A functional binder and a separator including the functional binder, in which the separator includes a porous polyolefin substrate and an organic-inorganic hybrid porous coating layer formed on at least one surface of the substrate and configured to include a mixture of inorganic particles and a binder compound, thus increasing binder-inorganic material adhesion and substrate-binder adhesion while preventing internal shorting from occurring by performing self-healing of damage to the separator, enhancing the adhesion of the separator to a cathode and an anode, and withstanding the dissolution of a transition metal of a cathode material. The binder contains 10 wt % or more of a hydroxyl group per molecule thereof.