Effects of Li Salt Anions and O2 Gas on Li Dissolution/Deposition Behavior at Li Metal Negative Electrode for Non-Aqueous Li-Air Batteries

To clarify the relationship between Li+ transport rate in glyme-based electrolytes and Li deposition/dissolution behavior at Li metal negative electrode (NE) in Li-air batteries (LAB) systems, 1.0 M tetraglyme (G4) electrolytes were prepared containing a Li salt of LiSO3CF3, LiN(SO2CF3)(2), or LiN(SO2F)(2). Two aspects of Li+ transfer between the two phases, i.e., G4 electrolyte vertical bar Li metal NE, were evaluated, namely i) Li+ supplying rate and ii) Li+ charge transfer rate through solid electrolyte interphase (SEI) films. The former was investigated by self-diffusion coefficients D of Li+, anions, and G4 solvent together with ionic conductivity sigma, viscosity, density, and apparent dissociation degree alpha(app) of the Li salts estimated by the Nernst-Einstein equation. The latter was evaluated with Li vertical bar Li symmetric and LAB (Li vertical bar O-2) cells containing the electrolytes. The Li deposition/dissolution reaction basically depended on the Li+ supplying rate in the Li vertical bar Li cell; however Li dendrites were formed. Conversely, the LAB cell performance was controlled by Li oxide layers formed on the NE, resulting in similar discharge/charge properties without Li dendrites. The effects of surface-oxidation was also confirmed with Li vertical bar Li cells containing O-2 gas, where both SEI and charge transfer resistances were reduced. (C) The Author(s) 2017. Published by ECS. All rights reserved.