Upcycling Spent LiFePO ₄ : Precisely Fe‐Sites Doped by Ti‐Atoms with Expanded Li‐Diffusion Channels Toward High Capacity

Abstract Direct regeneration of spent LiFePO ₄ (SLFP) is promising but faces challenges like inferior crystal channel and low intrinsic conductivity. Hopefully, Ti‐ions doping is proved to enhance the electrochemical performance of LFP. However, due to the similar chemical environments of Fe and Li in LFP, uncontrollable doping behavior will be caused by co‐doping of Fe/Li sites. Therefore, assisted by the Fe/Li‐vacancies in spent LFP, the method of filling Li‐site defects first and then occupying Fe‐site defects with Ti ⁴⁺ is carried to solve the problem. Inspired by the changeable size of Fe‐vacancies, LiFePO ₄ can be oxidized to Li ₃ Fe ₂ (PO ₄ ) ₃ during oxidation, generating Fe‐vacancies that are too small to be occupied by Li ⁺ . Therefore, Li‐site defects can be repaired preferably by lithium salt, which introduced during oxidation process, avoiding Li ⁺ to occupy Fe‐vacancies. Moreover, without the influence of Li‐site defects, Ti⁴⁺ will selectively occupied Fe‐site defects, introducing additional carriers to enhance conductivity. As the cathode of LIBs cathode, the sample with 2% optimized Ti content delivered a capacity of 155.5 mAh g ⁻¹ at 1.0 C, maintaining 90.3% capacity after 1000 cycles. This work is expected to provide guidance for the LiFePO ₄ recovering and shed light on the development orientation in the future.