NOVELTY - A lithium ion secondary battery comprises a spirally wound electrode body (10) in which a positive electrode (20) and a negative electrode (30) are laminated via a separator (41) and spirally wound with a center opening portion (50) of the spirally wound electrode body. The positive electrode includes an inner circumference side positive electrode active material layer, and an outer circumference side positive electrode active material layer.    USE - A lithium ion secondary battery used as a power source for an electronic apparatus, electronic tool, electric vehicle, and a power storage system (claimed).    ADVANTAGE - The secondary battery obtains excellent battery characteristics while suppressing fracturing of a positive electrode when coiling.    DETAILED DESCRIPTION - A lithium ion secondary battery comprises a spirally wound electrode body (10) in which a positive electrode (20) and a negative electrode (30) are laminated via a separator (41) and spirally wound with a center opening portion (50) of the spirally wound electrode body as a center so that the positive electrode is arranged more to an inner circumference side than the negative electrode. The positive electrode includes an inner circumference side positive electrode active material layer, and an outer circumference side positive electrode active material layer that are formed on a positive electrode collector while including a single side active material layer formation region in which only the outer circumference side positive electrode active material layer is formed on the positive electrode collector on an end portion of an inner circumference side in an active material layer formation region. The negative electrode includes a negative electrode active material that absorbs and discharges an electrode reactant. An INDEPENDENT CLAIM is included for a battery pack, comprising the lithium ion secondary battery; a control section that controls the secondary battery; and an outer packaging that contains the secondary battery.    DESCRIPTION OF DRAWING(S) - The drawing is a cross-sectional diagram of the secondary battery.    Spirally wound electrode body (10)    Positive electrode (20)    Negative electrode (30)    Separator (41)    Center opening portion (50)