Disclosed herein is a battery cell configured to have a structure in which an electrode assembly, including positive electrodes, negative electrodes, and separators disposed respectively between the positive electrodes and the negative electrodes, is mounted in a battery case, wherein the battery case includes an upper case and a lower case, the upper case being provided with a first receiving part, in which the electrode assembly is received, the lower case being provided with a second receiving part, in which the electrode assembly is received, the first receiving part and the second receiving part being configured to have structures of different sizes, and the electrode assembly has an external shape corresponding to internal shapes of the first receiving part and the second receiving part.