Highly Stable and Phenoxide/Alkoxide-Based All Magnesium Electrolytes for Rechargeable Magnesium-Ion Batteries

In the last few years, magnesium-ion batteries have received substantial amount of attention for rechargeable energy storage, mainly due to their advantages over traditional lithium-ion batteries in safety, cost and capacity. However, the lack of suitable electrolytes which are capable of depositing magnesium reversibly and efficiently has retarded the progress of magnesium-ion batteries for quite a long time. The current state of art for the design of high potential magnesium electrolytes is focused on the strong Lewis acid derived Grignard reagents or their derivatives. The use of these toxic, corrosive and sometimes combustible strong Lewis acids (aluminum or organoboron-based) brings about safety concern for both the preparation and storage of the electrolytes. As our ongoing effort to implement easily accessible, cost efficient and highly stable electrolytes for magnesium-ion batteries, herein we would like to present our recent progress towards the development of strong Lewis acid-free, highly stable and phenoxide/alkoxide-based magnesium electrolytes. The obtained all magnesium electrolytes possess the oxidative stability up to 3.5 V (vs Mg/Mg²⁺), which is superior to any strong Lewis acid AlCl₃ derived magnesium electrolytes and among the best of all reported magnesium electrolytes capable of depositing magnesium reversibly and efficiently. The excellent reversibility and compatibility in magnesium-ion batteries were further demonstrated using Chevrel phase Mo₆S₈ as the cathode material, highlighting the great potential of these novel electrolytes for high energy density magnesium-ion batteries. The mechanism behind the chemical reactions has also been extensively investigated by multiple techniques including single crystal X-ray diffraction, NMR and Raman spectroscopies, enabling a comprehensive understanding of the exceptional electrochemical performance of these novel strong Lewis acid-free electrolytes.