Revealing the role of Mg doping in LiFe0.39Mg0.01Mn0.6PO4/C cathode: Enhanced electrochemical performance from improved electrical conductivity and promoted lithium diffusion kinetics

Based on previous studies, doping of Mg2+ in the lattice can improve the electrochemical properties of cathode materials. This study further investigates the mechanism of Mg2+ doping in LiFe0.4Mn0.6PO4/C cathode material. First-principles calculations discovered that the introduction of Mg2+ into lattice leads to an increase in the amounts of electrons near the Fermi level, with the major contributions from Fe and O elements. Such a result causes a decrease in the band gap from 3.73 eV to 2.99 eV, thereby enhancing electronic conductivity, as confirmed by powder conductivity tests. Rietveld refinements further revealed an increase in the average LiO bond length following Mg2+ doping. The enlarged LiO bond enhances the Li+ diffusion kinetics. It is confirmed by DFT calculation that the migration energy barrier is reduced from 1.007 eV to 0.708 eV and therefore the diffusion coefficient is promoted from 9.48 × 10−15 to 7.83 × 10−14. As a result, the Mg-doped LiFe0.39Mg0.01Mn0.6PO4/C cathode displayed improved electrochemical performance with an initial specific capacity of 158.1 mAh·g−1, capacity retention of 96.3 % after 100 cycles at 0.5C and a reversible capacity of 131.52 mAh·g−1 at a high rate of 5C, indicating high potential for practical application.