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 Co-Chair (if applicable)

Wang, Hui

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.