A Comprehensive Study on the Parameters Affecting Magnesium Plating/Stripping Kinetics in Rechargeable Mg Batteries

Abstract

Mg metal anode-based battery is a more sustainable, lower cost, and higher energy density alternative to Li-ion. However, this battery chemistry also faces several challenges associated with the high charge density of Mg²⁺, including achieving high reversibility and low voltage hysteresis for Mg metal plating/stripping. While significant improvements are achieved in last decades, they involve rather complex electrolyte formulations and/or Mg salts difficult to produce, and the use of unpractical substrates such as platinum. Here, significant improvement in terms of Mg plating kinetics is achieved in electrolytes containing commercial magnesium bis(trifluoromethanesulfonyl)imide salt (Mg(TFSI)₂) by using titanium substrate with similar crystal structure and lattice parameter as Mg leading to lower nucleation overpotential. Low salt concentration electrolyte and addition of dibutyl magnesium (Mg(butyl)₂) also enable the formation of thinner interphase, richer in solvent based decomposition products, further improving Mg plating kinetics. This work highlights the complex role of Mg(butyl)₂, often considered as a simple drying agent, and how it impacts ion solvation favoring the mobility of electroactive cationic species, paving the way toward better electrolyte design with improved cation transference number.