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Understanding superionic conductivity in lithium and sodium salts of weakly coordinating closo-hexahalocarbaborate anions

DOI: 10.1021/acs.chemmater.9b04383 DOI Help

Authors: Mathias Jorgensen (University of Aarhus; Sandia National Laboratories) , Patrick T. Shea (Lawrence Livermore National Laboratory) , Anton W. Tomich (University of California, Riverside) , Joel B. Varley (Lawrence Livermore National Laboratory) , Marnik Bercx (University of Antwerp) , Sergio Lovera (University of California, Riverside) , Radovan Cerny (University of Geneva) , Wei Zhou (National Institute of Standards and Technology, United States) , Terrence J. Udovic (National Institute of Standards and Technology, United States) , Vincent Lavallo (University of California, Riverside) , Torben Jensen (Aarhus University) , Brandon C. Wood (Lawrence Livermore National Laboratory) , Vitalie Stavila (Sandia National Laboratories)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry Of Materials

State: Published (Approved)
Published: January 2020

Abstract: Solid-state ion conductors based on closo-polyborate anions combine high ionic conductivity with a rich array of tunable properties. Cation mobility in these systems is intimately related to the strength of the interaction with the neighboring anionic network and the energy for reorganizing the coordination polyhedra. Here, we explore such factors in solid electrolytes with two anions of the weakest coordinating ability, [HCB11H5Cl6]– and [HCB11H5Br6]–, and a total of eleven polymorphs are identified for their lithium and sodium salts. Our approach combines ab initio molecular dynamics, synchrotron X-ray powder diffraction, differential scanning calorimetry, and AC impedance measurements to investigate their structures, phase-transition behavior, anion orientational mobilities, and ionic conductivities. We find that M(HCB11H5X6) (M = Li, Na, X = Cl, Br) compounds exhibit order-disorder polymorphic transitions between 203 and 305 °C, and display Li and Na superionic conductivity in the disordered state. Through detailed analysis, we illustrate how cation disordering in these compounds originates from a competitive interplay among the lattice symmetry, the anion reorientational mobility, the geometric and electronic asymmetry of the anion, and the polarizability of the halogen atoms. These factors are compared to other closo-polyborate-based ion conductors to suggest guidelines for optimizing the cation-anion interaction for fast ion mobility. This study expands the known solid-state, poly(carba)borate-based materials capable of liquid-like ionic conductivities, unravels the mechanisms responsible for fast ion transport, and provides insights into the development of practical superionic solid electrolytes.

Journal Keywords: Chemical structure; Ionic conductivity; Anions; Cations; Group 17 compounds

Diamond Keywords: Batteries; Solid-State Batteries (SSB)

Subject Areas: Chemistry, Materials, Energy

Instruments: I11-High Resolution Powder Diffraction

Other Facilities: ESRF SwissNorwegian beamline (BM02.1); Petra III beamline P02.1

Added On: 27/01/2020 11:04

Discipline Tags:

Physical Chemistry Energy Energy Storage Materials Science Energy Materials Chemistry

Technical Tags:

Diffraction X-ray Powder Diffraction