Limited lithium resources in the Earth’s crust alongside the ever-growing demand for rechargeable batteries for portable electronics and electric vehicles (EVs) have led to extensive research on rechargeable battery systems beyond lithium-ion (Li-ion) technology. Among various possible technologies, multivalent-ion batteries offer the potential for cost-effective and safe energy storage devices with high energy density. However, the realization of multivalent-ion batteries depends on the development of electrolytes and cathode materials for these systems. Rechargeable aluminum batteries are promising alternative energy storage devices due to their low cost, abundance of Aluminum, and the potential for three-electron redox reaction leading to higher capacities. Aluminum has a theoretical volumetric capacity of 8040 mAh cm^-3 (four times higher than that of lithium). Also, it can be easily handled in open air resulting in an enhanced cell fabrication options and elimination of some of the safety issues associated with lithium and sodium batteries [1]. Various materials have been studied as potential cathodes for Aluminum batteries, however, most suffer from problems such as low capacity, lack of distinct voltage plateaus, and low cycle life with significant capacity decay over 100 cycles. Herein, we are presenting several members of two-dimensional (2D) transition metal carbides (called MXenes) as potential cathode materials for rechargeable Aluminum batteries utilizing a mixture of AlCl₃ and [EMIm]Cl as the electrolyte. MXenes are a family of 2D transition metal carbides and/or carbonitrides that are produced by selective removal of the A layer (i.e. Al) from MAX phases (i.e. Ti₂AlC), a large family of hexagonal layered ternary carbides and carbonitrides [2, 3]. The MXene based Aluminum batteries work by electrochemical deposition and dissolution of aluminum at the anode and intercalation/de-intercalation of Al³⁺ ions between the layers of 2D MXene nanosheets. Among different studied MXene materials, Ti₂CT_x (T_x represents different functional groups such as O, OH, and F on the surface of MXene sheets) and V₂CT_x showed distinct charge and discharge plateaus with first discharge cycle capacity of as high as 200 mAh/g and 400 mAh/g, respectively at current density of 100 mA/g. The capacity of Ti₂CT_x dropped to around 60 mAh/g over 50 cycles, however, the V₂CT_xmaintained a reversible capacity of 200 mAh/g over 50 cycles with a high coulombic efficiency of ~95%. The MXene based Al-ion batteries were cycled in 1.7 V potential window and showed a good rate-capability. Our results show the high potential of MXenes as aluminum battery cathodes and open a new direction in search for high capacity cathode materials for these battery systems.

 

Keywords: 2D, Transition Metal Carbides, MXenes, Aluminum battery

 

References

1. G. A. Elia, et al., Adv. Mater. 28, 7564-7579 (2016).

2. M. Naguib, et al., ACS Nano. 6, 1322–1331 (2012).

3. B. Anasori, M. R. Lukatskaya, Y. Gogotsi, Nat. Rev. Mater. 2, 16098 (2017).