CONICET | Buscador de Institutos y Recursos Humanos

The rechargeable Li?air battery exhibits a very large theoretical energy density that can compete with fossil fuels for electric vehicle applications with an extended mileage range. The non-aqueous Li?air battery introduced in 1996 by Abraham consists of a lithium metal anode that dissolves in a non aqueous electrolyte and the resulting Li+ ions react with oxygen to form insoluble lithium peroxide Li2O2 at a porous carbon cathode during discharge1.A stable electrolyte still remains one of the biggest challenges to resolve for improving a durability of the battery. While the majority of research effort has focused on organic solvents (initially alkyl carbonates, and later ethers, acetonitrile and dimethyl sulfoxide), there has been also some interest in the use of ionic liquids as electrolyte for the Li-oxygen system. However more fundamental studies on oxygen electroreduction reaction (ORR) in this media, as well as stability studies in the presence of reactive oxygen reduced species are needed.In ionic liquid N-butyl-N-methyl pyrrolidinium bis(trifluoromethane-sulfonyl) amide (PYR14TFSI), in the absence of protons and metal ions, reversible formation of O2/O2- couple is observed, an analogous behavior as in the solutions of tetralkylammonium salts in organic solvents2. We used Rotating Ring Disc Electrode in order to detect superoxide formation in ionic liquid and its dependence on increased lithium ion concentration, and we have detected the presence of superoxide anion up to concentration of 25 mmol of Li+. The implications on the mechanism of ORR in the presence of Li+ ion will be discussed.In order to investigate the PYR14TFSI-based electrolyte stability under conditions relevant to the Li−air cell operation, in situ infrared spectroscopy experiments were performed simultaneously with electrochemical experiments and complemented by differential electrochemical mass spectrometry (DEMS). While DEMS detects electrolyte decomposition products in the gas phase, in-situ SNIFTIRS allows detection of the decomposition products in the solvent phase, adjacent to the electrode surface.Ionic liquid anion was found to be stable, while the cation PYR14+ was found to decompose in studied conditions. In oxygen saturated bis(trifluoromethane)sulfonimide lithium (LiTFSI) salt containing PYR14TFSI electrolyte carbon dioxide and water were formed at potential 4.3 V either with or without previous oxygen electro-reduction reaction. However in deoxygenated LiTFSI contacting ionic liquid no formation of CO2 or water was observed, suggesting oxygen presence to be crucial in carbon dioxide production3.