Strong Solvent Coordination Effect Inducing Gradient Solid-Electrolyte-Interphase Formation for Highly Efficient Mg Plating/Stripping

Abstract

Developing simple Mg-salt electrolytes without chlorine-containing additives is vital for the technical viability of rechargeable magnesium batteries (RMBs). However, the formation of ion-blocking passivation layer on Mg anode in these electrolytes severely hinders the reversible Mg plating/stripping. Here, we successfully designed a highly efficient and chlorine-free Mg(SO3CF3)2/ether electrolyte by introducing 2-methoxyethylamine (MOEA) with a strongly nucleophilic amidogen (-NH2) donor to competing solvation coordination. The preferred decomposition of MOEA in MOEA-coordinated Mg-ion complex generates organic N-containing species in the inner layer, thus forming the gradient organic-inorganic SEI. This gradient SEI enables a fast interfacial Mg2+ migration and uniform Mg plating/stripping at 5 mA cm−2 with 5 mAh cm−2. The Mg(SO3CF3)2/ether/MOEA electrolyte exhibits high oxidation stability (3.5 V vs. Mg/Mg2+), high average Coulombic efficiency (99.3 %, 1000 cycles), excellent rate performance (low overpotential of 570 mV at 7.5 mA cm−2) and good compatibility with Mo6S8 cathode in coin (300 cycles at 1 C) and pouch cells, when using 50 μm Mg anode. Importantly, the relationships between solvation configuration, SEI chemistry and battery performance were successfully built for guiding the design of simple Mg-salt electrolytes in RMBs.

Keywords: magnesium battery electrolytes, solvation regulation, solid-electrolyte-interphase, magnesium plating/stripping, high rate