NOVELTY - A secondary battery consists of a positive electrode (21), a negative electrode (22), and a nonaqueous electrolyte. The nonaqueous electrolyte contains nitrogen-containing compound (I), cyano group-containing compound (II) or (III), and 2H-1,3-dioxol-2-one compound (IV)-(VII), carbonyl group-containing compound (VIII), or cyano group-containing compound (IX). The content of nitrogen-containing compound in the nonaqueous electrolyte is 2.5-6 mol/dm3.    USE - Secondary battery e.g. lithium secondary battery is used for forming battery pack used for electric vehicle, electric power storage system, electric tool, and electronic device (all claimed) e.g. mobile telephone and portable information terminal apparatus.    ADVANTAGE - The secondary battery has excellent charge or discharge cycle characteristics and high energy density.    DETAILED DESCRIPTION - A secondary battery consists of a positive electrode, a negative electrode, and a nonaqueous electrolyte. The nonaqueous electrolyte contains nitrogen-containing compound of formula: M+((Z1Y1)(Z2Y2)N)- (I), cyano group-containing compound of formula: R1-CN (II) or R2-X-CN (III), and 2H-1,3-dioxol-2-one compound of formulae (IV)-(VII), carbonyl group-containing compound of formula (VIII), or cyano group-containing compound of formula: R22-(CN)n (IX). The content of nitrogen-containing compound in the nonaqueous electrolyte is 2.5-6 mol/dm3.    M=metallic element;    Z1,Z2=fluoro, monovalent hydrocarbyl, or monovalent fluorohydrocarbyl, at least one being fluoro or monovalent fluorohydrocarbyl;    Y1,Y2=sulfonyl or carbonyl;    R1,R2=monovalent hydrocarbyl;    X=bivalent hydrocarbyl or group bonded with ether bond;    R3,R4=H or monovalent hydrocarbyl;    R5-R8=H, monovalent saturated hydrocarbyl, or monovalent unsaturated hydrocarbyl, at least one being monovalent unsaturated hydrocarbyl;    R9=H, monovalent hydrocarbyl, or CR10R11;    R12-R21=H, halo, monovalent hydrocarbyl, or monovalent halohydrocarbyl, at least one being halo or monovalent halohydrocarbyl;    R22=n-valent hydrocarbyl;and    n=2 or more.    INDEPENDENT CLAIMS are included for the following:    (1) electrolyte solution;    (2) battery pack, which consists of the secondary battery, a control unit for controlling operation of the secondary battery, and a switch unit for switching the operation of secondary battery with respect to indication of the control unit;    (3) electric vehicle, which consists of the secondary battery, a conversion unit for converting electric power supplied from the secondary battery into a driving force, a drive unit driven with respect to the driving force, and a control unit;    (4) electric power storage system, which consists of the secondary battery, an electric equipment, and the control unit;    (5) electric tool, which consists of the secondary battery, and a movable unit to which electric power is supplied from the secondary battery; and    (6) electronic device, which consists of the secondary battery as an electric power supply source.    DESCRIPTION OF DRAWING(S) - The drawing shows the cross-sectional view of secondary battery.    Battery can (11)    Battery cover (14)    Safety valve mechanism (15)    Positive electrode (21)    Negative electrode (22)