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: 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 and the anode; and a polymer matrix having affinity for the liquid-phase component and providing binding force with the cathode and the anode, characterized in that: - the polymer matrix is in the form of a mixture of linear polymer and cross-linked polymer, and - the weight ratio of the linear polymer to the cross-linked polymer is 1:9 to 8:2, the polymer matrix comprising 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, the oxide-based non-cross-linked polymer comprising at least one selected from the group consisting of poly(ethylene oxide), poly(propylene oxide), poly(oxymethylene), and poly(dimethylsiloxane), the polar non-cross-linked polymer comprising at least one selected from the group consisting of polyacrylonitrile, poly(methyl methacrylate), poly(vinyl chloride), poly(vinylidene fluoride), poly(vinylidenefluoride-co-hexafluoropropylene), poly(ethylene imine), and poly(p-phenylene terephthalamide), the cross-linked polymer comprising a polymer obtained from monomers having at least two functional groups or a copolymer obtained from monomers having at least two functional groups and polar monomers having one functional group, the monomers having at least two functional groups comprising 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, the polar monomers having one functional group comprising 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 fluoride. 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 and the anode; and a polymer matrix having affinity for the liquid-phase component and providing binding force with the cathode and the anode, characterized in that: - the polymer matrix is in the form of a mixture of linear polymer and cross-linked polymer, and - the weight ratio of the linear polymer to the cross-linked polymer is 1:9 to 8:2, - the polymer matrix is in the form of a mixture of linear polymer and cross-linked polymer, and - the weight ratio of the linear polymer to the cross-linked polymer is 1:9 to 8:2, the polymer matrix comprising 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, the oxide-based non-cross-linked polymer comprising at least one selected from the group consisting of poly(ethylene oxide), poly(propylene oxide), poly(oxymethylene), and poly(dimethylsiloxane), the polar non-cross-linked polymer comprising at least one selected from the group consisting of polyacrylonitrile, poly(methyl methacrylate), poly(vinyl chloride), poly(vinylidene fluoride), poly(vinylidenefluoride-co-hexafluoropropylene), poly(ethylene imine), and poly(p-phenylene terephthalamide), the cross-linked polymer comprising a polymer obtained from monomers having at least two functional groups or a copolymer obtained from monomers having at least two functional groups and polar monomers having one functional group, the monomers having at least two functional groups comprising 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, the polar monomers having one functional group comprising 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 fluoride.