Mixed-Coordination Electrolytes With Molecular Additives for Robust Interphases in High-Voltage Rechargeable...

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 Mg²⁺ 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.