Synergistic Lattice and Interface Engineering of Ti-Doped LiFe _0.5 Mn _0.5 PO ₄ /C Cathodes from Spent Lithium-Ion Batteries

Olivine-type LiFe0.5Mn0.5PO4 cathodes are attractive for lithium-ion batteries because of their structural stability and safety, yet their practical application is often hindered by limited lithium-ion diffusion and sluggish interfacial charge-transfer kinetics. In this work, Ti-doped LiFe0.5Mn0.5PO4/C composites are regenerated from spent lithium-ion batteries and engineered through the synergistic integration of lattice modulation and interface regulation. Ti4+ substitution induces lattice contraction and improves particle dispersion, while a uniform carbon coating enhances electronic conductivity and interfacial contact. Structural and electrochemical analyses reveal that the combined effects of Ti doping and carbon coating effectively suppress electrode polarization, accelerate lithium-ion transport, and improve reaction kinetics. As a result, the optimized LiFe0.5Mn0.5PO4/C−3%Ti cathode delivers a high reversible capacity of 164.32 mAh g−1 at 0.1 C and exhibits excellent cycling stability, retaining 97.29% of its initial capacity after 100 cycles and 92.12% after 500 cycles at 1 C. This study establishes a clear structure−interface−performance relationship for regenerated olivine phosphate cathodes and provides insights into the design of high-performance electrode materials through interface-engineered doping strategies.