Gradient Mg and Uniform Ti Co-Doping Suppresses Jahn-Teller Effect in LMFP via Optimized Ion-Transport Kinetics and Interfacial Reactions.

Abstract

LiMn0.6Fe0.4PO4 (LMFP), an olivine-type cathode material, is gaining attention in high-energy-density lithium-ion batteries due to its high operating voltage and cost-effectiveness. However, its practical use is limited by slow Li+ diffusion, poor electronic conductivity, and structural degradation caused by Jahn-Teller distortion from Mn3+. To tackle these challenges, we have developed a dry-and-wet synthesis method to produce Mg/Ti co-doped LMFP (Mg/Ti-LMFP). This approach ensures uniform Ti4+ doping at Fe sites and gradient Mg2+ doping at Li sites. Ti4+ strengthens the structural stability by forming M─O bonds, reducing Jahn-Teller distortion. Additionally, surface-enriched Mg2+ creates a protective layer, preventing manganese dissolution and electrolyte decomposition. The optimized structure and chemistry enhance Li+ transport kinetics, stability, electronic conductivity, and cycling durability. Mg/Ti-LMFP demonstrates 88.7% capacity retention after 200 cycles at 1C (25°C) and 88.2% after 100 cycles at 1C (55°C). This study lays a solid foundation for designing high-performance co-doped olivine-type cathode materials, guiding the development of future energy storage solutions.