A rechargeable Al-ion battery: Al/molten AlCl₃-urea/graphite

A new Al-ion battery based on an affordable and nontoxic liquid electrolyte made from molten AlCl₃/urea was assembled. As the cathode material, natural graphite shows two well-defined discharge voltage plateaus at about 1.9 and 1.5 V with a high specific capacity of 93 mA h g⁻¹ and excellent coulombic efficiency (>99%). The attractive capacity (about 78 mA h g⁻¹) is retained even at a high current density of 1000 mA g⁻¹. Moreover, no faster fading in capacity is observed after 500 cycles. This electrolyte could provide a new system for Al ion batteries, which can be used for large scale energy storage, owing to its cost advantages, high-rate capability and durability.