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

Abstract

Li 2B 12H 12, Na 2B 12H 12, and their closo-borate relatives 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. To this end, we use ab initio molecular dynamics simulations and density-functional calculations to explore the motivations for cation diffusion. We find that superionic behavior in Li 2B 12H 12 and Na 2B 12H 12 results from a combination of key structural, chemical, and dynamical factors that introduce intrinsic frustration and disorder. A statistical metric is used to show that the structures exhibit a high density of accessible interstitial sites and site types, which correlates with the flatness of the energy landscape and the observed cation mobility. Furthermore, cations are found to dock to specific anion sites, leading to a competition between the geometric symmetry of the anion and the symmetry of the lattice itself, which can facilitate cation hopping. Finally, facile anion reorientations and other low-frequency thermal vibrations lead to fluctuations in the local potential that enhance cation mobility by creating a local driving force for hopping. Inmore » conclusion, we discuss the relevance of each factor for developing new ionic conductivity descriptors that can be used for discovery and optimization of closo-borate solid electrolytes, as well as superionic conductors more generally.« less

Authors:
 [1]; ORCiD logo [1];  [1];  [2]; ORCiD logo [3];  [1];  [4];  [5]; ORCiD logo [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Materials Science Division
  2. San Francisco State Univ., CA (United States). Dept of Chemistry and Biochemistry
  3. Univ. of Notre Dame, IN (United States). Dept. of Chemical and Biomolecular Engineering
  4. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Center for Neutron Research
  5. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1418905
Report Number(s):
LLNL-JRNL-734199
Journal ID: ISSN 0897-4756
Grant/Contract Number:
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 29; Journal Issue: 21; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 25 ENERGY STORAGE

Citation Formats

Kweon, Kyoung E., Varley, Joel B., Shea, Patrick, Adelstein, Nicole, Mehta, Prateek, Heo, Tae Wook, Udovic, Terrence J., Stavila, Vitalie, and Wood, Brandon C. Structural, Chemical, and Dynamical Frustration: Origins of Superionic Conductivity in closo -Borate Solid Electrolytes. United States: N. p., 2017. Web. doi:10.1021/acs.chemmater.7b02902.
Kweon, Kyoung E., Varley, Joel B., Shea, Patrick, Adelstein, Nicole, Mehta, Prateek, Heo, Tae Wook, Udovic, Terrence J., Stavila, Vitalie, & Wood, Brandon C. Structural, Chemical, and Dynamical Frustration: Origins of Superionic Conductivity in closo -Borate Solid Electrolytes. United States. doi:10.1021/acs.chemmater.7b02902.
Kweon, Kyoung E., Varley, Joel B., Shea, Patrick, Adelstein, Nicole, Mehta, Prateek, Heo, Tae Wook, Udovic, Terrence J., Stavila, Vitalie, and Wood, Brandon C. Wed . "Structural, Chemical, and Dynamical Frustration: Origins of Superionic Conductivity in closo -Borate Solid Electrolytes". United States. doi:10.1021/acs.chemmater.7b02902.
@article{osti_1418905,
title = {Structural, Chemical, and Dynamical Frustration: Origins of Superionic Conductivity in closo -Borate Solid Electrolytes},
author = {Kweon, Kyoung E. and Varley, Joel B. and Shea, Patrick and Adelstein, Nicole and Mehta, Prateek and Heo, Tae Wook and Udovic, Terrence J. and Stavila, Vitalie and Wood, Brandon C.},
abstractNote = {Li2B12H12, Na2B12H12, and their closo-borate relatives 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. To this end, we use 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 results from a combination of key structural, chemical, and dynamical factors that introduce intrinsic frustration and disorder. A statistical metric is used to show that the structures exhibit a high density of accessible interstitial sites and site types, which correlates with the flatness of the energy landscape and the observed cation mobility. Furthermore, cations are found to dock to specific anion sites, leading to a competition between the geometric symmetry of the anion and the symmetry of the lattice itself, which can facilitate cation hopping. Finally, facile anion reorientations and other low-frequency thermal vibrations lead to fluctuations in the local potential that enhance cation mobility by creating a local driving force for hopping. In conclusion, we discuss the relevance of each factor for developing new ionic conductivity descriptors that can be used for discovery and optimization of closo-borate solid electrolytes, as well as superionic conductors more generally.},
doi = {10.1021/acs.chemmater.7b02902},
journal = {Chemistry of Materials},
number = 21,
volume = 29,
place = {United States},
year = {Wed Oct 11 00:00:00 EDT 2017},
month = {Wed Oct 11 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on October 11, 2018
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