Battery module including a portion of a coupling unit free of any screw surface and method of manufacturing the battery module

1. A battery module for accommodating a plurality of batteries connected to each other in a battery unit, the battery module comprising:

a pair of end plates facing each other;

a restrainer coupled to the pair of end plates, the restrainer being configured to restrain expansion of the battery unit; and

a coupling unit for coupling the end plates and the restrainer to each other,

wherein:

a portion of the coupling unit that contacts the end plate and the restrainer is free of any screw surface, and

the coupling unit includes:

a bolt, the bolt including:

a body extending through the restrainer and the end plate and having a screw surface on an outer circumferential surface thereof, and

a head on an end portion of the body;

a nut coupled to the screw surface of the bolt; and

a cylindrical member on the bolt between the head and the nut, an outer circumferential surface of the cylindrical member being concentric with the outer circumferential surface of the body such that the cylindrical member surrounds the screw surface of the body, the cylindrical member contacting the restrainer and the end plate, and the outer circumferential surface of the cylindrical member constituting the portion of the coupling unit that contacts the end plate and the restrainer.

2. The battery module as claimed in claim 1 , wherein the outer circumferential surface of the cylindrical member is substantially smooth.

3. The battery module as claimed in claim 1 , wherein the coupling unit further includes a washer compressed by the head.