High‐Performance, Activation‐Free Magnesium‐Ion Batteries Enabled by Ionic Liquid Electrolyte Additive

ABSTRACT

Magnesium‐ion batteries (MIBs), as a highly promising next‐generation energy storage technology, benefit from the high theoretical volumetric capacity (3833 mAh L ⁻¹ ) of magnesium metal and its intrinsic safety. However, its commercialization is still hindered by sluggish de‐solvation kinetics during cycling, which prolongs the activation periods to reach maximum capacity and impairs rate performance. To overcome this bottleneck, we add 4‐ethyl‐4‐methylmorpholinium cation (EMM ⁺ ) as an additive into the conventional all‐phenyl‐complex (APC) electrolyte. Density functional theory computations confirm that EMM ⁺ shows a strong affinity for chloride ions (−0.513 eV), which weakens the Mg–Cl coordination and, thus promotes Mg ²⁺ de‐solvation. In CuS‐based MIBs, the modified APC‐EMM electrolyte eliminates the activation cycles that are required with pure APC, and achieves a high specific capacity of 405.1 mAh g ⁻¹ at 100 mA g ⁻¹ , while maintaining excellent rate performance (220.1 mAh g ⁻¹ at 1 A g ⁻¹ ). Notably, this electrolyte also shows significant improvements in capacity, activation kinetics, and cycling stability when applied to other cathode materials, including CuSe, Cu ₇ Te ₄ , Mo ₆ S ₈ , and perylene‐3,4,9,10‐tetracarboxylic dianhydride. This study establishes a de‐solvation‐accelerated electrolyte design concept as a universal paradigm for the development of high‐performance MIBs.