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

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 (EtNH 3 Cl) and dimethylamine hydrochloride (Me 2 NH 2 Cl). The advantages of these alkylamine hydrochlorides over their tertiary amine counterparts (Me 3 NHCl and Et 3 NHCl) are their lower cost, odorless nature, and a lower molecular weight that would reduce the battery weight. Although the binary systems of EtNH 3 Cl–AlCl 3 and Me 2 NH 2 Cl–AlCl 3 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 AlCl 4 − 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 EtNH 3 Cl–Me 2 NH 2 Cl–AlCl 3 electrolyte is expected to advance Al batteries toward practical application and commercialization. • A novel chloroaluminate ionic liquid for rechargeable Al batteries is proposed. • The electrolyte comprises primary and secondary alkylamine hydrochlorides. • Advantages include low cost, odorless nature, and low molecular weight. • Lower intercalation stage than in conventional electrolyte is demonstrated.