NOVELTY - The battery has a layer that comprises the positive electrode active material that is provided on a surface of a positive electrode current collector. The positive and negative electrode sheets (101,103), and the separator (102,105) are wound, so that each of the positive and negative electrode sheets, and the separator comprises the first bent portion. The first bent portion comprises the first region where the layer comprising the positive electrode active material is not provided, and the second region where the layer comprising the active material is not provided.    USE - Battery such as square lithium secondary battery (claimed). Uses include but are not limited to clean energy vehicle such as hybrid electric vehicle (HEV), electric vehicle (EV), and plug-in hybrid electric vehicle (PHEV), personal digital assistants such as cellular phone, smart phone, and laptop computer, and portable consumer equipment such as portable music player, digital camera, radio receiver and tape recorder, etc.    ADVANTAGE - The increased margin of the structure reduces stress even when stress in the direction other than the perpendicular direction is applied on the wound surface, and thus prevents the active material mixture layer from being flaked or exfoliated from the current collector. The positive temperature coefficient (PTC) element prevents abnormal heating by limiting the amount of current by an increase in resistance. The display portions are protected, and thus possible to provide a tablet terminal with high durability and improved reliability for long-term use. The square lithium secondary battery is compact and lightweight with improved characteristics, and thus the vehicle is made lightweight and fuel efficiency is increased.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view illustrating the wound portion.    Positive electrode sheets (101)    Separators (102,105)    Negative electrode sheet (103)    Positive electrode lead (106)    Negative electrode lead (107)