Below the 12-vertex: 10-vertex carborane anions as non-corrosive, halide free, electrolytes for rechargeable Mg batteries

Abstract

The development of practical Mg based batteries is limited by the lack of a library of suitable electrolytes. Recently a 12-vertex closo-carborane anion based electrolyte has been shown to be the first electrolyte for Mg based batteries, which is both non-corrosive and has high electrochemical stability (+3.5 V vs. Mg^0/2+). Herein we show that smaller 10-vertex closo-carborane anions also enable electrolytes for Mg batteries. Reduction of the trimethylammonium cation of [HNMe₃¹⁺][HCB₉H₉¹⁻] with elemental Mg yields the novel magnesium electrolyte [Mg²⁺][HCB₉H₉¹⁻]₂. The electrolyte displays excellent electrochemical stability, is non-nucleophilic, reversibly deposits and strips Mg, and is halide free. This discovery paves the way for the development of libraries of Mg electrolytes based on more cost effective 10-vertex closo-carborane anions.