Electrode assembly and method for manufacturing the same

Abstract

The present invention provides an electrode assembly comprising a porous polymer substrate, a first porous coating layer formed on one surface of the porous polymer substrate, and a second porous coating layer formed on the other surface of the porous polymer substrate, wherein the separation membrane is bent into a zigzag shape; a negative electrode disposed between the first porous coating layers; and a positive electrode disposed between the second porous coating layers, wherein the first porous coating layer is used which has greater adhesion to the negative electrode than to the positive electrode, thereby reducing the deviation in electrode-separation membrane adhesion on both sides of the separation membrane and providing an electrode assembly with reduced bending.

Description

[Technical Field]

[0001] This application claims priority based on Korean Patent Application No. 10-2023-0057043, filed with the Korean Intellectual Property Office on 2 May 2023, and its contents are incorporated herein by reference.

[0002] The present invention relates to an electrode assembly including a zigzag-type separation membrane, and a method for manufacturing the same. [Background technology]

[0003] Electrochemical devices convert chemical energy into electrical energy using electrochemical reactions. In recent years, lithium-ion batteries, which have high energy density and voltage, long cycle life, and can be used in various fields, have become widely used. With the increasing demand for electric vehicles and energy storage devices, development is underway on materials and structures to maximize capacity and energy density.

[0004] A secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator membrane placed between the positive and negative electrodes, and the electrode assembly may be manufactured by housing it in a case together with an electrolyte. Depending on the shape of the case in which the electrode assembly is housed, secondary batteries can be classified into pouch type, cylindrical type, rectangular type, coin type, etc. Depending on the manufacturing method and shape of the electrode assembly, they can be classified into jelly roll type, stack type, etc.

[0005] Recently, an electrode assembly with a zigzag stacking method has been developed, in which a long sheet-shaped separator is folded in a zigzag shape while alternately arranging positive and negative electrodes between adjacent folds. For example, when a long sheet-type separator wound around a cylinder is supplied, the electrode assembly can be manufactured by tilting or swinging the table on which the electrode assembly is stacked, or reciprocating the supply roll that transfers the separator, while folding the separator in a zigzag and arranging each electrode between them. Zigzag stacking has the advantage of excellent productivity because the process is simpler compared to other types.

[0006] The separator used in zigzag stacking can be formed by coating a coating slurry on both sides of a porous polymer substrate, and the electrode can be formed by coating an active material slurry on both sides of an electrode current collector. While the separator is folded in a zigzag and a plurality of positive and negative electrodes are alternately arranged, the positive and negative electrodes adhere to the opposite surfaces of the separator. At this time, if there is a difference in the adhesive force between the separator and the positive electrode and the adhesive force between the separator and the negative electrode, that is, if the adhesive forces applied to both sides of the separator are different from each other, bending of the manufacturing process or the manufactured electrode assembly may occur. For example, if the adhesive force between the separator and the negative electrode is stronger than the adhesive force between the separator and the positive electrode, bending may occur in the direction where the negative electrode adheres in the separator. Bending of the electrode assembly may cause detachment of the electrode and the separator, or lead to a low stiffness of the electrochemical device, causing safety problems. If the heat and pressure applied to the electrode assembly are increased to prevent the occurrence of bending of the electrode assembly, the separator located on the outer periphery of the electrode assembly may have a problem that the air permeability decreases due to excessive compression and the electrical resistance increases. Summary of the Invention Problems to be Solved by the Invention

[0007] The present invention aims to provide a zigzag electrode assembly including a separation membrane in which porous coating layers on both sides are formed with different structures in consideration of the types of adjacent electrodes, and a method for manufacturing the same.

Means for Solving the Problems

[0008] One aspect of the present invention includes a porous polymer substrate, a first porous coating layer formed on one surface of the porous polymer substrate, and a second porous coating layer formed on the other surface of the porous polymer substrate, and an electrode assembly including a separation membrane bent in a zigzag shape, a negative electrode disposed between the first porous coating layers, and a positive electrode disposed between the second porous coating layers, wherein the first porous coating layer provides an electrode assembly having an adhesive force with the negative electrode greater than that with the positive electrode.

[0009] The second porous coating layer may have an adhesive force with the positive electrode greater than that with the negative electrode.

[0010] The adhesive force between the first porous coating layer and the negative electrode may be 0.8 to 1.2 times the adhesive force between the second porous coating layer and the positive electrode.

[0011] The first porous coating layer includes first binder particles and inorganic particles, and the average particle size of the first binder particles may be greater than or the same as the average particle size of the inorganic particles.

[0012] The first porous coating layer may contain the first binder particles and the inorganic particles in a weight ratio of 20:80 to 80:20.

[0013] The second porous coating layer includes second binder particles and inorganic particles, and the average particle size of the inorganic particles may be greater than the average particle size of the second binder particles.

[0014] The positive electrode comprises a positive electrode active material and a positive electrode binder resin, and the second binder particles and the positive electrode binder resin may be fluorine-based polymers.

[0015] The thickness of the first porous coating layer may be greater than or equal to the thickness of the second porous coating layer.

[0016] The electrode assembly may have a long side length of 500 to 600 mm.

[0017] The thickness of the electrode assembly may be 8 to 20 mm.

[0018] Another aspect of the present invention is to provide an electrochemical element including the electrode assembly.

[0019] The electrochemical element may be a lithium secondary battery. [Effects of the Invention]

[0020] The zigzag electrode assembly of the present invention maintains the advantage of excellent productivity while providing a structure in which the difference in adhesive strength between electrodes bonded to both sides of the separation membrane is low, thereby reducing bending due to the difference in electrode-separation membrane adhesive strength, and improving the safety of the electrochemical element including the electrode assembly. [Brief explanation of the drawing]

[0021] [Figure 1] This is a conceptual diagram showing a structure in which a separation membrane and an electrode are bonded together in an electrode assembly according to one specific example of the present invention.

[0022] [Figure 2] This is a conceptual diagram illustrating the process for evaluating the degree of bending of a secondary battery in an experimental example of the present invention. [Modes for carrying out the invention]

[0023] The following describes in more detail the various components of the present invention so that a person with ordinary skill in the art to which the present invention belongs can easily implement it. However, this is merely an example, and the scope of the rights of the present invention is not limited to the following.

[0024] As used herein, the term "including" is used to enumerate materials, compositions, apparatus, and methods useful for the present invention, and is not limited to such enumerated examples.

[0025] As used herein, “about” and “substantially” are used to mean within or near the range of numerical values ​​or degrees, taking into account inherent tolerances of manufacturing and materials, and are used to prevent infringers from unfairly exploiting the content of disclosures that refer to precise or absolute numerical values ​​provided to aid in understanding the invention.

[0026] As used herein, "electrochemical elements" may refer to primary batteries, secondary batteries, supercapacitors, and the like.

[0027] One specific example of the present invention provides an electrode assembly comprising a porous polymer substrate, a first porous coating layer formed on one surface of the porous polymer substrate, and a second porous coating layer formed on the other surface of the porous polymer substrate, a separation membrane that can be folded into a zigzag shape, a negative electrode disposed between the first porous coating layers, and a positive electrode disposed between the second porous coating layers. The first porous coating layer may have an adhesive force to the negative electrode that is greater than the adhesive force to the positive electrode.

[0028] The separation membrane has a structure in which a first porous coating layer and a second porous coating layer are laminated on both sides of a porous polymer substrate. The first porous coating layer and the second porous coating layer are arranged to face each other with the porous polymer substrate in between. Folding the separation membrane in a zigzag shape may mean folding the separation membrane at predetermined intervals. Preferably, all of these intervals may be the same. While folding the separation membrane, multiple positive electrodes and negative electrodes can be alternately arranged in between. The negative electrodes may be arranged between the first porous coating layers of the separation membrane, and the positive electrodes may be arranged between the second porous coating layers of the separation membrane.

[0029] The porous polymer substrate is a porous membrane with multiple pores formed therein, which electrically insulates the positive electrode and the negative electrode to prevent short circuits. For example, if the electrochemical element is a lithium secondary battery, the porous polymer substrate can be an ion-conducting barrier that blocks electrical contact between the positive electrode and the negative electrode while allowing lithium ions to pass through. At least some of the pores can form a three-dimensional network that connects the surface and the interior of the porous polymer substrate, allowing fluids to pass through the porous polymer substrate via the pores.

[0030] The porous polymer substrate can be made of a material that is physically and chemically stable with respect to an electrolyte, which is an organic solvent. For example, the porous polymer substrate may include, but is not limited to, polyolefins such as polyethylene, polypropylene, and polybutylene, polyvinyl chloride, polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimidoamide, nylon®, polytetrafluoroethylene, and copolymers or mixtures thereof. Preferably, polyolefin resins can be used. Polyolefin resins can be processed to a relatively thin thickness and are easy to apply coating slurries to, making them suitable for the manufacture of electrochemical elements with higher energy density.

[0031] The porous polymer substrate may have a single-layer or multilayer structure. The porous polymer substrate can provide a shutdown function in the event of a high-temperature runaway of the battery by including two or more polymer resin layers with different melting points (Tm). For example, the porous polymer substrate may include a polypropylene layer with a relatively high melting point and a polyethylene layer with a relatively low melting point. Preferably, the porous polymer substrate may have a three-layer structure in which polypropylene, polyethylene, and polypropylene are laminated in that order. The polyethylene layer can melt and shut down the pores as the battery temperature rises above a predetermined temperature, thereby preventing thermal runaway of the battery.

[0032] The thickness of the porous polymer substrate may be between 1 μm and 100 μm. Specifically, the thickness of the porous polymer substrate may be between 10 μm and 90 μm, between 20 μm and 80 μm, between 30 μm and 70 μm, or between 40 μm and 60 μm. Preferably, the thickness of the polymer substrate may be between 1 μm and 30 μm. More preferably, the thickness of the polymer substrate may be between 5 μm and 15 μm, or between 7 μm and 13 μm. By adjusting the thickness of the porous polymer substrate within the above range, it is possible to minimize the volume of the electrochemical element while electrically insulating the positive and negative electrodes, and to increase the amount of active material contained in the electrochemical element.

[0033] The porous polymer substrate may contain pores with an average diameter of 0.01 μm or more and 1 μm or less. Specifically, the size of the pores contained in the porous polymer substrate may be 0.01 μm or more and 0.09 μm or less, 0.02 μm or more and 0.08 μm or less, 0.03 μm or more and 0.07 μm or less, or 0.04 μm or more and 0.06 μm or less. Preferably, the size of the pores may be 0.02 μm or more and 0.06 μm or less. By adjusting the size of the pores in the porous polymer substrate within the above range, the air permeability and ionic conductivity of the entire separation membrane produced can be adjusted.

[0034] The porous polymer substrate can have an air permeability of 10 s / 100 cc or more and 100 s / 100 cc or less. Specifically, the air permeability of the porous polymer substrate may be 10 s / 100 cc or more and 90 s / 100 cc or less, 20 s / 100 cc or more and 80 s / 100 cc or less, 30 s / 100 cc or more and 70 s / 100 cc or less, or 40 s / 100 cc or more and 60 s / 100 cc or less. Preferably, the air permeability of the porous polymer substrate may be 50 s / 100 cc or more and 70 s / 100 cc or less. When the air permeability of the porous polymer substrate is within the above range, the air permeability of the manufactured separation membrane can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical element.

[0035] The aforementioned air permeability (s / 100cc) refers to the time (in seconds) it takes for 100cc of air to pass through a predetermined area of ​​a porous polymer substrate or separation membrane under constant pressure. This air permeability can be measured using a Gurley densometer in accordance with ASTM D726-58, ASTM D726-94, or JIS-P8117. For example, using a Gurley 4110N instrument, it can measure air at a pressure of 0.304 kPa or 1.215 kN / m³. 2 Under the pressure of water, 100cc of air will fill 1 square inch (or 6.54cm) 2 The time it takes for a sample to pass through can be measured. For example, using the EG01-55-1MR instrument from Asahi Seiko, the time it takes for 100cc of air to pass through a 1 square inch sample can be measured at room temperature and under constant pressure in a 4.8-inch volume of water.

[0036] The porous polymer substrate may have a porosity of 10 vol% to 60 vol%. Specifically, the porosity of the porous polymer substrate may be 15 vol% to 55 vol%, 20 vol% to 50 vol%, 25 vol% to 45 vol%, or 30 vol% to 40 vol%. Preferably, the porosity of the porous polymer substrate may be 30 vol% to 50 vol%. When the porosity of the porous polymer substrate is within the above range, the ionic conductivity of the manufactured separation membrane can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical element.

[0037] The porosity referred to above means the volume ratio of pores to the total volume of the porous polymer substrate. The porosity can be measured by methods known in the art. For example, it can be measured by the Brunauer Emmett Teller (BET) method utilizing nitrogen gas adsorption, the capillary flow porometer, or the water or mercury osmosis method.

[0038] The porous coating layer may encompass a first porous coating layer and a second porous coating layer. The first porous coating layer and the second porous coating layer are each formed on one surface of the porous polymer substrate and may contain a polymer binder and inorganic particles. The polymer binder can bind the inorganic particles, bond the porous coating layer and the porous polymer substrate, and impart adhesive force to the separation membrane to achieve adhesion to the electrode. The polymer binder may be spherical, elliptical, or otherwise shaped binder particles. The first porous coating layer may contain first binder particles and inorganic particles, and the second porous coating layer may contain second binder particles and inorganic particles. The first binder particles and the second binder particles contained in the first porous coating layer and the second porous coating layer, respectively, are different from each other, and the inorganic particles may be identical or different from each other.

[0039] Specifically, the first binder particles may contain an acrylic polymer. The acrylic polymer may be (meth)acrylic acid, (meth)acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate The material may contain one or more monomers selected from the group consisting of methacrylate, hydroxyethyl methacrylate, (meth)acrylonitrile butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-oxyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate, and pentafluorophenyl acrylate as repeating units.

[0040] For example, the acrylic polymer may include one or more selected from the group consisting of polyacrylic acid, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene-styrene rubber.

[0041] The average particle size (D50) of the first binder particles may be larger than or the same as the average particle size of the inorganic particles described later. Here, inorganic particles refer to those included in the first porous coating layer together with the first binder particles. The inorganic particles of the first porous coating layer may have an average particle size (D50) of 300 nm or more and 500 nm or less, and the first binder particles may have an average particle size (D50) of 500 nm or more and 1000 nm or less. Specifically, the first binder particles may have an average particle size of 550 nm or more and 950 nm or less, 600 nm or more and 900 nm or less, 650 nm or more and 850 nm or less, or 700 nm or more and 800 nm or less. Preferably, the first binder particles may have an average particle size of 500 nm or more and 700 nm or less. The first binder particles, which are acrylic polymers, may have a greater adhesive force to the negative electrode than the adhesive force of the second binder particles to the positive electrode. In this specific example, by adjusting the average particle size of the first binder particles to be greater than or equal to the average particle size of the inorganic particles within the range described above, the deviation in electrode-separation membrane adhesion force with each electrode on both sides of the separation membrane can be reduced, thereby preventing the formation of bending of the electrode assembly.

[0042] Specifically, the second binder particles may be a fluorine-based polymer. Preferably, the fluorine-based polymer may be a polyvinylidene fluoride-based polymer. For example, the fluorine-based polymer binder may be one or more selected from the group consisting of polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-trichloroethylene (PVDF-TCE), and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE), and more specifically, it may be a copolymer containing polyvinylidene fluoride.

[0043] The average particle size (D50) of the second binder particles may be smaller than the average particle size of the inorganic particles described later. Here, inorganic particles refer to those included in the second porous coating layer together with the second binder particles. The inorganic particles of the second porous coating layer may have an average particle size (D50) greater than 300 nm and greater than 500 nm, and the second binder particles may have an average particle size (D50) of 100 nm or more and less than or equal to 300 nm. Preferably, the second binder particles may have an average particle size of 200 nm or more and less than or equal to 300 nm. The second binder particles, which are fluorine-based polymers, may have a lower adhesion force to the positive electrode than the adhesion force of the first binder particles to the negative electrode. In this specific example, by adjusting the average particle size of the second binder particles to less than the average particle size of the inorganic particles within the range described above, the surface area on which the second binder particles can contact the electrode can be increased, thereby improving the electrode-separation film adhesion force with the positive electrode. This reduces the deviation in electrode-separation membrane adhesion strength between each electrode on both sides of the separation membrane, thereby preventing bending of the electrode assembly.

[0044] The inorganic particles can be those that are electrochemically stable. The inorganic particles are not particularly limited as long as oxidation and / or reduction reactions do not occur within the operating voltage range of the electrochemical device (for example, 0 to 5 V based on Li / Li + . In particular, when using inorganic particles with a high dielectric constant as the inorganic particles, it can contribute to an increase in the dissociation degree of electrolyte salts in the liquid electrolyte, such as lithium salts, and improve the ionic conductivity of the electrolyte solution. For the reasons described above, it is preferable that the inorganic particles include inorganic particles with a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles with a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), b 1-x La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Yttria (Y2O3), alumina (Al2O3), aluminum hydroxide (Al(OH)3), silicon carbide (SiC), aluminum oxyhydroxide (AlOOH), titanium dioxide (TiO2), or mixtures thereof, and the like.

[0045] In addition, as the inorganic particles, inorganic particles having lithium ion transfer ability, that is, inorganic particles containing a lithium element but having a function of moving lithium ions without storing lithium can be used. Non-limiting examples of inorganic particles having lithium ion transfer ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) such as 14Li2O-9Al2O3-38TiO2-39P2O5 x O ySeries of glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 S4 and other lithium germanium thiophosphates (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitrides such as Li3N (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glasses such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glasses such as LiI-Li2S-P2S5 (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), or mixtures thereof, etc.

[0046] Also, as the inorganic particles, inorganic particles having flame retardancy can be used, which can impart flame retardant properties to the separation membrane or prevent the temperature inside the electrochemical device from rising rapidly. Non-limiting examples of the inorganic particles having flame retardancy include Sb2O3, Sb2O4, Sb2O5, SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, Zn2SnO4, ZnSnO3, ZnSn(OH)6, ZrO2, Y2O3, SiO2, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, H3BO3, HBO2, and mixtures thereof, etc.

[0047] The first porous coating layer and the second porous coating layer may contain inorganic particles of the same type or different average particle sizes. For example, the first porous coating layer and the second porous coating layer may contain inorganic particles that are the same type but have different average particle sizes. Preferably, the first porous coating layer and the second porous coating layer may contain the same inorganic particles with an average particle size (D50) of 300 nm or more and 500 nm or less. By adjusting the average particle size of the inorganic particles within the above range, the deviation between the adhesive force between the first porous coating layer and the negative electrode and the adhesive force between the second porous coating layer and the positive electrode can be reduced, thereby preventing bending of the electrode assembly.

[0048] The porous coating layer may contain polymer binder and inorganic particles in a weight ratio of 20:80 to 80:20. Specifically, the porous coating layer may contain binder particles and inorganic particles in weight ratios of 25:75 to 75:25, 30:70 to 70:30, 35:65 to 65:35, 40:60 to 60:40, or 45:55 to 55:45. By adjusting the content of polymer binder and inorganic particles within the above ranges, thermal shrinkage of the porous polymer substrate can be prevented, preventing electrode short circuits due to shrinkage of the separation membrane and ensuring adhesion of the separation membrane to the electrodes. The content ratio of binder particles and inorganic particles in the first porous coating layer and the second porous coating layer may be the same or different. For example, the first porous coating layer may have a higher binder particle content than the second porous coating layer.

[0049] The porous coating layer may be formed by coating one surface of the porous polymer substrate with a coating slurry containing the binder particles, the inorganic particles, and the dispersion medium. The separation membrane may be manufactured by applying a first coating slurry for forming the first porous coating layer to one surface of the porous polymer substrate and a second coating slurry for forming the second porous coating layer to the other surface, and then drying to remove the dispersion medium. Preferably, the first coating slurry and the second coating slurry may be applied and dried simultaneously. The porous coating layer may have a porous structure by including interstitial volumes in which the inorganic particles are linked by the binder particles. The porous coating layer can adhere to the porous polymer substrate while allowing lithium ions to pass through, thereby preventing thermal shrinkage of the porous polymer substrate.

[0050] The coating slurry can disperse binder particles and inorganic particles by containing a dispersion medium. By adjusting the type and content of the dispersion medium, a coating slurry can be used in which the inorganic particles are uniformly dispersed. For example, it may be water.

[0051] The coating slurry can be further enriched with additives such as dispersants, surfactants, defoamers, flame retardants, and wetting agents to improve dispersibility and flame retardancy, and to enhance the uniformity of the resulting porous coating layer. For example, the dispersant may include one or more selected from the group consisting of oil-soluble polyamines, oil-soluble amine compounds, fatty acids, fatty alcohols, sorbitan fatty acid esters, tannic acid, and pyrogallol. Using the above-mentioned types of dispersants can improve the stability of the coating slurry and ensure the uniformity of the porous coating layer formed by the coating slurry.

[0052] The additive may be present in an amount of 0% to 5% by weight relative to the total weight of the coating slurry. Specifically, the content of the additive may be 0.01% to 4% by weight, 0.1% to 3% by weight, or 1% to 2% by weight. Preferably, the content of the additive may be 3% to 5% by weight. By adjusting the content of the additive within the above range, uniform dispersion and stability of the inorganic particles contained in the coating slurry can be achieved.

[0053] The dispersion medium contained in the coating slurry may be removed by drying or heating after the formation of the porous coating layer. For example, the porous coating layer may contain 5 ppm or less of the dispersion medium. Preferably, the porous coating layer may consist of binder particles and inorganic particles. Multiple pores may be formed on the surface and inside the porous coating layer during the process of removing the dispersion medium. These pores may include interstitial volumes formed between the inorganic particles and may have a structure that forms a three-dimensional network through which fluid can pass.

[0054] The thickness of the porous coating layer may be 1 μm or more and 15 μm or less. Specifically, the thickness of the porous coating layer may be 2 μm or more and 14 μm or less, 3 μm or more and 13 μm or less, 4 μm or more and 12 μm or less, 5 μm or more and 11 μm or less, 6 μm or more and 10 μm or less, or 7 μm or more and 9 μm or less. By adjusting the thickness of the porous coating layer within the above range, shrinkage of the porous polymer substrate can be minimized and stable adhesion to the porous polymer substrate can be achieved. Preferably, the thickness of the first porous coating layer may be greater than the thickness of the second porous coating layer.

[0055] The separation membrane for the electrochemical element may have an air permeability of 50 s / 100 cc to 300 s / 100 cc. Specifically, the air permeability of the separation membrane may be 100 s / 100 cc to 250 s / 100 cc, or 150 s / 100 cc to 200 s / 100 cc. Preferably, the air permeability of the separation membrane may be 100 s / 100 cc to 150 s / 100 cc. When the air permeability of the separation membrane is within the above range, the output, stability, and cycle characteristics of the electrochemical element can be ensured.

[0056] The positive electrode and the negative electrode may be coated with an electrode active material applied to and dried on both sides of their respective current collectors. The current collector may be made of a material that is conductive without causing a chemical change to the electrochemical element. For example, the positive electrode current collector may be made of aluminum, nickel, titanium, calcined carbon, stainless steel, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., but is not limited thereto. For example, the negative electrode current collector may be made of copper, nickel, titanium, calcined carbon, stainless steel, or copper or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., but is not limited thereto. The current collector may be in various forms such as a thin metal sheet, film, foil, net, porous material, or foam.

[0057] The positive electrode comprises a positive electrode current collector and a positive electrode active material layer on both sides of the current collector, containing a positive electrode active material, a conductive material, and a positive electrode binder resin. The positive electrode active material is a layered compound such as lithium manganese composite oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-xM x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 - 0.3); chemical formula LiMn 1-x M x Lithium manganese composite oxide represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 - 0.1), or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of Li in the chemical formula is substituted with alkaline earth metal ions; disulfide compound; It can contain a mixture of one or more of Fe2(MoO4)3. Preferably, the positive electrode active material can contain one or more transition metals.

[0058] The positive electrode binder resin uses a binder resin commonly used for electrodes of electrochemical elements, provided that it may contain a fluorine-based polymer. Specifically, the positive electrode binder resin can be a polyvinyl fluoride-based polymer or a mixture containing this. Preferably, the positive electrode binder resin can contain the same polymer as the second binder particles contained in the second porous coating layer. The second porous coating layer and the positive electrode active material layer can be the same or can contain polymers having the same polymer backbone as the second binder particles and the positive electrode binder resin, respectively. The second porous coating layer can exhibit a higher adhesive force with the positive electrode than with the negative electrode.

[0059] The negative electrode includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, a conductive material, and a negative electrode binder resin on both surfaces of the current collector. As the negative electrode active material, carbon such as lithium metal oxide, non-graphitizable carbon, graphite-based carbon; LixFe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), Si, SiO x (0 < x < 2), silicon-based materials such as SiC, Si alloy; Sn x Me 1-x Me’ y O z(Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8), etc. metal composite oxides; lithium metal; lithium alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; one or more mixtures selected from titanium oxides can be included.

[0060] The negative electrode binder resin uses a binder resin commonly used for the electrodes of electrochemical devices, provided that it may contain an acrylic polymer. Specifically, the negative electrode binder resin can be an acrylic polymer or a mixture containing the same. Preferably, the negative electrode binder resin can contain the same polymer as the first binder particles contained in the first porous coating layer. The first porous coating layer and the negative electrode active material layer can be the same or can each contain a polymer having the same polymer skeleton as the first binder particles and the negative electrode binder resin, respectively. The first porous coating layer can exhibit a higher adhesive force with the negative electrode than with the positive electrode.

[0061] The conductive material can be any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, carbon nanotube, activated carbon, and polyphenylene derivative, or a mixture of two or more of these conductive materials. The carbon nanotube has a cylinder shape with a nanosize diameter of the graphite sheet and sp 2The carbon nanotubes have a bonded structure and exhibit conductive or semiconductor properties depending on the angle and structure in which the graphite surface is wound. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) depending on the number of bonds forming the wall, and these carbon nanotubes can be appropriately selected depending on the application of the dispersion. More specifically, they may be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more conductive materials from this group.

[0062] In this specific example, the electrode assembly can reduce the deviation in electrode-separation membrane adhesion strength on both sides of the separation membrane by adjusting the average particle size of the binder particles contained in the porous coating layer, taking into consideration the type of electrode to be bonded to the porous coating layer in the separation membrane and its adhesive strength. Specifically, the first porous coating layer may have a higher adhesive strength to the negative electrode than to the positive electrode, and the second porous coating layer may have a higher adhesive strength to the positive electrode than to the negative electrode. The adhesive strength between the first porous coating layer and the negative electrode may be higher than the adhesive strength between the second porous coating layer and the positive electrode. By adjusting the average particle size of the first binder particles to be greater than or equal to the average particle size of inorganic particles, the contact area between the binder particles and the electrode can be reduced, thereby adjusting the adhesive strength between the first porous coating layer and the negative electrode to a level similar to that between the second porous coating layer and the positive electrode. By adjusting the average particle size of the second binder particles to be smaller than the average particle size of the inorganic particles, the contact area between the binder particles and the electrode can be increased, thereby adjusting the adhesion between the second porous coating layer and the positive electrode to a level similar to that between the first porous coating layer and the negative electrode. This reduces the deviation between the adhesion between the first porous coating layer and the negative electrode and the adhesion between the second porous coating layer and the positive electrode.

[0063] Figure 1 is a conceptual diagram showing a structure in which a separation membrane 100 is bonded to adjacent negative electrodes 200 and positive electrodes 300 in an electrode assembly according to the above specific example. The separation membrane 100 may include a first porous coating layer 120 formed on both sides of a porous polymer substrate 110 and a second porous coating layer 130 formed on the opposite side. The first porous coating layer 120 may contain first binder particles 121 and inorganic particles 122, and the second porous coating layer 130 may contain second binder particles 131 and inorganic particles 132. The inorganic particles 122 and 132 contained in each coating layer may be identical or different from each other, but it will be understood that the first binder particles 121 in the first porous coating layer 120 have an average particle size larger than that of the inorganic particles 122, and the second binder particles 131 in the second porous coating layer 130 have an average particle size smaller than that of the inorganic particles 132. The adhesive force between a single first binder particle 121 and the negative electrode 200 is greater than the adhesive force between a single second binder particle 131 and the positive electrode 300, but the second binder particles 131, being smaller in size than the inorganic particles 132, may have a larger surface area exposed to the adhesive surface with the positive electrode 300 than the surface area of ​​the first binder particle 121. As a result, the deviation between the adhesive force between the first porous coating layer 120 and the negative electrode 200 and the adhesive force between the second porous coating layer 130 and the positive electrode 300 may be small.

[0064] For example, the adhesive strength between the first porous coating layer and the negative electrode may be 0.8 to 1.2 times the adhesive strength between the second porous coating layer and the positive electrode. Specifically, the adhesive strength between the first porous coating layer and the negative electrode may be 0.85 to 1.15 times, 0.9 to 1.1 times, or 0.95 to 1.05 times the adhesive strength between the second porous coating layer and the positive electrode. Preferably, the two adhesive strengths may be the same. In an electrode assembly in which the electrode-separation film adhesive strength on both sides is adjusted as described above, bending may not occur or the degree of bending may be reduced.

[0065] In the electrode assembly described above, the deviation in electrode-separation membrane adhesion strength is small on both sides with reference to a portion of the separation membrane. This means that even if the dimensions of the electrode assembly increase or the thickness of the electrode assembly increases due to the stacking of multiple electrodes, bending of the separation membrane may not occur or may be reduced.

[0066] For example, the electrode assembly may have a rectangular shape with a long side and a short side in a plan view. Specifically, the electrode assembly may have a long side of 500 mm or more and a short side of 600 mm or less, and a short side of 80 mm or more and a short side of 150 mm or less. When the length of the long side of the electrode assembly is within the above range, the tension on the separation membrane may increase with increasing dimensions of the electrode assembly. However, in the electrode assembly according to this specific example, bending does not occur or the degree of bending can be reduced, so it can be used safely when installed in an electric vehicle.

[0067] For example, the electrode assembly may include multiple electrodes and have an overall thickness of 8 mm to 20 mm. When the thickness of the electrode assembly is within the above range, bending may occur as the cumulative value of the deviation of the adhesive force applied to the separation film increases. However, in the electrode assembly according to this specific example, bending may not occur or the degree of bending may be reduced, thus providing excellent safety and allowing it to be installed and used in an electric vehicle.

[0068] Another specific example of the present invention provides an electrochemical element including an electrode assembly according to the above-described example. The electrochemical element can be manufactured by inserting one or more electrode assemblies into a case or pouch and sealing it. Before sealing the case or pouch, an electrolyte can be poured in to impregnate the electrode assemblies with the electrolyte. The shape of the case or pouch is not limited. For example, the electrochemical element may be cylindrical, rectangular, coin-shaped, or pouch-type lithium secondary battery.

[0069] The aforementioned electrolyte is A + B - A salt with a structure like this, + Li + na+ , K + It contains alkali metal cations such as, or ions consisting of combinations thereof, B - PF6 - BF4 - Cl - , Br - , I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - Salts containing anions such as these, or ions consisting of combinations thereof, may be dissolved or dissociated in organic solvents consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone, or mixtures thereof.

[0070] The electrochemical element including the electrode assembly may be a lithium secondary battery. The battery can be used as a unit cell, a battery module including the unit cell, a battery pack including the battery module, or a device including the battery pack as a power source. Examples of such devices include, but are not limited to, small devices such as computers, mobile phones, and power tools, and electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs) that are powered by electric motors; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0071] Another specific example of the present invention provides a method for manufacturing the electrode assembly, which includes the steps of (S10) folding a separation membrane in a zigzag pattern and alternately arranging positive and negative electrodes between the layers to form a laminate, and (S20) applying heat and pressure to the laminate to manufacture the electrode assembly. In the description of the method for manufacturing the electrode assembly, the same content as the description of the electrode assembly described above will be replaced by the description of the above specific example.

[0072] Step (S10) is a step of forming a laminate by alternately arranging positive and negative electrodes in the folds formed by zigzag folding of the separation membrane. The separation membrane may have a length in the longitudinal direction (or MD direction; Machine Direction) that is longer than its length in the width direction (or TD direction; Transverse Direction). The separation membrane may be folded in a zigzag pattern along the MD direction at predetermined intervals. The arrangement of the positive and negative electrodes may be determined considering the type of binder particles contained in the porous coating layer of the separation membrane, with the negative electrode being arranged between first porous coating layers having a higher adhesion to the negative electrode, and the positive electrode being arranged between second porous coating layers. One more negative electrode may be used than the positive electrode, and the two electrodes located on the outermost periphery of the electrode assembly may all be negative electrodes.

[0073] The separation membrane, the positive electrode, and the negative electrode may, but are not limited to, a rectangular shape. For example, the separation membrane, the positive electrode, and the negative electrode may each have a rectangular shape in which the MD direction is longer than the TD direction. Multiple positive and negative electrodes may be arranged along the MD direction of the separation membrane, and they may be arranged so that the MD direction of the separation membrane and the TD directions of the positive and negative electrodes are parallel to each other. Preferably, the positive and negative electrodes may be aligned so that their centerlines in the TD directions coincide.

[0074] The (S20) step is a step in which the laminate formed in the (S10) step is thermocompressed to produce an electrode assembly in which the positive electrode and the separation membrane and the negative electrode and the separation membrane are bonded together. By thermocompression, the first porous coating layer of the separation membrane and the active material layer of the negative electrode may be bonded together, and the second porous coating layer and the active material layer of the positive electrode may be bonded together. The thermocompression may be performed by compressing the top and bottom layers of the laminate using a press device, and may be performed by applying a pressure of 1 to 7 MPa at a temperature of 45 to 80°C to one or more laminates for 1 to 30 seconds. By adjusting the temperature and pressure conditions of thermocompression within the above range, uniform bonding between the separation membrane and the electrodes constituting the laminate can be achieved without causing damage to the laminate. The type of press device is not limited as long as it can bond the separation membrane and the electrodes by applying heat and pressure to one or both sides of the laminate simultaneously or at different times while maintaining the alignment of the separation membrane and electrodes contained in the laminate.

[0075] Preferably, the thermocompression bonding can be divided into two or more stages. The (S20) stage may include a first thermocompression bonding in which a pressure of 1 to 6 MPa is applied at 45 to 65°C for 1 to 30 seconds to fix the relative position of the electrode to the separation membrane, and a second thermocompression bonding in which a pressure of 1 to 7 MPa is applied at 50 to 80°C for 1 to 30 seconds to completely bond the separation membrane and the electrode. The first thermocompression bonding may partially bond the separation membrane and the adjacent electrode to fix the position of the electrode. The second thermocompression bonding can completely bond the separation membrane and the electrode at the position determined by the first thermocompression bonding to produce an electrode assembly. The first and second thermocompression bonding can produce an electrode assembly with superior alignment and uniform electrode-separation membrane bonding compared to single-stage thermocompression bonding. The first and second thermocompression bonding can relax the thermocompression bonding conditions compared to single-stage thermocompression bonding, prevent damage to the separation membrane, and achieve superior production efficiency.

[0076] The present invention will be described in more detail below through specific examples and experimental cases. The following examples and experimental cases are for illustrative purposes only, and the present invention is not limited to the following examples and experimental cases.

[0077] Example 1 A first coating slurry was prepared by mixing alumina with an average particle size (D50) of 500 nm at room temperature and SBR (weight-average molecular weight: 300,000) with an average particle size (D50) of 700 nm in a weight ratio of 80:20 and dispersing them in water. A second coating slurry was prepared by mixing alumina with an average particle size (D50) of 500 nm at room temperature and PVdF-HFP (weight-average molecular weight: 400,000) with an average particle size (D50) of 300 nm in a weight ratio of 80:20 and dispersing them in water.

[0078] A 9 μm thick polyethylene substrate was simultaneously coated with a first coating slurry and a second coating slurry on each surface using a slot die, and then dried to produce a separation membrane (15 μm thick) with a first porous coating layer (3 μm thick) and a second porous coating layer (3 μm thick).

[0079] By folding the separation membrane in a zigzag pattern at 98.5 mm intervals, 30 positive electrodes (positive electrode binder resin: PVdF-HFP) measuring 90 mm × 315 mm and 125 μm thick, and 31 negative electrodes (negative electrode binder resin: SBR) measuring 95.5 mm × 320 mm and 150 μm thick were prepared. By folding the separation membrane in a zigzag pattern at 98.5 mm intervals, the negative electrodes were placed between the first porous coating layers and the positive electrodes were placed between the second porous coating layers to prepare a laminate. The laminate was placed on a press and heat-pressed at 60°C and 6 MPa for 1 second, then heat-pressed again at 70°C and 6 MPa for 1 second to produce an electrode assembly (thickness: 9.3 mm) with the shape shown in Figure 2.

[0080] A pouch outer casing made of CPP / aluminum / nylon was used as the case, the electrode assembly was placed inside the case, an ethyl methyl carbonate (EMC) electrolyte containing LiPF6 was injected, and the pouch outer casing was heat-sealed to complete the assembly of the secondary battery.

[0081] Subsequently, the secondary battery underwent a pre-activation heating and pressing process, followed by an activation process. The heating and pressing process involved a temperature of 30°C and a pressure of 3.0 kgf / cm². 2 The process was carried out for 5 minutes under the following pressure conditions: 50°C and 1.0 kgf / cm². 2 The secondary battery was charged at 0.5C under these pressure conditions.

[0082] Example 2 The electrode assembly and secondary battery were manufactured in the same manner as in Example 1, except that the first coating slurry used alumina with an average particle size (D50) of 300 nm and SBR (weight-average molecular weight: 300,000) with an average particle size (D50) of 500 nm in a weight ratio of 80:20.

[0083] Comparative Example 1 The electrode assembly and secondary battery were manufactured in the same manner as in Example 1, except that the first coating slurry used alumina with an average particle size (D50) of 500 nm and SBR (weight-average molecular weight: 300,000) with an average particle size (D50) of 300 nm in a weight ratio of 80:20.

[0084] Comparative Example 2 An electrode assembly and a secondary battery were manufactured in the same manner as in Example 1, except that the first coating slurry was made by using alumina with an average particle size (D50) of 500 nm and PVdF-HFP (weight-average molecular weight: 400,000) with an average particle size (D50) of 700 nm in a weight ratio of 80:20, so that the first porous coating layer produced by the first coating slurry adheres to the negative electrode.

[0085] Comparative Example 3 The electrode assembly and secondary battery were manufactured in the same manner as in Example 1, except that the second coating slurry used alumina with an average particle size (D50) of 500 nm and SBR (weight-average molecular weight: 300,000) with an average particle size (D50) of 300 nm in a weight ratio of 80:20.

[0086] Example 3 The electrode assembly and secondary battery were manufactured in the same manner as in Example 1, except that electrodes with a negative electrode having a long side of 525 mm and a positive electrode having a long side of 520 mm were used.

[0087] Comparative Example 4 The electrode assembly and secondary battery were manufactured using the same method as in Comparative Example 2, except that electrodes with a negative electrode having a long side of 525 mm and a positive electrode having a long side of 520 mm were used.

[0088] Comparative Example 5 Except for using 44 positive electrodes and 45 negative electrodes, the electrode assembly (thickness: 13.6 mm) and secondary battery were manufactured using the same method as in Comparative Example 2.

[0089] Experimental example Measurement of air permeability The permeability of the separation membranes manufactured during the preparation process of the electrode assemblies in the examples and comparative examples was confirmed.

[0090] Air permeability was measured using an air permeability tester (Gurley densometer) (Gurley, 4110N), with 100cc of air measuring a diameter of 28.6mm and an area of ​​645mm². 2 The time it took for the substance to pass through the separation membrane was measured.

[0091] Confirmation of the adhesion strength between the electrode and the separation membrane. The electrode-separation membrane adhesion strength was confirmed in the electrode assemblies manufactured in the examples and comparative examples.

[0092] The adhesive strength when peeling the electrodes from the separation membrane was measured at the adhesion surface between the negative electrode and the first porous coating layer of the separation membrane of each electrode assembly, and at the adhesion surface between the positive electrode and the second porous coating layer of the separation membrane, while peeling the electrodes layer by layer at a speed of 200 mm / min at a 90° angle. The results are summarized in Tables 1 and 2 below.

[0093] Checking the bending of the secondary battery Referring to Figure 2, the method for evaluating the degree of bending of a secondary battery will be explained. The secondary battery 10, including the electrode assemblies of the examples and comparative examples after the activation process, may have a shape in which one surface is curved in a concave manner. As shown in Figure 2, the secondary battery 10 was placed on a flat surface G with the concave surface facing upwards. A first ruler A was placed at both ends of the concave surface, and a second ruler B was placed perpendicular to the first ruler A. The longest distance (d, mm) between the secondary battery 10 and the first ruler A was evaluated as the degree of bending, and is shown in the table below. The degree of bending of the secondary battery can be evaluated as good when it is less than 5 mm.

[0094] [Table 1]

[0095] [Table 2] [Explanation of Symbols]

[0096] 100: Separation membrane 110: Porous polymer base material 120: First porous coating layer 121: First Binder Particle 122: Inorganic particles 130: Second porous coating layer 131: Second Binder Particle 132: Inorganic particles 200: Negative electrode 300: Positive electrode 10: Secondary battery A: First ruler B:Second ruler

Claims

1. A separation membrane comprising a porous polymer substrate, a first porous coating layer formed on one surface of the porous polymer substrate, and a second porous coating layer formed on the other surface of the porous polymer substrate, which can be folded into a zigzag shape; A negative electrode disposed between the first porous coating layers; and An electrode assembly including a positive electrode disposed between the second porous coating layers, An electrode assembly wherein the first porous coating layer has greater adhesive strength to the negative electrode than to the positive electrode.

2. The electrode assembly according to claim 1, wherein the second porous coating layer has greater adhesion to the positive electrode than adhesion to the negative electrode.

3. The electrode assembly according to claim 1, wherein the adhesive force between the first porous coating layer and the negative electrode is 0.8 to 1.2 times the adhesive force between the second porous coating layer and the positive electrode.

4. The first porous coating layer comprises a first binder particle and an inorganic particle, The electrode assembly according to claim 1, wherein the average particle size of the first binder particles is greater than or equal to the average particle size of the inorganic particles.

5. The electrode assembly according to claim 4, wherein the first porous coating layer contains the first binder particles and the inorganic particles in a weight ratio of 20:80 to 80:

20.

6. The second porous coating layer comprises a second binder particle and inorganic particles. The electrode assembly according to claim 1, wherein the average particle size of the inorganic particles is greater than the average particle size of the second binder particles.

7. The positive electrode comprises a positive electrode active material and a positive electrode binder resin. The electrode assembly according to claim 6, wherein the second binder particles and the positive electrode binder resin are fluorine-based polymers.

8. The electrode assembly according to claim 1, wherein the thickness of the first porous coating layer is greater than or equal to the thickness of the second porous coating layer.

9. The electrode assembly according to claim 1, wherein the length of the longest side is 500 to 600 mm.

10. The electrode assembly according to claim 1, wherein the thickness of the electrode assembly is 8 to 20 mm.

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