The invention relates to a pentacyclic anion salt and to the use thereof in electrolyte compositions. The compound comprises an inorganic, organic or organometallic cation M of valency m (1≦m≦3) and m anions corresponding to the formula (I) in which Rf is a —CFZ′Z″ group in which Z′ is F or a perfluoroalkyl group having from 1 to 3 carbon atoms, and Z″ is an H, F or Cl group, an optionally fluorinated or perfluorinated alkoxy group having from 1 to 5 carbon atoms, an optionally fluorinated or perfluorinated oxaalkoxy group having from 1 to 5 carbon atoms or an optionally fluorinated or perfluorinated alkyl group having from 1 to 5 carbon atoms; Z″ being other than F when Z′ is F. An electrolyte composition comprises said salt in solution in a liquid solvent or a polymer solvent.