A critical revelation of lithium ferromanganese phosphate (LMFP) performance in a Mn-rich cathode for Li-ion batteries using Fe equivalents to occupy a Mn site

Abstract

The modification of a polyanionic positive electrode material LiMnPO₄ by transition metal doping was experimentally studied on the basis of carbon coating in order to address the drawbacks of low electronic conductivity and charge–discharge performance. A hydrothermal procedure was successfully used to create a Li(Mn_1−xFe_x)PO₄/C (x = 0, 1/24, 1/12, 1/8, and 1/4) cathode material, and its performance was evaluated. After comparing the material's electrochemical performance at different doping concentrations, the ideal Fe content was found to be x = 1/4. The Li(Mn_1−xFe_x)PO₄/C sample exhibits excellent electrochemical performance, discharge ability of 141.6 mA h g⁻¹, 100 cycles at 1C rate, capacity retention ratio of 97.88%, and the best kinetic characteristics. First principles calculations showed that the Li(Mn_1−xFe_x)PO₄/C material has the smallest band gap, and the total state density is closest to the Fermi level; thus, more electrons can be used to transition to the conduction band, which is the reason for its excellent discharge ability. The introduction of Fe reduces the ELF function value near the original Mn position and decreases electron localization and the diffusion energy barrier, which is very conducive to electron movement and improves the diffusion kinetics of lithium ions in a doping system.