Study and Development of Al-Air Battery Applying Room Temperature Ionic Liquid Electrolyte

Abstract

Metal – air battery chemistry defers by the electrolyte of choice. Zn – Air, Al – Air and Fe – Air batteries were already reported utilizing aqueous alkaline and brine solutions as electrolytes. The main advantage of these specific electrolyte of choice is theirs high ionic conductivity and the ability to efficiently reduce oxygen into hydroxide anions. Nevertheless, such batteries systems suffers from major drawbacks, such as comparably low voltage and specific energy, for Zn and Fe, and extremely high corrosion rates under open circuit condition, for Al. To deal with such challenges a fairly new approach has been taken. The approach is based on Room Temperature Ionic Liquids (RTIL) utilization as electrolyte in Metal – air batteries research. Among these, one could find Na –and Si – air battery systems. RTILs offer unique properties, while serving as electrolytic media. Among the properties one can count their low vapor pressure, even at considerably elevated temperatures, the high intrinsic ionic conductivity, non-flammability, thermal and chemical stability with considerably large electrochemical windows (in some cases as much as 5 V) what makes them remarkable electrolytes for high-end electrochemical applications. In our recent report[1], a new Al – air battery was presented applying 1-ethyl-3-methylimidazolium oligoflourohydrogenat (EMIm(HF)2.3F) RTIL. The specific conductivity of this exact stoichiometry is 100 mS cm-1 at 298 K, one the highest of all RTIL family, comparable to that of 0.5 M KCl aqueous solution. The presented novel Al – air battery can sustain current densities up to 1.5 mA cm-2, producing capacities above 140 mA h cm-2, and thus utilizing above 70% of the theoretical Al capacity. This is equivalent to outstanding energy densities of 2300 W h kg-1 and 6200 W h L-1. In the current work a further investigation of the RTIL based Al – air battery is presented. Combining surface characterization with electrochemical experiments, both in half cell and also a full battery discharge, an ongoing progress in the study of this unique battery is shown. One of the main achievements in the study is related to the understanding of the operation voltage drop (deep). Conditions for elimination of this voltage deep were established and will be reported. [1] D. Gelman, B. Shvartsev, Y. Ein-Eli, J. Mater. Chem. A. 2.47 (2014) 20237-20242.