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



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


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.
Chemistry of Materials


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


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], (Accessed April 14, 2024)
Created October 10, 2017, Updated October 12, 2021