Synthesis and Surface Modification of Two-Dimensional Mxenes As Potential Magnesium Battery Cathodes

Rechargeable magnesium batteries may allow for safer and cheaper batteries compared to those based on Li-ion technology, mostly due to the possibility of utilizing magnesium metal as anode material without forming dendrites [1]. However, since the first prototype was reported in 2000 [2], limited improvements on the cathode side have been achieved, where either trapping of magnesium ions or low operating potentials limit the performance [3]. After its discovery in 2011 [4], a new group of two-dimensional materials, known as MXenes, has been proposed as possible cathode materials for rechargeable magnesium batteries, due to their good electronic properties and ion hosting capabilities [5]. Various MXenes have already shown promising behavior in Li-ion batteries [6]. Here, we present data from several compositions of MXenes formed by the selective etching of Al from the initial MAX phase precursor in concentrated HF acid. The MAX phases were produced by solid state reaction synthesis through careful control of temperature and stoichiometry to obtain the desired end compositions. After successful etching, different treatment methods have been investigated in order to control the surface termination groups together with the interlayer distance between the flakes. The materials were characterized by SEM, EDX, XRD and XPS to map out the elemental and structural changes resulting from these treatments. Electrochemical properties have also been assessed through cyclic voltammetry and galvanostatic charge/discharge analysis. References: [1] M. Masaki, Journal of Power Sources 196 (2011), 7048-7055 [2] D. Aurbach et al., Nature 407 (2000) 724-727 [3] P. Canepa et al., Chemical Reviews 117 (2017) 4287-4341 [4] Naguib et al., Adv. Mater. 23 (2011) 4248-4253. [5] Naguib et al., J. Am. Chem. Soc. 135 (2013) 15966-15969 [6] C. Eames, M. S. Islam, J. Am. Chem. Soc. 136 (2015) 16270-16276