An electrode assembly, comprises one or more first electrodes comprising a cathode; one or more second electrodes comprising an anode; and a separator sheet having a zigzag form interposed therebetween. The separator sheet comprises a first porous polymer substrate; a first coating layer formed on one surface of the first porous polymer substrate and comprising a polymer binder, the first coating layer being faced with the cathode; and a second coating layer formed on the other surface of the first porous polymer substrate and comprising a mixture a polymer binder and inorganic particles, the second coating layer being faced with the anode and having a composition, a thickness and a porosity different from those of the first porous coating layer. A separator has porous coating layers with a different composition, thickness or porosity formed on each surface thereof.