(146d) Eutectic Electrolytes for Secondary Al-CO2 Batteries

Metal-CO₂ batteries have emerged as a promising strategy for enhancing energy storage technology while capturing/concentrating carbon dioxide. We previously demonstrated an Al-CO₂ battery utilizing a homogeneous iodine-based redox mediator to enable the reversible discharge and charge of the battery with an ultra-low overpotential of 0.05V (Fetrow et al., ACS Appl. Mater. Interfaces 2023, 15, 10, 12908–12914). The imidazole-based electrolyte employed earlier is common for aluminum stripping/plating but is expensive, corrosive, and hygroscopic. In this study, we investigate several alternative electrolytes. These include AlCl₃-based melts previously explored for aluminum-ion batteries, as well as novel AlI₃-based eutectic melts. As shown in Figure 1, both urea- and acetamide-AlCl₃ melts are compatible with the aluminum iodide homogeneous catalyst. We characterized electrolyte performance electrochemically and investigated the mechanisms enabling ionic liquid formation and performance using Raman and NMR spectroscopies. These findings facilitate the development of a practical Al-CO₂ battery.

Figure 1: Cyclic voltammetry and galvanostatic discharge studies of alternative ionic liquids for Al-CO₂ batteries. A, B) Cyclic voltammogram of coin cells with aluminum and stainless steel electrodes using 1.3:1 AlCl₃:acetamide and 1.3:1 AlCl₃:urea electrolytes, respectively. Dashed lines indicate cells without added 0.05M AlI₃. C) Galvanostatic discharge of an Al-CO₂ battery with aluminum and nanostructured carbon cathodes using a 1.3:1 AlCl₃:acetamide electrolyte containing 0.05M AlI₃. Discharged at 20 mA/g_carbon to a capacity of 620 mAh/g_carbon.