Battery Module and Assembling Method of the Same

The present disclosure relates to a battery module and an assembling method of the same including: a cell assembly including a plurality of battery cells and a busbar assembly for electrically connecting the plurality of battery cells; a case forming a cell accommodating space for accommodating the cell assembly therein; and a filler portion provided between the plurality of battery cells and the busbar assembly inside the case and including a flame-retardant material.