An electrostatic potential study of LiM2O4 cathode material for lithium-ion battery: An insight into Li+ ion migration channels

Abstract

The electrostatic potentials (ESPs) of the dynamic charge densities of cubic and orthorhombic LiMn2O4 phases have been analyzed by using the structure factors calculated accurately from the independent atom model (IAM). The variations of the ESPs have been considered through two-dimensional contour maps in the planes perpendicular to the a, b and c axes. We have found 24 open channels with negative ESP values that Li + ion migration is possible along the [110], [11‾0], [011], [011‾], [101], [1‾01] directions in a cubic unit cell. Each channel is much wider than known radius of Li+ ion and the interior of it reveals the lowest level of the ESP and variation smaller than 0.3e/Å. One channel contains two linear chains and a Li+ ion is located at three-dimensional six channels. The ESP distributions suggest that Li + ion migration in cubic LiMn2O4 occurs not along the linear chain directions of Li + ions, but along the central axes of channels. These axes can be considered as possible Li+ ion migration pathways during charge/discharge. Although the orthorhombic LiMn2O4 phase has also similar Li + ion chains, because of much more variation of the ESP in spatial regions along the corresponding directions, it can be expected that its ionic conductivity decreases.