Low-cost ionic liquid electrolytes based on low-molecular-weight primary and secondary alkylamine hydrochlorides for rechargeable Al batteries

Abstract

Rechargeable batteries with Al metal as the negative electrode are promising candidates for post‑lithium-ion batteries. However, the cost of the most commonly used electrolytes, chloroaluminate ionic liquids based on 1-ethyl-3-methylimidazolium chloride (EMICl), is prohibitive. Herein, we report a novel, low-cost chloroaluminate ionic liquid electrolyte based on primary and secondary alkylamine hydrochlorides, namely, ethylamine hydrochloride (EtNH3Cl) and dimethylamine hydrochloride (Me2NH2Cl). The advantages of these alkylamine hydrochlorides over their tertiary amine counterparts (Me3NHCl and Et3NHCl) are their lower cost, odorless nature, and a lower molecular weight that would reduce the battery weight. Although the binary systems of EtNH3Cl–AlCl3 and Me2NH2Cl–AlCl3 are not liquids at room temperature, mixing the two systems results in an ionic liquid at room temperature. The electrodeposition of Al and intercalation of AlCl4− into graphite in this electrolyte system are demonstrated. The alkylammonium cations decompose only at potentials below −0.3 V vs. Al. The performance of Al–graphite batteries incorporating this low-cost electrolyte is comparable to that of batteries using the conventional expensive EMICl-based electrolytes under typical charge-discharge conditions. The low-cost EtNH3Cl–Me2NH2Cl–AlCl3 electrolyte is expected to advance Al batteries toward practical application and commercialization.