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Comparative Molecular Dynamics Study of the Roles of Anion– Cation and Cation–Cation Correlation in Cation Diffusion in Li2B12H12 and LiCB11H12

preprint
submitted on 11.01.2021, 09:56 and posted on 12.01.2021, 07:52 by Kartik Sau, Tamio Ikeshoji, Sangryun Kim, Shigeyuki Takagi, Shin-ichi Orimo
Complex hydrides are potential candidates for the solid electrolyte of all-solid-state batteries owing to their high ionic conductivities, in which icosahedral anion reorientational motion plays an essential role in high cation diffusion. Herein, we report molecular dynamics (MD) simulations based on a refined force field and first-principles calculations of the two complex hydride systems Li2B12H12 and LiCB11H12 to investigate their structures, order–disorder phase-transition behavior, anion reorientational motion, and cation conductivities. For both systems, force-field-based MD successfully reproduced the structural and dynamical behavior reported in experiments. Remarkably, it showed an entropy-driven order–disorder phase transition associated with high anion reorientational motion. Furthermore, we obtained comparative insights into the cation around the anion, cation site occupancy in the interstitial space provided by anions, cation diffusion route, role of cation vacancies, anion reorientation, and effect of cation–cation correlation on cation diffusion. We also determined the factors that activate anion reorientational motion leading to a low to high conductivity phase transition. These findings are of fundamental importance in fast ion-conducting solids to diminish the transition temperature for practical applications.

History

Email Address of Submitting Author

kartik.sau@gmail.com

Institution

MathAM-OIL, AIST, c/o Advanced Institute of Material Research (AIMR), Tohoku University

Country

Japan

ORCID For Submitting Author

0000-0003-2432-2015

Declaration of Conflict of Interest

No conflict of interest.

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