Sparse Cyclic Excitations Explain the Low Ionic Conductivity of Stoichiometric Li7La3Zr2O12

Mario Burbano, Dany Carlier, Florent Boucher, Benjamin Morgan, Mathieu Salanne

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Abstract

We have performed long time-scale molecular dynamics simulations of the cubic and tetragonal phases of the solid lithium-ion-electrolyte Li7La3Zr2O12 (LLZO), using a first-principles param- eterised interatomic potential. Collective lithium transport was analysed by identifying dynamical excitations; persistent ion displacements over distances comparable to the separation between lithium sites, and string-like clusters of ions that undergo cooperative motion. We find that dynamical excitations in c-LLZO are frequent, with participating lithium numbers following an exponential distribution, mirroring the dynamics of fragile glasses. In contrast, excitations in t-LLZO are both temporally and spatially sparse, consisting preferentially of highly concerted lithium motion around closed loops. This qualitative difference is explained as a consequence of lithium ordering in t-LLZO, and provides a mechanistic basis for the much lower ionic conductivity of t-LLZO compared to c-LLZO.
Original languageEnglish
Article number135901
Number of pages5
JournalPhysical Review Letters
Volume116
Publication statusPublished - 30 Mar 2016

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