Sulfur- and Selenium-Containing Compounds Potentially Exhibiting Al Ion Conductivity

Abstract

We have created a set of crystalline model structures exhibiting straight lines of Al³⁺ connected to chalcogenides (O^2- , S^2- , and Se^2- ) connected to metal cations of varying valence (Sr²⁺ , Y³⁺ , Zr⁴⁺ , Nb⁵⁺ , and Mo⁶⁺ ). They were relaxed with density functional theory computations and analysed by Bader partitioning. As Al³⁺ ions are supposed to strongly interact with their atomic environment, we studied the electron density topology induced by higher-valent cations in the extended chemical neighbourhood of Al. In fact, we found a general decrease of ionic charges and an increasing displacement of the chalcogenides towards higher-valent ions for the heavier chalcogens. Therefore, we comprehensively screened S- and Se-containing compounds for candidates theoretically exhibiting low migration barriers for Al³⁺ ions by using Voronoi-Dirichlet partitioning and bond valence site energy calculations. The basis for this search is the Inorganic Crystal Structure Database. Indeed, we could extract six promising candidates with low Al³⁺ migration barriers. which are even lower than the barriers for any other element inside of these materials. This will encourage efforts towards preparing suitable Al³⁺ conductors.

Keywords: Voronoi-Dirichlet; aluminium-ion battery; bond valence; density functional theory; ionic conductivity.