The invention relates to a process for preparing aromatic sulfonylimides, to the sulfonylimides obtained, and to the use thereof as salt of an electrolyte. The sulfonylimides correspond to the formula [R—SO2—N—SO2R′]rM (I). R′ is an ArZL- group. R′ is a perfluoroalkyl group or an ArZL- group. Z is an S, SO or SO2 group. L is a —(CF2)n—CFRf— group. n is 0 or 1; Rf represents F or a C1 to C8 perfluoroalkyl group; Ar is an aromatic group. M represents H, an alkali metal cation, an alkaline earth metal cation, a trivalent or tetravalent metal cation, or an organic cation. The process consists in preparing a compound RSO2N(R′)SO2R′ from RSO2F, and in replacing the group R′ by nucleophilic substitution reaction so as to obtain the compound (I), R′ being a benzyl or trimethylsilyl group.