Effects of Li Salt Anions and O 2 Gas on Li Dissolution/Deposition Behavior at Li Metal Negative Electrode for Non-Aqueous Li-Air Batteries

Abstract

© The Author(s) 2017. Published by ECS. All rights reserved. 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 | 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 σ, viscosity, density, and apparent dissociation degree αappof the Li salts estimated by the Nernst–Einstein equation. The latter was evaluated with Li | Li symmetric and LAB (Li | O2) cells containing the electrolytes. The Li deposition/dissolution reaction basically depended on the Li+supplying rate in the Li | 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 | Li cells containing O2gas, where both SEI and charge transfer resistances were reduced.