Phosphate-Based Electrolyte and Pristine Graphite Cathode for a High-Voltage Rechargeable Dual-Ion Magnesium Battery

The pristine graphite cathode and Mg anode magnesium dual-ion battery (MDIB) consists of a noncorrosive and nonvolatile electrolyte, i.e., 0.1 M magnesium trifluoromethanesulfonate (Mg(OTf)2), in a 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIMPF6) ionic liquid. In the TGA analysis, the thermal stability of the electrolyte at Tonset 383 °C indicated its high stability. The electrolytes define a wide potential window until 4.65 V vs Mg/Mg2+ when measured on a Pt plate and were examined by the linear cyclic voltammograms (LSV) technique. The electrochemical analysis of the magnesium–graphite cell in the electrolyte showed defined sharp anodic and cathodic peaks that correlate the intercalation and deintercalation of PF6– anions through the graphite lamellar spaces in addition to the dissolution and deposition of Mg that occur at the negative electrode. These results were confirmed by energy dispersive X-ray spectroscopy, the X-ray diffraction technique, and X-ray photoemission spectroscopy. The assessment of the charge–discharge analysis on the Mg–graphite cell showed a good capacity up to 51 mAh/g, retaining a 62% Coulombic efficiency that was sustained for >60 cycles. This work expands the possibility of incorporating ionic liquids in the design of a successful prototype MDIB.