Synergistic electrolyte engineering with TEABH4 additive: achieving oriented deposition and ultralong cycling in magnesium metal batteries

Abstract

Simple magnesium salt Mg(CF₃SO₃)₂-based electrolytes often exhibit elevated charge-transfer resistance at the electrode interface owing to surface adsorption phenomena. Herein, to overcome this limitation, tetraethylammonium borohydride (TEABH₄) was used as a moisture scavenger to chemically control the moisture content. Moreover, the uniform coverage of TEA⁺ cations on the Mg anode surface regulated the Mg²⁺ reduction rate and enabled the epitaxial growth of magnesium metal deposited along the (002) crystal plane. Electrochemical evaluation showed that the modified electrolyte (MAT-G2) remained stable for over 3500 hours at a current density of 1 mA cm⁻² and a capacity of 0.5 mA h cm⁻². Additionally, the fabricated Mg||Cu cells achieved a high coulombic efficiency of 97.3% (over 2500 cycles). The critical current density of the cells reached 5.5 mA cm⁻², achieving the highest value reported in similar works. This study underscores the critical role of eliminating water contamination and optimizing ion-transport kinetics in enhancing the performance of magnesium metal batteries.