A battery module comprising: a plurality of battery cells; a module case configured to receive the plurality of battery cells; and filling portions provided between the module case and the plurality of battery cells and between the plurality of battery cells, wherein the filling portions are transformed into a structure in which the volume of the filling portions is increased such that the plurality of battery cells are supported to prevent the plurality of battery cells from being swollen when an internal temperature of the battery module is lower than a predetermined temperature value, and are transformed into a structure in which the volume of the filling portions is decreased such that cooling passages are secured between the module case and the plurality of battery cells and between the plurality of battery cells when the internal temperature of the battery module is higher than or equal to the predetermined temperature value; and wherein the filling portions are formed of a shape transformation material with a shape that changes according to a temperature, and wherein the filling portions each comprise: a filling portion body having an upper body and a lower body of a plate-like shape individually formed thereon; and a pair of filling portion fixing portions positioned on both ends of the filling portion body to be attached to the inside of the module case such that the filling portion body is fixed; and wherein the filling portion body comprises: a first shape in which the upper body and the lower body are respectively bent in a direction in which the plurality of battery cells are disposed when the internal temperature of the battery module is lower than a predetermined range of temperature values; and a second shape in which the upper body and the lower body are respectively stretched in parallel when the internal temperature of the battery module is higher than or equal to the predetermined range of temperature values. a plurality of battery cells; a module case configured to receive the plurality of battery cells; and filling portions provided between the module case and the plurality of battery cells and between the plurality of battery cells, wherein the filling portions are transformed into a structure in which the volume of the filling portions is increased such that the plurality of battery cells are supported to prevent the plurality of battery cells from being swollen when an internal temperature of the battery module is lower than a predetermined temperature value, and are transformed into a structure in which the volume of the filling portions is decreased such that cooling passages are secured between the module case and the plurality of battery cells and between the plurality of battery cells when the internal temperature of the battery module is higher than or equal to the predetermined temperature value; and wherein the filling portions are formed of a shape transformation material with a shape that changes according to a temperature, and wherein the filling portions each comprise: a filling portion body having an upper body and a lower body of a plate-like shape individually formed thereon; and a pair of filling portion fixing portions positioned on both ends of the filling portion body to be attached to the inside of the module case such that the filling portion body is fixed; and wherein the filling portion body comprises: a first shape in which the upper body and the lower body are respectively bent in a direction in which the plurality of battery cells are disposed when the internal temperature of the battery module is lower than a predetermined range of temperature values; and a second shape in which the upper body and the lower body are respectively stretched in parallel when the internal temperature of the battery module is higher than or equal to the predetermined range of temperature values.