Cooperative Mechanism for the Diffusion of Li+ Ions in LiMgSO4F

Extensive molecular dynamics simulations are performed on tavorite-structured LiMgSO4F, in order to analyze the diffusion mechanism of the Li+ ions. In a first step, an interaction potential, including polarization effects, is parametrized from density functional theory calculations. This is then tested by reproducing experimental properties of the material, such as structural parameters (lattice constants and interatomic distances) and ionic conductivity to a high degree of accuracy. Next, the conduction mechanism is studied: the diffusion of the Li+ ions occurs via correlated hops inside diffusion channels, which reflects in the much larger values calculated for their collective diffusion coefficient compared to the individual ones (by I order of magnitude on average). The consequences (both scientific and technical) of this finding are discussed.