NOVELTY - An ionic liquid (L1) comprises a salt of formula selected from: ammonium salt (I), pyridinium salt (II), imidazolium salt (III), phosphonium salt (IV), oxazolium salt (V), and thiazolium salt (VI).    USE - As electrolytes for electrochemical devices, preferably in lithium secondary battery selected from a lithium battery, a lithium-ion battery, a lithium-sulfur battery, a lithium-air battery, a sodium ion battery, or a magnesium battery (all claimed).    ADVANTAGE - The ionic liquids provide lithium ion batteries having a high ionic conductivity, good solid electrolyte interphase (SEI) formation, high wettability, and high voltage stability.    DETAILED DESCRIPTION - An ionic liquid (L1) comprises a salt of formula selected from ammonium salt RR1R2R3N+ X- (I), pyridinium salt (II), imidazolium salt (III), phosphonium salt RR1R2R3P+ X- (IV), oxazolium salt (V), and thiazolium salt (VI).    R=-CH2Si(R')2(OSi(R')2)mOSi(R')3, -(R')-(OCH2CH2)n-(OR'a), 3-5C cyclic carbonate, sulfolane, oxalic borate, maleic anhydride, succinic anhydride, or 1-6C alkyl (substituted with isocyanate, sulfone, sulfolane, -OCO2R'a, 3-5C cyclic carbonate, or oxalic borate);    R'=1-4C alkylene;    R'a=alkyl;    R1-R3=haloalkyl, alkyl (optionally substituted by carboxylate, aminoalkyl, cycloalkyl, (hetero)aryl, or (hetero)aralkyl);or    two of R1-R3 together=4-5C alkylene;    R4-R8=H, (halo)alkyl, hydroxyalkyl, cycloalkyl, (hetero)aryl, or (hetero)aralkyl;    X-=anion selected from boron tetrafluoride, aluminate, bis(oxalato)borate, difluoro(oxalate)borate, phosphorus hexafluoride, alkyl sulfonate, fluoroalkyl sulfonate, aryl sulfonate, bis(alkylsulfonyl)amide, perchlorate, bis(fluoroalkylsulfonyl)amide, bis(arylsulfonyl)amide, alkyl fluorophosphate, (fluoroalkylsulfonyl)(fluoroalkylcarbonyl)amide, halide, nitrate, nitrite, sulfate, hydrogen sulfate, alkyl sulfate, aryl sulfate, carbonate, bicarbonate, perfluoroalkyl (substituted with carboxylate, phosphate, hydrogen phosphate, dihydrogen phosphate, or hypochlorite), or anionic site of a cation-exchange resin;    n=1-4;    m=0-10.    INDEPENDENT CLAIMS are included for the following:    (1) an electrolyte (E1) comprising the ionic liquid (L1); and    (2) an electrochemical device (D1) comprising a cathode, an anode, and the electrolyte (E1) comprising the ionic liquid (L1).