Separators for secondary batteries, including adhesive layers, and methods for manufacturing them.

Abstract

This disclosure relates to a separator. The separator includes an electrode adhesive portion having a high binder content and formed on the surface of the separator to provide increased adhesion to the electrodes and improved processability during battery manufacturing. Therefore, the separator and electrodes are in close contact with each other to prevent gap formation, thereby providing an effect of improved resistive characteristics. In addition, the separator includes an inorganic coating disposed on the surface of a porous substrate, wherein the inorganic coating has a porous structure derived from the interstitial volume between inorganic particles, and thus the separator has appropriate porosity and sufficient electrolyte retention. Furthermore, because the separator includes an inorganic coating on the surface of the porous substrate, the separator ensures heat resistance and prevents shrinkage even when the internal temperature of the battery rises. This disclosure also relates to a method of manufacturing a separator. The method includes forming an inorganic coating and an electrode adhesive portion disposed on the inorganic coating in a single step by using the density of the inorganic particles and the density of the binder resin particles, and therefore has advantages in terms of ease of processing.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2020-0130401, filed in Korea on October 8, 2020. This disclosure relates to a separator for an electrochemical device exhibiting low resistance and high adhesion to the counter electrode, and a method for manufacturing the same. Background Technology

[0002] Lithium-ion batteries are energy storage devices with a basic structure of positive electrode / negative electrode / separator / electrolyte. They are electrochemical devices that can be charged / discharged through the reversible conversion between chemical energy and electrical energy, exhibiting high energy density. These lithium-ion batteries are widely used in compact electronic devices such as mobile phones, laptops, and the like. Recently, the application of lithium-ion batteries has been rapidly expanded to hybrid electric vehicles (HEVs), plug-in electric vehicles (PHEVs), e-bikes, and energy storage systems (ESS) as a response to environmental issues, high oil prices, energy efficiency, and energy storage challenges.

[0003] Lithium-ion secondary batteries are stable electrochemical devices insulated by separators. However, short circuits between the positive and negative electrodes can occur due to heating and explosion caused by internal or external anomalies or impacts. Therefore, ensuring the thermal / chemical safety of the separator, which acts as an insulator, is a crucial consideration.

[0004] Polyolefin-based separators, frequently used in commercial lithium-ion secondary batteries, are porous membranes that provide pores as lithium-ion channels while preventing electrical short circuits between the positive and negative electrodes, and use polyethylene or polypropylene as the main component.

[0005] Generally, when the battery temperature rises to 100°C or higher due to internal or external stimuli, the polyolefin-based porous separator obtained through membrane orientation processes cannot prevent volume changes such as shrinkage or melting, which can cause an explosion due to an electrical short circuit between the positive and negative electrodes. Furthermore, when the separator cracks due to dendrite growth within the battery, an internal short circuit leading to a battery explosion may occur. To suppress this thermal shrinkage caused by high temperatures and battery instability caused by dendrites, separators comprising porous separator substrates have been proposed, with one or both surfaces coated with inorganic particles and a binder. The inorganic particles impart the function of inhibiting substrate shrinkage, and the inorganic coating provides a separator with enhanced safety.

[0006] Korean Patent Publication No. 10-0775310 discloses a method for manufacturing a porous separator having an organic / inorganic coating formed by coating an organic / inorganic coating of a slurry (PVDF-CTFE / BaTiO3 or PVDF-CTFE / Al2O3) containing a binder resin and inorganic particles in an organic solvent. This slurry allows interconnections between the porous substrate and the inorganic coating, as well as between the inorganic particles within the inorganic coating. Between battery assembly and operation, the separator obtained by this method can resist shrinkage caused by exothermic and external physical shock events without losing this interconnection.

[0007] However, in such cases, the binder solution dissolved in the organic solvent can penetrate into the pores of the porous substrate, thus requiring a sufficiently large amount of binder to achieve adequate adhesion between the inorganic particles and the porous substrate surface. Alternatively, the binder solution may undergo gelation as the solvent evaporates, leading to the creation of solvent-impermeable spaces, resulting in imbalances in the inorganic coating and reduced battery characteristics. Furthermore, as the binder concentration in the slurry increases, the slurry exhibits significantly high viscosity, making it difficult to form the organic / inorganic composite layer into a thin film, and potentially requiring high temperatures during the drying step. When the slurry viscosity remains at a low level, adhesion to the porous substrate or to the inorganic particles themselves may decrease, leading to easy detachment of the inorganic particles. For these reasons, binders have frequently been used in the form of emulsions or suspensions in which the binder is dispersed at a predetermined size. In some cases, binders dispersed at a predetermined size in an organic solvent (organic dispersion) have been used. In particular, the application of inorganic particles using a binder dispersed in an aqueous solvent (aqueous dispersion) at a predetermined size offers numerous environmental and processing advantages, leading to high preference. However, the problem is that using such a binder dispersed in an aqueous solvent alone cannot achieve sufficient adhesion between the inorganic particles themselves, or between the inorganic particles and the porous substrate.

[0008] Meanwhile, as a method to improve the adhesion between the porous substrate and the coating, Korean Patent Publication No. 10-2012-0052100 discloses a method for manufacturing a coated separator with two coatings, which includes casting a slurry containing styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) dissolved in acetone as an organic solvent onto a porous polyethylene membrane to form an organic / inorganic composite layer, and electrospinning a polymer solution thereon. However, when the organic / inorganic composite layer is formed by this method, the aforementioned problems related to the use of organic solvents may not be avoided. In addition, a method for manufacturing a three-layer coated separator by spinning on an inorganic coating has been disclosed to solve the problems of low adhesion to the substrate and inorganic particle detachment. However, in this case, from the perspective of the requirement for thin-film separator formation, it is difficult to overcome the limitation of controlling the coating thickness by spinning. Furthermore, this method provides pores with low uniformity. Therefore, when this separator is applied to a battery, the current cannot flow in a uniform distribution but concentrates in specific areas, leading to partial heat release, degradation, and explosion. As a result, it may not be possible to provide a fundamental technical solution for separators with organic / inorganic coatings. Summary of the Invention

[0009] Technical issues

[0010] This disclosure is designed to address the problems of related technologies, and therefore relates to providing a separator for secondary batteries exhibiting low resistance, appropriate porosity, and sufficient electrolyte retention while ensuring heat resistance. This disclosure also relates to a method for manufacturing a separator for secondary batteries having the aforementioned properties. These and other inventive objects and advantages of this disclosure can be achieved by the means and combinations thereof shown in the appended claims.

[0011] Technical solution

[0012] According to a first embodiment of the present disclosure, a separator for an electrochemical device is provided, comprising a porous separator substrate and an inorganic coating formed on at least one surface of the porous separator substrate, wherein the inorganic coating comprises high-density inorganic particles, low-density inorganic particles, and a particulate binder resin, wherein the density of the particulate binder resin relative to the density of the high-density inorganic particles (density of particulate binder resin / density of high-density inorganic particles) is greater than or equal to 0.2 and less than 0.33, and the density of the particulate binder resin relative to the density of the low-density inorganic particles (density of particulate binder resin / density of low-density inorganic particles) is from 0.33 to 0.5.

[0013] According to a second embodiment of this disclosure, a separator for an electrochemical device as defined in the first embodiment is provided, wherein the inorganic coating comprises a first layer adjacent to the porous separator substrate, a second layer formed on the surface of the first layer, and an electrode adhesive portion formed on the surface of the second layer, wherein the first layer comprises the high-density inorganic particles in the highest content, the second layer comprises the low-density inorganic particles in the highest content, and the electrode adhesive portion comprises the particulate adhesive resin in the highest content.

[0014] According to a third embodiment of this disclosure, a separator for an electrochemical device as defined in the first or second embodiment is provided, wherein the inorganic coating has porous properties derived from the gap volume formed between the high-density inorganic particles, the low-density inorganic particles, and the particulate binder resin.

[0015] According to a fourth embodiment of this disclosure, a separator for an electrochemical device as defined in any of the first to third embodiments is provided, wherein the particulate binder resin has a particle diameter (D) of 300 nm to 500 nm. 50 ).

[0016] According to a fifth embodiment of this disclosure, a separator for an electrochemical device as defined in any of the first to fourth embodiments is provided, wherein the low-density inorganic particles have a particle diameter (D) selected from the range of 500 nm to 1,000 nm. 50 The high-density inorganic particles have a particle diameter (D) selected from the range of 300 nm to 700 nm. 50 The high-density particles have a larger particle diameter (D) than the low-density particles. 50 Small particle diameter (D) 50 ).

[0017] According to a sixth embodiment of this disclosure, a separator for an electrochemical device as defined in any of the first to fifth embodiments is provided, wherein the particulate adhesive resin includes an acrylic adhesive resin.

[0018] According to a seventh embodiment of this disclosure, a separator for an electrochemical device is provided as defined in any of the first to sixth embodiments, wherein the low-density inorganic particles include at least one selected from aluminum hydroxide (Al(OH)3) and Mg(OH)2.

[0019] According to an eighth embodiment of this disclosure, a separator for an electrochemical device as defined in any of the first to seventh embodiments is provided, wherein the high-density inorganic particles include at least one selected from boehmite (AlOOH), alumina (Al2O3), and BaTiO3.

[0020] According to a ninth embodiment of this disclosure, a separator for an electrochemical device as defined in any of the first to eighth embodiments is provided, wherein the content of the low-density particles is 40% to 80% by weight based on 100% by weight of inorganic particles in the inorganic coating.

[0021] According to a tenth embodiment of this disclosure, a method for manufacturing a partition as defined in any of the first to ninth embodiments is provided, comprising: applying an aqueous slurry for forming an inorganic coating to at least one surface of a porous partition substrate, followed by drying.

[0022] The aqueous slurry comprises a granular adhesive resin, low-density inorganic particles, and high-density inorganic particles, and uses water as a solvent. As the aqueous slurry dries after being applied, a first layer, a second layer, and an electrode adhesive portion are formed depending on the difference in settling rate, thus the inorganic coating of the finished partition exhibits a three-layer structure.

[0023] According to the eleventh embodiment of this disclosure, a method for manufacturing a partition as defined in the tenth embodiment is provided, wherein the aqueous slurry has a viscosity of 100 cp or less.

[0024] Beneficial effects

[0025] In the separator according to embodiments of the present disclosure, an electrode adhesive portion having a high binder content is formed on the surface of the separator to provide increased adhesion to the electrodes and improved processability during battery manufacturing. Therefore, the separator and electrodes are in close contact with each other to prevent the formation of gaps, thereby providing an effect of improved resistivity characteristics. Furthermore, the separator according to embodiments of the present disclosure includes an inorganic coating disposed on the surface of a porous substrate, wherein the inorganic coating has a porous structure derived from the interstitial volume between inorganic particles, and thus the separator has appropriate porosity and sufficient electrolyte retention. Further, since the separator according to embodiments of the present disclosure includes an inorganic coating on the surface of the porous substrate, the separator ensures heat resistance and prevents shrinkage even when the internal temperature of the battery rises. Meanwhile, the method of manufacturing the separator for an electrochemical device according to embodiments of the present disclosure includes forming the inorganic coating and the electrode adhesive portion disposed on the inorganic coating in a single step by using the density of the inorganic particles and the density of the binder resin particles, and therefore has advantages in terms of ease of processing. Attached Figure Description

[0026] The accompanying drawings illustrate preferred embodiments of the present disclosure and, together with the following disclosure, are used to provide a further understanding of the technical features of the present disclosure; therefore, the present disclosure should not be construed as limited to the drawings.

[0027] Figure 1 This is a schematic cross-sectional view illustrating a partition according to an embodiment of the present disclosure, wherein an inorganic coating is formed on the surface of a porous substrate, and an electrode adhesive portion having a high binder resin content is formed on the surface of the inorganic coating. Detailed Implementation

[0028] In the following description, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Before the description, it should be understood that the terminology used in the specification and appended claims should not be construed as limited to its common or dictionary meaning, but rather should be interpreted based on its meaning and concept in relation to the technical aspects of the present disclosure, on the principle that the inventors are allowed to appropriately define the terminology for the best interpretation. Therefore, the descriptions presented herein are merely preferred examples for illustrative purposes and are not intended to limit the scope of the present disclosure; thus, it should be understood that other equivalents and modifications may be made thereto without departing from the scope of the present disclosure.

[0029] Throughout the specification, the statement "a portion includes an element" does not exclude the presence of any other elements, but rather implies that the portion may further include other elements.

[0030] As used herein, the terms “approximately,” “substantially,” or similar, when implying an acceptable degree of preparation and material error unique to the claimed meaning, are used to mean from or to the claimed value and to prevent unintentional infringers from improperly using the claimed disclosure, including accurate or absolute values ​​provided to aid in understanding this disclosure.

[0031] As used in this article, the expression "A and / or B" means "A, B, or both of them".

[0032] The specific terms used in the following description are for illustrative purposes and are not intended to be limiting. Terms such as “right,” “left,” “top surface,” and “bottom surface” indicate directions in the accompanying drawings in which they are mentioned. Terms such as “inward” and “outward” indicate directions toward and away from the geometric center of the respective device, system, and its components, respectively.

[0033] The separator for an electrochemical device according to embodiments of this disclosure is used as a separator for an electrochemical device—preferably a secondary battery—and is an element included in a unit cell. A secondary battery is a rechargeable battery and has the concept of encompassing lithium-ion batteries, nickel-cadmium batteries, nickel-metal hydride batteries, or the like.

[0034] In one aspect of this disclosure, a separator is provided, comprising a porous separator substrate and an inorganic coating formed on at least one surface of the porous separator substrate, wherein the inorganic coating has an adhesive portion formed on its surface to a predetermined thickness. The adhesive portion refers to a portion having a higher content of adhesive resin than other portions of the inorganic coating, and is used to provide adhesion to an electrode it faces.

[0035] A porous separator substrate refers to a porous ion-conducting barrier that allows ions to pass through while interrupting the electrical contact between the negative and positive electrodes, and has multiple pores formed therein. These pores are interconnected, allowing gas or liquid to pass from one surface of the substrate to the other.

[0036] The material forming the porous separator substrate can be any organic or inorganic material with electrical insulating properties. In particular, to impart a shut-off function to the substrate, a thermoplastic resin is preferred as the substrate forming material. Herein, the term "shut-off function" means the function of preventing battery thermal runaway by allowing the thermoplastic resin to melt and thus shutting off ion conduction when the battery temperature increases. Thermoplastic resins with a melting point below 200°C are suitable, and polyolefins are particularly preferred.

[0037] In addition to polyolefins, the thermoplastic resin may further include at least one polymer resin selected from polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, and polyethylene naphthalate.

[0038] According to embodiments of this disclosure, the porous partition substrate includes the polymer materials mentioned above, and may be provided in the form of a nonwoven web and / or a porous polymer membrane, either alone or in combination, comprising these materials.

[0039] According to embodiments of this disclosure, the porous separator substrate can be any porous polymer substrate, as long as it is a planar porous polymer membrane or nonwoven web for use in electrochemical devices. For example, an insulating film exhibiting high ion permeability and mechanical strength, and typically having a pore diameter of 0.01 μm to 0.10 μm and a thickness of 3 μm to 20 μm or 4 μm to 15 μm, can be used. Meanwhile, the porous separator substrate according to embodiments of this disclosure preferably has a porosity of 30% to 70%.

[0040] Inorganic coatings may include inorganic particles and particulate adhesive resins. Figure 1 This is a schematic diagram illustrating an inorganic coating formed on the surface of a porous substrate, wherein the inorganic coating comprises particulate binder resin, low-density inorganic particles, and high-density inorganic particles stacked in a layered structure. Figure 1 As shown, the top surface of the inorganic coating has a cross-sectional structure including an electrode adhesive portion having a predetermined thickness and primarily comprising particulate binder resin. As described below, the inorganic coating is formed using an aqueous slurry prepared by introducing inorganic particles and particulate binder resin into an aqueous solvent, and the multilayer structure is formed using density differences in the solid components (remaining components of the slurry excluding the solvent) contained in the slurry. Here, the electrode adhesive portion can have a non-uniform thickness across the entire surface of the separator.

[0041] According to embodiments of this disclosure, based on 100% by weight of the inorganic coating, the inorganic coating may include inorganic particles in an amount of 50% by weight or more, or 65% by weight or more. Simultaneously, based on 100% by weight of the inorganic coating, the adhesive resin is used in an amount of 50% by weight or less. Furthermore, according to this disclosure, the inorganic coating includes high-density particles and low-density particles with a lower density than the high-density particles as inorganic particles, with the high-density particles mainly distributed in the lower part of the inorganic coating and the low-density particles mainly distributed in the upper part of the inorganic coating. Here, the layer that is in direct contact with the surface of the porous substrate and mainly comprises high-density particles is referred to as the first layer, and the layer that mainly comprises low-density particles is referred to as the second layer. As used herein, the expression "mainly comprises / mainly distributed" means that the corresponding component is present in an amount of 50% by weight, preferably 75% by weight, and more preferably 90% by weight relative to other components. According to embodiments of this disclosure, in the distribution of adhesive resin particles, high-density inorganic particles, and low-density inorganic particles, the first layer includes high-density inorganic particles in the highest content, the second layer includes low-density inorganic particles in the highest content, and the electrode adhesive portion includes particulate adhesive resin in the highest content.

[0042] According to this disclosure, the term "density" can refer to true density. True density means the density of the portion completely filled with the corresponding component, excluding the gaps between particles and open pores. True density can be determined using the Archimedes method. For example, true density can be determined using a true density meter (Gas Pycnometer, G PYC-100, PMI, USA), and the true density value can be obtained by adsorbing a gas, such as helium, into the sample and measuring the pressure change caused by the decrease in the volume of the adsorbed gas. In particular, the volume (Vc) of the sample chamber into which the sample is introduced and the volume (Vr) of the reference chamber used only to increase the volume are measured. Next, the gas inlet valve is opened and helium is introduced into the sample chamber. Then, the equilibrium pressure in the sample chamber becomes P1, and the volume becomes Vc - Vs. Here, Vs refers to the volume of the sample. After that, the expansion valve is opened, and the new equilibrium pressure becomes P2, and the volume becomes Vc - Vs + Vr. This can be represented by the simple formula P1(Vc-Vs)=P2(Vc-Vs+Vr). The equilibrium pressures P1 and P2 are each measured using pressure transducers, and the volumes Vc and Vr of the two chambers are known. Therefore, Vs can be easily determined. As a result, the true density value can be obtained because the measured sample volume is the volume of the pure sample only, excluding all open pores present in the sample.

[0043] Simultaneously, the first and second layers include inorganic particles combined with a particulate adhesive resin, wherein the inorganic particles are bonded to each other by the adhesive resin to form an inorganic coating. Furthermore, the adhesive resin particles provide bonding strength so that the inorganic coating can be bonded to the porous substrate.

[0044] In other words, according to a preferred embodiment of this disclosure, the separator includes a porous separator substrate and an inorganic coating formed on at least one surface of the porous separator substrate, wherein the inorganic coating includes a first layer in contact with the porous separator substrate, a second layer formed on the top surface of the first layer, and an electrode adhesive portion formed on the top surface of the second layer. The first layer mainly comprises high-density particles, the second layer mainly comprises low-density particles having a relatively lower density than the high-density particles, and the electrode adhesive portion mainly comprises adhesive resin particles. The density of the adhesive resin particles is relatively lower than the density of the high-density particles and the density of the low-density particles. As described below, the layers are formed by differentiating themselves based on the degree of settling derived from the density of each type of particle in the slurry used to form the inorganic coating; the boundaries and composition of the layers may not be clearly distinguishable, and the main component of one layer may be incorporated into another layer. According to embodiments of this disclosure, a predetermined amount of adhesive resin particles may be incorporated into the first and second layers, and the inorganic particles may be bonded to each other through the incorporated adhesive resin particles, so that the inorganic particles do not detach from the layers and the layer structure can be stably maintained.

[0045] According to embodiments of this disclosure, the inorganic coating possesses porous properties through the interstitial volume formed between the binder resin particles and between the inorganic particles and the binder resin particles. The term "interstitial volume" refers to the space defined by substantially facing particles in a structure comprising particles stacked therein.

[0046] According to this disclosure, the ratio of the density of the adhesive resin to the density of the high-density inorganic particles (density of adhesive resin / density of high-density inorganic particles) (density ratio A) is greater than or equal to 0.2 and less than 0.33, and the ratio of the density of the adhesive resin to the density of the low-density inorganic particles (density of adhesive resin / density of low-density inorganic particles) (density ratio B) is between 0.33 and 0.5. When the above-defined ranges are met, different degrees of settling occur during the manufacturing process of the separator, thereby achieving a porous coating with the desired layered structure.

[0047] Furthermore, according to the embodiments of this disclosure, within the density ratios A and B defined above, the high-density particles can have a density of 2 g / cm³. 3 Up to 10g / cm 3 The density of high-density particles is 1 g / cm³, while low-density particles can have a density of 1 3 Up to 7g / cm 3 The density. In addition, the adhesive resin can have a density of 0.5 g / cm³. 3 Up to 5g / cm 3 The density. However, the density of each type of particle is not limited to the ranges mentioned above, as long as it meets the density ratios A and B defined above.

[0048] Furthermore, according to embodiments of this disclosure, the content of low-density particles can be from 40% to 80% by weight based on 100% by weight of inorganic particles in the inorganic coating. Within the above-defined range, the content of low-density particles can be 55% by weight or more, or 60% by weight or more. When the content of low-density particles is relatively higher as illustrated above, the second layer can be formed to have a greater thickness than the first layer, which is advantageous for ensuring high porosity and electrical resistance characteristics.

[0049] In addition, low-density particles can have particle diameters ranging from 500 nm to 1,000 nm (D 50 High-density particles can have particle diameters ranging from 300 nm to 700 nm (D). 50 When the low-density and high-density particles meet the above-defined ranges, the size of the voids formed between the particles in the first layer becomes smaller than the particle diameter of the low-density particles. Therefore, it prevents low-density particles from incorporating into the pores of the first layer, and the desired layered structure can be easily achieved. Simultaneously, the particulate adhesive resin preferably has a particle diameter (D) of 300 nm to 500 nm. 50 Due to this density difference, the adhesive resin is primarily disposed at the top layer relative to the first and / or second layers. However, the adhesive resin is smaller than the size of the voids formed in the first and second layers, and therefore can be introduced into both layers. Consequently, adhesive particles can be disposed in the first and second layers so that the particles in the inorganic coating can bond together to advantageously maintain their shape.

[0050] According to this disclosure, particle diameter (D) 50 Particle diameter (D) can be defined as the particle diameter at the 50% mark of the particle size distribution. According to embodiments of this disclosure, particle diameter (D) 50 It can be determined using the laser diffraction method.

[0051] Furthermore, according to embodiments of this disclosure, the second layer can have a greater thickness than the first layer. That is, the porosity of the inorganic coating can be increased by increasing the proportion of the second layer, which mainly contains low-density particles with larger particle diameters. In addition, the inorganic particles in the first layer have smaller particle diameters to increase the contact area between the porous substrate and the inorganic coating, resulting in increased peel strength.

[0052] According to embodiments of this disclosure, low-density inorganic particles may include at least one selected from aluminum hydroxide (Al(OH)3) and Mg(OH)2, while high-density inorganic particles may include at least one selected from boehmite (AlOOH), alumina (Al2O3), and BaTiO3. The inorganic particles are not limited to the compositions exemplified above, but the compositions exemplified above are advantageous for achieving the density ratios defined above.

[0053] According to embodiments of this disclosure, there are no particular limitations on the inorganic particles, as long as they are electrochemically stable and meet the density range of the inorganic coating defined above. That is, there are no particular limitations on the inorganic particles that can be used herein, as long as they are within the operating voltage range of the applicable electrochemical device (e.g., based on Li / Li). + The inorganic particles must not cause oxidation and / or reduction in a 0-5V environment and must meet the conditions specified above. Non-limiting examples of inorganic particles include Al2O3, AlOOH, Al(OH)3, AlN, BN, MgO, Mg(OH)2, SiO2, ZnO, TiO2, BaTiO3, or mixtures thereof.

[0054] Furthermore, according to the embodiments of this disclosure, the adhesive resin is not particularly limited, as long as it can be dispersed in an aqueous solvent in a particulate state. Specific examples of adhesive resins include, but are not limited to: polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetatebutyrate, and cellulose acetate propionate. Propionate, cyanoethyl pullullan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullullan, carboxyl methyl cellulose, or similar.

[0055] Furthermore, according to embodiments of this disclosure, the inorganic coating may have a thickness of 0.01 μm to 20 μm on one surface of a porous partition substrate.

[0056] The method for forming inorganic coatings will be explained below.

[0057] According to embodiments of this disclosure, the separator is obtained by mixing high-density particles, low-density particles, and an adhesive resin with a suitable aqueous solvent to prepare a slurry for forming an inorganic coating, then applying the slurry to the surface of a porous separator substrate, followed by drying. The slurry can be coated using at least one method suitable for use with dip coating, slot die coating, microgravure coating, line coating, and blade coating. According to embodiments of this disclosure, the slurry may have a solids content of about 25% to 40% by weight (the remaining components of the slurry excluding the solvent).

[0058] Drying can be carried out, for example, under convective conditions such as a convection oven at 80°C to 100°C.

[0059] The solvent may preferably include an aqueous solvent capable of dispersing the polymer resin. Specific examples of aqueous solvents may include water, isopropanol, propanol, or the like, and these solvents may be used alone or in combination.

[0060] As described above, each component exhibits a different settling rate due to its density difference, and therefore the inorganic coating can have a layered structure. That is, high-density inorganic particles first settle onto the surface of the porous separator substrate to form a first layer, and low-density particles settle on top of it to form a second layer. Simultaneously, a low-density binder resin exhibiting the lowest settling rate accumulates on the surface of the second layer to form an electrode adhesive portion. At the same time, a binder resin with the smallest particle size is introduced into the voids between the second and first layers to impart bonding strength to each layer.

[0061] Furthermore, according to specific embodiments of this disclosure, the slurry preferably has a viscosity of 100 cp or less. When the viscosity exceeds the range defined above, phase separation due to the density differences between low-density particles, high-density particles, and binder resin particles is not significant, making it difficult to achieve a layered structure and to ensure adhesion between the electrode and the separator.

[0062] In the method of manufacturing a separator according to this disclosure, the electrode adhesive portion is formed integrally and inseparably on the surface of the separator using a single step with different settling rates of different particles. Therefore, the method according to this disclosure offers high processing convenience. Furthermore, the inorganic particles are bonded together using a particulate adhesive resin, and the interstitial volume between the inorganic particles is maintained as vacant space to form pores. Therefore, the inorganic coating exhibits high porosity to provide improved electrolyte wettability. In addition, the electrode adhesive portion provides increased bonding force between the electrode and the separator, and thus reduces the interfacial resistance between the electrode and the separator.

[0063] In another aspect of this disclosure, an electrode assembly including the separator inserted between a positive electrode and a negative electrode is provided, and an electrochemical device including the electrode assembly is provided.

[0064] According to this disclosure, the positive electrode includes a positive current collector and a positive active material layer formed on at least one surface of the current collector, comprising a positive active material, a conductive material, and a binder resin. The positive active material may include any of the following: layered compounds, such as lithium manganese composite oxides (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), and lithium nickel oxide (LiNiO2), or those compounds substituted with one or more transition metals; such as compounds with the chemical formula Li 1+x Mn 2-x Those represented by O4 (where x is 0-0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxides (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; and those with the chemical formula LiNi 1- x M x Ni-type lithium nickel oxide represented by O2 (where M is Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x is 0.01-0.3); LiMn 2-x M x Lithium manganese complex oxides represented by O2 (where M is Co, Ni, Fe, Cr, Zn, or Ta) and x is 0.01-0.1) or Li2Mn3MO8 (where M is Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which Li is partially substituted by alkaline earth metal ions; disulfide compounds; and Fe2(MoO4)3, or mixtures of two or more of them.

[0065] According to this disclosure, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the current collector, comprising a negative electrode active material, a conductive material, and a binder resin. The negative electrode active material may include materials selected from lithium metal oxides; carbons such as difficult-to-graphitize carbon and graphite-based carbon; and materials such as Li... x Fe2O3 (0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me' y O zMetal composite oxides such as (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Group 1, 2 or 3 of the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; 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 type materials; and at least one of titanium oxides, or mixtures of two or more of them, as negative electrode active materials.

[0066] According to embodiments of this disclosure, the conductive material may be any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whiskers, conductive metal oxides, activated carbon, and polyphenylene derivatives, or a mixture of two or more of these conductive materials. More specifically, the conductive material may be any one selected from 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 dioxide, or a mixture of two or more of these conductive materials.

[0067] There are no particular restrictions on current collectors, as long as they do not cause chemical changes in the corresponding battery and have high conductivity. Specific examples of current collectors may include stainless steel, aluminum, nickel, titanium, calcined carbon, aluminum or stainless steel with carbon, nickel, titanium, or silver surface treatment, or the like.

[0068] The adhesive resin can be a polymer currently used for electrodes in the art. Non-limiting examples of adhesive polymers include, but are not limited to: polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalchol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methylcellulose, or similar.

[0069] The electrode assembly prepared as described above can be introduced into a suitable housing, and an electrolyte can be injected therein to obtain a battery. According to this disclosure, the electrolyte is a electrolyte having A + B - Salts of structure, in which A + Including, for example, Li + Na + K + alkali metal cations such as B, or combinations thereof, - Including PF6, etc. - BF4 - Cl - ,Br - I - ClO4- AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 - Anions such as 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 (γ-butyrolactone), ester compounds, and mixtures thereof. However, this disclosure is not limited thereto.

[0070] In addition, this disclosure provides a battery module including the electrode assembly as a unit cell, a battery pack including the battery module, and an apparatus including the battery pack as a power source. Specific examples of the apparatus include, but are not limited to: power tools driven by the power of an electric motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or the like; two-wheeled electric vehicles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; energy storage systems; or the like.

[0071] The embodiments will then be described in more detail so that this disclosure can be readily understood. However, the following embodiments may be embodied in many different forms and should not be construed as limited to the exemplary implementations set forth herein. Rather, these exemplary implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0072] Example 1

[0073] First, alumina (Al2O3, D) as high-density particles... 50 500nm, density: 4g / cm³ 3 ) and Al(OH)3(D) as low-density particles 50 800nm, density: 2.4g / cm³ 3The mixture is introduced into water, and styrene acrylate (gel content 98%, pH 3, particle diameter (D)) is used as an adhesive resin. 50 The resulting mixture (380 nm) was dispersed by stirring with a paint shaker (tungsten beads) for 2 hours, thereby preparing a slurry with a solids content of 30% by weight for forming an inorganic coating. The weight ratio of high-density particles, low-density particles, and binder was 35:35:30. The slurry was applied to a porous separator substrate (polyethylene, available from Toray Co., 9 μm thick, air permeation time 90 s / 100 cc) and dried at 80°C to 90°C to obtain the separator.

[0074] Example 2

[0075] First, alumina (Al2O3, D) as high-density particles... 50 500nm, density: 4g / cm³ 3 ) and Al(OH)3(D) as low-density particles 50 800nm, density: 2.4g / cm³ 3 The styrene acrylate (gel content 98%, pH 3, D) was introduced into the water and used as an adhesive resin. 50 380nm, density: 1.02g / cm³ 3 The mixture was introduced into the substrate, and the resulting mixture was dispersed by stirring with a paint shaker (tungsten beads) for 2 hours, thereby preparing a slurry with a solids content of 30% by weight for forming an inorganic coating. The weight ratio of high-density particles, low-density particles, and binder was 25:45:30. The slurry was applied to a porous separator substrate (polyethylene, available from Toray Co., 9 μm thick, air permeation time 90 sec / 100cc) and dried at a temperature of 80°C to 90°C to obtain the separator.

[0076] Example 3

[0077] First, alumina (Al2O3, D) as high-density particles... 50 500nm, density: 4g / cm³ 3 ) and Al(OH)3(D) as low-density particles 50 800nm, density: 2.4g / cm³ 3 The styrene acrylate (gel content 98%, pH 3, D) was introduced into the water and used as an adhesive resin. 50 380nm, density: 1.02g / cm³ 3The mixture was introduced into the substrate, and the resulting mixture was dispersed by stirring with a paint shaker (tungsten beads) for 2 hours, thereby preparing a slurry with a solids content of 30% by weight for forming an inorganic coating. The weight ratio of high-density particles, low-density particles, and binder was 15:55:30. The slurry was applied to a porous separator substrate (polyethylene, available from Toray Co., 9 μm thick, air permeation time 90 s / 100 cc) and dried at a temperature of 80°C to 90°C to obtain the separator.

[0078] Example 4

[0079] First, alumina (Al2O3, D) as high-density particles... 50 500nm, density: 4g / cm³ 3 ) and AlOOH (D) as low-density particles 50 200nm to 300nm, density: 3g / cm³ 3 The styrene acrylate (gel content 98%, pH 3, D) was introduced into the water and used as an adhesive resin. 50 380nm, density: 1.02g / cm³ 3 The mixture was introduced into the substrate, and the resulting mixture was dispersed by stirring with a paint shaker (tungsten beads) for 2 hours, thereby preparing a slurry with a solids content of 30% by weight for forming an inorganic coating. The weight ratio of high-density particles, low-density particles, and binder was 15:55:30. The slurry was applied to a porous separator substrate (polyethylene, available from Toray Co., 9 μm thick, air permeation time 90 s / 100 cc) and dried at a temperature of 80°C to 90°C to obtain the separator.

[0080] Comparative Example 1

[0081] First, aluminum oxide (Al2O3, D) 50 500nm, density: 4g / cm³ 3 ) and styrene acrylate (gel content 98%, pH 3, D 50 380nm, density: 1.02g / cm³ 3 The mixture was introduced into water, and the resulting mixture was dispersed by stirring with a paint shaker (tungsten beads) for 2 hours, thereby preparing a slurry with a solids content of 30% by weight for forming an inorganic coating. The weight ratio of inorganic particles to binder was 70:30. The slurry was applied to a porous separator substrate (polyethylene, available from Toray Co., 9 μm thick, air permeation time 90 s / 100 cc) and dried at a temperature of 80°C to 90°C to obtain separators.

[0082] Comparative Example 2

[0083] First, AlOOH(D) 50 200nm to 300nm, density: 3g / cm³ 3 ) and styrene acrylate (gel content 98%, pH 3, D 50 380nm, density: 1.02g / cm³ 3 The mixture was introduced into water, and the resulting mixture was dispersed by stirring with a paint shaker (tungsten beads) for 2 hours, thereby preparing a slurry with a solids content of 30% by weight for forming an inorganic coating. The weight ratio of inorganic particles to binder was 70:30. The slurry was applied to a porous separator substrate (polyethylene, available from Toray Co., 9 μm thick, air permeation time 90 s / 100 cc) and dried at a temperature of 80°C to 90°C to obtain separators.

[0084] Comparative Example 3

[0085] First, Al(OH)3(D 50 800nm, density: 2.4g / cm³ 3 ) and styrene acrylate (gel content 98%, pH 3, D 50 380nm, density: 1.02g / cm³ 3 The mixture was introduced into water, and the resulting mixture was dispersed by stirring with a paint shaker (tungsten beads) for 2 hours, thereby preparing a slurry with a solids content of 30% by weight for forming an inorganic coating. The weight ratio of inorganic particles to binder was 70:30. The slurry was applied to a porous separator substrate (polyethylene, available from Toray Co., 9 μm thick, air permeation time 90 s / 100 cc) and dried at a temperature of 80°C to 90°C to obtain separators.

[0086] [Table 1]

[0087]

[0088] As can be seen from Table 1, each separator according to Examples 1 to 4 exhibits a higher bulk density of inorganic coating loading based on the separator compared to the separators according to Comparative Examples 2 and 3. Therefore, each separator exhibits excellent thermal shrinkage properties and sufficient resistivity. In the case of Comparative Example 1, it exhibits a higher bulk density compared to the separators according to the examples on the same thickness, but shows excessively high Gurley values ​​and resistivity. As a result, the separators according to this disclosure demonstrate superior properties in terms of Gurley value, thermal shrinkage rate, and resistivity characteristics.

[0089] Test methods

[0090] (1) Air infiltration time (Gurley value)

[0091] An air permeation time meter (EG01-55-1MR, available from Asahi Seiko) was used to determine the time (sec) required for 100 mL of air to pass through a partition under constant pressure (0.05 MPa). The air permeation time was recorded as the average of the values ​​measured at three points, including one point each on the left, middle, and right sides.

[0092] (2) Measurement of resistance

[0093] Each separator obtained from the examples and comparative examples was inserted between SUS sheets to form a coin cell. To prepare the electrolyte for the coin cell, ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1:2, and LiPF6 was added at a concentration of 1 M. The resistance of each coin cell was measured by electrochemical impedance spectroscopy using a resistance analyzer (VMP3, Biologic Science Instrument) at 25°C with an amplitude of 10 mV and a scan range of 0.1 Hz to 1 MHz.

[0094] (3) Determination of thermal shrinkage rate

[0095] Each partition obtained from the examples and comparative examples was cut into 5cm × 5cm dimensions to prepare specimens, and each specimen was left to stand at 150°C for 0.5 hours. The length of each specimen after shrinkage was then compared with its initial length. Both longitudinal (MD) and transverse (TD) measurements were based on a porous partition substrate.

Claims

1. A separator for an electrochemical device, comprising a porous separator substrate and an inorganic coating layer formed on at least one surface of the porous separator substrate, wherein the inorganic coating layer comprises high-density inorganic particles, low-density inorganic particles, and a particulate adhesive resin, a ratio of a density of the particulate adhesive resin with respect to a density of the high-density inorganic particles, particulate adhesive resin density / high-density inorganic particle density, is greater than or equal to 0.2 and less than 0.33, and a ratio of a density of the particulate adhesive resin with respect to a density of the low-density inorganic particles, particulate adhesive resin density / low-density inorganic particle density, is 0.33 to 0.5, wherein the inorganic coating layer comprises a first layer adjoining the porous separator substrate, a second layer formed on a surface of the first layer, and an electrode adhesion portion formed on a surface of the second layer, the first layer comprises the high-density inorganic particles in the highest content, the second layer comprises the low-density inorganic particles in the highest content, and the electrode adhesion portion comprises the particulate adhesive resin in the highest content, the second layer has a greater thickness than the first layer. 2.The separator for an electrochemical device according to claim 1, wherein the inorganic coating layer has a porous property derived from a gap volume formed among the high-density inorganic particles, the low-density inorganic particles, and the particulate adhesive resin.

3. The separator for electrochemical devices according to claim 1, wherein the particulate type binder resin has a particle diameter D of 300 nm to 500 nm 50 .

4. The separator for electrochemical devices according to claim 1, wherein the low-density inorganic particles have a particle diameter D 50 selected from the range of 500 nm to 1,000 nm 50 , the high-density inorganic particles have a particle diameter D 50 selected from the range of 300 nm to 700 nm 50 , and the high-density inorganic particles have a particle diameter D 50 smaller than the particle diameter D 50 of the low-density inorganic particles. 5.The separator for an electrochemical device according to claim 1, wherein the particulate adhesive resin comprises an acrylic adhesive resin. 6.The separator for an electrochemical device according to claim 1, wherein the low-density inorganic particles comprise at least one selected from the group consisting of aluminum hydroxide Al(OH) 3 and Mg(OH) 2. 7.The separator for an electrochemical device according to claim 1, wherein the high-density inorganic particles comprise at least one selected from the group consisting of boehmite AlOOH, alumina Al 2O 3, and BaTiO 3. 8.The separator for an electrochemical device according to claim 1, wherein a content of the low-density inorganic particles is 40% to 80% by weight based on 100% by weight of inorganic particles in the inorganic coating layer.

9. A method of manufacturing a separator for an electrochemical device as defined in any one of claims 1 to 8, comprising: applying an aqueous slurry for forming an inorganic coating layer to at least one surface of a porous separator substrate, followed by drying, wherein the aqueous slurry comprises a particulate adhesive resin, low-density inorganic particles, and high-density inorganic particles and uses water as a solvent, and while the aqueous slurry is being dried after being applied, a first layer, a second layer, and an electrode adhesion portion are formed depending on a difference in settling rate, such that the inorganic coating layer of the finished separator shows a three-layer structure. 10.The method of manufacturing a separator for an electrochemical device according to claim 9, wherein the aqueous slurry has a viscosity of 100 cp or less.

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