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)