Abstract: In this paper, the model of Na-Ti co-doped LiFePO₄ was constructed based on the first-principles method of density functional theory, the electronic structure and elastic properties of the co-doped system were calculated using the CASTEP module. The calculated results show that due to the introduction of impurity atoms, the cell parameters of the co-doped system increase slightly, the band gap decreases from 0.695 eV to 0.473 eV, and the energy required for electronic transition decreases. The Li ion migration barrier decreases from 0.34 eV to 0.25 eV, which enhances the conductivity of the co-doped structure. The calculation of elastic properties shows that the bulk modulus, shear modulus and Young's modulus of the structure after co-doping decrease to varying degrees, while the calculated Poisson ratio shows that materials before and after doping are brittle. However, the plasticity of the co-doped material is stronger than that of the undoped material, and the anisotropy of the co-doped crystal weakens, which improves the ductility of LiFePO₄.

Key words: LiFePO₄, co-doping, first-principle, electronic structure, elastic property