Phosphonium-based deep eutectic solvents: Physicochemical properties and application in Zn-air battery

Abstract

Electrolytes play a significant role in metal-air batteries and influence the battery's performance. Deep eutectic solvents (DESs) are viable and attractive candidates as high-performance electrolytes in batteries. This study investigated the temperature-dependent physicochemical properties of several phosphonium-based DESs such as the freezing point, density, viscosity, surface tension, and conductivity. The viscosity of the DES electrolyte is correlated as a function of molar conductivity using Walden's rule. Subsequently, the electrochemical characterizations of a Zn-air battery with the DES electrolyte, such as the cell voltage, power density, and current limit are studied. The electrochemical and physicochemical profiles of the phosphonium-based DESs possess dependence on the salt-to-hydrogen bond donor (HBD) molar ratio and appear viable for further exploration in metal-air battery applications. To the best of our knowledge, this is the first study that investigates the efficacy of the phosphonium-based DESs as the electrolyte in Zn-air batteries.