Mixed‐Coordination Electrolytes With Molecular Additives for Robust Interphases in High‐Voltage Rechargeable Magnesium Batteries

ABSTRACT Rechargeable magnesium batteries (RMBs) offer a low‐cost and high‐capacity alternative to the current energy storage systems, yet achieving high‐energy density and stable operation at high‐voltage remains difficult, particularly due to oxidative decomposition in conventional ether‐based electrolytes. In this work, we introduce a mixed‐coordination electrolyte (MCE) combined with a molecular additive (MCE‐MA) designed to promote anion‐derived interphases and enhance cycling stability in high‐voltage RMBs. The MCE formulation integrates dissociative and associative coordinating salts to optimize both Mg ²⁺ transport and interphase formation, while the molecular additive facilitates the development of uniform, robust interphases. MCE‐MA exhibits improved Mg plating/stripping efficiency in Cu|Mg asymmetric cells and sustains over 250 h of stable cycling in Mg|Mg symmetric cells, significantly outperforming conventional halide‐free ether‐based electrolytes. Furthermore, MCE‐MA enables long‐term cycling of a full cell with oxide‐based cathode, achieving 200 cycles at 100 mA g ⁻¹ . X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) were employed systematically to reveal the origin of enhanced performance.