Compound

A compound of formula (I): (I) wherein: X is Al or B; M+ is a metal cation; and R1 in each occurrence is independently a linear C3 or C4 fluorinated alkyl. Preferably, at least one R1 is a linear C3 alkyl with fewer than 6 fluorine atoms. More preferably, at least one R1 contains a group of formula -CF2H. Even more preferably, at least one R1 is a group of formula -CH2CF2CF2H. Also, X is preferably boron and/or M+ is a lithium ion. The exemplified compound of formula (I) is wherein X is boron, M+ is a lithium ion and each R1 group is 2,2,3,3-tetrafluoropropyl. The compound of formula (I) may be used in an electrolyte in a metal or metal ion battery. In another aspect, a metal ion battery comprising an anode, a cathode and an electrolyte disposed between the anode and the cathode, wherein the electrolyte comprises a compound of formula (I).