Rechargeable magnesium batteries enabled by conventional electrolytes with multifunctional organic chloride additives

The development of a conventional electrolyte, based on commercially available magnesium (Mg) salts in organic solvents, remains one of the most challenging quests for rechargeable Mg batteries. Conventional electrolytes typically form a passivation layer on Mg metal anode, necessitating the extensive use of inorganic chloride additives such as MgCl2. Herein, for the first time, we introduce an organic chloride, tetrabutylammonium chloride (TBAC), as a multifunctional electrolyte additive for conventional magnesium triflate (Mg(OTf)2)-based electrolytes. TBAC was found to perform three major roles: (1) enhance Mg(OTf)2 dissociation in aprotic solvent, (2) inhibit the reduction of triflate anions through surface-adsorbed TBA+, and (3) act as a chloride source to form Mg complexes and stabilize the Mg anode-electrolyte interface. The novel electrolyte combination of TBAC and Mg(OTf)2 in 1,2-dimethoxyethane exhibits excellent Mg plating/stripping with Coulombic efficiency of 97.7% over 200 cycles at 0.5 mA cm−2 and 0.5 mAh cm-2. Postmortem analysis unveils uniform Mg deposition and stable solid electrolyte interphase formation on Mg anode, which enables reversible cycling with Mo6S8 cathode. Together with our findings on another organic chloride additive, 1-ethyl-3-methylimidazolium chloride, and in combination with different electrolyte salts and solvents, we showcase the general promise of high-performance conventional electrolytes for rechargeable Mg batteries.