Advancing Reversible Magnesium−Sulfur Batteries with a Self-Standing Gel Polymer Electrolyte

Magnesium (Mg) metal batteries exhibit great potential as energy storage systems beyond lithium, owing to their inherent safety, material sustainability, and low cost. However, their development is hindered by the lack of a suitable electrolyte enabling a reversible Mg deposition and dissolution. When combined with a sulfur (S) cathode, the formation of magnesium polysulfide intermediates further restricts the cycling stability of sulfur-based batteries. In this study, a flexible Mg-based gel polymer electrolyte is designed to address these challenges in Mg metal batteries. Fabricated through a straightforward solvent-casting approach using magnesium tetrakis(hexafluoroisopropyloxy)borate salt, the gel polymer electrolyte demonstrates positive interactions between the borate anion and polymer, facilitating efficient Mg-ion transfer. Remarkably, the gel polymer electrolyte exhibits reversible Mg plating/stripping over 1000 cycles and significantly enhanced cycling performance for up to 300 cycles when incorporated with a sulfur cathode. These findings highlight the potential of gel polymer electrolytes to enable reversible Mg deposition and dissolution, enhance the life span of Mg–S batteries, and advance the field of Mg metal batteries.