Direct regeneration of hard carbon anodes from spent sodium-ion batteries via flash Joule heating

Sodium-ion batteries (SIBs), having been commercialized in 2023, are projected to achieve considerable market penetration in the future. However, owing to the strong similarity in material composition to lithium-ion batteries (LIBs), integrated recycling strategies are essential to ensure both high efficiency and a low environmental footprint. Herein, we report an efficient and environmentally friendly flash Joule heating (FJH) method for regenerating degraded hard carbon anodes. The ultrafast high-temperature treatment induces the thermal decomposition of polymer binders while simultaneously carbonizing the organic components of the solid electrolyte interphase into conductive graphitic carbon coatings and restoring the graphitic lattice order in degraded hard carbon. Notably, the regenerated hard carbon exhibits superior electrical performance relative to new commercial-grade hard carbon, featuring an initial coulombic efficiency of 81%, a reversible capacity of 292.3 mAh g⁻¹ at 0.1 A g⁻¹, a capacity retention of 91% after 350 cycles, and a superb rate capability of 216.9 mAh g⁻¹ at 5 A g⁻¹. These findings demonstrate the viability of FJH in the sustainable and cost-effective regeneration of degraded hard carbon anodes from SIBs.