosphorus Species Enable Regeneration of Spent Graphite via Coupled Bulk Doping and Surface Interphase Engineering

With the rapid expansion of electric mobility and large-scale energy storage systems, the high-value regeneration of graphite anodes from retired lithium-ion batteries has attracted increasing attention. The degradation mechanism of graphite anodes involves multiple factors, including bulk structural damage and interfacial deterioration during cycling. However, state-of-the-art regeneration approaches have been restricted to addressing either structural degradation or interfacial instability in isolation, precluding the attainment of desirable electrochemical performance. To circumvent this fundamental limitation, we propose a phytic acid-assisted regeneration strategy for spent graphite anodes. This approach leverages the abundant intrinsic defects and edge sites present in cycled graphite, which serve as preferential reactive sites for subsequent modification. Upon subsequent facile thermal treatment, phosphorus species are incorporated into the graphite matrix, enabling bulk doping-induced structural reconstruction while simultaneously optimizing the surface chemistry and interfacial properties. Comprehensive characterizations reveal that a fraction of the incorporated phosphorus species diffuses into the bulk lattice and promotes structural restoration. These dopants modulate the local electronic structure and bonding configuration, thereby facilitating lithium-ion adsorption and accelerating diffusion kinetics. Meanwhile, the residual phosphorus species at the surface direct interfacial reactions toward the formation of a robust, inorganic-dominated solid electrolyte interphase (SEI) layer enriched with Li x PO y species, which significantly boosts Coulombic efficiency and long-term cycling stability. As a consequence, the revitalized graphite exhibits excellent electrochemical performance, delivering a specific capacity of 378 mAh g –1 after 500 cycles at a current density of 1 C. Moreover, it exhibits good rate capability, maintaining 330 mAh g –1 at 2.0 C. Further kinetic and interfacial analyses reveal that the improved performance is supported by enhanced charge transfer and ion diffusion, along with a stable and uniform interfacial structure. This work provides a simple and promising route for the high-value utilization of spent graphite and the sustainable design of energy storage materials.