• • [DESCRIPTION] INTEGRATED ELECTRODE ASSEMBLY AND SECONDARY BATTERY USING THE SAME [TECHNICAL FIELD] 5 The present invention relates to an integrated electrode assembly and a secondary battery using the same and more particularly to an integrated electrode assembly including a cathode, an anode, and a separation layer integrated between the cathode and the anode, the separation layer including 3 phases including a liquid-phase component containing an ionic salt, which partially flows from the separation layer into 10 the electrodes (i.e., the cathode and the anode) during preparation of the integrated electrode assembly to greatly improve wetting properties of the electrodes and to increase ionic conductivity of the electrodes, a solid-phase component supporting the separation layer between the cathode and the anode, and a polymer matrix having affinity for the liquid-phase component and providing binding force with the cathode 15 and the anode. [BACKGROUND ART] Increasing price of energy sources due to depletion of fossil fuels and an increased interest in environmental pollution have brought about increased demand for environmentally friendly alternative energy sources as an indispensable element for 20 future life. Studies on various power generation technologies such as nuclear, solar, -1- # • wind, and tidal power generation technologies have continued to be conducted and power storage devices for more efficient use of such generated energy also continue to be of great interest. Secondary batteries have been used as such power storage devices. Among secondary batteries, lithium secondary batteries have begun to be 5 used for mobile devices and, along with increasing demand for reduced weight and high voltage and capacity, recently, use of lithium secondary batteries has been significantly extended to electric vehicles, hybrid electric vehicles, and auxiliary power sources based upon smart grid. However, numerous challenges, which have yet to be addressed, remain before 10 lithium secondary batteries can be used as large-capacity power sources. One i important challenge is to improve energy density and increase safety. Another important challenge is to reduce process time and to achieve uniform wetting for largearea electrodes. Many researchers have conducted intensive studies on materials that can satisfy low cost requirements while increasing energy density and have also put 15 effort into studies on materials for improving safety. Ni-based or Mn-based materials having higher capacity than LiCoC>2, which has been conventionally used, are typical examples of materials being studied for energy density improvement. Materials that are based on Li alloying reactions with Si or Sn rather than based on intercalation reactions are typical examples of materials for 20 anodes being studied as alternatives to conventional graphite-based materials. A stable olivine-based cathode active material such as LiFePC>4, a cathode active material such as LLtTisOn, or the like have been studied to improve safety. However, such materials for safety improvement inherently have a low energy density and do not fundamentally solve safety problems associated with the structure of lithium • -2- secondary batteries. Secondary battery safety may be largely divided into internal safety and external safety and may further be divided into electrical safety, impact safety, and thermal safety. Occurrence of these safety problems commonly entails temperature 5 increase, which necessarily results in contraction of a stretched separator that is generally used. Although many researchers have suggested all-solid-state batteries to resolve this safety issue, all-solid-state batteries have a lot of problems in replacing batteries available on the market. 10 First, currently used electrode active materials are in a solid state. Thus, when a solid electrolyte or a polymer electrolyte is used, the surface area of the electrolyte in contact with the active material for lithium ion movement is significantly reduced. Therefore, the ionic conductivity is very low even when the solid or polymer electrolyte has a conductivity of 10"5 s/cm, similar to the current liquid electrolyte. Second, the 15 ionic conductivity at the solid-solid interface or the solid-polymer interface should be much lower for the same reason. Third, even when a solid electrolyte with high conductivity is used, the ionic conductivity is still very low due to a polymer binder that should be employed to provide binding force that is essential to battery formation. Fourth, to form a battery, not only the separation layer needs to have ionic conductivity 20 but the cathode and anode active materials also need to employ materials for ionic conductivity improvement to increase ionic conductivity of the electrodes. However, if a solid electrolyte or a polymer electrolyte is included as an electrode component, the capacity is reduced. -3- 1 - • Thus, there is a great need to provide a battery structure that prevents shortcircuiting due to separator contraction and provides excellent battery performance. [DISCLOSURE] [TECHNICAL PROBLEM] 5 Therefore, the present invention has been made to solve the above and other technical problems that have yet to be resolved. As a result of a variety of extensive and intensive studies and various experiments, the present inventors have found that an integrated electrode assembly, which includes a separation layer including three phases including a liquid-phase 10 component containing an ionic salt, a solid-phase component supporting the separation layer between a cathode and an anode, and a polymer matrix incorporating the liquid-phase component and the solid-phase component therein, prevents shortcircuiting due to separator contraction, greatly improves wetting properties of the electrodes, and increases ionic conductivity. The present invention has been 15 completed based on this finding. [TECHNICAL SOLUTION] Therefore, an integrated electrode assembly in accordance with the present invention includes a cathode, an anode, and a separation layer integrated between the cathode and the anode, the separation layer including 3 phases including a liquid-phase 20 component containing an ionic salt, the liquid-phase component partially flowing from .4. ] the separation layer into the cathode and the anode during preparation of the integrated electrode assembly to greatly improve wetting properties of the cathode and the anode and to increase ionic conductivity of the cathode and the anode, a solid-phase ; component supporting the separation layer between the cathode and the anode, and a 5 polymer matrix having affinity for the liquid-phase component and providing binding force with the cathode and the anode. Experiments conducted by the present inventors showed that the internal risk of the secondary battery is highest when the secondary battery is in a charged state with increased energy and, when the secondary battery is in a charged state, short- 10 circuiting may be caused by separator contraction or the like in four situations: (1) where a charged cathode and a charged anode contact each other, (2) where a charged cathode and an anode current collector contact each other, (3.) where an anode current collector and a cathode current collector contact each other, and (4) where a cathode current collector and a charged anode contact each other. 15 Experiments conducted in all of the situations with charged electrodes in a dry room showed that most serious thermal runaway occurred upon contact between a charged anode and a cathode current collector, contrary to what was expected. Through intensive study, we found that such thermal runaway was caused by, for example, a rapid exothermic reaction of 4Al+302 ->2Al203 at an Al foil which serves 20 as a cathode current collector. The shapes of Al foils were hard to identify in all occurrences of battery explosion. Although the experiments showed that thermal runaway occurred only when a charged anode and a cathode current collector contact each other, it cannot be concluded that the other three situations are safe. In batteries, any contact between -5- i portions of a cathode and an anode is risky. On the other hand, the integrated electrode assembly according to the present ,. invention has excellent high-temperature safety since a polymer matrix and a solidphase component do not contract at high temperature, preventing the occurrence of 5 mishaps such as explosion that occurred in the above experiments. In addition, it is possible to increase ionic conductivity of the electrodes (i.e., the anode and cathode), thereby improving battery performance, since the liquid-phase component flows into and impregnates the electrodes in an electrode assembly preparation process, for example, in a lamination process. Further, since the 10 electrodes are uniformly wetted by electrolyte, it is possible to minimize electrode degradation caused by non-uniform permeation of electrolyte, which is the most serious problem associated with large-area electrodes. Accordingly, the electrolyte state of the electrode assembly of the present invention may be defined such that a partial liquid-phase component derived from the separation layer is included or 15 incorporated in the electrodes. Here, the amount of the liquid-phase component derived from the separation layer which is included or incorporated in the electrodes is not particularly limited. For example, the amount of the liquid-phase component included or incorporated in the electrodes may be 10 to 90% based on the total amount of the liquid-phase component included in the electrode assembly. 20 The weight ratio of the liquid-phase component to the polymer matrix is preferably from 3:7 to 9:1. When the content of the liquid-phase component is excessively low, an insufficient amount of liquid-phase component may flow into the electrodes, failing to increase ionic conductivity of the electrodes. Conversely, when the content of the liquid-phase component is excessively high, an excess of liquid- -6- 3 I phase component may negatively affect the process. Therefore, the weight ratio of the liquid-phase component to the polymer matrix is more preferably from 5:5 to 8:2. The polymer matrix may be in the form of a mixture of linear polymer and cross-linked polymer. In this case, the weight ratio of the linear polymer to the 5 cross-linked polymer is preferably 1:9 to 8:2 although the weight ratio of the linear polymer to the cross-linked polymer is not particularly limited so long as a viscoelastic structure can be formed. An excessively low or high content of linear polymer is undesirable since this reduces elasticity and degrades mechanical properties, reducing impregnation performance of the liquid-phase component. 10 Although the types of the polymers that constitute the polymer matrix in the present invention are not particularly limited, preferred examples of the polymers include at least one selected from the group consisting of an oxide-based non-crosslinked polymer, a polar non-cross-linked polymer, and a cross-linked polymer having a three-dimensional network structure. 15 More preferably, the polymer matrix includes both an oxide-based non-crosslinked polymer and a polar non-cross-linked polymer. Non-limiting examples of the oxide-based non-cross-linked polymer include at least one selected from the group consisting of poly(ethylene oxide), polypropylene oxide), poly(oxymethylene), and poly(dimethylsiloxane). 20 Non-limiting examples of the polar non-cross-linked polymer include at least one selected from the group consisting of polyacrylonitrile, poly(methyl methacrylate), polyvinyl chloride), poly(vinylidene fluoride), -7- " . poly(vinylidenefluoride-co-hexafluoropropylene), poly(ethylene imine), and poly(pphenylene terephthalamide). The cross-linked polymer included in the polymer matrix in the present invention may include a polymer obtained from monomers having at least two 5 functional groups or a copolymer obtained from monomers having at least two functional groups and polar monomers having one functional group. Although the type of the monomers having at least two functional groups is not particularly limited, the monomers preferably include at least one selected from the group consisting of trimethylolpropane ethoxylate triacrylate, polyethylene glycol 10 dimethacrylate, polyethylene glycol diacrylate, divinylbenzene, polyester dimethacrylate, divinyl ether, trimethylolpropane, trimethylolpropane trimethacrylate, and ethoxylated bis phenol A dimethacrylate. Although the type of the polar monomers having one functional group is not particularly limited, the polar monomers preferably include at least one selected from 15 the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate, ethylene glycol methyl ether acrylate, ethylene glycol methyl ether methacrylate, acrylonitrile, vinyl acetate, vinyl chloride, and vinyl fluoride. The separation layer preferably includes 2 to 80% by weight of the solid- 20 phase component based on the weight of the polymer matrix. When the separation layer includes less than 2% by weight of the solid-phase component based on the weight of the polymer matrix, disadvantageous^, the effects of supporting the separation layer, for example, mechanical strength of the separation layer, may be -8- 1 insufficient. When the separation layer includes more than 80% by weight of the solid-phase component based on the weight of the polymer matrix, disadvantageous^, ionic conductivity may be decreased, reducing battery performance, and brittleness may occur during charge/discharge due to high rigidity. Therefore, the separation 5 layer more preferably includes 20 to 50% by weight of the solid-phase component based on the weight of the polymer matrix. Although the composition of the liquid-phase component is not particularly limited so long as the liquid-phase component can partially flow into the electrodes, increasing ionic conductivity of the electrodes, the liquid-phase component is 10 preferably an electrolyte containing an ionic salt. For example, the ionic salt may include, but is not limited to, a lithium salt and the lithium salt may include, but is not limited to, at least one selected from the group consisting of LiCl, LiBr, Lil, LiClCU, LiBF4, LiBioClio, LiPF6, LiCF3S03, LiCF3C02, LiAsF6, LiSbF6, LiAlCU, CH3S03Li, (CF3S02)2NLi, chloroborane lithium, 15 lower aliphatic carboxylic acid lithium, and lithium tetraphenylborate. The electrolyte may include, but is not limited to, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, sulfolane, methyl acetate, and methyl propionate. 20 The solid-phase component is a solid compound that is not reactive with lithium ions and preferably includes solid-phase particles having a mean particle diameter of 10 nm to 5 [xm. When the mean particle diameter of the solid-phase component is too small, disadvantageously, the solid-phase component may be present -9- i in the form of clusters, resulting in a failure to properly support the separation layer. Conversely, when the mean particle diameter of the solid-phase component is too great, • disadvantageously, the thickness of the separation layer may be greater than needed. Therefore, the mean particle diameter of the solid-phase component is more preferably 5 50 nm to 200 nm. In a preferred embodiment, the solid compound may include, but is not limited to, at least one selected from the group consisting of an oxide, a nitride, and a carbide that are not reactive with lithium ions. Preferred examples of the oxide that is not reactive with lithium ions may 10 include, without being limited to, at least one selected from the group consisting of MgO, Ti02 (rutile) and A1203. In the electrode assembly of the present invention, the cathode may be produced, for example, by adding a cathode mix including a cathode active material to a solvent such as NMP to prepare a slurry and applying the slurry to a cathode current 15 collector, followed by drying. Optionally, the cathode mix may further include a binder, a conductive material, a filler, a viscosity controller, and an adhesion promoter. The cathode current collector is generally manufactured to a thickness of 3 to 500 urn. Any cathode current collector may be used without particular limitation so long as high conductivity is provided without causing chemical changes in the battery. 20 Examples of the cathode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium or silver. Similar to the anode current collector, the cathode current collector may include fine irregularities on the surface thereof so as to enhance adhesion -10- to the cathode active material. In addition, the cathode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous structure, a foam and a nonwoven fabric. The cathode active material is a lithium transition metal oxide including two or 5 more transition metals as a substance that causes electrochemical reaction, and examples thereof include, but are not limited to, layered compounds such as lithium cobalt oxide (IJC0O2) or lithium nickel oxide (LiNiC^) substituted by one or more transition metals, lithium manganese oxide substituted by one or more transition metals, lithium nickel-based oxides represented by the formula LiNii-yMy02 (in which M=Co, 10 Mn, Al, Cu, Fe, Mg. B, Cr, Zn or Ga, the lithium nickel-based oxide including at least one of the elements, and 0.01 I • 15 A mixture of an organic electrolyte of 1M LiPF6 in EC:DEC (1:1), PEO, f PEGDMA, and AI2O3 in a weight ratio of 76:15.4:6.6:2 was prepared and benzoin was I added as a UV initiator in an amount of 3% by weight relative to PEGDMA to prepare a precursor of a 3-phase separation layer. The precursor was coated on a glass plate, which was then irradiated with ultraviolet light for 1 minute to produce a 3-phase 20 separation layer through photopolymerization. -18- i A mixture of an organic electrolyte of 1M LiPF6 in ECrDEC (1:1), PVdFHFPPVdF- HFP, and AI2O3 in a weight ratio of 76:22:2 was prepared, acetone was added as a solvent in an amount of 20% by weight relative to the total weight, and the mixture was homogenized. The mixture was then casted onto a glass plate and acetone 5 was evaporated for 10 hours under an argon gas atmosphere in a glove box to produce a solid electrolyte membrane. ; 1 Experimental Example 1> Ionic conductivity and tensile strength were measured for each of the 3-phase j 10 separation layer of Example 1 and the solid electrolyte membrane of Comparative Example 1. ! As a result, Example 1 and Comparative Example 1 exhibited similar levels of I ionic conductivity of 1.2 mS/cm and 1.7 mS/cm. On the other hand, as can be seen from FIG. 3, the measurement results of tensile strength showed that the tensile strength } 15 of the 3-phase separation layer of Example 1 having a viscoelastic structure was greatly > improved over that of the solid electrolyte membrane of Comparative Example 1. Graphite, PVdF and carbon black were added to N-methyl-pyrrolidinone to 20 prepare a slurry and the slurry was applied to a Cu foil. The slurry-applied Cu foil was ; then dried for 2 hours at about 130°C to prepare an anode. In addition, -19- r # Li(NiMnCo)02/LiMn02, PVdF and carbon black were added to N-methyl-pyrrolidinone to prepare a slurry and the slurry was applied to a Cu foil. The slurry-applied Cu foil was then dried for 2 hours at about 130°C to prepare a cathode. The 3-phase separation layer precursor of Example 1 was coated on the anode, 5 which was then irradiated with ultraviolet light for 1 minute to produce a 3-phase separation layer through photopolymerization. The cathode was placed on the anode coated with the 3-phase separation layer, followed by lamination to prepare an integrated electrode assembly. The integrated electrode assembly was then inserted into a pouch without an impregnation process to 10 fabricate a secondary battery. * A polyolefin-based separator was placed between the anode and cathode of Example 2, which was then inserted into a pouch. An electrolyte of 1M LiPF6 in 15 EC:DEC (1:1) was then introduced into the pouch to fabricate a secondary battery. Experimental Example 2> The secondary batteries of Example 2 and Comparative Example 2 were charged in a constant current (CC) mode at a current density of 0.1 C to 4.2 V and were ' 20 then maintained in a constant voltage (CV) mode at 4.2 V and charging was completed when current density reached 0.05 C. During discharge, the secondary batteries were -20- i I discharged in a CC mode at a current density of 0.1 C to 2.5V. Then, charge/discharge was repeated 50 times under the same conditions as above. Results are shown in FIG. 4. It can be seen from FIG. 4 that the secondary battery of Example 2 including 5 the integrated electrode assembly employing the 3-phase separation layer exhibits charge/discharge properties similar to the secondary battery of Comparative Example 2 employing the liquid electrolyte and the separator although the secondary battery of I Example 2 has not been subjected to an impregnation process. Therefore, the ; secondary battery of Example 2 is free from the problem of poor impregnation of 10 electrolyte which has been pointed out as a problem of the solid electrolyte. [INDUSTRIAL APPLICABILITY] As is apparent from the above description, an integrated electrode assembly according to the present invention has an advantage in that it is possible to prevent short-circuiting due to separator contraction. In addition, electrolyte is impregnated 15 into the electrodes during preparation of the electrode assembly. Therefore, it is possible to greatly alleviate the problem of increased process time and the problem of ' non-uniform electrodes associated with wetting., It is also possible to improve ionic conductivity of the electrodes. It will be apparent to those skilled in the art that various applications and 20 modifications can be made based on the above description without departing from the scope of the invention. -21- ; t i i [CLAIMS] [Claim 1 ] An integrated electrode assembly comprising a cathode, an anode, and a separation layer integrated between the cathode and the anode, the separation layer comprising 3 phases comprising: I 5 a liquid-phase component containing an ionic salt, the liquid-phase component partially flowing from the separation layer into the cathode and the anode during preparation of the integrated electrode assembly to increase ionic conductivity of the cathode and the anode; a solid-phase component supporting the separation layer between the cathode 10 and the anode; and a polymer matrix having affinity for the liquid-phase component and providing binding force with the cathode and the anode. [Claim 2] The integrated electrode assembly according to claim 1, wherein a weight ratio of the liquid-phase component to the polymer matrix is from 3:7 to 9:1. 15 [Claim 3] The integrated electrode assembly according to claim 1, wherein the polymer matrix comprises at least one selected from the group consisting of an oxide- [ based non-cross-linked polymer, a polar non-cross-linked polymer, and a cross-linked polymer having a three-dimensional network structure. -22-; [ i f [Claim 4] The integrated electrode assembly according to claim 3, wherein the oxide-based non-cross-linked polymer comprises at least one selected from the group consisting of poly(ethylene oxide), poly(propylene oxide), poly(oxymethylene), and poly(dimethylsiloxane). 5 [Claim 5] The integrated electrode assembly according to claim 3, wherein the polar non-cross-linked polymer comprises at least one selected from the group consisting of polyacrylonitrile, poly(methyl methacrylate), poly(vinyl chloride), poly(vinylidene fluoride), poly(vinylidenefluoride-co-hexafluoropropylene), 'v poly(ethylene imine), and poly(p-phenylene terephthalamide). j : 10 [Claim 6] The integrated electrode assembly according to claim 3, wherein the ' cross-linked polymer comprises a polymer obtained from monomers having at least i two functional groups or a copolymer obtained from monomers having at least two functional groups and polar monomers having one functional group. [Claim 7] The integrated electrode assembly according to claim 6, wherein the I 15 monomers having at least two functional groups comprise at least one selected from the group consisting of trimethylolpropane ethoxylate triacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, divinylbenzene, polyester dimethacrylate, divinyl ether, trimethylolpropane, trimethylolpropane trimethacrylate, and ethoxylated bis phenol A dimethacrylate. . 20 [Claim 8] The integrated electrode assembly according to claim 6, wherein the -23- polar monomers having one functional ..group comprise at least one selected from the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate, ethylene glycol methyl ether acrylate, ethylene glycol methyl ether methacrylate, acrylonitrile, vinyl acetate, vinyl chloride, and vinyl 5 fluoride. [Claim 9] The integrated electrode assembly according to claim 1, wherein the separation layer comprises 2 to 80% by weight of the solid-phase component based on the weight of the polymer matrix. [Claim 10] The integrated electrode assembly according to claim 1, wherein the 10 liquid-phase component is an electrolyte containing an ionic salt. [Claim l l ] The integrated electrode assembly according to claim 10, wherein the ionic salt is a lithium salt. [Claim 12] The integrated electrode assembly according to claim 11, wherein the lithium salt comprises at least one selected from the group consisting of LiCl, 15 LiBr, Lil, LiC104, LiBF4, LiBioClio, LiPF6, L1CF3SO3, LiCF3C02, LiAsF6, LiSbF6, LiAlCU, CH3S03Li, (CF3S02)2NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, and lithium tetraphenylborate. [Claim 13] The integrated electrode assembly according to claim 10, wherein the electrolyte comprises at least one selected from the group consisting of ethylene -24- carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, sulfolane, methyl acetate, and methyl propionate. [Claim 14l The integrated electrode assembly according to claim 1, wherein the 5 solid-phase component is a solid compound that is not reactive with lithium ions and comprises solid-phase particles having a mean particle diameter of 10 nm to 5 urn. [Claim 15] The integrated electrode assembly according to claim 14, wherein the solid compound comprises at least one selected from the group consisting of an oxide, a nitride, and a carbide that are not reactive with lithium ions. 10 [Claim 16] The integrated electrode assembly according to claim 15, wherein the oxide that is not reactive with lithium ions comprises at least one selected from the group consisting of MgO, Ti02 (rutile) and AI2O3. [Claim 17] A method for preparing the integrated electrode assembly according to claim 1, the method comprising: 15 (1) homogenizing a linear polymer, monomers for a cross-linked polymer, a liquid-phase component comprising an ionic salt, a solid-phase component, and a polymerization initiator into a mixture; (2) coating the mixture on one electrode; -25- (3) inducing polymerization reaction through UV irradiation or heating to form a separation layer; and (4) placing a counter electrode on the separation layer, followed by pressing. [Claim 18] A lithium secondary battery comprising the integrated electrode 5 assembly according to any one of claims 1 to 16. [Claim 19] A battery module comprising the lithium secondary battery according to claim 18 as a unit battery. [Claim 20] A battery pack comprising the battery module according to claim 19. [Claim 21] The battery pack according to claim 20, wherein the battery pack is 10 used as a power source of a middle or large-sized device. [Claim 22] The battery pack according to claim 21, wherein the middle or largesized device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system-