MIL-53(Al) metal-organic framework/carbon nanofibers and Al-nanoflakes/carbon composites for a stable Al-battery

Rechargeable aluminum-batteries are a promising class of energy storage devices primarily due to the high abundance of Al-ore in earth's crust, safety, high theoretical capacity and low cost. In this work, a unique nanocomposite of Al-based metal-organic framework (MOF), and carbon nanofibers (conical, graphitic) functionalized with poly(allyl amine hydrochloride) (MIL(53)-Al/p-CNFs) and a composite of Al-nanoflakes and activated carbon derived from onion peels (Al-NFs/C), are employed as cathode and anode in an Al-battery, with an AlCl3/1-ethyl-3-methyl imidazolium chloride [EMIM]+[Cl]− mixture as the electrolyte. Benefitting from the substantial effective surface area (162 m2 g−1) and the wide average pore-dimensions (∼17 nm) of the MIL53(Al)/p-CNFs composite coupled with the high electrical conductivity of p-CNFs (33 mS cm−1) and their nanostructured platelet like morphology, AlCl4− ion adsorption/reaction in the charging cycle are kinetically facilitated and maximized in the composite, resulting in a capacity of 265 mAh g−1 at 40 mA g−1, with ∼79 % capacity retention after 600 cycles, over a voltage window of 0.2–2 V, significantly enhanced compared to that of sole Al-MOF (80 mAh g−1 and 37.5 % retention after 100 cycles). AlCl4− intercalation at the cathode is confirmed from the uniform Cl distribution in the elemental map and the Cl2p doublet for the charged pristine MIL(53)-Al anode. Concurrently, the novel Al-NFs/C anode exhibits no signs of dendritic growth, and allows a uniform plating of elemental Al, during the charging process, thus resulting in the formation of a robust Al-battery. By considering the dual-ion mechanism of charge storage in the MIL-53(Al)/p-CNFs/[EMIM]+[AlCl4]−/Al-NFs/C battery, as dictated by the ratio of the electrolyte ions, the cell-level capacity and energy density are deduced to be 17.6 mAh g−1 and ∼ 21 Wh kg−1, thus paving a way forward for developing durable high performance non-aqueous Al-batteries.