A Low-Cost Al-Graphite Battery with Urea and Acetamide-Based Electrolytes

A key challenge facing future battery technologies is finding alternatives for currently used raw materials, which are often expensive and are becoming increasingly scarce. In recent years, Al-graphite batteries have been proposed as a valid alternative to Li-ion systems due to their low-cost and sustainability.^[1]<br/>In contrast to commonly used expensive ionic liquid based electrolytes e.g. [EMIm]Cl/AlCl₃, our reported batteries use urea/AlCl₃ and acetamide/AlCl₃ deep eutectic solvents (DES) as low-cost alternative.^[2]<br/>By carefully selecting amide composition, Al speciation in the DESs can be modified, as confirmed by Raman and NMR spectroscopy. Al₂Cl₇^– and AlCl₄^– are actively involved in Al dissolution and deposition on the Al electrode, whereas AlCl₄^– is intercalated between layers of graphite on the cathode.^[3]<br/>Hence, battery performance such as specific capacity, long-term stability and self-discharge is greatly influenced by electrolyte composition as well as structure and morphology of the graphite cathode. We correlate the electrolyte speciation changes with resulting battery performance by systematic electrochemical investigations employing urea and acetamide eutectics of different compositions. The reversible graphite intercalation is examined for minimally processed natural graphite flakes of different particle sizes employing electrochemical methods and Raman spectroscopy.<br/>In addition to this optimization of abundant raw materials, specific capacities can be enhanced by electrochemical treatment of the assembled batteries.<br/>Cycling experiments employing urea electrolyte with &gt;8000 cycles, exhibiting a specific capacity of around 50 mAh/g at 2.5 A/g (50C) demonstrate the long-term stability. The development of a corrosion stable pouch cell design allows practical application of these batteries. Thanks to its high rate capability and stable long-term cycle life Al-graphite batteries are a promising candidate for high power applications.<br/><br/>Literature:<br/>[1] G. A. Elia, N. A. Kyeremateng, K. Marquardt, R. Hahn, <i>Batteries & Supercaps</i> <b>2019</b>, <i>2</i>, 83. [2] F. Jach, M. Wassner, M. Bamberg, E. Brendler, G. Frisch, U. Wunderwald, J. Friedrich, <i>ChemElectroChem</i> <b>2021</b>, <i>8</i>, 1988. [3] M. Angell, G. Zhou, M.-C. Lin, Y. Rong, H. Dai, <i>Adv. </i><i>Funct. </i><i>Mater.</i> <b>2020</b>, <i>30</i>, 1901928.