Antisite defects and Mg doping in LiFePO4: a first-principles investigation

Atomic and electronic structures of LiFePO4 with the antisite defect and Mg doping at Li and Fe sites have been investigated using first-principles density-functional theory with the on-site Coulomb interaction taken into account. It is demonstrated that the most favorable antisite defect type is the exchange defect, in which Li and Fe ions exchange positions. The resultant longer Fe-O bond and narrower band gap drop a hint that the electronic and ionic transport properties may be improved. For the case of Mg doping, Mg is preferentially doped at the Fe site instead of the Li site to form a new LiFe1-y Mg (y) PO4 solid solution, leading to a higher ionic conductivity. Moreover, the dependence of the electrochemical properties on the concentration of Mg dopant has also been discussed.