Effect of Guest Solvents on the Ionic Conductivity and Electrochemical Performance of Metal-Organic Framework-Based Magnesium Semi-Solid Electrolytes

Developing suitable electrolytes is crucial for the advancement of rechargeable magnesium batteries. Recently, metal-organic frameworks (MOFs) have shown a great interest in the field of solid electrolytes for metal ion batteries. However, the ionic conductivity as well as the electrolyte stability in the presence of Mg electrodes are shown to be strongly dependent on the guest solvent used to solvate Mg salts in MOFsSEs. Our measurements showed that full evacuation of the MOF structure before semi-solid electrolytes (sSEs) preparation is crucial for achieving relatively low Mg overpotentials regardless of the ionic conductivity values. Moreover, the behavior of the anode/MOFsSEs interfaces (MOF: alpha-Mg3[HCOO]6; Mg salt : MgCl2-Mg[TFSI]2 (1 : 1 wt %); guest solvent: acetone, DMF, DEG, DME and tetraglyme) was investigated by EIS, CV and galvanostatic measurements. The current comparative study of the electrochemical deposition processes of magnesium from MOFsSEs revealed that magnesium deposition/dissolution reactions vary depending on the MOF structure, the guest anion species as well as the nature of the guest solvents. The image shows how the complete evacuation of a metal organic framework (MOF) from the remaining solvent molecules strongly affects the ability to deposit Mg. Our results reveal that the remaining DMF in the MOF may result in (pseudo) high ionic conductivity values; however, its presence, even at low concentrations, leads to the passivation of Mg electrodes. This should be considered when utilizing MOFs in Mg-ion batteries.image