Resumen de Design of new ionic liquid-based electrolyte for lithium-oxygen battery
The lithium-oxygen (Li-O2) battery has received much interest in the last few years as global energy demand is growing and availability of fossil energies becomes limited. With its high theoretical energy density approaching that of gasoline, this technology is potentially one of the best solutions for electric vehicles (EV). However, this new technology will remain a research topic for at least the next 20 following years, due to the low cyclability, the limited electrical efficiency, the low rate capability and the difficulty of assembling a safe practical cell working in ambient atmosphere as good as at the laboratory scale under well-controlled conditions. Recently, Room Temperature Ionic Liquids (RTILs) attracted much attention. Indeed, their high thermal stability, non-flammability, low vapor pressure and wide potential window can offer an interesting alternative to the traditional organic solvents for Li-O2 battery electrolyte. In this context, the chemical and physical properties of RTILs are determined in order to design a suitable RTIL-based electrolyte. The study of these parameters, compared to the electrochemical performance of the battery, enables to find a correlation between the viscosity, the lithium solvation of the electrolyte and the capacity of the battery. Given that RTILs viscosity is too high for adequate battery reaction kinetics, a mixture of an organic solvent and a RTIL is then studied. Electrolytes composed by dimethylsulfoxide (DMSO), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI TFSI) and LiClO4 are characterized, evaluating the suitability of such electrolyte. The optimum concentration of EMI TFSI enables to reduce the overpotential from 1.43 V to 1.06 V, with a cyclability of 69 cycles with 200 mAh g-1 of limited capacity. Thereafter, a real-time synchrotron X-ray diffraction technique is applied to analyze the oxidation/reduction of lithium oxide derivatives in an operating battery cell. Four different electrolytes composed of DMSO, a RTIL and LiClO4 are tested. This study proves that the lithium used as anode material is reacting with the RTIL, forming continuously LiOH, independently of the cycling stage. The comparisons between the different electrolytes provide insights for future investigation on the improvement of electrolyte design of this technology.
