First Principles Study on Na_xLi_1-xFePO₄ As Cathode Material for Rechargeable Lithium Batteries

The electronic structure and ionic dynamic properties of pure and Na doped (Li site) LiFePO₄ have been investigated by first-principles calculations. The band gap of the Na doped material is much narrow than that of the undoped one, indicating of better electronic conductive properties. First-principles based molecular dynamic simulations have been performed to examine the migration energy barriers for the Li ion diffusion. The results shown that the energy barriers for Li diffusion decreased a little along the one-dimensional diffusion pathway, indicating that the ionic conductive property is also improved, as compared with the high valance doping (such as Cr) cases.