NOVELTY - An electrochemical device has a composite separator (10a) with a porous substrate (1) having pores, a porous coated layer (a) (2) having mixture of cathode active material particles and binder polymer (i) formed on an upper surface of the porous substrate and a porous coated layer (b) (5) containing mixture of anode active material particles and binder polymer (ii) formed on a lower surface of the porous substrate, a cathode current collector (20) provided to face the porous coated layer (a) and an anode current collector (30) provided to face the porous coated layer (b).    USE - Electrochemical device such as lithium secondary battery (claimed) for cellular phones, camcorder, notebook computer and electric cars.    ADVANTAGE - The electrochemical device has excellent stability and economical efficiency.    DETAILED DESCRIPTION - An electrochemical device has a composite separator with a porous substrate having pores, a porous coated layer (a) having mixture of cathode active material particles and binder polymer (i) formed on an upper surface of the porous substrate and a porous coated layer (b) containing mixture of anode active material particles and binder polymer (ii) formed on a lower surface of the porous substrate, a cathode current collector provided to face the porous coated layer (a) and an anode current collector provided to face the porous coated layer (b). The cathode active material particles contain lithium-cobalt oxide, lithium-nickel oxide, lithium-manganese oxide, lithium-cobalt phosphate, lithium-iron phosphate, lithium-nickel-manganese-cobalt oxide or complex oxide of lithium-nickel-cobalt (LiNi1-x-y-zCoxM1yM2zO2), where M1,M2 are aluminum, nickel, cobalt, iron, manganese, vanadium, chromium, titanium, tungsten, tantalum, magnesium or molybdenum, x, y and z are greater than 0 and less than 0.5. The anode active material particles contain natural graphite, artificial graphite, carbonaceous material, low temperature oxide, silicon and/or tin. An INDEPENDENT CLAIM is included for method for manufacturing electrochemical device.    DESCRIPTION OF DRAWING(S) - The drawing shows the sectional view of the electrochemical device.    Porous substrate (1)    Porous coated layers (2,5)    Composite separator (10a)    Cathode current collector (20)    Anode current collector (30)