Date on Master's Thesis/Doctoral Dissertation


Document Type

Master's Thesis

Degree Name



Mechanical Engineering

Degree Program

Mechanical Engineering, MS

Committee Chair

Narayanan, Badri

Committee Member

Wang, Hui

Committee Member

Sumanasekera, Gamini U.

Author's Keywords

solid state battery; solid state electrolytes; solid electrolytes; NSS; sodium ion electrolytes; sodium sulfide electrolytes


In this thesis, we employ a combination of density functional theory (DFT) calculations, and ab initio molecular dynamics (AIMD) simulations to identify the effect of chemical doping on (a) thermodynamic phase stability, and (b) Na-ion conduction in Na3SbS4 (NSS) solid-state electrolytes. We found that (a) Se doped electrolytes, namely, Na3SbSexS4-x undergo a tetragonal-to-cubic structural phase transition at x > 3 (Se-rich), and (b) the size, valence, and electronegativity of chemical dopants that substitute Na in Na3SbS4 have a cumulative profound impact on Na-ion conductivity. Specifically, substituting Na with higher valence dopant (e.g., In3+) that are similar in size to Na can result in substantial improvement in Na-ion conduction (~2-2.5 times that in undoped case) owing to the increased Na-vacancy concentration in the doped electrolytes. AIMD trajectories also elucidate the effect of dopant on the atomic-scale pathways underlying Na-conduction.