Battery pack with improved safety

A battery pack comprising:

• a cell module assembly including:
• a battery cell stack including a plurality of stacked battery cells, each battery cell having an electrode lead;
• and
• a busbar housing assembly in which the electrode leads of the plurality of battery cells is coupled to a busbar electrode;
• a pack case configured to house the cell module assembly, the pack case having an open upper surface;
• and
• a fire extinguishing tank configured to cover an upper surface of the cell module assembly, the fire extinguishing tank including:
• an internal space configured to house a fire extinguishing agent;
• and
• a base plate having a plurality of fragile portions that are thin relative to remaining portions of the base plate, the plurality of fragile portions are configured to be melted and create openings in the base plate by a thermal event of at least one of the plurality of battery cells,
• wherein a portion of the base plate of the fire extinguishing tank that is located at least above the electrode leads of the plurality of battery cells protrudes downward toward the electrode leads of the plurality of battery cells.