Design of a unique anion framework in halospinels for outstanding performance of all solid-state Li-ion batteries: first-principles approach

Abstract

A solid-state electrolyte (SSE) is a key component in the performance control of all-solid-state Li-ion batteries. The development of a promising material has, however, come to a standstill due to the undesirably low ionic conductivity and stability. Using first-principles calculations, we propose that halospinels, i.e., Li₂Sc_2/3X₄ (X = Cl, Br, and I), should be encouraging materials to surmount the long-standing challenges. Density functional theory (DFT) calculations unveil their underlying mechanisms that the incorporated halogen anion and Sc form unique ionic pairs to create the atomic environment required for the dramatic facilitation of Li-ion diffusion to a superionic conductor level. In addition, collective ionic motions near the halogen species in the halospinel solid electrolyte promote the substantial enhancement of the electrochemical stability and interface compatibility with the electrodes. We demonstrate that a crucial factor is the rational selection of the halogen anion to achieve the maximal performance of the electrolyte. Ab initio molecular dynamics (AIMD) simulations consistently pinpoint that the halospinel with Cl anion, Li₂Sc_2/3Cl₄, is the best choice to maintain the high functionality of Li-ion conductivity, electrochemical stability, and interface compatibility with the LiCoO₂ electrode in Li-ion battery applications. Our study provides a fundamental ground on chemical design principles for a breakthrough in advancing solid-state electrolytes towards a wide commercialization of all-solid-state Li-ion batteries.