An energy storage system includes a housing in which a plurality of storage cells are arranged. The storage cells are thermally insulated from each other via a device arranged between the storage cells. The device is designed in such a way that the storage cells are spaced apart from each other. The device is made from temperature-resistant material. The device has projections and depressions. The device contains a material which is configured to be subjected to an endothermic chemical conversion when a temperature of 200° C. is exceeded.