Joining method

A joining method of joining two adjacent separators in a fuel cell stack in which unit cells are stacked, each of the unit cells including a membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly,

• wherein the two adjacent separators are a first separator covering a cathode of a first membrane electrode assembly and a second separator covering an anode of a second membrane electrode assembly,
• the first separator includes a plurality of first inward ridges that are in contact with the cathode of the first membrane electrode assembly and a plurality of first outward ridges that protrude toward the second separator, and
• the second separator includes a plurality of second inward ridges that are in contact with the anode of the second membrane electrode assembly and a plurality of second outward ridges that protrude toward the first separator,
• the joining method comprising:
• bringing the first separator and the second separator into contact with each other;
• bringing a first welding electrode into contact with the plurality of first inward ridges;
• bringing a second welding electrode into contact with the plurality of second inward ridges;
• and
• welding a plurality of portions where the first outward ridges and the second outward ridges are in contact with each other by causing a current to flow between the first welding electrode and the second welding electrode.