Boosting Mg deposition and dissolution from ionic liquids - The role of different additives for applications in Mg-ion batteries

In this work, Mg deposition from 0.1 M Mg(TFSI)2 dissolved in a hydrophobic ionic liquid (IL) is found to occur, regrettably at very high overpotential, which is accompanied by electrolyte decomposition. To address this issue, we have systematically improved the electrochemical performance of the Mg-IL system through three stages of electrolyte optimization. The first two stages involved investigating the effects of different co-solvents and Mg (BH4)2 as electrolyte additives, while the third stage comprised a detailed study of various ratios between the ionic liquid and different co-solvents to achieve an optimized system. Notably, a ratio of 1:3 MPPip-TFSI to diglyme exhibited higher cathodic and anodic currents, lower overpotential, and improved cycling stability compared to other co-solvents. Scanning electron microscopy micrographs and X-ray diffraction revealed uniform and reversible Mg deposition and dissolution. The optimized electrolyte was tested with WS2/PANI as cathode material to validate our electrolyte system in a Mg battery application, achieving a specific capacity of 197 mAh center dot g-1 at 20 mA center dot g-1 at room temperature.