Aluminum Intercalation and High Capacity of Two-Dimensional (2D) Vanadium Carbide (MXene) Cathode in Rechargeable Aluminum Batteries

Abstract

Rechargeable aluminum batteries that utilize aluminum metal as the anode are one of the most promising alternative energy storage systems for current Li-ion batteries that suffer from flammability, safety issues, high cost, and limited lithium resources. Aluminum is the most abundant metal in Earth’s crust, offers three-electron redox reactions in electrochemical systems, and has the highest theoretical volumetric capacity of 8040 mAh cm-3 among all metals and reasonably high theoretical gravimetric capacity of 2980 mAh g-1. Also, aluminum metal can be handled in the open air; thus, aluminum batteries benefit from high safety and facile cell fabrication and operation compared to lithium and sodium battery systems [1]. However, development of these battery systems is mostly hindered by a lack of cathode materials that can host aluminum cations and offer high capacities and insertion potentials. In this presentation, we show reversible intercalation of aluminum in two-dimensional (2D) vanadium carbides (V2C), a member of MXene family of materials, as a potential high-performance cathode material for rechargeable aluminum batteries. MXenes with a general formula of Mn+1Xn (n=1,2, and 3, M is a transition metal, and X is carbon and/or nitrogen) are a family of 2D transition metal carbides and/or carbonitrides that are produced by selective etching of the A layer elements (i.e. Al) from MAX phases (i.e. V2AlC), a large group of layered ternary carbides, nitrides, and carbonitrides [2-4]. The Aluminum battery cells incorporating V2C MXene as cathode operates by electrochemical deposition and dissolution of aluminum at the anode and intercalation/de-intercalation of Al3+ ions in between the layers of 2D nanosheets of MXene cathode. Our study shows that through a careful and proper fabrication of electrode structure, V2C cathodes can deliver reversible capacities more than ~ 200 mAh g-1 at a high charge and discharge rate of 100 mA g-1, comparable to current cathode materials for lithium and sodium-ion batteries. V2C cathode exhibits a high Coulombic efficiency of above 95% and delivers a good rate capability in a 1.7 V potential window. We also show that change in the oxidation state of the transition metal in the MXene structure plays an important role in charge storage mechanism of MXenes as cathode materials for Aluminum batteries. Keywords: 2D, Vanadium carbide, MXenes, Aluminum battery