Electrical structures, magnetic polaron and lithium ion dynamics in three transition metal doped LiFe1-xMxPO4 (M = Mn, Co and La) cathode material for Li ion batteries from density functional theory study

Abstract

In this work, the simulation models of pure and doped LiFePO4 crystal with dopants (Mn, Co and La) on iron site substituted were performed by Vienna Ab Initio Simulation Package (VASP). The Electronic structure and magnetic polarization mechanisms of these systems, the partial density of states (PDOS) characters of the electrons near the Fermi level, the presence of doping-induced states near the band gap, the magnetic polarization process of doping have been investigated with GGA + U and PBE incorporates exchange and correlation effects implementations of density functional theory methods. The results are in good agreement with some experiment works, it is able to consider the presence of states below the conduction band which located near the Fermi level, which are also observed by experimentally. The corresponding electronic states are localized on 3d levels character of the transition metal. In addition, the lithium migration paths are simulated using nudged elastic band method, the results show that lithium vacancies create a strongly holes to Lithium diffusion in LiFePO4 and the effect of doping can be improved lithium ion diffusion capacity. The energy barriers of lithium migration in the four compounds (ranges from 0.23 to 0.67 eV) in the [010] direction are the easiest pathway. The evolution of structure of LiFePO4 were also investigated, the mean square displacement parameters (MSD) was used to study the lithium ions diffusion. Radial distribution function (RDF) which is commonly used to describe the strength of the bonding interaction between atom species in an equilibrium system, it is worth studying in order to understand the intensity of the peaks shown in the RDF function. By molecular dynamics simulation, the diffusion coefficients of Li+ ion diffusion process were also calculated, the results showed that with high valence metallic ions doping can significantly improve the electrochemical properties of materials. (C) 2016 Published by Elsevier B.V.