A family of air-stable chalcogenide solid electrolytes in Li$_2$BMQ$_4$ (B = Ca, Sr and Ba; M = Si, Ge and Sn; Q = O, S and Se) systems

TL;DR

This study combines computational and experimental methods to discover and synthesize a new family of air-stable, high-conductivity lithium chalcogenide solid electrolytes in the Li$_2$BMQ$_4$ system, promising for lithium-ion batteries.

Contribution

It introduces a novel family of stable, fast lithium-ion conductors in the Li$_2$BMQ$_4$ system with demonstrated synthesis, stability, and enhanced conductivity through doping.

Findings

Most sulfides and selenides have ultralow Li$^+$ migration activation energy.

Synthesized Li$_2$BaSnS$_4$ and Li$_2$SrSiS$_4$ show excellent moisture stability.

Doping with Cl$^-$ significantly increases ionic conductivity.

Abstract

Combining high-throughput first-principles calculations and experimental measurements, we have identified a novel family of fast lithium-ion chalcogenide conductors in Li$_2$BMQ$_4$ (2114, B = Ca, Sr and Ba; M = Si, Ge and Sn; Q = O, S and Se) systems. Our calculations demonstrate that most of the thermodynamically and kinetically stable sulfides and selenides in this new system exhibit ultralow Li$^+$ ion migration activation energy (0.16 eV ~ 0.56 eV) and considerable bandgaps varying between ~ 2 eV and 3.5 eV. We have successfully synthesized Li$_2$BaSnS$_4$ and Li$_2$SrSiS$_4$, and they exhibit excellent moisture stability through H$_2$S gas measurements. Electrochemical impedance measurements indicate 2114 systems show the typical features of solid ionic conductors, with a room-temperature Li$^+$ conductivity close to 5$\times$10$^{-4}$ mS/cm aligning with our molecular dynamics simulations. Furthermore, we have theoretically investigated the substitution of Cl$^-$ at S$^{2-}$ site. The doped compounds display significantly higher conductivity, with an increase of about three orders of magnitude (up to a maximum of 0.72 mS/cm) compared to the undoped compounds. These findings offer valuable insights for the further exploration of potential chalcogenide solid electrolyte materials with robust air stability and enhanced ionic conductivity for practical applications in lithium-ion batteries.