Ambient Air Operation in Non-Aqueous Li-Air Batteries: Influence of Water on Electrochemical Li Cycling
Ambient air operation is one of the key points to realize the Li-air battery system. So far, to simplify the mechanistic understanding of problems and to highlight the material aspects obviously, pure O2 gas has been preferably used for this study. However, the utilization of ambient air into the system is undoubtedly essential to make it viable. A few preliminary studies have just considered the effect of water on Li-air battery performances [1-3], but much effort need to be devoted to this research. We have already demonstrated ionic liquid based Li-air batteries [4-7]. Some ionic liquids have great chemical and electrochemical properties against O2radical species as well as Li metal. Furthermore, since ionic liquids have a promising feature of non-volatility, they possess some advantages as the battery electrolyte considering ambient air operation.
In this presentation, we will focus on a Li anode side in the ionic liquid electrolyte under presence of water . Some ionic liquids were compared with typical organic solvents as described in Figure 1. Figure 1 shows the voltage profiles of electrochemical Li cycling in the (a) PC-LiTFSI organic electrolyte and (b) PP13TFSI-LiTFSI ionic liquid electrolyte. Black and red lines represent the electrolyte without and with 1% of water, respectively. These cells were operated at room temperature at a constant current density of 0.1 mA/cm2. In the PC based electrolyte without water, the potentials observed during Li cycling were continuously much lower than that in the PP13TFSI based electrolyte under the same condition. However, in the PC based system, 1 % of water drastically changed the electrochemical behavior during Li cycling, while it did not have such big impact in the PP13TFSI based system. This difference should be originated from not only nature of solid electrolyte interface (SEI) but also state of water in the media. This discussion will become some clues of future material design as well as entire cell design, leading to the enhancement of Li-air battery performances.
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