Fluorine-Based Localization Effect for Stabilized High-Voltage Magnesium Phenolic Electrolyte

Abstract

The design of electrolytes with excellent compatibility and high oxidation stability has long been the prerequisite for realizing high-voltage rechargeable magnesium batteries (RMBs). Compared with other chlorine-containing electrolytes, phenol-based magnesium electrolytes possess better water-oxygen resistance, simpler synthesis steps, and lower ingredient costs making it very promising for applications. However, lower oxidation stability renders it difficult to be applied in high-voltage RMBs. Herein, for the first time, we propose to utilize the fluorine-based localization effect (fluorine substitution from 2,4 o-para site on phenol enhances electrolyte oxidation stability) to design M24AT electrolyte (2,4-F₂PhOMgCl + AlCl₃ / THF). As-prepared M24AT electrolyte exhibits superior oxidation stability (3.9V vs. Mg/Mg²⁺) than any other phenol-based electrolyte. Additionally, it in-situ generates a fluorinated solid electrolyte interface (SEI) that stabilizes the Mg anode during cycling. Consequently, the Mg||Mo₆S₈ cells with M24AT electrolyte demonstrate ∼100% capacity retention after 500 cycles at 1C. Besides, the high-voltage stability of the M24AT electrolyte is displayed by electrochemical testing with Mg||PAQI full cells, which operate at voltages up to 3.0V and exhibit greater than 300 stable cycles at 200mA g⁻¹, with average coulombic efficiency (CE) of ∼98%. The proposed design strategy of fluorine-based localization facilitates the application of phenol-based electrolytes in high-voltage RMBs.