An electrode assembly is prepared by stacking and winding a first electrode, a second electrode, and a separator disposed between the first and second electrodes. The electrode assembly is curved to the center of an axis that is substantially parallel to a length direction of the electrode assembly, and the separator has a coated layer of a thermoplastic polymer on at least one side thereof. A battery cell including the electrode assembly, and a method of preparing the battery cell have also been disclosed. The battery cell including the electrode assembly may have a high strength.