Widening Electrochemical Window of Mg Salt by Weakly Coordinating Perfluoroalkoxyaluminate Anion for Mg Battery Electrolyte

Work performed at Argonne National Laboratory (JCESR managing partner), Sandia National Laboratories (JCESR partner) and Lawrence Berkeley National Laboratory (JCESR partner) by Ka-Cheong Lau, Trevor J. Seguin, Emily V. Carino, Nathan T. Hahn, Justin G. Connell, Brian J. Ingram, Kristin A. Persson, Kevin R. Zavadil, and Chen Liao, J. Electrochem. Soc., 163(3), DOI: 10.1149/2.0751908jes

Scientific Achievement

Mg[Al{OC(CF3)3}4]2 (Mg[TPFA]2 ) with perfluorinated, e- deficient anions ([TPFA]−) possesses high thermodynamic oxidative stability with high coulombic efficiency for Mg plating/stripping.

Significance and Impact

The electrochemical window of Mg salt was widened to 4.9 V vs Mg/Mg2+ using a synthetic approach: t-butyl perfluorinated aluminate anion was first demonstrated in a MV salts. The weakly associating concept was adapted to increase thermodynamic stability of anions by decreasing  the propensity of ion pair formation and consequent charge transfer decomposition.

Research Details

  • Alcoholysis of LiAlH4 with (CF3)3COH followed by Li/H cation exchange to generate H[TPFA], which later reacts with Mg(HMDS)2 gives a pure salt of Mg[TPFA]2.
  • Computational and electrochemical analyses suggested a mitigated cathodic decomposition as well as enhanced anodic stability from electron-withdrawing CF3 groups.
  • Detailed NMR, IR and SEM/EDX further support that the weak coordination to Mg2+ in solution is important for maintaining the wide electrochemical window of Mg salt.

DOI: 10.1149/2.0751908jes

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