Method for manufacturing an electrode assembly, electrode assembly, and electrochemical device including the same

Abstract

Disclosed is a method for manufacturing an electrode assembly, wherein, in the steps of stacking and pressing an electrode and a separator, pressing is performed in a state where pores of a separator porous substrate to be used as a separator are filled with a polymer solution. Due to the polymer solution, the shape or volume of the pores is not changed. Therefore, the porosity of the separator after manufacturing the electrode assembly is similar to the porosity of the separator before stacking. As a result, a battery including the electrode assembly has high ionic conductivity and excellent performance.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 2019-0130851, filed on October 21, 2019, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing an electrode assembly, and more particularly, to a method for manufacturing an electrode assembly capable of preventing a decrease in the porosity of a porous substrate when laminating a separator having the porous substrate to manufacture the electrode assembly, an electrode assembly manufactured by the manufacturing method, and an electrochemical device including the electrode assembly. Background Art

[0003] A separator, which is an element constituting a secondary battery, is a polymer film located between a positive electrode and a negative electrode, and the polymer film has a porous structure. The separator allows an electrolyte and ions to pass through while isolating the positive electrode and the negative electrode from each other to prevent an electrical short circuit between the two electrodes. The separator itself does not participate in the electrochemical reaction of the battery. However, the separator affects the performance and safety of the battery due to its physical properties, such as electrolyte solution wettability and porosity.

[0004] The output of the battery increases in proportion to the ionic conductivity in the battery. That is, when the time required for ions to pass through the separator is shortened, the performance of the battery is further improved. The time required for ions to pass through the separator is represented by the Gurley number. The Gurley number is affected by the pore ratio, pore diameter, pore deformation degree, and thickness of the separator. In order to improve the performance of the battery, it is important to provide a separator configured such that the overall thickness of the separator is small and the separator has large pores with a low degree of deformation.

[0005] Patent Document 1 uses a nanofiber nonwoven fabric instead of a conventional polyolefin-based separator to improve the heat resistance and air permeability of the separator, but does not recognize a method for uniformly forming pores while reducing the pore deformation degree.

[0006] Patent Document 2 discloses a separator including a fiber layer having pores arranged at a predetermined interval. The fiber layer is arranged such that the pores are vertically positioned, thereby uniformly dispersing external stress and exhibiting compression resistance. However, the separator has a double-layer structure, thereby reducing the ionic conductivity of the battery.

[0007] Research has been conducted to improve the performance of the battery through conventional separators. Specifically, research has been conducted to increase the porosity of a porous substrate used as a separator or to change the structure of the porous substrate to ensure a high porosity.

[0008] Figure 1It is a schematic diagram showing a conventional method of pressing a positive electrode, a negative electrode, and a separator in a state where the separator is interposed between the positive electrode and the negative electrode.

[0009] In the case of stacking in a conventional manner, where the positive electrode 100, the negative electrode 200, and the separator porous substrate 300 are pressed in a state where the separator is interposed between the positive electrode and the negative electrode, as Figure 1 shown, by the pressing force 400, the pores 310 may be deformed, or the size of the pores may be reduced. As a result, even in the case of improving the performance of the separator porous substrate 300 by increasing the porosity or changing the structure of the porous substrate, the effect is reduced when stacking the separator porous substrate 300 to manufacture an electrode assembly. Figure 1 The separator porous substrate 300 shown is composed of a separate porous substrate or includes an inorganic material coated on at least one surface of the porous substrate. The same applies to the separator porous substrate 300 described below in the present invention. The inorganic layer that can be coated on at least one surface of the porous substrate is not shown in Figure 1 Furthermore, in Figure 1 each pore 310 of the separator is simplified to a straight line. However, each pore of the separator according to the present invention is not limited to a straight line.

[0010] -Prior Art Documents-

[0011] -Patent Documents-

[0012] (Patent Document 1) Korean Patent Application Publication No. 2014-0060044 (May 19, 2014)

[0013] (Patent Document 2) Korean Patent Application Publication No. 2014-0050874 (April 30, 2014) Summary of the Invention

[0014] Technical problem

[0015] The present invention has been completed in view of the above problems, and an object of the present invention is to provide a method for manufacturing an electrode assembly that can prevent a decrease in the porosity of a separator when laminating the separator to manufacture an electrode assembly, an electrode assembly manufactured by the manufacturing method, and an electrochemical device including the electrode assembly.

[0016] Technical solution

[0017] To achieve the above object, the present invention provides a method for manufacturing an electrode assembly, comprising: 1) dissolving a polymer soluble in an electrolyte solution in a solvent to produce a polymer solution; 2) filling pores of a separator porous substrate to be used as a separator with the polymer solution of step 1); 3) pressing to produce a stack including the separator of step 2) and an electrode; 4) injecting an initial electrolyte solution into the stack of step 3) to discharge the polymer solution in the pores of the separator porous substrate to the outside; and 5) injecting a second electrolyte solution into the stack of step 4).

[0018] The solvent in step 1) may not be an electrolyte solution.

[0019] Filling the pores of the separator porous substrate with the polymer solution in step 2) may include applying the polymer solution to the separator porous substrate or impregnating the separator porous substrate with the polymer solution.

[0020] The method for manufacturing the electrode assembly may further include drying the separator porous substrate after step 2).

[0021] The method for manufacturing the electrode assembly may further include further coating at least one surface of the separator porous substrate after step 2).

[0022] In step 3), stacking may be performed to include a heat-resistant layer.

[0023] The pressing in step 3) may be performed under high pressure or high temperature conditions.

[0024] The initial electrolyte solution and the second electrolyte solution may be miscible with each other.

[0025] The initial electrolyte solution and the second electrolyte solution may be the same as each other.

[0026] The polymer soluble in the electrolyte solution in step 1) may be a PVdF-based polymer, and the solvent may be an organic solvent.

[0027] The method for manufacturing the electrode assembly may further include performing an initial charge and discharge after step 5).

[0028] The present invention can provide an electrode assembly manufactured by the above manufacturing method.

[0029] Furthermore, the present invention can provide an electrochemical device including the electrode assembly.

[0030] In the present invention, one or more configurations that do not conflict with each other may be selected and combined from the above configurations. Description of the Drawings

[0031] Figure 1It is a schematic view showing a conventional method of pressing a positive electrode, a negative electrode, and a separator in a state where the separator is interposed between the positive electrode and the negative electrode.

[0032] Figure 2 It is a view showing, in the form of a diagram, a method of manufacturing an electrode assembly according to the present invention.

[0033] Figures 3a to 3d It is a 2500-fold field emission scanning electron microscope (FE-SEM) photograph showing the surface of a polyethylene porous substrate before and after pressing an electrode assembly according to a comparative example and an example of the present invention.

[0034] Figure 4 It is a graph showing measured resistance values of coin cells using a comparative example (before and after pressing) and an example (before and after pressing and after discharging a polymer from pores) of the present invention.

[0035] Figure 5 It is a graph showing capacity measurement results when performing 400 charge and discharge cycles using a comparative example (A) and an example (B) of the present invention. Detailed Description

[0036] Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, so that the preferred embodiments of the present invention can be easily implemented by those of ordinary skill in the art to which the present invention pertains. However, when a detailed description of known functions and configurations included herein may obscure the subject matter of the present invention when describing the operating principles of the preferred embodiments of the present invention in detail, a detailed description thereof will be omitted.

[0037] Throughout the specification, when it is described that one component is connected to another component, not only can one component be directly connected to another component, but also one component can be indirectly connected to another component through yet another component. In addition, including a certain element does not mean excluding other elements, but means that these elements can be further included unless otherwise specified.

[0038] Hereinafter, the present invention will be described in more detail.

[0039] Figure 2 It is a view showing, in the form of a diagram, a method of manufacturing an electrode assembly according to the present invention.

[0040] In the method of manufacturing an electrode assembly according to the present invention, 1) a polymer soluble in an electrolyte solution is dissolved in a solvent to prepare a polymer solution 500; 2) the pores 310 of a separator porous substrate 300 to be used as a separator are filled with the polymer solution 500, as shown in Figure 2 (a), to form a separator porous substrate 300 having pores 310 filled with the polymer solution, as shown in Figure 2 (b).

[0041] Any material can be used as a polymer soluble in the electrolyte solution, as long as the material is a polymer soluble in the electrolyte solution and does not react with other materials used in the battery. The polymer soluble in the electrolyte solution can be a PVdF-based polymer. The PVdF-based polymer can be one of PVdF, PVdF-VDF, PVdF-HFP, PVdF-TFE, PVdF-TrFE-CTFE, and PVdF-TrFE-CFE or a mixture thereof. The size (molecular weight) and specific composition ratio of the polymer are not limited, as long as the polymer is dissolved in the solvent to fill the pores 310 of the separator porous substrate 300.

[0042] The solvent can be a material other than the electrolyte solution. Preferably, the solvent can dissolve the polymer well so that the pores 310 are uniformly filled with the polymer solution 500. Any material can be used as the solvent, as long as the material is a solvent capable of dissolving the polymer and has a lower reactivity with the polymer than the electrolyte solution. The solvent can be an organic solvent. For example, any one of the following can be used: aliphatic hydrocarbon-based solvents such as pentane, n-hexane, octane, cyclopentane, or cyclohexane; aromatic hydrocarbon-based solvents such as benzene, toluene, or xylene; aldehyde-based solvents such as furfural; ketone-based solvents such as acetone, methyl ethyl ketone, cyclopentanone, or cyclohexanone; ester-based solvents such as butyl acetate, ethyl acetate, methyl acetate, butyl propionate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, or 3-methoxybutyl acetate ethylene glycol diacetate; ether-based solvents such as tetrahydrofuran, dioxane, or ethylene glycol dimethyl ether; alcohol-based solvents such as methanol, ethanol, n-propanol, isopropanol, butanol, octanol, cyclohexanol, allyl alcohol, benzyl alcohol, cresol, or furfuryl alcohol; polyol-based solvents such as glycerol, ethylene glycol, or diethylene glycol; alcohol ether-based solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, or diethylene glycol monobutyl ether; and aprotic polar solvents such as N-methyl-2-pyrrolidone, dimethyl sulfoxide, or dimethylformamide, or a mixture of two or more of them can be used. Preferably, a ketone-based solvent that does not chemically react with the PVdF-based material is used.

[0043] The solvent is used in an amount of 10 parts by weight to 800 parts by weight, preferably 50 parts by weight to 300 parts by weight, based on 100 parts by weight of the polymer material.

[0044] A polymer solution 500 is manufactured by dissolving a polymer in a solvent within a temperature range of 0 °C to 60 °C. At this time, only the polymer and the solvent may be dissolved, or a material other than the polymer and the solvent, which is configured to assist the polymer in dissolving well in the electrolyte solution in a subsequent step without reacting with the pores 310 of the separator porous substrate 300, may be added to manufacture the polymer solution 500.

[0045] Any porous substrate used in a battery may be used as the separator porous substrate 300. Preferably, a porous substrate having high ionic conductivity is used. At this time, the diameter of each pore 310 of the separator porous substrate 300 is generally 0.01 μm to 10 μm, and the thickness of the separator porous substrate 300 is generally 5 μm to 300 μm. The separator porous substrate 300 may include a polyolefin-based resin (such as polyethylene, polypropylene, polybutene, or polyvinyl chloride) or a mixture or copolymer thereof, or may include a resin such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimide-amide, polyaramide, nylon, or polytetrafluoroethylene. Among them, a polyolefin-based resin is preferably used because the polyolefin-based resin has high applicability to a slurry for an additional coating including an inorganic material, and the thickness of the polyolefin-based resin is reduced, so that the percentage of the electrode active material layer in the battery increases, thereby increasing its capacity per unit volume. At this time, in the case of using a solid electrolyte such as a polymer as the electrolyte, the solid electrolyte may also be used as the separator.

[0046] The separator may be made only of a porous substrate, or at least one surface of the porous substrate may be coated with an inorganic material to manufacture the separator. The separators described in the specification of the present invention include the case where the separator is made only of a porous substrate and the case where at least one surface of the porous substrate is coated with an inorganic material to manufacture the separator. However, in the drawings of the present invention, for convenience, only the separator porous substrate 300 using only the porous substrate is shown.

[0047] As Figure 2 (a) shown, the polymer solution may be applied to the separator porous substrate 300 such that the pores 310 of the separator porous substrate 300 are filled with the polymer solution due to gravity or diffusion. Alternatively, the separator porous substrate 300 may be impregnated with the polymer solution such that the pores 310 of the separator porous substrate 300 are filled with the polymer.

[0048] When applying the polymer solution 500 to fill the pores 310, it is preferred that the polymer solution 500 has a predetermined viscosity or higher. When the viscosity of the polymer solution 500 is low, the polymer solution 500 passes through the separator porous substrate 300 before being evenly distributed in the pores 310, thus failing to achieve the object of the present invention. Therefore, the polymer solution 500 preferably has a viscosity at a predetermined level or higher. When the polymer solution 500 is applied to the separator porous substrate 300, although the time may vary depending on the viscosity of the polymer solution 500, the molecular weight of the polymer, the mixing ratio of the polymer, etc., the application time is preferably about 5 minutes to about 2 hours. When the application time is less than 5 minutes, the polymer solution 500 is not evenly distributed in the pores 310. When the application time exceeds 2 hours, the processing time is too long and the efficiency is low.

[0049] When impregnating the separator porous substrate 300 with the polymer solution 500 to fill the pores 310, it is preferred to soak the separator porous substrate 300 in a container containing the polymer solution 500 for about 5 minutes to about 10 minutes.

[0050] After filling the pores 310 of the separator porous substrate 300 with the polymer solution 500, the step of drying the separator porous substrate 300 can be carried out.

[0051] The drying step can be varied depending on the solvent used and the method of filling the pores. As an example, the drying step can be carried out in a heating chamber or a vacuum oven at a temperature of 50°C to 100°C. For example, drying with warm air, hot air or low-humidity air, vacuum drying or drying based on (far) infrared or electron beam radiation can be used as the drying method. In addition, a method of placing the separator porous substrate at room temperature so that the residual solvent volatilizes from the surface of the separator porous substrate can be used. Conditions with a temperature range of 10°C to 35°C and a relative humidity of 40% or lower can be considered. Although the drying time is not particularly limited, drying is generally carried out in the range of 30 seconds to 24 hours. After the drying process, a cooling process can be further carried out. In the cooling process, the separator porous substrate can be slowly cooled to room temperature.

[0052] When applying the polymer solution 500 to fill the pores 310 of the separator porous substrate 300, the applied polymer solution 500 can be removed and then the drying step can be carried out, or the drying step can be carried out without removing the applied polymer solution 500. On the other hand, when impregnating the separator porous substrate 300 with the polymer solution 500 to fill the pores 310, it is preferred to dry the separator porous substrate 300 in a state where the separator porous substrate 300 is impregnated with the polymer solution 500.

[0053] After the step of filling the pores 310 of the separator porous substrate 300 with the polymer solution 500, a step of further coating at least one surface of the separator porous substrate 300 may be performed. The coating formed by coating may include an organic material and / or an inorganic material to improve the heat resistance of the separator. The coating may further include a flame retardant.

[0054] The inorganic material for the coating is not particularly limited as long as the inorganic material improves the heat resistance of the separator, forms additional pores, provides a uniform thickness to the coating, and does not undergo oxidation and / or reduction within the operating voltage range of the secondary battery to which the present invention is applied. Specifically, in the case of using inorganic particles having ion transport ability, the ionic conductivity of the electrochemical device can be improved, thereby improving the performance of the electrochemical device. In addition, in the case of using inorganic particles having a high dielectric constant as the inorganic particles, the degree of dissociation of the electrolyte salt (e.g., lithium salt) in the liquid electrolyte can be increased, thereby improving the ionic conductivity of the electrolyte solution.

[0055] In recent years, although alumina (Al 2 O 3 ) has been mainly used as the inorganic material, metal hydroxides or metal oxide hydroxides are also used as the inorganic material in order to improve the flame retardancy. In addition, in addition to metal hydroxides or metal oxide hydroxides, metal oxides may be further mixed in the coating.

[0056] The porosity of the coating may be in the range of 10% to 90%, preferably 30% to 50%. Considering the purpose of forming a coating with a uniform thickness and an appropriate porosity, D50 may have a range of 50 nm to 2.0 μm, but the particle size of the organic material and / or the inorganic material is not particularly limited.

[0057] Based on 100 parts by weight of the total solid content of the coating, the content of the inorganic material may be 50 parts by weight to 95 parts by weight, specifically 60 parts by weight to 95 parts by weight. In the case where the content of the inorganic material is less than 50 parts by weight based on 100 parts by weight of the total solid content of the coating, the content of the binder is too high, whereby the number of voids formed between the inorganic particles is reduced, resulting in a possible decrease in the pore diameter and porosity, and thus the performance of the battery may be reduced, which is not desirable. In the case where the content of the inorganic material is greater than 90 parts by weight based on 100 parts by weight of the total solid content of the coating, the content of the binder is too low, whereby the adhesion force between the inorganic particles may be reduced, and as a result, the mechanical properties of the separator may be reduced, which is also not desirable.

[0058] The coating may include an adhesive. The adhesive is used to stably fix the organic material and / or inorganic material to the surface of the separator porous substrate 300. For example, the adhesive may be any one selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinylacetate, polyethyleneoxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxylmethylcellulose, tannic acid, a compound having a large number of OH groups in the molecule (such as tannic acid), or a mixture of two or more of them.

[0059] To further improve the dispersibility of organic materials and / or inorganic materials, the coating may further include a dispersant. The dispersant is used to keep the organic materials and / or inorganic materials evenly dispersed in the binder when manufacturing the coating slurry, and at least one selected from the group consisting of oil-soluble polyamines, oil-soluble amine compounds, fatty acids, fatty alcohols, and sorbitan fatty acid esters may be used. Specifically, a high molecular weight polyamine amide carboxylate may be used as the dispersant. Based on 100 parts by weight of the organic materials and / or inorganic materials, the content of the dispersant may be 0.2 parts by weight to 10 parts by weight. In the case where the dispersant is included in a proportion less than 0.2 parts by weight, the inorganic materials are likely to precipitate. On the other hand, in the case where the dispersant is included in a proportion greater than 10 parts by weight, the adhesion of the coating to the separator porous substrate 300 decreases, or when manufacturing a secondary battery, the dispersant reacts with the electrolyte solution, thereby generating impurities.

[0060] The following method can be used for coating: forming a slurry; distributing the slurry on the separator porous substrate; and uniformly dispersing the slurry using a doctor blade, die casting method, comma coating method, or screen printing method. In addition, the slurry can be formed on a separate substrate, and the slurry can be bonded to the porous substrate using a pressing or lamination method. At this time, the thickness of the final coating can be adjusted by adjusting the concentration of the solution or the number of coating times. In addition, the coating can be performed using a method of applying a linear dispersion solution. The linear dispersion solution can be applied multiple times to obtain a final coating or a flame retardant layer with a desired thickness.

[0061] The coating step can be performed before the drying step or can be performed after the drying step. In the case where the coating step is performed after the drying step, a separate drying step can be further performed.

[0062] 3) A step of pressing can be performed including the separator porous substrate 300 obtained in the step of filling the pores 310 with the polymer solution 500( Figure 2 (b)) and the stack of the electrodes, as Figure 2 (c) shows.

[0063] The positive electrode 100 and the negative electrode 200 used in the battery can be used as electrodes.

[0064] A high-pressure pressing device can be used to press a stack in which the positive electrode 100, the separator porous substrate 300, and the negative electrode 200 are stacked in sequence under high temperature and high pressure of 400. Preferably, the pressure during pressing is 3 MPa to 20 MPa and the temperature during pressing is 50 °C to 100 °C. However, the temperature and pressure during pressing are not particularly limited as long as the separator porous substrate 300 used as the separator does not separate from the electrodes 100 and 200 from each other. The stack may include a heat-resistant layer. The heat-resistant layer may be located between each electrode and the separator porous substrate 300. The heat-resistant layer may include an inorganic filler, a binder, and a thickener. The weight ratio P of the binder to the thickener (binder / thickener) in the heat-resistant layer is less than 7.2.

[0065] Preferably, a material that has high tolerance to abnormal heat generated by the battery and is electrochemically stable during normal use of the battery is used as the inorganic filler. For example, at least one selected from the group consisting of alumina (Al 2 O 3 ), alumina hydrate (e.g., boehmite (Al 2 O 3 ·H 2 O)), zirconia (ZrO 2 ), magnesia (MgO), aluminum hydroxide (Al(OH) 3 ), magnesium hydroxide (Mg(OH) 2 ), and magnesium carbonate (MgCO 3 ) can be used as the inorganic filler.

[0066] There is no limitation on the binder as long as it can bond materials, and at least one selected from the group consisting of acrylic-based resins, styrene-butadiene rubbers, polyolefin-based resins, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and polyacrylic acid can be used as the binder.

[0067] At least one selected from the group consisting of carboxymethyl cellulose, methyl cellulose, polyacrylic acid, and polyethylene oxide can be used as the thickener. Depending on the types of the binder and the inorganic filler and the degree of the solvent, the thickener configured to provide viscosity to the heat-resistant layer may not be included in the heat-resistant layer.

[0068] An initial electrolyte solution can be injected into the pressed stack to discharge the polymer solution 500 in the pores 310 of the separator porous substrate 300 to the outside, as shown in Figure 2 (d). In the step of injecting the initial electrolyte solution, the stack may be in a state of being accommodated in the battery case, or may be in a state of not being accommodated in the battery case.

[0069] When the stack is accommodated in the battery case, the battery case may be provided with an electrolyte solution discharge port. When the stack is not accommodated in the battery case, the pressed stack may be immersed in a container containing an initial electrolyte solution, and then only the stack may be accommodated in the battery case.

[0070] Perform a step of discharging the polymer solution 500 to the outside to discharge the polymer solution 500 filling the pores 310 of the separator porous substrate 300 to the outside without affecting the battery function. Preferably, the stack 5 is impregnated with the initial electrolyte solution for 5 minutes to 2 hours.

[0071] A device configured to discharge the polymer solution 500 to the outside without damaging the separator porous substrate 300 may be added to discharge the polymer solution 500 in the pores 310 of the separator porous substrate 300 to the outside. A device configured to apply vibration to the separator including the separator porous substrate 300 or move the initial electrolyte solution in which the separator including the separator porous substrate 300 is impregnated using ultrasonic waves may be added. As a result, the polymer solution 500 in the pores 310 can be removed more easily.

[0072] The initial electrolyte solution may be composed of a non-aqueous electrolyte solution and a lithium salt. A non-aqueous organic solvent is used as the non-aqueous electrolyte solution. However, the present invention is not limited thereto.

[0073] An aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate or ethyl propionate may be used as the non-aqueous organic solvent.

[0074] The lithium salt is a material that is soluble in the non-aqueous electrolyte solution. For example, LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiAlCl 4, CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2 ) 2 Lithium salts such as NLi, lithium chloroborate, lithium lower aliphatic carboxylate, lithium tetraphenylborate, or imide can be used.

[0075] 5) The step of injecting the second electrolyte solution into the stack can be carried out after the step of injecting the initial electrolyte solution into the stack.

[0076] The step of injecting the second electrolyte solution is carried out after the stack is accommodated in the battery case, as shown in Figure 2 (e). The step of accommodating the stack in the battery case can be carried out before the step shown in Figure 2 (d). After injecting the second electrolyte solution, the initial charge and discharge can be carried out in a state where the battery case is completely or temporarily sealed or in a state where the battery case is not sealed.

[0077] The second electrolyte solution can be a material miscible with the initial electrolyte solution. In addition, the initial electrolyte solution and the second electrolyte solution can be the same material.

[0078] The second electrolyte solution can be composed of a non-aqueous electrolyte solution and a lithium salt. A non-aqueous organic solvent is used as the non-aqueous electrolyte solution. However, the present invention is not limited thereto.

[0079] Aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate or ethyl propionate can be used as the non-aqueous organic solvent.

[0080] The lithium salt is a material soluble in the non-aqueous electrolyte solution. For example, LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO2 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2 ) 2 Lithium salts such as NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, or imide can be used.

[0081] In addition, in order to improve charge and discharge characteristics and flame retardancy, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, ethylene glycol dimethyl ether, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, or the like can be added to the non-aqueous electrolyte solution. Optionally, in order to impart non-flammability thereto, the non-aqueous electrolyte solution may further include a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene. In addition, in order to improve its high-temperature storage characteristics, the non-aqueous electrolyte solution may further include carbon dioxide gas. Further, fluoroethylene carbonate (FEC) and propene sultone (PRS) may be further included.

[0082] In the case of stacking solid electrolytes, such as batteries, rather than the separator including the separator porous substrate 300 according to the present invention, the second electrolyte solution may not be injected.

[0083] Hereinafter, the present invention will be described with reference to the following examples. The examples are provided only for easier understanding of the present invention and should not be construed as limiting the scope of the present invention.

[0084] In the following examples and comparative examples, a positive electrode obtained by coating a slurry of a mixture of LiCoO as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder, and carbon as a conductive agent on an aluminum foil, and a negative electrode obtained by coating a slurry of a mixture of graphite as a negative electrode active material and styrene-butadiene rubber as a binder on copper are used. A polyethylene porous substrate is used as the separator porous substrate, and no separate coating is formed on the separator porous substrate. 2

[0085] <Example>

[0086] In an embodiment of the present invention, an electrode assembly according to the present invention is manufactured by the following steps.

[0087] ① Dissolve PVdF-HFP in acetone as a ketone solvent to prepare a polymer solution.

[0088] ② Apply the polymer solution to a polyethylene porous substrate as a separator for 10 minutes, and then dry it.

[0089] ③ Coat alumina particles with a D50 of 50 nm to 2.0 μm on the separator obtained in step ②.

[0090] ④ Stack the coated separator obtained in step ③ with the positive electrode and the negative electrode, and use a high-pressure pressing device to press the stack at a pressure of about 19.61 MPa (200 kgf / cm 2 ) and a temperature of 50 °C.

[0091] <Comparative Example>

[0092] In the comparative example provided for comparison with the present invention, the steps of preparing and applying the polymer solution corresponding to steps ① and ② of the present invention are not included.

[0093] <Test Example 1>

[0094] Measure the thickness of the electrode assemblies according to the examples and the comparative example before pressing and after pressing with a high-pressure pressing device. Only measure the thickness of the pore part of the polyethylene porous substrate through the electron micrographs of the samples before and after pressing. The 2500-fold photographs of the sample surface measured using a field emission scanning electron microscope (FE-SEM) (Hitachi S-4800 Scanning Electron Microscope) are shown in Figures 3a to 3d . Figures 3a to 3d are 2500-fold field emission scanning electron microscope (FE-SEM) photographs showing the surfaces of the polyethylene porous substrates before and after pressing the electrode assemblies according to the comparative example and the examples of the present invention. Here, A represents the comparative example, and B represents the example. Figure 3a and Figure 3b are the photographs before pressing, Figure 3c and 3d are the photographs after pressing. Only measure the thickness of the polyethylene porous substrate, and the average values of the measured values are shown in Table 1 below.

[0095] <Test Example 2>

[0096] Measure the weight per unit area of the electrode assemblies according to the examples and the comparative example before pressing and after pressing with a high-pressure pressing device. The measured values are shown in Table 1 below.

[0097] <Test Example 3>

[0098] The air permeability ( Gurley number ) of each electrode assembly according to the examples and comparative examples was measured using the ASTM D726-94 method. Here, the air permeability ( Gurley number ), which is the air flow resistance, was measured using a Gurley densometer. Here, the air permeability value is represented by the time ( seconds ) required for 100 cc of air to pass through a 1 mm 2 cross-section of each electrode assembly fabricated according to the examples and comparative examples under a pressure of 12.2 in.H 2 O, that is, the air penetration time. The results are shown in Table 1 below.

[0099] [Table 1]

[0100]

[0101] As shown in Table 1 above, when comparing the comparative example before and after pressing, the thickness of the comparative example decreased by about 7%, and the time required for 100 cc of air to pass through the comparative example increased. In contrast, it can be seen that in the present invention, the thickness and air permeability did not change.

[0102] In the comparative example and the example, the weight per unit area did not change before and after pressing. The reason that the weight per unit area of the example is about 100 times that of the comparative example is that the pores of the separator porous substrate in the example were filled with the polymer solution. If the size of the pores in the example changed by pressing, there might be a difference in the weight before and after pressing in the example. As can be seen from Table 1 above, there is no difference in the weight before and after pressing in the example. Therefore, it can be indirectly seen that in the electrode assembly according to the present invention, the shape and size of the pores before pressing were maintained.

[0103] In the comparative example, even though its thickness decreased after pressing, the weight per unit area did not differ. This is because the pores in the comparative example were filled with air, and the change in the amount of air due to the decrease in thickness was substantially very small.

[0104] The reason that the Gurley number representing the air permeability is large in the example is that the movement of air was delayed because the pores of the separator porous substrate according to the example were filled with the polymer solution.

[0105] The results show that the air permeability of the example according to the present invention is not good compared with the comparative example. However, this is caused by the polymer solution. From the results in the above table, it can be seen that the thickness and physical properties of the pores of the porous substrate in the example of the present invention did not change even after pressing.

[0106] Figures 3a to 3d are electron micrographs showing the electrode assemblies of the comparative example and the example according to the present invention before pressing and after pressing using a high-pressure pressing device. Figures 3a to 3d Mainly shows the porous substrate. In Figures 3a to 3dIn [the figure], A represents the photograph of the comparative example, and B represents the photograph of the example. "Before pressing" is represented by "Before lamination", and "after pressing" is represented by "After lamination". Figures 3a to 3d The numerical values shown in [the figure] only represent the measured thickness of the porous substrate. The values shown in Table 1 only represent the average value of the thickness of the porous substrate.

[0107] The thickness of the porous substrate according to the present invention before pressing is 7 μm. From Figures 3a to 3d it can be seen that the thicknesses of the porous substrates according to the comparative example before and after pressing are different from each other. The thickness of the thin part (highly pressed part) of the pressed porous substrate is 4.5 μm, and the thickness of the thick part (unpressed part) of the pressed porous substrate is 7 μm. Therefore, it can be seen that the porous substrate has undergone a large deformation and the change of the porous substrate is non-uniform.

[0108] In contrast, it can be seen that the thickness of the porous substrate according to the example of the present invention hardly changes before and after pressing, and the thickness of the porous substrate is very uniform. The measured thickness of the porous substrate according to the example after pressing is 6.9 μm, which is very similar to the thickness (7 μm) of the porous substrate before pressing. It can be seen that the porous substrate of the electrode assembly according to the present invention hardly changes before and after pressing, and the porous substrate is also uniform.

[0109] <Test Example 4>

[0110] In Test Example 4, coin cells were manufactured using the electrode assemblies according to the example and the comparative example, and the impedance values of the coin cells were measured using Solartron analytical EIS under the conditions of a frequency of 300,000 Hz to 0.1 Hz and an AC amplitude of 10 mA. Figure 4 The resistance values in the results are shown. Figure 4 is a graph showing the measured resistance values of the coin cells using the comparative example (before and after pressing) and the example (before and after pressing and after discharging the polymer from the holes) of the present invention.

[0111] In the electrode assembly, the positive electrode and the negative electrode are stacked on the separator and then laminated. However, in order to confirm the effects according to the present invention, the electrode assemblies according to the example and the comparative example were measured using various methods.

[0112] B: In order to remove the polymer solution filling the pores of the electrode assembly according to the example, propylene carbonate as the initial electrolyte solution was injected to discharge the PVdF-HFP located in the pores of the separator to the outside, and a second electrolyte solution made of the same material as the initial electrolyte solution was injected to manufacture a coin cell.

[0113] B”: A coin cell is manufactured using the electrode assembly according to the embodiment, and propylene carbonate is used as the electrolyte solution. Compared with B, there is no step of removing the polymer solution using the initial electrolyte solution.

[0114] B’: Compared with B”, the difference is only that the electrode assembly of the embodiment is not pressed.

[0115] A”: Compared with B”, the difference is only that the electrode assembly according to the comparative example is used.

[0116] A’: Compared with B’, the difference is only that the electrode assembly according to the comparative example is used.

[0117] Reference Figure 4 , it can be seen that in the comparative example, the resistance value of the battery changes from 0.53 Ω (before pressing) to 0.57 Ω (after pressing), showing a significant difference; however, in the present invention, the resistance value of the battery before pressing is 0.55 Ω, and the resistance value of the battery after pressing is 0.55 Ω, which are equal to each other.

[0118] In the case of B, the initial electrolyte solution is used to remove the polymer material in the pores, and the resistance value after pressing is 0.53 Ω, which is equal to the resistance value in the initial state (A’) where there is no polymer material in the pores and no pressing is performed. As a result, it can be seen that in the case of using the method for manufacturing the electrode assembly according to the present invention, the physical properties of the porous substrate are substantially unchanged.

[0119] <Test Example 5>

[0120] The coin cells according to B and A” are charged to 0.5C and 1.1V at 23 °C and discharged at a constant current of 1C to 3.0V. In this way, 400 charge and discharge cycles are performed, and the capacity is measured every 50 cycles. The results are shown in Figure 5 in.

[0121] Figure 5 is a graph showing the results of capacity measurement during 400 charge and discharge cycles using the comparative example (A) and the embodiment (B) of the present invention.

[0122] As Figure 5 shown, it can be seen that the capacity retention rate of the battery according to the embodiment of the present invention is greater than that of the battery according to the comparative example. This indirectly indicates that the porosity of the separator remains uniform and the deformation of the separator is very small.

[0123] Although the specific details of the present invention have been described in detail, those skilled in the art will understand that the detailed description only discloses the preferred embodiments of the present invention and thus does not limit the scope of the present invention. Accordingly, those skilled in the art will understand that various changes and modifications can be made without departing from the scope and technical concept of the present invention, and it is obvious that these changes and modifications fall within the scope of the appended claims.

[0124] -Description of Reference Numerals-

[0125] 100: Positive electrode

[0126] 200: Negative electrode

[0127] 300: Separator porous substrate

[0128] 310: Pore

[0129] 400: Pressing

[0130] 500: Polymer solution

[0131] Industrial Applicability

[0132] As is obvious from the above description, in the method for manufacturing an electrode assembly according to the present invention, in the steps of stacking and pressing the electrodes and the separator, the pores of the separator porous substrate to be used as the separator are filled with the polymer solution, and thus the shape or volume of the pores does not change. Therefore, the porosity of the separator after manufacturing the electrode assembly is similar to the porosity of the separator before stacking. As a result, a battery including the electrode assembly according to the present invention has high ionic conductivity and excellent performance.

[0133] Therefore, in the case of using the method for manufacturing an electrode assembly according to the present invention, an electrode assembly that is economical, simple, and greatly improved in terms of its performance and lifespan can be provided.

Claims

1. A method for manufacturing an electrode assembly, comprising: 1) Dissolving a polymer soluble in an electrolyte solution in a solvent to produce a polymer solution; 2) Filling pores of a separator porous substrate to be used as a separator with the polymer solution of step 1); 3) Manufacturing a stack including the separator of step 2) and an electrode by pressing; 4) Injecting an initial electrolyte solution into the stack of step 3) to discharge the polymer solution in the pores of the separator porous substrate to the outside; and 5) Injecting a second electrolyte solution into the stack of step 4).

2. The method for manufacturing an electrode assembly according to claim 1, wherein the solvent of step 1) is not an electrolyte solution.

3. The method for manufacturing an electrode assembly according to claim 1, wherein filling the pores of the separator porous substrate with the polymer solution in step 2) includes applying the polymer solution to the separator porous substrate or impregnating the separator porous substrate with the polymer solution.

4. The method for manufacturing an electrode assembly according to claim 1, further comprising: Drying the separator porous substrate after step 2).

5. The method for manufacturing an electrode assembly according to claim 1, further comprising: Further coating at least one surface of the separator porous substrate after step 2).

6. The method for manufacturing an electrode assembly according to claim 1, wherein stacking in step 3) includes a heat-resistant layer.

7. The method for manufacturing an electrode assembly according to claim 1, wherein the pressing in step 3) is performed at a pressure of 3 MPa to 20 MPa and a temperature of 50 °C to 100 °C.

8. The method for manufacturing an electrode assembly according to claim 1, wherein the initial electrolyte solution and the second electrolyte solution are miscible with each other.

9. The method for manufacturing an electrode assembly according to claim 1, wherein the initial electrolyte solution and the second electrolyte solution are the same as each other.

10. The method for manufacturing an electrode assembly according to claim 1, wherein the polymer soluble in the electrolyte solution in step 1) is a PVdF-based polymer, and the solvent is an organic solvent.

11. The method for manufacturing an electrode assembly according to claim 1, further comprising performing an initial charge and discharge after step 5).

12. An electrode assembly manufactured by the manufacturing method according to any one of claims 1 to 11.

13. An electrochemical device comprising the electrode assembly according to claim 12.

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