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Exploring Li-Ion Conductivity in Cubic, Tetragonal and Mixed-Phase Al-Substituted Li 7La 3Zr2O 12 Using Atomistic Simulations and Effective Medium Theory

35 Pages Posted: 11 Apr 2019 First Look: Accepted

See all articles by Mauricio R. Bonilla

Mauricio R. Bonilla

Basque Center for Applied Mathematics

Fabián A. García Daza

Basque Center for Applied Mathematics; CIC EnergiGUNE

Javier Carrasco

CIC EnergiGUNE

Elena Akhmatskaya

Basque Center for Applied Mathematics; Basque Government - Basque Foundation for Science (IKERBASQUE)

Abstract

Garnet Li7La3Zr2O12(LLZO) is a promising solid electrolyte candidate for solid-state Li-ion batteries, but at room temperature it crystallizes in a poorly Li-ion conductive tetragonal phase. To this end, partial substitution of Li+ by Al3+ ions is an effective way to stabilize the highly conductive cubic phase at room temperature. Yet, fundamental aspects regarding this aliovalent substitution remain poorly understood. In this work, we use molecular dynamics and advanced hybrid Monte Carlo methods for systematic study of the room temperature Li-ion diffusion in tetragonal and cubic LLZO to shed light on important open questions. We find that Al substitution in tetrahedral sites of the tetragonal LLZO allows previously inaccessible sites to become available, which enhances Li-ion conductivity. In contrast, in the cubic phase Li-ion diffusion paths become blocked in the vicinity of Al ions, resulting in a decrease of Li-ion conductivity. Moreover, combining the conductivities of individual phases through an effective medium approximation allowed us to estimate the conductivities of cubic/tetragonal phase mixtures that are in good agreement with those reported in several experimental works. This suggests that phase coexistence (due to phase equilibrium or gradients in Al content within a sample) could have a significant impact on the conductivity of Al-substituted LLZO, particularly at low contents of Al3+. Overall, by making a thorough comparison with reported experimental data, the theoretical study and simulations of this work advance our current understanding of Li-ion mobility in Al-substituted LLZO garnets and might guide future in-depth characterization experiments of this relevant energy storage material.

Keywords: Al-substituted LLZO, Atomistic Simulations, Effective Medium Theory, Phase Coexistence, Solid State Batteries

Suggested Citation

Bonilla, Mauricio R. and Daza, Fabián A. García and Carrasco, Javier and Akhmatskaya, Elena, Exploring Li-Ion Conductivity in Cubic, Tetragonal and Mixed-Phase Al-Substituted Li 7La 3Zr2O 12 Using Atomistic Simulations and Effective Medium Theory (April 11, 2019). Available at SSRN: https://ssrn.com/abstract=3370234

Mauricio R. Bonilla (Contact Author)

Basque Center for Applied Mathematics ( email )

Mazarredo, 14
Bilbao, Bizkaia 48603
Spain

Fabián A. García Daza

Basque Center for Applied Mathematics

Mazarredo, 14
Bilbao, Bizkaia 48603
Spain

CIC EnergiGUNE

Spain

Javier Carrasco

CIC EnergiGUNE

Spain

Elena Akhmatskaya

Basque Center for Applied Mathematics

Mazarredo, 14
Bilbao, Bizkaia 48603
Spain

Basque Government - Basque Foundation for Science (IKERBASQUE)

Bilbao, 48011
Spain

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