Direct Regeneration of Spent LiFePO 4 Using Methionine for Defect Repair and N/S‐Doped Interface Construction

ABSTRACT The coming wave of end‐of‐life electric vehicles presents a formidable challenge for the recycling of spent Li‐ion batteries, particularly those with LiFePO 4 cathodes. The degradation of the LiFePO 4 cathode is primarily attributed to Li loss‐induced lattice defects and the formation of Fe(III) phase. Traditional recycling methods are often plagued by high energy consumption, environmental pollution, and low economic value. Herein, we propose a targeted direct regeneration strategy using methionine as a multifunctional reducing agent to simultaneously repair bulk crystal defects and construct a N/S‐doped interface. Methionine acts as an efficient reductant, facilitating the reduction of Fe(III) to Fe(II) and the elimination of Fe‐Li anti‐site defects, thereby reconstructing rapid the Li + diffusion pathways. Simultaneously, it can serve as a single‐source precursor for in situ formation of a N/S‐doped carbon coating during subsequent annealing. This multifunctional interface not only significantly enhances electronic conductivity but also stabilizes the crystal structure. As a result, the regenerated LiFePO 4 (R‐LFP) exhibits a high discharge capacity of 150.76 mAh g −1 at 1.0 C and outstanding cycling stability with >87% capacity retention after 800 cycles, a performance comparable to commercial LFP. This work provides an efficient and sustainable solution for the upcycling of spent Li‐ion battery cathodes.