The effect of additive supporting electrolytes on transport and electrochemical properties of deep eutectic solvent (DES) applied in non-aqueous redox flow batteries

Although the utilization of deep eutectic solvents (DES) as non-aqueous electrolyte of redox flow batteries has received enormous attention, its properties like high viscosity and low conductivity always remain a matter of concern, due to their negative effect on final battery power performance. Herein, the introduction of two types of additive supporting electrolytes (one: a mixture of dimethyl carbonate (DMC) and ethylene carbonate (EC) and the other: ethyl acetate (EA)) remarkably decreasing the viscosity and impedance of the DES with iron ions is reported, especially for DMC+EC. In addition, the cyclic voltammetry results show that the reversibility of Fe(III)/Fe(II) redox couple, and the reaction kinetics are improved after adding DMC+EC, while EA has little effect on improving the electrochemical performance. From Raman spectroscopy, it is found that a distinct characteristic peak occurs at 895 cm−1 for DMC+EC mixture, whereas the intensity of this peak is weak for EA. It is highly probable that the appearance of this characteristic peak serves to improve the electrochemical properties of DES.