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

Mg-based batteries, which use the Mg2+ shuttle, offer several advantages compared to the Li technology such as higher theoretical volumetric capacity (3833 mA h cm-3) of the Mg-metal anode, the possibility to be safely handled in air and dendrite-free electrodeposition. In this study, VOCl was employed as electrode material in a Mg-based battery. Since the cell delivered just 45 mA h g-1 in the first cycle, we tried to improve the delivered capacity by a 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-pre-treatment was able to promote the specific capacity by a factor of four (170 mA h g-1) after the first discharge at 298 K. Over 130 mA h g-1 were retained at 5 mA g-1 after 70 cycles. The structural and electrochemical characterization were carried out by means of galvanostatic charge/discharge tests, cyclic voltammetry (CV) and ex-situ X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) as well as transmission electron microscopy (HR-TEM) coupled with energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS). Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the concentration of lithium in the electrode.