A common electrolyte for a lithium secondary battery may be employed as the electrolyte contained in a pouch case together with the electrode assembly. The pouch case is formed of sheet material and has an accommodating portion for accommodating the electrode assembly. Preferably, the pouch case is formed by coupling a first case and a second case, which are prepared by processing a sheet material into a predetermined shape. The sheet material of the pouch case has a multi-layered structure including an outer resin layer provided at an outermost side and made of an insulating material such as polyethylene terephthalate (PET) or nylon, a metal layer made of an aluminum material to maintain mechanical strength and prevent penetration of moisture and oxygen, and an inner resin layer made of a polyolefin-based material and serving as a sealing material due to thermal adhesiveness.

In the sheet material of the pouch case, a predetermined adhesive resin layer may be interposed between the inner resin layer and the metal layer and between the outer resin layer and the metal layer, if necessary. The adhesive resin layer is intended for smooth attachment between different kinds of materials and is formed as a single layer or a multilayer. The adhesive material may be commonly made of a polyolefin resin, or a polyurethane resin for smooth processing, or a mixture thereof.

In the cell assembly 10, the plurality of cells are disposed at predetermined intervals in the thickness direction to form a substantially stacked structure.