Electrical structure, magnetic polaron and lithium ion dynamics in four mixed-metal oxide multiple-phase electrode cathode material for Li ion batteries from density functional theory study

Abstract

This study present results derived from first-principles calculations, at density functional level, and molecular dynamics simulations. Calculations of perfect LiMO2 (M = Mn, Co and Ni) and their mixed-metal oxide (LiMn1/3Co1/3Ni1/3O2) were performed by PBE with the GGA method in the VASP Package. Atomistic simulation calculation was used for searching the electrical structure, magnetic polaron and lithium ion dynamics properties. The results were suitable for the measured valence-band structure, also with the magnetic and electrical properties of the Li-transition metal oxide. The band gap is determined by the charge-transfer and the main contributions from the magnetic polaron produced spin electron - hole pairs that were smaller than that of the states of the M3d and O2p orbitals. When anisotropic O2p-M3d orbital hybridization occurs, a highly-delocalized characteristic was shown in the M3d hole state owing to the states mixing. The extended M4p orbital improved the exchange interaction between Mn3d and Op which led to an asymmetric charge distribution in the M-O bonds. The delocalized characteristic of Mn3d holes is a vital part of the mechanism of spin-dependent ligand (O-2) hybridization. Due to the decrease in inter-molecular attractive forces, a decrease in the order parameter of crystalline was derived from the increase of temperature. Moreover, the transition metal-oxygen and lithium-oxygen radial distribution functions (RDF) at temperatures of 300 and 900 K were compared to each other. The results indicate that the height of the peaks decrease and the system becomes more stable due to increasing temperature. Overall, because of the increase of thermal motion with increasing temperature, lithium ions showed a gradual evolution of mobility. (C) 2017 Elsevier B.V. All rights reserved.