Arrhenius plot of diffusion coefficients in Li2S. Diffusion coefficient in the pristine structure is shown by D dis since in this case Li ion migration takes place via temperature–induced disorder (interstitial Li). Li diffusion in Li2S with a single vacancy is illustrated by vac&dis as charge carriers are both Li vacancy and disorder (interstitial Li). The inset presents total mean square displacements (MSD) versus lag time calculated for 40?ps AIMD simulations.
We have studied temperature-induced superionic phase transition in Li2S, which is one of the most promising Li-S battery cathode material. Concentration of ionic carriers at low and
high temperature was evaluated from thermodynamics of defects (using density functional theory) and detailed balance condition (using ab initio molecular dynamics (AIMD)),
respectively. Diffusion coefficients were also obtained using AIMD simulations. Calculated ionic conductivity shows that superionic phase transition occurs at T?=?900?K, which is in
agreement with reported experimental values. The superionic behavior of Li2S is found to be due to thermodynamic reason (i.e. a large concentration of disordered defects).