Transport of secondary carriers in a solid lithium ion conductor
Abstract Inorganic solid lithium electrolytes are typically thought of as single ion conductors, but the presence of secondary carriers can strongly affect their performance. Conventional descriptions of multi carrier transport neglect both interactions between mobile species and stress diffusion phenomena which can markedly impact the electrical response. We apply irreversible thermodynamics to develop a chemomechanical transport model for elastic solid ionic conductors containing two mobile ions. We simulate lithium ion conducting Li 5 La 3 Nb 2 O 12 (LLNO) garnet oxide, a material within which experiments have shown that mobile protons can be freely substituted for lithium to form Li 5 1 y H 5 y La 3 Nb 2 O 12 When subjected to a current, we find that proton substituted LLNO exhibits bulk lithium polarization, whose extent is partially controlled by cation/cation interactions. Secondary carriers segregate naturally if their global concentration is low, accumulating in a thin boundary layer near the cathode. We quantify the limiting current and Sand's time, and analyze experimental data to show how competitive proton transport affects LLNO performance.