Magnesium ion dynamics in Mg(BH4)2(1−x)X2x(X = Cl or AlH4) from first-principles molecular dynamics simulations

We use large-scale first-principles molecular dynamics simulations to find possible ways to make magnesium dication conductors based on Mg(BH4)2. The Mg atoms are confined in a tetrahedral cage of BH4 groups and coordinated by eight hydrogen atoms from these groups. These Mg atoms do not move outside the cage either in high- or low-temperature phases. After introducing larger-sized AlH−4 anions by substitution of 20% BH−4, the Mg atoms are able to move outside the cage with coordination from hydrogen atoms of BH−4 located outside the cage. Substitution by Cl− and I− anions did not allow large Mg movements.