Energy storage device

An energy storage device comprising:

• an electrode assembly including a positive electrode and a negative electrode;
• a plate member;
• and
• an electrically conductive layer interposed between the electrode assembly and the plate member, wherein:
• the electrically conductive layer includes
• a first metal portion having a form of a plate and having a first surface that contacts the electrode assembly,
• a second metal portion having a form of a plate and having a second surface that contacts the plate member, and
• an insulating portion disposed in a central region of the first surface of the first metal portion and in contact with the electrode assembly;
• a third surface of the first metal portion and a fourth surface of the second metal portion face each other and are connected together, the third surface being a surface opposite to the first surface, and the fourth surface being a surface opposite to the second surface;
• and
• a coefficient of thermal expansion of the first metal portion is higher than a coefficient of thermal expansion of the second metal portion.