Interlayer-Expanded Vanadium Oxychloride as an Electrode Material for Magnesium-Based Batteries

Mg-based batteries, which use the Mg2+ shuttle, theoretically offer several advantages compared to the Li technology, such as higher theoretical volumetric capacity (3833mAhcm(-3)) of the Mg-metal anode, the possibility to be safely handled in air, and dendrite-free electrodeposition. In this study, vanadium oxychloride was employed as an electrode material in a Mg-based battery. As the cell delivered just 45mAhg(-1) in the first cycle, we tried to improve the delivered capacity through preliminary cycling of the VOCl electrode with Li. The strategy is based on the ability of VOCl to expand its interlayer spacing upon intercalation of ions or molecules within them. In fact, a VOCl electrode with expanded interlayer spacing should facilitate the intercalation of Mg2+, thus leading to higher specific capacities. The Li pretreatment was able to promote the specific capacity by a factor of four (170mAhg(-1)) after the first discharge at 298K. Over 130mAhg(-1) was retained at 5mAg(-1) after 70 cycles. Structural and electrochemical characterization was carried out by means of galvanostatic charge/discharge tests, cyclic voltammetry, ex situ X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy. Inductively coupled plasma optical emission spectrometry was used to determine the concentration of lithium in the electrode.