Dual-loop upcycling of spent LiFePO4: defect inheritance enables durable and fast-charging sodium-ion batteries

ion de-/intercalation, achieving 80% state-of-charge within 6 min and retaining 82.9% capacity after 4000 cycles at a high rate of 10 C. The proposed dual-loop upcycling model further enhances economic returns by 65% and reduces environmental footprint by 29%. This work pioneers a sustainable paradigm that transforms degradation mechanisms of LIBs into foundational design strategies for next-generation batteries.