NOVELTY - A secondary battery comprises electrode element and electrolyte solution. The electrode element contains positive electrode (c) and negative electrode (a) including negative electrode active substance containing metal capable of alloying with lithium and/or metal oxide capable of occluding and releasing lithium ions. The electrolyte solution is non-aqueous electrolyte containing carbonyl compound (I), and electrolyte salt dissolved in non-aqueous solvent.    USE - Secondary battery e.g. lithium-ion secondary battery is used for assembled battery for vehicle (all claimed). Uses include but are not limited to notebook computer, mobile telephone, electric train, satellite, submarine, electric vehicle, hybrid car, electric motorcycle, electric-power-assisted bicycle and uninterruptible power supply.    ADVANTAGE - The secondary battery has excellent cycle characteristics even at high-temperature environment.    DETAILED DESCRIPTION - A secondary battery comprises electrode element and electrolyte solution. The electrode element contains positive electrode and negative electrode including negative electrode active substance containing metal capable of alloying with lithium and/or metal oxide capable of occluding and releasing lithium ions. The electrolyte solution is non-aqueous electrolyte containing carbonyl compound of formula: R1-C(=O)-CC-CC-C(=O)-R1 (I) and electrolyte salt dissolved in non-aqueous solvent.    R1=H, cycloalkyl, alkenyl, alkynyl, oxyalkylene group of formula: -(R21O)n-R22, oxyalkyleneoxy of formula: -O-(R21O)n-R22, cycloalkyloxy, alkenyloxy, alkynyloxy, or alkoxy, alkyl, aryl or aryloxy (both optionally substituted), or;    R21=1-6C alkylene;    R22=1-12C hydrocarbyl;and    n=1-10.    INDEPENDENT CLAIMS are included for the following:    (1) assembled battery; and    (2) vehicle.    DESCRIPTION OF DRAWING(S) - The drawing shows the (Drawing includes non-English language text)    Negative electrode (a)    Positive electrode (c)    Negative electrode electrical power collector (d)    Positive electrode electrical power collector (e)    Positive electrode terminal (f)