Structural properties and antisite defect formation in monoclinic Li2FeSiO4 – a DFT aspect

Abstract

Properties of monoclinic Li2FeSiO4, which is a prominent candidate for future use as a cathode in lithium ion batteries, have been investigated by DFT+U method, using GGAPBE approximation, plane wave basis set and periodic boundary conditions. All calculations were performed in an antiferromagnetic state, which has been found to be energetically slightly more stable than ferromagnetic. Optimized lattice parameters and atomic coordinates have been compared to the literature data in order to verify the model. In addition, a particular attention was paid to the possibility of the formation of an antisite defect, which was introduced as the interchange between Fe and Li ions at both Li1 and Li2 crystallographic positions. The concentration of defect was varied from 0 to 25 molar per cent. Changes of structural, energetic, and magnetic properties of monoclinic Li2FeSiO4 upon increase of Li1-Fe and Li2-Fe antisite defect concentration have been analyzed and discussed in light of available experimental results.