NOVELTY - A nonaqueous electrolyte is obtained by dissolving an electrolyte salt in nonaqueous solvent. The nonaqueous solvent contains 0.001-5 %mass diisocyanate compound (I), and 0.001-5 %mass at least one compound chosen from phosphoric acid ester compound (II), cyclic sulfonic acid ester compound (III), isocyanate compound (IV) having ester structure, and triple bond-containing compound (V).    USE - Nonaqueous electrolyte is used for electrical storage device (claimed) e.g. lithium ion capacitor and lithium ion secondary battery for electronic devices e.g. mobile telephone, notebook computer and electric vehicles.    ADVANTAGE - The nonaqueous electrolyte provides electrical storage device having excellent electrochemical characteristics and capacitance maintenance factor at high temperature, and reduces the increase rate of electrode thickness.    DETAILED DESCRIPTION - A nonaqueous electrolyte is obtained by dissolving an electrolyte salt in nonaqueous solvent. The nonaqueous solvent contains 0.001-5 %mass diisocyanate compound of formula (I), and 0.001-5 %mass at least one compound chosen from phosphoric acid ester compound of formula (II), cyclic sulfonic acid ester compound of formula (III), isocyanate compound of formula (IV) having ester structure, and triple bond-containing compound of formula (V).    L=4-12C alkylene;    R1,R2=1-6C alkyl or haloalkyl;    R3=1-6C alkyl, 2-6C alkenyl or 3-6C alkynyl;    R4=H, halo or 1-4C alkyl;    R6,R7=halo or 1-6C alkyl optionally substituted by at least one halo;    X=-CH(OR8)- or -C(=O)-;    R8=formyl, 2-7C alkyl carbonyl, 3-7C alkenyl carbonyl or 7-13C arylcarbonyl (all optionally substituted by halo);    R9=1-6C alkyl, 2-6C alkenyl, 6-12C aryl, 1-6C alkoxy, 2-6C alkenyloxy, 2-6C isocyanate alkyloxy or 6-12C aryloxy (all optionally substituted by halo);    Y'=2-6C bivalent coupling group including at least one ether bond or 1-6C linear or branched alkylene, in which at least one H is substituted by halo;    Z=R10-O-C(=O)-, R11-O-C(=O)-C(=O)- or R12-S(=O)2-;    W'=H or -CH2-O-S(=O)2-R13;and    R10-R13=2-6C alkenyl, 2-6C alkynyl, 6-12C aryl or 1-6C alkyl, in which at least one H is substituted by halo.    (i) When W' is H, Z is R10-O-C(=O)- or R11-O-C(=O)-C(=O)-. An INDEPENDENT CLAIM is included for electrical storage device.