Impact of Proton Contamination on the Solid Electrolyte Li7La3Zr2O12 (LLZO)

Abstract

Inorganic solid-state electrolytes are receiving attention due to the safety issues associated with flammable organic liquid electrolytes used in modern Li-ion batteries. Solid electrolytes can also enable higher energy density batteries by allowing use of metallic anodes. Li7La3Zr2O12 (LLZO) is one of the most promising solid electrolytes due to its high ionic conductivity (∼1 mS/cm), wide electrochemical window, and stability with respect to lithium. However, recent experimental evidence suggests that LLZO is unstable when exposed to humid air, resulting in proton exchange with lithium in the bulk and surface carbonation preceded by hydration (LiOH formation).1 Here, first principles calculations were used to investigate the reaction thermodynamics for surface hydration and carbonation of LLZO. Furthermore, ab-initio molecular dynamics (AIMD) were performed to examine the effect of proton substitution on diffusion within the Li sublattice. AIMD calculations indicate that moderate levels of protonation (up to ~10% H+ substitution) results in only a minor decease in Li-ion conductivity. On the other hand, higher proton concentrations can limit this conductivity significantly. [1] G. Larraz, A. Orera and M. L. Sanjuan J. Mater. Chem. A, 1, 11419 (2013)