Power supply device

A power supply device comprising:

• a plurality of battery cells each having a rectangular outer shape;
• a plurality of separators each configured to insulate adjacent battery cells, the plurality of separators each including:
• an interposed plate disposed between the adjacent battery cells;
• a heat insulating member having a sheet-like shape and disposed between the interposed plate and a corresponding one of the adjacent battery cells;
• peripheral walls protruding from the interposed plate toward the adjacent battery cells and defining a housing space housing the adjacent battery cells;
• and
• a plurality of ribs provided inside each of the peripheral walls, the plurality of ribs holding the heat insulating member;
• and
• a restraining member configured to assemble the plurality of battery cells and the plurality of separators.