Disclosed herein is a battery cell constructed in a structure in which an electrode assembly of a cathode/separator/anode structure is mounted in a battery case formed of a laminate sheet including a resin layer and a metal layer while the electrode assembly is connected to electrode terminals extruding out of the battery case, wherein the battery case is provided at an outer circumferential end thereof with a sealing part formed by thermally welding upper and lower parts of the laminate sheet, and a sheet-type member (‘a thermally conductive sheet’) to accelerate the dissipation of heat from the battery cell extends to the sealing part while the thermally conductive sheet partially covers the battery cell.