Synergistic Interaction between Saturated MgCl2–H2O/PEG Electrolyte and Mg Alloy Anode Enables High-Performance Aqueous Magnesium-Ion Batteries

Compared to conventional organic electrolytes, aqueous magnesium-ion batteries (AMIBs) have emerged as a research hotspot due to their superior safety, environmental compatibility, and cost-effectiveness. However, the further development of AMIBs has been impeded by their short cycling lifespan, primarily caused by the aqueous corrosion of Mg anodes in water-containing electrolytes, which generates inorganic passivation layers (e.g., Mg(OH)2 and MgO) on the anode surface. To address this challenge, we propose a collaborative two-pronged approach, involving the adoption of a novel electrolyte system (saturated MgCl2 aqueous solution containing 25 vol % PEG, SMP-3) and the use of a Mg alloy anode. Electrochemical investigations suggest that the PEG molecules form hydrogen bonds with H2O molecules, effectively suppressing water activity and thereby enhancing anode stability. The assembled PTO/Mg alloy full cell exhibited a stable discharge plateau at 1.5 V with an initial discharge capacity of 176.24 mAh g–1 at 200 mA g–1. Remarkably, the cell demonstrated exceptional cycling stability, maintaining a capacity of 150 mAh g–1 after 300 cycles (85% capacity retention), with an average Coulombic efficiency approaching 100%. The results demonstrate the feasibility of stabilizing Mg alloy anodes through an interfacial engineering strategy based on a water-in-salt electrolyte design. This strategic approach provides a novel pathway for developing low-cost, high-performance AMIBs.