Combined Effects of LiCl Addition and Solvent-in-Water Approaches on Aqueous Magnesium-Ion Battery Performance

The advancement of a competitive Mg-ion battery is restricted by the limited mobility of Mg ions in the current host materials. Herein, LiCl is added as a supporting salt to an MgCl₂ salt-based, polyethylene glycol (PEG) solvent-in-water electrolyte (SIW) to obtain the H-PG-Mg electrolyte. The LiCl addition is employed to benefit from its reported synergistic effects in minimizing cell potential and shielding effects, suppressing dendritic formation, and promoting the ability of MgCl₂ deposits to dissolve and expose a fresh anode surface. The H-PG-Mg@Li electrolyte shows the highest electrochemical stability window (ESW) of 3.3 V, which is 1.5 times higher than the LiCl-free electrolyte, and the highest ion transference number of 0.70. MgO-V₂O₅–P₂S₅ (G) electrode is tested in a three-electrode configuration and displays superior capacity retention of 60% after 1000 cycles. The G/H-PG-Mg@Li/Mg cell exhibits the best cycling stability of up to 150 cycles. The ability of the G cathode to reversibly accommodate Mg²⁺ cations in H-PG-Mg@Li due to lower overall charge density was highlighted using ex-situ elemental analysis, where the ratio of the ions followed the charging and discharging processes. These results highlight LiCl addition and SIW strategies as effective approaches to upgrading the electrochemical performance of current aqueous Mg batteries.