FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENT RULES, 2003 COMPLETE SPECIFICATION (See Section 10 and Rule 13) TITLE OF INVENTION: SEPARATOR AND ELECTROCHEMICAL DEVICE HAVING THE SAME APPLICANT: LG CHEM, LTD. A company incorporated in Republic of Korea 128, Yeoui-daero Youngdungpo-gu Seoul 150-721, Republic of Korea The following specification particularly describes the invention and the manner in which it is to be performed. 2 TECHNICAL FIELD The present invention relates to a separator for an electrochemical device such as a lithium secondary battery, and an electrochemical device having the same. More particularly, the present invention relates to a separator having a first porous coating layer comprising an organic-inorganic mixture and a second porous coating layer which is a binder layer using a non-solvent, and an electrochemical device having the same. The present application claims priority to Korean Patent Application No. 10-2011- 0117862 filed in the Republic of Korea on November 11, 2011 and Korean Patent Application No. 10-2012-0126795 filed in the Republic of Korea on November 9, 2012, the disclosures of which are incorporated herein by reference. BACKGROUND ART Recently, there has been an increasing interest in energy storage technology. Electrochemical devices have been widely used as energy sources in the fields of cellular phones, camcorders, notebook computers, PCs and electric cars, resulting in intensive research and development into them. In this regard, electrochemical devices are one of the subjects of great interest. Particularly, development of rechargeable secondary batteries has been the focus of attention. Recently, research and development of such batteries are focused on the designs of new electrodes and batteries to improve capacity density and specific energy. Many secondary batteries are currently available. Among these, lithium secondary batteries developed in the early 1990’s have drawn particular attention due to their advantages of higher operating voltages and much higher energy densities than conventional aqueous electrolyte-based batteries, for example, Ni-MH, Ni-Cd, and H2SO4-Pb batteries. However, such lithium ion batteries suffer from safety problems, such as fire and explosion, when encountered with the use of organic electrolytes and are disadvantageously complicated to fabricate. In attempts to overcome the disadvantages of lithium ion batteries, lithium ion polymer batteries have been developed as next-generation batteries. More research is still urgently needed to improve the relatively low 3 capacities and insufficient low-temperature discharge capacities of lithium ion polymer batteries in comparison with lithium ion batteries. Many companies have produced a variety of electrochemical devices with different safety characteristics. It is very important to evaluate and ensure the safety of such electrochemical devices. The most important consideration for safety is that operational failure or malfunction of electrochemical devices should not cause injury to users. For this purpose, regulatory guidelines strictly restrict potential dangers (such as fire and smoke emission) of electrochemical devices. Overheating of an electrochemical device may cause thermal runaway or a puncture of a separator may pose an increased risk of explosion. In particular, porous polyolefin substrates commonly used as separators for electrochemical devices undergo severe thermal shrinkage at a temperature of 100 ºC or higher in view of their material characteristics and production processes including elongation. This thermal shrinkage behavior may cause electrical short between a cathode and an anode. In order to solve the above safety problems of electrochemical devices, a separator comprising a highly porous substrate and a porous organic/inorganic coating layer formed by coating with a mixture of an excess of inorganic particles and a binder polymer on at least one surface of the porous substrate has been proposed. However, if the porous organic/inorganic coating layer is formed on both surfaces of the porous substrate, the thickness of the separator becomes too thick, thereby reducing the capacity of an electrochemical device and increasing the resistance thereof, and if the porous organic/inorganic coating layer is formed on one surface of the porous substrate, the adhesiveness of the other surface reduces. DISCLOSURE Technical Problem The present invention is designed to solve the problems of the prior art, and therefore it is an object of the present invention to provide a separator having a porous organic-inorganic coating layer, which can have good thermal safety, low resistance and superior adhesiveness. 4 Technical Solution In accordance with one aspect of the present invention, there is provided a separator comprising a porous substrate; a first porous coating layer formed on one surface of the porous substrate and comprising a mixture of inorganic particles and a first binder polymer; and a second porous coating layer formed on the other surface of the porous substrate and comprising a product obtained by drying a mixture of a solvent, a non-solvent and a second binder polymer. The second porous coating layer may be formed on a part of the other surface of the porous substrate. Also, the separator may further comprise an electrode-adhesive layer formed on the surface of the first porous coating layer and comprising a third binder polymer. The porous substrate may be made of a polyolefin-based polymer, but is not particularly limited thereto. The polyolefin-based polymer is preferably selected from polyethylene, polypropylene, polybutylene and polypentene. The solvent may be acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, or cyclohexane, but is not particularly limited thereto. Also, the non-solvent may be methanol, ethanol, isopropyl alcohol or water, but is not particularly limited thereto. In the present invention, the solvent and the non-solvent are preferably used in a weight ratio of 50:50 to 99:1. The inorganic particles used in the present invention may be inorganic particles having a dielectric constant of 5 or higher, inorganic particles having the ability to transport lithium ions, or a mixture thereof. Examples of the inorganic particles having a dielectric constant of 5 or higher include BaTiO3, Pb(Zrx,Ti1-x)O3 (PZT, 0 100: Separator 10: Porous Substrate 20: First Porous Coating Layer 30: Second Porous Coating Layer BEST MODE Hereinafter, the present invention will be described in detail with reference to the drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. FIG. 1 shows the cross-section of a separator according to a preferred embodiment of the present invention. However, the embodiments and the drawings proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the disclosure, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the disclosure. A separator 100 according to the present invention has a porous substrate 10; a first porous coating layer 20 formed on one surface of the porous substrate and comprising a mixture of inorganic particles and a first binder polymer; and a second porous coating layer 30 formed by applying a mixture of a solvent, a non-solvent and a second binder polymer on the other surface of the porous substrate, followed by drying. The porous substrate 10 may be any planar porous substrate conventionally used in electrochemical devices, including a membrane or non-woven fabric form made of various polymers. For example, a polyolefin-based porous membrane which is used as a separator in electrochemical devices, particularly, a lithium secondary battery, or a non-woven fabric made of polyethylene terephthalate fiber may be used, and their material or form may be variously selected depending on a desired purpose. For example, the polyolefin-based porous membrane may be obtained from a polyolefin-based polymer, for example, polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene and ultra-high molecular weight polyethylene, 7 polypropylene, polybutylene, polypentene or a mixture thereof, and the non-woven fabric may be obtained from a fiber made of such a polyolefin-based polymer or a polymer having a higher heat-resistance than the polyolefin-based polymer. The porous substrate has preferably a thickness of 1 to 100 m, more preferably 5 to 50 m, but is not particularly limited thereto. Also, the porous substrate has a pore size of 0.01 to 50 m and a porosity of 10 to 95 %, but is not particularly limited thereto. On one surface of the porous substrate 10 according to the present invention, the first porous coating layer 20 made of a mixture of inorganic particles and a first binder polymer is formed. The first porous coating layer 20 is formed by applying a slurry comprising a mixture of inorganic particles and a first binder polymer on one surface of the porous substrate 10, followed by drying. In the first porous coating layer 20, the first binder polymer allows the adhesion of inorganic particles so that the inorganic particles can be bound with each other (i.e., the binder polymer connects and immobilizes the inorganic particle therebetween). Also, the first porous coating layer 20 comes in contact with the porous substrate 10 by the binder polymer and has adhesiveness with an electrode active material. In such porous coating layer 20, the inorganic particles are substantially present in contact with each other to form a closest packed structure, and an interstitial volume generated from the contact of the inorganic particles with each other becomes a pore of the first porous coating layer 20. The separator 100 having such a first porous coating layer 20 has good heat resistance and enhanced stability, however, may have a high electrical resistance due to the binder polymer. Accordingly, in order to minimize an electrical resistance due to the binder polymer, in the separator 100 of the present invention, the first porous coating layer 20 is provided in only one surface of the porous substrate, not both surfaces thereof. In addition, if the first porous coating layer 20 made of a mixture of inorganic particles and a first binder polymer is formed on both surfaces of the porous substrate, the thickness of the separator becomes thick, thereby deteriorating the capacity of electrochemical devices. Accordingly, in the present invention, the first porous coating layer 20 is formed on only one surface of the porous substrate 10 to improve the capacity of electrochemical devices. Meanwhile, the other surface of the porous substrate 10 on which the first porous coating layer 20 is not formed may be poor in adhesiveness with an electrode. Accordingly, in order to provide superior adhesiveness with an electrode, in 8 the separator 100 of the present invention, the second porous coating layer 30 made of a binder polymer is provided in the other side of the porous substrate. However, if the application of the binder polymer on the porous substrate is made by a conventional coating method, the binder polymer penetrates into the pores of the porous substrate to reduce the porosity of the porous substrate, thereby causing resistance increase. Accordingly, in the separator 100 of the present invention, a non-solvent is used to accelerate a phase separation between the second binder polymer and the non-solvent, thereby minimizing the penetration of the second binder polymer into the pores of the porous substrate. Also, the second porous coating layer 30 may be formed on only a part of the surface of the porous substrate to minimize the porosity decrease of the porous substrate and resistance increase. Also, the separator may further comprise an electrode-adhesive layer formed on the surface of the first porous coating layer and comprising a third binder polymer. The inorganic particles are not particularly limited if they are electrochemically stable. That is, the inorganic particles which may be used in the present invention are not particularly limited unless an oxidation-reduction reaction occurs in an operating voltage range (for example, 0 to 5 V based on Li/Li+) of an applied electrochemical device. Particularly, inorganic particles having a high dielectric constant may be used to increase a dissociation rate of an electrolyte salt, e.g., a lithium salt, in a liquid electrolyte, thereby improving an ionic conductivity of the electrolyte. For the foregoing reasons, the inorganic particles used in the present invention preferably include inorganic particles having a dielectric constant of 5 or higher, preferably 10 or higher. Non-limiting examples of the inorganic particles having a dielectric constant of 5 or higher include BaTiO3, Pb(Zrx,Ti1-x)O3 (PZT, 0