NOVELTY - The battery comprises: a flat winding electrode assembly (14) formed by winding an elongated positive electrode and an elongated negative electrode with an elongated separator placed between the electrodes; and a prismatic outer body (25) storing the electrode assembly and a nonaqueous electrolyte, where the electrode assembly includes a positive electrode substrate exposed portion (15) wound on an end and a negative electrode substrate exposed portion wound on the other end. A winding number of the positive and the negative exposed portions is greater than 30.    USE - The nonaqueous electrolyte secondary battery is useful as a power supply for: driving a portable electronic equipment such as smartphone, portable personal computer, personal digital assistant and portable music player; driving electric vehicles and hybrid electric vehicles; and in stationary storage battery systems for suppressing output fluctuation of solar power generation and wind power generation.    ADVANTAGE - The battery provides excellent cycling characteristics, and has high capacity, safety and output characteristics.    DETAILED DESCRIPTION - The battery comprises: a flat winding electrode assembly (14) formed by winding an elongated positive electrode and an elongated negative electrode with an elongated separator placed between the electrodes; and a prismatic outer body (25) storing the electrode assembly and a nonaqueous electrolyte, where the electrode assembly includes a positive electrode substrate exposed portion (15) wound on an end and a negative electrode substrate exposed portion wound on the other end. A winding number of the positive and the negative exposed portions is greater than 30, where the positive exposed portion has an outermost surface welded and connected with a positive electrode collector (17). The negative exposed portion has an outermost surface welded and connected with a negative electrode collector. The nonaqueous electrolyte contains a lithium salt having an oxalate complex as an anion at the time of making the battery. The layers of the positive exposed portion are melted at a welded connection portion that is formed between the positive exposed portion and the positive collector at a point on each of both sides across a winding central position of the electrode assembly, and the layers of the negative exposed portion are melted at the welded connection portion that is formed between the negative exposed portion and the negative collector at a point on each of both sides across the winding central position of the electrode assembly. The positive exposed portion has a melting area of greater than 2.7 mm2 in a plane passing through the central axis of the welded connection portion and being perpendicular to the winding axis of the winding electrode assembly within the welded connection portion with the positive collector. The negative exposed portion has a melting area of greater then 1.8 mm2 in a plane passing through the central axis of the welded connection portion and being perpendicular to the winding axis of the winding electrode assembly within the welded connection portion with the negative collector. Each exposed portions are divided into two segments, where the segments of the positive portion are placed such that a positive electrode conductive member (29) is arranged between the segments. The segments of the negative portion are placed such that a negative electrode conductive member is arranged between the segments. A set of positive and negative electrode conductive members are held in positive and negative electrode intermediate members having electric insulating properties. The battery has a capacity of greater than 20 Ah. The present amount of the lithium salt is 0.01-2 mole/l at the time of making the battery. The nonaqueous electrolyte contains lithium difluorophosphate at the time of making the battery. The positive collector comprises a rib formed in a region facing the positive exposed portion and on an end on the center side of the electrode assembly. The negative collector comprises a rib formed in a region facing the negative exposed portion and on an end on the center side of the electrode assembly.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic sectional view of a prismatic nonaqueous electrolyte secondary battery.    Winding electrode assembly (14)    Positive electrode substrate exposed portion (15)    Positive electrode collector (17)    Prismatic outer body (25)    Positive electrode conductive member. (29)