Dual‐Salt Carbothermal Shock Strategy Enabling Ultrafast and Sustainable Regeneration of Spent LiFePO 4 Cathode Materials

ABSTRACT Degradation in spent LiFePO 4 (SLFP) primarily stems from lithium loss, leading to lithium vacancy (Li v ) and Fe Li antisite defects, which are typically detrimental to performance. Conventional single‐salt lithium supplementation is time‐consuming and fails to fully address these structural defects. Herein, we present a dual‐salt carbothermal shock (CTS) using NaI and LiI to in situ repair the Li v with both Li + and Na + ions within seconds, yielding a Na + ‐pinned regenerated LFP (Na‐RLFP). Microstructural analysis and density functional theory (DFT) calculations reveal that the Na + ‐pinned LFP structure induces a controlled lattice expansion, facilitating a deeper Li replenishment within the lattice, while simultaneously lowering the Fe migration energy, thereby further reducing Fe Li antisite defects during the regeneration process. In cycling, the incorporated Na + stabilizes the framework and strengthens the Fe─O and P─O bonds, preserving the overall LFP integrity and enhancing Li + migration, thereby improving electrochemical performance. The resultant Na‐RLFP cathode exhibits exceptional cycling stability with retention of 92.8% at 3 C after 500 cycles in coin cell. Notably, it achieves 95% capacity retention after 100 cycles at 0.5 C in an Ah‐level pouch cell. This work provides an ultrafast, energy‐efficient, and scalable pathway to regenerate spent LFP cathodes, advancing the lithium‐ion battery recycling technologies.