Ionic liquid electrolytes for aluminium secondary battery: Influence of organic solvents

Abstract

Abstract Physical and electrochemical characteristics of aluminium secondary battery systems based on aluminium anodes, sulfur–carbon cathodes and ionic liquid electrolytes were investigated. Aluminium chloride (AlCl3)/triethylamine hydrochloride (Et3NHCl) ionic liquids were used as the electrolytes. Toluene, benzene, dichloromethane (DCM), and 1,2-dichlorethane (DCE) were tested as the additives to modify the performance of ionic liquid electrolytes. DCM and DCE were found to be the better choices, with 0.2 as the optimized volume ratio of organic solvent to ionic liquid. The additives have functions of reducing the viscosities and elevating the conductivities of ionic liquid electrolytes, while having little influence on the thermal stability of battery system in normal working temperature range. To assess the electrochemical properties of the electrolytes, galvanostatic charge/discharge studies were performed at the cell voltage of 2.4 V to 0.6 V at a constant current discharge of 15 mA/g. The cell exhibits well-defined discharge voltage plateaus near 1.8 V. A discharging capacity of 113.64 mAh/g at the first cycle is obtained for the cell based on DCM-ionic liquid electrolyte, in comparison with 85.23 mAh/g for the cell based on pure IL. The discharging capacity has the highest value of 131.67 mAh/g, and remains 104.69 mAh/g after 40 cycles. This study indicates that the performance of aluminium secondary battery can be greatly improved by adding a small volume of organic additives to the ionic liquid electrolytes.