Properties of Asymmetric Benzyl-Substituted Ammonium Ionic Liquids and Their Electrochemical Properties

Abstract

Benzyl-substituted quaternary ammonium ions were used to form room-temperature ionic liquids with chloroaluminate ions. Asymmetric ammonium structures significantly lowered the melting point of the ionic liquid. Asymmetric benzyl-substituted ammonium chlorides were mixed with AlCl 3 to form acidic room-temperature ionic liquids. It is shown that the melting point and viscosity are a function of the symmetry of the quaternary ammonium ion and its molecular weight. Asymmetry and low molecular weight favor lower viscosity and melting point, and higher conductivity. These liquids were neutralized with NaCl and tested as electrolytes for sodium batteries. The neutralized ionic liquid of benzyldimethylethylammonium chloride had a low self-discharge current ͑3.96 A/cm 2 ͒ at room temperature on a platinum electrode substrate.

DOE STI Product/Final Report Number 3 Electrochemical Investigation of Novel Electrolytes for Ambient Temperature Sodium Batteries

“…24 An acidic melt at a higher acidity (N=0.67) reported were applicable for aluminum plating. Table III-3.1 is the comparison of the two electrodes in the same melt at the same temperatures.…”

“…The discharge rate for salt VI though is similar to the value, 52.0 μA/cm 2 , observed for a salt III IL at 71°C. 24 The increased selfdischarge rate for salt VII is attributed to the reduced IL viscosity relative to the IL of salt III.…”

“…Salt III was chosen as a reference based on its ability to form a room temperature IL and support the reduction/reoxidation of sodium. 24 When mixed with AlCl 3 , salts I, VIII and IX did not form room temperature…”

“…Previously, we showed that the acidic and neutral mixtures formed from salt III were liquid at temperatures slightly below room temperature. 24 For mixtures formed with salt VII, melting points of 0.3°C and 3.7°C for the acidic and neutral mixtures, respectively, were measured. The acidic mixture with salt VI was also fluid at room temperature.…”

“…This kinematic viscosity is nearly onequarter of that measured for the IL of salt III, 222 mm 2 /s. 24 The higher conductivity and lower kinematic viscosity is a result of the smaller size of salt VII versus salt III.…”