Lawrence Berkeley National Laboratory Recent Work Title Reversible Electrochemical Interface of Mg Metal and Conventional Electrolyte Enabled by Intermediate Adsorption Permalink

35 36 Conventional electrolytes made by mixing simple Mg salts and aprotic solvents, 37 analogous to those in Li-ion batteries, are incompatible with Mg anodes because Mg metal 38 readily reacts with such electrolytes, producing a passivation layer which blocks Mg transport. 39 Here, we report that, through tuning a conventional electrolyte—Mg(TFSI)2 (TFSI is 40 N(SO2CF3)2) with an Mg(BH4)2 additive, highly reversible Mg plating/stripping with a high 41 coulombic efficiency is achieved, by neutralizing the first solvation shell of Mg cationic clusters 42 between Mg and TFSI and enhanced reductive stability of free TFSI . A critical adsorption 43 step between Mg atoms and active Mg cation clusters involving BH4 anions is identified to be 44 the key enabler for reversible Mg plating/stripping through analysis of distribution of relaxation 45 times (DRT) from operando electrochemical impedance spectroscopy (EIS), operando 46 electrochemical X-ray absorption spectroscopy (XAS), nuclear magnetic resonance (NMR), and 47 density functional theory (DFT) calculations. This study suggests a new approach for developing 48 advanced electrolytes for Mg batteries and provides a set of in-operando analysis tools for 49 probing electrified Mg/electrolyte interfaces. 50 51