A high voltage battery module includes a plurality of battery cells, a plurality of cooling fins dispersed between the battery cells, and a frame for holding the plurality of battery cells and the plurality of fins. An intumescent layer is proximate to at least one battery module component selected from the battery cells, the plurality of cooling fins, and the frame. The intumescent layer includes sodium silicate having formula Na2SiO3, pentaerythitol, a resin that is cross-linked by melamine, boron nitride particles, and triammonium phosphate.