Ion exchange membrane and flow battery including same

An ion exchange membrane comprising:

• a first ion exchange resin layer having a first and a second surface;
• a second ion exchange resin layer on the first surface of the first ion exchange resin layer;
• a third ion exchange resin layer on the second surface of the first ion exchange resin layer;
• a fourth ion exchange resin layer on a surface of the second ion exchange resin layer which is opposite to the surface in contact with the first surface of the first ion exchange resin layer;
• and
• a fifth ion exchange resin layer on a surface of the third ion exchange resin layer which is opposite to the surface in contact with the second surface of the first ion exchange resin layer,
• wherein the first, second, third, fourth and fifth ion exchange resin layers each independently comprise one or more ionomer, and
• the one or more ionomer included in each of the second ion exchange resin layer and the third ion exchange resin layer has a higher equivalent weight (EW) than the one or more ionomer of the first ion exchange resin layer;
• and
• the one or more ionomer included in each of the fourth ion exchange resin layer and the fifth ion exchange resin layer has a higher EW than the one or more ionomer of the second ion exchange resin layer and the third ion exchange resin layer.