The present invention provides a separator in which an electrolyte-soluble polymer, which is soluble in liquid electrolyte, is coated on one or both surfaces of the separator, as well as an electrochemical device including the separator. Also, the present invention provides a method for producing an electrochemical device, comprising the steps of: (a) coating an electrolyte-soluble polymer, which is soluble in liquid electrolyte, on one or both surfaces of a separator; (b) interposing the separator produced in the step (a) between a cathode and an anode so as to assemble an electrochemical device; and (c) injecting a liquid electrolyte into the electrochemical device produced in the step (b). The electrochemical device, such as a lithium secondary battery, produced by the inventive method, has an improved safety while deterioration in the battery performance is minimized.