Secondary energy storage element (50; 60) having the features a: it comprises a layer composite having an electrode layer comprising a positive electrode material and an electrode layer comprising a negative electrode material and a separator layer arranged therebetween, b: the separator layer comprises at least one ply composed of a microporous material having electrically insulating properties, c: it comprises a reference electrode (24A; 24B, 27), d: it comprises an electrolyte with which the layer composite is impregnated and via which the separator layer, the electrode layers (12 and 14) and the reference electrode (24A; 24B, 27) are in contact, e: it comprises a housing enclosing the layer composite, the reference electrode (24A; 24B, 27) and the electrolyte, f: the housing has three poles, which are electrically insulated from one another and able to be tapped from outside the housing, of which the first pole is electrically connected to the electrode layer comprising the positive electrode material, the second pole is electrically connected to the electrode layer comprising the negative electrode material and the third pole is electrically connected to the reference electrode (24A; 24B, 27), and the additional features g: within the layer composite, the positive and negative electrode layers enclose between them an overlap region, and h: the reference electrode or a constituent part of the reference electrode (24B, 27) is positioned between the at least one ply of the separator layer and one of the electrode layers and is electrically insulated from said electrode layer by means of an insulating means, and i: the reference electrode or the constituent part of the reference electrode (24B, 27) that is positioned there is at least one metal filament or a sheet-type metallic coating disposed within the overlap region on a surface of the at least one ply of the separator layer or a surface of the insulating means, and j: the at least one metal filament or the sheet-type metallic coating covers on said surface an area of a maximum of 5% of the area over which the overlap region extends. a: it comprises a layer composite having an electrode layer comprising a positive electrode material and an electrode layer comprising a negative electrode material and a separator layer arranged therebetween, b: the separator layer comprises at least one ply composed of a microporous material having electrically insulating properties, c: it comprises a reference electrode (24A; 24B, 27), d: it comprises an electrolyte with which the layer composite is impregnated and via which the separator layer, the electrode layers (12 and 14) and the reference electrode (24A; 24B, 27) are in contact, e: it comprises a housing enclosing the layer composite, the reference electrode (24A; 24B, 27) and the electrolyte, f: the housing has three poles, which are electrically insulated from one another and able to be tapped from outside the housing, of which the first pole is electrically connected to the electrode layer comprising the positive electrode material, the second pole is electrically connected to the electrode layer comprising the negative electrode material and the third pole is electrically connected to the reference electrode (24A; 24B, 27), g: within the layer composite, the positive and negative electrode layers enclose between them an overlap region, and h: the reference electrode or a constituent part of the reference electrode (24B, 27) is positioned between the at least one ply of the separator layer and one of the electrode layers and is electrically insulated from said electrode layer by means of an insulating means, and i: the reference electrode or the constituent part of the reference electrode (24B, 27) that is positioned there is at least one metal filament or a sheet-type metallic coating disposed within the overlap region on a surface of the at least one ply of the separator layer or a surface of the insulating means, and j: the at least one metal filament or the sheet-type metallic coating covers on said surface an area of a maximum of 5% of the area over which the overlap region extends.