Technical Field [1] The present invention relates to a novel organic/inorganic composite porous film that can show excellent thermal safety and lithium ion conductivity and a high degree of swelling with electrolyte compared to conventional polyolefin-based separators, and an electrochemical device comprising the same, which ensures safety and has improved quality. Background Art [2] Recently, there is an increasing interest in energy storage technology. Batteries have been widely used as energy sources in portable phones, camcorders, notebook computers, PCs and electric cars, resulting in intensive research and development into them. In this regard, electrochemical devices are subjects of great interest. Particularly, development of rechargeable secondary batteries is the focus of attention. [3] Secondary batteries are chemical batteries capable of repeated charge and discharge cycles by means of reversible interconversion between chemical energy and electric energy, and may be classified into Ni-MH secondary batteries and lithium secondary batteries. Lithium secondary batteries include lithium secondary metal batteries, lithium secondary ion batteries, lithium secondary polymer batteries, lithium secondary ion polymer batteries, etc. [4] Because lithium secondary batteries have drive voltage and energy density higher than those of conventional batteries using aqueous electrolytes (such as Ni-MH batteries), they are produced commercially by many production companies. However, most lithium secondary batteries have different safety characteristics depending on several factors. Evaluation of and security in safety of batteries are very important matters to be considered. Therefore, safety of batteries is strictly restricted in terms of ignition and combustion in batteries by safety standards. [5] Currently available lithium ion batteries and lithium ion polymer batteries use polyolefin-based separators in order to prevent short circuit between a cathode and an anode. However, because such polyolefin-based separators have a melting point of 200 °C or less, they have a disadvantage in that they can be shrunk or molten to cause a change in volume when the temperature of a battery is increased by internal and/or external factors. Therefore, there is a great possibility of short-circuit between a cathode and an anode caused by shrinking or melting of separators, resulting in accidents such as explosion of a battery caused by emission of electric energy. As a result, it is necessary to provide a separator that does not cause heat shrinking at high temperature. [6] To solve the above problems related with polyolefin-based separators, many attempts are made to develop an electrolyte using an inorganic material serving as a substitute for a conventional separator. Such electrolytes may be broadly classified into two types. The first type is a solid composite electrolyte obtained by using inorganic particles having lithium ion conductivity alone or by using inorganic particles having lithium ion conductivity mixed with a polymer matrix. See, Japanese Laid-Open Patent No. 2003-022707, ['Solid State fonics'-vol.158, n.3, p.275, (2003)], ['Journal of Power Sources'-vol.m, n.1, p.209, (2002)], ['Electrochimica Acta'-vol.48, n.14, p.2003, (2003)], etc. However, it is known that such composite electrolytes are not advisable, because they have low ion conductivity compared to liquid electrolytes and the in- terfacial resistance between the inorganic materials and the polymer is high while they are mixed. [7] The second type is an electrolyte obtained by mixing inorganic particles having lithium ion conductivity or not with a gel polymer electrolyte formed of a polymer and liquid electrolyte. In this case, inorganic materials are introduced in a relatively small amount compared to the polymer and liquid electrolyte, and thus merely have a sup- plementary function to assist in lithium ion conduction made by the liquid electrolyte. [8] However, because electrolytes prepared as described above have no pores therein or, if any, have pores with a size of several angstroms and low porosity, formed by in- troduction of an artificial plasticizer, the electrolytes cannot serve sufficiently as separator, resulting in degradation in the battery quality. Disclosure [9] We have found that an organic/inorganic composite porous film, formed by using (1) inorganic particles and (2) a binder polymer, improves poor thermal safety of a conventional polyolefin-based separator. Additionally, we have found that because the organic/inorganic composite porous film has a micropore structure formed by the inorganic particles present in the film, it provides an increased volume of space into which a liquid electrolyte infiltrates, resulting in improvements in lithium ion con- ductivity and degree of swelling with electrolyte. Therefore, the organic/inorganic composite porous film can improve the quality and safety of an electrochemical device using the same as separator. [10] Therefore, it is an object of the present invention to provide an organic/inorganic composite porous film capable of improving the quality and safety of an elec- trochemical device, a method for manufacturing the same and an electrochemical device comprising the same. [11] According to an aspect of the present invention, there is provided an organic/ inorganic composite porous film, which comprises (a) inorganic particles; and (b) a binder polymer coating layer formed partially or totally on the surface of the inorganic particles, wherein the inorganic particles are interconnected among themselves and are fixed by the binder polymer, and interstitial volumes among the inorganic particles form a micropore structure. There is also provided an electrochemical device (preferably, a lithium secondary battery) comprising the same. [12] According to another aspect of the present invention, there is provided a method for manufacturing an organic/inorganic composite porous film, which includes the steps of: (a) dissolving a binder polymer into a solvent to form a polymer solution; (b) adding inorganic particles to the polymer solution obtained from step (a) and mixing them; and (c) coating the mixture of inorganic particles with binder polymer obtained from step (b) on a substrate, followed by drying, and then detaching the substrate. [13] Hereinafter, the present invention will be explained in more detail. [14] The present invention is characterized in that it provides a novel organic/inorganic composite porous film, which serves sufficiently as separator to prevent electrical contact between a cathode and an anode of a battery and to pass ions therethrough and shows excellent thermal safety, lithium ion conductivity and degree of swelling with electrolyte. [15] The organic/inorganic composite porous film is obtained by using inorganic particles and a binder polymer. The uniform and heat resistant micropore structure formed by the interstitial volumes among the inorganic particles permits the organic/ inorganic composite porous film to be used as separator. Additionally, if a polymer capable of being gelled when swelled with a liquid electrolyte is used as the binder polymer component, the organic/inorganic composite porous film can serve also as electrolyte. [16] Particular characteristics of the organic/ inorganic composite porous film are as follows. [17] (1) The organic/inorganic composite porous film according to the present invention shows improved thermal safety by virtue of the inorganic particles present therein. [18] In other words, although conventional polyolefin-based separators cause heat shrinking at high temperature because they have a melting point of 120-140 °C , the organic/inorganic composite porous film comprising the inorganic particles and binder polymer does not cause heat shrinking due to the heat resistance of the inorganic particles. Therefore, an electrochemical device using the above organic/inorganic composite porous film as separator causes no degradation in safety resulting from an internal short circuit between a cathode and an anode even under extreme conditions such as high temperature, overcharge, etc. As a result, such electrochemical devices have excellent safety characteristics compared to conventional batteries. [19] (2) Conventional solid electrolytes formed by using inorganic particles and a binder polymer have no pore structure or, if any, have an irregular pore structure having a pore size of several angstroms. Therefore, they cannot serve sufficiently as spacer, through which lithium ions can pass, resulting in degradation in the quality of a battery. On the contrary, the organic/inorganic composite porous film according to the present invention has uniform micropore structures formed by the interstitial volumes among the inorganic particles as shown in FIGs. 1 and 2, and the micropore structures permit lithium ions to move smoothly therethrough. Therefore, it is possible to introduce a large amount of electrolyte through the micropore structures so that a high degree of swelling with electrolyte can be obtained, resulting in improvement in the quality of a battery. [20] (3) It is possible to control the pore size and porosity of the organic/inorganic composite porous film by varying the particle diameter of the inorganic particles and the mixing ratio of the inorganic particles with the polymer. The micropore structure is subsequently filled with a liquid electrolyte so that the interfacial resistance generating among the inorganic particles or between the inorganic particles and the binder polymer can be reduced significantly. [21] (4) When the inorganic particles used in the organic/inorganic composite porous film have a high dielectric constant and/or lithium ion conductivity, the inorganic particles can improve lithium ion conductivity as well as heat resistance, thereby con- tributing to improvement of battery quality. [22] (5) When the binder polymer used in the organic/inorganic composite porous film is one showing a high degree of swelling with electrolyte, the electrolyte injected after assemblage of a battery can infiltrate into the polymer and the resultant polymer containing the electrolyte infiltrated therein has a capability of conducting electrolyte ions. Therefore, the organic/inorganic composite porous film according to the present invention can improve the quality of an electrochemical device compared to con- ventional organic/inorganic composite electrolytes. Additionally, the organic/inorganic composite porous film provides advantages in that wettability with an electrolyte is improved compared to conventional hydrophobic polyolefin-based separators, and use of a polar electrolyte for battery is permitted. [23] (6) Finally, if the binder polymer is one capable of being gelled when swelled with electrolyte, the polymer reacts with the electrolyte injected subsequently and is gelled, thereby forming a gel type organic/inorganic composite electrolyte. Such electrolytes are produced with ease compared to conventional gel-type electrolytes and show excellent ion conductivity and a high degree of swelling with electrolyte, thereby con- tributing to improve the quality of a battery. [24] One component present in the organic/inorganic composite porous film according to the present invention is inorganic particles currently used in the art. The inorganic particles permit interstitial volumes to be formed among them, thereby serving to form micropores and to maintain the physical shape as spacer. Additionally, because the inorganic particles are characterized in that their physical properties are not changed even at a high temperature of 200 °C or higher, the organic/inorganic composite porous film using the inorganic particles can have excellent heat resistance. [25] There is no particular limitation in selection of inorganic particles, as long as they are electrochemically stable. In other words, there is no particular limitation in inorganic particles that may be used in the present invention, as long as they are not subjected to oxidation and/or reduction at the range of drive voltages (for example, 0-5 V based on Li/Li+) of a battery, to which they are applied. Particularly, it is preferable to use inorganic particles having ion conductivity as high as possible, because such inorganic particles can improve ion conductivity and quality in an electrochemical device. Additionally, when inorganic particles having a high density are used, they have a difficulty in dispersion during a coating step and may increase the weight of a battery to be manufactured. Therefore, it is preferable to use inorganic particles having a density as low as possible. Further, when inorganic particles having a high dielectric constant are used, they can contribute to increase the dissociation degree of an electrolyte salt in a liquid electrolyte, such as a lithium salt, thereby improving the ion conductivity of the electrolyte. [26] For these reasons, it is preferable to use inorganic particles having a high dielectric constant of 5 or more, preferably of 10 or more, inorganic particles having lithium con- ductivity or mixtures thereof. [27] Particular non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO3 , Pb(Zr,Ti)O3 (PZT), Pb 1-x Lax Zr1-y Tiy O3 (PLZT), PB(Mg3 Nb2/3 )O3 -PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2 , Y2 O3 , Al2O3 , TiO2 , SiC or mixtures thereof. [28] As used herein, 'inorganic particles having lithium ion conductivity' are referred to as inorganic particles containing lithium elements and having a capability of conducting lithium ions without storing lithium. Inorganic particles having lithium ion conductivity can conduct and move lithium ions due to defects present in their structure, and thus can improve lithium ion conductivity and contribute to improve battery quality. Non-limiting examples of such inorganic particles having lithium ion conductivity include: lithim phosphate (Li3PO4 ), lithium titanium phosphate (LixTiy (PO 4)3, 0