FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION (See Section 10; rule 13) “ORGANIC/INORGANIC COMPOSITE SEPARATOR HAVING POROUS ACTIVE COATING LAYER AND ELECTROCHEMICAL DEVICE CONTAINING THE SAME” LG CHEM, LTD. of the address: 20, Yoido-dong, Youngdungpo-gu, Seoul, 150-721, Republic of Korea. The following specification particularly describes and ascertains the nature of this invention and the manner in which it has to be performed: Description ORGANIC/INORGANIC COMPOSITE SEPARATOR HAVING POROUS ACTIVE COATING LAYER AND ELEC¬TROCHEMICAL DEVICE CONTAINING THE SAME Technical Field [1] The present invention relates to a separator of an electrochemical device such as a lithium secondary battery and an electrochemical device containing the same. More particularly, the present invention relates to an organic/inorganic composite separator in which a porous active layer is coated with a mixture of an inorganic particle and a polymer onto a surface of a porous substrate, and an electrochemical device containing the same. Background Art [2] Recently, there has been an increasing interest in energy storage technology. Batteries 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, the research and development into a novel electrode and a novel battery that can improve capacity density and specific energy have been made intensively in the field of the secondary batteries. [3] Among currently used secondary batteries, lithium secondary batteries developed in early 1990's have a higher drive voltage and a much higher energy density than those of conventional batteries using a liquid electrolyte solution such as Ni-MH batteries, Ni-Cd batteries, and H SO -Pb batteries. For these reasons, the lithium secondary 2 4 batteries have been advantageously used. However, such a lithium secondary battery has disadvantages in that organic electrolytes used therein may cause safety-related problems such as ignition and explosion of the batteries and that processes for manu¬ facturing such a battery are complicated. Recently, lithium-ion polymer batteries have been considered as one of the next-generation batteries since the above disadvantages of the lithium ion batteries are solved. However, the lithium-ion polymer batteries have a relatively lower battery capacity than those of the lithium ion batteries and an in¬ sufficient discharging capacity in low temperature, and therefore these disadvantages of the lithium-ion polymer batteries remain to be urgently solved. [4] Such electrochemical devices have been produced from many companies, and the battery stability has different phases in the electrochemical devices. Accordingly, it is important to evaluate and ensure the stability of the electrochemical batteries. First of all, it should be considered that errors in operation of the electrochemical device should not cause damage to users. For this purpose, the Safety Regulation strictly regulates ignition and explosion in the electrochemical devices. In the stability charac¬teristics of the electrochemical device, overheating of the electrochemical device may cause thermal runaway, and explosion may occur when a separator is pierced. In particular, a polyolefin porous substrate commonly used as a separator of an elec¬trochemical device shows extreme thermal shrinking behavior at a temperature of 100 C or above due to the features of its material and its manufacturing process such as elongation, so there may occur an electric short circuit between cathode and anode. [5] In order to solve the above safety-related problems of the electrochemical device, there has been proposed an organic/inorganic composite separator having a porous active layer formed by coating at least one surface of a polyolefin porous substrate having many pores with a mixture of inorganic particles and a binder polymer (see Korean Laid-open Patent Publication No. 10-2006-72065 and 10-2007-231, for example). The inorganic particles in the porous active layer formed on the polyolefin porous substrate act as a kind of spacer that keeps a physical shape of the porous active layer, so the inorganic particles restrain thermal shrinkage of the polyolefin porous substrate when the electrochemical device is overheated. In addition, interstitial volumes exist among the inorganic particles, thereby forming fine pores. [6] As mentioned above, at least a certain amount of inorganic particles should be contained such that the porous active layer formed on the organic/inorganic composite separator may restrain thermal shrinkage of the polyolefin porous substrate. However, as the content of inorganic particles is increased, a content of binder polymer is relatively decreased, which may cause the following problems. [7] First, due to the stress generated in an assembly process of an electrochemical device such as winding, inorganic particles may be extracted from the porous active layer, and the extracted inorganic particles act as a local defect of the electrochemical device, thereby giving a bad influence on the stability of the electrochemical device. [8] Second, an adhesion between the porous active layer and the polyolefin porous substrate is weakened, so the ability of the porous active layer to restrain thermal shrinkage of the polyolefin porous substrate is deteriorated. Thus, it is difficult to prevent an electric short circuit between cathode and anode even when the elec¬trochemical device is overheated. [9] On the contrary, if the content of binder polymer in the porous active layer is increased in order to prevent extraction of inorganic particles, the content of inorganic particles is relatively decreased, so thermal shrinkage of the polyolefin porous substrate may not be easily restrained. Accordingly, it is hard to prevent an electric short circuit between cathode and anode, and also the performance of the elec- trochemical device is deteriorated due to the decrease of porosity in the porous active layer. Disclosure of Invention Technical Problem [10] The present invention is designed to solve the problems of the prior art, and therefore an object of the invention is to provide an organic/inorganic composite separator capable of preventing extraction of inorganic particles in a porous active layer formed on a porous substrate during an assembly process of an electrochemical device, and also capable of restraining an electric short circuit between cathode and anode even when the electrochemical device is overheated. Technical Solution [11] In order to accomplish the first object, the present invention provides an organic/ inorganic composite separator, which includes (a) a polyolefin porous substrate having pores; and (b) a porous active layer containing a mixture of inorganic particles and a binder polymer, with which at least one surface of the polyolefin porous substrate is coated, wherein the porous active layer has a peeling force of 5 gf/cm or above, and a thermal shrinkage of the separator after being left alone at 150°C for 1 hour is 50% or below in a machine direction (MD) or in a transverse direction (TD). [12] The organic/inorganic composite separator of the present invention may solve the problem that inorganic particles in the porous active layer are extracted during an assembly process of an electrochemical device, though inorganic particles are suf¬ficiently contained over certain content. In addition, an adhesive force between the porous active layer and the polyolefin porous substrate is strong, so thermal shrinkage is restrained to some extent though the electrochemical device is overheated, thereby preventing an electric short circuit between the cathode and the anode. Accordingly, the stability of the electrochemical device is greatly improved. [13] In the organic/inorganic composite separator according to the present invention, the binder polymer is preferably a mixture of a first binder polymer having a contact angle to a water drop of 70° to 140°and a second binder polymer having a contact angle to a water drop of 1° to 69°. Since the first and second binder polymers with different hydrophile properties are used in a blend form to control the hydrophile property of the polymer blend, there may be obtained a synergistic effect in improvement of thermal stability of the organic/inorganic composite separator. [14] The first binder mentioned above may be any one polymer or a mixture of at least two polymers selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylacetate, polyethylene-co-vinyl acetate, polyimide and polyethylene oxide. [15] Also, the second binder polymer mentioned above may be any one polymer or a mixture of at least two polymers having at least one polar group selected from the group consisting of hydroxyl group (-OH), carboxyl group (-COOH), maleic anhydride group (-COOOC-), sulphonate group (-SO H) and pyrrolidone group (-NCO-). These second binder polymer may be cyanoethylpullulan, cyanoethylpolyvinylalcohol, cya-noethylcellulose, cyanoethylsucrose, carboxyl methyl cellulose, polyvinylalcohol, polyacrylic acid, polymaleic anhydride, or polyvinylpyrrolidone, for example. Brief Description of the Drawings [16] These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings: [17] FIGs. la to le are photographs showing a separator manufactured according to em- bodiments of the present invention and comparative examples, which illustrate heat shrinkage after the separator is left alone for 1 hour in an oven of 150°C; and [18] FIG. 2 is a photograph showing a test device for measuring a peeling force of a porous active layer formed on an organic/inorganic composite separator manufactured according to embodiments of the present invention and comparative examples. Best Mode for Carrying Out the Invention [19] Hereinafter, preferred embodiments of the present invention will be described in detail referring to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and 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. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention. [20] The present invention provides an organic/inorganic composite separator, which includes (a) a poly olefin porous substrate having pores; and (b) a porous active layer containing a mixture of inorganic particles and a binder polymer, with which at least one surface of the polyolefin porous substrate is coated, wherein the porous active layer has a peeling force of 5 gf/cm or above, and a thermal shrinkage of the separator after being left alone at 150°C for 1 hour is 50% or below in a machine direction (MD) or in a transverse direction (TD). [21] In the organic/inorganic composite separator of the present invention, the porous active layer has a peeling force of 5 gf/cm or above, so the porous active layer has an excellent peeling resistance, thereby solving the problem that inorganic particles in the porous active layer are extracted while assembling a charger chemical device. In addition, an adhesive force between the porous active layer and the polyolefin porous substrate is strong. Thus, though the battery is overheated, the porous active layer and the polyolefin porous substrate are not separated, and thermal shrinkage of the polyolefin porous substrate may be restrained. That is to say, since the organic/ inorganic composite separator shows a thermal shrinkage of 50% or below in a machine direction (MD) or in a transverse direction (TD), it is possible to prevent an electric short circuit between cathode and anode. In addition, though the porous substrate is overheated in the electrochemical device, both electrodes are not entirely short-circuited due to the porous active layer. Even if there occurs a short circuit, the short-circuited area is not enlarged, thereby improving stability of the electrochemical device. [22] In the organic/inorganic composite separator of the present invention, more preferably, the porous active layer has a peeling force of 10 gf/cm or above, and a thermal shrinkage of the separator after being left alone at 150°C for 1 hour is preferably 30% or below in a machine direction (MD) or in a transverse direction (TD), in aspect of stability of the electrochemical device and peeling resistance of the porous active layer. [23] In the organic/inorganic composite separator of the present invention, the binder polymer preferably uses a mixture of a first binder polymer having a contact angle to a water drop of 70° to 140°and a second binder polymer having a contact angle to a water drop of 1° to 69°. In the present invention, after a sample film was made using a corresponding binder polymer, a distilled water drop was fallen thereon, and then a contact angle formed on the water drop was set as 23 degrees. Also, the contact angle to a water drop was measured using a contact angle measurer model CA-DT-A (mfd. produced by Kyowa Kaimen Kagaku KK) under the condition of 50% RH. Contact angles were measured at two points (namely, left and right points) of each of three sample films, and six measured values are averaged and set as a contact angle. The distilled water drop has a diameter of 2 mm, and the contact angle value displayed on the measurer shows a contact angle measured 1 minute after the distilled water drop is fallen. [24] Since the first and second binder polymers having different hydrophile properties are used in a blend form to control a hydrophile property of the polymer blend as mentioned above, it is possible to realize a synergistic effect in improving thermal stability of the organic/inorganic composite separator. [25] More preferably, the first binder polymer has a contact angle to a water drop of 90° to 110°and the second binder polymer has a contact angle to a water drop of 20° to 40°. Also, the first binder polymer and the second binder polymer are preferably mixed in a weight ratio of 95:5 to 5:95, but not limitedly. [26] The first binder polymer mentioned above may be any one polymer or a mixture of at least two polymers selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylacetate, polyethylene-co-vinyl acetate, polyimide, and polyethylene oxide, but not limitedly. [27] Also, the second binder polymer is preferably a polymer or a mixture of at least two polymers having at least one polar group selected from the group consisting of hydroxyl group (-OH), carboxyl group (-COOH), maleic anhydride group (-COOOC-), sulphonate group (-SO H) and pyrrolidone group (-NCO-). The second binder polymer may be cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cya-noethylsucrose, carboxyl methyl cellulose, polyvinylalcohol, polyacrylic acid, polymaleic anhydride, or polyvinylpyrrolidone. [28] In addition, in the organic/inorganic composite separator according to the present invention, the number of inorganic particles per a unit area of the porous active layer is 15 30 2 preferably 1x10 to 1x10 /m in consideration of a common thickness of the porous active layer. If the number of inorganic particles per a unit area of the porous active layer is less than 1x10 , the thermal stability obtained by the inorganic particles may be deteriorated. Meanwhile, if the number of inorganic particles per a unit area of the 30 2 porous active layer is greater than 1x10 /m , dispersion in a coating solution and coating workability, required for forming the porous active layer, may be deteriorated. Also, a weight of the inorganic particles per a unit area of the porous active layer is preferably 5 to 100 g/m . [29] In the organic/inorganic composite separator according to the present invention, the inorganic particle used for forming the porous active layer is not specifically limited if it is electrically chemically stable. That is to say, an inorganic particle usable in the present invention is not specially limited if oxidation or reduction reaction does not occur in an operating voltage range (for example, 0 to 5V based on Li/Li+) of an applied electrochemical device. In particular, in case an inorganic particle with ion transferring capability is used, it is possible to enhance the performance by increasing ion conductivity in the electrochemical device. [30] In addition, in case an inorganic particle with a high dielectric constant is used, it contributes to the increase of dissociation of electrolyte salt, for example lithium salt, in the liquid electrolyte, thereby improving ion conductivity of the electrolyte. [31] Due to the above reasons, it is preferred that the inorganic particles are selected from the group consisting of inorganic particles having a dielectric constant of 5 or above, preferably 10 or above, inorganic particles having lithium-ion transferring capability, or their mixtures. The inorganic particle having a dielectric constant of 5 or above is any one inorganic particle or a mixture of at least two inorganic particles selected from the group consisting of BaTiO , Pb(Zr,Ti)0 (PZT), Pb La Zr Ti O (PLZT), PB(Mg Nb )0 -PbTiO (PMN-PT), hafnia (HfO ), SrTiO , SnO*, CeO 3 2/3 3 3 2 3 2 2 MgO, NiO, CaO, ZnO, ZrO , SiO , Y O , Al O , SiC and TiO , but not limitedly. 222323 2 In particular, the inorganic particles such as of BaTiO , Pb(Zr,Ti)0 (PZT), Pb La Zr TiO (PLZT), PB(Mg Nb )0-PbTiO (PMN-PT) and hafnia (HfO ) show a high l-y y 3 3 2/3 3 3 2 dielectric constant of 100 or above and have piezoelectricity since charges are generated to make a potential difference between both surfaces when a certain pressure is applied to extend or shrink them, so the above inorganic particles may prevent generation of an internal short circuit of both electrodes caused by an external impact and thus further improve the stability of the electrochemical device. In addition, in case the inorganic particles having a high dielectric constant are mixed with the inorganic particles having lithium ion transferring capability, their synergistic effect may be doubled. In the present invention, the inorganic particle having lithium ion transferring capability means an inorganic particle containing lithium atom and having a function of moving a lithium ion without storing the lithium. The inorganic particle having lithium ion transferring capability may transfer and move lithium ions due to a kind of defect existing in the particle structure, so it is possible to improve lithium ion con¬ductivity in the battery and also improve the performance of the battery. The inorganic particle having lithium ion transferring capability is any one inorganic particle or a mixture of at least two inorganic particles selected from the group consisting of lithium phosphate (Li PO ), lithium titanium phosphate (Li Ti (PO ) , 0 < x < 2, 0 < y < 3), 3 4 x y 4 3 lithium aluminum titanium phosphate (Li Al Ti (PO ) ,0