Composite Polymer Electrolyte for Highly Cyclable Room-Temperature Solid-State Magnesium Batteries

Developing an electrolyte candidate with a wide voltage window, highly reversible cycling with Mg-metal anode, and without the use of any flammable solvents is a major challenge for rechargeable Mg batteries. While there have been several reports on Mg2+-conducting polymer electrolytes with high ionic conductivities, studies to determine their cycling performance and Mg-deposition overpotentials have been scarce. Here, we report a composite polymer electrolyte that exhibits a highly reversible cycling with Mg-metal anode at room temperature. The synthesized polymer electrolyte has a high conductivity of 0.16 mS cm–1 at room temperature, and the galvanostatic cycling tests of Mg | Mg symmetric cells reveal that the reversible Mg deposition/stripping occurs at low overpotentials of 0.1–0.3 V for up to 400 cycles. The cycling stability of this composite polymer electrolyte is unprecedented among ambient-temperature solid-state Mg electrolytes, and the observed overpotential values are even comparable to those of the present state-of-the-art liquid electrolytes.