Non-Nucleophilic Electrolytes with Non-Fluorinated Hybrid Solvents for Long-Life Magnesium Metal Batteries

Abstract

Growing energy demands and the widespread of renewable power sources call for high-energy storage systems beyond lithium-ion batteries (LIBs). Rechargeable magnesium batteries (RMBs) are high-energy, safer, and more cost-effective alternatives to LIBs and lithium metal batteries (LMBs) thanks to Mg’s high volumetric capacity (3832 mAh cm-3)1, low theoretical potential (-2.37 V vs SHE)2 and earth-abundance3. Non-nucleophilic and non-fluorinated compounds are the most important class of materials to enable sustainable rechargeable magnesium (Mg) batteries, however, they suffer from poor stability due to the formation of unstable solid-electrolyte-interphase (SEI).4 Here, we design a hybrid-solvent electrolyte by dispersing a non-nucleophilic solution in a non-fluorinated weakly-coordinating solvent to prevent parasitic reactions and form stable SEI. This strategy significantly improved the cycle life of the Mg anode from 24 to 4000 hours (in Mg-Mg symmetric cells) and realized a stable cycle life of Mg-Mo6S8 full cells for more than 2300 hours with an average CE of 99.96%. The non-fluorinated weakly-coordinating solvent suppressed uneven Mg growth and contributed to the formation of polymeric SEI, which filled the cracks of pristine SEI, preventing side reactions and passivation. This strategy revealed the critical role of weakly-coordinating solvents in stabilizing Mg anode for reversible Mg batteries.