Secondary battery manufacturing method

Abstract

The present invention provides a method for manufacturing a secondary battery, the method including the steps of: manufacturing an electrode assembly in which electrodes and separators are alternately stacked, and an adhesive is applied to a surface of at least one of the electrodes and the separator to adhere the electrodes and the separator to each other; housing the electrode assembly in a battery case; injecting a gel polymer electrolyte composition into the battery case to impregnate the electrode assembly; and curing the gel polymer electrolyte composition, wherein the adhesive includes a first oligomer compound; the separator includes a porous substrate and ceramic coating layers disposed on both sides of the porous substrate, the ceramic coating layers including 92% by weight or more and less than 100% by weight of inorganic particles and more than 0% by weight and less than 8% by weight of a binder; and the gel polymer electrolyte composition includes a lithium salt, an organic solvent, a polymerization initiator, and a second oligomer compound.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0006031, filed January 14, 2022, and all contents disclosed in the documents of this Korean patent application 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 can be manufactured by, for example, housing an electrode assembly in which electrodes and separators are alternately stacked in a battery case, injecting an electrolyte into the battery case, and sealing the battery case.

[0005] The separator generally comprises a porous substrate and ceramic coating layers containing inorganic particles and a binder formed on both sides of the substrate. The binder is typically present in large amounts to facilitate adhesion between the electrode and the separator. However, excessive binder use can increase resistance and increase the thickness of the separator, resulting in a decrease in the energy density of the battery.

[0006] If the binder content in the ceramic coating layer included in the separator is reduced to prevent the above problems, the adhesive strength between the electrode and the separator may be reduced, resulting in a decrease in the rigidity of the cell and a risk of electrode misalignment, resulting in a deterioration in quality.

[0007] On the other hand, 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.

[0008] In light of this, research is being conducted 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 problems with higher interfacial resistance and lower ionic conductivity than liquid electrolytes.

[0009] In this respect, there is a need to develop a secondary battery that simultaneously reduces resistance and improves cell rigidity. Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to solve the above-mentioned problems and to provide a method for manufacturing a secondary battery that can reduce the resistance of the secondary battery and simultaneously improve the cell rigidity and mechanical durability. [Means for solving the problem]

[0011] The present invention provides a method for manufacturing a secondary battery, the method including the steps of: manufacturing an electrode assembly in which electrodes and separators are alternately stacked, and an adhesive is applied to a surface of at least one of the electrodes and the separator to adhere the electrodes and the separator to each other; placing the electrode assembly in a battery case; injecting a gel polymer electrolyte composition into the battery case to impregnate the electrode assembly; and curing the gel polymer electrolyte composition, wherein the adhesive comprises a first oligomer compound; the separator includes a porous substrate and ceramic coating layers disposed on both sides of the porous substrate, the ceramic coating layers comprising 92 wt % or more and less than 100 wt % inorganic particles and more than 0 wt % and 8 wt % or less of a binder; and the gel polymer electrolyte composition includes a lithium salt, an organic solvent, a polymerization initiator, and a second oligomer compound. [Effects of the Invention]

[0012] The method for manufacturing a secondary battery according to the present invention is characterized by manufacturing a secondary battery including an electrode assembly in which electrodes and separators are alternately stacked, and a gel polymer electrolyte, the separator containing inorganic particles and a binder in a specific content. The ceramic coating layer included in the separator contains a low content of binder, thereby preventing an increase in resistance due to an excessive amount of binder. The gel polymer electrolyte can compensate for the decrease in cell rigidity of the secondary battery that accompanies such a decrease in resistance. Therefore, the combination of the above components allows the secondary battery manufactured by the method for manufacturing a secondary battery according to the present invention to reduce the resistance of the secondary battery and simultaneously improve cell rigidity and mechanical durability.

[0013] In addition, a method for manufacturing a secondary battery according to the present invention includes: placing an electrode assembly, in which electrodes and separators are alternately stacked and bonded to each other with an adhesive, in a battery case; injecting a gel polymer electrolyte composition into the battery case; and curing the gel polymer electrolyte composition, wherein the adhesive includes a first oligomer compound. The adhesive includes a first oligomer compound, and the first oligomer compound also participates in curing the gel polymer electrolyte composition. Furthermore, the first oligomer compound not only bonds the electrodes and the separator together, preventing misalignment of the electrodes and separator during electrode assembly manufacturing, but also ultimately polymerizes as the gel polymer electrolyte composition cures, improving cell rigidity. [Brief explanation of the drawings]

[0014] [Figure 1] 2 is a schematic side view of an exemplary electrode assembly illustrating a manufacturing step of the electrode assembly in the manufacturing method of the secondary battery according to the present invention; FIG. [Figure 2] 2 is a schematic plan view of a separator or an electrode for explaining a step of manufacturing an electrode assembly in a method for manufacturing a secondary battery according to the present invention; FIG. [Figure 3] 3 is a schematic side view of a separator illustrating a step of manufacturing an electrode assembly in a method for manufacturing a secondary battery according to the present invention; FIG. [Figure 4] 1A to 1C are diagrams illustrating a method for manufacturing a secondary battery according to the present invention, and are diagrams illustrating a manufacturing process of an electrode assembly. [Figure 5] 1A to 1C are diagrams illustrating a method for manufacturing a secondary battery according to the present invention, and are diagrams illustrating a manufacturing process of an electrode assembly. [Figure 6] 1A to 1C are diagrams illustrating a method for manufacturing a secondary battery according to the present invention, and are diagrams illustrating a manufacturing process of an electrode assembly. [Figure 7] 1A to 1C are diagrams illustrating a method for manufacturing a secondary battery according to the present invention, and are diagrams illustrating a manufacturing process of an electrode assembly. [Figure 8]4A and 4B are views illustrating a step of accommodating an electrode assembly in the method for manufacturing a secondary battery according to the present invention; [Figure 9] 3A and 3B are views illustrating the steps of injecting a gel polymer electrolyte composition and impregnating an electrode assembly in the method for manufacturing a secondary battery according to the present invention; [Figure 10] 3A and 3B are diagrams illustrating a step of curing a gel polymer electrolyte in the method for producing a secondary battery according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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 inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0016] 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.

[0017] 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 components may have the same numerals even if they are shown 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.

[0018] <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.

[0019] The present invention provides a method for manufacturing an electrode assembly 100 in which electrodes 110, 120 and separators 130 are alternately stacked, and an adhesive 140 is applied to a 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; a method for manufacturing an electrode assembly 100 in which the electrodes 110, 120 and the separator 130 are adhered to each other; a method for accommodating the electrode assembly 100 in a battery case 300; a method for impregnating the electrode assembly 100 with a gel polymer electrolyte composition 200; and a method for curing the gel polymer electrolyte composition 200. the adhesive (140) comprises a first oligomer compound; the separator (130) comprises a porous substrate (131) and ceramic coating layers (132a, 132b) disposed on both sides of the porous substrate (131); the ceramic coating layers (132a, 132b) comprise 92 wt % or more and less than 100 wt % inorganic particles and more than 0 wt % and not more than 8 wt % of a binder; and the gel polymer electrolyte composition (200) comprises a lithium salt, an organic solvent, a polymerization initiator, and a second oligomer compound.

[0020] (1) Manufacturing steps of the electrode assembly Referring to Figures 1 and 2, first, an electrode assembly 100 is manufactured in which electrodes 110, 120 and separators 130 are alternately stacked, and an adhesive 140 is applied 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 or 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-c2 M c2Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3 Examples of suitable positive electrodes include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (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 Li metal positive electrode.

[0028] The binder contained in the electrode is selected from the group consisting of 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] 1 and 2, the electrode assembly 100 includes separators 130. The separators are stacked alternately with the electrodes.

[0032] 1, the separator 130 may be bent or folded in a zigzag pattern 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 bent to wrap around one end 110a of the first electrode 110 and then bent again to wrap around one end 110a of the second electrode 120 opposite the one end 110a of the first electrode 110. By repeating this folding process, the separator 130 may be bent or 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. 3, the separator 130 includes 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, or a copolymer or mixture of two or more of these, or a laminate structure of two or more layers thereof. The porous substrate 131 may be a porous film, nonwoven fabric, or a laminate structure of two or more layers thereof containing the polyolefin-based resin.

[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 serve as a kind of spacer that can maintain the physical shape of the porous substrate and minimize thermal shrinkage.

[0041] The inorganic particles can be used without any particular limitation as long as they are electrochemically stable within the operating voltage range of the battery (e.g., 0 V to 5 V based on Li / Li+) and do not cause oxidation and / or reduction reactions, i.e., electrochemical reactions. The inorganic particles can be lithium phosphate (Li3PO4); lithium titanium phosphate (Lix 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), such as 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5 of (LiAlTiP) x O y series glass (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 such as lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5); Lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2); SiS2 - based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4); P2S5 - based glass (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 of these, 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] Here, 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 cause an increase in the resistance of the secondary battery. On the other hand, if the binder is contained within the above range, there is a risk of a decrease in the cell rigidity of the secondary battery due to a decrease in the adhesive strength between the electrode and the separator. However, as described below, the present invention uses a separator having the above-mentioned characteristics in combination with a gel polymer electrolyte, thereby simultaneously improving the resistance of the secondary battery and improving the 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 disperses well with the inorganic particles during the preparation of the ceramic coating layer, thereby preventing the ceramic coating layer from separating into layers, with the binder in an upper layer and the inorganic particles in a lower layer. Such layer separation can result in interference with 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 can 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 examples include dip coating, die coating, roll coating, comma coating, and gravure coating. Specifically, gravure coating can be used. The drying method after application of the ceramic coating layer-forming composition can 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 low resistance.

[0054] In the electrode assembly 100, an adhesive 140 is applied to the surface of at least one of the electrodes 110 and 120 and the separator 130, thereby adhering the electrodes 110 and 120 and the separator 130 to each other.

[0055] The adhesive 140 may be introduced to bond the electrodes 110, 120 and the separator 130. Specifically, the adhesive 140 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 has a reduced binder content, which may result in insufficient adhesion between the electrodes and the separator during manufacturing of the secondary battery. The adhesive 140 compensates for this problem, easily bonding the electrodes and the separator, preventing separator misalignment during the manufacturing process of the electrode assembly and improving process efficiency and quality.

[0056] The adhesive includes a first oligomeric compound.

[0057] As used herein, "oligomeric compound" may refer to a compound in which about 10 or fewer monomers are polymerized, and the "oligomeric compound" may contain a crosslinkable group.

[0058] The first oligomer compound is included in the adhesive as an adhesive component for adhering the electrodes and the separator. After being used as an adhesive component for the electrodes and the separator, the first oligomer compound can be dissolved and polymerized by injecting the gel polymer electrolyte composition to become a component of the gel polymer electrolyte.

[0059] The first oligomer compound 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.

[0060] For example, the fluorine-based oligomer may specifically include a unit derived from a fluorine-based monomer. The fluorine-based oligomer has the advantage that the fluorine-based functional group contained therein can further improve battery stability by suppressing the generation of oxygen radicals caused by decomposition of the positive electrode active material, and that it has 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.

[0061] 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.

[0062] 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.

[0063] The weight average molecular weight of the first oligomer compound may be 1,000 g / mol to 50,000 g / mol, specifically 4,500 g / mol to 30,000 g / mol.

[0064] The adhesive 140 is used to manufacture the electrode assembly 100 by bonding the electrodes 110, 120 and the separator 130, and can be dissolved in the organic solvent contained in the gel polymer electrolyte composition 200 after the electrode assembly 100 is housed in the battery case 300 and the gel polymer electrolyte composition 200 is injected into the battery case 300. Because the adhesive 140 according to the present invention is dissolved after being used to manufacture the electrode assembly 100, it not only makes it possible to easily bond the electrodes 110, 120 and the separator 130 without increasing the amount of binder in the separator 130, but also prevents an increase in the thickness of the separator due to an increase in the amount of binder, thereby further improving the energy density of the secondary battery.

[0065] 2, the adhesive 140 may be applied in a plurality of patterns spaced apart from one another. Specifically, the adhesive 140 may be applied on the 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 the surface of at least one of the electrodes and the separator in a plurality of dots spaced apart from one another.

[0066] The adhesive application area may be more than 0% and 1% or less, specifically 0.0001% to 0.05%, of the surface area 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 can cause an increase in resistance.

[0067] An exemplary method for manufacturing the electrode assembly will now be described with reference to FIGS.

[0068] Specifically, referring to Figures 4 to 7, 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 (f).

[0069] (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 (f) folding the other side of the separator 130 to cover the second electrode 120;

[0070] 4, 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. 4 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.

[0071] Specifically, as shown in FIG. 4, the separator 130 may be unwound from a separator reel 630 and placed on the top surface of a table 700 .

[0072] Referring to FIG. 5, the separator 130 and the first electrode 110 are bonded together by the applied adhesive 140 .

[0073] 5, 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 110. 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.

[0074] Referring to FIG. 6, 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.

[0075] 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.

[0076] 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. 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 second electrode 120; or both the separator 130 and the second electrode 120.

[0077] Referring to FIG. 7, 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.

[0078] 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.

[0079] 7, the second electrode 120 may be formed by cutting a second 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.

[0080] 7, 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.

[0081] In the case of an electrode assembly including a separator folded in a zigzag pattern 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 can significantly prevent 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 complementing the adhesive strength of the separator in the present invention, which contains a low binder content.

[0082] (2) Electrode assembly accommodation step Referring to FIG. 8, the electrode assembly 100 is housed in a battery case 300 .

[0083] For ease of explanation, FIG. 8 shows a simplified representation of the electrode assembly.

[0084] The battery case 300 may be provided to accommodate the electrode assembly 100 and the gel polymer electrolyte 200 .

[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 that is a receiving space for receiving the electrode assembly.

[0088] The battery case 300 may include a cover 310, and after the electrode assembly is housed and the gel polymer electrolyte composition is cured and gelled, the battery case 300 may be sealed with the cover to manufacture a sealed secondary battery.

[0089] As shown in Fig. 8, a plurality of electrode tabs 400, 500 may be connected to the electrode assembly 100. Specifically, the plurality of electrode tabs 400, 500 may be 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. Also, while Fig. 8 illustrates two electrode tabs 400, 500 arranged in different directions relative 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. The plurality of electrode tabs 400, 500 may be positive electrode tabs and negative electrode tabs and may be connected to the positive and negative electrodes, respectively.

[0090] (3) Injection of gel polymer electrolyte composition and impregnation of electrode assembly 9, a gel polymer electrolyte composition 200 is injected into the battery case 300 to impregnate the electrode assembly 100. The gel polymer electrolyte composition 200 is impregnated into the electrode assembly 100, hardened, and disposed inside and outside the electrode assembly.

[0091] The gel polymer electrolyte 200a cured from the gel polymer electrolyte composition 200 has no fluidity, and the use of a gelled electrolyte can improve the cell rigidity of a secondary battery. In particular, the present invention makes it possible to realize a secondary battery with reduced resistance and improved cell rigidity by using the gel polymer electrolyte together with the separator described above. On the other hand, when the separator and liquid electrolyte described above are used, the cell rigidity is excessively reduced, which can lead to cell distortion, separator misalignment, and other problems that can lead to poor processability and product defects, reduced safety, and the risk of secondary battery explosion.

[0092] The gel polymer electrolyte composition 200 includes a lithium salt, an organic solvent, a polymerization initiator, and a second oligomer compound.

[0093] The lithium salt can be used to provide lithium ions to a secondary battery.

[0094] The lithium salt can be any compound capable of providing lithium ions used in secondary batteries. Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(C, F, SO), LiN(C, F, SO), LiN(CF, SO), LiCl, LiI, or LiB(C, O) . The lithium salt concentration is preferably in the range of 0.1 M to 5.0 M, and more preferably 0.1 M to 3.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0095] The polymerization initiator may be used to polymerize the oligomer compound contained in the gel polymer electrolyte composition to form a polymer network bound in a three-dimensional structure.

[0096] The polymerization initiator may be decomposed in the presence of heat or light to form radicals, thereby polymerizing the oligomer compound. Specifically, the polymerization initiator may polymerize the second oligomer compound contained in the gel polymer electrolyte composition and the first oligomer compound dissolved in the gel polymer electrolyte composition after being used to assemble the electrode assembly.

[0097] The polymerization initiator may be a photopolymerization initiator or a thermal polymerization initiator depending on the polymerization method.

[0098] 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.

[0099] 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).

[0100] 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.

[0101] The second oligomeric compound can be the same type of first oligomeric compound as described above. The first oligomeric compound and the second oligomeric compound can be the same or different.

[0102] Specifically, the second oligomer compound 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.

[0103] 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.

[0104] In addition, the polycarbonate oligomer has an affinity with the positive electrode, has a structure similar to that of an organic electrolyte, and has the advantage of being excellent in ionic conductivity or ionic dissociation.

[0105] 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.

[0106] The weight average molecular weight of the second oligomer compound may be 1,000 g / mol to 50,000 g / mol, specifically 4,500 g / mol to 30,000 g / mol.

[0107] The second oligomer compound may be included in the gel polymer electrolyte composition in an amount of 1 wt % to 20 wt %, specifically 3 wt % to 10 wt %, and within this range, the effect of improving the cell rigidity of the secondary battery may be excellent, and the ionic conductivity and lithium ion mobility of the gel polymer electrolyte may be excellent. The organic solvent may be used to dissolve or disperse the lithium salt and the second oligomer compound.

[0108] The organic solvent is one that is commonly used in secondary batteries, and examples thereof include ethers, esters (acetates, propionates), amides, linear or cyclic carbonates, and nitriles (acetonitrile, SN, etc.), which may be used alone or in combination of two or more.

[0109] 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.

[0110] 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.

[0111] 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 effectively dissociate lithium salts in the electrolyte. When such cyclic carbonates are mixed with a linear carbonate having low viscosity and low dielectric constant, 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.

[0112] Furthermore, among the organic solvents, the ester 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.

[0113] The first oligomer compound may be dissolved in the gel polymer electrolyte composition by injecting the gel polymer electrolyte composition. Specifically, the first oligomer compound used in assembling the electrode assembly may be dissolved in the gel polymer electrolyte composition by injecting the gel polymer electrolyte composition. As described below, the first oligomer compound is polymerized when the gel polymer electrolyte composition is cured.

[0114] The dissolution of the first oligomer compound may be facilitated by applying pressure during activation and degassing processes commonly performed in the secondary battery manufacturing process. The activation process is a process of forming a solid electrolyte interface layer (SEI layer) on the surface of the electrode plate of the electrode assembly through a charging process in an initial secondary battery, thereby allowing the secondary battery to supply power. The activation process may be performed at a temperature of 45°C or higher, specifically, 50°C to 70°C. The degassing process is a process of discharging gas generated during the activation process to the outside, and may include applying pressure to the secondary battery using a jig or the like. The first oligomer compound may be more smoothly dissolved or removed by the temperature increase and pressure.

[0115] The gel polymer electrolyte composition 200 is poured into the battery case 300, and the electrode assembly 100 is impregnated with the gel polymer electrolyte composition 200. The impregnation 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 60 hours.

[0116] (4) Curing step of gel polymer electrolyte composition Next, the gel polymer electrolyte composition 200 is cured, as shown in Figure 10. Specifically, the gel polymer electrolyte composition 200 is cured to form a gel polymer electrolyte 200a.

[0117] When the gel polymer electrolyte composition is cured, the oligomer compounds are crosslinked and cured to form a gel-like solidified electrolyte (gel polymer electrolyte). Specifically, the second oligomer compound contained in the gel polymer electrolyte composition and the first oligomer compound dissolved by the gel polymer electrolyte composition are crosslinked or polymerized with each other during the curing process to form a gelled electrolyte.

[0118] The gel polymer electrolyte formed by curing the gel polymer electrolyte composition can help improve the cell rigidity of a secondary battery. As described above, the separator according to the present invention can help reduce resistance by including a ceramic coating layer using a low content of binder. As a result, a secondary battery combining the separator and the gel polymer electrolyte can simultaneously reduce resistance and improve cell rigidity.

[0119] Here, the gel polymer electrolyte composition may be cured 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.

[0120] Meanwhile, the curing may be performed in a sealed state of the battery case 300. For example, the electrode assembly 100 and the battery case 300 containing the gel polymer electrolyte composition 200 may be sealed with a cover or the like, and then heat-treated to thermally cure the gel polymer electrolyte composition.

[0121] After the curing or sealing and curing, further steps such as activation, degassing, and resealing, which are known in the art, may be performed.

[0122] 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.

[0123] Examples and Comparative Examples Example 1 1. Separator manufacturing As inorganic particles, Al2O3 (average particle size (D 50 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.

[0124] 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).

[0125] 2. Manufacturing the electrode assembly The separator reel on which the separator was wound was unwound and placed on a table. An adhesive was applied to the separator in a pattern of spaced dots using a first nozzle. The adhesive used was a first oligomer compound, polycarbonate (weight average molecular weight Mw: 20,000). Then, the positive electrode sheet was unwound from the first electrode reel on which the separator was wound and cut with a first cutter to produce a positive electrode. The positive electrode was then transported by a first transport device and attached to a first header. The first header was moved toward the table, and the positive electrode was attached to the separator.

[0126] Next, the table was moved to the side, and the separator was folded to one side to cover the positive electrode.

[0127] 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.

[0128] Next, the negative electrode sheet was unwound from the second electrode reel and cut with a second cutter to produce a negative electrode, which was then 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).

[0129] Next, the table was moved sideways again, and the separator was folded to the other side to cover the negative electrode.

[0130] 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.

[0131] 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 resulting aluminum current collector was dried and rolled to form a positive electrode active material layer.

[0132] 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.

[0133] 3. Preparation of Gel Polymer Electrolyte Composition The gel polymer electrolyte composition was produced by mixing a polycarbonate oligomer (weight average molecular weight Mw: 20,000) as an oligomer, LiPF6 as a lithium salt, and AIBN (Azobisisobutyronitrile) as a polymerization initiator in a solvent.

[0134] The solvent was a mixture of ethyl carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, the lithium salt was contained in the gel polymer electrolyte composition at a concentration of 1.0 M, the oligomer was contained in the gel polymer electrolyte composition at 5 wt %, and the polymerization initiator was contained in the gel polymer electrolyte composition at 0.6 parts by weight relative to 100 parts by weight of the oligomer.

[0135] 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.

[0136] Next, a gel polymer electrolyte composition was injected into the battery case containing the electrode assembly, and after the injection of the gel polymer electrolyte composition, the battery case was vacuum sealed.

[0137] By injecting the gel polymer electrolyte composition, the adhesive present in the electrode assembly was dissolved by the solvent of the gel polymer electrolyte composition.

[0138] Next, the gel polymer electrolyte composition injected into the battery case was cured by heat treatment at a temperature of 60° C. for 5 hours.

[0139] The battery case was then cooled, sealed, and degassed to produce a secondary battery having a thickness of 0.8 cm.

[0140] Comparative Example 1 1. Separator manufacturing The same separator as that produced in Example 1 was used.

[0141] 2. Manufacturing the electrode assembly An electrode assembly was manufactured in the same manner as in Example 1, except that polyvinylidene fluoride (PVdF) was used as the adhesive.

[0142] 3. Preparation of Gel Polymer Electrolyte Composition The same gel polymer electrolyte composition as in Example 1 was prepared.

[0143] 4. Secondary battery manufacturing Except for using the electrode assembly prepared above, a secondary battery was fabricated in the same manner as in Example 1. The thickness of the secondary battery was 0.8 cm.

[0144] Comparative Example 2 1. Separator manufacturing As inorganic particles, Al2O3 (average particle size (D 50 ):0.5 μm) and PVdF as a binder were added to acetone as a solvent in a weight ratio of 70:30 to prepare a composition for forming a ceramic coating layer.

[0145] 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: vol%) by gravure coating and dried to form ceramic coating layers (thickness of one layer: 3 μm), thereby producing a separator (thickness: 15 μm = 3 μm + 9 μm + 3 μm).

[0146] 2. Manufacturing the electrode assembly A plurality of separators manufactured as described above were prepared. In addition, a plurality of positive electrodes and negative electrodes identical to those manufactured in Example 1 were prepared.

[0147] The first oligomer compound used as an adhesive in Example 1 was applied to one separator in a pattern of spaced apart dots. A positive electrode was attached to the separator. The first oligomer compound was applied to the positive electrode in a pattern of spaced apart dots, and another separator was attached to the positive electrode. Next, the first oligomer compound was applied to the separator in a pattern of spaced apart dots, and a negative electrode was attached to the separator.

[0148] The above process was repeated to fabricate an electrode assembly in which 18 basic units, each having a separator / positive electrode / separator / negative electrode stacked in that order, were stacked. Here, the two separators in each basic unit were separate separators and were not folded in a zigzag pattern as in Example 1.

[0149] 3. Preparation of Gel Polymer Electrolyte Composition The same gel polymer electrolyte composition as in Example 1 was prepared.

[0150] 4. Secondary battery manufacturing Except for using the electrode assembly prepared above, a secondary battery was fabricated in the same manner as in Example 1. The thickness of the secondary battery was 0.8 cm.

[0151] Experimental Example 1.Resistance evaluation (1) Measurement of initial resistance For the secondary batteries of Example 1, Comparative Example 1, and Comparative Example 2, the initial resistance values ​​calculated using the voltage change (ΔV) measured when discharging at a 0.33 C rate (C rate) for 30 seconds at an SOC of 100% are shown in Table 1 below.

[0152] (2) Resistance measurement after 100 charge / discharge cycles The secondary batteries of Example 1, Comparative Example 1, and Comparative Example 2 were subjected to 100 cycles of charge and discharge under the following charge and discharge conditions. Table 1 shows the 100-cycle resistance values ​​calculated using the voltage change (ΔV) measured when discharging for 30 seconds at a 0.33 C rate (C rate) at 100% SOC.

[0153] (3) Calculation of the resistance increase rate The resistance increase rate after 100 charge / discharge cycles was evaluated using the following formula and is shown in Table 1 below.

[0154] Resistance increase rate (%) = (resistance after 100 cycles - initial resistance) / initial resistance x 100

[0155] 2. Evaluation of life performance The secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2 manufactured as described above were charged and discharged 100 times at 45° C. under the following conditions, and the capacity retention rate after 100 cycles was evaluated.

[0156] *Charging and discharging conditions Charging: CC / CV mode; 0.33C; 4.2V, 1 / 20C cut-off Discharge: CC mode; 0.33C; 2.5V cut-off

[0157] The discharge capacity for the 100th cycle under the above experimental conditions was divided by the discharge capacity for the first cycle, and the value was defined as the capacity retention rate. The results are shown in Table 1 below.

[0158] 3. Cell Stiffness Measurement Using the three-point bending method, a downward force was applied to the center of each secondary battery at a rate of 10 mm / min, resulting in a displacement of 2 mm, and the stress value was measured. A preload of 30 gf was applied, and the experiment was conducted at room temperature. The stress value was measured using a universal testing machine (UTM). The results are shown in Table 1 below.

[0159] 4. Ignition temperature measurement test The secondary batteries of Example 1, Comparative Example 1, and Comparative Example 2 were fully charged to SOC 100%, then placed in a hot box and heated at a rate of 0.5°C / min. The ignition temperature was measured and shown in Table 1.

[0160] [Table 1]

[0161] Referring to Table 1, it can be seen that the secondary battery manufactured in Example 1 has low resistance and resistance increase rate, long life characteristics, and excellent thermal stability.

[0162] On the other hand, the secondary battery of Comparative Example 1 exhibits a higher resistance and resistance increase rate than those of Example 1. This is believed to be because no oligomer compound was used as the adhesive in manufacturing the electrode assembly.

[0163] The secondary battery of Comparative Example 2 used both a separator containing a large amount of binder and a gel polymer electrolyte. As a result, the secondary battery manufactured in Comparative Example 2 had significantly higher resistance and significantly reduced lifespan characteristics compared to Example 1. Meanwhile, the thermal stability of Comparative Example 2 was significantly reduced, which is believed to be due to the relatively low content of inorganic particles in the separator, which was unable to adequately prevent thermal shrinkage and short circuits of the separator. [Explanation of symbols]

[0164] 10 Secondary battery 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 200 Gel polymer electrolyte 300 Battery Case 310 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. manufacturing an electrode assembly in which electrodes and separators are alternately stacked, 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; housing the electrode assembly in a battery case; injecting a gel polymer electrolyte composition into the battery case to impregnate the electrode assembly; and curing the gel polymer electrolyte composition. the adhesive comprises a first oligomeric compound; the separator includes a porous substrate and ceramic coating layers disposed on both sides of the porous substrate; the ceramic coating layer comprises 92 wt % or more and less than 100 wt % of inorganic particles and more than 0 wt % and 8 wt % or less of a binder; The gel polymer electrolyte composition comprises a lithium salt, an organic solvent, a polymerization initiator, and a second oligomer compound.

2. By injecting the gel polymer electrolyte composition, the first oligomer compound is dissolved in the gel polymer electrolyte composition, The method for manufacturing a secondary battery according to claim 1 , wherein the first oligomer compound is cured together with the gel polymer electrolyte composition when the gel polymer electrolyte composition is cured.

3. The method of manufacturing a secondary battery according to claim 1 , wherein the adhesive is applied in a plurality of patterns spaced apart from each other.

4. The method for manufacturing a secondary battery according to claim 1 , wherein the adhesive is applied to an area that is greater than 0% and less than or equal to 1% of the area of ​​the surface where the separator and the electrode contact each other.

5. 2. The method for manufacturing a secondary battery according to claim 1, wherein the ceramic coating layer comprises 93 to 98% by weight of inorganic particles and 2 to 7% by weight of a binder.

6. The method for producing a secondary battery according to claim 1 , wherein the binder includes an acrylic binder.

7. 7. The method for producing a secondary battery according to claim 6, wherein the acrylic binder contains at least one selected from the group consisting of a copolymer of ethylhexyl acrylate and methyl methacrylate; polymethyl methacrylate; polyethylhexyl acrylate; polybutyl acrylate; polyacrylonitrile; and a copolymer of butyl acrylate and methyl methacrylate.

8. The method for manufacturing a secondary battery according to claim 1, wherein the ceramic coating layer has a thickness of 0.1 μm to 10 μm.

9. 2. The method for manufacturing a secondary battery according to claim 1, wherein the separator has a thickness of 1 μm to 20 μm.

10. 10. The method for producing a secondary battery according to claim 1, wherein the first oligomer compound and the second oligomer compound each independently comprise at least one selected from the group consisting of a fluorine-based oligomer, a polycarbonate-based oligomer, and a polysiloxane-based oligomer.

11. the electrodes include a first electrode and a second electrode; The method for manufacturing a secondary battery according to claim 1, wherein the electrode assembly is manufactured by a method including the following steps (a) to (f): (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 (f) folding the other side of the separator to cover the second electrode.

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