A single phase electrolyte medium comprising: - at least one salt of alkali or alkaline earth metal, preferably a lithium salt, - at least one hydrocarbon solvent, and - from 1% to 50%, by volume relative to the total volume of said medium, of at least one hydrocarbon solubilizing agent, distinct from said hydrocarbon solvent, corresponding to the formula: Z-[ -] q - -Y in which: - A and B, identical or different, have the formula -C a H 2a -, where a is an integer between 6 and 18, - X is chosen from among oxygen and sulfur atoms and the radicals -N(R 2)-, -B(R 2)- and -P(R 3 R 2)- where R 2 and R 3, identical or different, represent a hydrogen atom or an alkyl radical in C 1 to C 4, - q is equal to zero or is an integer varying from 1 to 8, where A and X may have identical or different definitions in each of the units -[ -]-, - Z represents a hydrogen atom or a group -OH, -OR 1, -OM, -NH 2, -NHR 1, - N(R 1) 2, -N(R 1) 3 +, -COOH, -COOM, -COOR 1, -OCOR 1, -CN, SO 3 H, or - SO 3 M, where R 1 is an alkyl radical in C 1 to C 4 and M is a metal ion, or alternatively Z is a cyclocarbonate radical with 5 or 6 links, - Y represents a group -OH, -OR 1, -OM, -NH 2, -NHR 1, -N(R 1)2, -N(R 1) 3 +,-COOH, -COOM, -COOR 1, -OCOR 1, -CN, -SO 3 H, or -SO 3 M where R 1 is an alkyl radical in C 1 to C 4 and M is a metal ion, or alternatively Y is a cyclocarbonate radical with 5 or 6 links, or - Y and Z are linked to one another to form a polar pattern of the oxo, ether, ester, amino or secondary or tertiary amine type. - at least one salt of alkali or alkaline earth metal, preferably a lithium salt, - at least one hydrocarbon solvent, and - from 1% to 50%, by volume relative to the total volume of said medium, of at least one hydrocarbon solubilizing agent, distinct from said hydrocarbon solvent, corresponding to the formula: Z-[ -] q - -Y in which: - A and B, identical or different, have the formula -C a H 2a -, where a is an integer between 6 and 18, - X is chosen from among oxygen and sulfur atoms and the radicals -N(R 2)-, -B(R 2)- and -P(R 3 R 2)- where R 2 and R 3, identical or different, represent a hydrogen atom or an alkyl radical in C 1 to C 4, - q is equal to zero or is an integer varying from 1 to 8, where A and X may have identical or different definitions in each of the units -[ -]-, - Z represents a hydrogen atom or a group -OH, -OR 1, -OM, -NH 2, -NHR 1, - N(R 1) 2, -N(R 1) 3 +, -COOH, -COOM, -COOR 1, -OCOR 1, -CN, SO 3 H, or - SO 3 M, where R 1 is an alkyl radical in C 1 to C 4 and M is a metal ion, or alternatively Z is a cyclocarbonate radical with 5 or 6 links, - Y represents a group -OH, -OR 1, -OM, -NH 2, -NHR 1, -N(R 1)2, -N(R 1) 3 +,-COOH, -COOM, -COOR 1, -OCOR 1, -CN, -SO 3 H, or -SO 3 M where R 1 is an alkyl radical in C 1 to C 4 and M is a metal ion, or alternatively Y is a cyclocarbonate radical with 5 or 6 links, or - Y and Z are linked to one another to form a polar pattern of the oxo, ether, ester, amino or secondary or tertiary amine type. - A and B, identical or different, have the formula -C a H 2a -, where a is an integer between 6 and 18, - X is chosen from among oxygen and sulfur atoms and the radicals -N(R 2)-, -B(R 2)- and -P(R 3 R 2)- where R 2 and R 3, identical or different, represent a hydrogen atom or an alkyl radical in C 1 to C 4, - q is equal to zero or is an integer varying from 1 to 8, where A and X may have identical or different definitions in each of the units -[ -]-, - Z represents a hydrogen atom or a group -OH, -OR 1, -OM, -NH 2, -NHR 1, - N(R 1) 2, -N(R 1) 3 +, -COOH, -COOM, -COOR 1, -OCOR 1, -CN, SO 3 H, or - SO 3 M, where R 1 is an alkyl radical in C 1 to C 4 and M is a metal ion, or alternatively Z is a cyclocarbonate radical with 5 or 6 links, - Y represents a group -OH, -OR 1, -OM, -NH 2, -NHR 1, -N(R 1)2, -N(R 1) 3 +,-COOH, -COOM, -COOR 1, -OCOR 1, -CN, -SO 3 H, or -SO 3 M where R 1 is an alkyl radical in C 1 to C 4 and M is a metal ion, or alternatively Y is a cyclocarbonate radical with 5 or 6 links, or - Y and Z are linked to one another to form a polar pattern of the oxo, ether, ester, amino or secondary or tertiary amine type.