Battery module having structure into which cooling water can be introduced when thermal runaway phenomenon occurs, and battery pack and energy storage device comprising same

A battery module comprising:

• a cell stack comprising a plurality of battery cells;
• a module housing in which the cell stack is received;
• an air inlet passing through the module housing on a first side of a stack direction of the cell stack;
• an air outlet passing through the module housing on a second side in the stack direction of the cell stack;
• and
• at least one expandable pad disposed inside of the air inlet and the air outlet to close the air inlet and the air outlet, by expansion upon contact with cooling water introduced into the module housing thereby preventing the cooling water introduced into the module housing from leaking out of the module housing.