Eco-friendly power source such as battery module for transportation vehicle

A battery module comprising:

• a first sub-module and a second sub-module respectively including a cell stack in which a plurality of battery cells are stacked;
• a central wall disposed between the first sub-module and the second sub-module;
• and
• an upper cover and a lower cover covering the first sub-module and the second sub-module,
• wherein the central wall includes a first central wall facing the first sub-module and a second central wall facing the second sub-module,
• wherein the first central wall and the second central wall have through holes extending from the lower cover to the upper cover,
• wherein the first central wall comprises at least one first groove portion disposed on a surface of the first central wall, but not completely penetrating through the first central wall, the at least one first groove portion on the surface of the first central wall contacting the first sub-module,
• wherein the second central wall comprises at least one second groove portion disposed on a surface of the second central wall, but not completely penetration through the second central wall, the at least one second groove portion on the surface of the second central wall contacting the second sub-module, and
• wherein the at least one first groove portion and the at least one second groove portion have a space to move gas emitted from the battery cells.