As described herein, magnesium salts suitable for use in an electrolyte for a magnesium ion electrochemical cell are magnesium tetra(perfluoroalkoxy)metalates, of Formula (I): Mg(Z)_n²⁺[M(OCR₃)₄^?]₂, wherein Z is an ether; n is 0 to about 7; M is Al or B; and each R independently is a perfluoroalkyl group. In some preferred embodiments, M is aluminum.

In some embodiments of Formula (I), each R independently is a C₁ to C₁₀ perfluoroalkyl group, e.g., a C₁ to C₈ perfluoroalkyl group, a C₁ to C₈ perfluoroalkyl group, a C₁ to C₆ perfluoroalkyl group, a C₁ to C₄ perfluoroalkyl group, or a C₁ to C₂ perfluoroalkyl group. The perfluoroalkyl groups can be linear or branched. Non-limiting examples of such perfluoroalkyl groups include trifluoromethyl, pentafluoroethyl, heptafluoro-1-propyl, heptafluoro-2-propyl, nonafluoro-1-butyl, nonafluoro-sec-butyl, nonafluoro-tert-butyl, undecafluorohexyl, pentadecafluorooctyl, and the like. In some preferred embodiments the perfluoroalkyl groups are independently selected from the group consisting of trifluoromethyl and pentafluoroethyl.

The ether, Z, in Formula (I) preferably is at least one ether selected from the group consisting of diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, dimethoxyethane, diglyme, triglyme, and tetraglyme. In some preferred embodiments, the ether, Z, is selected from the group consisting of tetrahydrofuran, diethyl ether, and a combination thereof.