In an embodiment, a method for manufacturing a pouch-type secondary battery comprises folding a pouch film to accommodate an electrode assembly in the pouch film, forming a first side sealing portion, a second side sealing portion, and an upper sealing portion at both end portions and an upper portion of the pouch film, and forming a folded portion by pressing a protrusion disposed on ends of the first and second side sealing portions, wherein the folded portion is formed by folding the protrusion towards a bottom portion of the pouch film.

A cell is provided. The cell includes a cell element including a positive electrode, a negative electrode, an electrolyte and a laminate film including an exterior layer, a metal layer, an interior layer, and a welded layer formed of the interior layer; wherein a thickness of the welded layer is larger than 5 m in a flat portion of the interior layer, wherein the welded layer increases in thickness from the flat portion to an end portion of the welded layer, and wherein when a thickness of the laminate film is t, a thickness of the interior layer is p and a thickness of the laminate film in the welded layer is t1, a following equation is satisfied: t2p2+5<t1<t25 (m).

A pouch-type secondary battery includes an electrode assembly including a first electrode plate, and a second electrode plate and a pouch film in which the electrode assembly is accommodated and including a sealing portion on three sides of the pouch film, wherein the pouch film includes a folded portion disposed at an end of the sealing portion, and formed by folding an end portion of the pouch film.

A cell is provided. The cell includes a cell element including a positive electrode, a negative electrode, an electrolyte and a laminate film including an exterior layer, a metal layer, an interior layer, and a welded layer formed of the interior layer; wherein a thickness of the welded layer is larger than 5 m in a flat portion of the interior layer, wherein the welded layer increases in thickness from the flat portion to an end portion of the welded layer, and wherein when a thickness of the laminate film is t, a thickness of the interior layer is p and a thickness of the laminate film in the welded layer is t1, a following equation is satisfied: t2p2+5<t1<t25 (m).