Ionic Liquid Analogs of AlCl₃ with Urea Derivatives as Electrolytes for Aluminum Batteries

Abstract

Low-cost aluminum-graphite batteries utilizing an AlCl 3 /urea ionic liquid analog are promising candidates for grid-scale electricity storage. This work describes the use of N-methyl and N-ethyl derivatives of urea, which yield lower viscosity electrolytes, as a result of a lower ionic concentration. These electrolytes have increased ionic conductivities, and higher discharge voltages due to the differences in concentrations of electroactive species.

Comparison of Chloroaluminate Melts for Aluminum Graphite Dual‐Ion Battery Application

“…The columbic efficiency behavior of the AGDICs links well with the anodic electrochemical stability of the various electrolytes (Figure 3c). The superior Urea : AlCl 3 stability against oxidation guarantees the best coulombic efficiency in AGDICs; result in agreement with other reports [17,22] . The Acetamide:AlCl 3 system shows a columbic efficiency of about 96–97 %, thus in line with this composition‘s lower anodic stability.…”

Comparative Study of Guanidine-, Acetamidine- and Urea-Based Chloroaluminate Electrolytes for an Aluminum Battery

“…The viscosity values found in this study are comparable to those reported in previous studies for the AlCl 3 :Urea (218–240 cP), ,,, AlCl 3 :Guanidine (51 cP), and AlCl 3 :Acetamidine (30–70 cP) electrolytes …”

“…Previous studies indicated that this peak can be associated with mixed ligand urea species, including [AlCl 3 (urea)], [AlCl 2 (urea) 2 ] + . This is characteristic of the acidic AlCl 3 :Urea system, in line with previous studies. ,,, The Al species and associated chemical shifts identified from these literature studies are presented in Table .…”

Ternary Ionic Liquid Analogues as Electrolytes for Ambient and Low-Temperature Rechargeable Aluminum Batteries

“…To better understand the different species present in the electrolyte mixtures and their local environments, liquid-state 27 Al and 1 H single-pulse NMR experiments were acquired under quantitative conditions (Figure ). The 27 Al and 1 H single-pulse NMR spectra of the binary mixtures ( X = 0 and 1) are both in good agreement with the literature. ,, The 27 Al single-pulse spectrum of the AlCl 3 –[EMIm]Cl (1.3:1, X = 0) electrolyte shows two 27 Al signals at 103.7 and 97.7 ppm, which are due to AlCl 4 – and Al 2 Cl 7 – , respectively . The addition of urea to the binary AlCl 3 –[EMIm]Cl mixture results in the generation of additional neutral and cationic species, specifically AlCl 3 (urea), [AlCl 2 (urea) 2 ] + , and AlCl 3 (urea) 2 complexes, which have 27 Al shifts of 89, 74, and 54 ppm, respectively. , As discussed below, rapid chemical exchange between these species results in significant 27 Al broadening.…”

“…The 27 Al and 1 H single-pulse NMR spectra of the binary mixtures ( X = 0 and 1) are both in good agreement with the literature. ,, The 27 Al single-pulse spectrum of the AlCl 3 –[EMIm]Cl (1.3:1, X = 0) electrolyte shows two 27 Al signals at 103.7 and 97.7 ppm, which are due to AlCl 4 – and Al 2 Cl 7 – , respectively . The addition of urea to the binary AlCl 3 –[EMIm]Cl mixture results in the generation of additional neutral and cationic species, specifically AlCl 3 (urea), [AlCl 2 (urea) 2 ] + , and AlCl 3 (urea) 2 complexes, which have 27 Al shifts of 89, 74, and 54 ppm, respectively. , As discussed below, rapid chemical exchange between these species results in significant 27 Al broadening. As the urea content increases, the 27 Al chemical shifts move to lower frequencies, indicating larger concentrations of the AlCl–urea complexes, as expected.…”