NOVELTY - An electrolyte composition comprises a combination of a conductive salt containing a cation and an anion and a fluorinated sulfonate salt.    USE - In electromechanical systems such as battery and rechargeable battery (preferably lithium battery) (claimed) (double-layer capacitor, super capacitor, fuel cell, electroplating and electrorefining system.    ADVANTAGE - The composition reduces high temperature capacity fade, aluminum current collector corrosion and improves safety while maintaining and improving conductivity, stability and compatibility with other cell components; provides all of the requisite functions of a battery electrolyte salt including solubility, ionic conductivity chemical and thermal stability; may lower surface tension thus allowing better wetting of battery component materials and expanding the range of electrolyte compositions available; can be used in small quantity additions to existing electrolyte formulations to enhance performance and provides for potential applications in variety of battery systems and capacitors.    DETAILED DESCRIPTION - An electrolyte composition comprises a conductive salt containing cation and anion and an additive sulfonate salt of formula RdSO3M. The cation is selected from alkali metal, alkaline earth metal, Group IIB metal, Group IIIB metal, transition metal, rare earth metal, nitrogen onium cation or a proton. The anion is selected from ((R1SO2)(R2SO2)N)- a group of formula (I), R4R5N-(CF2)n'SO2-X-, a group of formula (II), a bis-fluoroalkyl methide anion of formula R'fSO2-C-(R)-SO2-R''f, tris-(perfluoroalkanesulfonyl)methide anion of formula -C(SO2Ra)(SO2Rb)(SO2Rc) or a cyano-substituted amide or methide anion of formula R1-(Q-A(CN)n)y (preferably ((R1SO2)(R2SO2)N)- or formula (I)). The molar ratio of conductive salt to surfactant salt is 99.9:0.1 - 70:30 (preferably 99:1 - 90:10).    R1 and R2 = straight or branched 1-4C perfluoroalkyl;    R1 + R2 = 1-5C;    R3 = 2-4C perfluoroalkylene optionally substituted by straight or branched 1-2C perfluoroalkyl such that R3 has total of up to 4 carbon atoms;    X- = -O-, -N-SO2R4 or (R6SO2)-C-(SO2R7)-;    Z = CF2, O, -N(R8)- or SF4;    R4 and R5 = -CmF2m+1 or -(CF2)q-SO2-X-;    R6 and R7 = -CmF2m+1, -(CF2)4SO2-X-, (R1)(R2)N-(CF2)n'- or a group of formula (III);    R8 = -CmF2m+1 or (CF2)qSO2-X-;    R'6 and R'7 = perfluoroalkylene moiety of formula -CrF2r-;    n', r, m and q = 1-4;    R'f and R''f = 1-4C perfluoroalkyl;    R'f + R''f = 1-4C perfluoroalkyl;    R'f+ R''f = 1-5C;    R = H, CN, F, 1-6C alkyl or phenyl optionally substituted by 1-4C alkyl;    Ra, Rb and Rc = 1-4C perfluoroalkyl;    Ra + Rb + Rc = 1-6C;    R1 = fluorine monovalent or divalent optionally fluorinated optionally saturated 1-4C aliphatic group, 3-6C cycloaliphatic group, cycloaliphatic-1-2C aliphatic optionally substituted by halogen in which the carbon chain of the aliphatic or cycloaliphatic group is optionally interrupted by a catenary heteroatom;    n and y = 1 or 2;    A = C or N;    Q = linking group -SO2- or -C(O)-;    Rd = 4-16C perfluoroalkyl, a perfluorocycloalkyl or 3-7C perfluorocycloalkyl perfluoroalkyl with 1-4C atoms on alkyl chain (all optionally containing at least one heteroatom) or a partially fluorinated group with a maximum of 20% of the non-fluorine atoms are hydrogen.    When A is M, n is 1 and when A is C, n is 2.    INDEPENDENT CLAIMS are also included for:    (1) an electrochemical system comprising at least one positive electrode, at least one negative electrode and the electrolyte composition; and    (2) improving aluminum corrosion in the system, or high temperature capacity fade of systems involving the step of incorporating in a matrix material the electrolyte composition having up to 30 mole % of the sulfonate additive salt based on the total salt content.