Boosting Manganese-Based Phosphate Cathode Performance via Fe or Ni Solid Solution for Lithium-Ion Battery: A First-Principles and Experiment Study

Manganese-based phosphate cathodes of Li-ion batteries possess higher structural stability in the charging–discharging process, making them widely valuable for research. However, poor electron–ion conductivity and weak ion-diffusion ability severely limit their commercial application. In this study, starting from the most basic component and structure design, a new electronic state is formed at the Mn-3d orbital in the band gap of LiMnPO4 through the introduction of Fe and Ni. Fe-d and Ni-d orbitals generate some spins at the edge of the conduction band, which reduces the LiMnPO4 band gap to 3.25 and 2.78 eV, respectively, greatly improving the electronic conductivity. In the LiMn0.8Fe0.2PO4 material, the synergistic effect of Mn and Fe makes its performance the best. The experimental results show that MnSO4 is the best manganese source in the chemical coprecipitation method. The initial discharge capacity of the LiMn0.8Fe0.2PO4/C material is up to 150.2 mAh g–1 at 0.1C, and the coulomb efficiency is 95.1%. In addition, it has the best cycle and rate property, and the specific capacity is still higher than 125 mAh g–1 at 2C. The kinetic tests reveal that the Li+-diffusion coefficient (DLi+) of the LiMn0.8Fe0.2PO4/C material is 6.00 × 10–11 cm2·s–1, and all of the resistances, especially the charge-transfer resistance (Rct), are the lowest. It can greatly promote the migration of Li+ in the high-rate discharge process due to its lowest degree of polarization. In view of the excellent electrochemical performance of LiMn0.8Fe0.2PO4/C, the design idea of this study can provide valuable guidance for the development of manganese-based cathodes.