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Reversible Electrochemical Interface of Mg Metal and Conventional Electrolyte Enabled by Intermediate Adsorption

  • Author(s): Wang, H;
  • Feng, X;
  • Chen, Y;
  • Liu, YS;
  • Han, KS;
  • Zhou, M;
  • Engelhard, MH;
  • Murugesan, V;
  • Assary, RS;
  • Liu, TL;
  • Henderson, W;
  • Nie, Z;
  • Gu, M;
  • Xiao, J;
  • Wang, C;
  • Persson, K;
  • Mei, D;
  • Zhang, JG;
  • Mueller, KT;
  • Guo, J;
  • Zavadil, K;
  • Shao, Y;
  • Liu, J
  • et al.
Abstract

Conventional electrolytes made by mixing simple Mg2+ salts and aprotic solvents, analogous to those in Li-ion batteries, are incompatible with Mg anodes because Mg metal readily reacts with such electrolytes, producing a passivation layer that blocks Mg2+ transport. Here, we report that, through tuning a conventional electrolyte - Mg(TFSI)2 (TFSI- is N(SO2CF3)2-) - with an Mg(BH4)2 cosalt, highly reversible Mg plating/stripping with a high Coulombic efficiency is achieved by neutralizing the first solvation shell of Mg cationic clusters between Mg2+ and TFSI- and enhanced reductive stability of free TFSI-. A critical adsorption step between Mg0 atoms and active Mg cation clusters involving BH4- anions is identified to be the key enabler for reversible Mg plating/stripping through analysis of the distribution of relaxation times (DRT) from operando electrochemical impedance spectroscopy (EIS), operando electrochemical X-ray absorption spectroscopy (XAS), nuclear magnetic resonance (NMR), and density functional theory (DFT) calculations.

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