Sparse cyclic excitations explain the low ionic conductivity of stoichiometric Li7La3Zr2O12

Mario Burbano (1, 2, 3) , Dany Carlier (1, 3) , Florent Boucher (4) , Benjamin J. Morgan (5) , Mathieu Salanne (2, 6, 1)

1 RS2E - Réseau sur le stockage électrochimique de l'énergie
2 PHENIX - PHysicochimie des Electrolytes et Nanosystèmes InterfaciauX
3 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
4 IMN - Institut des Matériaux Jean Rouxel
5 University of Bath [Bath]
6 MDLS - Maison de la Simulation

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 parametrized interatomic potential. Collective lithium transport was analyzed by identifying dynamical excitations: persistent ion displacements over distances comparable to the separation between lithium sites, and stringlike clusters of ions that undergo cooperative motion. We find that dynamical excitations in c-LLZO (cubic) are frequent, with participating lithium numbers following an exponential distribution, mirroring the dynamics of fragile glasses. In contrast, excitations in t-LLZO (tetragonal) 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.

Domaines: Matériaux

Mario Burbano, Dany Carlier, Florent Boucher, Benjamin J. Morgan, Mathieu Salanne. Sparse cyclic excitations explain the low ionic conductivity of stoichiometric Li7La3Zr2O12. Physical Review Letters, 2016, 116 (13), 135901 (6 p.). ⟨10.1103/PhysRevLett.116.135901⟩. ⟨hal-01300141⟩