Synergistic V–Ti–F co-doping strategy for high-performance and long-cycling LiMn0.6Fe0.4PO4 cathodes

Abstract

LiMn_xFe_1−xPO₄ (LMFP) olivine cathodes exhibit high voltage platforms and cost efficiency but suffer from intrinsic limitations including low ionic conductivity, Jahn–Teller distortion, Li/Fe antisite defects, and transition metal dissolution. To address these challenges, we propose a synergistic V–Ti–F co-doping strategy is developed to enhance Li⁺ transport and structural stability. The materials were synthesized via an oxalate-assisted coprecipitation method combined with solid-state annealing, and the correlation between multi-component doping and the material's structural and electrochemical properties was systematically investigated. Structural analyses reveal that V³⁺ incorporates into the Mn/Fe sites while Ti⁴⁺ substitutes Li⁺, collectively narrowing Li⁺ diffusion paths. To mitigate cation doping-induced instability, F⁻ is introduced to partially replace O²⁻, reinforcing PO₄ tetrahedra, suppressing Li–Fe antisite defects, and alleviating Jahn–Teller effects. Additionally, residual F⁻ forms C–F bonds within the carbon coating, improving HF resistance. The optimized cathode exhibits a high initial capacity of 153.5 mA h g⁻¹ at 1C with minimal decay over 200 cycles, and delivers 144.7 mA h g⁻¹ even at 5C. This work demonstrates an effective doping strategy for developing long-life LMFP cathodes, highlighting their potential in sustainable energy storage systems.