Each cell of the cell assembly 10 has a thin plate-like body and preferably has a pouch cell structure. The pouch cell includes a positive electrode, a separator and a negative electrode, which are alternately stacked so that an electrode tab is drawn out from at least one side thereof. The positive electrode and the negative electrode are fabricated by coating slurry containing an electrode active material, a binder resin, a conductive agent and other additives to at least one side of a current collector. In the case of a positive electrode, a common positive electrode active material such as a lithium-containing transition metal oxide may be used as the electrode active material. In the case of a negative electrode, a common negative electrode active material such as a lithium metal capable of intercalating and de-intercalating lithium ions, a carbonaceous material, a metal compound, or compounds thereof may be used as the electrode active material. In addition, the separator may adopt a common porous polymer film used in a lithium secondary battery.