Magnesium Batteries: Electrolyte

Abstract

Electrolyte formagnesium secondary batteries must meet various requirements. In particular, the promotion of reversible magnesium deposition–dissolution, the negative electrode reaction, is the most important property of the electrolyte. The magnesium electrode process is not reversible and sometimes exhibits large overpotential, at the dissolution (discharge) reaction in conventional electrolyte systems, mainly due to the existence of surface passivation layer. Some magnesium halides soluble in non-aqueous solvents, such as Grignard reagent and its mixturewith Lewis acid, promote reversible magnesium deposition without overpotential via multinuclear magnesium halide complex (μ-complex), although their insufficient anodic stability and corrosive nature inhibit their use in practical battery systems. Recent progress is on the understanding of solution structure of non-aqueous magnesium salt electrolyte. As a result, a solvent-separated ion pair (SSIP) between magnesium ion and glyme solvent molecules is more favorable compared with a contact ion pair. Magnesium salts with some boron-based anions effectively provide SSIP with weakly coordinating glyme solvents, and thus promote reversible magnesium electrode process without overpotential.