NOVELTY - A thin-shaped lithium secondary battery has electric power generation element containing positive electrode material, negative electrode material, separator and electrolyte enclosed within cladding material having base material layer (101), barrier layer (102) and sealant layer (103). Sealant layer has triple-layer structure having outer acid-modified polypropylene layer (103a), polypropylene layer (103b) having thickness of 8-20 mu m and inner acid-modified polypropylene layer (103a') having thickness of 10-25 mu m.    USE - Thin-shaped lithium secondary battery is used as power supply for video camera, notebook personal computer, mobile telephone, and electric vehicles.    ADVANTAGE - The thin-shaped lithium secondary battery has excellent sealing performance and short circuit prevention function.    DETAILED DESCRIPTION - A thin-shaped lithium secondary battery has an electric power generation element containing positive electrode material, negative electrode material, separator and an electrolyte enclosed within the cladding material having sequential lamination of base material layer, barrier layer and sealant layer. The sealant layer has triple-layer structure having sequential lamination of outer acid-modified polypropylene layer, polypropylene layer and inner acid-modified polypropylene layer. The edge portion of the cladding material is heat-sealed, such that the positive electrode terminal is extended from positive electrode material to the battery exterior portion and the negative electrode terminal is extended from negative electrode material to battery exterior portion. The thickness ( alpha ) of the outer acid-modified polypropylene layer before heat sealing is 8-20 mu m. The thickness ( gamma ) of the inner acid-modified polypropylene layer is 10-25 mu m. The thickness ( alpha ), thickness ( beta ) of polypropylene layer, thickness ( gamma ), and thickness (T) ( mu m) of thicker electrode terminal satisfy a relation: 2T/3 less than or equal to ( alpha )+( beta )+( gamma ) less than or equal to 3T/2 (I).    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of terminal leading-out portion of thin-shaped lithium secondary battery.    Thin-shaped lithium secondary battery (1)    Positive electrode terminal (15)    Base material layer (101)    Barrier layer (102)    Sealant layer (103)    Outer acid-modified polypropylene layer (103a)    Inner acid-modified polypropylene layer (103a')    Polypropylene layer (103b)