The Role of Na and Mg Doping on the Electronic Conductivity of LiFePO<sub>4</sub> : First-Principles Investigations

Abstract

The effects of Na and Mg doped Li site for Li1-xMxFePO4 have been studied using first-principles within GGA+U. Elastic band method has been used to calculate the activation energy for Li diffusion. The calculated results mean that, the band gaps of the Na and Mg doped Li1-xMxFePO4 are both narrow than that of the un-doped. Especially Mg dopant gives rise to much narrow gap, which is attributed to the appearance of impurity level in the forbidden band of un-doped LiFePO4. The calculated activation energies for LiFePO4, Li0.875Na0.125Subscript textFePO4, and Li0.875Mg0.125FePO4 are 0.33eV, 0.31 eV, and 0.15 eV, respectively. From the calculated results of band gap and activation energy, we can find that Mg dopant will benefit for the hopping of electrons and the improvement of the electronic conductivity for LiFePO4.