Description ORGANIC/INORGANIC COMPOSITE POROUS MEMBRANE AND ELECTROCHEMICAL DEVICE USING THE SAME Technical Field [1] The present invention relates to a novel organic/inorganic composite porous separator that can ensure electrochemical safety and improve quality at the same time, and an electrochemical device using the same. More specifically, the present invention relates to a novel organic/inorganic composite porous separator which contains inorganic porous particles, each having a plurality of pores therein, as a coating material to form an organic/inorganic composite porous layer of a uniform pore size and porosity, and an electrochemical device comprising the same. Background Art [2] Recently, there is 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 for them. In this regard, electrochemical devices are the subject of great interest. Par- ticularly, development of rechargeable secondary batteries is the focus of attention. [3] Among the currently used secondary batteries, lithium secondary batteries, developed in early 1990's, have a drive voltage and an energy density higher than those of conventional batteries using aqueous electrolytes (such as Ni-MH batteries, Ni-Cd batteries and H2 SO4 -Pb batteries) and thus are spotlighted in the field of secondary batteries. However, lithium secondary batteries have problems related to their safety, due to ignition and explosion caused by the use of organic electrolytes, and are man- ufactured by a complicated process. lithium ion polymer batteries, appearing more recently, solve the above-mentioned disadvantages of secondary lithium ion batteries, and thus become one of the most potent candidates of next generation batteries. However, such secondary lithium ion polymer batteries still have low capacity compared to secondary lithium ion batteries. Particularly, they show insufficient discharge capacity at low temperature. Hence, there is an imminent need for the im- provement of secondary lithium ion batteries. [4] A lithium ion battery is manufactured by coating a cathode active material (e.g. IiCoO ) and an anode active material (e.g. graphite) which have crystal structures including interstitial volumes, onto the corresponding current collector (i.e. aluminum fell and copper foil, respectively) to provide a cathode and an anode. Then, a separator is interposed between both electrodes to form an electrode assembly, and an electrolyte is injected into the electrode assembly. During a charge cycle of the battery, lithium in- tercalated into the crystal structure of the cathode active material is deintercalated, and then intercalated into the crystal structure of the anode active material. On the other hand, during a discharge cycle, lithium intercalated into the anode active material is deintercalated again, and then intercalated back into the crystal structure of the cathode. As charge/discharge cycles are repeated, lithium ions reciprocate between the cathode and the anode. In this regard, a lithium ion battery is also referred to as a rocking chair battery. [5] Such batteries have been produced by many battery producers. However, most lithium secondary batteries have different safety characteristics depending on several factors. E/aluation of and security in safety of batteries are very important matters to be considered. Particularly, users should be protected from being damaged by mal- functioning batteries. Therefore, safety of batteries is strictly restricted in terms of ignition and combustion of batteries by safety standards. [6] Many attempts have been made to solve the problem related to the safety of a battery, However, ignition of a battery, caused by a forced internal short circuit due to external impacts (particularly, in the case of a customer-abused battery) cannot be solved yet. [7] Recently, US Patent No. 6,432,586 discloses a polyolefin-based separator coated with an inorganic layer such as calcium carbonate, silica, etc., so as to prevent an internal short circuit, caused by dendrite growth inside of a battery. Ebwever, in case of adopting such an inorganic composite layer, the battery, compared with the con- ventional battery using a polymer separator, gets heavier and its quality is deteriorated. In particular, since a part of non-porous inorganic particles in the inorganic material layer influences as resistance to the movement of lithium ions that determines quality of a battery, it is fundamentally not possible to avoid the quality deterioration of the battery. Moreover, an increase in weight by the inorganic material layer causes a decrease in energy density of the battery per unit weight. If the inorganic substance content in the coating layer is reduced to solve this, however, it poses another problem that a satisfactory level of an internal short circuit prevention function is not obtained. [8] Meanwhile, the international union of pure and applied chemistry (TUPAC) defines a pore of 2nm or shorter in diameter as a micropore, a pore of 2 to 50nm in diameter as a mesopore, and a pore of 50nm or greater in diameter as a macropore. Porous materials are expected to hold interest continuously not only for industrial applications but also for academic aspects. Pores are something to be removed in the field of powder metallurgy to obtain a sintered compact, and regarded as defects to be controlled in a casting process to manufacture a sound casting. Nevertheless, a porous material having pores of uniform size and regular arrangement is continuously utilized in various industries that appreciate adsorption and separation efficiency of the porous material. Manufacturing methods of such porous materials include a self-assembly technique, an aerogel manufacturing technique through a sol-gel process, an anodic oxidation technique of aluminum, a condensation drying technique and the like. However, these techniques are mainly used for manufacturing films or monolith porous materials, not for particles. Disclosure of Invention Technical Problem [9] In view of the foregoing problems, it is an object of the present invention to provide an organic/inorganic composite porous separator formed of (a) a porous substrate, (b) an organic/inorganic composite layer, and (c) inorganic particles with pore structures of uniform size, in which the organic/inorganic composite coating layer formed on the porous substrate contains inorganic porous particles having a number of macropores, so that the flow of lithium ions may progress smoothly, degree of swelling with electrolyte may be improved, and energy density per unit weight of a device may be significantly increased due to a substantial decrease in the weight of the organic/ inorganic composite porous separator. Technical Solution [10] An aspect of the present invention provides an organic/inorganic composite porous separator, which comprises: (a) a porous substrate having pores; and (b) an organic/ inorganic composite layer formed by coating at least one region selected from the group consisting of a surface of the substrate and a part of pores present in the substrate with a mixture of inorganic porous particles and a binder polymer, wherein the inorganic porous particles have a plurality of macropores with a diameter of 50nm or greater in the particle itself thereby form a pore structure; and an electrochemical device (preferably, a lithium secondary battery) comprising the same. [11] Another aspect of the present invention provides a manufacturing method of the orgamc/inorganic composite porous separator, which includes the steps of: (a) dispersing inorganic precursors and heat-decomposable compounds in a dispersion medium, misting the inorganic precursor solution, and performing a thermal de- composition and a crystallization processes, to thereby prepare inorganic porous particles; (b) adding and mixing the inorganic porous particles obtained from step (a) with a polymer solution containing a binder polymer; and (c) coating the mixture obtained from step (b) on at least one region selected from the group consisting of a surface of the substrate having pores and a part of the pores in the substrate, followed by drying. [12] Hereinafter, the present invention will be explained in further detail. [13] The present invention is characterized in that it utilizes inorganic porous particles as a component for an organic/inorganic composite layer (active layer) coated on a porous substrate having pores. [14] As an attempt to resolve poor thermal safety of a conventional polymer separator, a composite separator containing inorganic particles in a polymer separator substrate was used. However, the inorganic particles provided here were non-porous inorganic particles (see FIG. 3). Besides, even though there may be some pores, they were only micropores having a diameter of 2nm or less (see FIG. 4). Therefore, the conventional separator as an end product (i.e., a solid electrolyte) also has a dense inorganic coating layer with no pores, or, if any, it fails to serve as an effective spacer for transmitting lithium ions because it has an irregular pore structure with the pore size in unit of angstrom (A) (see FIG. 1 for reference). In other words, despite the improvement of thermal safety, the battery can still have a degraded quality due to a low porosity. [15] On the contrary, the organic/inorganic composite porous separator according to the present invention is distinct from the ones in the art in that it contains many inorganic porous particles with macropores of uniform size and shape (see FIG. 5). [16] Pores in the separator function not only as a pathway of an active component, e.g., lithium ions (Li+) resulting in electrochemical reactions in an electrochemical device, but also as a space where an electrolyte transmitting lithium ions swells. After all, an increase of pores means an increase of the pathway for lithium ions and an expansion of the electrolyte swelling space. From this viewpoint, the pore size and the porosity are very important factors for the control of ion conductivity in a battery and thus, are directly related to the quality of the battery. [17] That is, in a case that lithium ions causing an electrochemical reaction in a lithium secondary battery travel to both electrodes, pores in a separator placed between both electrodes can theoretically work as a pathway for the lithium ions as long as the pores have a diameter equal to or greater than that of the lithium ion. For information, the diameter of the lithium ion is several angstroms (A). In reality, however, when lithium ions travel to both electrodes, they do not travel alone but are solvated by a number of molecules of carbonate based compounds for example in the electrolyte as a transfer medium. Therefore, if pore size or porosity of the separator is within the approximate range of the diameter of the lithium ion, the mobility of lithium ions is reduced and hence, their ion conductivity in the battery is decreased, leading to degraded battery quality. [18] For example, in a case that the electrolyte contains ethylene carbonate (EC) dimethyl carbonate (DMC) and the like, lithium ions are solvated, being tightly en- compassed by four EC or DMC molecules relatively bigger than them, and travel towards both electrodes. Here, the size of electrolyte molecules is about 1 to 2nm or bigger. To improve the battery quality, therefore, it is important to take both the size of a lithium ion and the size of an electrolyte molecule into consideration. [19] The organic/inorganic composite porous separator (membrane) according to the present invention consists of (a) a porous substrate; and (b) an organic/inorganic composite layer formed on the substrate. As shown in FIGs. 2, 6 and 7, both the porous substrate (a) and the organic/inorganic composite layer (b) have a number of regular (or uniform) pore structures that are large enough for the electrolyte molecules and the solvated lithium ions to pass through and at the same time, the inorganic particles (c) contained in the organic/inorganic composite layer are structurally characterized with macropores that are sufficiently large to be able to transmit the electrolyte molecules and the solvated lithium ions. Such a triple porous structure means a high degree of swelling of electrolytes as well as an increase in the pathway of Hthium ions in the electrolyte-filled space, so the lithium ion conductivity may be improved and elec- trochemical reactions in the battery are activated, demonstrating an equivalent performance to the conventional polyolefin-based separator (see FIG. 1). [20] In addition, although the organic/inorganic composite layer used as a component or a coating component of the conventional separator could ensure safety of a battery, its use of non-porous inorganic particles which are heavy brought an increase in the total weight of the battery. On the other hand, the present invention used inorganic porous particles retaining a number of macropores therein, to thereby achieve improved safety and quality of a battery as well as a markedly reduced weight. This leads to a reduction of the battery weight, eventually increasing energy density per unit weight of the battery. [21] In the organic/inorganic composite porous separator according to the present invention, one component present in the organic/inorganic composite porous separator coated onto the surface of a porous substrate and/or part of the pores in the substrate is inorganic particles that are typically used in the art. Hence, there is no particular limitation in selection of inorganic particles in terms of components and shapes, as long as they are big enough to transmit electrolyte molecules and solvated lithium ions. Nevertheless, it is preferable to use inorganic particles having macropores of 50nm or greater in diameter. [22] As aforementioned, a macropore is defined by IUPAC as a pore having a diameter of 50nm or greater. The macropores may exist individually or combined in the particle. [23] There is no particular limitation in porosity of the inorganic porous particles. The porosity can be adjusted diversely within a range of 30 to 95%, preferably, 50 to 90%. If porosity of the porous particle is below 30%, it is difficult to expect swelling of an electrolyte to the pores existing in the porous particle and further the improvement of battery performance. Meanwhile, if porosity of the porous particle exceeds 95%, mechanical strength of the particle itself can be weakened. Such a pore structure within the set range serves as an additional pathway of lithium ions and the space for electrolyte to swell, contributing to the improvement of battery performance. [24] Moreover, as surface area of the inorganic porous particle increases significantly due to plural pores existing in the particle itself, the density is reduced. In the field, inorganic particles with high density are not easily dispersed during a coating process and cause a problem like an increase in the weight of a battery. Therefore, it is desired to use inorganic particles with density as low as possible. For example, the density and the surface area of the inorganic porous particle may fall within a range of 1 to 4g/cc and a range of 10 to 50m2/g, respectively. [25] Furthermore, the inorganic porous particle in the organic/inorganic composite layer formed on the porous substrate serves to form pores with an interstitial volume formed among inorganic particles as they bond to each other and at the same time, functions as a spacer helping the organic/inorganic composite layer maintain its physical shape. [26] There is no particular limitation in materials for the inorganic porous particles as long as they are electrochemically stable and are not subjected to oxidation and/or reduction at the range of drive voltages (for example, 0-5V based on Li/Li ) of a battery to which they are applied. In particular, it is preferable to use inorganic particles having ion conductivity as high as possible, because such inorganic particles can improve ion conductivity and performance in an electrochemical device. Ad- ditionally, inorganic particles having high dielectric constant are desirably used because they can contribute to an increase in the dissociation degree of an electrolyte salt in a liquid electrolyte, say, a lithium salt, to thereby improve the ion conductivity of the electrolyte. [27] For these reasons, it is desirable to use inorganic particles having a high dielectric constant of 5 or more, inorganic particles having lithium conductivity or mixtures thereof. [28] Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO , Pb(Zr,Ti)0 (PZT) Pb La Zr Ti O (PLZT) PB(Mg Nb )0 - 3 3 1-x x 1-y y 3 3 2/3 3 PbTiO (PMN-PT) hafnia (HfO ) SrTiO , SnO , CeO , MgO, NiO, CaO, ZnO, ZrO , 3 2 3 2 2 2 Y O , Al O , TiO SiC or mixtures thereof. 2 3 2 3 2, [29] 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 the im- provement of battery performance. Non-limiting examples of such inorganic particles having lithium ion conductivity include: lithim phosphate (Ii PO ) lithium titanium 3 4 phosphate (Ii Ti (PO ) , 0