Structural, Chemical, and Dynamical Frustration: Origins of Superionic Conductivity in closo-Borate Solid Electrolytes

Published

October 11, 2017

Author(s)

Kyoung E. Kweon, Joel B. Varley, Patrick Shea, Nicole Adelstein, Prateek Mehta, Tae Wook Heo, Terrence J. Udovic, Vitalie Stavila, Brandon C. Wood

Abstract

Li₂B₁₂H₁₂ and Na₂B^12^H₁₂ closoboranes exhibit unusually high ionic conductivity, making them attractive as a new class of candidate electrolytes in solid-state Li- and Na-ion batteries. However, further optimization of these materials requires a deeper understanding of the fundamental mechanisms underlying ultrafast ion conduction in these materials. To this end, we use a combination of ab initio molecular dynamics simulations and density-functional calculations to explore the motivations for cation diffusion. We find that superionic behavior in Li₂B₁₂H₁₂ and Na₂B₁₂H₁₂ likely results from a combination of key structural, chemical, and dynamical factors that introduce frustration and prevent cation ordering. First, the crystals possess vacant interstitial sites, and cations show preference for more than one type of interstitial site, flattening the energy landscape. Second, the dynamics show that cations dock to specific anion sites, leading to a competition between the geometric symmetry of the anion and the symmetry of the lattice itself. Third, facile anion reorientations lead to fluctuations in the local potential that enhance cation conductivity. We discuss the relevance of each factor for developing new ionic conductivity descriptors that can be used to optimize closeborane solid electrolytes and other similar classes of emerging materials.

Citation

Chemistry of Materials

Volume

29

Pub Type

Journals

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Keywords

ab initio molecular dynamics, B12H12, closo-boranes, conductivity, density functional theory, diffusion, frustration, ionic conductivity, molecular dynamics

Citation

Kweon, K. , Varley, J. , Shea, P. , Adelstein, N. , Mehta, P. , Heo, T. , Udovic, T. , Stavila, V. and Wood, B. (2017), Structural, Chemical, and Dynamical Frustration: Origins of Superionic Conductivity in closo-Borate Solid Electrolytes, Chemistry of Materials, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=923812 (Accessed December 5, 2024)