NOVELTY - A secondary battery has a positive electrode (21), a negative electrode (22) and an electrolyte solution containing benzylidene aniline compound(s) (I) and (II).    USE - Secondary battery e.g. lithium ion secondary battery is used for battery pack, electric vehicle, electric power storage system, electric tool and electronic device (all claimed). Uses include but are not limited to electric motorbike, hybrid vehicle, photovoltaic power generator, wind-powered generator, refrigerator, air-conditioner, television, water heater, thermal power station, nuclear power station, water power station, and wind power station.    ADVANTAGE - The secondary battery has excellent battery characteristics.    DETAILED DESCRIPTION - A secondary battery has a positive electrode, a negative electrode and an electrolyte solution containing benzylidene aniline compound(s) of formulae (I) and (II).    X1=hydroxy, alkoxy (-OR1), metal alkoxy (-OM1), thiol, thioalkoxy (-SR1), metal sulfide (-SM1), sulfonic acid group, sulfonic acid ester group (-SO3R1), metal sulfonic acid group (-SO3M1), cyano, carboxy, carboxylate-ester (-COOR1), amino (-N(R2)2), amido (-NHCOR1), sulfonamide (-SO2N(R1)2), silyl ether (-OSi(R1)3), borate (-B(R1)2) or phosphine (-P(R1)2);    R2=H or alkyl;    M1=alkali metal, alkaline-earth metal or transition metal;    M2=transition metal;    Y1=halo, carboxy or carboxylate-ester (-COOR6);    R1,R6=alkyl, aryl, haloalkyl or haloaryl;    R3,R7=alkyl, cycloalkyl or aryl;    R4,R8=H, alkyl, cycloalkyl or aryl;    R5,R9=halo, alkyl, cycloalkyl or aryl;    n1-n5=0 or more;and    m1=one or more.    when X1 is hydroxy, then n2 is one or more. INDEPENDENT CLAIMS are included for the following:    (1) electrolyte solution, which contains at least one of benzylidene aniline compounds (I) and (II);    (2) battery pack, which has a secondary battery, a control portion which controls the use condition of secondary battery, and switch portion which switches the use condition of secondary battery according to instruction of control portion;    (3) electric vehicles, which has a secondary battery, a conversion portion which converts the electric power supplied from secondary battery into driving force, driving portion driven according to driving force, and control portion which controls the use condition of secondary battery;    (4) electric power storage system, which has secondary battery, electric equipment(s), and control portion;    (5) electric tool, which has a secondary battery and a movable portion to which the electric power is supplied from secondary battery; and    (6) electronic device, which has secondary battery as electric power supply source.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of portion of winding electrode component. (Drawing includes non-English language text)    Winding electrode component (20)    Positive electrode (21)    Positive electrode collector (21A)    Positive electrode active material layer (21B)    Negative electrode (22)    Separator (23)