A Low-Cost Rechargeable Aluminum/Natural Graphite Battery Utilizing Urea-based Ionic Liquid Analog

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The rising demand for rechargeable energy storage systems along with the market-driven increase of raw material prices have led to extensive research and development on post-lithium-ion battery systems. Among emerging candidates, aluminum (Al)-based batteries are particularly appealing due to the abundance of material, low cost, ease of handling in an ambient environment, and high theoretical gravimetric and volumetric capacities. To date, most studies on Al batteries employ Al as the anode, carbonaceous/graphitic materials as the cathode, and dialkylimidazolium chloride-based chloroaluminate ionic liquids as the electrolyte. Despite the excellent performance delivered by such systems, drawbacks such as complicated and energy-intensive preparation processes of the cathode materials as well as the high cost of dialkylimidazolium chloride, greatly diminish the various benefits of employing metallic Al as the anode materials. Inspired and motivated by the drawbacks faced in previous studies, we investigated a new class of ionic liquids, namely ionic liquid analogs (ILAs), which can be derived from a mixture of AlCl3 and urea. Considering its large production rate and its environmental friendliness as a commercial fertilizer, energy storage systems that utilize urea-based electrolyte will have significant economic and environmental cost advantages over conventional. In addition, to further enhance the scalability of Al batteries employing urea-based electrolytes, we selected widely available natural graphite (NG) flakes as the cathode material. It has been shown that with a simple ultrasonication process of NG flakes for 30 min, the assembled battery exhibited an average specific capacity of 49.5 mA g-1 at a high current density of 600 mA g-1 (~12 C) with ~96.2 % Coulombic efficiency (CE) across 1,000 cycles with two distinct discharge voltage plateaus at 2.0-1.8 and 1.6-1.3 V, respectively. In addition, the cell could also sustain a high current density of 1,000 mA g-1 (~20 C) while delivering an appreciable capacity of ~32 mAh g-1 with ~97.5% CE. This fast-charge capability and long-term stability of ambient temperature Al batteries employing urea-based electrolyte are the first reported in this study. By considering the overall cell performance as well as the costs of components used in this battery, we consider this battery as a promising candidate for future large-scale energy storage systems. Technical charts to be inserted once cleared by U of T publication.

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