Non-nucleophilic electrolyte with non-fluorinated hybrid solvents for long-life magnesium metal batteries

Abstract

Non-nucleophilic and non-fluorinated compounds are the most important class of solvents to enable sustainable rechargeable magnesium (Mg) batteries; however, they suffer from poor stability due to the formation of an unstable solid–electrolyte-interphase (SEI). Here, we design a hybrid-solvent electrolyte by dispersing a non-nucleophilic Mg(TFSI)₂–MgCl₂-1,2-dimethoxyethane (DME) solution in a non-fluorinated weakly coordinating solvent (tetrahydrofuran, THF) to prevent the decomposition of DME and form a stable SEI. This strategy significantly improved the cycle life of a 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 THF suppressed uneven Mg growth and contributed to the formation of a polymeric SEI, which filled the cracks of the pristine SEI, preventing side reactions and passivation. This strategy revealed the critical role of weakly coordinating solvents in stabilizing the Mg anode for reversible Mg batteries.