A joint experimental and theoretical study on the effect of manganese doping on the structural, electrochemical and physical properties of lithium iron phosphate

Abstract

Mn doped LiFe_1−xMn_xPO₄ (x = 0, 0.01, 0.03, 0.05, 0.07) cathode materials are synthesized by a carbothermal reduction method. The structure, morphology and electrochemical performance of the samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman, and charging–discharging tests. It is found that an appropriate amount of Mn doping did not affect the olivine structure and morphology of LiFePO₄, but greatly improves its electrochemical performance. Especially, the LiFe_0.97Mn_0.03PO₄ sample exhibits the best electrochemical performance, which shows the maximum discharge capacity of 148.2 mA h g⁻¹ at 0.1 C and a capacity retention ratio of 98% after 60 cycles at various rates. Based on first-principles density functional theory (DFT), the lithium ion migration channels, energy band structures, densities of states, and charge density diffusion of LiFePO₄ and LiFe_15/16Mn_1/16PO₄ are calculated to further investigate the influence of Mn doping on the LiFePO₄ lattice. The results prove that the higher lithium ion conduction and electronic conductivity of LiFe_15/16Mn_1/16PO₄ are attributed to Mn doping.