Secondary batteries typically comprise an electrode assembly in which a positive electrode plate and a negative electrode plate are spirally wound with a strip-shaped separator interposed therebetween. The positive electrode plate includes a strip-shaped current collector and a positive electrode material mixture layer formed on the current collector. The negative electrode plate includes a strip-shaped current collector and a negative electrode material mixture layer formed on the current collector. The innermost winding turn of the spirally-wound electrode assembly has an exposed portion of the positive electrode current collector on which no positive electrode material-mixture layer is formed. In the structure called a positive electrode lead forward structure, a positive electrode lead is connected to the exposed portion of the positive electrode current collector, in other words, the positive electrode lead is connected to the winding start portion of the electrode assembly.
In order to prevent an internal short-circuit from occurring in the electrode assembly having such positive electrode lead forward structure, an arrangement is proposed in which the distance between the positive electrode lead and the negative electrode plate is increased (see, for example, Patent Document 1 and Patent Document 2).    Patent Document 1: Japanese Patent No. 3237015    Patent Document 2: Japanese Patent No. 3373934