Insights into stability, electronic properties, defect properties and Li ions migration of Na, Mg and Al-doped LiVPO4F for cathode materials of lithium ion batteries: A first-principles investigation

The effects of Na, Mg and Al doping on the structure, electronic property, defect property and Li ions migration of LiVPO4F were investigated by the first-principles method. Calculations show that the processes of forming Li0.875Na0.125VPO4F, alpha- and beta-iMg(0.375)V(0.75)PO(4)F, alpha- and beta-LiAl0.125V0.875PO4F are all feasible. Na, Mg and Al doping significantly improve the electrical conductivity of LiVPO4F and simultaneously maintain their structural stability attributing to the reduction of band gaps through variations of V-3d spin up orbitals. Li vacancy defects of LiVPO4F are not ignorable, and vacancy defects with a lower activation energy for Li atom are far more likely to occur than Frenkel defects for Li and vacancy defects for other atoms. For pristine LiVPO4F, path D along [0.012 0.(1) over bar7 0.572] direction is found to have the lowest activation energy of 0.418 eV, suggesting that anisotropic nature of Li ion conduction and LiVPO4F is a one-dimensional (1D)-ion conductor. The corresponding diffusion coefficient was estimated to be 2.82 x 10(-9) cm(2)/s, which is in good agreement with those experimental values. (C) 2016 Elsevier Inc. All rights reserved.