NOVELTY - Secondary battery comprises a cathode (21), an anode (22), and an electrolytic solution, where an open-circuit voltage under a fully-charged state per pair of the cathode and the anode is greater than 4.3 V, and the electrolytic solution includes an unsaturated cyclic ester carbonate (I).    USE - The secondary battery is useful as a lithium-ion secondary battery in a battery pack, an electric power tool, an electronic unit used as a power supply source (all claimed) and portable home appliances such as electric shavers, memory units such as backup power supplies and memory cards, where the secondary battery is cylindrical type, the electric power tool is electric drill and electric saw and the electronic unit is video camera, digital still camera, cellular phone, notebook personal computers, cordless telephones, headphone stereos, portable radios, portable TV, and personal digital assistants, and the battery packs used as power supplies of notebook personal computers, medical electronic units such as pacemakers and hearing aids, electric vehicles such as electric cars (including hybrid vehicles), and electric energy storage system such as household battery systems.    ADVANTAGE - The secondary battery has high superior battery capacity, cycle characteristics and storage characteristics.    DETAILED DESCRIPTION - Secondary battery comprises a cathode (21), an anode (22), and an electrolytic solution, where an open-circuit voltage under a fully-charged state per pair of the cathode and the anode is greater than 4.3 V, and the electrolytic solution includes an unsaturated cyclic ester carbonate of formula (I).    X = a divalent group in which m-number of a divalent group of formula (A) and n-number of a divalent group of formula (B) are bonded in any order;    R1-R4 = H, halo, preferably F, Cl, B or I, a monovalent hydrocarbon group, a monovalent halogenated hydrocarbon group, a monovalent oxygen-containing hydrocarbon group, or a monovalent halogenated oxygen-containing hydrocarbon group, where any two or more of R1-R4 are bonded to one another;    m = greater than or equal to 1; and    n= greater than or equal to 0.    INDEPENDENT CLAIMS are included for:    (1) a battery pack comprising the secondary battery, a control section controlling a usage state of the secondary battery, and a switch section switching the usage state of the secondary battery according to an instruction from the control section; and    (2) an electric power tool comprising the secondary battery, and a movable section receiving electric power from the secondary battery.    DESCRIPTION OF DRAWING(S) - The diagram shows a sectional view of a secondary battery.    Insulating plates (12, 13)    Battery cover (14)    Cathode (21)    Anode (22)    Center pin. (24)