The Role of Na and Mg Doping on the Electronic Conductivity of LiFePO_4: First-principles Investigations

摘要

The effects of Na and Mg doped Li site for Li_(1-x)M_xFePO_4 have been studied using firstprinciples 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 Li_(1-x)M_xFePO_4 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 LiFePO_4. The calculated activation energies for LiFePO_4, Li_(0.875)Na_(0.125)FePO)_4, and Li_(0.875)Mg_(0.125)FePO_4 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 LiFePO_4.