Study of electrochemical properties, mechanical properties, and lithium ion diffusion of Ni and N co- doped LiFePO4 based on first principles

Abstract

This study analyzes the stability, volume change rate, embedding voltage, lithium ion diffusion, and mechanical properties of Ni, N co-doped LiFePO₄ using density functional theory (DFT) calculations. Ni,N doping reduces formation energy to −1.5 eV compared to pristine LiFePO₄, stabilizing the olivine framework during lithiation/de-lithiation. The doping of Ni and N introduces impurity bands, and the band gap before and after doping decreases from 3.71 eV to 1.2 eV, which enhances the electronic conductivity. Meanwhile, the migration barrier is reduced from 0.57 eV to about 0.45 eV and the diffusion coefficient is improved by two orders of magnitude. In addition, nickel doping leads to changes in the local electronic structure, and the reduced electron localization helps the migration of lithium ions. Finally, doping enhances the stiffness, hardness of the material, which further improves its overall performance.