Abstract: A battery module is disclosed. The battery module includes a battery cell assembly including a plurality of battery cells; a case assembly accommodating the battery cell assembly; the case assembly including a top case positioned on the battery cell assembly; and a bus bar assembly including a bus bar unit electrically connecting the plurality of battery cells, a connection frame connected to the bus bar unit and positioned under the top case, and an expansion sheet positioned between the connection frame and the top case. When a heat is applied to the expansion sheet and a temperature of the expansion sheet is higher than or equal to a predetermined temperature, the expansion sheet expands toward the top case.