Fuel cell stack

1. A fuel cell stack comprising:

a box-shaped casing; and

a stack body provided in said box-shaped casing, said stack body being formed by stacking a plurality of unit cells in a stacking direction, said unit cells each including an electrolyte electrode assembly and metal separators sandwiching said electrolyte electrode assembly, said metal separators being corrugated plates, said electrolyte electrode assembly including a pair of electrodes each having a gas diffusion layer and a catalyst layer, and an electrolyte interposed between said electrodes, wherein said casing comprises:

end plates provided at opposite ends of said stack body in the stacking direction;

a plurality of side plates provided on sides of said stack body;

coupling members for coupling adjacent ends of said side plates; and

a coupling pin for coupling said end plate and said side plate,

wherein each of the corrugated plates includes a plurality of alternating ridges and grooves on one side and a plurality of alternating ridges and grooves on an opposed side, the grooves and ridges being linear and oriented perpendicular to the stacking direction of the fuel cell stack, wherein a ridge on one side of the plate corresponds to a groove on the opposed side of the plate,

wherein a coolant flow field is formed between adjacent separators by direct contact of the ridges of one of the adjacent separators with the ridges of the other of the adjacent separators, wherein the corrugated plates include connecting portions extending from one end of a groove to a corresponding end of a ridge to directly connect the ridge to the groove, the connecting portions being both linear and slant such that the connecting portions are neither perpendicular nor parallel to the stacking direction of the fuel cell stack, so that the corrugated plates have elasticity in the stacking direction, wherein

terminal plates are provided at opposite ends of said stack body in the stacking direction, and a spatially insulating spacer member for absorbing dimensional variation of the stack body in the stacking direction is interposed between at least one of said terminal plates and said end plate, the fuel cell stack including only a single spatially insulating spacer member at a single end of the fuel cell stack, and a tightening force applied to the fuel cell stack is adjusted by a thickness of the insulating spacer member,

wherein the fuel cell stack is free of a spring member between the box-shaped casing and the terminal plates, and

outer marginal regions of the metal separators comprise one or more sealing elements, and the sealing elements extend in the stacking direction only a portion of the distance between adjacent separators so that a gap exists between each sealing element and a seal of an adjacent separator.

2. A fuel cell stack according to claim 1 , wherein said coupling member is an angle member.

3. A fuel cell stack according to claim 2 , wherein said angle member is fixed to adjacent ends of said side plates by a screw.

4. A fuel cell stack according to claim 1 , wherein a tab of said end plate and a tab of said side plate are positioned alternately, and said coupling pin is inserted into said tab of said end plate and said tab of said side plate.

5. A fuel cell stack according to claim 1 , wherein said end plate has a rectangular shape, and each side of said rectangular end plate is connected to said side plate by said coupling pin.

6. A fuel cell stack according to claim 1 , wherein said unit cells are stacked in a horizontal direction.

7. A fuel cell stack according to claim 1 , wherein sealing members are formed between the metal separators and the casing to cover outer edges of the metal separators.

8. A fuel cell stack according to claim 7 , wherein a seal is interposed between the sealing members to prevent an outer edge of the electrolyte from contacting the casing.