Separator for rechargeable battery and rechargeable battery comprising the same

Abstract

A separator for a rechargeable battery and a rechargeable battery including the separator are provided. The separator for the rechargeable battery includes a porous substrate and a coating on at least one surface of the porous substrate, wherein the coating includes a crosslinking product comprising a mixture of a first binder and a second binder and a crosslinking agent; and a filler. The first binder is an aqueous binder, and the second binder is a carboxyalkyl cellulose compound or a salt thereof. The crosslinking agent includes citric acid, and the content of citric acid is about 5 to 50 parts by weight relative to the total amount of 100 parts by weight of the first binder and the second binder.

Description

[0001] This application claims priority to Korean Patent Application No. 10-2025-0012538, filed on January 31, 2025, with the Korean Intellectual Property Office; Korean Patent Application No. 10-2025-0012542, filed on January 31, 2025, with the Korean Intellectual Property Office; Korean Patent Application No. 10-2025-0012543, filed on January 31, 2025, with the Korean Intellectual Property Office; Korean Patent Application No. 10-2025-0012550, filed on January 31, 2025, with the Korean Intellectual Property Office; and Korean Patent Application No. 10-2025-0012551, filed on January 31, 2025, with the Korean Intellectual Property Office. The entire disclosure of each of these applications is incorporated herein by reference. Technical Field

[0002] This disclosure relates to a separator for a rechargeable battery and a rechargeable battery including the separator. Background Technology

[0003] With the increasing use of battery-powered electronic devices (such as mobile phones, laptops, and electric vehicles), the demand for rechargeable batteries with high energy density and high capacity is growing. Therefore, improving the performance of rechargeable lithium batteries can be beneficial.

[0004] Rechargeable lithium batteries typically include positive and negative electrodes containing active materials capable of inserting and deintercalating lithium ions, and generate electrical energy through redox reactions as lithium ions deintercalate from the negative electrode and intercalate into the positive electrode, and deintercalate from the positive electrode and intercalate into the negative electrode.

[0005] Rechargeable lithium batteries may include a separator between the positive and negative electrodes. Reducing or preventing battery fires and explosions due to external impacts can be advantageous. Summary of the Invention

[0006] This disclosure includes a separator for rechargeable batteries that can suppress ignition and explosion of batteries due to external impact.

[0007] This disclosure also includes a separator for rechargeable batteries having low thermal shrinkage and high adhesion to a substrate.

[0008] This disclosure also includes a separator for rechargeable batteries with low thermal shrinkage, low permeability and low resistance.

[0009] This disclosure also includes a separator for rechargeable batteries that improves the high-temperature life of the battery.

[0010] This disclosure also includes a separator for rechargeable batteries with improved shut-off temperature and breakdown voltage.

[0011] This disclosure also includes a separator for rechargeable batteries that improves the high-temperature life of the battery.

[0012] This disclosure also includes a rechargeable battery comprising a positive electrode, a negative electrode, and a separator for the rechargeable battery located between the positive and negative electrodes.

[0013] One example embodiment includes a separator for a rechargeable battery.

[0014] The separator for a rechargeable battery includes a porous substrate and a coating on at least one surface of the porous substrate. The coating includes: a crosslinking product of a mixture of a first binder and a second binder and a crosslinking agent; and a filler. The first binder is an aqueous binder, the second binder is a carboxyalkyl cellulose compound or a salt thereof, and the crosslinking agent includes citric acid, wherein the citric acid content is from about 5 parts by weight to about 50 parts by weight relative to a total of 100 parts by weight of the first binder and the second binder.

[0015] Another example embodiment includes a separator for a rechargeable battery.

[0016] The separator for a rechargeable battery includes a porous substrate and a coating on at least one surface of the porous substrate. The coating is formed by or includes a composition for coating, the composition comprising a first binder, a second binder, a filler, a crosslinking agent, and an alcohol. The first binder is an aqueous binder, the second binder is a carboxyalkyl cellulose compound or a salt thereof, and the crosslinking agent includes citric acid, wherein the citric acid content is from about 5 parts by weight to about 50 parts by weight relative to a total of 100 parts by weight of the first and second binders.

[0017] Another example embodiment includes a separator for a rechargeable battery.

[0018] The separator for a rechargeable battery includes a porous substrate and a coating on at least one surface of the porous substrate. The coating includes a crosslinking product of a mixture of a first binder and a second binder and a crosslinking agent; and a mixture of a first filler and a second filler, wherein the first filler and the second filler have different aspect ratios. The first binder is an aqueous binder, the second binder is a carboxyalkyl cellulose compound or a salt thereof, the crosslinking agent includes citric acid, wherein the citric acid content is from about 2 parts by weight to about 50 parts by weight relative to 100 parts by weight of the total amount of the first and second binders, and the aspect ratio of the second filler is higher than that of the first filler. The weight ratio of the second filler to the first filler is in the range of from about 1:1 to about 1:10.

[0019] Another example embodiment includes a separator for a rechargeable battery.

[0020] The separator for a rechargeable battery includes a porous substrate and a coating on at least one surface of the porous substrate. The coating includes a crosslinking product of a mixture of a first binder and a second binder and a crosslinking agent; a filler; and polymer particles with a melting point in the range of about 80°C to about 135°C. The first binder is an aqueous binder, the second binder is a carboxyalkyl cellulose compound or a salt thereof, and the crosslinking agent includes citric acid, wherein the citric acid content is about 5 parts by weight to about 50 parts by weight relative to a total of 100 parts by weight of the first and second binders.

[0021] Another example embodiment includes a separator for a rechargeable battery.

[0022] The separator for a rechargeable battery includes a porous substrate and a coating on at least one surface of the porous substrate. The coating includes a crosslinking product of a mixture of a first binder and a second binder and a crosslinking agent; a filler; and lithium cations. The first binder is an aqueous binder, the second binder is an alkali metal salt of a carboxyalkyl cellulose compound, and at least one of the alkali metals is lithium or includes lithium. The crosslinking agent contains citric acid, wherein the citric acid content is from about 5 parts by weight to about 50 parts by weight relative to a total of 100 parts by weight of the first and second binders, and the lithium cation content in the coating is from about 50 ppm to about 200 ppm.

[0023] Another example embodiment includes a rechargeable battery.

[0024] The rechargeable battery includes a positive electrode, a negative electrode, and a separator for the rechargeable battery located between the positive and negative electrodes.

[0025] A separator for a rechargeable battery according to an example embodiment can suppress battery fire and explosion caused by external impact, thereby improving battery reliability and stability. Furthermore, the separator can have a low thermal shrinkage rate and high adhesion to the substrate, thereby increasing battery life.

[0026] A separator for a rechargeable battery according to an example embodiment can suppress battery fire and explosion caused by external impact, thereby improving battery reliability and stability. Furthermore, the separator can have low thermal shrinkage, low permeability, and low resistance, thereby increasing battery life.

[0027] A separator for a rechargeable battery according to an example embodiment can suppress battery fire and explosion caused by external impact, thereby improving battery reliability and stability. Furthermore, the separator can provide a low shrinkage rate, thereby improving battery safety. Additionally, the separator can improve the battery's high-temperature lifespan, thereby improving battery lifespan and reliability.

[0028] A separator for a rechargeable battery according to one example embodiment can improve the shut-off temperature and breakdown voltage, thereby providing a battery with enhanced safety. A separator for a rechargeable battery according to one example embodiment can have a low thermal shrinkage rate, thereby providing a battery with the desired reliability and lifespan.

[0029] According to one example embodiment, a separator for a rechargeable battery can replenish lithium ions that may be lost during repeated charging and discharging of the battery, thereby improving battery life at high temperatures. Attached Figure Description

[0030] The above and other objects, features, and advantages of this disclosure will become more apparent to those skilled in the art from the detailed description of exemplary embodiments with reference to the accompanying drawings, in which: Figure 1 This is a cross-sectional view of a separator for a rechargeable lithium battery according to a first exemplary embodiment; Figure 2 This is a cross-sectional view of a separator for a rechargeable lithium battery according to a second exemplary embodiment; Figure 3 This is a cross-sectional view of a separator for a rechargeable lithium battery according to a third exemplary embodiment; Figure 4 This is a scanning electron microscope (SEM) image of the second packing material; Figure 5 The aspect ratio of the second packing is shown; Figure 6 This is the SEM image of the first filler; Figure 7 The aspect ratio of the first packing is shown; Figures 8 to 11 All are cross-sectional views showing a separator for a rechargeable lithium battery according to a fourth exemplary embodiment; Figure 12 This is a cross-sectional view of a separator for a rechargeable lithium battery according to a fifth exemplary embodiment; and Figures 13 to 16 This is a schematic cross-sectional view of a rechargeable lithium battery according to an example embodiment. Detailed Implementation

[0031] Example embodiments of the present disclosure are described in detail below. However, these embodiments are presented by way of example, and the present disclosure is not limited thereto, and is limited only by the scope of the appended claims.

[0032] Unless otherwise stated herein, when a part such as a layer, membrane, region, plate, etc., is described as being disposed "on" another part, it includes not only the case where the part is "directly" on that other part, but also the case where there are other parts between them.

[0033] Unless otherwise stated herein, the singular may also include the plural. Furthermore, unless otherwise stated, the term "A or B" may mean "including A, including B, or including both A and B".

[0034] In this specification, "combination thereof" may mean a mixture, stack, complex, copolymer, alloy, blend, or reaction product of the components.

[0035] Unless otherwise defined herein, “particle size D100” can refer to the size of particles that constitute 100% of the cumulative volume in a particle size distribution. Particle size distribution can be measured using methods known to those skilled in the art. For example, particle size distribution can be measured using a particle size analyzer, transmission electron microscopy (TEM) images, or scanning electron microscopy (SEM) images. Alternatively, particle size distribution can be obtained by measuring particle size using a measuring device that utilizes dynamic light scattering, performing data analysis to count the number of particles in each particle size range, and then calculating the particle size D100 from this data. Optionally, particle size distribution can be measured using laser diffraction. When measuring particle size distribution using laser diffraction, for example, particle size D100 based on 100% particle size distribution in the measuring device can be calculated by dispersing the particles to be measured in a dispersion medium, introducing the dispersion medium into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and irradiating it with ultrasound at approximately 28 kHz using a 60 W output.

[0036] In this specification, "particle size D50" refers to the size of particles that constitute 50% of the cumulative volume in the particle size distribution. The particle size distribution can be obtained by referring to the method described above for "particle size D100".

[0037] If the particle is spherical, the size can be expressed as the diameter.

[0038] In the following text, unless otherwise defined, “substitution” means that hydrogen in a compound is substituted by a substituent, which is such as or includes C1 to C30 alkyl, C2 to C30 alkenyl, C2 to C30 alkynyl, C6 to C30 aryl, C7 to C30 alkylaryl, C1 to C30 alkoxy, C1 to C30 heteroalkyl, C3 to C30 heteroalkylaryl, C3 to C30 cycloalkyl, C3 to C15 cycloalkenyl, C6 to C30 cycloalkynyl, C2 to C30 heterocycloalkyl, halogen (F, Cl, Br or I), hydroxyl (-OH), nitro (-NO2), cyano (-CN), amino (-NRR') (here, R and R' are each independently hydrogen or C1 to C6 alkyl), sulfobetaine (-RR'N) + (CH2) n SO3 - n is a natural number in the range of 1 to 10 (here, R and R' are each independently C1 to C20 alkyl groups), carboxybenzene group (-RR'N) + (CH2) n COO - The following groups are used: n is a natural number in the range of 1 to 10 (where R and R' are each independently C1 to C20 alkyl), azide (-N3), amidine (-C(=NH)NH2), hydrazine (-NHNH2), hydrazone (=N(NH2)), carbamoyl (-C(O)NH2), thiol (-SH), acyl (-C(=O)R, where R represents hydrogen, C1 to C6 alkyl, C1 to C6 alkoxy or C6 to C12 aryl), carboxyl (-COOH) or a salt thereof (-C(=O)OM, where M represents an organic or inorganic cation), sulfonic acid (-SO3H) or a salt thereof (-SO3M, where M represents an organic or inorganic cation), phosphate (-PO3H2) or a salt thereof (-PO3MH or -PO3M2, where M represents an organic or inorganic cation), and at least one combination thereof.

[0039] In the following text, C1 to C3 alkyl groups may be or include methyl, ethyl, or propyl. C1 to C10 alkylene groups may be, for example, C1 to C6 alkylene groups, C1 to C5 alkylene groups, or C1 to C3 alkylene groups, and may be, for example, methylene, ethylene, or propylene. C3 to C20 cycloalkylene groups may be, for example, C3 to C10 cycloalkylene groups or C5 to C10 cycloalkylene groups, such as cyclohexylene. C6 to C20 arylene groups may be, for example, C6 to C10 arylene groups, such as phenylene. C3 to C20 heterocyclic groups may be, for example, C3 to C10 heterocyclic groups, such as pyridyl.

[0040] In the following text, “heterogeneous” means including one or more heteroatoms (such as or including at least one of N, O, S, Si and P).

[0041] Furthermore, in chemical formulas, symbols This indicates the portion bonded to the same or different atoms, groups, or structural units. Unless otherwise specified in the chemical formula described herein, hydrogen may be considered bonded within the structure of the chemical formula.

[0042] In the following text, "alkali metals" refers to elements belonging to Group 1 of the periodic table, such as lithium, sodium, potassium, rubidium, cesium, or francium, which can exist in either a cation or a neutral state.

[0043] In this specification, when describing a range of values, “X to Y” means “X or greater and Y or less (greater than or equal to X and less than or equal to Y)”.

[0044] When the terms “about” or “substantially” are used in conjunction with numerical values ​​in this specification, the relevant numerical value is intended to include a tolerance of ±10% around the stated value. The expression “up to…” includes the quantity from zero to the stated upper limit and all values ​​in between. When a range is specified, the range includes all values ​​in between, such as increments of 0.1%.

[0045] The separator for a secondary battery according to the first exemplary embodiment According to one example embodiment, a separator for a rechargeable battery includes a porous substrate and a coating on at least one surface of the porous substrate. The coating includes: a crosslinking product of a mixture of a first binder and a second binder and a crosslinking agent; and a filler. The first binder is an aqueous binder, the second binder is a carboxyalkyl cellulose compound or a salt thereof, and the crosslinking agent contains citric acid, wherein the citric acid content is from about 5 parts by weight to about 50 parts by weight relative to a total of 100 parts by weight of the first binder and the second binder.

[0046] According to one example embodiment, the separator may be a separator for a rechargeable lithium battery.

[0047] The diaphragm can provide a low dry heat shrinkage rate. In one example embodiment, the dry shrinkage rate of the diaphragm in each of the machine direction (MD) and transverse direction (TD), measured after being placed at 150°C for 1 hour, can be about 6% or less, for example, 5% or less. Here, MD and TD can each be in the same direction as the porous substrate.

[0048] Citric acid can crosslink with the first binder, thereby reducing the thermal shrinkage rate of the membrane in the electrolyte. In one example embodiment, the thermal shrinkage rate of the membrane in each direction of MD and TD, measured after being placed in the electrolyte at 150°C for 1 hour, can be about 10.0% or less, for example, 8% or less.

[0049] Since the separator comprises a crosslinking product of a first binder, a second binder, and a crosslinking agent (i.e., a crosslinking product of the first binder, a carboxyalkyl cellulose compound or its salt, and citric acid), the separator can suppress battery fire and explosion due to external impact, thereby improving battery reliability and stability, and can also promote improved adhesion to the substrate.

[0050] Citric acid is a polycarboxylic acid with a hydroxyl group, as shown in the chemical formula below.

[0051] Chemical formula: .

[0052] Citric acid can crosslink with carboxyalkyl cellulose compounds or their salts, and also with the first binder. Citric acid exhibits high dispersibility in the mixture of the first binder and the carboxyalkyl cellulose compound or its salt, and is highly crosslinked with each of the first binder and the carboxyalkyl cellulose compound or its salt; therefore, citric acid can promote an increase in the modulus of the coating. Increased modulus is beneficial in suppressing battery ignition and explosion caused by external impacts.

[0053] The citric acid content is in the range of about 5 parts by weight to about 50 parts by weight relative to the total of 100 parts by weight of the first and second binders. When the citric acid content is less than about 5 parts by weight relative to the total of 100 parts by weight, the minimum increase in the coating modulus may reduce the effectiveness in suppressing battery fire and explosion caused by external impact. When the citric acid content exceeds 50 parts by weight relative to the total of 100 parts by weight, separation between the coating and the substrate occurs in the separator due to low substrate adhesion, thereby reducing reliability. In one example embodiment, the citric acid content relative to the total of 100 parts by weight can be 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, or 27 parts by weight. 28 parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, 47 parts by weight, 48 parts by weight, 49 parts by weight, or 50 parts by weight, 10 to 50 parts by weight, or 10 to 20 parts by weight. Within the above ranges, the aforementioned significant effects of the diaphragm can be observed.

[0054] In one example embodiment, the substrate adhesion force of the diaphragm can be about 2N or greater. Here, "substrate" can be or includes porous substrates as described below, such as polyethylene substrates.

[0055] In one example embodiment, the total amount of the first binder and the second binder can be about 95 wt% or more of the mixture, for example, in the range of about 95 wt% to about 100 wt%, 99 wt% to 100 wt%, or 100 wt%. Within the above range, the aforementioned effects of the diaphragm can be easily achieved.

[0056] In one example embodiment, the citric acid content can be about 95 wt% or more of the crosslinking agent, for example, in the range of about 95 wt% to about 100 wt%, 99 wt% to 100 wt%, or 100 wt%. Within the above range, the aforementioned effects of the diaphragm can be easily achieved.

[0057] In one example embodiment, the crosslinking product may be or include a thermally crosslinked product.

[0058] In one example embodiment, the coating may be formed by or comprise a composition for a first coating, the composition for a first coating comprising a first binder, a second binder (i.e., a carboxyalkyl cellulose compound or a salt thereof), a crosslinking agent (such as citric acid), and a filler.

[0059] Each component of the composition used for the first coating is described in detail below.

[0060] First adhesive The first binder can be included in a desired amount relative to the second binder. The first and second binders can be included in a weight ratio (first binder: second binder) in the range of about 80:20 to about 20:80, relative to the total amount of 100 parts by weight of the first and second binders. Within this range, the separator can exhibit lower dry heat shrinkage, lower heat shrinkage in the electrolyte, higher substrate adhesion, and higher battery stability due to external impact. For example, the weight ratio of the first binder to the second binder can be 80:20, 75:25, 70:30, 65:35, 60:40, 55:45, 50:50, 45:55, 40:60, 35:65, 30:70, 25:75, 20:80, 80:20 to 25:75, or 80:20 to 30:70. Within this range, the aforementioned significant effects of the separator can be exhibited.

[0061] The first binder is an aqueous binder. Because the aqueous binder has high dispersibility in coating compositions comprising carboxyalkyl cellulose or its salts and citric acid, it is able to achieve the effect of a diaphragm.

[0062] The first adhesive may be a water-based heat-resistant adhesive, which may be or include (meth)acrylic adhesive.

[0063] The first binder may include one or more of the crosslinking units that are crosslinked with citric acid, such as units derived from (meth)acrylic acid or its salts, units derived from (meth)acrylamide, units derived from hydroxyalkyl (meth)acrylic acid esters, units derived from (meth)acrylonitrile, units derived from (meth)acrylamido-2-methylpropanesulfonic acid and its salts, and units derived from ethyleneimine.

[0064] In one example embodiment, the content of the crosslinking unit with citric acid can be in the range of about 10 mol% to about 100 mol% of the first binder, for example, 10 mol%, 11 mol%, 12 mol%, 13 mol%, 14 mol%, 15 mol%, 16 mol%, 17 mol%, 18 mol%, 19 mol%, 20 mol%, 21 mol%, 22 mol%, 23 mol%, 24 mol%, 25 mol%, 26 mol%, 27 mol%, 28 mol%, 29 mol%, 30 mol%, 31 mol%, 32 mol%, 33 mol%, 34 mol%, 35 mol%, 36 mol%, 37 mol%, 38 mol%, 39 mol%, 40 mol%, 41 mol%, 42 mol%, 43 mol%, 44 mol%, 45 mol%, 46 mol%, 47 mol%, 48 mol%, 49 mol%, 50 mol%, 51 mol%, 52 mol%, 53 mol%. 54 mol%, 55 mol%, 56 mol%, 57 mol%, 58 mol%, 59 mol%, 60 mol%, 61 mol%, 62 mol%, 63 mol%, 64 mol%, 65 mol%, 66 mol%, 67 mol%, 68 mol%, 69 mol%, 70 mol%, 71 mol%, 72 mol%, 73 mol%, 74 mol%, 75 mol%, 76 mol%, 77 mol%, 78 mol%, 79 mol%, 80 mol%, 81 mol%, 82 mol%, 83 mol%, 84 mol%, 85 mol%, 86 mol%, 87 mol%, 88 mol%, 89 mol%, 90 mol%, 91 mol%, 92 mol%, 93 mol%, 94 mol%, 95 mol%, 96 mol%, 97 mol%, 98 mol%, 99 mol% or 100 mol%, or 10 mol% to 95 mol%, for example, 30 mol% to 95 mol%. Within the above range, the modulus of the coating can be increased, and the increase in air permeability caused by a significant or excessively high modulus of the coating can be reduced or prevented.

[0065] (Meth)acrylic binders may include structural units containing sulfonate groups. Structural units containing sulfonate groups can improve the heat resistance and membrane resistance of the diaphragm.

[0066] The content of structural units containing sulfonate groups can range from about 0.1 mol% to about 65 mol% of the (meth)acrylic acid binder, for example, 0.1 mol% to 60 mol%, 0.1 mol% to 20 mol%, 0.1 mol% to 10 mol%, 1 mol% to 20 mol%, for example, 1 mol% to 10 mol%, or for example, 20 mol% to 65 mol% or 30 mol% to 65 mol%. When the content of structural units containing sulfonate groups falls within the above range, the membrane can exhibit desired or improved adhesion, heat resistance, air permeability, and oxidation resistance.

[0067] (Metha)acrylic adhesives may also include one or more structural units derived from (meth)acrylates or (meth)acrylic acid, structural units containing cyano groups, and structural units derived from (meth)acrylamide.

[0068] For example, (meth)acrylic adhesives may include structural units derived from (meth)acrylates or (meth)acrylic acid, or structural units derived from (meth)acrylamide, such as structural units derived from (meth)acrylic acid. Structural units derived from (meth)acrylic acid and structural units derived from (meth)acrylamide can provide crosslinking sites with citric acid.

[0069] The content of structural units derived from (meth)acrylate or (meth)acrylic acid can range from about 0 mol% to about 70 mol% of the (meth)acrylic acid binder, for example, 10 mol% to 70 mol%, 10 mol% to 60 mol%, 20 mol% to 60 mol%, 10 mol% to 50 mol%, 30 mol% to 60 mol%, 10 mol% to 40 mol%, or 40 mol% to 55 mol%. Within the above range, the membrane can exhibit desired or improved adhesion, heat resistance, air permeability, and oxidation resistance.

[0070] The content of cyano-containing structural units can range from about 0 mol% to about 85 mol% of the (meth)acrylic acid binder, for example, 30 mol% to 85 mol%, 30 mol% to 70 mol%, 30 mol% to 60 mol%, 35 mol% to 60 mol%, or 35 mol% to 55 mol%. Within the above range, the membrane can ensure desired or improved antioxidant properties and exhibit adhesion, heat resistance, and breathability.

[0071] The content of structural units derived from (meth)acrylamide can range from about 0 mol% to about 95 mol% of the (meth)acrylic acid binder, for example, 40 mol% to 85 mol%, 50 mol% to 85 mol%, 55 mol% to 95 mol%, 60 mol% to 85 mol%, 75 mol% to 95 mol%, or 80 mol% to 95 mol%. Within the above range, the membrane can ensure desired or improved antioxidant properties and exhibit adhesion, heat resistance, and breathability.

[0072] According to one example embodiment, the (meth)acrylic acid binder may have structural units comprising sulfonate groups ranging from about 0.1 mol% to about 30 mol% (e.g., 0.1 mol% to 10 mol%), structural units derived from (meth)acrylate or (meth)acrylic acid ranging from about 10 mol% to about 60 mol% (e.g., 10 mol% to 40 mol%), and structural units containing cyano groups ranging from about 30 mol% to about 85 mol% (e.g., 30 mol% to 80 mol%) (referred to as binder 1-1). In one example embodiment, relative to 100 mol% of the (meth)acrylic acid binder, the total content of structural units comprising sulfonate groups, structural units derived from (meth)acrylate or (meth)acrylic acid, and structural units containing cyano groups may be about 95 mol% or more, for example, 95 mol% to 100 mol% or 100 mol%.

[0073] According to another example embodiment, the (meth)acrylic acid binder may have structural units comprising sulfonate groups ranging from about 1 mol% to about 20 mol% (e.g., 5 mol% to 20 mol%) and structural units derived from (meth)acrylamide ranging from about 80 mol% to about 99 mol% (e.g., 80 mol% to 95 mol%) (referred to as binders 1-2). In one example embodiment, the total amount of structural units comprising sulfonate groups and structural units derived from (meth)acrylamide relative to 100 mol% of the (meth)acrylic acid binder may be about 95 mol% or more, for example, 95 mol% to 100 mol% or 100 mol%.

[0074] According to yet another example embodiment, the (meth)acrylic acid binder may have structural units comprising sulfonate groups, structural units derived from (meth)acrylate or (meth)acrylic acid, and structural units derived from (meth)acrylamide (referred to as binders 1-3). In one example embodiment, the total content of the structural units comprising sulfonate groups, structural units derived from (meth)acrylate or (meth)acrylic acid, and structural units derived from (meth)acrylamide relative to 100 mol% of the (meth)acrylic acid binder may be about 95 mol% or more, for example, 95 mol% to 100 mol% or 100 mol%.

[0075] For example, the (meth)acrylic binder can be binder 1-1 or binder 1-2. Binder 1-1 or binder 1-2 can have a better effect on improving film resistance and heat resistance.

[0076] The structural units of (meth)acrylic adhesives are described in detail below.

[0077] Structural units derived from (meth)acrylates or (meth)acrylic acid can be represented by at least one or a combination of the following chemical formulas 1, 2, or 3: Chemical Formula 1: .

[0078] Chemical formula 2: .

[0079] Chemical formula 3: .

[0080] In chemical formulas 1 to 3 R 1 To R 6 Each is independently either hydrogen or methyl, and In chemical formula 2, M is or includes alkali metals.

[0081] Alkali metals can be, or include, for example, lithium, sodium, potassium, rubidium, or cesium.

[0082] In one example, the structural units derived from (meth)acrylate or (meth)acrylic acid may include structural units represented by Formula 2 and structural units represented by Formula 3. In this case, the structural units represented by Formula 2 and the structural units represented by Formula 3 may be included in a molar ratio in the range of about 10:1 to 1:2, 10:1 to 1:1, or 5:1 to 1:1.

[0083] The structural unit containing a cyano group can be represented by, for example, the following chemical formula 4.

[0084] Chemical formula 4: .

[0085] In chemical formula 4, R 7 and R 8 Each is independently hydrogen or includes C1 to C3 alkyl groups. L 1 It is or includes -C(=O)-, -C(=O)O-, -OC(=O)-, -O-, or -C(=O)NH-. x is an integer in the range of 0 to 2. L 2 It is or includes substituted or unsubstituted C1 to C10 alkylene groups, substituted or unsubstituted C3 to C20 cycloalkylene groups, substituted or unsubstituted C6 to C20 arylene groups, or substituted or unsubstituted C3 to C20 heterocyclic groups, and y is an integer in the range of 0 to 2.

[0086] The cyano-containing structural unit may be or includes, for example, structural units derived from (meth)acrylonitrile, acrylonitrile, (meth)acrylic acid cyanoalkyl ester, or 2-(ethoxy)alkane nitrile. Here, the olefin may be a C2 to C20 olefin, a C2 to C10 olefin, or a C2 to C6 olefin; the alkyl may be a C1 to C20 alkyl, a C1 to C10 alkyl, or a C1 to C6 alkyl; and the alkane may be a C1 to C20 alkane, a C1 to C10 alkane, or a C1 to C6 alkane.

[0087] Acrylonitrile can be, for example, allyl cyanide, 4-pentenonitrile, 3-pentenonitrile, 2-pentenonitrile, or 5-hexenonitrile. (Meth)acrylate cyanoalkyl ester can be, for example, (meth)acrylate methyl cyanoacrylate, (meth)acrylate ethyl cyanoacrylate, (meth)acrylate propyl cyanoacrylate, or (meth)acrylate octyl cyanoacrylate. 2-(ethoxy)alkane nitrile can be, for example, 2-(ethoxy)acetonitrile or 2-(ethoxy)propionitrile.

[0088] The structural unit containing the sulfonate group can be or includes a structural unit containing a conjugate base comprising sulfonic acid, sulfonate, sulfonate ester, or a derivative thereof. For example, the structural unit containing the sulfonate group can be represented by at least one or a combination of the following chemical formulas 5, 6, and 7.

[0089] Chemical formula 5: .

[0090] Chemical formula 6: .

[0091] Chemical Formula 7: .

[0092] In chemical formulas 5 to 7 R 9 To R 14 Each is independently hydrogen or includes C1 to C3 alkyl groups. L 3 L 5 and L 7 Each is independently -C(=O)-, -C(=O)O-, -OC(=O)-, -O-, or -C(=O)NH-. L 4 L 6 and L 8 Each is independently or comprises a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, and a, b, c, d, e, and f are each an independent integer in the range of 0 to 2, and In chemical formula 6, M is or includes alkali metals.

[0093] As an example, in chemical formulas 5 to 7, L 3 L 5 and L 7 Each can be independently -C(=O)NH- or include -C(=O)NH-. L 4 L 6 and L 8 Each can be, independently or include, C1-C10 alkylene groups, and a, b, c, d, e, and f can all equal 1.

[0094] The structural unit containing a sulfonate group may include only one or more of the structural units represented by chemical formula 5, chemical formula 6, and chemical formula 7. In one example, the structural unit containing a sulfonate group may include the structural unit represented by chemical formula 6, and in another example, the structural unit containing a sulfonate group may include both the structural unit represented by chemical formula 6 and the structural unit represented by chemical formula 7.

[0095] The structural unit containing the sulfonate group can be or includes, for example, structural units derived from vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, anisolesulfonic acid, (meth)acrylamidoalkylsulfonic acid, (meth)acrylate sulfonyl ester, or salts thereof. Here, the alkane can be a C1 to C20 alkane, a C1 to C10 alkane, or a C1 to C6 alkane, and the alkyl can be a C1 to C20 alkyl, a C1 to C10 alkyl, or a C1 to C6 alkyl. The salt can consist of the aforementioned sulfonic acid and the desired ion. The ion can be or include, for example, an alkali metal ion, and in this case, the salt can be or include an alkali metal salt of sulfonic acid.

[0096] (Methacrylamidoalkyl sulfonic acid may be or include, for example, 2-(meth)acrylamido-2-methylpropanesulfonic acid, and (meth)acrylic acid sulfonyl ester may be or include, for example, (meth)acrylic acid-2-sulfoethyl ester or (meth)acrylic acid-3-sulfopropyl ester.

[0097] The structural unit derived from (meth)acrylamide can be represented by the following chemical formula 8.

[0098] Chemical formula 8: .

[0099] In chemical formula 8, R 15 and R 16 Each is independently either hydrogen or methyl.

[0100] (Meth)acrylic binders may include alkali metals. Alkali metals may exist in cationic form and may be, for example, lithium, sodium, potassium, rubidium, or cesium. For example, alkali metals may be conjugated with (meth)acrylic binders and exist in the form of salts. Alkali metals can facilitate the synthesis of (meth)acrylic binders in aqueous solvents, improve coating adhesion, and enhance the heat resistance, permeability, and oxidation resistance of the membrane.

[0101] The alkali metal content can be from about 1 wt% to about 40 wt% of the alkali metal and (meth)acrylic binder, for example, from 1 wt% to 30 wt%, from 1 wt% to 20 wt%, or from 10 wt% to 20 wt%. For example, the (meth)acrylic binder and alkali metal can be included in a weight ratio ranging from about 99:1 to about 60:40 or 99:1 to 70:30, for example, from 99:1 to 80:20, or for example, from 90:10 to 80:20.

[0102] Furthermore, the alkali metal content, relative to the total content of the alkali metal and (meth)acrylic binder, can range from about 0.1 mol% to about 1.0 mol%. When the alkali metal content falls within the above range, the coating can have desired or improved adhesion, and the diaphragm comprising it can exhibit desired or improved heat resistance, breathability, and oxidation resistance.

[0103] (Meth)acrylic adhesives can exist in various forms, such as alternating copolymers with alternating structural units, random copolymers with randomly distributed structural units, or graft copolymers with some structural units grafted onto each other.

[0104] The weight-average molecular weight (Mw) of the (meth)acrylic acid binder can range from 200,000 g / mol to 700,000 g / mol, for example, 200,000 g / mol to 600,000 g / mol or 300,000 g / mol to 600,000 g / mol. Within these ranges, the membrane can exhibit desired or improved adhesion, heat resistance, air permeability, and oxidation resistance. In this specification, the weight-average molecular weight can be the average molecular weight converted from polystyrene, measured using, for example, gel permeation chromatography (GPC).

[0105] The glass transition temperature of the (meth)acrylic binder can be in the range of about 200°C to about 280°C, 210°C to 270°C, or 210°C to 260°C. Within these ranges, the membrane can exhibit desired or improved heat resistance, permeability, and oxidation resistance. The glass transition temperature can be a value measured by, for example, differential scanning calorimetry (DSC).

[0106] (Meth)acrylic adhesives can have a melting point (Tm) of about 160°C or higher.

[0107] In this specification, the "melting point" can be measured by the following methods: Using a differential scanning calorimeter (DSC, device name: DSC Q20, manufacturer: TA instrument), the temperature was increased to 200°C at 10°C / min (cycle 1), isothermaled at 200°C for 1 minute, cooled to 40°C at 10°C / min, and then isothermaled at 40°C for 1 minute before being reheated to 200°C at 10°C / min (cycle 2). The temperature of the maximum point of the endothermic peak in the obtained DSC curve was taken as the melting temperature. T m (℃), and the temperature of the maximum point of the exothermic peak is measured as the crystallization temperature (℃). T c ℃). Here, melting temperature ( T m ) and crystallization temperature ( Tc All results are presented as measurements taken during the second cycle (cycle 2) of temperature rise and fall.

[0108] (Meth)acrylic acid binders can be prepared by solution polymerization.

[0109] According to one example embodiment, the (meth)acrylic adhesive may be included in the coating of the diaphragm in the form of a film.

[0110] Second adhesive The second binder is or includes a carboxyl cellulose compound or a salt thereof. When combined with the first binder and citric acid, the carboxyl cellulose compound or its salt can help suppress battery ignition and explosion due to external impact due to high substrate adhesion. For example, the second binder can be or includes carboxymethyl cellulose or an alkali metal salt thereof, such as a sodium salt of carboxymethyl cellulose.

[0111] The weight-average molecular weight of carboxyalkyl cellulose compounds or their salts can be in the range of about 50,000 g / mol to about 1,000,000 g / mol, for example, 100,000 g / mol to 600,000 g / mol. Within this range, the dispersibility of citric acid can be ensured because the viscosity of the composition used for coating will not become significantly high or excessive.

[0112] Citric acid The citric acid content relative to 100 parts by weight of the first adhesive can range from about 4 parts by weight to about 200 parts by weight, for example, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight. Quantities: 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, 47 parts by weight, 48 parts by weight, 49 parts by weight, 50 parts by weight, 51 parts by weight, 52 parts by weight, 53 parts by weight, 54 parts by weight, 55 parts by weight, 56 parts by weight, 57 parts by weight, 58 parts by weight, 59 parts by weight, 60 parts by weight, 61 parts by weight, 62 parts by weight, 63 parts by weight Servings, 64 servings, 65 servings, 66 servings, 67 servings, 68 servings, 69 servings, 70 servings, 71 servings, 72 servings, 73 servings, 74 servings, 75 servings, 76 servings, 77 servings, 78 servings, 79 servings, 80 servings, 81 servings, 82 servings, 83 servings, 84 servings, 85 servings, 86 servings, 87 servings, 88 servings, 89 servings, 90 servings, 91 servings, 92 servings, 93 servings, 94 servings, 95 servings, 96 servings The amounts are 97 parts by weight, 98 parts by weight, 99 parts by weight, 100 parts by weight, 105 parts by weight, 110 parts by weight, 115 parts by weight, 120 parts by weight, 125 parts by weight, 130 parts by weight, 135 parts by weight, 140 parts by weight, 145 parts by weight, 150 parts by weight, 155 parts by weight, 160 parts by weight, 165 parts by weight, 170 parts by weight, 175 parts by weight, 180 parts by weight, 185 parts by weight, 190 parts by weight, 195 parts by weight, or 200 parts by weight, ranging from about 5 parts by weight to about 200 parts by weight or from 10 parts by weight to 100 parts by weight. Within the above ranges, it is able to suppress battery ignition and explosion caused by external impact, and provides low thermal shrinkage and high adhesion to the substrate.

[0113] Relative to 100 parts by weight of the second adhesive, in the range of about 4 parts by weight to about 200 parts by weight, for example 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 3 2 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, 47 parts by weight, 48 parts by weight, 49 parts by weight, 50 parts by weight, 51 parts by weight, 52 parts by weight, 53 parts by weight, 54 parts by weight, 55 parts by weight, 56 parts by weight, 57 parts by weight, 58 parts by weight, 59 parts by weight, 60 parts by weight, 61 parts by weight, 62 parts by weight, 63 parts by weight, 64 parts by weight, 65 parts by weight Servings, 66 servings, 67 servings, 68 servings, 69 servings, 70 servings, 71 servings, 72 servings, 73 servings, 74 servings, 75 servings, 76 servings, 77 servings, 78 servings, 79 servings, 80 servings, 81 servings, 82 servings, 83 servings, 84 servings, 85 servings, 86 servings, 87 servings, 88 servings, 89 servings, 90 servings, 91 servings, 92 servings, 93 servings, 94 servings, 95 servings, 96 servings, 97 servings, 98 servings. 99 parts by weight, 100 parts by weight, 105 parts by weight, 110 parts by weight, 115 parts by weight, 120 parts by weight, 125 parts by weight, 130 parts by weight, 135 parts by weight, 140 parts by weight, 145 parts by weight, 150 parts by weight, 155 parts by weight, 160 parts by weight, 165 parts by weight, 170 parts by weight, 175 parts by weight, 180 parts by weight, 185 parts by weight, 190 parts by weight, 195 parts by weight, or 200 parts by weight; 5 parts by weight to 200 parts by weight; 4 parts by weight to 100 parts by weight; 4 parts by weight to 50 parts by weight; or 10 parts by weight to 100 parts by weight. Within the above ranges, it is able to suppress battery ignition and explosion caused by external impact, and provides low thermal shrinkage and high adhesion to the substrate.

[0114] filler The filler can have a particle size (D100) of about 0.7 μm or smaller. Within this range, both the dry shrinkage rate in the diaphragm and the shrinkage rate in the electrolyte can be achieved. For example, the particle size (D100) of the filler can be 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm or 0.7 μm, 0.55 μm or smaller, or 0.3 μm to 0.5 μm.

[0115] According to one example embodiment, the particle size (D50) of the filler can be about 0.4 μm or less, 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm or 0.4 μm, for example, 0.35 μm or less, for example, 0.1 μm to 0.3 μm. Within the above range, the diaphragm can exhibit improved heat resistance.

[0116] The filler may be or includes, for example, inorganic fillers, organic fillers, inorganic / organic composite fillers, or combinations thereof. Inorganic fillers may be or include ceramic materials that can improve heat resistance. Inorganic fillers may include, for example, at least one of metal oxides, quasi-metal oxides, metal fluorides, metal hydroxides, or combinations thereof. Inorganic fillers may include, for example, at least one of Al₂O₃, SiO₂, TiO₂, SnO₂, CeO₂, MgO, NiO, CaO, GaO, ZnO, ZrO₂, Y₂O₃, SrTiO₃, BaTiO₃, Mg(OH)₂, boehmite, or combinations thereof, but this disclosure is not limited thereto. Organic fillers may include at least one of acryloyl compounds, imide compounds, amide compounds, or combinations thereof, but this disclosure is not limited thereto. Organic fillers may have a core-shell structure, but this disclosure is not limited thereto. For example, the filler may include one or more of boehmite, Al₂O₃, BaTiO₃, and Mg(OH)₂.

[0117] The packing material can be spherical, plate-shaped, cubic, or without a fixed shape. Preferably, the packing material can be plate-shaped or cubic.

[0118] The mass ratio of the mixture of the first and second binders to the filler can be in the range of about 1:10 to about 1:50, for example, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, or 1:20 to 1:30. Within the above range, the diaphragm can exhibit increased adhesion.

[0119] The filler content relative to the total weight of the coating can range from about 50 wt% to about 99 wt%, for example, 70 wt% to 99 wt%, for example, 75 wt% to 99 wt%, for example, 80 wt% to 99 wt%, for example, 85 wt% to 99 wt%, for example, 90 wt% to 99 wt%, or for example, 95 wt% to 99 wt%. When the filler content falls within the above range, desired or improved heat resistance, durability, oxidation resistance, and stability can be exhibited.

[0120] The thickness of the coating can range from about 0.01 μm to about 20 μm, for example, 1 μm to 10 μm, 1 μm to 5 μm or 1 μm to 3 μm.

[0121] The ratio of the coating thickness to the thickness of the porous substrate can be in the range of about 0.05 to about 0.5, for example, 0.05 to 0.4, 0.05 to 0.3, or 0.1 to 0.2. Within the above range, the diaphragm can exhibit desired or improved permeability, heat resistance, and adhesion. As used herein, "coating thickness" refers to the thickness of one coating when the coating is formed on only one surface of the porous substrate, or the thickness of two coatings when the coating is formed on both surfaces of the porous substrate.

[0122] A coating can be formed by coating a porous substrate to a desired or predetermined thickness with a composition for coating, and then curing the resulting porous substrate at a temperature in the range of about 85°C to about 120°C for about 15 hours or longer (e.g., in the range of about 15 hours to about 24 hours).

[0123] porous substrate Porous substrates can be or include substrates with multiple pores conventionally used in electrochemical devices. Porous substrates can be, without limitation, polymer films formed from or comprising any polymer or copolymers or mixtures of two or more of the following: polyolefins (such as polyethylene, polypropylene, etc.), polyesters (such as polyethylene terephthalate, polybutylene terephthalate, etc.), polyacetal, polyamide, polyimide, polycarbonate, polyetheretherketone, polyaryletheretherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, and polytetrafluoroethylene (e.g., Teflon).

[0124] The porous substrate can be or includes, for example, a polyolefin substrate comprising polyolefins, and the polyolefin substrate can contribute to improved battery safety due to desired or improved shut-off functionality. For example, the polyolefin substrate can be or includes at least one of a polyethylene monolayer, a polypropylene monolayer, a polyethylene / polypropylene bilayer, a polypropylene / polyethylene / polypropylene trilayer, and a polyethylene / polypropylene / polyethylene trilayer. Furthermore, in addition to olefin resins, the polyolefin substrate can include non-olefin resins or copolymers of olefin monomers and non-olefin monomers.

[0125] The thickness of the porous substrate can be in the range of about 1 μm to about 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm or 5 μm to 15 μm.

[0126] A separator for a rechargeable lithium battery according to an example embodiment can exhibit desired or improved air permeability and can have an air permeability value of less than about 200 seconds / 100cc, for example, 190 seconds / 100cc or less, or 180 seconds / 100cc or less. That is, the separator can have an air permeability of less than about 40 seconds / 100cc·1μm per unit thickness, for example, 30 seconds / 100cc·1μm or less, or 25 seconds / 100cc·1μm or less. Here, air permeability is the time (in seconds) it takes for 100cc of air to pass through a unit thickness of the separator. The air permeability per unit thickness can be obtained by measuring the air permeability of the total thickness of the separator and dividing the air permeability by the thickness. The air permeability can be measured by measuring the time (in seconds) it takes for 100cc of air to pass through using an air permeability measuring device (Asahi Seiko, EG01-55-1MR).

[0127] Figure 1 This is a cross-sectional view of a separator for a rechargeable battery according to an example embodiment.

[0128] Reference Figure 1 The separator for a rechargeable lithium battery includes a porous substrate 1 and coatings 2 on two surfaces of the porous substrate 1. The coatings 2 include fillers 3 and a crosslinking product 4 of a first binder, a second binder, and a crosslinking agent.

[0129] The composition for coating the diaphragm may also include alcohols, which will be described below.

[0130] A separator for a rechargeable battery according to a second exemplary embodiment. The separator can suppress battery fire and explosion caused by external impact. In addition, the separator can provide low thermal shrinkage, low gas permeability and low resistance.

[0131] The membrane includes a porous substrate and a coating on at least one surface of the porous substrate. The coating is formed by or includes a composition comprising a first binder, a second binder, a crosslinking agent, a filler, and an alcohol, wherein the first binder is an aqueous binder, the second binder is a carboxyalkyl cellulose compound or a salt thereof, and the crosslinking agent comprises citric acid. The citric acid content is in the range of about 5 parts by weight to about 50 parts by weight relative to the total amount of the first and second binders (100 parts by weight).

[0132] The diaphragm can provide a low dry heat shrinkage rate. In one example embodiment, measured after being placed at 150°C for 1 hour, the diaphragm can have a dry shrinkage rate of about 5% or less in each of the longitudinal (MD) and transverse (TD) directions.

[0133] Citric acid can crosslink with the first binder, thereby reducing the thermal shrinkage rate of the membrane in the electrolyte. In one example embodiment, measured after 1 hour of immersion in the electrolyte at 150°C, the membrane can have a thermal shrinkage rate of about 10% or less in each direction of MD and TD.

[0134] Since the separator may be formed of a composition comprising a first binder, a second binder, a crosslinking agent and a filler, or a coating comprising a composition comprising a first binder, a second binder, a crosslinking agent and a filler, the separator can suppress battery fire and explosion caused by external impact, thereby improving the reliability and stability of the battery.

[0135] Citric acid can crosslink with carboxyalkyl cellulose compounds or their salts, and also with the first binder. Due to its high dispersibility in the mixture of the first binder and the carboxyalkyl cellulose compound or its salt, citric acid can be highly crosslinked with each of the first binder and the carboxyalkyl cellulose compound or its salt, thereby promoting an increase in the modulus of the coating. Because of the increased modulus of the coating, it is possible to suppress battery ignition and explosion caused by external impact.

[0136] The citric acid content, relative to 100 parts by weight of the first and second binders, ranges from about 5 parts by weight to about 50 parts by weight. When the citric acid content is less than about 5 parts by weight relative to 100 parts by weight of the first and second binders, a slight increase in the coating modulus reduces the effectiveness in suppressing battery fires and explosions caused by external impacts. When the citric acid content exceeds about 50 parts by weight relative to 100 parts by weight of the first and second binders, the substrate adhesion of the separator decreases, causing separation between the separator coating and the substrate, thereby reducing reliability. In one example embodiment, the citric acid content, relative to 100 parts by weight of the first and second binders, can range from about 10 parts by weight to about 50 parts by weight, for example, 10 parts by weight to 20 parts by weight. Within the above range, the aforementioned significant effects of the separator can be exhibited.

[0137] The coating can be formed by thermosetting (curing) a composition comprising a first binder, a second binder (i.e., a carboxyalkyl cellulose compound or a salt thereof), a crosslinking agent (i.e., citric acid), and a filler. Thermosetting may include a first crosslinking between citric acid and the first binder, and a second crosslinking between citric acid and the second binder. During the first and second crosslinking, byproducts may be generated, including citric acid products formed by the dehydration reaction of citric acid itself. These byproducts may reduce the crosslinking density of the coating and increase the permeability and electrical resistance of the membrane. The byproducts are generated by the dehydration of citric acid and may include cyclic compounds such as cyclic anhydrides and / or aconitine, but this disclosure is not limited thereto.

[0138] Alcohols can volatilize during the crosslinking reaction, which can accelerate dehydration and promote crosslinking. However, byproducts may not volatilize easily and therefore cannot promote crosslinking. Specifically, since the coating is an aqueous coating using water as a solvent, alcohols are not only readily miscible within the composition but also readily volatilized. Specifically, since membranes containing salts (e.g., MgSO4) instead of alcohols have low crosslinking, their permeability and electrical resistance are desirable or improved, but the membranes may produce adverse results regarding external shocks.

[0139] In one example embodiment, the diaphragm may have an air permeability of about 140 seconds / 100cc or less, for example, 105 seconds / 100cc or less.

[0140] In one example embodiment, the diaphragm may have a resistance of about 0.8 Ω or less, for example, 0.6 Ω or less.

[0141] In one example embodiment, thermosetting may include curing at a temperature ranging from about 85°C to about 120°C for about 15 hours or longer, for example, from about 15 hours to about 24 hours.

[0142] In one example embodiment, the total amount of the first binder and the second binder can be about 95 wt% or more of the mixture, for example, in the range of about 95 wt% to about 100 wt%, 99 wt% to 100 wt%, or 100 wt%. Within the above range, the aforementioned effects of the diaphragm can be easily achieved.

[0143] In one example embodiment, citric acid may be about 95 wt% or more of the crosslinking agent, for example, in the range of about 95 wt% to about 100 wt%, 99 wt% to 100 wt%, or 100 wt%. Within the above range, the aforementioned effects of the diaphragm can be readily achieved.

[0144] In one example embodiment, the crosslinking product may be or include a thermally crosslinked product.

[0145] Each component of the composition used for coating is described in detail below.

[0146] First adhesive The first adhesive is substantially the same as the first adhesive described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of the first adhesive is omitted.

[0147] Second adhesive The second adhesive is substantially the same as the second adhesive described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of the second adhesive is omitted.

[0148] Citric acid Citric acid is substantially the same as that described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of citric acid is omitted.

[0149] filler The filler is substantially the same as that described in "Separator for Rechargeable Battery according to First Example Embodiment". Therefore, a detailed description of the filler is omitted.

[0150] alcohol Alcohols evaporate at crosslinking temperatures, and there are no particular restrictions, as long as the alcohol is of the type that allows byproducts to evaporate during the evaporation process.

[0151] In one example embodiment, the alcohol may have a boiling point of about 60°C or higher, for example, a boiling point in the range of about 60°C to about 85°C. Within the above range, the alcohol may readily volatilize at the crosslinking temperature.

[0152] In one example embodiment, the alcohol is a straight-chain or branched monohydric alcohol having one to four carbon atoms in the main chain, and may include, for example, ethanol, methanol, isopropanol, n-butanol, etc.

[0153] The alcohol content relative to 100 parts by weight of the first binder can range from about 5 parts by weight to about 50 parts by weight, for example, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, etc. The amounts are 28 parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, 47 parts by weight, 48 parts by weight, 49 parts by weight, or 50 parts by weight, 5 to 30 parts by weight, 5 to 20 parts by weight, or 10 to 20 parts by weight. Within the above ranges, air permeability and electrical resistance can be improved by removing byproducts, and the deterioration of the physical properties of the coating due to residues in the coating can be reduced or prevented.

[0154] The alcohol content relative to 100 parts by weight of the second binder can range from about 5 parts by weight to about 50 parts by weight, for example, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, and 30 parts by weight. 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, 47 parts by weight, 48 parts by weight, 49 parts by weight or 50 parts by weight, 5 parts by weight to 30 parts by weight, 5 parts by weight to 20 parts by weight or 10 to 30 parts by weight. Within the above ranges, air permeability and electrical resistance can be improved by removing byproducts, and the deterioration of the physical properties of the coating due to residues in the coating can be reduced or prevented.

[0155] porous substrate The porous substrate is substantially the same as the porous substrate described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of the porous substrate is omitted.

[0156] Figure 2 This is a cross-sectional view of a separator for a rechargeable lithium battery according to an example embodiment.

[0157] Reference Figure 2 The separator for a rechargeable lithium battery includes a porous substrate 1 and a coating 2 on two surfaces of the porous substrate 1. The coating 2 includes a filler 3 and a crosslinked product 4 comprising a first binder, a second binder, and a crosslinking agent. The coating 2 is formed by or includes a composition comprising a first binder, a second binder, a crosslinking agent, a filler, and an alcohol.

[0158] The filler in the diaphragm coating may include a mixture of a first filler and a second filler with different aspect ratios. Therefore, the filler is described below.

[0159] A separator for a rechargeable battery according to a third exemplary embodiment. The separator can suppress battery fire and explosion caused by external impact. The separator can have a low thermal shrinkage rate. The separator can improve the battery's high-temperature lifespan.

[0160] The separator can suppress battery fire and explosion caused by external impacts, thereby improving battery reliability and stability. Furthermore, the separator provides a low shrinkage rate, thus improving battery safety. Additionally, the separator can improve the battery's high-temperature lifespan, thereby increasing battery life and reliability.

[0161] According to one example embodiment, the membrane includes a porous substrate and a coating on at least one surface of the porous substrate, wherein the coating includes a crosslinking product of a mixture of a first binder and a second binder and a crosslinking agent; and a mixture of a first filler and a second filler having different aspect ratios. The first binder is or includes an aqueous binder, the second binder is or includes a carboxyalkyl cellulose compound or a salt thereof, the crosslinking agent contains citric acid, and the citric acid content is in the range of about 5 parts by weight to about 50 parts by weight relative to a total of 100 parts by weight of the first binder and the second binder. The second filler has a higher aspect ratio than the first filler, and the weight ratio of the second filler to the first filler (second filler: first filler) is in the range of about 1:1 to about 1:10.

[0162] Due to their high tensile strength, the crosslinked products of compositions containing citric acid as a crosslinking agent in a mixture comprising a first binder and a second binder exhibit high tensile strength. This can suppress battery fires and explosions caused by external impacts, thereby improving battery reliability and safety. Coatings comprising first and second fillers with different aspect ratios, as well as the crosslinked products, can promote a reduction in the thermal shrinkage rate of the separator and improve battery cycling at high temperatures.

[0163] Citric acid is a polycarboxylic acid with a hydroxyl group, as shown in the chemical formula above.

[0164] Citric acid can crosslink with the first binder and carboxyalkyl cellulose compounds or their salts. Due to the high dispersibility of citric acid in the mixture of the first binder and carboxyalkyl cellulose compounds or their salts, citric acid can be highly crosslinked with each of the first binder and carboxyalkyl cellulose compounds or their salts, thus easily increasing the tensile strength of the crosslinked product. Increasing the tensile strength of the crosslinked product can suppress battery ignition and explosion caused by external impacts.

[0165] The coating comprises a crosslinking product and a mixture of a first filler and a second filler as fillers. In this disclosure, a mixture of a first filler and a second filler having different aspect ratios is included, and the weight ratio between the first filler and the second filler is adjusted.

[0166] First, the aspect ratio is described below.

[0167] The length-to-diameter ratio can refer to the ratio of the length or thickness of the packing material to the diameter of its cross-section. Here, "diameter" can refer to the maximum length that can be obtained from the cross-section of the packing material.

[0168] In this disclosure, a second packing material is used as a packing material with a large length-to-diameter ratio. Figure 4 It is an SEM image of the second filler according to an example embodiment, and Figure 5 The aspect ratio of the second packing is shown.

[0169] Reference Figure 5 The second packing material can have a length significantly longer than its cross-sectional diameter. The second packing material can be needle-shaped or rod-shaped, for example, needle-shaped packing. Figure 4 SEM images of needle-shaped fillers are shown.

[0170] Reference Figure 5 The aspect ratio of the second packing can refer to the ratio of the packing length (L2) to the maximum diameter of the cross section (D2). Here, needle packing has a relatively smaller aspect ratio than fibrous packing, and needle packing is defined as having an aspect ratio of 100 or less, while fibrous packing is defined as having an aspect ratio greater than 100.

[0171] In this disclosure, the first packing is used as a packing with a small aspect ratio. Figure 6 It is an SEM image of the first filler according to an example embodiment, and Figure 7 The aspect ratio of the first packing is shown.

[0172] Reference Figure 7 The first packing material can be a packing material whose length and thickness are substantially similar. The first packing material can be one or more of cubic packing, plate packing, spherical packing, and packing without a fixed shape, such as cubic packing or plate packing. Figure 6 This is an SEM image of the cubic packing material. See also... Figure 7 The aspect ratio of the first packing can be the ratio of the thickness (D1) of the first packing to the maximum length (L1) of the cross section of the first packing.

[0173] In this disclosure, in a coating comprising crosslinked products, first and second fillers with different aspect ratios are introduced to increase the density of the coating by filling the spaces between the fillers without increasing permeability, and to reduce surface roughness by eliminating irregularities on the coating surface, thereby increasing adhesion to electrode plates including positive or negative electrodes. Therefore, even at high temperatures, the separator remains firmly bonded to the electrode plates, which can help improve the high-temperature life of the battery.

[0174] In one example embodiment, the separator may have a surface roughness (Ra) of about 0.5 μm or less. Within this range, the high-temperature life of the battery can be improved.

[0175] The second packing has a higher length-to-diameter ratio than the first packing, and the second packing and the first packing are included in a weight ratio (second packing: first packing) in the range of about 1:1 to about 1:10.

[0176] When the weight ratio is less than 1:1, the dry heat shrinkage rate and the heat shrinkage rate in the electrolyte both increase due to the inclusion of a relatively small amount of the first filler in the coating, and the surface of the coating has significant or excessive irregularity due to the inclusion of a relatively large amount of the second filler, and the high-temperature life of the battery may be reduced.

[0177] When the weight ratio is higher than 1:10, the second filler will be included in the coating in a relatively small amount, thereby reducing the density of the coating, thus reducing the heat resistance of the separator and shortening the high-temperature life of the battery.

[0178] For example, the weight ratio can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, 1:1 to 1:9 or 1:4 to 1:9.

[0179] The citric acid content may range from about 5 parts by weight to about 50 parts by weight relative to the total amount of 100 parts by weight of the mixture of the first and second adhesives.

[0180] When the citric acid content is less than about 5 parts by weight relative to a total of 100 parts by weight, the increase in coating modulus is negligible, and citric acid may be detrimental to suppressing battery ignition and explosion due to external impact. When the citric acid content is greater than about 50 parts by weight relative to a total of 100 parts by weight, the adhesion of the separator to the substrate decreases, causing the coating to separate from the porous substrate of the separator, thus reducing reliability. In one example embodiment, the citric acid content relative to a total of 100 parts by weight can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, or 27 parts by weight. 28 parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, 47 parts by weight, 48 parts by weight, 49 parts by weight, or 50 parts by weight, 10 to 50 parts by weight, or 10 to 20 parts by weight. Within the above ranges, the aforementioned significant effects of the diaphragm can be observed.

[0181] In one example embodiment, after being placed at 150°C for 1 hour, the thermal shrinkage rate of the diaphragm in each direction of MD and TD can be about 5% or less.

[0182] In one example embodiment, after being placed in the electrolyte at 150°C for 1 hour, the thermal shrinkage rate of the diaphragm in each direction of MD and TD can be about 5% or less.

[0183] In one example embodiment, the total amount of the first binder and the second binder can be about 95 wt% or more of the mixture, for example, in the range of about 95 wt% to about 100 wt%, 9 wt% to 100 wt%, or 100 wt%. Within the above range, the above-described effects of the diaphragm can be easily achieved.

[0184] In one example embodiment, the citric acid content can be about 95 wt% or more of the crosslinking agent, for example, in the range of about 95 wt% to about 100 wt%, 99 wt% to 100 wt%, or 100 wt%. Within the above range, the aforementioned effects of the diaphragm can be easily achieved.

[0185] In one example embodiment, the crosslinking product may be or include a thermally crosslinked product.

[0186] In one example embodiment, the coating may include: a first binder; a second binder, namely, a carboxyalkyl cellulose compound or a salt thereof; a crosslinking agent, namely, citric acid; and a first filler and a second filler. The coating may be formed by or include a composition for coating such that the weight ratio of the second filler to the first filler is in the range of about 1:1 to about 1:10.

[0187] Each component of the composition used for coating is described in detail below.

[0188] First adhesive The first adhesive is substantially the same as the first adhesive described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of the first adhesive is omitted.

[0189] Second adhesive The second adhesive is substantially the same as the second adhesive described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of the second adhesive is omitted.

[0190] Citric acid Citric acid is substantially the same as that described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of citric acid is omitted.

[0191] First packing The first packing material can be spherical, plate-shaped, cubic, or without a fixed shape. For example, the first packing material can be cubic or plate-shaped, for example, it can be cubic.

[0192] The first packing material can have a particle size (D100) of about 0.7 μm or smaller. Within the above range, the diaphragm can easily achieve a dry shrinkage rate and a shrinkage rate in the electrolyte. For example, the particle size (D100) of the first packing material can be 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm or 0.7 μm, 0.55 μm or smaller, or in the range of about 0.3 μm to about 0.5 μm.

[0193] According to one example embodiment, the particle size (D50) of the first filler can be about 0.4 μm or smaller, for example, 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm or 0.4 μm, 0.3 μm or smaller, for example, in the range of about 0.1 μm to about 0.3 μm. Within the above range, the diaphragm can exhibit an improved heat resistance effect.

[0194] According to one example embodiment, the first packing may have an aspect ratio of less than about 100.

[0195] The first filler may be or include, for example, inorganic fillers, organic fillers, inorganic / organic composite fillers, or combinations thereof. The inorganic filler may be or include ceramic materials that can improve heat resistance. The inorganic filler may include, for example, at least one of metal oxides, quasi-metal oxides, metal fluorides, metal hydroxides, or combinations thereof. The inorganic filler may include, for example, at least one of Al₂O₃, SiO₂, TiO₂, SnO₂, CeO₂, MgO, NiO, CaO, GaO, ZnO, ZrO₂, Y₂O₃, SrTiO₃, BaTiO₃, Mg(OH)₂, boehmite, or combinations thereof, but this disclosure is not limited thereto. The organic filler may include at least one of acrylic compounds, imide compounds, amide compounds, or combinations thereof, but this disclosure is not limited thereto. The organic filler may have a core-shell structure, but this disclosure is not limited thereto. Preferably, the first filler may be or include one or more of boehmite, Mg(OH)₂, Al₂O₃, and BaTiO₃.

[0196] For the first filler, the mixture of the first and second binders and the mixture of the first and second fillers can be included in a mass ratio (mixture of first and second binders : mixture of first and second fillers) from about 1:10 to about 1:50, for example, within the range of 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:10 to 1:30, or 1:20 to 1:30. Within the above ranges, the adhesiveness of the diaphragm can be increased.

[0197] The first filler can be in the range of about 50 wt% to about 99 wt% relative to the total amount of the coating, for example, 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt%, 55 wt%, 56 wt%, 57 wt%, 58 wt%, 59 wt%, 60 wt%, 61 wt%, 62 wt%, 63 wt%, 64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt%, 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 7 8wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, 89wt%, 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, 98wt% or 99wt%, 70wt% to 99wt%, 75wt% to 99wt%, for example, 80wt% to 99wt%, 85wt% to 99wt%, 90wt% to 99wt% or 95wt% to 99wt%. Within the above ranges, the diaphragm can exhibit desired or improved heat resistance, durability, oxidation resistance and stability.

[0198] Second packing The second packing material can have a larger aspect ratio than the first packing material. For example, the aspect ratio of the second packing material can be about 100 or smaller, such as 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50. 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100, or 5 to 100. Within the above range, the surface roughness of the coating can be reduced.

[0199] In one example embodiment, the average diameter of the second filler can be in the range of about 5 nm to about 100 nm, for example, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31nm, 32nm, 33nm, 34nm, 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, 41nm, 42nm, 43nm, 44nm, 45nm, 46nm, 47n m, 48nm, 49nm, 50nm, 51nm, 52nm, 53nm, 54nm, 55nm, 56nm, 57nm, 58nm, 59nm, 60nm, 61nm, 62nm, 63nm, 6 4nm, 65nm, 66nm, 67nm, 68nm, 69nm, 70nm, 71nm, 72nm, 73nm, 74nm, 75nm, 76nm, 77nm, 78nm, 79nm, 80nm , 81nm, 82nm, 83nm, 84nm, 85nm, 86nm, 87nm, 88nm, 89nm, 90nm, 91nm, 92nm, 93nm, 94nm, 95nm, 96nm, 97 The aspect ratio can be 98nm, 99nm, or 100nm, 30nm to 50nm, and the average length of the second filler can be 0.5μm to 10μm, for example, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm or 10μm or 3μm to 6μm. Within the above range, the above aspect ratio can be achieved, and the increase in the permeability of the diaphragm can be reduced or prevented.

[0200] The second packing material may be or include needle-shaped packing or rod-shaped packing, for example, needle-shaped packing.

[0201] The second filler may be or include, for example, inorganic fillers, organic fillers, inorganic / organic composite fillers, or combinations thereof. Inorganic fillers may be or include ceramic materials that can improve heat resistance. Inorganic fillers may include, for example, at least one of metal oxides, quasi-metal oxides, metal fluorides, metal hydroxides, or combinations thereof. Inorganic fillers may include, for example, at least one of Al₂O₃, SiO₂, TiO₂, SnO₂, CeO₂, MgO, NiO, CaO, GaO, ZnO, ZrO₂, Y₂O₃, SrTiO₃, BaTiO₃, Mg(OH)₂, boehmite, or combinations thereof, but this disclosure is not limited thereto. Organic fillers may include at least one of acrylic compounds, imide compounds, amide compounds, or combinations thereof, but this disclosure is not limited thereto. Organic fillers may have a core-shell structure, but this disclosure is not limited thereto. For example, the second filler may be or include one or more of boehmite, Mg(OH)₂, Al₂O₃, and BaTiO₃.

[0202] In one example embodiment, the first filler may be or include boehmite, and the second filler may also be or include boehmite. Since boehmite has hydroxyl groups on its surface without requiring additional surface treatment, the bonding between the first and second fillers can be increased.

[0203] The second filler may be or include fillers whose surfaces are unmodified or surface-modified. Surface-modified second fillers may further increase adhesion to the first filler. In one example embodiment, surface modification may include introducing hydrophilic groups (such as or including at least one of hydroxyl, carboxylic acid, amide, amino, or combinations thereof) onto the surface of the second filler. Surface modification may be performed by surface treatment with a compound having the aforementioned functional groups (e.g., a silane compound having hydroxyl, carboxylic acid, amino, or amide groups).

[0204] The content of the second filler can be from about 1 wt% to about 10 wt% of the total amount of the coating, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 1 wt% to 5 wt%, or 1 wt% to 3 wt%. Within the above range, the diaphragm can exhibit desired or improved heat resistance, durability, oxidation resistance, and stability.

[0205] The thickness of the coating can be in the range of about 0.01 μm to about 20 μm, and within the above range, the coating can have a thickness of 1 μm to 10 μm, 1 μm to 5 μm or 1 μm to 3 μm.

[0206] The ratio of the coating thickness to the thickness of the porous substrate can be in the range of about 0.05 to about 0.5, for example, 0.05 to 0.4, 0.05 to 0.3, or 0.1 to 0.2. Within the above range, the diaphragm can exhibit desired or improved permeability, heat resistance, and adhesion. Here, "coating thickness" refers to the thickness of a single coating when the coating is formed on only one surface of the porous substrate, and to the thickness of two coatings when the coating is formed on both surfaces of the porous substrate.

[0207] A coating can be formed by coating a porous substrate to a desired or predetermined thickness with a composition for coating, and then curing the coated substrate at 85°C to 120°C for about 15 hours or longer (e.g., in the range of about 15 hours to about 24 hours).

[0208] porous substrate The porous substrate is substantially the same as the porous substrate described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of the porous substrate is omitted.

[0209] A separator for a rechargeable lithium battery according to an example embodiment may exhibit desired or improved permeability, for example, less than about 200 seconds / 100cc, such as 190 seconds / 100cc or less, or 180 seconds / 100cc or less.

[0210] Figure 3 This is a cross-sectional view of a separator for a rechargeable lithium battery according to an example embodiment.

[0211] Reference Figure 3 The separator for a rechargeable lithium battery includes a porous substrate 1 and coatings 2 on two surfaces of the porous substrate 1. The coating 2 includes: a first filler 3a; a crosslinked product 4 of a first binder, a second binder, and citric acid; and a second filler 3b.

[0212] The coating of the diaphragm may also comprise polymer particles with melting points in the range of about 80°C to about 135°C. The coating is described below.

[0213] A separator for a rechargeable battery according to a fourth exemplary embodiment. The diaphragm can improve shut-off temperature and breakdown voltage. The diaphragm can provide low thermal shrinkage.

[0214] Because the separator improves the shut-off temperature and breakdown voltage, it can provide a battery with enhanced safety. Since the separator for a rechargeable battery according to one example embodiment has a low thermal shrinkage rate, it can provide a battery with desired or improved reliability and lifespan.

[0215] The separator includes a porous substrate and a coating on at least one surface of the porous substrate, wherein the coating comprises: a crosslinking product comprising a mixture of a first binder and a second binder and a crosslinking agent; a filler; and polymer particles having a melting point in the range of about 80°C to about 135°C. The first binder is an aqueous binder, the second binder is a carboxyalkyl cellulose compound or a salt thereof, and the crosslinking agent comprises citric acid, wherein the citric acid content is about 5 parts by weight to about 50 parts by weight relative to a total of 100 parts by weight of the first binder and the second binder. When polymer particles having the same average particle size are included, the separator can significantly improve battery safety by significantly reducing the shut-off temperature and significantly increasing the breakdown voltage.

[0216] Typically, polymer particles with melting points in the range of about 80°C to about 135°C are known to lower the shut-off temperature and improve the breakdown voltage. Polymer particles with melting points of 80°C to 135°C are aqueous particles that can be dispersed in aqueous solvents and then used to form coatings. However, citric acid is readily soluble in aqueous solvents and has a specific chemical formula described below. It can be assumed that due to the interaction between citric acid and polymer particles with melting points of 80°C to 135°C, the polymer particles are stably fixed within the coating, thereby significantly improving the shut-off temperature and breakdown voltage; however, this disclosure is not limited thereto.

[0217] The diaphragm, including the coating, can also have a low thermal shrinkage rate. In this disclosure, citric acid is used as a crosslinking agent to crosslink the adhesive. Since citric acid is included in the coating containing polymer particles with a melting point of 80°C to 135°C, the thermal shrinkage rate of the diaphragm can be significantly reduced.

[0218] In one example embodiment, the diaphragm can provide a low dry heat shrinkage rate. In one example embodiment, measured after being placed at 150°C for 1 hour, the diaphragm can have a dry shrinkage rate of about 5% or less in each direction of MD and TD.

[0219] In another example embodiment, the diaphragm can provide a low thermal shrinkage rate in the electrolyte. In one example embodiment, measured after being placed at 150°C for 1 hour, the diaphragm may have a shrinkage rate of about 10% or less, for example 5% or less, in the electrolyte on each of the MD and TD.

[0220] The content of polymer particles with melting points in the range of about 80°C to about 135°C can be from about 5 wt% to about 30 wt% of the coating, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, or 30 wt%, 7 wt% to 25 wt%, 10 wt% to 25 wt%, or 15 wt% to 25 wt%. Within the above range, the effects of improving both breakdown voltage and thermal shrinkage rate can be achieved.

[0221] In one example embodiment, the content of polymer particles may be in the range of about 5 wt% to about 30 wt% of the total amount of the first coating and the second coating, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt% or 30 wt%, 7 wt% to 25 wt%, 10 wt% to 25 wt%, or 15 wt% to 25 wt%. In another example embodiment, the content of polymer particles may be in the range of about 5 wt% to about 30 wt% of the total amount of the first coating, adhesive layer and second coating, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt% or 30 wt%, 7 wt% to 25 wt%, 10 wt% to 25 wt% or 15 wt% to 25 wt%. In yet another example embodiment, the content of polymer particles may be in the range of about 5 wt% to about 30 wt% of the total amount of the third coating and the second coating, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt% or 30 wt%, 7 wt% to 25 wt%, 10 wt% to 25 wt%, or 15 wt% to 25 wt%. In yet another example embodiment, the content of polymer particles can be in the range of about 5 wt% to about 30 wt% of the fourth coating, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, or 30 wt%, 7 wt% to 25 wt%, 10 wt% to 25 wt%, or 15 wt% to 25 wt%. Within the above range, the effect of improving both breakdown voltage and heat shrinkage rate can be achieved.

[0222] The first coating, the second coating, the adhesive layer, the third coating, and the fourth coating are described in detail below.

[0223] The citric acid content is in the range of about 5 parts by weight to about 50 parts by weight relative to 100 parts by weight of the first and second adhesives. When the citric acid content is less than about 5 parts by weight relative to 100 parts by weight of the adhesives, there may be a challenge of reduced thermal shrinkage in the electrolyte. When the citric acid content exceeds about 50 parts by weight relative to 100 parts by weight of the adhesives, there may be a challenge of reduced adhesion between the diaphragm and the porous substrate, leading to separation between the diaphragm coating and the porous substrate, thereby reducing reliability.

[0224] For example, the citric acid content relative to 100 parts by weight of the binder can range from about 5 parts by weight to about 30 parts by weight or from 10 parts by weight to 20 parts by weight. Within the above range, the separator is effective and can improve battery reliability by suppressing battery fire and explosion caused by external impact.

[0225] Here, external impact can be measured using the following methods: Cylindrical batteries with a separator and 50% state of charge (SOC) are evaluated using the international standard UN internal short-circuit test method (referred to as the UN impact test). In this method, the battery is placed on a test block (SS41 steel, flat, thickness: 70 mm), and a cylindrical weight of 9.1 ± 0.1 kg with a diameter of 15.8 ± 0.1 mm is dropped freely onto the battery from a height of 630 ± 25 mm to check for explosion or fire. The number of all evaluated samples (10 samples) that pass the impact test (i.e., do not exhibit battery explosion, rupture, or fire) is given. If the number of failures (samples that fail) is 2 or fewer, the result is evaluated as OK; and if the number of failures is 3 or more, the result is evaluated as NG (bad / failed).

[0226] In one example embodiment, the total content of the first binder and the second binder can be about 95 wt% or more of the mixture, for example, in the range of about 95 wt% to about 100 wt%, or 99 wt% to 100 wt% or 100 wt%. Within the above range, the above-described effects of the diaphragm can be easily achieved.

[0227] In one example embodiment, the citric acid content can be about 95 wt% or more of the crosslinking agent, for example, in the range of about 95 wt% to about 100 wt%, 99 wt% to 100 wt%, or 100 wt% of the crosslinking agent. Within the above range, the above-mentioned effects of the diaphragm can be easily achieved.

[0228] In one example embodiment, the crosslinking product may be or include a thermally crosslinked product.

[0229] The components of the coating are described in detail below.

[0230] First adhesive The first adhesive is substantially the same as the first adhesive described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of the first adhesive is omitted.

[0231] Second adhesive The second adhesive is substantially the same as the second adhesive described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of the second adhesive is omitted.

[0232] Citric acid Citric acid is substantially the same as that described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of citric acid is omitted.

[0233] filler The filler is substantially the same as that described in "Separator for Rechargeable Battery according to First Example Embodiment". Therefore, a detailed description of the filler is omitted.

[0234] Polymer particles with melting points in the range of about 80°C to about 135°C Polymer particles with a melting point in the range of about 80°C to about 135°C can reduce the temperature at which the cell shuts down when a conventional battery cell explodes, thereby suppressing heat generation in the early stages of the battery.

[0235] In one example embodiment, the melting point of the polymer particles can be lower than that of the porous substrate. In this case, the polymer particles melt before the substrate, forming a film on the separator to induce an initial shutdown, followed by shutdown within the substrate, which can further enhance the battery's puncture safety. For example, the melting point of the polymer particles can be in the range of about 90°C to about 120°C.

[0236] The polymer particles can have an average particle size (D50) in the range of about 0.1 μm to 2 μm, for example, 0.1 μm to 1 μm. Within this range, ensuring battery performance can be facilitated by reducing or minimizing resistance during lithium-ion migration, and the shutdown function can be further enhanced.

[0237] The polymer particles may include one or more of polyolefins, polyolefin derivatives, and polyolefin waxes. For example, polyolefins may include one or more of low-density polyethylene, ultra-low-density polyethylene, and high-density polyethylene.

[0238] The weight-average molecular weight of the polymer particles can range from about 300 g / mol to about 30,000 g / mol, for example, from 2,000 g / mol to 10,000 g / mol. Within this range, battery performance can be ensured by reducing or minimizing resistance during lithium-ion migration, and the shutdown function can be further enhanced.

[0239] The polymer particles can be dispersed throughout the coating. Alternatively, the polymer particles can be included in a single outermost layer of the coating.

[0240] As mentioned above, polymer particles can be included in the coating at a desired concentration.

[0241] The coating may be or include a stacked structure of the first and second coatings below.

[0242] The coating may be or include a stacked structure of the following first coating, adhesive layer and second coating.

[0243] The coating may be or include a stacked structure of the third and second coatings below.

[0244] The coating may be or include the fourth coating below.

[0245] Coating form Reference Figures 8 to 11 Describe the form of the coating. Figures 8 to 11 Each is a cross-sectional view of a separator for a rechargeable battery according to an example embodiment.

[0246] Figures 8 to 11 The diagram shows a case where the coating is formed on only one surface of the porous substrate, but the coating can also be formed on both surfaces of the porous substrate.

[0247] Reference Figure 8 The separator for a rechargeable battery includes a porous substrate 1 and a first coating 2a and a second coating 2b stacked (e.g., sequentially stacked) on one surface of the porous substrate 1. The first coating 2a may include a filler 3 and a crosslinking product 4, and the second coating 2b may include polymer particles 6 with a melting point in the range of about 80°C to about 135°C.

[0248] Reference Figure 9The separator for a rechargeable battery includes a porous substrate 1 and a first coating 2a, an adhesive layer 7, and a second coating 2b stacked (e.g., sequentially stacked) on one surface of the porous substrate 1. The first coating 2a may include a filler 3 and a crosslinking product 4, the second coating 2b may include polymer particles 6 with a melting point of 80°C to 135°C, and the adhesive layer 7 may include an adhesive 8. The adhesive may include conventional adhesives known to those skilled in the art, such as (meth)acrylic acid adhesives.

[0249] Reference Figure 10 The separator for a rechargeable battery includes a porous substrate 1 and a third coating 2c and a second coating 2b stacked on one surface of the porous substrate 1. The third coating 2c includes a filler 3, a crosslinking product 4, and an adhesive 8. The second coating 2b may include polymer particles 6 with a melting point in the range of about 80°C to about 135°C. The adhesive may include conventional adhesives known to those skilled in the art, such as (meth)acrylic acid adhesives.

[0250] Reference Figure 11 The separator for a rechargeable battery includes a porous substrate 1 and a fourth coating 2d stacked on one surface of the porous substrate 1. The fourth coating 2d may include filler 3, crosslinking product 4, and polymer particles 6 with a melting point in the range of about 80°C to about 135°C.

[0251] The thickness of the coating can be in the range of about 0.01 μm to about 20 μm, and within the above range, the coating can have a thickness of 1 μm to 10 μm, 1 μm to 5 μm or 1 μm to 4 μm.

[0252] porous substrate The porous substrate is substantially the same as the porous substrate described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of the porous substrate is omitted.

[0253] The diaphragm can exhibit desired or improved air permeability, which can be, for example, less than about 200 seconds / 100cc, such as 190 seconds / 100cc or less, or 180 seconds / 100cc or less. That is, the diaphragm can have an air permeability of less than about 40 seconds / 100cc·1μm per unit thickness, such as 30 seconds / 100cc·1μm or less, or 25 seconds / 100cc·1μm or less.

[0254] The membrane may also include lithium cations. This is described in detail below.

[0255] A separator for a rechargeable battery according to a fifth exemplary embodiment. A separator can improve battery life at high temperatures. The separator replenishes lithium ions that may be lost during repeated charging and discharging, thus improving battery life at high temperatures.

[0256] When a battery is repeatedly charged and discharged, lithium cations are inevitably lost. For example, the lithium cation content in the battery may decrease due to electrode degradation and dendrite formation during repeated charging and discharging. This loss of lithium cations may further increase when the battery is operated at high temperatures.

[0257] According to one example embodiment, the separator can improve battery life at high temperatures by replenishing lithium ions lost during battery charging and discharging. In this regard, the separator allows the coating to readily include a specific range of lithium ions by including a first binder and a second binder as sources of lithium ions. Furthermore, the separator can facilitate the elution of lithium ions from the network structure formed by crosslinking the first and second binders using citric acid, thereby increasing the elution rate of lithium ions from the first and second binders. Lithium ions can be included in the first and second binders, but when a voltage is applied while the separator is immersed in the electrolyte, lithium ions can be released through the first and second binders and supplied to the outside of the separator.

[0258] According to one example embodiment, the membrane may include a porous substrate and a coating on at least one surface of the porous substrate, wherein the coating includes a crosslinking product comprising a mixture of a first binder and a second binder and a crosslinking agent; a filler; and a lithium cation, wherein the first binder is an aqueous binder, the second binder is a carboxyalkyl cellulose compound or a salt thereof, and the crosslinking agent comprises citric acid. The citric acid content is in the range of about 5 parts by weight to about 50 parts by weight relative to the total amount of the first and second binders (100 parts by weight), and the lithium cation content in the coating is in the range of about 50 ppm to about 200 ppm.

[0259] Citric acid is a crosslinking agent that crosslinks the first and second adhesives. Citric acid is a compound having hydroxyl groups and three carboxylic acid groups as shown in the chemical formula above, and it has high hydrophilicity. Therefore, citric acid can have high reactivity in aqueous compositions that include the first adhesive as an aqueous adhesive.

[0260] The citric acid content, relative to the total of 100 parts by weight of the first and second binders, can range from about 5 parts by weight to about 50 parts by weight. Within this range, the diaphragm can exhibit desired or improved heat resistance and high-temperature life. For example, relative to a total of 100 parts by weight, the citric acid content can be 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 3 parts by weight, 4 parts by weight, ... 0 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, 47 parts by weight, 48 parts by weight, 49 parts by weight, or 50 parts by weight, or 5 parts by weight to 40 parts by weight, 5 parts by weight to 30 parts by weight, 5 parts by weight to 25 parts by weight, or 5 parts by weight to 20 parts by weight. Within the above ranges, the above-mentioned effects of the diaphragm can be significant.

[0261] The membrane comprises a first binder and a second binder as sources of lithium cations. That is, the first binder has lithium cations, and the second binder has lithium cations. The first and second binders used herein are of the type described below, and optimal elution of lithium cations can be provided by crosslinking with citric acid.

[0262] The lithium cation content in the coating ranges from about 50 ppm to about 200 ppm. The lithium cations can originate from the first and second binders of the coating.

[0263] When the lithium cation content is less than about 50 ppm, even when the first and second binders are crosslinked with citric acid, the lithium cation content in the coating is significantly low, resulting in low elution of lithium cations from the crosslinking products of the first and second binders. This may lead to a decrease in capacity retention at high temperatures. When the lithium cation content is greater than about 200 ppm, lithium cations are significantly or excessively included in the coating, leading to defects in the battery. For example, the lithium cation content in the coating can range from about 70 ppm to about 150 ppm. For example, the lithium cation content in the coating can be 50ppm, 51ppm, 52ppm, 53ppm, 54ppm, 55ppm, 56ppm, 57ppm, 58ppm, 59ppm, 60ppm, 61ppm, 62ppm, 63ppm, 64ppm, 65ppm, 66ppm, 67ppm, 68ppm, 69ppm, 70ppm, 71ppm, 72ppm, 73ppm, 74ppm, 75ppm, 76ppm, 77ppm, 78ppm, 79ppm, or 80ppm. 81ppm, 82ppm, 83ppm, 84ppm, 85ppm, 86ppm, 87ppm, 88ppm, 89ppm, 90ppm, 91ppm, 92ppm, 93ppm, 94ppm, 95ppm, 96ppm, 97ppm, 98ppm, 99ppm, 100ppm, 101ppm, 102ppm, 103ppm, 104ppm, 105ppm, 106ppm, 107ppm, 108ppm, 109ppm, 110ppm, 111ppm, 112ppm , 113ppm, 114ppm, 115ppm, 116ppm, 117ppm, 118ppm, 119ppm, 120ppm, 121ppm, 122ppm, 123ppm, 124ppm, 125ppm, 126ppm, 12 7ppm, 128ppm, 129ppm, 130ppm, 131ppm, 132ppm, 133ppm, 134ppm, 135ppm, 136ppm, 137ppm, 138ppm, 139ppm, 140ppm, 141ppm , 142ppm, 143ppm, 144ppm, 145ppm, 146ppm, 147ppm, 148ppm, 149ppm, 150ppm, 151ppm, 152ppm, 153ppm, 154ppm, 155ppm, 156 ppm, 157ppm, 158ppm, 159ppm, 160ppm, 161ppm, 162ppm, 163ppm, 164ppm, 165ppm, 166ppm, 167ppm, 168ppm, 169ppm, 170ppm,171ppm, 172ppm, 173ppm, 174ppm, 175ppm, 176ppm, 177ppm, 178ppm, 179ppm, 180ppm, 181ppm, 182ppm, 183ppm, 184ppm, 185ppm, 186ppm, 187ppm, 188ppm, 189ppm, 190ppm, 191ppm, 192ppm, 193ppm, 194ppm, 195ppm, 196ppm, 197ppm, 198ppm, 199ppm or 200ppm. ,

[0264] The lithium cation content in the coating can be measured by methods described below, such as inductively coupled plasma optical emission spectrometry (ICP-OES).

[0265] In one example embodiment, the total amount of the first binder and the second binder can be about 95 wt% or more, for example, in the range of about 95 wt% to about 100 wt%, 99 to 100 wt%, or 100 wt%. Within the above range, the above-described effects of the diaphragm can be easily achieved.

[0266] In one example embodiment, the citric acid content can be about 95 wt% or more of the crosslinking agent, for example, in the range of about 95 wt% to about 100 wt%, 99 wt% to 100 wt%, or 100 wt%. Within the above range, the aforementioned effects of the diaphragm can be easily achieved.

[0267] In one example embodiment, the crosslinking product may be or include a thermally crosslinked product.

[0268] In one example embodiment, the coating may be formed by or comprise a composition for coating, the composition for coating comprising a first binder, a second binder, a crosslinking agent (i.e., citric acid), and a filler.

[0269] Each component of the composition used for coating is described in detail below.

[0270] First adhesive The first adhesive may be substantially the same as the first adhesive described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, only the first adhesive not described in "Separator for a Rechargeable Battery according to a First Example Embodiment" will be further described.

[0271] The first binder may include units having lithium cations as shown in the following chemical formula 2-1.

[0272] Chemical formula 2-1: .

[0273] In chemical formula 2-1, R 3 and R 4 Each is, independently, either having or including the same meaning as defined in Chemical Formula 2.

[0274] The first binder may include structural units containing lithium salts of sulfonic acid.

[0275] The structural unit of lithium salt containing sulfonic acid can be represented by the following chemical formula 9.

[0276] Chemical formula 9: .

[0277] In chemical formula 9, R 9 and R 10 Each is independently hydrogen or includes C1 to C3 alkyl groups. L 3 It is or includes -C(=O)-, -C(=O)O-, -OC(=O)-, -O-, or -C(=O)NH-. L 4 It is or includes substituted or unsubstituted C1 to C10 alkylene groups, substituted or unsubstituted C3 to C20 cycloalkylene groups, substituted or unsubstituted C6 to C20 arylene groups, or substituted or unsubstituted C3 to C20 heterocyclic groups, and a and b are each an independent integer in the range of 0 to 2.

[0278] In one example embodiment, in chemical formula 9, L3 can be or include -C(=O)NH-, L 4 It may be or include C1 to C10 alkylene groups, and a and b can be integers equal to 1.

[0279] The structural units of lithium salts containing sulfonic acids can be, or include, structural units derived from, for example, lithium salts derived from vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, anisolesulfonic acid, (meth)acrylamidoalkylsulfonic acid, or (meth)acrylate sulfonyl esters. Here, the alkane can be a C1 to C20 alkane, a C1 to C10 alkane, or a C1 to C6 alkane, and the alkyl group can be a C1 to C20 alkyl group, a C1 to C10 alkyl group, or a C1 to C6 alkyl group. The salt can consist of the aforementioned sulfonic acid and suitable ions.

[0280] (Methacrylamidoalkyl sulfonic acid may be or include, for example, 2-(meth)acrylamido-2-methylpropanesulfonic acid, and (meth)acrylic acid sulfonyl ester may be or include, for example, (meth)acrylic acid-2-sulfoethyl ester or (meth)acrylic acid-3-sulfopropyl ester.

[0281] The first binder may include one or more of the following: structural units containing alkali metal salts of sulfonic acid represented by Formula 5, structural units containing sulfonic acid represented by Formula 6, and structural units containing sulfonates represented by Formula 7. (Meth)acrylic acid binders can be prepared by polymerizing a mixture of monomers that provide the above-mentioned units.

[0282] In one example embodiment, the (meth)acrylic acid binder can be prepared by polymerizing a mixture comprising a monomer providing formula 5, a monomer providing formula 6, and a monomer providing formula 8.

[0283] In another example embodiment, the (meth)acrylic acid binder can be prepared by the following steps: preparing a prepolymer by polymerizing a mixture comprising monomers providing Formula 6 and monomers providing Formula 5, and lithiating a portion of M in Formula 6 of the prepolymer with lithium. The lithium cation content in the coating can be adjusted by regulating the lithiation rate. Lithiation of the portion of M in Formula 6 can be carried out by reacting the prepolymer with a lithium cation source (such as LiOH or Li₂CO₃). The lithiation rate can be determined by adjusting the content of the lithium cation source reacting with the prepolymer.

[0284] Second adhesive The second binder is an alkali metal salt of a carboxyalkyl cellulose compound, and at least one of the alkali metals is lithium.

[0285] When the first binder and citric acid are combined, the alkali metal salt of the carboxyalkyl cellulose compound can be crosslinked with the first binder by citric acid, which can improve the elution of lithium cations from the coating.

[0286] For example, alkali metal salts of carboxyl cellulose compounds may include lithium salts of carboxymethyl cellulose according to the following formula 10: Chemical Formula 10: .

[0287] In chemical formula 10, n is the number of moles of the repeating unit.

[0288] Alkali metal salts of carboxyl cellulose compounds may also include alkali metal salts of carboxymethyl cellulose of formula 11: Chemical Formula 11: .

[0289] In chemical formula 11, M is sodium, potassium, rubidium, or cesium, and n is the number of moles of the repeating unit.

[0290] Alkali metal salts of carboxyalkyl cellulose compounds can be prepared by methods known to those skilled in the art.

[0291] For example, alkali metal salts of carboxyalkyl cellulose compounds can be prepared by lithiation of a portion M in a compound of formula 11 containing carboxymethyl cellulose using lithium. The lithium cation content in the coating can be adjusted by regulating the lithiation rate. Lithiation of the portion M in formula 11 can be carried out by reacting a prepolymer with a lithium cation source (such as LiOH or Li₂CO₃). The lithiation rate can be determined by adjusting the content of the lithium cation source reacting with the prepolymer.

[0292] The weight-average molecular weight of alkali metal salts of carboxyalkyl cellulose compounds can be in the range of about 50,000 g / mol to about 1,000,000 g / mol, for example, 100,000 g / mol to 600,000 g / mol. Within the above range, the viscosity of the composition used for coating is not significantly high or excessively high, thus the dispersibility of citric acid can be easily ensured.

[0293] Citric acid The citric acid content relative to 100 parts by weight of the first binder can range from about 5 parts by weight to about 50 parts by weight, for example, from 10 parts by weight to 30 parts by weight. Within the above range, it can exhibit heat resistance and the effect of regulating the lithium cation elution rate.

[0294] The citric acid content relative to 100 parts by weight of the second binder can range from about 5 parts by weight to about 50 parts by weight, for example, from 10 parts by weight to 30 parts by weight. Within the above range, it can exhibit heat resistance and the effect of regulating the lithium cation elution rate.

[0295] filler The filler is substantially the same as that described in "Separator for Rechargeable Battery according to First Example Embodiment". Therefore, a detailed description of the filler is omitted.

[0296] porous substrate The porous substrate is substantially the same as the porous substrate described in "Separator for a Rechargeable Battery according to a First Example Embodiment". Therefore, a detailed description of the porous substrate is omitted.

[0297] According to one example embodiment, the separator for a rechargeable lithium battery can exhibit desired or improved permeability, which can be, for example, less than about 200 seconds / 100cc, such as 190 seconds / 100cc or less, or 180 seconds / 100cc or less.

[0298] Figure 12 This is a cross-sectional view of a separator for a rechargeable lithium battery according to an example embodiment.

[0299] Reference Figure 12 The separator for a rechargeable lithium battery includes a porous substrate 1 and coatings 2 on two surfaces of the porous substrate 1. The coating 2 includes: a filler 3; a crosslinking product 4 of a first binder, a second binder, and a crosslinking agent; and a lithium cation (not shown).

[0300] Rechargeable lithium batteries Another example embodiment includes a rechargeable lithium battery, which includes a separator for a rechargeable lithium battery according to an example embodiment; a positive electrode; and a negative electrode.

[0301] The separator used in rechargeable lithium batteries is described above. The separator for rechargeable lithium batteries can be located between the positive and negative electrodes.

[0302] positive electrode The positive electrode for a rechargeable lithium battery may include a current collector and a layer of positive electrode active material on the current collector. The positive electrode active material layer may include positive electrode active material and may also include a binder and / or conductive material. For example, the positive electrode may also include additives that can constitute a sacrificial positive electrode.

[0303] Positive electrode active material The positive electrode active material may include compounds capable of intercalating and deintercalating lithium (lithiation intercalation compounds). For example, at least one of the composite oxides of lithium and metals such as or including at least one of cobalt, manganese, nickel and combinations thereof may be used.

[0304] The composite oxide can be or includes lithium transition metal composite oxides. Examples of composite oxides may include at least one of lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free lithium nickel manganese oxides, or combinations thereof.

[0305] As an example, the following compounds, represented by any of the following chemical formulas, can be used. Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5 and 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5 and 0≤c≤0.05); Lia Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5 and 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5 and 0<α<2); Li a Ni b Co c L 1 d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5 and 0≤e≤0.1); Li a NiG b O2 (0.90≤a≤1.8 and 0.001≤b≤0.1); Li a CoG b O2 (0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn 1-b G b O2 (0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn2G b O4 (0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn 1-g G g PO4 (0.90≤a≤1.8 and 0≤g≤0.5); Li (3-f) Fe2(PO4)3 (0≤f≤2); or Li a FePO4 (0.90≤a≤1.8).

[0306] In the above chemical formula, A is or includes at least one of Ni, Co, Mn, or a combination thereof; X is or includes at least one of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is or includes at least one of O, F, S, P, or a combination thereof; G is or includes at least one of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 It is or includes at least one of Mn, Al, or combinations thereof.

[0307] The positive electrode active material can be, or includes, for example, a high-nickel positive electrode active material, based on 100 mol% of metal other than lithium in a lithium transition metal complex oxide. The nickel content of the high-nickel positive electrode active material is greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol% and less than or equal to about 99 mol%. High-nickel positive electrode active materials can achieve high capacity and can be applied to high-capacity, high-density rechargeable lithium batteries.

[0308] Based on a 100 wt% positive electrode active material layer, the amount of positive electrode active material can range from about 90 wt% to about 99.5 wt%. Based on a 100 wt% positive electrode active material layer, the amounts of binder and conductive material can each range from about 0.5 wt% to about 5 wt%.

[0309] The binder causes the positive electrode active material particles to adhere to each other and also adheres the positive electrode active material to the current collector. As a non-limiting example, examples of binders may include at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylate resin, polyester resin, nylon, etc.

[0310] Conductive materials can impart conductivity (e.g., electrical conductivity) to electrodes. Any material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in rechargeable lithium batteries) and conducts electrons can be used in batteries. Examples of conductive materials can include: carbon-based materials, such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials, including at least one of copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fibers; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0311] Al can be used as a current collector, but it is not limited to this.

[0312] negative electrode The negative electrode for a rechargeable lithium battery may include a current collector and a layer of negative electrode active material on the current collector. The negative electrode active material layer may include a negative electrode active material and may also include a binder and / or a conductive material (e.g., an electrically conductive material).

[0313] For example, the negative electrode active material layer may include a negative electrode active material in the range of about 90 wt% to about 99 wt%, a binder in the range of about 0.5 wt% to about 5 wt%, and a conductive material in the range of about 0 wt% to about 5 wt%.

[0314] Negative electrode active material The negative electrode active material may include at least one of a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, or a transition metal oxide.

[0315] The material capable of reversibly inserting / extracting lithium ions may include a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Crystalline carbon may be graphite, such as natural graphite or artificial graphite in an irregular shape, flaky, lamellar, spherical, or fibrous form. Amorphous carbon may be or include at least one of soft carbon, hard carbon, mesophase pitch carbonized product, calcined coke, etc.

[0316] The lithium metal alloy includes an alloy of lithium and a metal such as or including at least one of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0317] The material capable of doping / dedoping lithium may be or include a Si-based negative electrode active material or a Sn-based negative electrode active material. The Si-based negative electrode active material may include silicon, a silicon-carbon composite, SiO x (0 < x < 2), a Si-Q alloy (where Q is or includes at least one of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof). The Sn-based negative electrode active material may include at least one of Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0318] The silicon-carbon composite may be or include a composite of silicon and amorphous carbon. According to an exemplary embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite may include secondary particles (cores) in which primary silicon particles are assembled, and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon may also be between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0319] The silicon-carbon composite may also include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating on the surface of the core.

[0320] Si-based or Sn-based negative electrode active materials can be used in combination with carbon-based negative electrode active materials.

[0321] The binder enables the negative electrode active material particles to adhere to each other and also to the negative electrode active material onto the current collector. The binder may include non-aqueous binders, aqueous binders, dry binders, or combinations thereof.

[0322] Non-aqueous adhesives may include at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0323] The waterborne adhesive may be or include at least one of styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0324] When using an aqueous binder as the negative electrode binder, it may also include a cellulose compound capable of imparting viscosity. The cellulose compound may include at least one of carboxymethyl cellulose, hydroxypropyl methylcellulose, methylcellulose, or an alkali metal salt thereof. The alkali metal may include at least one of Na, K, or Li.

[0325] Dry adhesives can be or include polymeric materials capable of being fibrous. For example, dry adhesives can be or include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0326] Conductive materials can impart conductivity (e.g., electrical conductivity) to electrodes. Any material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in rechargeable lithium batteries) and conducts electrons can be used in batteries. Non-limiting examples of conductive materials may include: carbon-based materials, such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials, including at least one of copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fibers; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0327] The negative electrode current collector may include at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0328] Rechargeable lithium batteries may also include an electrolyte solution.

[0329] Electrolyte solution Electrolyte solutions used in rechargeable lithium batteries may include non-aqueous organic solvents and lithium salts.

[0330] Non-aqueous organic solvents can serve as media for transporting ions that participate in the electrochemical reactions of a battery.

[0331] Non-aqueous organic solvents may be or include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0332] Carbonate solvents may include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC).

[0333] Ester solvents may include at least one of the following: methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, caprolactone, etc.

[0334] Ether solvents may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Additionally, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc. Aprotic solvents may include at least one of the following: nitriles, such as R-CN (wherein R is a C2 to C20 straight-chain, branched, or cyclic hydrocarbon group, and includes double bonds, aromatic rings, or ether bonds, etc.); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane; etc.

[0335] Non-aqueous organic solvents can be used alone or in combination of two or more solvents.

[0336] Furthermore, when using carbonate solvents, cyclic carbonates and chain carbonates can be mixed together, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0337] Lithium salts dissolved in organic solvents supply lithium ions in batteries, enabling rechargeable lithium batteries to operate fundamentally and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 At least one of the following: (SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0338] Rechargeable lithium batteries can be classified according to their shape as cylindrical batteries, prismatic batteries, pouch batteries, or coin-shaped batteries, etc.

[0339] Figures 13 to 16 This is a schematic diagram illustrating a rechargeable lithium battery according to an example embodiment. Figure 13 A cylindrical battery is shown. Figure 14 A prismatic battery is shown, and Figure 15 and Figure 16 A pouch-type battery is shown. (See reference) Figures 13 to 16 The rechargeable lithium battery 100 may include an electrode assembly 40 and a housing 50. The electrode assembly 40 includes a separator 30 between a positive electrode 10 and a negative electrode 20, and the electrode assembly 40 is housed within the housing 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 13 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of a sealed housing 50. Figure 14 In this context, the rechargeable lithium battery 100 may include a positive electrode lead connector 11, a positive terminal 12 connected to the positive electrode lead connector 11, a negative electrode lead connector 21, and a negative terminal 22 connected to the negative electrode lead connector 21. For example... Figure 15 and Figure 16 As shown, the rechargeable lithium battery 100 may include Figure 16 The electrode terminal 70 shown, or for example, Figure 15 The positive electrode terminal 71 and negative electrode terminal 72 shown herein form an electrical path for guiding the current generated in the electrode assembly 40 to the outside of the rechargeable lithium battery 100.

[0340] As a non-limiting example, the rechargeable lithium battery according to the example embodiment can be applied to, for example, automobiles, mobile phones and / or various types of electrical devices.

[0341] Examples and comparative examples of this disclosure are described below. However, the following examples are merely examples of this disclosure, and this disclosure is not limited to these examples.

[0342] Preparation Example 1 In a 10L four-necked flask equipped with a stirrer, thermometer, and condenser, distilled water (6,361 g), acrylamide (9.5 mol), potassium persulfate (0.01 mol), 2-acrylamido-2-methylpropanesulfonic acid (0.5 mol), and a 5N lithium hydroxide aqueous solution (totaling 1.05 equivalents relative to 2-acrylamido-2-methylpropanesulfonic acid) were added. The internal pressure was then reduced to 10 mmHg using a diaphragm pump and restored to atmospheric pressure using nitrogen three times. The reaction proceeded for 12 hours, with the temperature of the reaction solution maintained between 65°C and 70°C. After cooling to room temperature, the pH of the reaction solution was adjusted to 7-8 using a 25% ammonia solution. Poly(acrylamido-co-2-acrylamido-2-methylpropanesulfonic acid) lithium salt was prepared using the above method. The molar ratio of acrylamide to 2-acrylamido-2-methylpropanesulfonic acid was 95:5. Take about 10 mL of the reaction solution (reaction product) and measure the content of the non-volatile component, which is 9.5 wt% (theoretical value: 10 wt%).

[0343] Preparation Example 2 In a 3L four-necked flask equipped with a stirrer, thermometer, and condenser, distilled water (968g), acrylic acid (0.39mol), ammonium persulfate (2.85mmol), 2-acrylamido-2-methylpropanesulfonic acid (0.02mol), and a 20% aqueous lithium hydroxide solution (0.8 equivalents relative to the total amount of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid) were added. The internal pressure was reduced to 10 mmHg using a diaphragm pump and then restored to atmospheric pressure using nitrogen three times. Acrylonitrile (0.59mol) was then added. The reaction proceeded for 18 hours, with the temperature of the reaction solution maintained between 65°C and 70°C. Ammonium persulfate (0.95mmol) was then added, and the temperature was raised to 80°C, followed by another 4 hours of reaction. After cooling to room temperature, the pH of the reaction solution was adjusted to between 7 and 8 using a 25% ammonia solution.

[0344] Poly(acrylic acid-co-lithium co-acrylate-co-acrylonitrile-co-2-acrylamido-2-methylpropanesulfonate) was prepared as an acrylic binder using the above method. The molar ratio of acrylic acid and lithium acrylate, and acrylonitrile and lithium 2-acrylamido-2-methylpropanesulfonate was 39:59:2. Approximately 10 mL of the reaction solution (reaction product) was taken and the content of the non-volatile component was measured, which was 9.0 wt% (theoretical value: 10 wt%).

[0345] Example 1 The dispersion was prepared by the following steps: the acrylic binder (10 wt% in distilled water) prepared in Preparation Example 1 was mixed with boehmite (particle size (D100): 500 nm, particle size (D50): 200 nm, plate-like) as filler, water was added as solvent, and the mixture was ground at 25°C for 30 minutes using a bead mill, and then the ground mixture was dispersed.

[0346] A composition for coating was prepared by adding sodium carboxymethyl cellulose (CMC-Na, weight average molecular weight: 200,000 g / mol) and citric acid to a dispersion, and adding water to make the total solids content 20 wt%.

[0347] The composition for coating comprises, relative to 100 parts by weight of acrylic binder and sodium carboxymethyl cellulose, 50 parts by weight of acrylic binder; 50 parts by weight of sodium carboxymethyl cellulose; and 10 parts by weight of citric acid. The composition for coating has a weight ratio of 1:20 between the total amount of acrylic binder and sodium carboxymethyl cellulose and the filler.

[0348] A diaphragm was prepared by coating two surfaces of a polyethylene membrane (thickness: 8 μm (SK), air permeability: 120 sec / 100 cc, puncture strength: 480 kgf) to a thickness of 2 μm using a molding method, and then drying and curing the resulting membrane in an oven at 85 °C for 16 hours.

[0349] Examples 2 to 7 The membrane was prepared in the same manner as in Example 1, except that the contents of the acrylic binder, sodium carboxymethyl cellulose, and citric acid used in Example 1 were varied as shown in Table 1 below.

[0350] Example 8 The diaphragm was prepared in the same manner as in Example 1, except that the binder of Preparation Example 2 was used instead of the binder of Preparation Example 1.

[0351] Comparison Examples 1 to 5 The membrane was prepared in the same manner as in Example 1, except that the contents of the acrylic binder, sodium carboxymethyl cellulose, and citric acid used in Example 1 were varied as shown in Table 1 below.

[0352] Comparison Example 6 The membrane was prepared in the same manner as in Example 1, except that adipic acid was used instead of citric acid, which was used as a crosslinking agent in Example 1.

[0353] Dry shrinkage rate (unit: %) Samples were prepared by cutting the septa of the example and control examples into 5cm × 5cm dimensions. After placing each sample in an oven at 150°C for 1 hour, the shrinkage rate in the longitudinal (MD) and transverse (TD) directions was calculated. The shrinkage rate was calculated using Formula 1 below.

[0354] Mathematical formula 1: Shrinkage rate = (L0-L1) / L0×100.

[0355] L0 is the initial length of the diaphragm, and L1 is the length of the diaphragm after being placed at 150°C for 1 hour.

[0356] Shrinkage rate in electrolyte (unit: %) Samples were prepared by cutting the diaphragms of the example and comparative examples into 3cm × 8cm dimensions. A positive electrode slurry was prepared by mixing 97 wt% lithium cobalt nickel aluminum oxide as the positive electrode active material, 1.5 wt% carbon nanotubes as the conductive material, and 1.5 wt% polyvinylidene fluoride, and adding N-methyl-2-pyrrolidone. A positive electrode was prepared by coating aluminum foil with the prepared positive electrode slurry, drying, and rolling the resulting aluminum foil. A negative electrode slurry was prepared by mixing 97.4 wt% graphite as the negative electrode active material, 1.0 wt% carboxymethyl cellulose, 1.5 wt% styrene-butadiene rubber, and 0.1 wt% carbon nanotubes as the conductive material, and adding distilled water. A negative electrode was prepared by coating copper foil with the prepared negative electrode slurry, drying, and rolling the resulting copper foil.

[0357] A sample was placed between the positive and negative electrodes to form a three-stage stack (positive electrode-sample-negative electrode), and then the stack was placed in a bag. 2.5 g of electrolyte (ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate dissolved in 1.5 M LiPF6 (volume ratio 30:50:20)) was injected to completely immerse the stack in the electrolyte. The bag was sealed and placed at 25°C for 12 hours, followed by an oven drying at 150°C for 1 hour. Afterward, the sample was removed from the bag, and the shrinkage rates on MD and TD were calculated. The shrinkage rate can be calculated using Equation 1 above.

[0358] Substrate adhesion: (unit: N) The prepared diaphragm was cut into dimensions of 3cm (width) × 8cm (length), and adhesive tape (3M, width: 10mm) was cut into 150mm lengths. Then, using a roller made of 3kg bubble-free rubber, the tape was adhered to the diaphragm coating along the MD (diaphragm diameter). After separating the tape from the diaphragm by approximately 50mm, the diaphragm was secured to the upper clamp, and the tape to the lower clamp. The gap between the clamps was 20mm. After the sample was secured, the tape was peeled off in a 180° direction at a speed of 20mm / min. The average force was obtained by measuring the force required to peel 40mm from the start of peeling three times.

[0359] Battery characteristics: Cylindrical batteries with individual separators and a state of charge (SCO) of 50% were evaluated using the international standard UN internal short-circuit test method, with example and comparative examples. In this method, the battery was placed on a test block (SS41 steel, flat, thickness: 70 mm), and a cylindrical weight of 9.1 ± 0.1 kg with a diameter of 15.8 ± 0.1 mm was dropped freely onto the battery from a height of 630 ± 25 mm to check for explosion or fire. The number of all evaluated samples (10 samples) that passed the impact test (i.e., did not exhibit battery explosion, rupture, or fire) is given. A result is evaluated as OK if the number of failures (unsuccessful samples) is 2 or fewer, and a result is evaluated as NG (bad / failed) if the number of failures is 3 or more.

[0360] Table 1:

[0361] In Table 1 above, Weight ratio 1: The weight ratio of the first adhesive to the second adhesive; Parts by weight 2: The content of crosslinking agent relative to the total amount of 100 parts by weight of the first and second binders; Weight ratio 3: The weight ratio of the total amount of the first and second binders to the filler.

[0362] As shown in Table 1, the example separators are able to suppress battery fire and explosion due to external impact and provide low thermal shrinkage and high adhesion to the substrate. However, referring to Table 1, Comparative Examples 1 to 3, which do not contain any of the first binder, second binder, and citric acid of this disclosure, exhibit insignificant battery protection against external impact. Furthermore, Comparative Examples 4 and 5, which are outside the citric acid content range of this disclosure, and Comparative Example 6, which uses adipic acid instead of citric acid, exhibit high shrinkage in the electrolyte and only provide insignificant battery protection against external impact.

[0363] Example 9 The dispersion was prepared by the following steps: the acrylic binder (10 wt% in distilled water) prepared in Preparation Example 1 was mixed with boehmite (particle size (D100): 500 nm, particle size (D50): 200 nm, plate-like) as filler, water was added as solvent, and the mixture was ground at 25°C for 30 minutes using a bead mill, and then the ground mixture was dispersed.

[0364] CMC-Na (weight average molecular weight: 200,000 g / mol) and citric acid were added to the dispersion. Then, water and ethanol were added to bring the total solids content to 20 wt% to prepare the composition for coating.

[0365] The composition for coating comprises, relative to 100 parts by weight of the acrylic binder and CMC-Na, 50 parts by weight of the acrylic binder; 50 parts by weight of CMC-Na; and 10 parts by weight of citric acid. In the composition for coating, the total weight ratio of the acrylic binder and CMC-Na to the filler is 1:20. The composition for coating comprises 10 parts by weight of ethanol relative to 100 parts by weight of CMC-Na.

[0366] A diaphragm was prepared by coating two surfaces of a polyethylene membrane (thickness: 8 μm (SK), air permeability: 120 sec / 100 cc, puncture strength: 480 kgf) to a thickness of 2 μm using a molding method, and then drying and curing the resulting membrane in an oven at 100 °C for 16 hours.

[0367] Examples 10 to 15 and Example 17 The membrane was prepared in the same manner as in Example 9, except that the contents of the acrylic binder, CMC-Na and citric acid, as well as the type and contents of the alcohol, were varied as shown in Table 2 below.

[0368] Example 16 The diaphragm was prepared in the same manner as in Example 9, except that the binder of Preparation Example 2 was used instead of the binder of Preparation Example 1 used in Example 9.

[0369] Comparison Examples 7 to 11 Except for changing the contents of acrylic binder, sodium carboxymethyl cellulose, and citric acid used in Example 9 as shown in Table 2 below, the membrane was prepared in the same manner as in Example 9.

[0370] Compare Example 12 The membrane was prepared in the same manner as in Example 9, except that adipic acid was used instead of citric acid as a crosslinking agent.

[0371] Dry shrinkage rate (unit: %) The dry shrinkage rate is measured in the same manner as the method described above for measuring the dry shrinkage rate.

[0372] Shrinkage rate in electrolyte (unit: %) The shrinkage rate of the electrolyte is measured in the same manner as described in the method for measuring the shrinkage rate in the electrolyte described above.

[0373] Breathability (unit: seconds / 100cc) Air permeability is measured in the same manner as the air permeability measurement described above.

[0374] Membrane resistance (unit: Ω) The membrane resistance is measured in the same manner as the membrane resistance measurement described above.

[0375] Battery characteristics: Battery characteristics are measured in the same manner as those described above.

[0376] Table 2:

[0377] In Table 2, Weight ratio 1: The weight ratio of the first adhesive to the second adhesive; Weight ratio 2: The weight ratio of the total amount of the first and second binders to the filler.

[0378] As shown in Table 2 above, the example separator can suppress battery fire and explosion caused by external impacts, thereby improving battery reliability and stability. Furthermore, the example separator provides low thermal shrinkage, low permeability, and low resistance, thereby increasing battery life.

[0379] However, as shown in Table 2 above, the diaphragm of the comparative example cannot achieve the aforementioned effects of the diaphragm of the example.

[0380] Example 18 The dispersion was prepared by the following steps: the acrylic binder (10 wt% in distilled water) prepared in Preparation Example 1, boehmite (particle size (D100): 500 nm, particle size (D50): 200 nm, aspect ratio: less than 100, cubic) as the first filler, and boehmite (length: 5 μm, diameter: 50 nm, aspect ratio: 100, unmodified, needle-like) as the second filler were mixed, water was added as a solvent, and the mixture was ground at 25 °C for 30 minutes using a bead mill, and then the ground mixture was dispersed.

[0381] A composition for coating was prepared by adding CMC-Na (weight average molecular weight: 200,000 g / mol) and citric acid to a dispersion and adding water to make the total solids content 20 wt%.

[0382] The composition for coating comprises, relative to 100 parts by weight of acrylic binder and CMC-Na, 50 parts by weight of acrylic binder; 50 parts by weight of CMC-Na; and 10 parts by weight of citric acid. In the composition for coating, the weight ratio of needle-shaped second filler to cubic first filler is 1:1. In the composition for coating, the weight ratio of the total amount of acrylic binder and CMC-Na to the mixture of the first and second fillers is 1:20.

[0383] A diaphragm was prepared by coating two surfaces of a polyethylene membrane (thickness: 8 μm (SK), air permeability: 120 sec / 100 cc, puncture strength: 480 kgf) to a thickness of 2 μm using a molding method, and then drying and curing the resulting membrane in an oven at 100 °C for 16 hours.

[0384] Examples 19 to 26 The membrane was prepared in the same manner as in Example 18, except that the contents of the acrylic binder, CMC-Na, citric acid, and the first and second fillers used in Example 18 were varied as shown in Table 3 below.

[0385] Example 27 The diaphragm was prepared in the same manner as in Example 18, except that the binder used in Preparation Example 2 was used instead of the binder used in Preparation Example 18.

[0386] Compare Examples 13 to 15 The membrane was prepared in the same manner as in Example 18, except that the contents of the acrylic binder, CMC-Na, citric acid, and the first and second fillers used in Example 18 were varied as shown in Table 3 below.

[0387] Dry shrinkage rate (unit: %) The dry shrinkage rate is measured in the same manner as the method described above for measuring the dry shrinkage rate.

[0388] Shrinkage rate in electrolyte (unit: %) The shrinkage rate of the electrolyte is measured in the same manner as described in the method for measuring the shrinkage rate in the electrolyte described above.

[0389] Battery characteristics Battery characteristics are measured in the same manner as those described above.

[0390] High temperature lifespan A positive electrode paste was prepared by adding lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVdF), and carbon black in a weight ratio of 96:2:2 to N-methyl-2-pyrrolidone. The positive electrode was then prepared by coating aluminum foil with the paste and drying and rolling the resulting aluminum foil.

[0391] A negative electrode slurry was prepared by adding graphite, styrene-butadiene rubber, and carboxymethyl cellulose in a weight ratio of 98:1:1 to distilled water. The negative electrode was then prepared by coating copper foil with the slurry and drying and rolling the resulting copper foil.

[0392] The separators of the example and comparative examples were each inserted between the prepared positive and negative electrodes to prepare core electrode assemblies with a wound structure. Electrodes prepared by adding 1.15 M LiPF6 to a solvent containing ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 3:5:2 were injected into the prepared electrode assemblies, and the electrode assemblies were sealed to manufacture the corresponding rechargeable lithium batteries.

[0393] The rechargeable lithium battery was initially charged and discharged at 55°C with a constant current of 0.1C to a maximum voltage of 4.25V, and then discharged with a constant current of 0.1C to a discharge cutoff voltage of 3.5V. Afterward, the charge and discharge cycles were repeated 10 times at 0.5C within a voltage range of 3.5V to 4.25V.

[0394] After 10 cycles, the temperature of the rechargeable lithium battery is measured, and the increase in temperature relative to the initial temperature is designated as ΔT. Additionally, the efficiency is calculated according to Formula 2 below. ΔT is preferably 5°C or less, and the efficiency is preferably 97.5% or greater.

[0395] Mathematical formula 2: Efficiency = (Discharge capacity after 10 cycles / Discharge capacity after 1 cycle) × 100.

[0396] Table 3:

[0397] In Table 3, Weight ratio 1: The weight ratio of the first adhesive to the second adhesive; Weight ratio 2: weight ratio of second packing (needle-shaped) to first packing (cubic); Weight ratio 3: The weight ratio of the mixture of the first binder and the second binder to the mixture of the first filler and the second filler.

[0398] As shown in Table 3 above, the example separator can improve battery reliability and stability because it can suppress battery fire and explosion caused by external impacts. Furthermore, battery safety can be increased because the example separator provides a low shrinkage rate. Additionally, the example separator can improve the battery's high-temperature lifespan, thereby increasing battery lifespan and reliability.

[0399] However, as shown in Table 3 above, the diaphragm of the comparative example shows a worse performance compared to the diaphragm of the example.

[0400] Example 28 The dispersion was prepared by the following steps: the acrylic binder (10 wt% in distilled water) prepared in Preparation Example 1 was mixed with boehmite (particle size (D100): 500 nm, particle size (D50): 200 nm, plate-like) as filler, water was added as solvent, and the mixture was ground at 25°C for 30 minutes using a bead mill, and then the ground mixture was dispersed.

[0401] A composition for the first coating was prepared by adding CMC-Na (weight average molecular weight: 200,000 g / mol) and citric acid to a dispersion and adding water to make the total solids content 20 wt%.

[0402] The composition for the first coating comprises, relative to 100 parts by weight of acrylic binder and CMC-Na, 50 parts by weight of acrylic binder; 50 parts by weight of CMC-Na; and 10 parts by weight of citric acid. In the composition for the first coating, the total weight ratio of acrylic binder and CMC-Na to filler is 1:20.

[0403] The first coating (thickness: 2 μm) was prepared by coating both surfaces of a polyethylene film (thickness: 10 μm (SK), air permeability: 120 sec / 100 cc, puncture strength: 600 kgf) to a thickness of 2 μm using a molding method, and the resulting film was dried and cured in an oven at 85 °C for 16 hours.

[0404] A diaphragm was prepared by dissolving polyethylene wax (average particle size (D50): 0.5 μm, melting point: 110 °C) in an aqueous solvent to form a second coating (thickness: 2.0 μm), applying it to the first coating to a predetermined thickness, and drying and curing the resulting layer in an oven at 85 °C for 16 hours.

[0405] Examples 29 and 30 Except for changing the weight ratio of acrylic binder and CMC-Na and / or the content of citric acid used in Example 29, a diaphragm in which a first coating and a second coating are sequentially formed on two surfaces of a porous substrate is prepared in the same manner as in Example 28.

[0406] Example 31 The dispersion was prepared by the following steps: the acrylic binder (10 wt% in distilled water) prepared in Preparation Example 1 was mixed with boehmite (particle size (D100): 500 nm, particle size (D50): 200 nm, plate-like) as filler, water was added as solvent, and the mixture was ground at 25°C for 30 minutes using a bead mill, and then the ground mixture was dispersed.

[0407] A composition for the first coating was prepared by adding CMC-Na (weight average molecular weight: 200,000 g / mol) and citric acid to a dispersion and adding water to make the total solids content 20 wt%.

[0408] The composition for the first coating comprises, relative to 100 parts by weight of acrylic binder and CMC-Na, 50 parts by weight of acrylic binder; 50 parts by weight of CMC-Na; and 10 parts by weight of citric acid. In the composition for the first coating, the total weight ratio of acrylic binder and CMC-Na to filler is 1:20.

[0409] The first coating (thickness: 2 μm) was prepared by coating both surfaces of a polyethylene film (thickness: 10 μm (SK), air permeability: 120 sec / 100 cc, puncture strength: 600 kgf) to a thickness of 2 μm using a molding method, and the resulting film was dried and cured in an oven at 85 °C for 16 hours.

[0410] An adhesive layer (thickness: 1 μm) is formed on the first coating by coating the first coating with polymethyl methacrylate (PMMA) as an adhesive and drying and curing the resulting layer in an oven at 85°C for 16 hours.

[0411] A diaphragm was prepared by dissolving polyethylene wax (average particle size (D50): 0.5 μm, melting point: 110 °C) in an aqueous solvent to form a second coating (thickness: 2 μm), applying it to the first coating to a predetermined thickness, and drying and curing the resulting layer in an oven at 85 °C for 16 hours.

[0412] Example 32 The dispersion was prepared by the following steps: the acrylic binder (10 wt% in distilled water) prepared in Preparation Example 1 was mixed with boehmite (particle size (D100): 500 nm, particle size (D50): 200 nm, plate-like) as filler, water was added as solvent, and the mixture was ground at 25°C for 30 minutes using a bead mill, and then the ground mixture was dispersed.

[0413] A composition for a third coating was prepared by adding CMC-Na (weight average molecular weight: 200,000 g / mol) and citric acid to a dispersion, adding water to have a total solids content of 20 wt%, and including PMMA as a binder.

[0414] The composition for the third coating comprises, relative to 100 parts by weight of the acrylic binder and CMC-Na, 50 parts by weight of the acrylic binder; 50 parts by weight of CMC-Na; and 10 parts by weight of citric acid. In the composition for the third coating, the total weight ratio of the acrylic binder and CMC-Na to the filler is 1:20. The content of the adhesive is 25 parts by weight relative to 100 parts by weight of the acrylic binder and CMC-Na.

[0415] The third coating (thickness: 2 μm) was prepared by coating two surfaces of a polyethylene film (thickness: 10 μm (SK), air permeability: 120 sec / 100 cc, puncture strength: 600 kgf) to a thickness of 2 μm using a mold coating method, and the resulting film was dried and cured in an oven at 85 °C for 16 hours.

[0416] The diaphragm was prepared by dissolving polyethylene wax (average particle size (D50): 0.5 μm, melting point: 110 °C) in an aqueous solvent to form a second coating (thickness: 2 μm), applying it to a third coating to a predetermined thickness, and drying and curing the resulting layer in an oven at 85 °C for 16 hours.

[0417] Compare Example 16 The membrane was prepared in the same manner as in Example 28, except that a aziridine crosslinking agent (trimethylolpropane tris(2-methyl-1-aziridine propionate)) was used instead of citric acid in Example 28, and 10 parts by weight of aziridine crosslinking agent were added relative to 100 parts by weight of acrylic acid and CMC-Na.

[0418] Compare Example 17 Except that a carbodiimide crosslinking agent (polycarbodiimide compound, CARBODILITE V-50 (Nisshinbo Chemical)) is used instead of citric acid in Example 28, and the content of the carbodiimide crosslinking agent is 10 parts by weight relative to the total amount of 100 parts by weight of acrylic binder and CMC-Na, the membrane is prepared in the same manner as in Example 28.

[0419] Compare Example 18 Except that an epoxy crosslinking agent (diethylene glycol diglycidyl ether) is used instead of citric acid in Example 28, and the content of epoxy crosslinking agent is 10 parts by weight relative to the total amount of 100 parts by weight of acrylic binder and CMC-Na, the membrane is prepared in the same manner as in Example 28.

[0420] Compare Example 19 The membrane was prepared in the same manner as in Example 28, except that citric acid was not included in Example 28.

[0421] Comparison Example 20 The diaphragm was prepared in the same manner as in Example 28, except that the content of adipic acid was 10 parts by weight relative to the total amount of 100 parts by weight of acrylic binder and sodium carboxymethyl cellulose.

[0422] Breakdown voltage (unit: V) The insulation properties (breakdown voltage, BDV) of each diaphragm prepared in the example and comparative examples were measured. BDV was measured using a KIKISUI TOS5301 while the diaphragm was placed between stainless steel (SUS) plates. The BDV value was defined as the voltage at the point where a current value of 3mA or greater is confirmed by increasing the voltage, i.e., the voltage at the point where voltage increase stops (i.e., breakdown or short circuit).

[0423] Shutdown temperature (unit: °C) When using each battery manufactured in the example and comparative examples, the resistance was evaluated based on its change with temperature. When measuring resistance relative to temperature, the temperature at which the resistance first increases with increasing initial temperature is defined as the shut-off temperature.

[0424] Shrinkage rate in electrolyte (unit: %) The shrinkage rate of the electrolyte is measured in the same manner as the method described above for measuring the shrinkage rate in the electrolyte.

[0425] Table 4:

[0426] In Table 4, Weight ratio: The weight ratio of the first adhesive (acrylic adhesive) to the second adhesive (CMC-Na); Content: The content of crosslinking agent (unit: parts by weight) relative to the total amount of 100 parts by weight of the first and second adhesives. PE content: The proportion of the coating containing PE (second coating) in the total coating on the porous substrate stacked on the diaphragm.

[0427] As shown in Table 4 above, the example separators can improve shut-off temperature and breakdown voltage, thereby providing enhanced battery safety. Because the example separators have a low thermal shrinkage rate, they can provide batteries with desired or improved reliability and lifespan.

[0428] However, as shown in Table 4 above, the diaphragm of the comparative example has significantly lower breakdown voltage, shut-off temperature, and thermal shrinkage rate than the example.

[0429] Example 33 Preparation of the first adhesive In a 10L four-necked flask equipped with a stirrer, thermometer, and condenser, after adding distilled water (6361g), acrylamide (9.5mol), potassium persulfate (0.01mmol), 2-acrylamido-2-methylpropanesulfonic acid (0.5mol), and 5N sodium hydroxide aqueous solution (total amount of 2-acrylamido-2-methylpropanesulfonic acid 1.05 equivalents), the internal pressure was reduced to 10mmHg using a diaphragm pump and then restored to atmospheric pressure using nitrogen gas three times.

[0430] The reaction was carried out for 12 hours while maintaining the temperature of the reaction solution between 65 and 70°C. After cooling to room temperature, the pH of the reaction solution was adjusted to 7 to 8 using a 25% ammonia solution.

[0431] Poly(acrylamide-co-2-acrylamido-2-methylpropanesulfonate sodium salt) was prepared using the above method. The molar ratio of acrylamide to 2-acrylamido-2-methylpropanesulfonate sodium salt was 95:5. Approximately 10 mL of the reaction solution (reaction product) was taken, and the content of the non-volatile component was measured, which was 9.5 wt% (theoretical value 10 wt%).

[0432] The first binder is prepared by the following steps: the prepared poly(acrylamide-co-2-acrylamido-2-methylpropanesulfonate sodium salt) is dissolved in an acidic solution, and a predetermined amount of lithium source LiOH is added, such that 25.9% (lithiation 1) of the total molar amount of sodium cations in the prepared poly(acrylamide-co-2-acrylamido-2-methylpropanesulfonate sodium salt) is replaced by lithium cations.

[0433] Preparation of the second adhesive The second binder is prepared by the following steps: CMC-Na (weight average molecular weight: 200,000 g / mol) is dissolved in an acidic solution and a predetermined amount of LiOH is added, such that 3.77% (lithiation 2) of the total sodium cations in CMC-Na are replaced by lithium cations.

[0434] Preparation of diaphragm The dispersion was prepared by the following steps: the first binder solution (10 wt% in distilled water) was mixed with boehmite (particle size (D100): 500 nm, particle size (D50): 200 nm, plate-like) as filler, water was added as solvent, and the mixture was ground at 25 °C for 30 minutes using a bead mill, and then the ground mixture was dispersed.

[0435] A composition for coating was prepared by adding the prepared second binder and citric acid to the dispersion and adding water to make the total solids content 20 wt%.

[0436] The composition for coating comprises, relative to 100 parts by weight of the first binder and the second binder, 50 parts by weight of the first binder; 50 parts by weight of the second binder; and 10 parts by weight of citric acid. The total weight ratio of the first binder and the second binder to the filler is 1:20.

[0437] A diaphragm was prepared by coating two surfaces of a polyethylene membrane (thickness: 8 μm (SK), air permeability: 120 sec / 100 cc, puncture strength: 480 kgf) to a thickness of 1.5 μm using a molding method, and then drying and curing the resulting membrane in an oven at 100 °C for 16 hours.

[0438] Examples 34 to 39 Except for changing the lithiation rate 1, lithiation rate 2, the weight ratio between the first binder and the second binder, and / or the content of the crosslinking agent used in Example 33 as shown in Table 5 below, the membrane was prepared in the same manner as in Example 33.

[0439] Comparative Examples 21 to 25 Except for changing the lithiation rate 1, lithiation rate 2, the weight ratio between the first binder and the second binder, and / or the content of the crosslinking agent used in Example 33 as shown in Table 5 below, the membrane was prepared in the same manner as in Example 33.

[0440] Compare Example 26 The membrane was prepared in the same manner as in Example 34, except that the aziridine crosslinking agent trimethylolpropane tris(2-methyl-1-aziridinepropionate) was used instead of citric acid as the crosslinking agent used in Example 34.

[0441] Lithium cation content in the membrane coating (unit: ppm) Coatings were prepared according to the examples and comparative examples. For each prepared coating, the lithium cation content was measured using the following method: The lithium cation content was measured by ICP-OES. A sample solution was prepared by melting each coating. A set of calibration solutions was prepared, wherein solutions with precisely known concentrations of lithium cations were prepared. The calibration solution set was injected into the ICP-OES instrument, plasma was introduced, and the light emission intensity was measured according to the lithium cation concentration to obtain a calibration map. Subsequently, the sample solution was introduced into the ICP-OES instrument, plasma was applied, and the light emission intensity was measured to obtain the lithium cation concentration through the calibration map.

[0442] Capacity retention rate after 300 cycles (in %) Batteries were manufactured using the various separators prepared in the example and comparative examples.

[0443] A positive electrode slurry was prepared by mixing 97 wt% lithium-cobalt-nickel-aluminum oxide as the positive electrode active material, 1.5 wt% carbon nanotubes as the conductive material, and 1.5 wt% polyvinylidene fluoride, and adding N-methyl-2-pyrrolidone. The positive electrode was then prepared by coating aluminum foil with the prepared positive electrode slurry, followed by drying and rolling. A negative electrode slurry was prepared by mixing 97.4 wt% graphite as the negative electrode active material, 1.0 wt% carboxymethyl cellulose, 1.5 wt% styrene-butadiene rubber, and 0.1 wt% carbon nanotubes as the conductive material, and adding distilled water. The negative electrode was then prepared by coating copper foil with the prepared negative electrode slurry, followed by drying and rolling.

[0444] A separator is placed between the positive and negative electrodes to form a three-stage stacked structure (positive electrode-separator-negative electrode), and then the stacked structure is placed in a bag. 2.5g of electrolyte (ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate dissolved in 1.5M LiPF6 (volume ratio 30:50:20)) is injected, and the mixture is placed at 25°C for 12 hours, and then placed in an oven at 150°C for 1 hour to manufacture the battery.

[0445] Each rechargeable lithium battery underwent initial charging and discharging by charging at a constant current of 0.5C to a maximum voltage of 4.35V at 55°C, and then discharging at a constant current of 2C to a discharge cutoff voltage of 2.5V. Subsequently, the battery was cycled 300 times at 0.5C within a voltage range of 2.5V to 4.25V. Capacity retention is the percentage of the discharge capacity after 300 cycles to the discharge capacity of the first cycle.

[0446] Table 5:

[0447] In Table 5, Weight ratio 1: The weight ratio of the first adhesive to the second adhesive; Weight ratio 2: The weight ratio of the total amount of the first and second binders to the filler.

[0448] As shown in Table 5 above, the example separator can significantly improve battery life at high temperatures. However, as shown in Table 5 above, the comparative separator does not have a high life retention rate at high temperatures compared to the example separator.

[0449] Although exemplary embodiments of the present disclosure have been described above, the present disclosure is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the present disclosure, and the accompanying drawings. These modifications also fall within the scope of the present disclosure.

Claims

1. A separator for a rechargeable battery, the separator comprising: A porous substrate and a coating on at least one surface of the porous substrate. The coating comprises: a crosslinking product of a mixture and a crosslinking agent, the mixture comprising a first binder and a second binder; and a filler. The first adhesive is a water-based adhesive, and the second adhesive is a carboxyl cellulose compound or a salt thereof. The crosslinking agent includes citric acid, and The citric acid content is in the range of 5 to 50 parts by weight relative to the total amount of 100 parts by weight of the first adhesive and the second adhesive.

2. The diaphragm according to claim 1, wherein, The coating comprises a composition including the first adhesive, the second adhesive, the crosslinking agent, and the filler.

3. The diaphragm according to claim 1, wherein, The second binder comprises carboxymethyl cellulose or an alkali metal salt thereof.

4. The diaphragm according to claim 1, wherein, The carboxyalkyl cellulose compounds or their salts have a weight-average molecular weight in the range of 100,000 g / mol to 600,000 g / mol.

5. The diaphragm according to claim 1, wherein, The first adhesive and the second adhesive comprise a weight ratio in the range of 80:20 to 20:80 relative to the total amount of 100 parts by weight of the first adhesive and the second adhesive.

6. The diaphragm according to claim 1, wherein, The citric acid content is in the range of 5 to 200 parts by weight relative to 100 parts by weight of the first adhesive, and the citric acid content is in the range of 5 to 200 parts by weight relative to 100 parts by weight of the second adhesive.

7. The diaphragm according to claim 1, wherein, The filler has a particle size D100 of 0.7 μm or smaller.

8. The diaphragm according to claim 1, wherein, The filler comprises boehmite and is plate-shaped.

9. The diaphragm according to claim 1, wherein, The first adhesive comprises a (meth)acrylic acid adhesive, the (meth)acrylic acid adhesive comprising crosslinking units with citric acid, the crosslinking units comprising one or more of units derived from (meth)acrylic acid or salts thereof, units derived from (meth)acrylamide, units derived from hydroxyalkyl (meth)acrylic acid esters, units derived from (meth)acrylonitrile, units derived from (meth)acrylamido-2-methylpropanesulfonic acid or salts thereof, and units derived from ethyleneimine.

10. The diaphragm according to claim 9, wherein, The content of the crosslinking unit with citric acid is in the range of 10 mol% to 100 mol% of the (meth)acrylic acid adhesive.

11. The diaphragm according to claim 9, wherein, The (meth)acrylic adhesive comprises structural units containing sulfonate groups.

12. The diaphragm according to claim 11, wherein, The (meth)acrylic adhesive further includes one or more structural units derived from (meth)acrylates or (meth)acrylic acid, structural units containing cyano groups, and structural units derived from (meth)acrylamide.

13. The diaphragm according to claim 2, wherein, The citric acid content in the crosslinking agent is 95 wt% or more.

14. The diaphragm according to claim 2, wherein, The mass ratio of the mixture of the first adhesive and the second adhesive to the filler is in the range of 1:10 to 1:

50.

15. The diaphragm according to claim 2, wherein, The composition for coating also includes an alcohol.

16. The diaphragm according to claim 15, wherein, The alcohol has a boiling point of 60°C or higher.

17. The diaphragm according to claim 15, wherein, The alcohols include monohydric alcohols with a main chain carbon number ranging from 1 to 4.

18. The diaphragm according to claim 15, wherein, The alcohol content is in the range of 5 to 50 parts by weight relative to 100 parts by weight of the second binder.

19. The diaphragm according to claim 1, wherein, The packing material comprises a mixture of a first packing material and a second packing material, wherein the first packing material and the second packing material have different aspect ratios from each other.

20. The diaphragm according to claim 19, wherein, The second packing includes needle-shaped packing, and the first packing includes cubic packing.

21. The diaphragm according to claim 19, wherein, The second packing material comprises boehmite, and the first packing material comprises boehmite.

22. The diaphragm according to claim 1, wherein, The coating also includes polymer particles with melting points in the range of 80°C to 135°C.

23. The diaphragm according to claim 22, wherein, The polymer particles, with melting points in the range of 80°C to 135°C, are present in the coating at a content of 5 wt% to 30 wt%.

24. The diaphragm according to claim 22, wherein, The polymer particles having a melting point in the range of 80°C to 135°C include one or more of polyolefins, polyolefin derivatives, and polyolefin waxes.

25. The diaphragm according to claim 22, wherein, The polymer particles have an average particle size D50 in the range of 0.1 μm to 2 μm.

26. The diaphragm according to claim 22, wherein, The coating is a stacked structure of a first coating and a second coating. The first coating comprises the filler and the crosslinking product, and The second coating comprises the polymer particles with melting points in the range of 80°C to 135°C.

27. The diaphragm according to claim 22, wherein, The coating comprises a stacked structure of a first coating, an adhesive layer, and a second coating. The first coating comprises the filler and the crosslinking product. The adhesive layer includes an adhesive bonding agent, and The second coating comprises the polymer particles with melting points in the range of 80°C to 135°C.

28. The diaphragm according to claim 22, wherein, The coating comprises a third coating and a second coating, wherein the third coating comprises a filler, the crosslinking product, and an adhesive binder, and The second coating comprises the polymer particles with melting points in the range of 80°C to 135°C.

29. The diaphragm according to claim 1, wherein, The coating comprises lithium cations and has a lithium cation content in the range of 50 ppm to 200 ppm.

30. The diaphragm according to claim 29, wherein, The first adhesive comprises structural units containing lithium salts of sulfonic acid.

31. The diaphragm according to claim 30, wherein, The structural unit of the lithium salt containing sulfonic acid is represented by chemical formula 9: Chemical formula 9: in: R 9 and R 10 Each independently comprises hydrogen or C1 to C3 alkyl groups. L 3 Including -C(=O)-, -C(=O)O-, -OC(=O)-, -O-, or -C(=O)NH-. L 4 This includes substituted or unsubstituted C1 to C10 alkylene groups, substituted or unsubstituted C3 to C20 cycloalkylene groups, substituted or unsubstituted C6 to C20 arylene groups, or substituted or unsubstituted C3 to C20 heterocyclic groups. a and b are each an independent integer in the range of 0 to 2.

32. The diaphragm according to claim 30, wherein, The alkali metal salts of the carboxyl cellulose compounds include lithium salts of carboxymethyl cellulose of formula 10: Chemical Formula 10: ； Where n is the number of moles of the repeating unit.

33. The diaphragm according to claim 30, wherein, The alkali metal salts of the carboxyl cellulose compounds also include the alkali metal salt of carboxymethyl cellulose of formula 11: Chemical Formula 11: ； Where M includes sodium, potassium, rubidium or cesium, and n is the number of moles of the repeating unit.

34. A rechargeable battery, said rechargeable battery comprising: Positive electrode; negative electrode; as well as The separator for a rechargeable battery according to any one of claims 1 to 33 is located between the positive electrode and the negative electrode.

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