A composition including: (i) a lithium salt of imidazole compound of formula (I): wherein Rf is a fluorinated alkyl group having 1 to 5 carbon atoms, or a fluorine atom; and (ii) at least one cation selected from the group A including sodium, potassium, calcium, iron, magnesium, manganese, strontium, vanadium, ammonium, silver, aluminium, arsenic, barium, silicon, cadmium, cobalt, chromium, copper, nickel, lead, antimony, selenium, tin, strontium and titanium; and (iii) at least one anion chosen from the group B including fluoride, chloride, nitrate, sulphate, phosphate, trifluoroacetate, pentafluoroacetate and the anion of formula (II), with all the cation(s) and anion(s) being more than 0 wt % and at most 1 wt % of the composition. Also, the preparation of the composition as well as to the use of the composition as a battery electrolyte.