Secondary battery manufacturing method

Abstract

The present invention provides a method for producing a secondary battery, the method including the steps of (S1) accommodating an electrode assembly in a battery case, (S2) injecting a first electrolyte composition into the battery case to impregnate the electrode assembly, (S3) injecting a second electrolyte composition into the battery case, and (S4) curing the second electrolyte composition, wherein an electrode tab is connected to the electrode assembly and the electrode tab is extended to the outside of the electrode assembly, the first electrolyte composition includes a 1-1 lithium salt including at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and a first solvent, the second electrolyte composition includes an oligomer and a second solvent, and the second electrolyte composition does not include lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application Nos. 10-2022-0005910, filed January 14, 2022, and 10-2022-0006029, filed January 14, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing a secondary battery. [Background technology]

[0003] BACKGROUND ART Along with technological development and increasing demand for electronic devices, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries, which have high energy density and voltage, have been commercialized and are widely used.

[0004] The secondary battery may be manufactured by, for example, placing an electrode assembly, in which electrodes and separators are alternately stacked, and electrode tabs connected to the electrode assembly in a battery case, injecting an electrolyte into the battery case, and sealing the battery case.

[0005] Conventionally, liquid electrolytes, particularly ion-conductive organic liquid electrolytes in which salts are dissolved in non-aqueous organic solvents, have been mainly used as electrolytes for secondary batteries. However, such liquid electrolytes have problems such as the possibility of leakage to the outside of the secondary battery, reduced safety, and reduced cell rigidity.

[0006] In light of this, research is underway to commercialize polymer electrolytes, such as gel polymer electrolytes, instead of liquid electrolytes. Gel polymer electrolytes have the advantages of preventing leakage to the outside of secondary batteries and providing excellent cell rigidity. However, gel polymer electrolytes have drawbacks, such as higher interfacial resistance and lower ionic conductivity than liquid electrolytes.

[0007] On the other hand, in consideration of reducing the resistance and thermal stability of secondary batteries, methods using lithium salts such as lithium bis(fluorosulfonyl)imide (LiFSI) are being considered. However, lithium salts such as lithium bis(fluorosulfonyl)imide have the problem of corroding the electrode tabs of secondary batteries, which is problematic from the perspective of long-term life characteristics. Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to solve the above problems and to provide a method for manufacturing a secondary battery that reduces the resistance of the secondary battery, improves cell rigidity and thermal stability, prevents corrosion of the electrode tabs, and is advantageous in terms of long life. [Means for solving the problem]

[0009] The present invention provides a method for manufacturing a secondary battery, the method comprising the steps of: (S1) accommodating an electrode assembly in a battery case; (S2) injecting a first electrolyte composition into the battery case to impregnate the electrode assembly; (S3) injecting a second electrolyte composition into the battery case; and (S4) curing the second electrolyte composition, wherein an electrode tab is connected to the electrode assembly and extended to the outside of the electrode assembly; the first electrolyte composition comprises a first solvent and a 1-1 lithium salt containing at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); and the second electrolyte composition comprises an oligomer and a second solvent, and the second electrolyte composition does not contain lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). [Effects of the Invention]

[0010] The method for manufacturing a secondary battery according to the present invention includes a two-step process of injecting an electrolyte composition. The first electrolyte composition is a liquid electrolyte composition or a gel polymer electrolyte composition containing lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide as a lithium salt. The first electrolyte composition is used to impregnate an electrode assembly and contributes to reducing the resistance and improving the thermal stability of the secondary battery. The second electrolyte composition does not contain lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide and is cured outside the electrode assembly to form a gel polymer electrolyte. Through the two-step process of injecting and curing the electrolyte composition, lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide are located exclusively inside the electrode assembly, thereby reducing the resistance and improving the thermal stability of the secondary battery, improving cell rigidity, preventing leakage to the outside of the secondary battery, and preventing corrosion of the electrode tabs, thereby improving long-term battery life. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a plan view illustrating step (S1) of the method for manufacturing a secondary battery according to the present invention, showing an electrode assembly housed in a battery case. [Figure 2] 1 is a side view illustrating the electrode assembly housed in the battery case, illustrating step (S1) of the method for manufacturing a secondary battery according to the present invention. FIG. [Figure 3] 1 is a schematic side view of an electrode assembly for explaining step (S1) of the method for manufacturing a secondary battery according to the present invention. [Figure 4] 2 is a schematic side view of a separator for explaining step (S1) of the method for manufacturing a secondary battery according to the present invention. FIG. [Figure 5] 2 is a schematic plan view of a separator or an electrode for explaining step (S1) of the method for manufacturing a secondary battery according to the present invention. FIG. [Figure 6] 1 is a diagram illustrating step (S1) of the method for manufacturing a secondary battery according to the present invention, and is a diagram illustrating a manufacturing process of an electrode assembly. [Figure 7] 1 is a diagram illustrating step (S1) of the method for manufacturing a secondary battery according to the present invention, and is a diagram illustrating a manufacturing process of an electrode assembly. [Figure 8] 1 is a diagram illustrating step (S1) of the method for manufacturing a secondary battery according to the present invention, and is a diagram illustrating a manufacturing process of an electrode assembly. [Figure 9] 1 is a diagram illustrating step (S1) of the method for manufacturing a secondary battery according to the present invention, and is a diagram illustrating a manufacturing process of an electrode assembly. [Figure 10] FIG. 2 is a plan view illustrating step (S2) of the method for producing a secondary battery of the present invention, and is a view illustrating a step of injecting a first electrolyte composition after step (S1). [Figure 11] FIG. 2 is a side view illustrating step (S2) of the method for producing a secondary battery of the present invention, and is a side view illustrating the step of injecting a first electrolyte composition after step (S1). [Figure 12] FIG. 2 is a plan view illustrating step (S3) of the method for producing a secondary battery of the present invention, and is a view illustrating a step of injecting a second electrolyte composition after step (S2). [Figure 13] FIG. 2 is a plan view illustrating step (S4) of the method for producing a secondary battery of the present invention, and is a view illustrating a step of curing the second electrolyte composition after step (S3). [Figure 14] FIG. 2 is a side view illustrating step (S4) of the method for producing a secondary battery of the present invention, and is a view illustrating a step of curing the second electrolyte composition after step (S3). [Figure 15] 1 is a photograph of the surface of a separator included in a secondary battery manufactured by the manufacturing method of Example 1A. DETAILED DESCRIPTION OF THE INVENTION

[0012] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that an inventor can appropriately define the concepts of terms in order to best explain his or her invention.

[0013] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0014] Hereinafter, the secondary battery of the present invention will be described in detail with reference to the drawings. When assigning reference numerals to components in each drawing, the same reference numerals may be assigned to the same components even if they appear in different drawings. Furthermore, when describing the present invention, if it is determined that a detailed description of related known configurations or functions may obscure the gist of the present invention, the detailed description may be omitted.

[0015] <Secondary battery manufacturing method> The present invention relates to a method for manufacturing a secondary battery, and more particularly to a method for manufacturing a lithium secondary battery.

[0016] The present invention provides a method for manufacturing a secondary battery, the method comprising the steps of: (S1) accommodating an electrode assembly in a battery case; (S2) injecting a first electrolyte composition into the battery case to impregnate the electrode assembly; (S3) injecting a second electrolyte composition into the battery case; and (S4) curing the second electrolyte composition, wherein an electrode tab is connected to the electrode assembly and extended to the outside of the electrode assembly; the first electrolyte composition comprises a first solvent and a 1-1 lithium salt containing at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); and the second electrolyte composition comprises an oligomer and a second solvent, and the second electrolyte composition does not contain lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0017] (1) Electrode Assembly Storage Step (S1 Step) 1 and 2, the electrode assembly 100 is first placed in the battery case 300. Here, electrode tabs 400 and 500 are connected to the electrode assembly 100, and the electrode tabs 400 and 500 protrude outward from the electrode assembly 100.

[0018] The electrode assembly 100, the battery case 300, and the electrode tabs 400, 500 will be described below.

[0019] electrode assembly For convenience of explanation, FIGS. 1 and 2 simply show the configuration of the electrode assembly 100, and exemplary configurations of the electrode assembly 100 can be described with reference to FIGS.

[0020] Referring to FIG. 3, the electrode assembly 100 may be manufactured by alternately stacking electrodes 110, 120 and separators 130, and applying adhesive 140 to the surface of at least one of the electrodes 110, 120 and the separator 130 to bond the electrodes 110, 120 and the separator 130 to each other.

[0021] The electrode assembly 100 includes a plurality of electrodes 110, 120 stacked in a vertical direction P. The number of the electrodes 110, 120 may be two or more. In this specification, the term "vertical direction" may refer to a vertical direction based on the ground, and is intended to describe the stacking direction of the electrodes, but is not intended to limit the angle of the stacking direction.

[0022] The electrodes 110, 120 can include a first electrode 110 and a second electrode 120. As shown in FIG. 1, the first electrodes 110 and the second electrodes 120 can be alternately stacked. The electrodes 110, 120 can be alternately stacked with a separator 130 sandwiched between them. The first electrode 110 can be a positive electrode and the second electrode 120 can be a negative electrode. Alternatively, the first electrode 110 can be a negative electrode and the second electrode 120 can be a positive electrode. There can be one or more first electrodes and two or more second electrodes, respectively.

[0023] The first electrode 110 and the second electrode 120 may have a structure in which an active material slurry is applied to a current collector. The first electrode 110 and the second electrode 120 may have a structure in which the active material slurry is applied to both sides of a current collector, dried, and rolled. The active material slurry may be formed by adding a granular active material, a conductive material, a binder, etc. to a solvent and stirring the mixture. The first electrode 110 and the second electrode 120 may use, without limitation, any active material, conductive material, binder, etc. that is used for positive or negative electrodes in the art.

[0024] The current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the current collector can include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and aluminum-cadmium alloy. For example, if the electrodes 110 and 120 are positive electrodes, the current collectors used for the electrodes 110 and 120 can include aluminum, and if the electrodes 110 and 120 are negative electrodes, the current collectors used for the electrodes 110 and 120 can include copper.

[0025] The current collector may be used in various forms such as a film, sheet, foil, net, mesh, porous body, foam, nonwoven fabric, etc. The current collector may also include a polymer layer and metal layers disposed on both sides of the polymer layer, and the metal layers may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and aluminum-cadmium alloy.

[0026] Specifically, when the electrodes 110 and 120 are negative electrodes, the negative electrode active material may be, for example, a compound capable of reversible intercalation and deintercalation of lithium. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO β(0<β<2) Metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. One or a mixture of two or more of these may be used. Furthermore, a thin film of metallic lithium may be used as the negative electrode active material. Furthermore, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0027] Specifically, when the electrodes 110 and 120 are positive electrodes, the positive electrode active material contained therein is not particularly limited, and for example, the positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2Ni-site type lithium nickel oxide represented by the chemical formula LiMn 2-c3 Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxides represented by Mc3O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be a metallic lithium (Li-metal) positive electrode.

[0028] Examples of binders contained in the electrodes include polyvinylidene fluoride polymer, polyvinyl alcohol, styrene butadiene rubber, polyethylene oxide, carboxyl methyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl sucrose. The binder polymer may be any one selected from the group consisting of sucrose, pullulan, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-vinyl acetate copolymer, polyarylate, and low molecular weight compounds having a molecular weight of 10,000 g / mol or less, or a mixture of two or more of these.

[0029] The conductive material contained in the electrode is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0030] An example of the thickener contained in the electrode is carboxymethyl cellulose (CMC).

[0031] 3, the electrode assembly 100 can include separators 130. The separators are stacked alternately with the electrodes.

[0032] 3, the separator 130 may be zigzag-bent or folded to wrap around one end of the electrodes 110, 120. For example, when the first electrode 110 and the second electrode 120 are alternately stacked as shown in FIG. 1, the separator 130 may be folded to wrap around one end 110a of the first electrode 110 and the second electrode 120 located on the opposite side of the end 110a of the first electrode 110. 120 The separator 130 may be folded so as to wrap around one end of the separator 130. As this folding is repeated, the separator 130 may be folded in a zigzag pattern. The electrode assembly 100 may include one separator 130.

[0033] The electrode assembly 100 may be a zigzag stack type electrode assembly in which the separator 130 is bent or folded in a zigzag shape, and one or more, specifically two or more, basic units each having the first electrode 110, the separator 130, the second electrode 120, and the separator 130 stacked in order are stacked.

[0034] As shown in FIG. 4, the separator 130 may include a porous substrate 131 and ceramic coating layers 132a and 132b disposed on both sides of the porous substrate.

[0035] The porous substrate 131 is not particularly limited as long as it is typically used as a separator for a secondary battery. Specifically, the porous substrate 131 preferably has low resistance to ion migration of the electrolyte and excellent electrolyte moisture absorption capacity. More specifically, the porous substrate 131 may contain at least one selected from the group consisting of polyolefin-based resins such as polyethylene, polypropylene, polybutylene, and polypentene; fluorine-based resins such as polyvinylidene fluoride and polytetrafluoroethylene; polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate; polyacrylonitrile resins; and cellulose-based resins. The porous substrate 131 may be a porous film or nonwoven fabric containing one or more of these resins, or a laminate structure of two or more layers of these resins. The porous substrate 131 may be a porous film, nonwoven fabric, or a laminate structure of two or more layers of these resins containing the polyolefin-based resins.

[0036] The size and porosity of the pores present in the porous substrate 131 are not particularly limited. Specifically, the porous substrate 131 may be a porous substrate containing pores having an average pore diameter of 0.01 μm to 1 μm, specifically 20 nm to 60 nm, at a porosity of 10 vol% to 90 vol%, specifically 30 vol% to 60 vol%. This is preferable in that it improves the mechanical strength of the porous substrate 131 and allows ionic substances to move more smoothly between the positive and negative electrodes. The average pore size and porosity can be measured by focused ion beam (FIB) analysis, gas adsorption, or mercury intrusion porosimetry.

[0037] The thickness of the porous substrate 131 is not particularly limited, but may be specifically 1 μm to 100 μm, more specifically 2 μm to 15 μm, taking into consideration appropriate mechanical strength as a separator and ease of movement of ionic substances.

[0038] The ceramic coating layers 132 a and 132 b are disposed on both sides of the porous substrate 131 .

[0039] The ceramic coating layers 132a and 132b include inorganic particles and a binder. More specifically, the ceramic coating layers may consist of only the inorganic particles and the binder.

[0040] The inorganic particles may be introduced to prevent thermal shrinkage of the porous substrate at high temperatures and the resulting short circuit between the positive and negative electrodes. The inorganic particles may also function as a kind of spacer that can maintain the physical shape of the porous substrate and minimize thermal shrinkage.

[0041] The inorganic particles may be those having a voltage range within the operating voltage range of the battery (e.g., Li / Li +It can be used without particular limitation as long as it is electrochemically stable in the range of 0 V to 5 V with respect to the reference and does not cause oxidation and / or reduction reactions, that is, electrochemical reactions. The inorganic particles include lithium phosphate (Li3PO4); lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3); lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glasses (glass) (0 < x < 4, 0 < y < 13); lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3); Li 3.25 Ge 0.25 P 0.75 S4 and other lithium germanium thiophosphates (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5); lithium nitrides such as Li3N (Li x N y , 0 < x < 4, 0 < y < 2); SiS2-based glasses such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4); P2S5-based glasses such as LiI-Li2S-P2S5 (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7); Al2O3; AlOOH; BaTiO3; BaSO4; MgO; CaO; CeO2; NiO; SiO2; SnO2; SrTiO3; TiO2; Y2O3; ZnO; ZrO2; Pb(Zr, Ti)O3 (PZT); Pb 1-x La x Zr 1-y Ti y O3 (PLZT); PB(Mg3Nb 2 / 3)O3-PbTiO3 (PMN-PT); hafnia (HfO2); a mixture of two or more thereof. Specifically, the inorganic particles may be Al2O3; AlOOH; BaTiO3; BaSO4; MgO; CaO; CeO2; NiO; SiO2; SnO2; SrTiO3; TiO2; Y2O3; ZnO; ZrO2; Pb(Zr,Ti)O3 (PZT); Pb 1-x La x Zr 1-y Ti y O3(PLZT);PB(Mg3Nb 2 / 3 )O3-PbTiO3 (PMN-PT); hafnia (HfO2); a mixture of two or more thereof, and more specifically, it may contain at least one selected from the group consisting of Al2O3; AlOOH; BaTiO3; BaSO4; and MgO.

[0042] The average particle size (D 50 ) can be 0.1 μm to 1 μm, specifically 0.2 μm to 0.7 μm.

[0043] The inorganic particles are contained in the ceramic coating layers 132a and 132b in an amount of 92 wt% to less than 100 wt%. The content of the inorganic particles should be considered in relation to the content of the binder, which will be described later, and can be adjusted to prevent a decrease in thermal stability due to thermal shrinkage of the porous substrate and an increase in resistance due to an excessive amount of binder. Specifically, the inorganic particles can be contained in the ceramic coating layers in an amount of 93 wt% to 98 wt%.

[0044] The binder may be included in the ceramic coating layers 132a and 132b to bind inorganic particles and to bind the separator and electrodes.

[0045] The binder is contained in the ceramic coating layer in an amount greater than 0 wt % and less than 8 wt %. If the binder is contained in an amount greater than 8 wt %, the excessive binder content in the ceramic coating layer may increase the resistance of the secondary battery. However, if the binder is contained within the above range, the adhesion between the electrode and the separator may be reduced, resulting in a decrease in the cell rigidity of the secondary battery. However, as described below, the present invention uses a separator having the above-described characteristics in combination with a gel polymer electrolyte, thereby simultaneously improving the resistance of the secondary battery, as well as cell rigidity and mechanical durability.

[0046] Specifically, the binder may be included in the ceramic coating layer in an amount of 2 wt % to 7 wt %, and within this range, the binding strength of the inorganic particles can be maximized and an increase in the resistance of the secondary battery can be prevented.

[0047] The binder may be a hydrophobic binder containing one or more hydrophobic functional groups in the molecule, such as a fluorine group (-F), an acrylate group (CH2=CHCOO-), a methacrylate group (CH2=C(CH3)COO-), a vinyl acetate group (-CH2=CHOCO-), or a nitrile group (-C≡N), or a hydrophilic binder containing one or more polar groups, such as a hydroxyl group (-OH), a carboxyl group (-COOH), a maleic anhydride group (-COOOC-), a sulfonic acid group (-SO3H), or an isocyanate group (-NCO-), and any one or a mixture of two or more of these may be used. More specifically, the hydrophobic binder may be polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylacetate, ethylene-vinylacetate copolymer, polyimide, polyethylene oxide, etc.In addition, the hydrophilic binder may be cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, carboxyl methyl cellulose, polyvinyl alcohol, polyacrylic acid, polymaleic anhydride, polyvinylpyrrolidone, or the like.

[0048] Specifically, the binder may be an acrylic binder. The acrylic binder facilitates the dispersion of the inorganic particles during the preparation of the ceramic coating layer, thereby preventing the ceramic coating layer from being separated into layers, with the binder in the upper layer and the inorganic particles in the lower layer. Such layer separation can result in impeding ion migration in the anode and cathode, leading to increased resistance. Therefore, when an acrylic binder is used as the binder, the resistance reduction effect targeted by the present invention can be more effectively achieved.

[0049] The acrylic binder may include at least one selected from the group consisting of a copolymer of ethylhexyl acrylate and methyl methacrylate; polymethylmethacrylate; polyethylhexylacrylate; polybutylacrylate; polyacrylonitrile; and a copolymer of butyl acrylate and methyl methacrylate.

[0050] The ceramic coating layer may contain inorganic particles and a binder in a weight ratio of 92:8 or more and less than 100:0, specifically 93:7 to 98:2.

[0051] The thickness of the ceramic coating layers 132a and 132b may be 0.1 μm to 10 μm, specifically 0.5 μm to 5 μm, and more specifically 1.0 μm to 2.5 μm. Because the ceramic coating layers 132a and 132b contain the binder in the above-mentioned low content, a thin separator can be realized, which can further improve the energy density of the secondary battery and achieve low resistance. The thickness of the ceramic coating layer may refer to the thickness of one ceramic coating layer formed on one surface of the porous substrate.

[0052] The ceramic coating layers 132a and 132b may be formed by applying a ceramic coating layer-forming composition, which is prepared by dispersing inorganic particles and a binder in a solvent, to the porous substrate and then drying the composition. The method for applying the ceramic coating layer-forming composition is not particularly limited, and may include dip coating, die coating, roll coating, comma coating, and gravure coating. Specifically, gravure coating may be used. The drying method after application of the ceramic coating layer-forming composition may include natural drying, heat drying, or hot air drying.

[0053] The thickness of the separator 130 may be 1 μm to 20 μm, specifically 5 μm to 14 μm. According to the present invention, a thinner separator can be realized by reducing the binder content in the ceramic coating layer, thereby further improving the energy density of the secondary battery and achieving lower resistance.

[0054] As described above, the ceramic coating layer included in the separator contains a small amount of binder, thereby preventing an increase in resistance due to an excessive amount of binder. Meanwhile, in the case of a secondary battery according to the present invention, a gel polymer electrolyte is used as the electrolyte, and the gel polymer electrolyte can compensate for the decrease in cell rigidity of the secondary battery that accompanies such a decrease in resistance. Therefore, a secondary battery manufactured by the manufacturing method of a secondary battery according to the present invention can simultaneously reduce the resistance of the secondary battery and improve its cell rigidity and mechanical durability by combining the above components.

[0055] As shown in FIGS. 3 and 5, the electrode assembly 100 may have an adhesive 140 applied to the surface of at least one of the electrodes 110, 120 and the separator 130, thereby adhering the electrodes 110, 120 and the separator 130 to each other.

[0056] The adhesive 140 may be introduced to bond the electrodes 110, 120 and the separator 130. Specifically, the adhesive may be introduced to fix the alignment position of the electrodes and the separator during the process of laminating, assembling, and stacking them during the manufacturing process of the secondary battery. As described above, the separator 130 according to the present invention may have insufficient adhesive strength between the electrodes and the separator during manufacturing of the secondary battery due to the reduced binder content. The adhesive 140 compensates for this problem, easily bonding the electrodes and the separator, and prevents the separator from shifting during the manufacturing process of the electrode assembly, thereby improving process efficiency and quality.

[0057] The adhesive may be an acrylate adhesive, which can be easily dissolved and removed.

[0058] Specifically, the acrylate adhesive may include a copolymer including repeating units derived from at least one monomer selected from the group consisting of methyl methacrylate (MMA), 2-ethylhexyl acrylate (2-EHA), and 2-hydroxyethyl acrylate (2-HEA).

[0059] The weight-average molecular weight (Mw) of the copolymer may be 120,000 g / mol to 140,000 g / mol. The molecular weight of the copolymer can be measured by a conventional method well known in the art. For example, the molecular weight can be measured by end-group quantitative analysis of functional groups at the molecular chain ends to determine the molecular weight; comprehensive methods (separator permeation method, vapor pressure osmometry, etc.) using physical properties such as osmotic pressure, vapor pressure depression, boiling point elevation, and freezing point depression; light scattering; ultracentrifugation, which measures the molecular weight by analyzing the sedimentation velocity or concentration distribution after centrifuging a polymer solution; viscosimetry, which measures the viscosity of the polymer solution; gel permeation chromatography (GPC), which uses high-performance liquid chromatography (HPLC), etc.

[0060] The adhesive is used to manufacture an electrode assembly by bonding an electrode and a separator, and can be dissolved in an organic solvent contained in the first electrolyte composition and / or the second electrolyte composition, specifically the first electrolyte composition, after the electrode assembly is housed in a battery case and the first electrolyte composition and / or the second electrolyte composition, specifically the first electrolyte composition, is injected into the battery case. Since the adhesive according to the present invention is dissolved and removed after being used to manufacture the electrode assembly, it not only facilitates bonding of the electrode and separator without increasing the amount of binder in the separator, but also prevents an increase in separator thickness due to an increase in the amount of binder, thereby further improving the energy density of the secondary battery.

[0061] The adhesive may be applied in a plurality of patterns spaced apart from one another. Specifically, the adhesive may be applied on a surface of at least one of the electrodes and the separator in a plurality of patterns spaced apart from one another. Specifically, the adhesive may be applied on a surface of at least one of the electrodes and the separator in a plurality of dots spaced apart from one another.

[0062] The adhesive may be removed by injecting a first electrolyte composition, which will be described later, and adhesive traces may remain on the surfaces of at least one of the electrodes 110, 120 and the separator 130. Specifically, when the first electrolyte composition is injected into a battery case housing the electrode assembly, the adhesive may be dissolved and removed by an organic solvent in the first electrolyte composition, leaving behind adhesive traces.

[0063] The adhesive application area may be more than 0% and 1% or less, specifically 0.0001% to 0.05%, of the area of ​​the surface where the separator and the electrode contact each other. This range is preferable because it allows the electrode and the separator to be bonded with sufficient adhesive strength and prevents the problem of excessive adhesive being applied and remaining undissolved in the solvent, which causes an increase in resistance.

[0064] An exemplary method for manufacturing the electrode assembly will now be described with reference to FIGS.

[0065] Specifically, referring to Figures 6 to 9, the electrodes 110, 120 include a first electrode 110 and a second electrode 120, and the electrode assembly 100 can be manufactured by a method including the following steps (a) to (d).

[0066] (a) applying the adhesive 140 to at least a portion of the separator 130 and the first electrode 110; (b) bonding the separator 130 and the first electrode 110 with the applied adhesive 140; (c) folding one side of the separator 130 to cover the first electrode 110; (d) applying the adhesive 140 to at least a portion of the separator 130 and the second electrode 120; (e) bonding the separator 130 and the second electrode 120 with the applied adhesive 140; and (d) folding the other side of the separator 130 to cover the second electrode 120 .

[0067] 6, the adhesive 140 is applied to at least a portion of the separator 130 and the first electrode 110. The application of the adhesive 140 may be performed by applying the adhesive 140 to at least a portion of the separator 130 and the first electrode 110 using a first nozzle 1110. While FIG. 6 illustrates the adhesive 140 being applied to the separator 130, the present invention is not limited thereto, and the adhesive 140 may be applied to at least a portion of the separator 130; the first electrode 110; or both the separator 130 and the first electrode 110.

[0068] Specifically, as shown in FIG. 6, the separator 130 may be unwound from a separator reel 630 and placed on the top surface of a table 700 .

[0069] Referring to FIG. 7, the separator 130 and the first electrode 110 are bonded together by the applied adhesive 140 .

[0070] 9, the first electrode 110 may be formed by cutting a first electrode sheet 1101 unwound from a first electrode reel 610 by a first cutter 810. Here, when a first transfer device 910 transfers the first electrode 110, a first header 1010 may adsorb the first electrode. Next, as the first header 1010 and / or the table 700 move, the first electrode 110 may be placed or disposed on the separator 130.

[0071] Referring to FIG. 8, one side of the separator 130 may be folded to cover the first electrode 110, and the adhesive 140 may be applied to at least a portion of the separator 130 and the second electrode 120.

[0072] After the first electrode 110 is attached on the separator 130, one side of the separator 130 is folded to cover the first electrode 110. For example, the separator 130 may be folded by moving the table 700 laterally.

[0073] Meanwhile, the adhesive 140 is applied to at least a portion of the separator 130 and the second electrode 120. The application of the adhesive 140 may be performed by applying the adhesive 140 to at least a portion of the separator 130 and the second electrode 120 using a second nozzle 1120. Although FIG. 8 illustrates the adhesive 140 being applied to the separator 130, the present invention is not limited thereto, and the adhesive 140 may be applied to at least a portion of the separator 130; the second electrode 120; or both the separator 130 and the second electrode 120.

[0074] Referring to FIG. 9, the separator 130 and the second electrode 120 are bonded together by the applied adhesive 140, and the other side of the separator 130 is folded to cover the second electrode 120.

[0075] The second electrode 120 is attached to the surface of the separator 130 opposite to the surface where the separator 130 and the first electrode 110 are in contact.

[0076] 9, the second electrode 120 may be formed by cutting a first electrode sheet 1201 unwound from a second electrode reel 620 by a second cutter 820. Here, when a second transfer device 920 transfers the second electrode 120, a second header 1020 may adsorb the second electrode. Then, as the second header 1020 and / or the table 700 move, the second electrode may be placed or adhered on the separator.

[0077] 9, after the second electrode 120 is attached, the other side of the separator 130 is folded to cover the second electrode 120. This allows for the manufacture of an electrode assembly in which first and second electrodes are alternately stacked, a separator is interposed between the first and second electrodes, and the separator is folded in a zigzag pattern. Next, by repeating the above process, an electrode assembly in which a plurality of first and second electrodes are alternately stacked can be realized.

[0078] In the case of an electrode assembly including a separator folded in a zigzag shape as described above, the bending or folding of the separator during the manufacturing process can cause misalignment of the separator and / or electrode, which can lead to problems such as poor quality and reduced process efficiency. However, according to the present invention, an adhesive is applied to bond the electrode and separator, which significantly prevents the above-mentioned misalignment of the electrode and / or separator, thereby enabling the manufacture of a secondary battery with improved quality. The application of such an adhesive is particularly preferable in terms of supplementing the adhesive strength of the separator of the present invention, which contains a low content of binder.

[0079] Electrode tab As shown in FIGS. 1 and 2, electrode tabs 400 and 500 are connected to the electrode assembly 100, and the electrode tabs 400 and 500 protrude outward from the electrode assembly 100.

[0080] There may be a plurality of electrode tabs 400, 500. Specifically, the plurality of electrode tabs 400, 500 are connected to the electrodes 110, 120 of the electrode assembly 100, more specifically, the first electrode 110 and the second electrode 120, respectively, and may protrude to the outside of the battery case 300 to serve as a path for electron movement. In addition, although the two electrode tabs 400, 500 are illustrated in FIGS. 1 and 2 as being arranged in different directions with respect to the electrode assembly 100, the present invention is not limited thereto, and the electrode tabs may protrude in parallel in the same direction from one side of the electrode assembly 100.

[0081] The plurality of electrode tabs 400, 500 may be positive electrode tabs and negative electrode tabs, and may be connected to positive and negative electrodes, respectively.

[0082] The electrode tab may contain aluminum. As described below, since the first electrolyte composition containing at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide does not come into contact with the electrode tab, the electrode tab may be significantly less susceptible to damage due to corrosion of aluminum, and long-term life characteristics may be improved.

[0083] Specifically, the electrode tabs may include a positive electrode tab and a negative electrode tab, the positive electrode tab may include aluminum, and the negative electrode tab may include nickel.

[0084] Battery case The battery case 300 may be provided to house the electrode assembly 100. In addition, within the battery case 300, a first electrolyte composition 210 (described later) may be disposed inside the electrode assembly 100, and a second electrolyte composition 220 (described later) may be hardened and disposed outside the electrode assembly 100.

[0085] The battery case 300 may be a pouch-shaped case made of a flexible material, for example, an aluminum pouch battery case.

[0086] When the battery case 300 is an aluminum pouch battery case, the battery case 300 may be formed of a pouch film in which, for example, a polypropylene layer (PP layer), an aluminum layer, and a polyethylene terephthalate layer (PET layer) are laminated in this order from the inside.

[0087] The battery case 300 may include a cup portion 310 that is a receiving space for receiving the electrode assembly.

[0088] The battery case 300 may include a cover 320, and after the electrode assembly is housed and the gel polymer electrolyte composition is hardened and gelled, the battery case 300 may be sealed with the cover to manufacture a sealed secondary battery.

[0089] (2) Injection of the first electrolyte composition and impregnation of the electrode assembly (Step S2) 10 and 11, a first electrolyte composition 210 is injected into the battery case 300 to impregnate the electrode assembly 100. Here, the first electrolyte composition 210 includes a first lithium salt containing lithium bis(fluorosulfonyl)imide, a first oligomer, and a first solvent.

[0090] The first electrolyte composition 210 is introduced to impregnate the electrode assembly 100 and to be disposed inside the electrode assembly 100 .

[0091] Specifically, the first electrolyte composition 210 may be injected so as not to come into contact with the electrode tabs 400 and 500 disposed outside the electrode assembly 100. This prevents lithium bis(fluorosulfonyl)imide contained in the first electrolyte composition 210 from coming into contact with the electrode tabs 400 and 500, specifically, the electrode tabs 400 and 500 containing aluminum, which may cause corrosion.

[0092] The first electrolyte composition 210 is injected into the electrode assembly 100 to impregnate the electrode assembly 100. Specifically, the first electrolyte composition 210 may be injected in an amount calculated in advance in consideration of the size, volume, etc. of the electrode assembly 100 so as to impregnate the electrode assembly 100 without contacting the electrode tabs 400 and 500.

[0093] The impregnation of the first electrolyte composition 210 may be performed at a temperature of 10° C. to 30° C. for 0.5 to 72 hours, and preferably at a temperature of 15° C. to 30° C. for 40 to 65 hours.

[0094] The first electrolyte composition 210 includes a first lithium salt including at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI, LiN(FSO2)2) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, LiN(CF3SO2)2), a first oligomer, and a first solvent.

[0095] The lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide contained in the 1-1 lithium salt is injected into the electrode assembly, thereby reducing the resistance of the electrode assembly and improving the thermal stability of the secondary battery. Meanwhile, the second electrolyte composition injected and disposed outside the electrode assembly does not contain lithium bis(fluorosulfonyl)imide, which significantly reduces the possibility of lithium bis(fluorosulfonyl)imide coming into contact with the electrode tabs 400 and 500, thereby preventing corrosion of the electrode tabs.

[0096] The 1-1 lithium salt may be included in the first electrolyte composition at a molar concentration of 0.5 M or more, specifically 0.65 M or more. Within this range, the effects of reducing the resistance and improving the thermal stability of the secondary battery may be more favorably achieved. The upper limit of the molar concentration of the 1-1 lithium salt is not particularly limited, and may be 5 M or less in terms of easy dissolution of the 1-1 lithium salt. In this specification, the term "molar concentration" refers to the molar content of a component relative to the volume of the composition, and the unit "M" of "molar concentration" may refer to "mol / L."

[0097] The first electrolyte composition may further contain a 1-2 lithium salt in addition to the 1-1 lithium salt for the purpose of further reducing resistance and preventing corrosion.

[0098] The first and second lithium salts include lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroantimonate (LiSbF6), lithium tetraoxoaluminate (LiAlO4), lithium tetrachloroaluminate (LiAlCl4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium nonafluorobutanesulfonate (LiC 4F9SO3), lithium chloride (LiCl), lithium iodide (LiI), lithium bis(oxalato)borate (LiBOB, LiB(C2O4)2), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI, LiN(C2F5SO2)2), lithium fluoroalkylborate (LiFAB), and lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), and specifically, LiPF6 may be included.

[0099] In the first electrolyte composition, the ratio of the molar concentration of the 1-1 lithium salt to the molar concentration of the 1-2 lithium salt may be 0.9:1 to 10:1, and when it is in this range, the resistance of the secondary battery can be improved and the thermal stability of the secondary battery can be improved to a preferable level. In the first electrolyte composition, the ratio of the molar concentration of the 1-1 lithium salt to the molar concentration of the 1-2 lithium salt may be more specifically 0.9:1 to 5:1, and even more specifically 0.9:1 to 1.2:1.

[0100] The ratio of the molar concentration of the 1-1 lithium salt to the molar concentration of the 1-2 lithium salt may be 1.1 or more, and when it is in this range, the resistance of the secondary battery can be improved and the thermal stability of the secondary battery can be improved to a preferable level. More specifically, the ratio of the molar concentration of the 1-1 lithium salt to the molar concentration of the 1-2 lithium salt can be 2.5 or more. The upper limit of the ratio of the molar concentration of the 1-1 lithium salt to the molar concentration of the 1-2 lithium salt is not particularly limited and can be 10 or less, specifically 5 or less.

[0101] In the first electrolyte composition, the sum of the molar concentrations of the 1-1 lithium salt and the 1-2 lithium salt may be 0.7 M or more, specifically 1.2 M or more. When the sum is in this range, the resistance of the secondary battery can be improved and the thermal stability of the secondary battery can be improved to a preferred level. The upper limit of the sum of the molar concentrations of the 1-1 lithium salt and the 1-2 lithium salt is not particularly limited, and may be 5 M or less, specifically 1.8 M or less.

[0102] The first solvent may be used to dissolve or disperse the first-1 lithium salt. The first solvent may be an organic solvent.

[0103] The first solvent is one that is commonly used in secondary batteries, and may be, for example, ether, ester (acetates, propionates), amide, linear or cyclic carbonate, nitrile (acetonitrile, SN, etc.), etc., which may be used alone or in combination of two or more.

[0104] Among them, typically, carbonate-based solvents containing carbonate compounds such as cyclic carbonates, linear carbonates, or mixtures thereof can be used as the first solvent.

[0105] Specific examples of the cyclic carbonate compound include a single compound or a mixture of at least two compounds selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, and halides thereof. Specific examples of the linear carbonate compound include a compound or a mixture of at least two compounds selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC), but are not limited thereto.

[0106] In particular, among the carbonate solvents, cyclic carbonates such as propylene carbonate and ethylene carbonate are preferred because they are high-viscosity organic solvents with high dielectric constants and can easily dissociate lithium salts in the electrolyte. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as ethyl methyl carbonate, diethyl carbonate, or dimethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be obtained, and therefore, the cyclic carbonates can be more preferred.

[0107] In addition, the ester of the first solvent may be a single compound or a mixture of at least two compounds selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α-valerolactone, and ε-caprolactone, but is not limited thereto.

[0108] The first electrolyte composition 210 can be a liquid electrolyte composition or a gel polymer electrolyte composition.

[0109] When the first electrolyte composition 210 is a liquid electrolyte composition, the first electrolyte composition 210 may be free of oligomers for the formation of a gel polymer electrolyte.

[0110] When the first electrolyte composition 210 is a gel polymer electrolyte composition, the first electrolyte composition may further include an oligomer. The oligomer may include at least one selected from the group consisting of polyether-based oligomers, polycarbonate-based oligomers, acrylate-based oligomers, polysiloxane-based oligomers, phosphagen-based oligomers, polyethylene-based oligomers, urethane-based oligomers, epoxy-based oligomers, fluorine-based oligomers, polyethylene oxide, polyester sulfide, polyvinyl alcohol, and polyvinylidene fluoride, specifically at least one selected from the group consisting of fluorine-based oligomers, polycarbonate-based oligomers, and polysiloxane-based oligomers.

[0111] For example, the fluorine-based oligomer may specifically contain a unit derived from a fluorine-based monomer. The fluorine-based oligomer has the advantage that the fluorine-based functional group contained therein suppresses the generation of oxygen radicals caused by decomposition of the positive electrode active material, thereby further improving battery stability and having excellent flame retardancy. More specifically, the fluorine-based oligomer may include at least one selected from tetrafluoroethylene (TFE)-vinyl acetate copolymer, (allyl 1,1,2,2-tetrafluoroethyl ether)-(2,2,2-trifluoroethyl acrylate) copolymer, tetrafluoroethylene-(2-vinyl-1,3-dioxolane) copolymer, and tetrafluoroethylene-vinyl methacrylate copolymer.

[0112] The polycarbonate oligomer has an affinity for the positive electrode, a structure similar to that of an organic electrolyte, and excellent ionic conductivity or ionic dissociation. The polycarbonate oligomer may be a polycarbonate having a weight-average molecular weight of 1,000 g / mol to 50,000 g / mol, specifically 4,500 g / mol to 30,000 g / mol, and more specifically 10,000 g / mol to 25,000 g / mol.

[0113] In addition, the polysiloxane oligomer can function as a scavenger for gases (such as HF) generated by side reactions in the electrolyte, thereby improving high-temperature storage characteristics.

[0114] The weight average molecular weight of the oligomer can be 1,000 g / mol to 50,000 g / mol, specifically 4,500 g / mol to 30,000 g / mol.

[0115] The oligomer may be included in the first electrolyte composition in an amount of 0.1 wt % to 30 wt %, specifically 1 wt % to 10 wt %, and within this range, the gel polymer electrolyte may exhibit excellent ionic conductivity and lithium ion mobility.

[0116] When the first electrolyte composition 210 is a gel polymer electrolyte composition, the first electrolyte composition 210 may be cured after step (S2), if necessary.

[0117] This step is not essential, and as will be described later, after the injection of the second electrolyte composition, both the first electrolyte composition 210 and the second electrolyte composition 220 can be cured in step (S4). However, when the curing step is performed after the impregnation of the first electrolyte composition 210, there are advantages in that the first electrolyte composition 210 can be prevented from flowing out of the electrode assembly 100 before the injection of the second electrolyte composition 220, and the first electrolyte composition 210 and the second electrolyte composition 220 can be prevented from being mixed with each other.

[0118] Here, the curing may be carried out at a temperature of 50° C. to 100° C. for 0.5 to 48 hours, and preferably at a temperature of 60° C. to 80° C. for 0.5 to 24 hours.

[0119] When the first electrolyte composition 210 is cured after step (S2), the first electrolyte composition 210 may further include a polymerization initiator for polymerizing and crosslinking the oligomer. The types of polymerization initiators will be described later.

[0120] (3) Injection of second electrolyte composition (Step S3) 12, after step (S2), a second electrolyte composition 220 is injected into the battery case 300. Here, the second electrolyte composition 220 includes an oligomer and a second solvent, and does not include lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0121] 12, the second electrolyte composition 220 injected into the battery case 300 may be injected outside the electrode assembly 100. The second electrolyte composition 220 does not contain lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide, and therefore may not cause corrosion problems in the electrode tabs 400 and 500 located outside the electrode assembly 100.

[0122] The second electrolyte composition 220 includes an oligomer and a second solvent. The second electrolyte composition includes the oligomer, so that the second electrolyte composition can form a gel polymer electrolyte 220a.

[0123] The oligomer can be polymerized and crosslinked by the curing process of the second electrolyte composition.

[0124] The oligomer may include at least one selected from the group consisting of polyether-based oligomers, polycarbonate-based oligomers, acrylate-based oligomers, polysiloxane-based oligomers, phosphagen-based oligomers, polyethylene-based oligomers, urethane-based oligomers, epoxy-based oligomers, fluorine-based oligomers, polyethylene oxide, polyester sulfide, polyvinyl alcohol, and polyvinylidene fluoride, specifically at least one selected from fluorine-based oligomers, polycarbonate-based oligomers, and polysiloxane-based oligomers.

[0125] For example, the fluorine-based oligomer may specifically contain a unit derived from a fluorine-based monomer. The fluorine-based oligomer has the advantage that the fluorine-based functional group contained therein suppresses the generation of oxygen radicals caused by decomposition of the positive electrode active material, thereby further improving battery stability and having excellent flame retardancy. More specifically, the fluorine-based oligomer may include at least one selected from tetrafluoroethylene (TFE)-vinyl acetate copolymer, (allyl 1,1,2,2-tetrafluoroethyl ether)-(2,2,2-trifluoroethyl acrylate) copolymer, tetrafluoroethylene-(2-vinyl-1,3-dioxolane) copolymer, and tetrafluoroethylene-vinyl methacrylate copolymer.

[0126] The polycarbonate oligomer has an affinity for the positive electrode, a structure similar to that of an organic electrolyte, and excellent ionic conductivity or ionic dissociation. The polycarbonate oligomer may be a polycarbonate having a weight-average molecular weight of 1,000 g / mol to 50,000 g / mol, specifically 4,500 g / mol to 30,000 g / mol, and more specifically 10,000 g / mol to 25,000 g / mol.

[0127] In addition, the polysiloxane oligomer can function as a scavenger for gases (such as HF) generated by side reactions in the electrolyte, thereby improving high-temperature storage characteristics.

[0128] The weight average molecular weight of the oligomer can be 1,000 g / mol to 50,000 g / mol, specifically 4,500 g / mol to 30,000 g / mol.

[0129] The oligomer may be included in the second electrolyte composition in an amount of 0.1 wt % to 30 wt %, specifically 1 wt % to 10 wt %. When the content is in this range, the second electrolyte composition disposed outside the electrode assembly hardens, thereby improving the rigidity of the secondary battery, preventing leakage of the secondary battery, and further improving the safety of the secondary battery.

[0130] The type of the second solvent can be the same as that exemplified for the first solvent, but the first solvent and the second solvent may be the same or different.

[0131] The second electrolyte composition 220 may further include a second lithium salt to improve the resistance of the secondary battery.

[0132] The second lithium salt may be lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroantimonate (LiSbF6), lithium tetraoxoaluminate (LiAlO4), lithium tetrachloroaluminate (LiAlCl4), lithium trifluoromethanesulfonate (LiCF3SO3), or lithium nonafluorobutanesulfonate. The second lithium salt may include at least one selected from the group consisting of (LiC4F9SO3), lithium chloride (LiCl), lithium iodide (LiI), lithium bis(oxalato)borate (LiBOB, LiB(C2O4)2), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI, LiN(C2F5SO2)2), lithium fluoroalkylborate (LiFAB), and lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), specifically LiPF6. Here, the second lithium salt may be free of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide in order to prevent corrosion of the electrode tab.

[0133] In order to improve the resistance of the secondary battery, the second lithium salt may be contained in the second electrolyte composition at a molar concentration of 0.1M to 3.0M, specifically 0.5M to 1.5M.

[0134] (4) Hardening of the second electrolyte composition (Step S4) 13 and 14, the second electrolyte composition 220 is cured. The second electrolyte composition 220 injected into the battery case 300 can be cured to form a gel polymer electrolyte 220a. When the first electrolyte composition 210 is a gel polymer electrolyte composition, both the first electrolyte composition 210 and the second electrolyte composition 220 can be cured in step (S4).

[0135] 13 and 14, after step (S4), the first electrolyte composition may be disposed inside the electrode assembly. If the first electrolyte composition is a liquid electrolyte composition, it may be disposed in a state of being impregnated inside the electrode assembly. Alternatively, if the first electrolyte composition is a gel polymer electrolyte composition, it may be hardened and disposed inside the electrode assembly in the form of a gel polymer electrolyte 210a. The gel polymer electrolyte 220a formed from the second electrolyte composition 220 may be disposed outside the electrode assembly 100.

[0136] The second electrolyte composition 220 or the first electrolyte composition 210 and the second electrolyte composition 220 may be cured by a photocuring or thermal curing process, and specifically, may be cured by a thermal curing process.

[0137] The second electrolyte composition 220, or the first electrolyte composition 210 and the second electrolyte composition 220, can be cured in the presence of a polymerization initiator, which can be used to polymerize the oligomers contained in the electrolyte composition to form a polymer network connected in a three-dimensional structure.

[0138] The polymerization initiator may be included in the second electrolyte composition 220. The second electrolyte composition may undergo a curing process due to the formation of radicals by the polymerization initiator.

[0139] Meanwhile, the polymerization initiator may not be included in the second electrolyte composition 220, but may be added to the battery case 300 in a separate process to help harden the second electrolyte composition 220. Specifically, the method for manufacturing a secondary battery of the present invention may further include a step of injecting a polymerization initiator into the battery case 100 before performing step (S4), specifically, after performing step (S3) and before performing step (S4). This is advantageous in that pre-gelation, in which the second electrolyte composition hardens due to radicals randomly generated without a polymerization initiator, can be prevented, and the electrode assembly can be sufficiently impregnated and the secondary battery manufacturing process can be smoothly controlled.

[0140] The polymerization initiator may be a photopolymerization initiator or a thermal polymerization initiator depending on the polymerization method.

[0141] Specifically, typical examples of the photopolymerization initiator include 2-hydroxy-2-methylpropiophenone (HMPP), 1-hydroxy-cyclohexylphenyl-ketone, benzophenone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, oxy-phenylacetic acid 2-[2-iodine-2phenyl-acetoxy-ethoxy]-ethyl ester, oxy-phenyl-acetic 2-[2-hydroxyethoxy]-ethyl ester, alpha-dimethoxy-alpha-phenylacetophenone, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl ]-1-butanone, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis(eta5-2,4-cyclopentadien-1-yl), bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium, 4-isobutylphenyl-4'-methylphenyliodonium, hexafluorophosphate, and at least one compound selected from the group consisting of methylbenzoylformate.

[0142] Representative examples of the thermal polymerization initiator include at least one compound selected from the group consisting of benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, hydrogen peroxide, 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN), and 2,2'-azobisdimethyl-valeronitrile (AMVN).

[0143] The polymerization initiator can be decomposed in the secondary battery by heat at 30°C to 100°C or by light such as UV at room temperature (5°C to 30°C) to form radicals, which can form crosslinks through free radical polymerization, thereby polymerizing the oligomer.

[0144] The curing can be carried out at a temperature of 50° C. to 100° C. for 0.5 to 48 hours, and preferably at a temperature of 60° C. to 80° C. for 0.5 to 24 hours.

[0145] Meanwhile, the curing may be performed in a state where the battery case 300 is sealed. For example, the battery case 300 containing the electrode assembly 100, the first electrolyte composition 210, and the second electrolyte composition 220 is covered with a 320 After sealing with, for example, heat treatment can be performed to thermally cure the second electrolyte composition 220.

[0146] After step (S4), the first electrolyte composition 210 is disposed inside the electrode assembly 100, and the second electrolyte composition 220 is cured to form a gel polymer electrolyte 220a, which may be disposed outside the electrode assembly 100. The first electrolyte composition impregnates the inside of the electrode assembly to reduce the resistance of the secondary battery, and the second electrolyte composition forms a gel polymer electrolyte outside the electrode assembly to improve cell rigidity and prevent electrolyte leakage. Furthermore, the first electrolyte composition 210 contains lithium bis(fluorosulfonyl)imide, while the second electrolyte composition 220 does not contain lithium bis(fluorosulfonyl)imide, thereby reducing the resistance of the secondary battery, improving thermal stability, and effectively preventing corrosion of the electrode tabs.

[0147] After step (S4), a step of cooling the hardened second electrolyte composition may be further performed. For example, the cooling may be performed by leaving the hardened second electrolyte composition at room temperature.

[0148] After step (S4), the battery case 300 may be sealed to create a vacuum atmosphere inside the battery case 300. The vacuum atmosphere may allow degassing of gases generated during curing.

[0149] While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein, and that the invention may be embodied in various different forms without departing from the spirit or scope of the present invention.

[0150] Examples and Comparative Examples Experimental Example A: Use of a First Electrolyte Composition (Liquid Electrolyte Composition) and a Second Electrolyte Composition (Gel Polymer Electrolyte Composition) Example 1A 1. Separator manufacturing As inorganic particles, Al2O3 (average particle size (D50 A ceramic coating layer-forming composition was prepared by adding 100% acrylic acid (0.5 μm) and an acrylic binder to water as a solvent in a weight ratio of 96:4. The acrylic binder used was a mixture of TRD 202A manufactured by JSR Corporation and AP-0821 manufactured by APEC Corporation.

[0151] The ceramic coating layer-forming composition was applied to both sides of a polyethylene porous substrate (thickness: 9 μm, average pore diameter: 0.05 μm, porosity: 45% by volume) by gravure coating and dried to form ceramic coating layers (thickness of one layer: 1.5 μm), thereby producing a separator (thickness: 12 μm = 1.5 μm + 9 μm + 1.5 μm).

[0152] 2. Manufacturing the electrode assembly The separator reel on which the separator was wound was unwound, and the separator was placed on a table. An adhesive was applied to the separator using a first nozzle in a pattern of a plurality of spaced apart dots. The adhesive application area (5.8875 mm) was 2 ) is the contact area between the separator and the positive electrode (24,889 mm 2 ) was 0.002366%. The adhesive was an acrylate-based adhesive, which is a copolymer containing repeating units derived from methyl methacrylate (MMA), 2-ethylhexyl acrylate (2-EHA), and 2-hydroxyethyl acrylate (2-HEA) in a weight ratio of 40:30:30. Next, the positive electrode sheet was unwound from the first electrode reel and cut with a first cutter to produce a positive electrode. The positive electrode was then transported by a first transport device and adsorbed onto a first header. The first header was moved toward the table, and the positive electrode was attached to the separator.

[0153] Next, the table was moved to the side, and the separator was folded to one side to cover the positive electrode.

[0154] Next, the same adhesive as used above was applied to the surface of the separator (the surface opposite to the surface where the separator and the positive electrode contact) using a second nozzle in a pattern of multiple dots spaced apart from each other.

[0155] Next, the negative electrode sheet was unwound from the second electrode reel and cut with a second cutter to produce a negative electrode, and the negative electrode was transported by a second transport device and attached to a second header. The second header was then moved toward the table, and the negative electrode was attached to the surface of the separator (the surface opposite the surface where the separator and positive electrode contact).

[0156] Next, the table was moved sideways again, and the separator was folded to the other side to cover the negative electrode.

[0157] The above process was repeated several times to prepare an electrode assembly having 18 stacked basic units, each of which was stacked in the order of separator / positive electrode / separator / negative electrode. Here, the separator was folded in a zigzag pattern.

[0158] Here, an aluminum electrode tab (positive electrode tab) was connected to the positive electrode, and a nickel electrode tab (negative electrode tab) was connected to the negative electrode.

[0159] Here, in the case of the positive electrode, the positive electrode active material is Li[Ni 0.8 Co 0.1 Mn 0.1 ]O2, PVdF as a binder, and carbon black as a conductive material were added to N-methylpyrrolidone (NMP) as a solvent in a weight ratio of 97.5:1.5:1.0 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of an aluminum current collector as a positive electrode current collector, and the aluminum current collector was dried and rolled to form a positive electrode active material layer.

[0160] In addition, for the negative electrode, graphite as a negative electrode active material, styrene-butadiene rubber as a binder, carbon black as a conductive material, and carboxymethyl cellulose (CMC) as a thickener were added to water as a solvent in a weight ratio of 95.5:2.5:1.0:1.0 to prepare a negative electrode slurry. The negative electrode slurry was applied to both sides of a copper current collector as a negative electrode current collector, and then dried and rolled to form a negative electrode active material layer.

[0161] 3. Preparation of Electrolyte Composition (1) Preparation of the first electrolyte composition Lithium bis(fluorosulfonyl)imide (LiFSI) as the first lithium salt and LiPF6 as the second lithium salt were added to a solvent ( ethylene A first electrolyte composition was prepared by adding the above-mentioned mixture to a mixture of ethyl methyl carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0162] (2) Preparation of the second electrolyte composition LiPF6 as a second lithium salt was added to the second electrolyte composition so that the molar concentration of the second electrolyte composition was 1.0 M, and trimethylolpropane triacrylate as an oligomer was added to the second electrolyte composition so that the content of the second lithium salt was 5 wt % of the second electrolyte composition in a solvent ( ethylene The second electrolyte composition was prepared by adding the above-mentioned mixture to a mixture of ethyl methyl carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and adding AIBN (Azobisisobutyronitrile) as a polymerization initiator in an amount of 0.02 wt % based on the weight of the second electrolyte composition.

[0163] 4. Secondary battery manufacturing A pouch-type battery case made of aluminum was prepared as the battery case, and the electrode assembly was housed in the housing space of the battery case, where the positive and negative electrode tabs were connected to the electrode assembly and arranged to protrude outside the electrode assembly.

[0164] Next, the amount of the first electrolyte composition was calculated and adjusted so that only the electrode assembly was impregnated, and the first electrolyte composition was injected into the battery case to impregnate the electrode assembly. After injecting the first electrolyte composition, the battery case was vacuum sealed and the inside of the electrode assembly was impregnated at room temperature for 60 hours.

[0165] Next, the second electrolyte composition was injected so as to be disposed outside the electrode assembly. After the injection of the second electrolyte composition, the battery case was vacuum sealed.

[0166] Next, the second electrolyte composition injected into the battery case was cured to form a gel polymer electrolyte by heat treatment at a temperature of 65° C. for 5 hours.

[0167] The battery case was then cooled, sealed and degassed to prepare a secondary battery.

[0168] Meanwhile, the adhesive present in the electrode assembly was dissolved and removed by the solvent of the first electrolyte composition due to the injection of the first electrolyte composition. As will be described later, the adhesive was removed, and traces of the adhesive remained on the separator and electrodes.

[0169] Example 2A A first electrolyte composition was prepared in the same manner as in Example 1A, except that the 1-1 lithium salt and the 1-2 lithium salt were added to the solvent to have molar concentrations of 0.7 M and 0.7 M, respectively.

[0170] A secondary battery was fabricated in the same manner as in Example 1A, except that the first electrolyte composition prepared above was used.

[0171] Example 3A A first electrolyte composition was prepared in the same manner as in Example 1A, except that the 1-1 lithium salt and the 1-2 lithium salt were added to the solvent to have molar concentrations of 0.6 M and 0.2 M, respectively.

[0172] A secondary battery was manufactured in the same manner as in Example 1A, except that the first electrolyte composition prepared above was used and no additional lithium salt addition step was performed.

[0173] Example 4A A secondary battery was produced in the same manner as in Example 1A, except that the second lithium salt was not added to the second electrolyte composition.

[0174] Example 5A A secondary battery was produced in the same manner as in Example 2A, except that the second lithium salt was not added to the second electrolyte composition.

[0175] Comparative Example 1A 1. Preparation of Electrolyte Composition An electrolyte composition was prepared in the same manner as the first electrolyte composition of Example 1A, except that the first lithium salt was not used and the first lithium salt (LiPF) was added to the solvent to a molar concentration of 1.0 M.

[0176] 2. Secondary battery manufacturing A pouch-type battery case made of aluminum was prepared as the battery case, and the electrode assembly was placed in the battery case. Here, the positive electrode tab and the negative electrode tab were connected to the electrode assembly and arranged to protrude outside the electrode assembly. The battery case, electrode assembly, positive electrode tab, and negative electrode tab used above were the same as those used in Example 1A.

[0177] Next, the prepared electrolyte composition was injected into the inner space of the battery case, vacuum sealed, and allowed to impregnate the inside of the electrode assembly at room temperature for 60 hours.

[0178] The battery case was then cooled, sealed and degassed to prepare a secondary battery.

[0179] The secondary battery fabrication method described above differs from Example 1A in that one electrolyte composition was injected into the battery case in one step instead of using two different electrolyte compositions, and that only a liquid electrolyte was used instead of a gel polymer electrolyte.

[0180] Comparative example 2A 1. Preparation of Electrolyte Composition An electrolyte composition was prepared in the same manner as the first electrolyte composition of Example 1A, except that the first-2 lithium salt was not used and the first-1 lithium salt (LiFSI) was added to the solvent to a molar concentration of 1.0 M.

[0181] 2. Secondary battery manufacturing A pouch-type battery case made of aluminum was prepared as the battery case, and the electrode assembly was housed in the housing space of the battery case.

[0182] Next, the prepared electrolyte composition was injected into the inner space of the battery case, vacuum sealed, and allowed to impregnate the inside of the electrode assembly at room temperature for 60 hours.

[0183] The battery case was then cooled, sealed and degassed to prepare a secondary battery.

[0184] The secondary battery fabrication method described above differs from Example 1A in that one electrolyte composition was injected into the battery case in one step instead of using two different electrolyte compositions, and that only a liquid electrolyte was used instead of a gel polymer electrolyte.

[0185] Comparative example 3A 1. Preparation of Electrolyte Composition An electrolyte composition was prepared in the same manner as in the first electrolyte composition of Example 1A, except that the 1-1 lithium salt and the 1-2 lithium salt were added to the solvent to give molar concentrations of 0.3 M and 0.7 M, respectively.

[0186] 2. Secondary battery manufacturing A pouch-type battery case made of aluminum was prepared as the battery case, and the electrode assembly was housed in the housing space of the battery case.

[0187] Next, the prepared electrolyte composition was injected into the inner space of the battery case, vacuum sealed, and allowed to impregnate the inside of the electrode assembly at room temperature for 60 hours.

[0188] The battery case was then cooled, sealed and degassed to prepare a secondary battery.

[0189] The secondary battery fabrication method described above differs from Example 1A in that one electrolyte composition was injected into the battery case in one step instead of using two different electrolyte compositions, and that only a liquid electrolyte was used instead of a gel polymer electrolyte.

[0190] Experimental Example 1A. Observation of adhesive marks on the separator surface The separator corresponding to the surface where the electrode and separator were in contact in the secondary battery of Example 1A was cut, and the surface was observed. A photograph of the surface of the separator separated from the secondary battery of Example 1A is shown in Figure 15.

[0191] As shown in FIG. 15, traces of adhesive application were observed in the photograph of the surface of the separator of Example 1A.

[0192] Experimental Example 2A. Resistance Evaluation For the secondary batteries of Examples 1A to 5A and Comparative Examples 1A to 3A, the resistance value was calculated using the voltage change (ΔV) measured when discharging at a 2.5C rate for 10 seconds at an SOC of 50%.

[0193] When the resistance value of the secondary battery of Comparative Example 1A was taken as 100%, the relative ratios of the resistance values ​​of the secondary batteries of Examples 1A to 5A and Comparative Examples 1A to 3A are shown in Table 1 below.

[0194] Experimental Example 3A. Observation of Tab Corrosion The secondary batteries manufactured in Examples 1A to 5A and Comparative Examples 1A to 3A were fully charged and then stored at 60°C for two weeks, after which the positive electrode tab was visually inspected for corrosion. Five secondary batteries each in Examples 1A to 5A and Comparative Examples 1A to 3A were prepared, and the experiment was performed five times.

[0195] If no corrosion occurred on the positive electrode tab, it was evaluated as "Pass," and if corrosion occurred, it was evaluated as "Fail." The number of times that the test was evaluated as "Pass" out of the total number of tests (represented as "Total," 5 times) is shown in Table 1.

[0196] Experimental Example 4A. Leakage volume measurement The amount of electrolyte leakage was measured for Examples 1A to 5A and Comparative Examples 1A to 3A. A 5 cm cut was made in the side of each secondary battery, and the cut part was set as the bottom end and left for 3 days, after which the amount of electrolyte leakage was measured for each secondary battery. The results are shown in Table 1 below.

[0197] [Table 1]

[0198] Referring to Table 1, the secondary batteries of Examples 1A to 5A had reduced resistance, no tab corrosion was observed, and electrolyte leakage was hardly observed.

[0199] However, in the case of Comparative Example 1A, since lithium bis(fluorosulfonyl)imide was not used, corrosion of the electrode tab did not occur, but the resistance increased significantly and the gel polymer electrolyte was not placed outside the electrode assembly, resulting in a considerable amount of electrolyte leakage outside the secondary battery.

[0200] In addition, in Comparative Examples 2A and 3A, lithium bis(fluorosulfonyl)imide was placed outside the electrode assembly and came into contact with the electrode tab, which resulted in corrosion of the electrode tab, which is undesirable. Also, since the gel polymer electrolyte was not placed outside the electrode assembly, a considerable amount of electrolyte leakage occurred outside the secondary battery.

[0201] Experimental Example B: Use of the first electrolyte composition (gel polymer electrolyte composition) and the second electrolyte composition (gel polymer electrolyte composition) Example 1B 1. Separator manufacturing As inorganic particles, Al2O3 (average particle size (D 50 A ceramic coating layer-forming composition was prepared by adding acrylic binder (0.5 μm) and water (solvent) in a weight ratio of 96:4. The acrylic binder used was a mixture of TRD 202A manufactured by JSR Corporation and AP-0821 manufactured by APEC Corporation.

[0202] The ceramic coating layer-forming composition was applied to both sides of a polyethylene porous substrate (thickness: 9 μm, average pore diameter: 0.05 μm, porosity: 45% by volume) by gravure coating and dried to form ceramic coating layers (thickness of one layer: 1.5 μm), thereby producing a separator (thickness: 12 μm = 1.5 μm + 9 μm + 1.5 μm).

[0203] 2. Manufacturing the electrode assembly The separator reel on which the separator was wound was unwound, and the separator was placed on a table. An adhesive was applied to the separator in a pattern of multiple dots spaced apart from each other using a first nozzle. The adhesive application area (5.8875 mm 2 ) is the contact area between the separator and the positive electrode (24,889 mm 2 ) was 0.002366%. The adhesive was an acrylate-based adhesive, which is a copolymer containing repeating units derived from methyl methacrylate (MMA), 2-ethylhexyl acrylate (2-EHA), and 2-hydroxyethyl acrylate (2-HEA) in a weight ratio of 40:30:30. Next, the positive electrode sheet was unwound from the first electrode reel and cut with a first cutter to produce a positive electrode. The positive electrode was then transported by a first transport device and adsorbed onto a first header. The first header was moved toward the table, and the positive electrode was attached to the separator.

[0204] Next, the table was moved to the side, and the separator was folded to one side to cover the positive electrode.

[0205] Next, the same adhesive as used above was applied to the surface of the separator (the surface opposite to the surface where the separator and the positive electrode contact) using a second nozzle in a pattern of multiple dots spaced apart from each other.

[0206] Next, the negative electrode sheet was unwound from the second electrode reel and cut with a second cutter to produce a negative electrode, and the negative electrode was transported by a second transport device and attached to a second header. The second header was then moved toward the table, and the negative electrode was attached to the surface of the separator (the surface opposite the surface where the separator and positive electrode contact each other).

[0207] Next, the table was moved sideways again, and the separator was folded to the other side to cover the negative electrode.

[0208] The above process was repeated several times to prepare an electrode assembly having 18 stacked basic units, each of which was stacked in the order of separator / positive electrode / separator / negative electrode. Here, the separator was folded in a zigzag pattern.

[0209] Here, an aluminum electrode tab (positive electrode tab) was connected to the positive electrode, and a nickel electrode tab (negative electrode tab) was connected to the negative electrode.

[0210] Here, in the case of the positive electrode, the positive electrode active material is Li[Ni 0.8 Co 0.1 Mn 0.1 ]O2, PVdF as a binder, and carbon black as a conductive material were added to N-methylpyrrolidone (NMP) as a solvent in a weight ratio of 97.5:1.5:1.0 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of an aluminum current collector as a positive electrode current collector, and then dried and rolled to form a positive electrode active material layer.

[0211] In addition, for the negative electrode, graphite as a negative electrode active material, styrene-butadiene rubber as a binder, carbon black as a conductive material, and carboxymethyl cellulose (CMC) as a thickener were added to water as a solvent in a weight ratio of 95.5:2.5:1.0:1.0 to prepare a negative electrode slurry. The negative electrode slurry was applied to both sides of a copper current collector as a negative electrode current collector, and then dried and rolled to form a negative electrode active material layer.

[0212] 3. Preparation of Gel Polymer Electrolyte Composition (1) Preparation of First Gel Polymer Electrolyte Composition A first gel polymer electrolyte composition was produced by adding lithium bis(fluorosulfonyl)imide (LiFSI) as the 1-1 lithium salt and LiPF6 as the 1-2 lithium salt to a solvent (a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7) to give molar concentrations of 0.9 M and 0.3 M, respectively, adding trimethylolpropane triacrylate as an oligomer to the solvent to give 5 wt % relative to the weight of the composition, and adding AIBN (Azobisisobutyronitrile) as a polymerization initiator to the solvent to give 0.02 wt % relative to the weight of the composition.

[0213] (2) Preparation of the second gel polymer electrolyte composition A second gel polymer electrolyte composition was produced in the same manner as the first gel polymer electrolyte composition, except that the 1-1 lithium salt and the 1-2 lithium salt were not contained.

[0214] 4. Secondary battery manufacturing A pouch-type battery case made of aluminum was prepared as the battery case, and the electrode assembly was housed in the housing space of the battery case, where the positive and negative electrode tabs were connected to the electrode assembly and arranged to protrude outside the electrode assembly.

[0215] Next, the amount of the first gel polymer electrolyte composition was calculated and adjusted so that only the electrode assembly was impregnated, and the first gel polymer electrolyte composition was injected into the battery case to impregnate the electrode assembly. After injecting the first gel polymer electrolyte composition, the battery case was vacuum sealed, and the inside of the electrode assembly was impregnated at room temperature for 60 hours.

[0216] Next, the second gel polymer electrolyte composition was injected so as to be disposed outside the electrode assembly, and after the injection of the second gel polymer electrolyte composition, the electrode assembly was vacuum sealed.

[0217] Next, the first gel polymer electrolyte composition and the second gel polymer electrolyte composition injected into the battery case were cured by heat treatment at a temperature of 65° C. for 5 hours.

[0218] The battery case was then cooled, sealed and degassed to produce a secondary battery.

[0219] Meanwhile, the adhesive present in the electrode assembly was dissolved and removed by the solvent of the first gel polymer electrolyte composition due to the injection of the first gel polymer electrolyte composition. As will be described later, the adhesive was removed, leaving traces of the adhesive on the separator and electrodes.

[0220] Example 2B A first gel polymer electrolyte composition was prepared in the same manner as in Example 1B, except that the 1-1 lithium salt and the 1-2 lithium salt were added to the solvent to have molar concentrations of 0.8 M and 0.4 M, respectively.

[0221] A secondary battery was fabricated in the same manner as in Example 1B, except that the first gel polymer electrolyte composition prepared above was used.

[0222] Example 3B A first gel polymer electrolyte composition was prepared in the same manner as in Example 1B, except that the 1-1 lithium salt and the 1-2 lithium salt were added to the solvent to have molar concentrations of 0.7 M and 0.5 M, respectively.

[0223] A secondary battery was fabricated in the same manner as in Example 1B, except that the first gel polymer electrolyte composition prepared above was used.

[0224] Example 4B A first gel polymer electrolyte composition was prepared in the same manner as in Example 1B, except that the 1-1 lithium salt and the 1-2 lithium salt were added to the solvent to have molar concentrations of 0.6 M and 0.2 M, respectively.

[0225] A secondary battery was fabricated in the same manner as in Example 1B, except that the first gel polymer electrolyte composition prepared above was used.

[0226] Comparative example 1B 1. Electrode assembly manufacturing An electrode assembly was prepared in the same manner as in Example 1B.

[0227] 2. Preparation of Gel Polymer Electrolyte Composition A gel polymer electrolyte composition was prepared in the same manner as the first gel polymer electrolyte composition of Example 1B, except that the first lithium salt was not used and the first lithium salt (LiPF) was added to the solvent to a molar concentration of 1.0 M.

[0228] 3. Secondary battery manufacturing A pouch-type battery case made of aluminum was prepared as the battery case, and the electrode assembly was placed in the battery case. Here, the positive and negative electrode tabs were connected to the electrode assembly and arranged to protrude outside the electrode assembly. The battery case, electrode assembly, positive and negative electrode tabs used were the same as those used in Example 1B.

[0229] Next, the gel polymer electrolyte composition prepared above was injected into the inner space of the battery case, vacuum sealed, and allowed to impregnate the inside of the electrode assembly at room temperature for 60 hours.

[0230] Next, the gel polymer electrolyte composition injected into the battery case was cured by heat treatment at a temperature of 65° C. for 5 hours.

[0231] The battery case was then cooled, sealed and degassed to prepare a secondary battery.

[0232] The secondary battery manufactured as described above differs from Example 1B in that two different gel polymer electrolyte compositions were not used, but one gel polymer electrolyte composition was injected into the battery case in a single step and cured.

[0233] Comparative Example 2B Instead of the second gel polymer electrolyte composition prepared in Example 1B, the same gel polymer electrolyte composition as the first gel polymer electrolyte composition prepared in Example 1B was prepared as a second gel polymer electrolyte composition.

[0234] A secondary battery was fabricated in the same manner as in Example 1B, except that the second gel polymer electrolyte composition prepared above was used.

[0235] Experimental example Experimental Example 1B. Resistance Evaluation For the secondary batteries of Examples 1B to 4B, Comparative Example 1B, and Comparative Example 2B, the resistance values ​​calculated using the voltage change (ΔV) measured when discharging at a 2.5C rate for 10 seconds at an SOC of 50% and the results are shown in Table 2 below.

[0236] Experimental Example 2B. Evaluation of thermal stability The secondary batteries of Examples 1B to 4B and Comparative Examples 1B and 2B were fully charged to SOC 100%, and then placed in a hot box and heated at a rate of 0.5°C / min. After the temperature in the hot box reached 150°C, the temperature was maintained for 2 hours to evaluate whether ignition occurred.

[0237] If no ignition occurred, the test was evaluated as "Pass," and if ignition occurred, the test was evaluated as "Fail." The results are shown in Table 2.

[0238] Experimental Example 3B. Observation of Tab Corrosion The secondary batteries manufactured in Examples 1B to 4B and Comparative Examples 1B and 2B were fully charged and then stored at 60° C. for two weeks, and then visually inspected for the occurrence of corrosion on the positive electrode tab.

[0239] If no corrosion occurred on the positive electrode tab, it was rated as "Pass," and if corrosion occurred, it was rated as "Fail." The results are shown in Table 2.

[0240] [Table 2]

[0241] Referring to Table 2, it can be seen that the secondary batteries of Examples 1B to 3B not only have reduced resistance and excellent thermal stability, but also no tab corrosion is observed.

[0242] On the other hand, Example 4B has a slightly increased resistance compared to Examples 1B to 3B, but is excellent in thermal stability and tab corrosion prevention.

[0243] However, in the case of Comparative Example 1B, lithium bis(fluorosulfonyl)imide is not used, and therefore the thermal stability shows very poor results.

[0244] In addition, in Comparative Example 2B, lithium bis(fluorosulfonyl)imide was disposed outside the electrode assembly and contacted the electrode tabs, which was undesirable because corrosion of the electrode tabs was observed. [Explanation of symbols]

[0245] 100 electrode assembly U base unit 110 1st electrode 110a One side end of the first electrode 120 2nd electrode 120a One side end of the second electrode 130 Separator 131 Porous substrate 132a, 132b ceramic coating layer 140 applied adhesive 210 First electrolyte composition 220 Second electrolyte composition 220a Gel polymer electrolyte 300 Battery Case 310 Cup section 320 Cover 400, 500 electrode tabs 610 First electrode reel 620 Second electrode reel 630 Separator Reel 700 tables 810 First Cutter 820 Second Cutter 910 1st transfer device 920 Second transfer device 1010 First Header 1020 Second Header 1101 First electrode sheet 1201 Second electrode sheet 1110 No. 1 nozzle 1120 No. 2 nozzle

Claims

1. (S1) housing the electrode assembly in a battery case; (S2) injecting a first electrolyte composition into the battery case to impregnate the electrode assembly; (S3) injecting a second electrolyte composition into the battery case; (S4) curing the second electrolyte composition; An electrode tab is connected to the electrode assembly, and the electrode tab is extended to the outside of the electrode assembly. the first electrolyte composition includes a first-1 lithium salt including at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and a first solvent; the second electrolyte composition includes an oligomer and a second solvent; The method for producing a secondary battery, wherein the second electrolyte composition does not contain lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

2. The method for producing a secondary battery according to claim 1 , wherein the first electrolyte composition is a liquid electrolyte composition.

3. the first electrolyte composition is a gel polymer electrolyte composition; The method for manufacturing a secondary battery according to claim 1 , wherein the first electrolyte composition further comprises an oligomer.

4. The method for producing a secondary battery according to claim 3 , wherein in the step (S4), both the first electrolyte composition and the second electrolyte composition are cured.

5. The method for manufacturing a secondary battery according to claim 3 , further comprising the step of curing the first electrolyte composition after the step (S2).

6. The first electrolyte composition is lithium hexafluorophosphate (LiPF ６ ), lithium perchlorate (LiClO ４ ), lithium hexafluoroarsenate (LiAsF ６ ), lithium tetrafluoroborate (LiBF ４ ), lithium hexafluoroantimonate (LiSbF ６ ), lithium tetraoxoaluminate (LiAlO ４ ), lithium tetrachloroaluminate (LiAlCl ４ ), lithium trifluoromethanesulfonate (LiCF ３ SO ３ ), lithium nonafluorobutanesulfonate (LiC ４ F ９ SO ３ ), lithium chloride (LiCl), lithium iodide (LiI), lithium bis(oxalato)borate (LiB(C ２ O ４ ) ２ ), lithium bis(pentafluoroethanesulfonyl)imide (LiN(C) ２ F ５ SO ２ ) ２ 2. The method for producing a secondary battery according to claim 1, further comprising a first-second lithium salt containing at least one selected from the group consisting of lithium fluoroalkylborate (LiFAB), lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI).

7. the second electrolyte composition further comprises a second lithium salt; The second lithium salt is lithium hexafluorophosphate (LiPF ６ ), lithium perchlorate (LiClO ４ ), lithium hexafluoroarsenate (LiAsF ６ ), lithium tetrafluoroborate (LiBF ４ ), lithium hexafluoroantimonate (LiSbF ６ ), lithium tetraoxoaluminate (LiAl0 ４ ), lithium tetrachloroaluminate (LiAlCl ４ ), lithium trifluoromethanesulfonate (LiCF ３ SO ３ ), lithium nonafluorobutanesulfonate (LiC ４ F ９ SO ３ ), lithium chloride (LiCl), lithium iodide (LiI), lithium bis(oxalato)borate (LiB(C ２ O ４ ) ２ ), lithium bis(pentafluoroethanesulfonyl)imide (LiN(C) ２ F ５ SO ２ ) ２ 2. The method for producing a secondary battery according to claim 1, wherein the catalyst contains at least one selected from the group consisting of lithium fluoroalkylborate (LiFAB), lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), and lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI).

8. 2. The method for producing a secondary battery according to claim 1, wherein the oligomer includes at least one selected from the group consisting of a fluorine-based oligomer, a polycarbonate-based oligomer, and a polysiloxane-based oligomer.

9. The method for manufacturing a secondary battery according to claim 1 , wherein the second electrolyte composition further comprises a polymerization initiator.

10. The method for manufacturing a secondary battery according to claim 1 , wherein the electrode tab comprises aluminum.

11. The method of claim 1 , wherein the first electrolyte composition is injected so as not to come into contact with the electrode tab.

12. The method of claim 1 , wherein in step (S3), the second electrolyte composition is injected outside the electrode assembly.

13. After step (S4), the first electrolyte composition is disposed inside the electrode assembly, The method of claim 1 , wherein the second electrolyte composition is cured to form a gel polymer electrolyte, and the gel polymer electrolyte is disposed outside the electrode assembly.

14. 14. The method for manufacturing a secondary battery according to claim 1, wherein the electrode assembly is formed by alternately stacking electrodes and separators, and an adhesive is applied to a surface of at least one of the electrodes and the separators to adhere the electrodes and the separators to each other.

15. the separator includes a porous substrate and ceramic coating layers disposed on both sides of the porous substrate; The method for manufacturing a secondary battery according to claim 14 , wherein the ceramic coating layer comprises 92% by weight or more and less than 100% by weight of inorganic particles and more than 0% by weight and 8% by weight or less of a binder.

16. The method of manufacturing a secondary battery according to claim 14 , wherein the adhesive is applied in a plurality of patterns spaced apart from each other.

17. The method for manufacturing a secondary battery according to claim 14 , wherein the adhesive is dissolved in the first electrolyte composition by injecting the first electrolyte composition.

18. The method for manufacturing a secondary battery according to claim 17 , wherein after the adhesive is dissolved, traces of adhesive remain on the surface of one of the separator and the electrode.

19. the electrodes include a first electrode and a second electrode; The electrode assembly is (a) applying the adhesive to at least a portion of the separator and the first electrode; (b) bonding the separator and the first electrode with the applied adhesive; (c) folding one side of the separator to cover the first electrode; (d) applying the adhesive to at least a portion of the separator and the second electrode; (e) adhering the separator and the second electrode with the applied adhesive; and (d) folding the other side of the separator to cover the second electrode. The method for producing the secondary battery according to claim 14 , wherein the secondary battery is produced by a method comprising the steps of:

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