Effect of Ambient Conditions on Ionic-Liquid-Electrolyte Aluminium-Air Batteries
Authors: Aslanbas Özgür , Durmus Y. Emre , Tempel Hermann , Schierholz Roland , de Haart L.G.J. , Kungl Hans , Eichel Rüdiger-Albrecht 
Published: February 2020

Increasing energy demand and environmental concerns dictate the utilization of renewable energy sources into the electricity networks globally. Commonly used renewable sources, such as solar and wind power supply a fluctuating power output both daily and annually that can create excess electricity when it is not demanded. Therefore, this excess energy has to be stored to supply future demands. However, such storage systems should be based on cheaper and more abundant materials considering the amount of energy will be stored.

One option to provide cheap and sustainable energy storage is the aluminium-air battery due to its high theoretical energy density (2980 Ah kg-1 for Al) and high natural abundance of aluminium (8.1% in earth’s crust). Research on aluminium anodes with alkaline electrolytes has been conducted since 1960s1. In these systems, high corrosion rates, surface passivation and evaporation of the aqueous electrolyte resulted in low discharge capacities and low anode mass utilizations. A recent work about Al-Air batteries with room temperature ionic liquid electrolyte showed, that high anode mass utilization up to 70% could be obtained2.

This work investigates the battery performance of Al-Air batteries with oligo-fluorinate ionic liquid electrolytes under different operating and ambient conditions. The objective was to identify the influence of the temperature on the performance, corrosion rates and mass utilizations of the anode. The methods applied in the study contain the characterization of electrochemical properties of the cells, such as open circuit potentials (OCP) and the potentials at various discharge current densities as a function of temperature. In the scope of the investigations, variations of the water content of the room temperature ionic liquid electrolytes and its effect on the cell characteristics were analysed. The microstructures of the anode surfaces were investigated at the different stages of the battery operation via microscopy techniques.

Room temperature electrochemical experiments showed that, at high current densities (1.5 mA/cm2) relatively high discharge capacities up to 120 mAh can be achieved and high mass utilizations can be accomplished with such battery systems. These mass utilizations are lower than those of the alkaline electrolyte based Al-Air battery systems. Low current density discharge experiments indicated that, rising temperatures increased both OCP and discharge potentials. However, the corrosion rate is increased and the mass utilization is substantially decreased at low current densities. Higher temperature promotes corrosion rate of the anodes and reduces anode mass utilization as well as the discharge capacity.  Therefore, a better understanding of the temperature driven processes on the cell performance of the battery is necessary.

1.             Zaromb, S. The Use and Behavior of Aluminum Anodes in Alkaline Primary Batteries. J. Electrochem. Soc. 109, 1125 (1962).

2.            
Gelman, D., Shvartsev, B. & Ein-Eli, Y. Aluminum–air battery based on an ionic liquid electrolyte. J. Mater. Chem. A 2, 20237–20242 (2014).