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The cycle stability of lithium negative electrodes for Li-air secondary batteries was studied under oxygen atmosphere using Li|Li symmetric cells with three organic electrolyte solutions: 1.0 M LiCF3SO3/tetraglyme (G4), 1.0 M LiN(SO2CF3)2/G4, and 1.0 M LiNO3/G4. Of these, 1.0 M LiNO3/G4 showed excellent stability without dendrite deposition, even for increased dissolution/deposition capacity from 0.50 to 2.0 mAh cm-2. These results are considered to be due to the stable Li2O passivation layer that was formed, not only by the direct reaction with oxygen, but also by the action of NO3 - as an oxidant, which released NO2 - as a redox mediator. Li-O2 cells with 1.0 M LiNO3/G4 showed a clear charging voltage plateau at 3.7 V, which evidenced the redox mediator effect of NO2 -, and cell cycleability was enhanced to 25 cycles. [ABSTRACT FROM AUTHOR]

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 αapp of 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 O2 gas, where both SEI and charge transfer resistances were reduced. [ABSTRACT FROM AUTHOR]