An electrode assembly for a battery. The electrode assembly includes a positive electrode with a positive electrode active material layer and a negative electrode with a negative electrode active material layer. The assembly further includes a separator that has a porous layer formed of a ceramic material and a binder and a polyolefin resin layer. The porous layer has a thickness of about 4 to 6 μm and the polyolefin resin layer has a thickness of about 12 to 16 μm.