Application of Single-Ion Conducting Gel Polymer Electrolytes in Magnesium Batteries

The development of polymer electrolytes for magnesium batteries has been hindered by difficulties related to achieving sufficient magnesium ion conduction and magnesium electrodeposition. The high charge density of the magnesium cation causes it to interact with both the polar polymer matrix and any counteranions, challenging ion transport. Solvents and salts that are known to be incompatible with the magnesium electrode have widely been used in prior reports to increase ionic conductivity. Herein we report the use of a single-ion conducting magnesium gel polymer electrolyte consisting of a poly(ethylene glycol) dimethacrylate (PEGDMA) crosslinker that is copolymerized with an anionic monomer and subsequently swelled in solvents compatible with magnesium metal. Sufficient magnesium ion conductivities (>10−4 S/cm at 25 °C) were able to be achieved with specific solvents and solvent mixtures. Constant potential holds were used to interrogate magnesium electrodeposition from these electrolytes. Small amounts of magnesium deposits were identified; however, the large interfacial impedances appear to impact the degree of deposition. It is hypothesized that the large interfacial impedance is due to the charge transfer resistance associated with the solvated magnesium cation. Thus, it is proposed that the solvated magnesium cation species that is transported in this electrolyte cannot effectively electrodeposit.