Site Selection of Niobium-Doped LiMn_0.6Fe_0.4PO₄ and Effect on Electrochemical Properties

Ion doping is one of the primary means to enhance the properties of phosphate cathode materials. In this document, the DFT+U method is used to determine the selection of ion doping sites from the energy band perspective and density of state. Further, different contents of niobium-doped LiMn_0.6Fe_0.4-xNb_xPO₄(0≤x≤0.2) were obtained by the solid-phase method and synthesized samples were also measured and analyzed. The results show that the ion-doped modification principle is the introduction of impurity bands between the band gaps, and transition metal ions are more inclined to occupy metal sites. LiMn_0.6Fe_0.25Nb_0.15PO₄ possesses an excellent electrochemical performance, exhibiting a specific discharge capacity of 156.7 mAh g⁻¹ at 0.2 C. EIS proves that the electrochemical impedance of the sample is significantly reduced, and the lithium-ion diffusion coefficient increase after an appropriate amount of doping.