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First-principles simulations to understand the structural and electrolyte properties
of idealized Li7.5B10S18X1.5 (X =
Cl, Br, I)
Yan Li and N.A.W. Holzwarth
Physical Review Materials 6 , 045403 (2022)
Local copy: PDF
Recently, researchers at the University of Waterloo (Canada) and Oak Ridge National Laboratory (Oak
Ridge, TN) reported a new family of lithium thioborate halide electrolytes with the composition
Li7.5B10S18X1.5 (X = Cl, Br, I) having very impressive
ionic room-temperature conductivity of magnitude σ =
1 mS/cm. The researchers characterized the structures of the three materials in terms of a well-defined
thioborate framework with a void structure containing fractionally occupied Li and X sites. The space
group of the materials was identified to be monoclinic (C2/c, No. 15). We report the results of
first-principles simulations of these materials focusing on understanding the idealized ground-state
structures, the mechanisms of Li ion migration, and the overall stability of the materials. A systematic
search of many possible stoichiometric crystalline configurations found ordered ground-state realizations
of the materials for each of the three halides, X = Cl, Br, I. Molecular dynamics simulations based on
the initially ordered structures at various temperatures show significant Li ion hopping within the void
channels of the structures at temperatures as low as T = 400 K. Simulations of possible decomposition
products suggest that these electrolytes are also chemically stable. Overall, the simulations are
consistent with the experimentally reported findings indicating that these materials are very promising
solid electrolytes for possible use in solid-state Li ion batteries.