Electrolyte for magnesium ion batteries

A liquid electrolyte composition consisting essentially of:

• i) magnesium trifluoromethanesulfonate;
• ii) magnesium chloride;
• and
• iii) a solvent comprising 1,2-dimethoxyethane,
• wherein the magnesium ions and the chloride ions are present in the electrolyte composition in a [Mg2+]:[Cl−] ratio of from >1:1 to about 5:1.

An electrochemical cell comprising:

• a) a positive electrode;
• b) a magnesium negative electrode;
• and
• c) a liquid electrolyte composition consisting essentially of:
• (i) a magnesium salt comprising a trifluoromethane sulfonate anion;
• (ii) an additive comprising an organic halide salt, an inorganic halide salt or a mixture thereof;
• and
• iii) a solvent comprising one or more ethers,
• wherein the organic halide salt comprises a halide anion and a cation selected from an optionally substituted quaternary ammonium or a three to nine membered N-heterocyclic cation, and the cation comprises at least one protonated nitrogen capable of dissociating the trifluoromethane sulfonate anion from the magnesium salt, and
• wherein the cation of the inorganic halide salt is a lithium ion, a sodium ion, a cesium ion, a magnesium ion, or a barium ion and the total concentration of the cation and magnesium ions of the magnesium salt divided by the concentration of anions of the inorganic halide salt is greater than 1 in the electrolyte composition,
• wherein the positive electrode and the magnesium negative electrode are in fluid communication with the electrolyte.