Inhibiting Manganese Dissolution in LiFe0.4Mn0.6PO4 Through Synergistic Effect of Ti-Doping and LiTiOPO4-Coating

Lithium iron manganese phosphate (LiFe_0.4Mn_0.6PO₄, LFMP) cathodes offer higher energy density than LiFePO₄ but face challenges with poor cycle stability, primarily due to severe manganese dissolution caused by Jahn-Teller distortion, phase transition stress, and electrolyte corrosion. This study proposes a dual Ti-modification strategy combining Ti-doping and LiTiOPO₄ (LTOP) coating to address these challenges. The Ti-doped LFMP@C@LTOP (LFMP-Ti5) was synthesized via a scalable spray-drying method. Ti-doping reduces octahedral distortion, alleviates lattice misfit during phase transitions, and enhances lithium-ion diffusion. Meanwhile, the LTOP coating suppresses Mn dissolution by shielding the cathode from interfacial side reactions. Electrochemical tests demonstrate that LFMP-Ti5 retains capacity of 92.4% after 900 cycles at 1C (room temperature) and 99.6% after 300 cycles at 45°C, outperforming unmodified LFMP (84.5% and 94.0%, respectively). Structural and spectroscopic analyses confirm reduced Mn dissolution (0.79% in LFMP-Ti5 vs. 5.47% in LFMP), minimal lattice volume change (−0.11% vs. −0.93%), reduced lattice volume misfits (6.2% vs. 6.7%), and suppressed Jahn-Teller distortion in charged states. The synergistic Ti-doping and LTOP-coating strategy effectively stabilizes the LFMP structure, and the practical usability of LFMP-Ti5 is validated by the excellent performance in pouch cells.