TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - The porous heat-resistant layer is positioned along at least one side of the positive and/or negative electrode mixture layers. An exposed part (15) of positive electrode current collector on which the positive electrode mixture layer is not carried is provided along shorter side(s) of positive electrode, and the porous heat-resistant layer is provided along the boundary between the positive electrode mixture layer and the exposed part of positive electrode current collector. The porous heat-resistant layer may be provided to face the boundary between the positive electrode mixture layer and the exposed part of positive electrode current collector with the separator interposed between them. The exposed part of positive electrode current collector is provided along a shorter side of positive electrode on the winding end side. An exposed part of positive electrode current collector on which the positive electrode mixture layer is not carried may be provided along longer side(s) of positive electrode, and the porous heat-resistant layer is provided along at least one boundary between the positive electrode mixture layer and the exposed part of positive electrode current collector. The porous heat-resistant layer may be provided to face at least one boundary between the positive electrode mixture layer and the exposed part of positive electrode current collector with the separator interposed between them. An exposed part of negative electrode current collector on which the negative electrode mixture layer is not carried is provided along longer side(s) of negative electrode, and the porous heat-resistant layer is provided along at least one boundary between the negative electrode mixture layer and the exposed part of negative electrode current collector. The porous heat-resistant layer may be provided to face at least one boundary between the negative electrode mixture layer and the exposed part of negative electrode current collector with the separator interposed between them. The exposed parts of positive and negative electrode current collectors are respectively provided at two end faces of the electrode group. A positive electrode current collecting terminal is welded to the exposed part of positive electrode current collector, and a negative electrode current collecting terminal is welded to the exposed part of negative electrode current collector. Preferred Dimensions: When the porous heat-resistant layer is provided from an edge of winding initiation side to a given position on at least one of the positive and negative electrode mixture layers, and the area of porous heat-resistant layer is represented by A and the area of mixture layer is represented by B, the ratio of area A to area B is 0.02-0.3. When the porous heat-resistant layer is provided on the negative electrode mixture layer, and the area of porous heat-resistant layer is represented by A and the area of negative electrode mixture layer is represented by B1, the ratio of area A to area B1 is 0.02- 0.3. The width of negative electrode mixture layer is larger than the width of positive electrode mixture layer. The thickness of porous heat-resistant layer is 1-10 microns.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Materials: The porous heat-resistant layer comprises insulating filler and binder (1-5 pbw/100 pbw insulating filler). The insulating filler comprises alumina, magnesia, titania, zirconia, and/or silica.    TECHNOLOGY FOCUS - POLYMERS - Preferred Materials: The binder comprises modified rubber particle containing acrylonitrile unit, and/or polyvinylidene fluoride.