Secondary battery and method for manufacturing the same

Abstract

To provide a secondary battery in which the resistance of the secondary battery is reduced while simultaneously improving cell rigidity and mechanical durability. To provide a method for manufacturing a secondary battery in which the resistance of the secondary battery is reduced while simultaneously improving cell rigidity and mechanical durability. [Solution] The present invention relates to a secondary battery comprising an electrode assembly including alternately stacked electrodes and a separator, a gel polymer electrolyte, and a battery case housing the electrode assembly and the gel polymer electrolyte, wherein the separator includes a porous substrate and a ceramic coating layer disposed on both sides of the porous substrate, and the ceramic coating layer comprises 92% by weight or more and less than 100% by weight of inorganic particles and a binder greater than 0% by weight and less than or equal to 8% by weight.

Description

[Technical Field]

[0001] This application claims priority rights under Korean Patent Application No. 10-2022-0006030 dated January 14, 2022, and Korean Patent Application No. 10-2022-0006033 dated January 14, 2022, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein by reference.

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

[0003] With the development of technologies related to electronic devices and the increasing demand, the demand for secondary batteries as an energy source has increased rapidly. Among these secondary batteries, lithium-ion batteries, which have high energy density and voltage, have been commercialized and are widely used.

[0004] The aforementioned secondary battery can be manufactured, for example, by 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 it.

[0005] Here, the separator is generally one in which a ceramic coating layer containing inorganic particles and a binder is formed on both sides of a porous substrate. Here, the binder is generally included in large quantities to facilitate adhesion between the electrode and the separator, but in this case, there is a problem that the resistance increases due to the excessive use of binder and the energy density of the battery decreases due to the increase in the thickness of the separator.

[0006] On the other hand, if the binder content in the ceramic coating layer contained in the separator is reduced to prevent the aforementioned problems, the rigidity of the cell may decrease due to a reduction in the adhesive strength between the electrode and the separator, potentially leading to a decline in quality, such as misalignment of the electrodes.

[0007] In such aspects, there is a situation where it is necessary to develop a secondary battery with reduced resistance and improved cell rigidity at the same time.

Summary of the Invention

Problems to be Solved by the Invention

[0008] One problem of the present invention is to solve the above problems, and to provide a secondary battery in which the resistance of the secondary battery is reduced and the cell rigidity and mechanical durability are improved at the same time.

[0009] Another problem of the present invention is to provide a method for manufacturing a secondary battery in which the resistance of the secondary battery is reduced and the cell rigidity and mechanical durability are improved at the same time.

Means for Solving the Problems

[0010] The present invention includes an electrode assembly including electrodes and separators laminated alternately, a gel polymer electrolyte, and a battery case housing the electrode assembly and the gel polymer electrolyte. The separator includes a porous base material and ceramic coating layers disposed on both surfaces of the porous base material. The ceramic coating layer includes inorganic particles of 92% by weight or more and less than 100% by weight and a binder of more than 0% by weight and 8% by weight or less, and provides a secondary battery.

[0011] The present invention also includes steps of housing an electrode assembly in the battery case, injecting a gel polymer electrolyte composition into the battery case, curing the gel polymer electrolyte, and sealing the battery case. The electrode assembly includes a first electrode and a second electrode laminated alternately, and a separator interposed between the plurality of electrodes. The separator is zigzag-folded to wrap one end of any one of the first electrodes and one end of any one of the second electrodes. The separator includes a porous base material and ceramic coating layers disposed on both surfaces of the porous base material. The ceramic coating layer includes inorganic particles of 92% by weight or more and less than 100% by weight and a binder of more than 0% and 8% by weight or less. The present invention provides a method for manufacturing a secondary battery, wherein the electrode assembly is manufactured by a method including the following steps (a) to (d). (a) Placing the first electrode on the separator; (b) Folding one side of the separator to cover the first electrode; (c) Placing a second electrode on the opposite surface of the separator where the separator and the first electrode contact each other; and (d) Folding the other side of the separator to cover the second electrode. [Advantages of the Invention][[ID=ll]]

[0012] The secondary battery according to the present invention includes an electrode assembly in which electrodes and separators are laminated alternately and a gel polymer electrolyte. The ceramic coating layer included in the separator contains inorganic particles and a binder in specific contents. Since the ceramic coating layer included in the separator contains a small amount of binder, an increase in resistance due to an excess of binder can be prevented, and the gel polymer electrolyte can complement a decrease in cell rigidity of the secondary battery accompanying such a reduction in resistance. Therefore, the secondary battery according to the present invention can simultaneously improve the reduction in resistance of the secondary battery and the cell rigidity and mechanical durability by the combination of the above-described configurations.

[0013] Furthermore, the method for manufacturing a secondary battery according to the present invention is a method for manufacturing a secondary battery comprising an electrode assembly including a plurality of electrodes and a separator interposed between the electrodes and folded in a zigzag shape, and a gel polymer electrolyte, characterized in that the ceramic coating layer contained in the separator contains inorganic particles and a binder in specific amounts. Since the ceramic coating layer contained in the separator contains a small amount of binder, an increase in resistance due to an excess of binder can be prevented, and the gel polymer electrolyte can compensate for the decrease in cell rigidity of the secondary battery that occurs with such a reduction in resistance. Therefore, a secondary battery manufactured by the method for manufacturing a secondary battery according to the present invention can simultaneously reduce the resistance of the secondary battery and improve cell rigidity and mechanical durability through the combination of the above configurations. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic side view of a secondary battery according to one embodiment of the present invention. [Figure 2] This is a schematic side view of an electrode assembly included in a secondary battery according to one embodiment of the present invention. [Figure 3] This is a schematic side view of a separator included in a secondary battery according to one embodiment of the present invention. [Figure 4] This is a schematic side view of an electrode assembly included in a secondary battery according to another embodiment of the present invention. [Figure 5] This is a plan view of a separator or electrode illustrating the application marks of adhesive contained in a secondary battery according to another embodiment of the present invention. [Figure 6] This is a schematic side view of an electrode assembly included in a secondary battery according to yet another embodiment of the present invention. [Figure 7] This is a diagram illustrating the manufacturing method of the secondary battery of the present invention. [Figure 8] This is a diagram illustrating the manufacturing method of the secondary battery of the present invention. [Figure 9] This is a diagram illustrating the manufacturing method of the secondary battery of the present invention. [Figure 10] This is a diagram illustrating the manufacturing method of the secondary battery of the present invention. [Figure 11] This is a photograph of the surface of the separator included in the secondary battery of Example 1. [Figure 12] This is a photograph of the surface of the separator contained in the secondary battery of Comparative Example 1. [Modes for carrying out the invention]

[0015] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[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 The particle size can be measured, for example, using the laser diffraction method. This laser diffraction method can generally measure particle sizes from the submicron region to several millimeters in size, and can yield highly reproducible and high-resolution results.

[0017] The secondary battery of the present invention will be described in detail below with reference to the drawings. When assigning reference numerals to the components in each drawing, the same component may be given the same reference numeral as much as possible, even if it is shown in different drawings. Furthermore, when describing the present invention, if it is determined that a specific description of a related known configuration or function would obscure the gist of the present invention, such a detailed description may be omitted.

[0018] <Secondary battery> This invention relates to a secondary battery, specifically a lithium secondary battery.

[0019] The following describes a secondary battery according to one embodiment of the present invention with reference to Figures 1 to 3. Specifically, Figure 1 is a schematic side view illustrating a secondary battery according to one embodiment of the present invention, Figure 2 is a schematic side view illustrating an electrode assembly included in a secondary battery according to one embodiment of the present invention, and Figure 3 is a schematic side view illustrating a separator included in a secondary battery according to one embodiment of the present invention.

[0020] Referring to Figures 1 to 3, a secondary battery 10 according to one embodiment of the present invention includes an electrode assembly 100 including alternately stacked electrodes 110, 120 and a separator 130, a gel polymer electrolyte 200, and a battery case 300 that houses the electrode assembly 100 and the gel polymer electrolyte 200, wherein the separator 130 includes a porous substrate 131 and ceramic coating layers 132a and 132b disposed on both sides of the porous substrate 131, and the ceramic coating layers 132a and 132b include inorganic particles of 92% by weight or more and less than 100% by weight and a binder of more than 0% by weight and 8% by weight or less.

[0021] [Electrode assembly 100] For the sake of explanation, Figure 1 shows a simplified view of the electrode assembly 100, and Figure 2 shows a more detailed view of the electrode assembly 100.

[0022] The electrode assembly 100 includes electrodes 110, 120 and a separator 130. Here, the electrodes 110, 120 and the separator 130 can be stacked alternately.

[0023] The electrode assembly 100 may include a plurality of electrodes 110, 120 stacked vertically. The electrodes 110, 120 may be two or more. In this specification, "vertical direction" may mean a direction vertical with respect to the ground, and is used to describe the direction of stacking of electrodes, and is not intended to limit the angle of the stacking direction.

[0024] Specifically, the electrodes 110 and 120 are multiple in number, the multiple electrodes 110 and 120 are stacked vertically, and the separator 130 can be bent in a zigzag shape so as to wrap around one end of any of the electrodes 110 and 120.

[0025] The electrodes 110 and 120 may include a first electrode 110 and a second electrode 120. As illustrated in Figure 2, the first electrode 110 and the second electrode 120 may be stacked alternately on top of each other with a separator 130 in between. The first electrode 110 may be the positive electrode and the second electrode 120 may be the negative electrode. Or the first electrode 110 may be the negative electrode and the second electrode 120 may be the positive electrode. There may be one or more first electrodes and two or more second electrodes, respectively.

[0026] The electrode assembly 100 can be a stack-type electrode assembly in which one or more, specifically two or more, basic units, each consisting of a first electrode 110, a separator 130, a second electrode 120, and a separator 130 stacked in that order, are stacked. Alternatively, the electrode assembly can be a zigzag-stack type electrode assembly in which the separator is bent or folded in a zigzag shape, and one or more, specifically two or more, basic units, each consisting of a first electrode, a separator, a second electrode, and a separator stacked in that order, are stacked.

[0027] The first electrode 110 and the second electrode 120 may have a structure in which an active material slurry is coated onto a current collector. The first electrode 110 and the second electrode 120 may have a structure in which the active material slurry is coated onto both sides of the current collector, dried, and rolled. The active material slurry can be formed by adding granular active material, conductive material, binder, etc., to a solvent and stirring. Active materials, conductive materials, binders, etc., used for positive or negative electrodes in this art can be used for the first electrode 110 and the second electrode 120 without limitation.

[0028] 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 may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy. For example, if electrodes 110 and 120 are positive electrodes, the current collector used for electrodes 110 and 120 may include aluminum, and if electrodes 110 and 120 are negative electrodes, the current collector used for electrodes 110 and 120 may include copper.

[0029] The current collector can be used in various forms, such as films, sheets, foils, nets, meshes, porous materials, foams, and nonwoven fabrics. The current collector may also include a polymer layer and metal layers disposed on both sides of the polymer layer, wherein the metal layers may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloys.

[0030] Specifically, when electrodes 110 and 120 are negative electrodes, the negative electrode active material can be, for example, a compound capable of reversible intercalation and deintercalation of lithium. Specific examples of negative electrode active materials 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, or Al alloys; and SiO2. βExamples include metal oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more mixtures of these can be used. A metallic lithium thin film may also be used as the negative electrode active material. In addition, both low-crystallinity carbon and high-crystallinity carbon can be used as the carbon material. Examples of low-crystalline carbon include soft carbon and hard carbon, while examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0031] Furthermore, 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 can 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; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2Ni-site type lithium nickel oxide represented as Mc2O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.3); chemical formula LiMn 2-c3 Lithium manganese composite oxides represented as Mc3O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 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); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited to these. The positive electrode may be a Li metal positive electrode.

[0032] The binders contained in the electrode 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 one selected from the group consisting of sucrose, pullulan, polymethyl methacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyarylate, and low molecular weight compounds with a molecular weight of 10,000 g / mol or less, or a mixture of two or more of these.

[0033] 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 is conductive. Examples of such materials include 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 fibers and metal fibers; 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.

[0034] An example of a thickening agent included in the electrode is carboxymethylcellulose (CMC).

[0035] As illustrated in Figure 2, the electrode assembly 100 includes a separator 130. The separator 130 can be bent or folded in a zigzag pattern to enclose one end of either electrode 110 or 120. For example, as illustrated in Figure 2, when the first electrode 110 and the second electrode 120 are stacked alternately, the separator 130 can be bent to enclose one end 110a of the first electrode 110, and then bent again to enclose one end 120a of the second electrode 120, which is on the opposite side of the first end 110a of the first electrode 110. By repeating such bending, the separator 130 can be bent or folded in a zigzag pattern. The electrode assembly 100 may include one separator 130.

[0036] The electrode assembly 100 can be a zigzag stack type electrode assembly in which the separator 130 is bent or folded in a zigzag shape, and one or more basic units U, specifically two or more, are stacked, with the first electrode 110, the separator 130, the second electrode 120, and the separator 130 stacked in order.

[0037] As shown in Figure 3, the separator 130 includes a porous substrate 131 and ceramic coating layers 132a and 132b arranged on both sides of the porous substrate.

[0038] The porous substrate 131 is not particularly limited as long as it is commonly used as a separator in secondary batteries. Specifically, the porous substrate 131 is preferably one that has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity. More specifically, the porous substrate 131 may contain at least one selected from the group consisting of polyolefin resins such as polyethylene, polypropylene, polybutylene, and polypentene; fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polyacrylonitrile resins; and cellulose resins, and may be a porous film or nonwoven fabric containing one or more copolymers or mixtures of these, or a laminated structure of two or more layers thereof. The porous substrate 131 may be a porous film, nonwoven fabric, or a laminated structure of two or more layers thereof containing the polyolefin resin.

[0039] The size and porosity of the pores present in the porous substrate 131 are not particularly limited. Specifically, the porous substrate 131 can be a porous substrate containing pores with an average pore diameter of 0.01 μm to 1 μm, specifically 20 nm to 60 nm, at a porosity of 10 volume% to 90 volume%, specifically 30 volume% to 60 volume%, which is preferable in terms of improving the mechanical strength of the porous substrate 131 and allowing ionic substances to move more smoothly between the positive and negative electrodes. The average pore diameter and porosity can be measured by analysis using a focused ion beam (FIB), gas adsorption method, or mercury intrusion method.

[0040] The thickness of the porous substrate 131 is not particularly limited, but in consideration of appropriate mechanical strength as a separator and ease of movement of ionic substances, specifically, it can be 1 μm to 100 μm, and more specifically, 2 μm to 15 μm.

[0041] The ceramic coating layers 132a and 132b are disposed on both surfaces of the porous substrate 131.

[0042] The ceramic coating layers 132a and 132b contain inorganic particles and a binder. More specifically, the ceramic coating layer can consist only of the inorganic particles and the binder.

[0043] The inorganic particles can be introduced in terms of preventing thermal shrinkage of the porous substrate at high temperatures and short-circuiting of the positive and negative electrodes due to this. The inorganic particles can be provided as a kind of spacer that maintains the physical form of the porous substrate and minimizes thermal shrinkage.

[0044] As the inorganic particles, any material can be used without particular limitation as long as it is electrochemically stable within the operating voltage range of the battery (for example, 0 V to 5 V based on the Li / Li+ standard) and does not cause oxidation and / or reduction reactions, that is, electrochemical reactions. The inorganic particles are 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 glass (0 < x < 4, 0 < y < 13); lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3); Li 3.25 Ge0.25 P 0.75 Lithium germanium thiophosphate such as S4 (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5); Lithium nitride such as Li3N (Li x N y , 0 < x < 4, 0 < y < 2); SiS2-based glass such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4); P2S5-based glass 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); It can be a mixture of two or more of these. Specifically, the inorganic particles are 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); It can be a mixture of two or more of these, and more specifically, it can contain at least one selected from the group consisting of Al2O3; AlOOH; BaTiO3; BaSO4; and MgO.

[0045] The average particle size (D 50The particle size can be 0.1 μm to 1 μm, specifically 0.2 μm to 0.7 μm.

[0046] The inorganic particles are contained in the ceramic coating layers 132a and 132b in an amount of 92% by weight or more and less than 100% by weight. The content of the inorganic particles must be considered in relation to the content of the binder, which will be described later, and can be adjusted in a way that prevents a decrease in thermal stability due to thermal shrinkage of the porous substrate and prevents an increase in resistance due to an excess of binder. Specifically, the inorganic particles can be contained in the ceramic coating layer in an amount of 93% to 98% by weight.

[0047] The binder may be included in the ceramic coating layers 132a and 132b for the purpose of binding inorganic particles and binding the separator and electrodes.

[0048] Here, the binder is included in the ceramic coating layer in an amount greater than 0% by weight and less than 8% by weight. If the binder is included in an amount greater than 8% by weight, the binder will be excessively included in the ceramic coating layer, which may cause an increase in the resistance of the secondary battery. On the other hand, if the binder is included in 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 will be described later, since the present invention uses a separator having the above characteristics in combination with a gel polymer electrolyte, it is possible to simultaneously improve the resistance of the secondary battery as well as the cell rigidity and mechanical durability.

[0049] Specifically, the binder can be included in the ceramic coating layer in an amount of 2% to 7% by weight. When the amount is within this range, it is possible to maximize the binding force of inorganic particles and prevent an increase in the resistance of the secondary battery.

[0050] The binder may be a hydrophobic binder containing one or more hydrophobic functional groups in its 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 one or more of these may be used as a mixture. More specifically, the hydrophobic binder can be polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene-covinylacetate, polyimide, polyethylene oxide, and the like.Furthermore, the hydrophilic binder may be cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, carboxyl methyl cellulose, polyvinyl alcohol, polyacrylic acid, polymaleic anhydride, or polyvinylpyrrolidone.

[0051] Specifically, the binder can be an acrylic binder. The acrylic binder ensures good dispersion with the inorganic particles during the manufacturing of the ceramic coating layer, thereby preventing the ceramic coating layer from separating into layers, with the binder in the upper layer and the inorganic particles in the lower layer. Such layer separation hinders ion movement at the negative and positive electrodes, leading to increased resistance. Therefore, using an acrylic binder allows the resistance reduction effect targeted by the present invention to be achieved at a more superior level.

[0052] The acrylic binder may include at least one selected from the group consisting of copolymers of ethylhexyl acrylate and methyl methacrylate; polymethyl methacrylate; polyethylhexyl acrylate; polybutyl acrylate; polyacrylonitrile; and copolymers of butyl acrylate and methyl methacrylate.

[0053] 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.

[0054] The thickness of the ceramic coating layers 132a and 132b can be 0.1 μm to 10 μm, specifically 0.5 μm to 5 μm, and more specifically 1.0 μm to 2.5 μm. Since the ceramic coating layers 132a and 132b contain the binder in the small amount described above, it is possible to realize a thin separator, 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 a single ceramic coating layer formed on one surface of the porous substrate.

[0055] The ceramic coating layers 132a and 132b can be manufactured by applying a ceramic coating layer-forming composition, which comprises inorganic particles and a binder dispersed in a solvent, to the porous substrate and drying it. The method of applying the ceramic coating layer-forming composition is not particularly limited, and dip coating, die coating, roll coating, comma coating, gravure coating, etc., can be used, and specifically, gravure coating can be used. As for the drying method after application of the ceramic coating layer-forming composition, natural drying, heat drying, or hot air drying can be used.

[0056] The thickness of the separator 130 can be 1 μm to 20 μm, specifically 5 μm to 14 μm. According to the present invention, by reducing the binder content in the ceramic coating layer, it is possible to realize a thinner separator, which in turn can further improve the energy density of the secondary battery and achieve lower resistance.

[0057] As illustrated in Figure 1, the secondary battery may further include a plurality of electrode tabs 400, 500 connected to the electrode assembly. Specifically, the plurality of electrode tabs 400, 500 can be connected to the first electrode 110 and the second electrode 120 of the electrode assembly 100, respectively, and can protrude to the outside of the battery case 300, becoming pathways through which electrons can move. Although Figure 1 illustrates two electrode tabs 400, 500 positioned in different directions relative to the electrode assembly 100, the battery is not limited to this, and can also protrude parallel to one side of the electrode assembly 100 in the same direction. The plurality of electrode tabs 400, 500 can be positive electrode tabs and negative electrode tabs, and can be connected to the positive and negative electrodes, respectively.

[0058] [Gel polymer electrolyte 200] The gel polymer electrolyte 200 is injected into or housed in a battery case 300, which will be described later. The gel polymer electrolyte 200 can be impregnated into and cured in the electrode assembly 100, and then placed inside and outside the electrode assembly.

[0059] The gel polymer electrolyte 200 is non-fluid and uses a gelled electrolyte, which can improve the cell rigidity of the 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 may lead to reduced processability and product defects due to cell deflection, separator displacement, etc., thus reducing safety and potentially causing the secondary battery to explode.

[0060] The gel polymer electrolyte 200 may be a cured product of a gel polymer electrolyte composition containing a lithium salt, a polymerization initiator, and an oligomer compound. When the gel polymer electrolyte composition cures, the oligomer compound is crosslinked and hardened, forming an electrolyte (gel polymer electrolyte) that has solidified into a gel form. Specifically, the gel polymer electrolyte 200 may contain the cured product of the oligomer compound and a lithium salt.

[0061] The aforementioned lithium salt can be used for the purpose of supplying lithium ions to a secondary battery.

[0062] The lithium salt can be any compound capable of providing lithium ions for use in secondary batteries, without any particular limitations. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1M to 5.0M, more preferably 0.1M to 3.0M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0063] The polymerization initiator can be used to polymerize oligomer compounds and form a polymer network bonded to a three-dimensional structure.

[0064] The polymerization initiator can be a photopolymerization initiator or a thermal polymerization initiator, depending on the polymerization method.

[0065] Specifically, the aforementioned photopolymerization initiators include, as typical examples, 2-hydroxy-2-methylpropiophenone (HMPP), 1-hydroxycyclohexylphenyl ketone, benzophenone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, 2-[2-iodine-2phenylacetoxyethoxy]ethyl ester, 2-[2-hydroxyethoxy]ethyl ester, alpha-dimethoxy-alpha-phenylacetophenone, and 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl This may include at least one compound selected from the group consisting of ]-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(ethanol-5-2,4-cyclopentadien-1-yl), bis[2,6-difluoro-3-(1H-pyrrole-1-yl)phenyl]titanium, 4-isobutylphenyl-4'-methylphenyliodonium, hexafluorophosphate, and methylbenzoyl formate.

[0066] Furthermore, the thermal polymerization initiator may include, as typical examples, 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).

[0067] 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 then form crosslinks through free radical polymerization, thereby polymerizing the oligomer.

[0068] On the other hand, the polymerization initiator can be used in an amount of 0.001 to 10 parts by weight, preferably 0.0015 to 1 part by weight, and more preferably 0.002 to 0.7 parts by weight, per 100 parts by weight of the oligomer compound. When the amount of polymerization initiator used is within this range, the amount of unreacted polymerization initiator that could adversely affect battery performance can be minimized. Furthermore, when the polymerization initiator is used within this range, the gelation of the electrolyte composition can be properly performed.

[0069] The oligomer compound may include one or more selected from the group consisting of polyether oligomers, polycarbonate oligomers, acrylate oligomers, polysiloxane oligomers, phosphagen oligomers, polyethylene oligomers, urethane oligomers, epoxy oligomers, fluorine oligomers, polyethylene oxide, polyester sulfide, polyvinyl alcohol, and polyvinylidene fluoride. Specifically, it may include at least one selected from fluorine oligomers, polycarbonate oligomers, and polysiloxane oligomers.

[0070] For example, the fluorinated oligomer may specifically contain units derived from fluorinated monomers. The fluorinated oligomer has the advantage of improving battery stability by suppressing the generation of oxygen radicals caused by the decomposition of the positive electrode active material through the fluorinated functional groups it contains, and also has excellent flame retardancy. More specifically, the fluorinated oligomer may contain 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.

[0071] Furthermore, the polycarbonate oligomer has the advantages of being compatible with the positive electrode, having a structure similar to that of an organic electrolyte, and exhibiting excellent ionic conductivity or ionic dissociation. The polycarbonate oligomer can 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.

[0072] Furthermore, the polysiloxane oligomer can function as a scavenger for gases (such as HF) generated by electrolyte side reactions, thereby improving high-temperature storage characteristics.

[0073] The weight-average molecular weight of the oligomer compound can range from 1,000 g / mol to 50,000 g / mol, specifically from 4,500 g / mol to 30,000 g / mol.

[0074] The oligomer compound can be included in the gel polymer electrolyte composition in an amount of 1% to 20% by weight, specifically 3% to 10% by weight. When the amount is within this range, the effect of improving the cell rigidity of the secondary battery is excellent, and the ionic conductivity and lithium ion mobility of the gel polymer electrolyte can be exhibited at excellent levels.

[0075] The gel polymer electrolyte composition may further contain a solvent along with the lithium salt, polymerization initiator, and oligomer compound. The solvent can be used for the purpose of dissolving or dispersing the lithium salt, polymerization initiator, and oligomer compound.

[0076] The aforementioned solvents are those commonly used in secondary batteries, and can be used individually or in combination of two or more, such as ethers, esters (acetates, propionates), amides, linear or cyclic carbonates, and nitriles (acetonitrile, SN, etc.).

[0077] Among these, carbonate-based solvents containing carbonate compounds such as cyclic carbonates, linear carbonates, or mixtures thereof can typically be used as the first solvent.

[0078] Specific examples of the cyclic carbonate compounds include single compounds or mixtures 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 their halides. Specific examples of the linear carbonate compounds include, but are not limited to, 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), or mixtures of at least two compounds.

[0079] In particular, among the carbonate-based solvents, propylene carbonate and ethylene carbonate, which are cyclic carbonates, can be preferably used because they have a high dielectric constant as high-viscosity organic solvents and readily dissociate lithium salts in the electrolyte. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as ethyl methyl carbonate, diethyl carbonate, or dimethyl carbonate, in appropriate ratios, an electrolyte with high electrical conductivity can be obtained, and this method can be more preferably used.

[0080] Furthermore, among the solvents, the ester can 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.

[0081] Here, the curing of the gel polymer electrolyte composition can be carried out at a temperature of 50°C to 100°C for 0.5 hours to 48 hours, preferably at a temperature of 60°C to 80°C for 0.5 hours to 24 hours.

[0082] [Battery case 300] The battery case 300 can be provided for the purpose of housing the electrode assembly 100 and the gel polymer electrolyte 200.

[0083] The battery case 300 can be a pouch-like case made of a flexible material, for example, an aluminum pouch battery case.

[0084] If the battery case 300 is an aluminum pouch battery case, the battery case 300 can be formed from 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 that order from the inside out.

[0085] The battery case 300 may include a cup section which is a storage space for housing the electrode assembly.

[0086] The battery case 300 may include a cover 310, and after housing the electrode assembly, curing and gelling of the gel polymer electrolyte composition, the battery case 300 can be sealed with the cover to produce a sealed secondary battery.

[0087] The secondary battery can be manufactured by a method comprising the steps of: housing an electrode assembly in a battery case; injecting a gel polymer electrolyte composition into the battery case; curing the gel polymer electrolyte composition; and sealing the battery case. After sealing the battery case, further steps known in the art, such as activation, degassing, and resealing, may be performed.

[0088] The secondary battery according to another embodiment of the present invention will be described below with reference to Figures 4 and 5. Figure 4 is a schematic side view illustrating an electrode assembly included in the secondary battery according to another embodiment of the present invention. Figure 5 is a schematic plan view of one of the electrodes 110, 120, or separator 130 included in the secondary battery according to another embodiment of the present invention.

[0089] Referring to Figure 4, a secondary battery according to another embodiment of the present invention can be identical to the secondary battery described above, except that the electrode assembly 100 is manufactured by applying an adhesive to at least one of the electrodes 110, 120 and the separator 130 so that the electrodes 110, 120 and the separator 130 are bonded to each other, the adhesive is removed when the gel polymer electrolyte 200 and the electrode assembly 100 are housed in the battery case 300, and adhesive residue 140 remains on at least one of the electrodes 110, 120 and the separator 130.

[0090] The adhesive can be used to provide adhesion between the electrodes 110, 120 and the separator 130. Specifically, the adhesive can be used to fix the alignment of the electrodes and separators in 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, and the adhesive strength between the electrodes and separators may not be sufficient during the manufacturing of the secondary battery. Therefore, the adhesive can compensate for this problem, easily bonding the electrodes and separators, preventing the separator from shifting during the manufacturing process of the electrode assembly, and improving the efficiency and quality of the process.

[0091] The adhesive is used to manufacture an electrode assembly by bonding the electrode and the separator, and can be removed after the electrode assembly is housed in the battery case and the gel polymer electrolyte is housed therein. Specifically, the adhesive can be dissolved and removed by the solvent in the gel polymer electrolyte composition for forming the gel polymer electrolyte. In other embodiments of the present invention, the secondary battery can be easily bonded to the electrode and the separator without increasing the amount of binder in the separator by using the adhesive, and can also prevent an increase in the separator thickness due to an increase in the amount of binder, thereby further improving the energy density of the secondary battery.

[0092] The adhesive can be applied to at least one of the electrodes and the separator in a plurality of spaced-apart patterns. Specifically, the adhesive can be applied to at least one of the electrodes and the separator in a plurality of spaced-apart dots.

[0093] As illustrated in Figures 4 and 5, the adhesive is removed by housing the gel polymer electrolyte in the battery case or by injecting the gel polymer electrolyte composition into the battery case, and adhesive residue 140 may remain on at least one surface of the electrodes 110, 120 and the separator 130. Specifically, when the gel polymer electrolyte composition is injected into the battery case housing the electrode assembly, the adhesive may be dissolved and removed by the solvent in the gel polymer electrolyte composition, while leaving adhesive residue.

[0094] The dissolution or removal of the adhesive can be more smoothly performed by pressurizing during the activation and degassing processes, which are commonly carried out in the manufacturing process of the secondary battery. The activation process is a process in which a solid electrolyte interface film (SEI layer, Surface Electrolyte Interface layer) is formed on the surface of the electrode plates of the electrode assembly during the charging process in the initial secondary battery, thereby making it electrically charged, and thus enabling the secondary battery to supply power. This can be performed, for example, at 45°C or higher, specifically at 50°C to 70°C. The degassing process is a process of discharging gas generated in the activation process to the outside, and the degassing process may be accompanied by a process of pressurizing the secondary battery with a jig or the like. The adhesive can be more smoothly dissolved or removed by such temperature increases and pressurization.

[0095] The area over which the adhesive is applied can be more than 0% and less than or equal to 1% of the surface area where the separator and the electrode are in contact, specifically 0.0001% to 0.05%. When the area is within this range, the electrode and the separator can be bonded with sufficient adhesive strength, and the problem of excessive adhesive application that does not dissolve in the solvent and remains, causing an increase in resistance, is prevented, which is preferable.

[0096] The adhesive may be an acrylate-based adhesive. By using the acrylate-based adhesive, the above-mentioned adhesive can be easily dissolved and removed.

[0097] Specifically, the acrylate-based adhesive may include a copolymer containing 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).

[0098] The weight-average molecular weight (Mw) of the copolymer can be 120,000 g / mol to 140,000 g / mol. The molecular weight of the copolymer can be measured using conventional methods well known in the art. For example, the molecular weight can be measured using end-group determination methods, which involve quantitative analysis of functional groups at the ends of the molecular chain to determine the molecular weight; comprehensive methods using physical properties such as osmotic pressure, vapor pressure depression, boiling point elevation, and freezing point depression (e.g., separator osmosis method, vapor pressure osmosis method); light scattering methods; ultracentrifugation methods, which measure the molecular weight by analyzing the sedimentation velocity or concentration distribution after centrifuging the polymer solution; viscosity methods, which use the viscosity of the polymer solution; and gel permeation chromatography (GPC) using high-performance liquid chromatography (HPLC).

[0099] As illustrated in Figure 4, the electrode assembly includes a plurality of electrodes 110, 120 and one separator 130, and the separator may be bent in a zigzag shape so that it is interposed between the electrodes. This allows the electrode assembly to be in a form in which the electrodes 110, 120 and the separator 130 are stacked alternately. Specifically, the electrode assembly may be made up of one or more, specifically two or more, basic units U, each containing the separator 130, the first electrode 110, the separator 130, and the second electrode 120. Here, the adhesive application marks 140 are formed by the application and removal of the adhesive, and exist between the surfaces of the electrodes 110, 120 and the separator 130 that are in contact with each other, and may remain on at least one surface of the electrodes 110, 120 and the separator 130. In the case of electrode assemblies including a separator bent in a zigzag shape, the bending or folding of the separator during the manufacturing process can cause displacement of the separator and / or electrodes, which leads to problems such as poor quality and reduced process efficiency. However, according to the present invention, by applying an adhesive to bond the electrodes and separator, the aforementioned displacement of the electrodes and / or separators can be prevented to a significant degree, making it possible to manufacture secondary batteries of improved quality.

[0100] A secondary battery according to yet another embodiment of the present invention will be described below with reference to Figure 6.

[0101] A secondary battery according to yet another embodiment of the present invention can be identical to the secondary battery described with reference to Figures 4 and 5, except that adhesive application marks 141 and 142 are arranged between electrodes 110 and 120 and a separator 130, and the adhesive application marks 141 and 142, which are arranged in adjacent layers, may be arranged in a crossing manner.

[0102] For example, as shown in Figure 6, the first adhesive application mark 141 located between the lower part of the first electrode 110 and the separator 130, and the second adhesive application mark 142 located between the upper part of the first electrode 110 and the separator 130, may be positioned so as to intersect each other. Here, the positions of the first adhesive application mark 141 and the second adhesive application mark 142 only intersect each other; their spacing from each other can be the same. This can be similarly explained for the adhesive application marks 141 and 142 located between the second electrode 120 and the separator 130.

[0103] In the case of such an intersecting arrangement of adhesive application marks, it is preferable because it can minimize the risk of increased cell thickness due to adhesive application and allows the adhesive to dissolve more smoothly.

[0104] <Manufacturing method for secondary batteries> Furthermore, the present invention provides a method for manufacturing a secondary battery. The method for manufacturing the secondary battery may be the method for manufacturing a secondary battery described above.

[0105] Specifically, the method for manufacturing the secondary battery includes the steps of housing an electrode assembly in the battery case, injecting a gel polymer electrolyte composition into the battery case, curing the gel polymer electrolyte, and sealing the battery case, wherein the electrode assembly includes alternately stacked first and second electrodes, and a separator interposed between the plurality of electrodes, the separator is bent in a zigzag shape so as to wrap around one end of the first electrode and one end of the second electrode, the separator includes a porous substrate and a ceramic coating layer disposed on both sides of the porous substrate, the ceramic coating layer includes 92% by weight or more and less than 100% by weight of inorganic particles and a binder greater than 0% by weight and less than or equal to 8% by weight, and the electrode assembly is manufactured by a method including the following steps (a) to (d).

[0106] (a) The step of placing the first electrode on the separator; (b) Folding one side of the separator to cover the first electrode; (c) The step of placing the second electrode on the opposite side of the separator from the surface in contact with the first electrode; and (d) The step of folding the other side of the separator to cover the second electrode.

[0107] The secondary battery can be manufactured by a method comprising the steps of: housing an electrode assembly in a battery case; injecting a gel polymer electrolyte composition into the battery case; curing the gel polymer electrolyte composition; and sealing the battery case. After sealing the battery case, further steps known in the art, such as activation, degassing, and resealing, may be performed.

[0108] The electrode assembly, the first electrode, the second electrode, the separator, the battery case, the gel polymer electrolyte composition, etc., are described above.

[0109] The manufacturing process of the electrode assembly included in the method for manufacturing a secondary battery according to the present invention will be described in detail below with reference to Figures 7 to 10.

[0110] Referring to Figure 7, the first electrode 110 is placed on the separator 130.

[0111] As illustrated in Figure 7, specifically, the separator 130 may be unwound from the separator reel 630 and placed on the upper surface of the table 700.

[0112] The first electrode 110 can be formed by cutting a first electrode sheet 1101, which has been unwound on a first electrode reel 610, by a first cutter 810, as shown in Figure 7. When the first transfer device 910 transfers the first electrode 110, the first header 1010 can pick up the first electrode. Next, as the first header 1010 and / or table 700 move, the first electrode 110 can be placed or positioned on the separator 130.

[0113] Referring to Figure 8, after the first electrode 110 is placed on the separator 130, one side of the separator 130 is folded to cover the first electrode 110. For example, the folding of the separator 130 can be done by moving the table 700 laterally.

[0114] Referring to Figure 9, the second electrode 120 is positioned on the opposite side of the separator 130 from the surface where the separator 130 and the first electrode 110 are in contact.

[0115] The second electrode 120 can be formed by cutting the first electrode sheet 1201, which has been unwound on the second electrode reel 620, by the second cutter 820, as shown in Figure 9. Here, as the second transfer device 920 transfers the second electrode 120, the second header 1020 can pick up the second electrode. Then, as the second header 1020 and / or the table 700 move, the second electrode can be placed or positioned on the separator.

[0116] Referring to Figure 10, after the placement of the second electrode 120, the other side of the separator 130 is folded to cover the second electrode 120. This makes it possible to manufacture an electrode assembly in which the first and second electrodes are stacked alternately, 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, it is possible to realize an electrode assembly in which multiple first and second electrodes are stacked alternately.

[0117] In the method for manufacturing a secondary battery of the present invention, the placement of the first electrode on the separator may be performed after applying an adhesive to at least a portion of the separator and the first electrode, and the placement of the second electrode on the separator may be performed after applying an adhesive to at least a portion of the separator and the second electrode.

[0118] For example, as illustrated in Figures 7 to 10, the placement of the first electrode 110 onto the separator 130 can be performed after applying adhesive 140a to at least a portion of the separator 130 and the first electrode 110 using a first nozzle 1110 containing adhesive. Similarly, the placement of the second electrode 120 onto the separator 130 can be performed after applying adhesive 140a to at least a portion of the separator 130 and the second electrode 120 using a second nozzle 1120 containing adhesive.

[0119] In the case of an electrode assembly including a separator bent in a zigzag shape as described above, the bending or folding of the separator during the manufacturing process can cause displacement of the separator and / or the electrode, which leads to problems such as poor quality and reduced process efficiency. However, according to the present invention, by applying an adhesive to bond the electrode and the separator, the aforementioned displacement of the electrode and / or separator can be prevented to a significant degree, making it possible to manufacture a secondary battery of improved quality. Applying such an adhesive is particularly preferable in terms of complementing the adhesive strength of the separator in the present invention, which contains a low amount of binder.

[0120] The adhesive can be applied in a plurality of spaced-apart patterns. Specifically, the adhesive can be applied in a plurality of spaced-apart patterns to at least one surface of the first electrode and the separator; and to at least one surface of the second electrode and the separator. Specifically, the adhesive can be applied in a plurality of spaced-apart dots to at least one surface of the first electrode and the separator; and to at least one surface of the second electrode and the separator.

[0121] The adhesive can be dissolved and removed by the gel polymer electrolyte composition injected into the battery case. The gel polymer electrolyte composition may further contain a solvent along with the lithium salt, polymerization initiator, and oligomer compound described above, and the adhesive can be dissolved and removed by the solvent contained in the gel polymer electrolyte composition.

[0122] The adhesive is removed by housing the gel polymer electrolyte in the battery case or by injecting the gel polymer electrolyte composition into the battery case, and adhesive residue may remain on at least one surface of the separator and the first electrode; and at least one surface of the separator and the second electrode. Specifically, when the gel polymer electrolyte composition is injected into the battery case housing the electrode assembly, the adhesive may be dissolved and removed by the solvent in the gel polymer electrolyte composition, while leaving adhesive residue.

[0123] The dissolution or removal of the adhesive can be carried out more smoothly by pressurizing during the activation and degassing processes, which are commonly performed in the secondary battery manufacturing process. The activation process is a process in which a solid electrolyte interface film (SEI layer, Surface Electrolyte Interface layer) is formed on the surface of the electrode plates of the electrode assembly during the charging process in the initial secondary battery, causing it to become charged, thereby enabling the secondary battery to supply power. This can be carried out at, for example, 45°C or higher, specifically 50°C to 70°C. The degassing process is a process of discharging gas generated in the activation process to the outside, and the degassing process may be accompanied by a process of pressurizing the secondary battery with a jig or the like. The adhesive can be dissolved or removed more smoothly by such temperature increases and pressurization.

[0124] The adhesive may be an acrylate-based adhesive. By using the acrylate-based adhesive, the above-mentioned adhesive can be easily dissolved and removed.

[0125] Specifically, the acrylate-based adhesive may include a copolymer containing 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).

[0126] The weight-average molecular weight (Mw) of the copolymer can be 120,000 g / mol to 140,000 g / mol. The molecular weight of the copolymer can be measured using conventional methods well known in the art. For example, the molecular weight can be measured using end-group determination methods, which involve quantitative analysis of functional groups at the ends of the molecular chain to determine the molecular weight; comprehensive methods using physical properties such as osmotic pressure, vapor pressure depression, boiling point elevation, and freezing point depression (e.g., separator osmosis method, vapor pressure osmosis method); light scattering methods; ultracentrifugation methods, which measure the molecular weight by analyzing the sedimentation velocity or concentration distribution after centrifuging the polymer solution; viscosity methods, which use the viscosity of the polymer solution; and gel permeation chromatography (GPC) using high-performance liquid chromatography (HPLC).

[0127] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0128] [Examples and Comparative Examples] Example 1 1. Manufacturing of separators As inorganic particles, Al2O3 (average particle size (D 50 A ceramic coating layer-forming composition was prepared by adding a 0.5 μm particle and an acrylic binder in a weight ratio of 96:4 to water, which was used as the solvent. As the acrylic binder, a mixture of TRD 202A manufactured by JSR and AP-0821 manufactured by APEC was used.

[0129] A ceramic coating layer was formed by applying the ceramic coating layer-forming composition to both sides of a porous polyethylene substrate (thickness: 9 μm, average pore diameter: 0.05 μm, porosity: 45 vol%) by gravure coating and drying, thereby forming a ceramic coating layer (thickness of one layer: 1.5 μm), and producing a separator (thickness: 12 μm = 1.5 μm + 9 μm + 1.5 μm).

[0130] 2. Manufacturing of electrode assemblies The separator was unwound from the separator reel and placed on the table. Adhesive was applied to the separator using the first nozzle in a pattern of multiple spaced-apart dots. The adhesive application area was 5.8875 mm². 2 ) is the area of ​​the surface where the separator and the positive electrode are in contact (24,889 mm²). 2 The concentration was 0.002366% of the total. The adhesive was an acrylate-based adhesive, 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 on which it was wound, cut with a first cutter to produce the positive electrode, and the positive electrode was transferred by a first transfer device and adsorbed onto the first header. The first header was moved to the table side and the positive electrode was attached to the separator.

[0131] Next, the table was moved to the side, and the separator was folded to one side to cover the positive electrode.

[0132] Next, the same adhesive used above was applied to the surface of the separator (the surface opposite to the surface in contact with the positive electrode) using a second nozzle, in a pattern of multiple spaced-apart dots.

[0133] Next, the negative electrode sheet was unwound from the second electrode reel, cut with a second cutter to produce the negative electrode, and then transferred by a second transfer device and adsorbed onto the second header. The second header was then moved toward the table side, and the negative electrode was attached to the surface of the separator (the surface opposite to the surface where the separator and the positive electrode are in contact).

[0134] Next, the table was moved to the side again, and the separator was folded to the other side to cover the negative electrode.

[0135] The above process was repeated several times to produce an electrode assembly in which 18 basic units, each consisting of a separator / positive electrode / separator / negative electrode stacked in that order, were stacked. In this assembly, the separators were folded in a zigzag pattern.

[0136] Here, in the case of the positive electrode, Li[Ni] is used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 A positive electrode slurry was prepared by adding O2, PVdF as a binder, and carbon black as a conductive material in a weight ratio of 97.5:1.5:1.0 to N-methylpyrrolidone (NMP) as a solvent. As a positive electrode current collector, the positive electrode slurry was applied to both sides of an aluminum current collector, which was then dried and rolled to form a positive electrode active material layer.

[0137] Furthermore, in the case of the negative electrode, graphite was added as the negative electrode active material, styrene-butadiene rubber as the binder, carbon black as the conductive material, and carboxymethylcellulose (CMC) as the thickener in a weight ratio of 95.5:2.5:1.0:1.0 to water, which was used as the solvent, to produce a negative electrode slurry. A copper current collector was then coated with the negative electrode slurry on both sides, dried, and rolled to form a negative electrode active material layer.

[0138] 3. Preparation of gel polymer electrolyte composition The gel polymer electrolyte composition was prepared by mixing polycarbonate (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.

[0139] 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 included in the gel polymer electrolyte composition at a concentration of 1.0 M, the oligomer was included in the gel polymer electrolyte composition at 5% by weight, and the polymerization initiator was included in the gel polymer electrolyte composition at 0.6 parts by weight per 100 parts by weight of the oligomer.

[0140] 4. Manufacturing of rechargeable batteries A pouch-type battery case made of aluminum was prepared as the battery case, and the electrode assembly was stored in the storage space of the battery case.

[0141] Next, the gel polymer electrolyte composition was injected into the battery case containing the electrode assembly. After the injection of the gel polymer electrolyte composition, the case was vacuum-sealed.

[0142] Upon injection of the gel polymer electrolyte composition, the adhesive present in the electrode assembly was dissolved and removed by the solvent of the gel polymer electrolyte composition. As will be described later, the adhesive was removed, but traces of adhesive application remained on the separator and electrodes.

[0143] Next, the gel polymer electrolyte composition injected into the battery case was cured. This curing was performed by heat treatment at a temperature of 60°C for 5 hours.

[0144] Next, the battery case was cooled, sealed, and degassed to manufacture a rechargeable battery. The thickness of the rechargeable battery was 0.8 cm.

[0145] Comparative Example 1 1. Manufacturing of separators As inorganic particles, Al2O3 (average particle size (D 50 A ceramic coating layer-forming composition was prepared by adding a 0.5 μm (0.5 μm) and PVdF as a binder in a weight ratio of 70:30 to acetone, which was used as the solvent.

[0146] A ceramic coating layer-forming composition was applied to both sides of a porous polyethylene substrate (thickness: 9 μm, average pore diameter: 0.05 μm, porosity: volume%) by gravure coating and dried to form a ceramic coating layer (thickness of one layer: 3 μm), thereby producing a separator (thickness: 15 μm = 3 μm + 9 μm + 3 μm).

[0147] 2. Manufacturing of electrode assemblies Unlike Example 1, a secondary battery was manufactured in the same manner as in Example 1, except that no adhesive was applied and the separator manufactured as described above was used.

[0148] 3. Manufacturing of liquid electrolyte compositions A liquid electrolyte composition was prepared by using a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 as the solvent, and adding lithium salt LiPF6 at a concentration of 1.0 M to the solvent.

[0149] 4. Manufacturing of rechargeable batteries A pouch-type battery case made of aluminum was prepared as the battery case, and the electrode assembly manufactured as described above was placed in the storage space of the battery case.

[0150] Next, the liquid electrolyte composition prepared as described above was injected and the area was vacuum-sealed.

[0151] The battery case was cooled, sealed, and degassed to manufacture the rechargeable battery.

[0152] The thickness of the aforementioned secondary battery was 0.8 cm.

[0153] Comparative Example 2 1. Manufacturing of separators The same separator used in Comparative Example 1 was employed.

[0154] 2. Manufacturing of electrode assemblies The same electrode assembly used in Comparative Example 1 was employed.

[0155] 3. Preparation of gel polymer electrolyte composition The same gel polymer electrolyte composition used in Example 1 was employed.

[0156] 4. Manufacturing of rechargeable batteries A secondary battery was manufactured in the same manner as in Example 1, except that the separator and electrode assembly prepared as described above were used.

[0157] The thickness of the aforementioned secondary battery was 0.8 cm.

[0158] Comparative Example 3 1. Manufacturing of separators The same separator manufactured in Example 1 was used.

[0159] 2. Manufacturing of electrode assemblies The same electrode assembly used in Example 1 was used.

[0160] 3. Manufacturing of liquid electrolyte compositions The same liquid electrolyte composition used in Comparative Example 1 was employed.

[0161] 4. Manufacturing of rechargeable batteries A secondary battery was manufactured in the same manner as in Comparative Example 1, except that the separator and electrode assembly prepared as described above were used.

[0162] The thickness of the aforementioned secondary battery was 0.8 cm.

[0163] [Experimental Example] 1. Observation of adhesive application marks on the separator surface. In the secondary batteries of Example 1 and Comparative Example 1, the separator corresponding to the surface where the electrode and separator were in contact was cut, and its surface was observed. Figure 11 shows a photograph of the surface of the separator separated from the secondary battery of Example 1, and Figure 12 shows a photograph of the surface of the separator separated from the secondary battery of Comparative Example 1.

[0164] As shown in Figure 11, traces of adhesive application were observed in the photograph of the separator surface of Example 1.

[0165] On the other hand, as shown in Figure 12, since no adhesive was used in the manufacture of the electrode assembly of Comparative Example 1, no traces of adhesive application were observed in the photograph of the separator surface of Comparative Example 1.

[0166] 2. Evaluation of Resistance Table 1 below shows the resistance values ​​and their results calculated using the voltage change (ΔV) measured when the secondary batteries of Example 1 and Comparative Examples 1-3 were discharged for 10 seconds at a 2.5C rate with a SOC of 50%.

[0167] 3. Evaluation of lifespan performance The secondary batteries of Example 1 and Comparative Examples 1-3 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.

[0168] *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

[0169] Under the aforementioned experimental conditions, the capacity retention rate was defined as the value obtained by dividing the discharge capacity for the 100th cycle by the discharge capacity for the first cycle. The results are shown in Table 1 below.

[0170] 4. Measurement of cell stiffness The stress values ​​were measured when a downward force was applied to the center of each secondary battery at a speed of 10 mm / min using the 3-point bending method, resulting in a displacement of 2 mm. A preload of 30 gf was applied, the experiment was conducted at room temperature, and the stress values ​​were measured using a universal testing machine (UTM). The results are shown in Table 1 below.

[0171] 5. Nail-piercing test A metal nail with a diameter of 3.0 mm was dropped at a speed of 800 mm / min onto fully charged lithium secondary batteries manufactured in Example 1 and Comparative Examples 1-3. After dropping, a thermocouple was attached to the surface of the secondary battery to evaluate whether or not ignition occurred.

[0172] The experiment was conducted a total of three times, and if no ignition occurred, it was evaluated as a "Pass." The results are shown in Table 1 below.

[0173] [Table 1]

[0174] Referring to Table 1, it can be confirmed that the secondary battery of Example 1 according to the present invention simultaneously exhibits excellent levels of reduced resistance, improved lifespan, increased cell rigidity, and improved safety.

[0175] On the other hand, while Comparative Example 1 has a resistance level equivalent to Example 1, it can be confirmed that the cell rigidity is reduced, safety is compromised, and lifespan performance is reduced.

[0176] Furthermore, while Comparative Example 2 exhibits superior cell rigidity, the use of a large amount of binder in both the separator and the gel polymer electrolyte results in a 6.8% increase in resistance compared to Example 1, leading to a significant decrease in lifespan performance.

[0177] Furthermore, in the case of Comparative Example 3, although the resistance is somewhat lower than that of Example 1, the cell rigidity is significantly reduced, and in particular, all cells ignite during the nail-piercing test, confirming that it is very unsafe. [Explanation of Symbols]

[0178] 10 Secondary battery 100 electrode assembly U base unit 110 1st electrode 110a One end of the first electrode 120 2nd electrode 120a One end of the second electrode 130 Separator 131 Porous substrate 132a, 132b Ceramic coating layer 140, 141, 142 Adhesive application marks 140a 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 Nozzle No. 1 1120 Nozzle No. 2 P: Perpendicular to the ground

Claims

1. An electrode assembly including alternately stacked electrodes and separators, Gel polymer electrolyte, The battery includes the electrode assembly and the gel polymer electrolyte, The separator includes a porous substrate and a ceramic coating layer disposed on both sides of the porous substrate. A secondary battery wherein the ceramic coating layer comprises 92% by weight or more and less than 100% by weight of inorganic particles and a binder that is more than 0% by weight and 8% by weight or less.

2. The aforementioned electrodes are multiple, The aforementioned plurality of electrodes are stacked in the vertical direction, The secondary battery according to claim 1, wherein the separator is bent in a zigzag shape so as to enclose one end of the electrodes.

3. The 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.

4. The secondary battery according to claim 1, wherein the binder includes an acrylic binder.

5. The secondary battery according to claim 3, wherein the acrylic binder comprises 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.

6. The secondary battery according to claim 1, wherein the thickness of the ceramic coating layer is 0.1 μm to 10 μm.

7. The secondary battery according to claim 1, wherein the thickness of the separator is 1 μm to 20 μm.

8. The secondary battery according to claim 1, wherein the gel polymer electrolyte is a cured product of a gel polymer electrolyte composition comprising a lithium salt, a polymerization initiator, and an oligomer compound.

9. The secondary battery according to claim 8, wherein the oligomer compound is contained in the gel polymer electrolyte composition in an amount of 1% to 20% by weight.

10. The secondary battery according to claim 8, wherein the oligomer compound comprises at least one selected from the group consisting of fluorine-based oligomers, polycarbonate-based oligomers, and polysiloxane-based oligomers.

11. The electrode assembly is manufactured by applying an adhesive to at least one surface of the electrode and the separator, and bonding the electrode and the separator together. The secondary battery according to claim 1, wherein the adhesive is removed when the gel polymer electrolyte and the electrode assembly are housed in the battery case, and traces of adhesive application remain on the surface of at least one of the electrodes and the separator.

12. The secondary battery according to claim 11, wherein the adhesive is applied to the surface of at least one of the electrodes and the separator in a plurality of patterns spaced apart from each other.

13. The secondary battery according to claim 11, wherein the application area of ​​the adhesive is more than 0% and 1% or less of the surface area in contact between the separator and the electrode.

14. The electrode includes a first electrode and a second electrode, The secondary battery according to claim 1, wherein the first electrode and the second electrode are stacked alternately.

15. The steps include: housing the electrode assembly in the battery case, The steps include injecting a gel polymer electrolyte composition into the battery case, The steps include curing the gel polymer electrolyte composition, The step includes sealing the battery case, The electrode assembly includes alternately stacked first and second electrodes, and a separator interposed between the plurality of electrodes. The separator is bent in a zigzag shape so as to wrap around one end of the first electrode and one end of the second electrode. The separator includes a porous substrate and a ceramic coating layer disposed on both sides of the porous substrate. The ceramic coating layer comprises 92% by weight or more and less than 100% by weight of inorganic particles and a binder that is more than 0% by weight and 8% by weight or less. A method for manufacturing a secondary battery, wherein the electrode assembly is manufactured by a method comprising the following steps (a) to (d). (a) The step of placing the first electrode on the separator; (b) Folding one side of the separator to cover the first electrode; (c) The step of placing the second electrode on the opposite side of the separator from the surface in contact with the first electrode; and (d) The step of folding the other side of the separator to cover the second electrode.

16. The placement of the first electrode onto the separator is carried out after applying adhesive to at least a portion of the separator and the first electrode. The method for manufacturing a secondary battery according to claim 15, wherein the placement of the second electrode on the separator is performed after applying an adhesive to at least a portion of the separator and the second electrode.

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

18. The method for manufacturing a secondary battery according to claim 16, wherein the adhesive is dissolved and removed by the gel polymer electrolyte composition injected into the battery case.

19. The method for manufacturing a secondary battery according to claim 18, wherein, after the adhesive is removed, traces of adhesive application are present on at least one surface of the separator and the first electrode; and at least one surface of the separator and the second electrode.

20. The method for manufacturing a secondary battery according to claim 16, wherein the adhesive is an acrylate-based adhesive.

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