Development of Aluminum Air Battery Using an Ionic Liquid Electrolyte Solution

Abstract

Introduction. Metal air batteries are attracting attention as an automobile power.There is a use track record of already zinc as an electrode for air battery, but the light metal such as Li and Mg also has been attracting attention as an electrode for air battery. Al as the metal active material is attractive because it is rich in resources and the energy density of Al is high. In alkaline aqueous solution, Al is dissolved and emits electrons. But It would be self-discharge by the corrosion reaction with hydrogen occurs even at no load. This reaction is independent of the cell reaction, resulting in extra material loss. Therefore, by limiting the water content using a hydrophobic ionic liquid, we consider a mechanism for controlling the self-discharge reaction of Al. In this study, since the air electrode didn’t work in hydrophobic ionic liquid, we aimed to develop a new metal-air battery incorporating a mechanism for controlling the self-discharge of the Al with a hydrophobic ionic liquid. Experiment. Al plates (purity 99%, thickness 0.5 mm) was used and cut into an appropriate size. Air electrode supported carbon powder to nickel and sealed with silicon sheet was used . Hydrophobic ionic liquids ( Emim-TFSI,1-Ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide ) and hydrophilic ionic liquid(EMISE, 1-Ethyl-3-methylimidazolium ethyl sulfate ) was used in the experiment and vacuum dried it for 24h. In addition, the electrolytic solution was also used DMSO. The electrochemical cell was self-made. This cell is composed of two tanks and the ion exchange membrane. It is composed of Tank A and Tank B, and using a cation exchange membrane as a partition. Tank A is where to put the ionic liquid or DMSO in and put KOH pellet in. Also Al plate was immersed in the A tank. Tank B is where to put 1M KOH or 8M KOH solution in. In this experimental system, it is possible to take out current by adding water to the A tank. However, when the experiments using ionic liquid, temperature of Tank A was maintained at approximately 50 degrees using a heater and a thermocouple. In case of DMSO, the temperature of Tank A was room temperature. It was measured voltage-current characteristic curve of the total of six types of electrochemical cells by the combination of the electrolyte of the tankA and tankB. Moreover, we carried out Electrochemical impedance measurements for an electrochemical cell with EMIM-TFSI and 8M KOH and carried out an analysis of the electrochemical cell. Results. We were able to obtain 6 kinds of current-voltage characteristic curve. Judging from the Current-voltage characteristic curve, we can obtain the non-ideal curve, namely ohmic curves. Among the results obtained, The electrochemical cell were found to show high performance when we used the hydrophilic ionic liquid (EMISE) or hydrophobic ionic liquid (EMIM-TFSI) in the A tank and the 8M KOH in the B tank. However, while the fluidity of the EMIM-TFSI was maintained, the fluidity of EMISE was lost after the experiments. From the results of impedance measurement, We were able to measure the magnitude of the resistance component of the anion permeable membrane.