NOVELTY - A gel electrolyte comprises lithium salt, copolymer of ester-containing monomer (I) or ether-containing monomer (II) and vinyl monomer (IV), phosphorus-containing oxo acid ester derivative (V), (VI) or (VII), and disulfonate compound chosen from cyclic disulfonate (VIII) or linear disulfonate (IX).    USE - Gel electrolyte for lithium ion secondary battery (claimed), electrical double layer capacitor and lithium ion capacitor used as power supply for mobile telephone, notebook personal computer and motor vehicle.    ADVANTAGE - The gel electrolyte provides batteries with improved lifetime and high safety.    DETAILED DESCRIPTION - A gel electrolyte comprises lithium salt, copolymer of ester-containing monomer of formula: H2C=C(-R1)-C(=O)-O-CH2R2 (I) or ether-containing monomer of formula: H2C=CH-CH2OCH2R2 (II) and vinyl monomer of formula: H2C=C(-R4)-R5 (IV), phosphorus-containing oxo-acid ester derivative of formula: R13O-P(-OR12)(=O)-OR11 (V), X21-P(-OR22)(=O)-OR21 (VI) or X31-P(-OR31)(=O)-X32 (VII), disulfonate compound chosen from cyclic disulfonate compound of formula (VIII) and linear disulfonate of formula: R8-S(=O)2-C(-R9)(-R6)-S(=O)2-R7 (IX).    R1=H or CH3;    R2=substituents chosen from formulae (a)-(d);    R3=1-6C alkyl;    R4=H or CH3;    R5=-COOCH3,-COOC2H5, -COOC3H7, -COOC4H9, -COOCH2CH(CH3)2, -COO(CH2CH2O)nCH3, -COO(CH2CH2O)nC4H9, -COO(CH2CH2CH2O)nCH3, -COO(CH2CH(CH3)O)nCH3, -COO(CH2CH(CH3)O)nC2H5, -OCOCH3, -OCOC2H5 or -CH2OC2H5;    n=1-3;    R11-R13,R21,R22,R31=alkyl, aryl, alkenyl, cyano, phenyl, amino, nitro, alkoxy or cycloalkyl, or halo-substituted group;    two R11-R13,R21,R22=cyclic structure;    X21,X31,X32=halo;    Q=O, methylene or single bond;    A1=1-5C alkylene, 1-5C perfluoro alkylene, 2-6C fluoro alkylene (all optionally substituted, optionally branched and optionally containing ether bond), carbonyl or sulfinyl;    A2=alkylene or fluoro alkylene (both optionally substituted) or oxygen;    R6,R9=1-5C alkyl, 1-5C alkoxy, 1-5C fluoroalkyl (all optionally substituted), 1-5C polyfluoroalkyl group, -SO2X3, SY1, -COZ or H;    X3,Y1=optionally substituted 1-5C alkyl;    Z=H, optionally substituted 1-5C alkyl or halo;    R7,R8=1-5C alkyl, 1-5C alkoxy, phenoxy, 1-5C fluoroalkyl, 1-5C polyfluoroalkyl, 1-5C fluoro alkoxy (all optionally substituted), 1-5C polyfluoro alkoxy, hydroxy, halo or -NX4X5;    X4,X5=H or optionally substituted 1-5C alkyl, -NY2CONY3Y4;and    Y2-Y4=H or optionally substituted 1-5C alkyl.    DESCRIPTION OF DRAWING(S) - The drawings show the top view and side view of the positive electrode.    Positive electrode (1)    Aluminum foil (2)    Positive electrode active material coated portion (3)    Positive electrode active material single spread portion (4)    Positive electrode active material non-coated portion (5)