Degree

Doctor of Philosophy (PhD)

Department

The Gordon A. and Mary Cain Department of Chemical Engineering

Document Type

Dissertation

Abstract

In this thesis we theoretically explore the different fundamental phenomena associated with metal-air batteries (where the metal can be Li, Na or K) using first principles density functional theory. We start by investigating the adsorption of the starting reactants/primary intermediates i.e. metal superoxides and superoxide anion on Au(111) and Au(211). We elucidate the influence of electric fields and the importance of including explicit solvents on the adsorption energy of these intermediates. We show that these effects are considerable and should be included for future reaction modeling of these batteries. Following this we investigate the reaction of M+ and O2‑ in solution phase where the solvents considered are dimethyl sulfoxide (DMSO) and Acetonitrile (ACN), which are commonly used electrolytes in these batteries. We show the for Li-O2 pair the peroxide species is the most stable final product while for Na-O2 and K-O2 pairs the metal superoxide is the most stable species. We explore the possibility of dimerization and trimerization of the metal superoxide and peroxide in solvent and show that only Li2O2 tends form clusters in solution. Next we proceed to investigate the discharge product formed as a result of the metal assited oxygen reduction reaction (M-ORR). We only consider the discharge product for Li-O2 batteries where the primary discharge product is Li2O2. We show that doping the discharge product during the electrochemical growth phase with solvated dopant/metal cations could lead to microdomains of discharge product. We use evolutionary algorithm as implemented in the USPEX package in conjunction with DFT to probe the potential energy surface for novel configurations of composition Li15DO16 (stoichiometric composition) and Li14DO16 (composition representing a structure with vacancy). Where D is the dopant atom. We consider Ba, Co, Mg Na and Ni ions as dopants which are commonly found as solvated ions in batteries. We show thermodynamically that these structures can viably form as compared to the P63/mmc Föppl structure of Li2O2. Additionally, we show that novel doped structures improve on the electron mobility through the bulk aiding in reduction of overpotential.

Date

4-17-2020

Committee Chair

Xu, Ye

DOI

10.31390/gradschool_dissertations.5243

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