An electrolytic composition comprising at least one low melting-point compound, the cation of which is of the onium type having at least one heteroatom such as N, 0, S or P bearing the positive charge and the anion of which totally or partly includes at least one imide ion of the type (FX 1 O) N - (OX 2 F) wherein X 1 and X 2 are identical or different and comprise SO or PF, said composition containing at least one other component comprising a metal salt, a polar polymer and/or an aprotic solvent, said electrolytic composition being characterized by the fact that said low melting-point compound has a cation of the onium type of formula: of formula of formula of formula or wherein - W is 0, S or N, and wherein N is optionally substituted with R 1 when valency allows this; - R 1, R 3 and R 4 are either identical or different and represent: - H; - alkyl, alkenyl, oxaalkyl, oxaalkenyl, azaalkyl, azaalkenyl, thiaalkyl, thiaalkenyl, dialkylazo radicals, said radicals may be linear, branched or cyclic and comprising from 1 to 18 carbon atoms; - aliphatic cyclic or heterocyclic radicals from 4 to 26 carbon atoms optionally comprising at least one side chain comprising one or several heteroatoms; - aryls, arylalkyls, alkylaryls, and alkenylaryls from 5 to 26 carbon atoms optionally comprising one or several heteroatoms in the aromatic ring; - groups comprising several aromatic or heterocyclic rings either fused or not, optionally comprising one or several nitrogen, oxygen, sulfur or phosphorus atoms, two groups R 1, R 3 or R 4 may form a ring or a heterocycle from 4 to 9 atoms, one or several groups R 1, R 3 or R 4 on a same cation may be part of a polymer chain; - and R2 and R5 to R9 are either identical or different and represent R 1, R 1 O-, (R 1) 2 N-, R 1 S-, R 1 being as defined previously. - W is 0, S or N, and wherein N is optionally substituted with R 1 when valency allows this; - R 1, R 3 and R 4 are either identical or different and represent: - H; - alkyl, alkenyl, oxaalkyl, oxaalkenyl, azaalkyl, azaalkenyl, thiaalkyl, thiaalkenyl, dialkylazo radicals, said radicals may be linear, branched or cyclic and comprising from 1 to 18 carbon atoms; - aliphatic cyclic or heterocyclic radicals from 4 to 26 carbon atoms optionally comprising at least one side chain comprising one or several heteroatoms; - aryls, arylalkyls, alkylaryls, and alkenylaryls from 5 to 26 carbon atoms optionally comprising one or several heteroatoms in the aromatic ring; - groups comprising several aromatic or heterocyclic rings either fused or not, optionally comprising one or several nitrogen, oxygen, sulfur or phosphorus atoms, two groups R 1, R 3 or R 4 may form a ring or a heterocycle from 4 to 9 atoms, one or several groups R 1, R 3 or R 4 on a same cation may be part of a polymer chain; - H; - alkyl, alkenyl, oxaalkyl, oxaalkenyl, azaalkyl, azaalkenyl, thiaalkyl, thiaalkenyl, dialkylazo radicals, said radicals may be linear, branched or cyclic and comprising from 1 to 18 carbon atoms; - aliphatic cyclic or heterocyclic radicals from 4 to 26 carbon atoms optionally comprising at least one side chain comprising one or several heteroatoms; - aryls, arylalkyls, alkylaryls, and alkenylaryls from 5 to 26 carbon atoms optionally comprising one or several heteroatoms in the aromatic ring; - groups comprising several aromatic or heterocyclic rings either fused or not, optionally comprising one or several nitrogen, oxygen, sulfur or phosphorus atoms, - and R2 and R5 to R9 are either identical or different and represent R 1, R 1 O-, (R 1) 2 N-, R 1 S-, R 1 being as defined previously.