Discovery of Ag+ superionic state in delafossite AgAlO2

Abstract

Concerns regarding cost and safety have prompted an investigation into the feasibility of Ag⁺ ion batteries as a promising alternative to lithium-ion batteries. In this work, machine-learned force fields (MLFF) were employed to elucidate the diffusion mechanism of Ag⁺ ions in delafossite AgAlO2. The demonstration was made through analysis of atomic trajectories, mean squared displacement (MSD), and radial distribution function (RDF), we demonstrated that Ag⁺ ions diffuse through channels formed by a novel [AlO₂]^- sublattice. The Madelung energy analysis indicates that electrostatic interactions within the sublattices are stronger than those between the sublattices and Ag⁺, enabling Ag⁺ ions to overcome these constraints and achieve free diffusion at elevated temperatures. By introducing defects, the energy barrier was reduced from 0.547 eV to 0.337 eV, leading to a superionic transition temperature of 700 K. This work has discovered an interesting phenomenon of superionic state in delafossite AgAlO₂, adding new vitality to the delafossite family.