Direct calculation of effective mobile ion concentration in lithium superionic conductors

In the realm of lithium superionic conductors, pursuing higher ionic conductivity is imperative, with the variance in lithium-ion concentration playing a determining role. Due to the permanent and temporary site-blocking effects, especially at non-dilute concentrations, not all Li-ions contribute to ionic conductivity. Here, we propose a strategy to directly calculate effective mobile ion concentration in which multiple-ion correlated migration is considered in the percolation analysis with the input of Li-ion distributions and hopping behavior based on kinetic Monte Carlo simulation, termed P-KMC. We provide examples of two representative lithium superionic conductors, cubic garnet-type Li_xA₃B₂O₁₂ (0 ≤ x ≤ 9; A and B represent different cations) and perovskite-type Li_xLa_2/3−x/3TiO₃ (0 ≤ x ≤ 0.5), to demonstrate the direct dependence of the ionic conductivity on the effective mobile ion concentration. This methodology provides a robust tool to identify the optimal compositions for the highest ionic conductivity in superionic conductors.