Contribution of Ti-Doping to the Cyclic Stability of LiFe0.6Mn0.4PO4/C

Li(Fe0.6Mn0.4)1–xTixPO4/C cathode materials, with x values of 0, 0.01, 0.02, 0.03, and 0.04, were fabricated through a dual-stage synthesis process, incorporating both coprecipitation and high-temperature solid-phase techniques. The composition, microstructure, and surface morphology of these materials were thoroughly characterized using a suite of analytical techniques. These analyses confirmed the successful doping of Ti ions into the olivine lattice, resulting in a decrease in unit cell volume and the formation of an amorphous carbon layer on the particles' surfaces, which also improved particle dispersion. The electrochemical performance of the Li(Fe0.6Mn0.4)1–xTixPO4/C samples was assessed using techniques including constant current charge–discharge testing, cyclic voltammetry, and electrochemical impedance spectroscopy. The findings showed that Ti-doping markedly diminishes potential polarization in these materials and the strong Ti–O coordination suppresses the Jahn–Teller effect of Mn3+, effectively enhancing the stability and lithium-ion diffusion rate of the material. Additionally, density functional theory (DFT) calculations were conducted to assess the impact of Ti-doping on LFMP. The findings reveal that Ti-doping reduces the bandgap of the material and increases the bond length of Li–O, thereby further confirming that Ti-doping can enhance electronic conductivity. Among them, the Li(Fe0.6Mn0.4)1–xTixPO4/C-3%Ti cathode material exhibited the best electrochemical performance. The optimized sample demonstrated a specific discharge capacity of 163.53 mAh·g–1 at 0.1C, accompanied by an initial coulombic efficiency of 93.18%. At 1C, it provided a capacity of 140.59 mAh·g–1, sustaining a capacity retention of 93.58% after 500 cycles, and delivered a discharge capacity of 94.08 mAh·g–1 at 5C.