Doping in garnet-type electrolytes: Kinetic and thermodynamic effects from molecular dynamics simulations

Abstract

To shed light on the impact of doping on the conductivity of garnet-type electrolytes, we use molecular dynamics with an ab initio designed force-field to investigate the complex interplay between the carrier concentration and the kinetic and thermodynamic changes induced by the addition of hypervalent dopants. We focus in particular on the effect of the distribution of the doping agents, and we find that there is a need to perform a proper average over the frozen disorder introduced by the doping in order to achieved converged properties. We observe the competing effects induced by the decrease in concentration of the conducting ions (Li+) and by the perturbation of the energy landscape resulting from the insertion of hypervalent dopants. These two phenomena give rise to an intricate balance between thermodynamic and kinetic properties, which make the interpretation of the experiments very challenging. In particular, while the increase in the dopant concentration stabilizes the conductive cubic phase of these garnet-type materials, the kinetic effects have two distinct components, one promoting and one hindering diffusion.