Site Selection of Niobium-Doped LiMn0.6Fe0.4PO4 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 LiMn0.6Fe0.4-xNbxPO4(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. LiMn0.6Fe0.25Nb0.15PO4 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.