Separator for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

A separator for a rechargeable lithium battery and a rechargeable lithium battery including the same are provided. The separator includes one or more fiber layers wherein at least one of the fiber layers includes a fiber network of fibers comprising a first copolymer, or at least one of the fiber layers includes a network of core-shell type fibers comprising a first copolymer. The first copolymer includes a copolymer of a monomer mixture, the copolymer including: a first structural unit including a unit derived from an aromatic unsaturated monomer; a second structural unit derived from a (meth) acrylic monomer, the (meth) acrylic monomer including an alkyl group having four or more carbon atoms in the main chain in an ester moiety; and a third structural unit derived from a sulfonic acid group-containing monomer.

Description

[0001] This application claims priority to Korean Patent Application No. 10-2024-0157090, filed on November 7, 2024, with the Korean Intellectual Property Office, the entire disclosure of which 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 prevalence 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-ion batteries can be advantageous.

[0004] A rechargeable lithium battery includes a positive electrode and a negative electrode containing active materials capable of inserting and deintercalating lithium ions, and generates electrical energy through oxidation and reduction reactions when lithium ions are deintercalated from the positive electrode and inserted into the negative electrode, and deintercalated from the negative electrode and inserted into the positive electrode. Summary of the Invention

[0005] This disclosure describes a separator for rechargeable batteries that does not have a porous substrate and provides desired or improved heat resistance, low membrane resistance and high adhesion.

[0006] This disclosure also describes a rechargeable battery including a separator for the rechargeable battery.

[0007] One aspect of this disclosure includes a separator for a rechargeable battery.

[0008] The separator for a rechargeable battery comprises one or more fiber layers, at least one of which comprises a fiber network containing fibers of a first copolymer, or at least one of which comprises a network of core-shell fibers containing the first copolymer. The first copolymer comprises a copolymer including: a first structural unit comprising a unit derived from an aromatic unsaturated monomer; a second structural unit derived from a (meth)acrylic acid monomer, wherein the (meth)acrylic acid monomer contains an alkyl group having four or more carbon atoms in its main chain in the ester moiety; and a third structural unit derived from a monomer containing a sulfonic acid group. Here, the first, second, and third structural units are included in the ranges of about 5 mol% to about 80 mol%, about 10 mol% to about 60 mol%, and about 5 mol% to about 80 mol%, respectively, relative to 100 mol% of the copolymer.

[0009] Another aspect of this disclosure includes a rechargeable battery.

[0010] A rechargeable battery includes a positive electrode, a negative electrode, and a separator between the positive and negative electrodes for rechargeable battery use.

[0011] Because the separator used in rechargeable batteries does not have a porous substrate, the overhanging portion of the separator does not shrink when the battery is exposed to heat, thereby reducing or preventing short circuits and improving battery reliability. According to one example embodiment, the separator for rechargeable batteries can improve battery capacity, safety, and lifespan by providing desired or improved heat resistance, high adhesion, and low film resistance. Attached Figure Description

[0012] 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: Figures 1 to 4 This is a schematic cross-sectional view of a rechargeable lithium battery according to an example embodiment; Figures 5 to 9 This is a schematic cross-sectional view of a separator for a rechargeable battery according to an example embodiment. Detailed Implementation

[0013] Hereinafter, exemplary embodiments of the present disclosure are described in detail. However, the 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.

[0014] Unless otherwise stated herein, when a component such as a layer, membrane, region, and plate is described as being disposed “on” another component, it includes not only the case where the component is “directly on” another component, but also the case where there are other components between them.

[0015] Unless otherwise stated herein, the singular may also include the plural. Additionally, unless otherwise stated, the term "A or B" may mean "including A, including B, or including both A and B".

[0016] In this specification, "combination thereof" may mean a mixture, stack, complex, copolymer, alloy, blend, or reaction product of the components.

[0017] Unless otherwise defined herein, “particle size D50” refers to the size of particles that constitute 50% of the cumulative volume in a particle size distribution. Particle size D50 can be measured by methods known to those skilled in the art, and for example, using a particle size analyzer, transmission electron microscopy (TEM) images, or scanning electron microscopy (SEM) images. Alternatively, particle size D50 can be obtained by measuring the particle size using a measuring device that utilizes dynamic light scattering, counting the number of particles in each particle size range for data analysis, and then calculating the particle size D50 from this data. Optionally, particle size D50 can be measured using laser diffraction. When measuring particle size by laser diffraction, for example, by dispersing the particles to be measured in a dispersion medium, then introducing the dispersion medium into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and irradiating with ultrasonic waves at approximately 28 kHz with a 60 W output, particle size D50 can be calculated based on 50% of the particle size distribution in the measuring device.

[0018] If the particle is spherical (when the particle is spherical), the size can be expressed as the diameter.

[0019] In this specification, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid.

[0020] In the following text, unless otherwise defined, “substitution” means that hydrogen in a compound is substituted by a substituent such as or including at least one of the following: 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') (wherein R and R' are both independently hydrogen or C1 to C6 alkyl), sulfobetaine (-RR'N+(CH2)). n SO3- (where n is a natural number from 1 to 10), carboxylic acid betaine group (-RR'N+(CH2)). nCOO-, n is a natural number from 1 to 10 (here, R and R' are both 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 its salt (-C(=O)OM, where M represents an organic or inorganic cation), sulfonic acid (-SO3H) or its salt (-SO3M, where M represents an organic or inorganic cation), phosphate (-PO3H2) or its salt (-PO3MH or -PO3M2, where M represents an organic or inorganic cation) and combinations thereof.

[0021] In the following text, C1 to C3 alkyl groups may be or include methyl, ethyl, or propyl. C1 to C10 alkylene groups may be or include, for example, C1 to C6 alkylene groups, C1 to C5 alkylene groups, or C1 to C3 alkylene groups, and may be or include, for example, methylene, ethylene, or propylene. C3 to C20 cycloalkylene groups may be or include, for example, C3 to C10 cycloalkylene groups or C5 to C10 cycloalkylene groups (e.g., cyclohexylene). C6 to C20 arylene groups may be or include, for example, C6 to C10 arylene groups (e.g., phenylene). C3 to C20 heterocyclic groups may be or include, for example, C3 to C10 heterocyclic groups (e.g., pyridine groups).

[0022] In the following text, “heterogeneous” means one or more heteroatoms including or containing at least one of N, O, S, Si and P.

[0023] Additionally, in chemical formulas, the symbol * refers to a part that is attached to the same or different atoms, groups, or structural units.

[0024] Unless otherwise specified in the chemical formulas described herein, hydrogen can be considered to be bonded in the structure of the chemical formulas.

[0025] In the following text, "alkali metals" refers to elements that belong to Group 1 of the periodic table, such as lithium, sodium, potassium, rubidium, cesium, or francium, and can exist in either a cation or a neutral state.

[0026] In this specification, when describing a range of values, “X to Y” means “X or greater and Y or less (X ≤ and ≤ Y)”.

[0027] When the terms “about” or “substantially” are used in conjunction with numerical values ​​in this specification, it is intended that the relevant numerical value includes a tolerance of ±10% around the stated value. When a range is specified, the range includes all values ​​within that range, such as increments of 0.1%.

[0028] The present disclosure is described in detail below. A separator for rechargeable lithium-ion batteries is described below. However, the separator of the present disclosure can also be applied to rechargeable batteries other than rechargeable lithium-ion batteries.

[0029] Because the separator used in rechargeable batteries does not have a porous substrate, the overhanging portion of the separator does not shrink when the battery is exposed to heat, thereby reducing or preventing short circuits and improving battery reliability.

[0030] Separators used in rechargeable batteries can improve battery capacity, safety, and lifespan by providing desired or improved heat resistance, high adhesion, and low membrane resistance.

[0031] A separator for a rechargeable lithium-ion battery according to an example embodiment includes one or more fiber layers, wherein at least one of the fiber layers includes a fiber network comprising fibers of a first copolymer. The first copolymer includes a copolymer comprising: a first structural unit comprising a unit derived from an aromatic unsaturated monomer; a second structural unit derived from a (meth)acrylic acid monomer, said (meth)acrylic acid monomer comprising an alkyl group having four or more carbon atoms in its main chain in the ester moiety; and a third structural unit derived from a sulfonic acid-containing monomer. Here, the first structural unit, the second structural unit, and the third structural unit are included in the ranges of about 5 mol% to about 80 mol%, about 10 mol% to about 60 mol%, and about 5 mol% to about 80 mol%, respectively, relative to 100 mol% of the copolymer.

[0032] In this specification, "fiber layer" can refer to a layer formed into a network (or mesh) resembling a web using fibers. Here, fibers can include one or more types of nanofibers and microfibers. Although not particularly limited, fibers can be manufactured by electrospinning. Electrospinning can be performed using conventional methods known in the art. The electrospinning method is described in detail below.

[0033] The fiber may have an average size in the range of about 300 nm or smaller (e.g., 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 185 nm, 190 nm, 195 nm, 200 nm, 50 nm to 200 nm).

[0034] The thickness of each fiber layer can be approximately 20 μm or less (e.g., 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 2 μm to 10 μm). Within this range, the fiber layers can be used in batteries.

[0035] The thickness of the separator can be about 20 μm or less (e.g., 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 8 μm or less or 5 μm to 10 μm). Within this range, the separator can be used in the battery.

[0036] The separator may not include a conventionally known porous substrate (e.g., a porous polyolefin substrate). Porous substrates are manufactured by stretching and may undergo thermal shrinkage and melting at high temperatures, which could cause overhangs in the separator to shrink when the battery is exposed to heat, resulting in a short circuit. However, because the separator does not include a porous substrate, battery reliability can be improved by reducing the likelihood of short circuits.

[0037] Because at least one of the fiber layers comprises a fiber network containing fibers of a first copolymer, the separator can be used in batteries without a porous substrate. The separator can improve battery capacity, safety, and lifespan by providing desired or improved heat resistance, high adhesion, and low membrane resistance.

[0038] First copolymer: The first copolymer comprises a copolymer including: a first structural unit comprising a unit derived from an aromatic unsaturated monomer; a second structural unit derived from an alkyl-containing (meth)acrylic acid monomer having four or more main chain carbon atoms in the ester moiety; and a third structural unit derived from a sulfonic acid-containing monomer. Based on 100 mol% of the copolymer, the first structural unit is present in an amount ranging from about 5 mol% to about 80 mol%, the second structural unit is present in an amount ranging from about 10 mol% to about 60 mol%, and the third structural unit is present in an amount ranging from about 5 mol% to about 80 mol%.

[0039] The first copolymer can reduce the membrane resistance of the separator, thereby improving the capacity of the lithium secondary battery, and can provide high adhesive strength, thereby improving the safety and lifespan of the lithium secondary battery. In addition, the first copolymer provides high electrolyte moisture content and improved flexibility, which improves resistance. Furthermore, the first copolymer can provide high capacity retention and low DC internal resistance variation at both room temperature (e.g., about 20°C to about 30°C) and high temperature (e.g., about 40°C to about 50°C).

[0040] According to one example embodiment, the first copolymer is used as a binder to ensure adhesion between the diaphragm and the electrode. Membrane resistance and adhesion are typically in balance. The first copolymer can reduce the membrane resistance of the diaphragm while also increasing adhesion.

[0041] If present (and when present), the first copolymer may have a glass transition temperature (Tg) in the range of about 60°C to about 80°C (e.g., 60°C to 70°C). Within this range, the first copolymer exhibits desired or improved adhesion to the electrode and good ionic conductivity. The Tg of the first copolymer can be measured using, for example, thermomechanical analysis (TMA) methods known to those skilled in the art. For example, the glass transition temperature can be measured as follows: 1. Cut the copolymer or binder to be analyzed into 0.5mm × 8mm size to prepare the sample, attach it to the support, and place it on the sample probe of the TMA device.

[0042] 2. Set the mechanical load to 0.0150 N, the heating rate to 5 °C / min, and measure the sample length according to the temperature change.

[0043] 3. The temperature at which the slope of the curve obtained from the TMA device changes is designated as the glass transition temperature.

[0044] For the first copolymer, the total amount of the first, second, and third structural units can be included in about 95 mol% or more (e.g., 95 mol% to 100 mol% (e.g., 100 mol%)). Within this range, the above-described separation membrane effect can be easily achieved.

[0045] First structural unit: The first structural unit includes units derived from aromatic unsaturated monomers. Aromatic unsaturated monomers may include aromatic vinyl monomers. Units derived from aromatic unsaturated monomers can provide adhesion, allowing the first coating to adhere to the electrode and improving the permeability of the diaphragm.

[0046] The unit derived from aromatic unsaturated monomers is represented by the following chemical formula 1, and the copolymer may include one or more units represented by the following chemical formula 1: Chemical Formula 1: .

[0047] In chemical formula 1, R 1 and R 2 Each is independently or includes hydrogen or substituted or unsubstituted C1 to C5 alkyl groups, and Ar is or includes substituted or unsubstituted monocyclic or polycyclic aryl groups from C6 to C20.

[0048] In the example, Ar in Formula 1 is or includes a monocyclic or polycyclic C6 to C20 aryl group, and may be or include at least one of, for example, phenyl, naphthyl, anthraceneyl and pyreneyl.

[0049] In the example, the unit derived from the aromatic unsaturated monomer is represented by the following chemical formula 2, and the copolymer may include one or more units represented by the following chemical formula 2: Chemical formula 2: .

[0050] In chemical formula 2, R 3 and R 4 Each is independently or includes hydrogen or substituted or unsubstituted C1 to C5 alkyl groups. R is or includes one or more of substituted or unsubstituted C1 to C20 alkyl, substituted or unsubstituted C3 to C20 cycloalkyl, substituted or unsubstituted C1 to C20 alkoxy, and substituted or unsubstituted C3 to C20 aryl, and m is an integer in the range of 0 to 5.

[0051] In the example, R in Formula 2 can be or includes substituted or unsubstituted C1 to C20 alkyl or substituted or unsubstituted C1 to C20 alkoxy. In the example, m in Formula 2 can be equal to 0 or 1.

[0052] For example, aromatic unsaturated monomers may include one or more of styrene, α-methylstyrene, 4-butylstyrene (such as 4-n-butylstyrene, 4-isobutylstyrene and 4-tert-butylstyrene), butoxystyrene containing 4-butoxystyrene (such as 4-n-butoxystyrene, 4-isobutoxystyrene and 4-tert-butoxystyrene), halogenated styrene (such as chlorostyrene, bromostyrene and fluorostyrene), vinyltoluene (such as 4-vinyltoluene, 3-vinyltoluene and 2-vinyltoluene), and vinylnaphthalene (such as 1-vinylnaphthalene and 2-vinylnaphthalene).

[0053] In addition to units derived from aromatic unsaturated monomers, the first structural unit may also include units derived from (meth)acrylic acid monomers, wherein the (meth)acrylic acid monomer contains an alkyl group having one to three carbon atoms in the main chain in the ester moiety. Units derived from (meth)acrylic acid monomers can provide additional adhesive properties.

[0054] The unit derived from the (meth)acrylic acid monomer is represented by the following chemical formula 3, and the copolymer may include one or more units represented by the following chemical formula 3: Chemical formula 3: .

[0055] In chemical formula 3, R 5 and R 6 Each is independently or includes hydrogen or methyl, and L 1 It is or includes substituted or unsubstituted straight-chain or branched C1 to C3 alkyl groups.

[0056] In the example, the (meth)acrylic monomer may include one or more of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate.

[0057] For example, homopolymers of (meth)acrylic acid monomers can have a glass transition temperature of about 50°C or higher (e.g., 50°C to 150°C). Within this range, the glass transition temperature of the copolymers described above can be readily achieved. For example, the (meth)acrylic acid monomer can be or include at least one of methyl methacrylate and ethyl methacrylate.

[0058] The first structural unit is included in an amount ranging from about 5 mol% to about 80 mol% relative to 100 mol% of the copolymer. When the first structural unit is included in an amount of about 5 mol% or more, electrolyte wettability can be improved, and capacity retention at high temperatures can be high. When the first structural unit is included in an amount of about 80 mol% or less, membrane resistance does not increase, and capacity retention at both room temperature and high temperatures can be high. For example, relative to 100 mol% of the copolymer, it can be expressed in the following percentages: 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 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%. The first structural unit comprises amounts ranging from 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%, about 10 mol% to about 70 mol%, or about 30 mol% to about 60 mol%. When the first structural unit is included within the above range, the membrane can exhibit low membrane resistance, desired or improved adhesion to the electrode, gas permeability, and oxidation resistance.

[0059] Relative to 100 mol% of the copolymer, units derived from aromatic unsaturated monomers can be present in quantities from about 5 mol% to about 80 mol% (e.g., 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 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%). The amounts within the range of 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%, 10 mol% to 70 mol%, 10 mol% to 60 mol%, 10 mol% to 35 mol%, 15 mol% to 30 mol%, or 5 mol% to 35 mol% are included. Within the above range, the above-mentioned effects of the diaphragm can be easily achieved.

[0060] Relative to 100 mol% of the copolymer, units derived from (meth)acrylic acid monomers can be present in quantities from about 0 mol% to about 80 mol% (e.g., 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 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%, 4 The membrane is present in amounts ranging from 6 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%, 5 mol% to 80 mol%, 10 mol% to 70 mol%, 10 mol% to 60 mol%, 10 mol% to 35 mol%, 15 mol% to 30 mol%, or 5 mol% to 35 mol%. Within these ranges, the aforementioned effects of the diaphragm can be easily achieved.

[0061] According to the example embodiment, relative to 100 mol% of the copolymer, units derived from aromatic unsaturated monomers and units derived from (meth)acrylic acid monomers can be included in a molar ratio ranging from about 1:0.5 to 1:2 (e.g., 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:1 to 1:2). Within the above range, the aforementioned effects of the diaphragm can be readily achieved.

[0062] Second structural unit: The second structural unit is derived from a (meth)acrylic acid monomer, wherein the (meth)acrylic acid monomer contains an alkyl group having four or more carbon atoms in the main chain within the ester moiety. The second structural unit can improve the dispersibility of the coating slurry and also improve the electrolyte wettability and flexibility of the coating.

[0063] The units derived from (meth)acrylic acid monomers are represented by the following chemical formula 4, and the copolymer may include one or more structural units represented by the following chemical formula 4: Chemical formula 4: .

[0064] In chemical formula 4, R 7 and R 8 Each is independently or includes hydrogen or methyl, and L 2 It is or includes substituted or unsubstituted straight-chain or branched C4 to C30 alkyl groups.

[0065] In this case, the alkyl group can be or includes C4 to C20 alkyl, C4 to C10 alkyl, or C4 to C8 alkyl.

[0066] According to example embodiments, the (meth)acrylate monomer may include one or more of 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, and isodecyl (meth)acrylate.

[0067] The second structural unit is included in an amount ranging from about 10 mol% to about 60 mol% relative to 100 mol% of the copolymer. When the second structural unit is included in an amount of about 10 mol% or more, the membrane resistance can be reduced upon impregnation with the electrolyte, and the capacity retention at room temperature and high temperature can be high. When the second structural unit is included in an amount of about 60 mol% or less, air permeability can be improved, and the capacity retention at room temperature and high temperature can be high. For example, the second structural unit can be included in an amount of 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% relative to 100 mol% of the copolymer. Amounts ranging from 1%, 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%, and from about 15 mol% to about 35 mol% (e.g., 20 mol% to 60 mol%, 20 mol% to 30 mol%) are included. Within the above range, adhesion to the electrode and flexibility of the coating can be increased.

[0068] Third structural unit: The third structural unit is derived from a sulfonic acid-containing monomer. This unit, derived from the sulfonic acid-containing monomer, can reduce the membrane resistance by increasing the likelihood of lithium-ion migration in the presence of the first and second structural units.

[0069] According to an example embodiment, the third structural unit increases the glass transition temperature of the copolymer by including a bulky functional group derived from (meth)acrylamide sulfonic acid or a salt thereof, and thus provides structural safety. Furthermore, when the third structural unit is or includes a functional group derived from a salt of (meth)acrylamide sulfonic acid, the metal (M) can move through the third structural unit by substituting the metal-containing sulfonic acid functional group, and therefore the membrane resistance of the diaphragm can be significantly reduced.

[0070] The third structural unit can be represented by any one of the following chemical formulas 5, 6, and 7. The copolymer may include one or more third structural units represented by the following chemical formulas 5, 6, and 7: Chemical formula 5: .

[0071] Chemical Formula 6: .

[0072] Chemical Formula 7: .

[0073] In chemical formulas 5 to 7 R 9 R 10 R 11 R 12 R 13 and R 14 Each is independently hydrogen or includes C1 to C3 alkyl groups. L 3 L 5 and L 7 Each of these 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 includes 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 all independent integers in the range of 0 to 2, and In chemical formula 6, M is or includes alkali metals.

[0074] In the example, in chemical formulas 5 to 7, L 3 L 5 and L 7 They can all be or include -C(=O)NH- independently. L 4 L 6 and L 8 They may each be independently or include C1 to C10 alkylene groups, and a, b, c, d, e, and f can all equal 1.

[0075] The sulfonic acid-containing structural unit may include only one of the structural units represented by chemical formulas 5 to 7, or two or more of the structural units represented by chemical formulas 5 to 7. In one example, the sulfonic acid-containing structural unit may include the structural unit represented by chemical formula 6, and in another example, the sulfonic acid-containing structural unit may include both the structural unit represented by chemical formula 6 and the structural unit represented by chemical formula 7.

[0076] The sulfonic acid-containing structural unit may be or includes, for example, a structural unit derived from at least one of vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, anethole sulfonic acid, (meth)acrylamidoalkane sulfonic acid, (meth)acrylic acid sulfonyl ester and its salts.

[0077] Here, alkanes can be or include C1 to C20 alkanes, C1 to C10 alkanes, or C1 to C6 alkanes, and alkyl groups can be or include C1 to C20 alkyl groups, C1 to C10 alkyl groups, or C1 to C6 alkyl groups. A salt refers to a salt composed of the aforementioned sulfonic acid and a suitable ion. The ion can be, for example, an alkali metal ion, and in this case, the salt can be or include an alkali metal sulfonate salt.

[0078] (Methacrylamidoalkane sulfonic acid may be or include at least one of, for example, 2-(meth)acrylamido-2-methylpropane sulfonic acid, and (meth)acrylate sulfonyl ester may be or include, for example, (meth)acrylate 2-sulfoethyl ester or (meth)acrylate 3-sulfopropyl ester, etc.

[0079] The third structural unit is included in an amount ranging from about 5 mol% to about 80 mol% relative to 100 mol% of the copolymer. When the third structural unit is included in an amount of about 5 mol% or more, the membrane resistance of the separator can be reduced, and the rate of change of DC-IR at room temperature and high temperature can be reduced. When the third structural unit is included in an amount of about 80 mol% or less, the capacity retention of the battery at room temperature and high temperature can be increased, and the rate of change of DC-IR at room temperature and high temperature can be reduced.

[0080] For example, relative to 100 mol% of the copolymer, the third structural unit can be in the following proportions: 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 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%, 4 The third structural unit may be included in amounts ranging from about 10 mol% to about 60 mol% relative to 100 mol% of the copolymer. For example, the third structural unit may be included in amounts ranging from about 20 mol% to about 60 mol% relative to 100 mol% of the copolymer. When the third structural unit is included within the above-mentioned range, the membrane resistance of the binder and the separator including it can be significantly reduced, the capacity retention rate of the battery at room temperature and high temperature can be increased, and the DC-IR change rate at room temperature and high temperature can be reduced.

[0081] The binder may include an alkali metal. The alkali metal may be present in cationic form and may be or include at least one of, for example, lithium, sodium, potassium, rubidium, and cesium. For example, the alkali metal may exist in the form of a salt by combining with a copolymer. Alkali metals can help synthesize monomer mixtures into copolymers in aqueous solvents and improve coating adhesion, membrane permeability, and oxidation resistance, etc.

[0082] The copolymer can have a glass transition temperature in the range of about 60°C to about 80°C. In the example, the glass transition temperature can be within the range of 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 62°C to 78°C (e.g., 64°C to 75°C). Within the above ranges, the coating can have desired or improved adhesion, and the membrane including the coating can exhibit desired or improved permeability and oxidation resistance. The glass transition temperature of the copolymer can be measured by typical methods known to those skilled in the art (such as thermomechanical analysis (TMA)). For example, the glass transition temperature can be measured as follows: 1. Cut the copolymer or binder to be analyzed into 0.5mm × 8mm size to prepare the sample, attach it to the support, and place it on the sample probe of the TMA device.

[0083] 2. Set the mechanical load to 0.0150 N, the heating rate to 5 °C / min, and measure the sample length according to the temperature change.

[0084] 3. The temperature at which the slope of the curve obtained from the TMA device changes is designated as the glass transition temperature.

[0085] In binders comprising alkali metals and copolymers, the alkali metals may be included in an amount ranging from about 1 wt% to about 40 wt% (e.g., 1 wt%, 2 wt%, 3 wt%, 4 wt%, 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%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 10 wt% to 20 wt%). For example, the copolymer and alkali metal may be included in a weight ratio ranging from about 99:1 to about 60:40 or from 99:1 to 70:30 (e.g., from about 99:1 to about 80:20 or from 90:10 to 80:20).

[0086] The alkali metal may be included in an amount ranging from about 0.1 mol% to about 1.0 mol% relative to the total amount of the copolymer of the alkali metal and monomer mixture. When the alkali metal is included in the above range, the coating may have desired or improved adhesion, and the diaphragm including it may exhibit desired or improved permeability and oxidation resistance.

[0087] Binders that include copolymers of monomer mixtures can take various forms, such as alternating polymers in which structural units are distributed alternately, random polymers in which structural units are distributed randomly, and grafted polymers in which some of the structural units are grafted.

[0088] Binders comprising copolymers of monomer mixtures can have a weight-average molecular weight in the range of about 100,000 g / mol to 1,000,000 g / mol, 100,000 g / mol to 500,000 g / mol, 100,000 g / mol to 150,000 g / mol, 200,000 g / mol to 130,000 g / mol, or 300,000 g / mol to 900,000 g / mol. When the weight-average molecular weight of the binder comprising copolymers of monomer mixtures meets the above ranges, it can exhibit desired or improved adhesion and low electrical resistance. The weight-average molecular weight can be the average molecular weight converted from polystyrene, measured using, for example, gel permeation chromatography.

[0089] The first copolymer of the monomer mixture can be prepared by solution polymerization.

[0090] The membrane includes at least one fiber layer comprising a fiber network containing a first copolymer without a porous substrate. The fiber layer can help reduce the thermal shrinkage rate of the membrane in the electrolyte and reduce its resistance.

[0091] The diaphragm may include at least one fiber layer, the at least one fiber layer comprising a fiber network containing a first copolymer.

[0092] According to one example embodiment, the diaphragm may include two or more fiber layers, the two or more fiber layers comprising a fiber network containing a first copolymer.

[0093] The first copolymer may be present in an amount of at least about 50 wt% of the fiber (e.g., in the range of about 60 wt% to about 100 wt%).

[0094] The separator may include fiber layers comprising a fiber network containing a first copolymer. The separator may be a single-layer separator or a multilayer separator comprising multiple fiber layers. Here, a multilayer separator refers to a separator comprising multiple fiber layers stacked together. Multilayer separators can readily combine various polymers under different electrospinning conditions to form a separator, and enhance the strength of the separator.

[0095] The membrane, comprising multiple fiber layers, is described in detail below.

[0096] Multi-layer diaphragm: Multilayer membranes may include a fiber network comprising fibers of a first copolymer.

[0097] According to one example embodiment, the multilayer membrane may include one or more fiber layers, or two or more fiber layers, the fiber layers comprising a fiber network containing fibers of a first copolymer.

[0098] The multilayer membrane may also include one or more fiber layers, or two or more fiber layers, said fiber layers comprising a fiber network containing one or more types of fibers of a second copolymer different from the first copolymer.

[0099] In one example embodiment, the multilayer membrane may be or include three layers of membrane, in which fiber layers comprising a network of fibers containing a first copolymer, fiber layers comprising a network of fibers containing a second copolymer, and fiber layers comprising a network of fibers containing the first copolymer are stacked (e.g., stacked sequentially).

[0100] In another example embodiment, the multilayer membrane may be or include a three-layer membrane, in which fiber layers comprising a network of fibers containing a second copolymer, fiber layers comprising a network of fibers containing a first copolymer, and fiber layers comprising a network of fibers containing a second copolymer are stacked (e.g., stacked sequentially).

[0101] In yet another example embodiment, the multilayer membrane may include one or more fiber layers, or two or more fiber layers comprising a network of core-shell fibers containing a first copolymer. Here, the first copolymer may also be contained within the core or shell of the core-shell fibers.

[0102] The multilayer membrane may also include one or more fiber layers, or two or more fiber layers, which include a network of fibers comprising one or more types of second copolymers that may be different from the first copolymer.

[0103] The multilayer membrane may also include one or more fiber layers, or two or more fiber layers, which include a network of fibers comprising a first copolymer.

[0104] In one example embodiment, the multilayer membrane may be or include three layers of membrane, in which stacked (e.g., sequentially stacked) are fiber layers comprising a network of fibers containing one or more types of second copolymers, fiber layers comprising a network of core-shell fibers, and fiber layers comprising a network of fibers containing one or more types of second copolymers. The core-shell fibers may be or include fibers comprising a core containing a first copolymer and a shell containing a second copolymer. Optionally, the core-shell fibers may be or include fibers comprising a core containing a second copolymer and a shell containing a first copolymer.

[0105] In another example embodiment, the multilayer membrane may be or include a three-layer membrane, in which stacked (e.g., sequentially stacked) fiber layers comprising a network of core-shell fibers, fiber layers comprising a network of fibers containing one or more types of second copolymers, and fiber layers comprising a network of core-shell fibers. The core-shell fibers may be or include fibers comprising a core containing a first copolymer and a shell containing a second copolymer. Optionally, the core-shell fibers may be or include fibers comprising a core containing a second copolymer and a shell containing a first copolymer.

[0106] In yet another example embodiment, the multilayer membrane may include one or more fiber layers, or two or more fiber layers comprising a network of fibers comprising a mixture of a first copolymer and a second copolymer.

[0107] In the mixture, the first copolymer may be present in an amount from about 10 wt% to about 90 wt% (e.g., 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%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, 51 wt%). The range of wt%, 52wt%, 53wt%, 54wt%, 55wt%, 56wt%, 57wt%, 58wt%, 59wt%, 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 66wt%, 67wt%, 68wt%, 69wt%, 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, 89wt%, 90wt%, 20wt% to 50wt%) is included, and the second copolymer may be in the range of 10wt% to 90wt% (e.g., 20wt% to 50wt%).10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20w t%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt%, 40wt%, 41w t%, 42wt%, 43wt%, 44wt%, 45wt%, 46wt%, 47wt%, 48wt%, 49wt%, 50wt%, 51wt%, The range of 52wt%, 53wt%, 54wt%, 55wt%, 56wt%, 57wt%, 58wt%, 59wt%, 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 66wt%, 67wt%, 68wt%, 69wt%, 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, 89wt%, 90wt%, and 50wt% to 80wt% is included.

[0108] The multilayer membrane may also include one or more fiber layers, or two or more fiber layers, which include a network of fibers comprising a first copolymer.

[0109] A multilayer membrane may include one or more fiber layers, or two or more fiber layers, the fiber layers comprising a network of fibers containing a second copolymer.

[0110] In one example embodiment, the multilayer membrane may be or include three layers of membrane, in which fiber layers comprising a network of fibers containing a first copolymer and a second copolymer, fiber layers comprising a network of fibers containing a second copolymer, and fiber layers comprising a network of fibers containing a first copolymer and a second copolymer are stacked (e.g., stacked sequentially).

[0111] In another example embodiment, the multilayer membrane may be or include a three-layer membrane, in which a fiber layer comprising a network of fibers containing a second copolymer, a fiber layer comprising a network of fibers containing a first copolymer and a second copolymer, and a fiber layer comprising a network of fibers containing a second copolymer are stacked (e.g., stacked sequentially).

[0112] The second copolymer is described in detail below.

[0113] Second copolymer: The second copolymer may be different from the first copolymer.

[0114] According to one example embodiment, the second copolymer may include units having monomers derived from monomers different from those of the first copolymer, or copolymers of monomers having different molar ratios.

[0115] The second copolymer can be prepared into fibers by electrospinning, and there are no particular restrictions, as long as it does not affect the performance of the diaphragm.

[0116] The second copolymer may include any one or more of the following: polyacrylonitrile, polyaniline, polypyrrole, polyrhodanine, melamine, polyurea, polyvinyl chloride, polyvinyl alcohol, polyethylene oxide, polymethyl methacrylate, polyacrylic acid, polylactic acid, polyimide, polyamide-imide, polyarylamide, polybenzylimazole, polypropylene, resorcinol-formaldehyde resin, melamine-formaldehyde resin, asphalt, sucrose, glucose, cellulose, and polyvinylidene fluoride.

[0117] In one example embodiment, the second copolymer may be or include polyimide or a mixture containing about 50 wt% or more of polyimide. The second copolymer can improve the heat resistance of the separator and, when combined with a fiber layer comprising a network of fibers containing the first copolymer, can advantageously reduce battery resistance, improve adhesion, lower turn-off temperature, and improve processability. The first copolymer may have a desired or improved effect in offsetting resistance compared to the second copolymer comprising polyimide or a mixture containing about 50 wt% or more of polyimide.

[0118] In another example embodiment, the second copolymer may be or include polyvinylidene fluoride (PVDF) or a mixture containing about 50 wt% or more PVDF. Such a second copolymer can increase the flexibility of the diaphragm and also increase its adhesiveness.

[0119] In another example embodiment, the second copolymer may be or include a mixture comprising about 50 wt% or more of a mixture of polyimide and polyvinylidene fluoride. Such a second copolymer can increase the flexibility of the diaphragm, also increase the adhesiveness of the diaphragm, and improve the processability of the diaphragm by counteracting the brittleness of the polyimide.

[0120] Electrospinning: The fiber layer can be manufactured by electrospinning a solution comprising a first copolymer and a second copolymer, respectively.

[0121] The solution can promote the dispersion and dissolution of the first and second copolymers, thereby promoting electrospinning. The solvent may be, or include, at least one of methylformamide, dimethylacetamide, dimethyl sulfoxide, and methylpyrrolidone, but this disclosure is not limited thereto. Stirring and / or heating may also be performed to increase the dispersion and dissolution of the copolymers.

[0122] Electrospinning can be performed in an environment with an internal temperature of approximately 25°C or higher (e.g., 25°C to 60°C). Within this range, since most of the solvent in the electrospinning solution evaporates, there is almost no residual solvent, thus reducing the impact of solvent on the battery.

[0123] Electrospinning can be performed as follows: a nozzle assembly (consisting of tips with needle sizes ranging from about 23 G to about 30 G) is positioned at a predetermined interval with a collecting roller; an electrospinning solution is added to the tips; the substrate is positioned on the contact roller; and a voltage ranging from about 35 kV to about 90 kV is applied to the tips. The gap between the nozzle assembly and the active material layer can be in the range of about 10 cm to about 20 cm. When the needle size of the tip is in the range of about 25 G to 30 G, the needle size can be suitable because a fiber layer with the desired shape can be formed.

[0124] According to the electrospinning process, as the electrospinning solution is spun and stretched into a fiber shape, a layer comprising nanofibers can be formed on a substrate. This is because the electrospinning solution is suspended in droplets on a tip due to surface tension, and when a voltage is applied, charges accumulate on the surface of the solution, resulting in repulsive forces between the charges. When the repulsive forces between the charges exceed the critical voltage of the solution's surface tension, a conical Taylor cone is generated, and a jet of the electrospinning solution is ejected from the tip of the cone. The jet is highly elongated to form nanofibers, which are then collected on the substrate to form a fiber layer.

[0125] The nozzle pressure can be approximately 1 MPa or higher. Within this range, the solvent evaporates to a high degree, thus reducing the impact of residual solvent on the battery.

[0126] Properly regulating the tip air can be advantageous, minimizing interference between tips and enabling uniform electrospinning. The tip air can be regulated by flowing compressed air at a pressure ranging from about 0.1 MPa to about 0.3 MPa.

[0127] The speed of the collecting roller can be adjusted so that the fiber layer can be formed to an appropriate thickness, and the speed of the collecting roller can be, for example, in the range of about 1 m / min to about 3 m / min. Additionally, the flow rate of the electrospinning solution can be adjusted so that the electrospinning solution is discharged from the tip at a rate in the range of about 20 μL / min to about 200 μL / min. In one example embodiment, after the electrospinning process, a drying process can be performed at a temperature in the range of about 20°C to about 30°C.

[0128] Core-shell fibers can be manufactured by injecting a first copolymer and a second copolymer into the nozzle of the core and the nozzle of the shell, respectively, and then electrospinning the first copolymer and the second copolymer simultaneously or synchronously. Methods for manufacturing core-shell fibers are generally known to those skilled in the art.

[0129] Diaphragm manufacturing: A membrane can be manufactured by producing and pressing fiber layers.

[0130] According to one example embodiment, a diaphragm can be manufactured by producing multiple individual fiber layers and then stacking and pressing the fiber layers together.

[0131] According to another example embodiment, the diaphragm can be manufactured by injecting an electrospinning solution containing the copolymer into a positioned (e.g., sequentially positioned) nozzle, causing the copolymer to spin or spin sequentially, and pressing the copolymer simultaneously or synchronously.

[0132] The pressing step can be performed by pressing with rollers, but this disclosure is not limited thereto.

[0133] The diaphragm can have desired or improved air permeability, for example, less than about 250 sec / 100 cc (e.g., 230 sec / 100 cc or less, or 200 sec / 100 cc or less). That is, the diaphragm can have an air permeability of less than about 40 sec / 100 cc·1 μm per unit thickness (e.g., 30 sec / 100 cc·1 μm or less, or 25 sec / 100 cc·1 μm or less). Here, air permeability is the time (in seconds) it takes for 100 cc of air to pass through a unit thickness of the diaphragm. The air permeability per unit thickness can be obtained by measuring the air permeability of the entire thickness of the diaphragm and dividing the measured air permeability by the thickness. Air permeability can be measured using an air permeability measuring device (Asahi Seiko, EG01-55-1MR) for the time (in seconds) required for 100 cc of air to pass through.

[0134] The separator can have a shrinkage rate of about 0.1% or less (e.g., 0% to 0.1% or 0%) in the electrolyte. Within this range, battery reliability can be improved.

[0135] Figures 5 to 9 This is a schematic cross-sectional view of a separator for a rechargeable battery according to an example embodiment.

[0136] Reference Figure 5 The membrane may include: layer 210, which includes a fiber network comprising fibers 211 of a first copolymer; layer 220, which includes a fiber network comprising polyimide fibers 221; and layer 230, which includes a fiber network comprising fibers 211 of the first copolymer.

[0137] Reference Figure 6 The diaphragm may include: layer 210, which includes a fiber network of polyimide fibers 221 and fibers 211 comprising a first copolymer; layer 220, which includes a fiber network of polyimide fibers 221; and layer 230, which includes a fiber network of polyimide fibers 221 and fibers 211 comprising a first copolymer.

[0138] Reference Figure 7 The diaphragm may include: layer 210, which includes a fiber network of core-shell fibers 212 comprising a first copolymer; layer 220, which includes a fiber network of polyimide fibers 221; and layer 230, which includes a fiber network of core-shell fibers 212 comprising the first copolymer.

[0139] Reference Figure 8 The diaphragm may include: layer 210, comprising a fiber network of polyimide fibers 221; layer 220, comprising a fiber network of core-shell fibers 212 comprising a first copolymer; and layer 230, comprising a fiber network of polyimide fibers 221.

[0140] Reference Figure 9 The diaphragm may include: layer 210, which includes a fiber network of fibers 213; layer 220, which includes a fiber network of polyimide fibers 221 and fibers 211 comprising a first copolymer; and layer 230, which includes a fiber network of fibers 213.

[0141] Rechargeable lithium batteries According to one example embodiment, a rechargeable lithium battery includes a separator, a positive electrode, and a negative electrode for the rechargeable lithium battery.

[0142] 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.

[0143] 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 a positive electrode active material, and may also include a binder and / or a conductive material.

[0144] For example, the positive electrode may also include additives that can constitute a sacrificial positive electrode.

[0145] 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.

[0146] 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 nickel manganese oxides, and combinations thereof.

[0147] 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); Li a 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 bO2 (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); and Li a FePO4 (0.90≤a≤1.8).

[0148] In the above chemical formulas, A is or includes at least one of Ni, Co, Mn, and combinations thereof; X is or includes at least one of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is or includes at least one of O, F, S, P, and combinations thereof; G is or includes at least one of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; and L 1 It is or includes at least one of Mn, Al and combinations thereof.

[0149] The positive electrode active material can be, or includes, for example, a high-nickel positive electrode active material, based on 100 mol% of metals 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.

[0150] 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%.

[0151] The binder causes the positive electrode active material particles to adhere to each other and to adhere the positive electrode active material to the current collector. As a non-limiting example, examples of binders may include at least one of the following: 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, and nylon, etc.

[0152] Conductive materials can impart electrical conductivity (e.g., electroconductivity) to electrodes. Any material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in a rechargeable lithium battery) and conducts electrons can be used in a battery. Examples of conductive materials may include: carbon-based materials, such as at least one of natural graphite, synthetic 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 powders or metal fibers; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0153] Al can be used as a current collector, but current collectors are not limited to this.

[0154] 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).

[0155] For example, the negative electrode active material layer may include about 90 wt% to about 99 wt% of negative electrode active material, about 0.5 wt% to about 5 wt% of binder, and about 0 wt% to about 5 wt% of conductive material.

[0156] Negative electrode active material The negative electrode active material may include at least one of the following: materials capable of reversibly inserting / deintercalating lithium ions, lithium metal, lithium metal alloys, materials capable of doping / dedoping lithium, and transition metal oxides.

[0157] Materials capable of reversibly inserting / deintercalating lithium ions can include carbon-based negative electrode active materials, such as crystalline carbon, amorphous carbon, or combinations thereof. Crystalline carbon can be graphite such as amorphous, flake-like, spherical, or fibrous natural or artificial graphite. Amorphous carbon can be or includes at least one of soft carbon, hard carbon, mesophase pitch carbonization products, and calcined coke.

[0158] 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.

[0159] The material capable of doping / dedoping lithium can 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 can 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 can include at least one of Sn, SnO2, a Sn-based alloy, and a combination thereof.

[0160] The silicon-carbon composite can be or include a composite of silicon and amorphous carbon. According to an exemplary embodiment, the silicon-carbon composite can be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite can include secondary particles (cores) in which primary silicon particles are assembled and an amorphous carbon coating (shell) on the surface of the secondary particles. The amorphous carbon can also be between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed in an amorphous carbon matrix.

[0161] The silicon-carbon composite can also include crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core.

[0162] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0163] The binder can cause the negative electrode active material particles to adhere to each other and can adhere the negative electrode active material to the current collector. The binder can include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0164] The non-aqueous binder can include at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and a combination thereof.

[0165] 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.

[0166] When an aqueous binder is used 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 methyl cellulose, methyl cellulose, and their alkali metal salts. The alkali metal may include at least one of Na, K, and Li.

[0167] Dry adhesives can be or include fibrous polymeric materials. For example, dry adhesives can be or include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, and combinations thereof.

[0168] Conductive materials can impart electrical conductivity (e.g., electroconductivity) to electrodes. Any material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in a rechargeable lithium battery) and conducts electrons can be used in a battery. Non-limiting examples of conductive materials may include: carbon-based materials, such as or including 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, and silver, in the form of metal powder or metal fibers; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0169] The negative electrode current collector may include at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0170] Rechargeable lithium batteries may also include an electrolyte.

[0171] electrolyte Electrolytes used in rechargeable lithium batteries may include non-aqueous organic solvents and lithium salts.

[0172] Non-aqueous organic solvents can serve as media for transporting ions that participate in the electrochemical reactions of a battery.

[0173] Non-aqueous organic solvents may be or include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, and combinations thereof.

[0174] 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).

[0175] 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, valproic acid lactone, and caprolactone.

[0176] Ether solvents may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Additionally, ketone solvents may include cyclohexanone. Alcohol solvents may include ethanol and isopropanol. 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); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane and 1,4-dioxolane; and sulfolane.

[0177] Non-aqueous organic solvents can be used alone or in combination of two or more solvents.

[0178] In addition, 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.

[0179] Lithium salts dissolved in organic solvents supply lithium ions in batteries, enabling rechargeable lithium batteries to operate 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 in the range of 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluorobis(oxalate)phosphate (LiDFBOP), lithium difluoro(oxalate)borate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0180] Rechargeable lithium batteries can be classified according to their shape, such as cylindrical, prismatic, pouch-shaped, or coin-shaped batteries.

[0181] Figures 1 to 4 This is a schematic diagram illustrating a rechargeable lithium battery according to an example embodiment. Figure 1 A cylindrical battery is shown. Figure 2 A prismatic battery is shown. Figure 3 and Figure 4 A pouch-type battery is shown. (See reference) Figures 1 to 4 The rechargeable lithium battery 100 may include an electrode assembly 40 and a housing 50. The electrode assembly 40 includes a positive electrode 10, a negative electrode 20, and a separator 30 between the positive electrode 10 and the negative electrode 20. 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 1 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of the sealed housing 50. Figure 2 In this context, the rechargeable lithium battery 100 may include a positive electrode lead connector 11, a positive electrode terminal 12 connected to the positive electrode lead connector 11, a negative electrode lead connector 21, and a negative electrode terminal 22 connected to the negative electrode lead connector 21. For example... Figure 3 and Figure 4 As shown, the rechargeable lithium battery 100 may include Figure 4 The electrode terminal 70 shown, or for example Figure 3 The positive electrode terminal 71 and negative electrode terminal 72 shown in the figure form an electrical path for inducing current formed in the electrode assembly 40 to the outside of the battery 100.

[0182] As a non-limiting example, the rechargeable lithium battery according to the example embodiment can be used in, for example, automobiles, mobile phones and / or various types of electronic devices.

[0183] Examples and comparative examples of this disclosure are described below. However, the examples below are merely examples of this disclosure, and this disclosure is not limited to the examples below.

[0184] 1. Verification of the first copolymer Preparation Example 1 In a 3L four-necked separable flask equipped with a stirrer, thermometer, and condenser, 850g of DMAc, styrene (SM, 36.45g, 0.35mol), methyl methacrylate (MMA, 35.04g, 0.35mol), 2-ethylhexyl acrylate (EHA, 36.83g, 0.20mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 20.73g, 0.10mol) were added, along with 1.1mol of LiOH relative to AMPS. After adding the initiator AIBN (0.164g, 0.001mol), the internal pressure was reduced to 10cmmHg using a diaphragm pump and then restored to atmospheric pressure using nitrogen gas, repeated three times.

[0185] The reaction was carried out for 12 hours, while heating was controlled to keep the temperature of the reaction solution stable between 65°C and 70°C.

[0186] After cooling to room temperature, approximately 10 mL of the reaction solution was taken to measure the non-volatile (NV) component, indicating that a copolymer of 9.8 wt% (theoretical value: 10 wt%) was obtained. In the lithium poly(styrene-co-methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamido-2-methylpropanesulfonic acid) salt, which is the obtained copolymer, the molar ratio of the first structural unit derived from styrene and methacrylate, the second structural unit derived from 2-ethylhexyl acrylate, and the third structural unit derived from 2-acrylamido-2-methylpropanesulfonic acid is 70:20:10, and the copolymer has a glass transition temperature (Tg) of 65.1 °C.

[0187] Preparation Examples 2 to 7 The first copolymer was prepared in the same manner as in Preparation Example 1, except that the molar ratio of the monomers in a total of 100 mol% styrene (SM), methacrylate (MMA), 2-ethylhexyl acrylate (EHA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) was changed as shown in Table 1 below.

[0188] Comparative preparation examples 1 to 5 The first copolymer was prepared in the same manner as in Preparation Example 1, except that the molar ratio of the monomers in a total of 100 mol% styrene (SM), methacrylate (MMA), 2-ethylhexyl acrylate (EHA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) was changed as shown in Table 1 below.

[0189] Table 1 below shows the molar ratios of monomers in the binders prepared in Preparation Examples 1 to 7 and Comparative Preparation Examples 1 to 5.

[0190] Table 1:

[0191] Refer to Example 1 A composition for an adhesive layer was prepared by mixing 10 parts by weight of the adhesive of Preparation Example 1 with 90 parts by weight of distilled water.

[0192] The composition for the adhesive layer was applied to both sides of a porous polyethylene membrane (thickness: 5.5 μm, CZMZ, air permeability: 110 sec / 100 cc, needle punch: 360 kgf) at a speed of 80 m / min using a die coating method. The composition was applied at 14 g / m³ at 60 °C. 3 The material is dried under an absolute vapor load (average value) to form an adhesive layer with a total thickness of 1.4 μm. As a result, a separator for rechargeable lithium batteries is manufactured.

[0193] Refer to Examples 2 to 12 The separator for the rechargeable lithium battery is manufactured in the same manner as in Reference Example 1, except that the type of binder used in Reference Example 1 is changed as shown in Tables 2 and 3.

[0194] Battery manufacturing Manufacturing of the negative electrode: A negative electrode active material slurry was prepared by mixing 97 wt% graphene particles with an average particle size of 25 μm as the negative electrode active material, 1.5 wt% styrene-butadiene rubber (SBR) binder, and 1.5 wt% carboxymethyl cellulose (CMC), adding distilled water to the mixture, and stirring the result with a mechanical stirrer for 60 minutes. The slurry was then applied to a 10 μm thick copper current collector using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, dried again under vacuum at 120°C for 4 hours, and rolled to produce the negative electrode.

[0195] Manufacturing of the positive electrode: A slurry for the positive electrode active material was prepared by mixing 97 wt% LiCoO2 as the positive electrode active material, 1.5 wt% carbon black powder as the conductive material, and 1.5 wt% polyvinylidene fluoride (PVdF). The mixture was then added to an N-methyl-2-pyrrolidone solvent, and the mixture was stirred using a mechanical stirrer for 30 minutes. The slurry was then applied to a 20 μm thick copper current collector using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, and then dried again under vacuum at 120°C for 4 hours and rolled to produce the positive electrode.

[0196] Core-type electrode assembly: A core-type electrode assembly was fabricated by placing the diaphragm obtained according to the example and comparative example between the positive and negative electrodes fabricated above and winding it. After inserting the core into a bag and injecting electrolyte, the bag was vacuum-sealed. As the electrolyte, a mixture of 1.3 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:5:2 was used. The core inserted into the bag was pressed at 80°C for 3 minutes while applying 11.7 kgf / cm². 2 The pressure is to manufacture rechargeable lithium batteries.

[0197] Breathability (unit: sec / 100cc) The air permeability of the manufactured diaphragm was measured by measuring the time (in seconds) required for 100cc of air to pass through the diaphragm using a measuring device (EG01-55-1MR, Asahi Seiko).

[0198] Air permeability measurement device settings: Measured pressure: 0.5 kg / cm 2 Cylinder pressure: 2.5 kg / cm² 2 And set time: 10 seconds Electrolyte absorption rate (unit: wt%) The binder prepared above was dried in an oven at 120°C for 12 hours to obtain a membrane (thickness: 20 μm, weight W1 measured before impregnation). The membrane was placed in a manufactured bag and immersed in the electrolyte, and the bag was vacuum sealed. After placing the sealed bag in an oven at 60°C for 72 hours, the membrane was immediately removed and its weight W2 was measured. The electrolyte absorption rate was measured as W2 / W1×100.

[0199] Positive electrode adhesion force (unit: N) The separator was attached to the positive electrode (manufactured in the same manner as in battery manufacturing), inserted into a bag, and injected with electrolyte (1.3 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) in a volume ratio of 3 / 5 / 2). The bag was then left to stand for 12 hours. The assembly was then subjected to a temperature of 10 kgf / cm². 2 Up to 20 kgf / cm 2 Press the material under pressure and at a temperature of 70°C to 90°C for 5 to 20 seconds, then disassemble. After removing the diaphragm and positive electrode from the bag, unfold the positive electrode and diaphragm 180° and use a tensile testing machine (Tinius Olsen, HT400) to measure the force required to tear the positive electrode from the diaphragm.

[0200] Membrane resistance (unit: Ω) Membrane resistance was evaluated as electrochemical impedance spectroscopy (EIS) resistance. Each membrane fabricated in the example and comparative examples was impregnated with an electrolyte (1.5 M LiPF6 dissolved in a mixed solvent of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate in a volume ratio of 3 / 5 / 2), then mounted between aluminum foil electrodes with leaded terminals and sealed in an aluminum cask to fabricate a test cell. The resistance (Ω) of this test cell was measured at 20°C using AC impedance spectroscopy (measurement frequency: 100 kHz).

[0201] Capacity retention after 200 cycles (in %) Each of the batteries manufactured using the separators from the example and comparative examples was charged at a constant current at a rate of 0.5C at 25°C and 45°C until the voltage reached 4.2V, then cut off at a rate of 0.025C in constant voltage mode, and then discharged at a rate of 0.5C until the voltage reached 2.5V. This charge / discharge cycle was repeated 200 times, and the capacity retention rate, i.e., the lifetime characteristics, was evaluated based on the number of cycles. Thus, the results were obtained.

[0202] DC internal resistance (DC-IR) (unit: mΩ) Each of the 75mAh batteries manufactured using the separators from the example and comparative examples was charged at 25°C and 45°C with a constant current / constant voltage of 0.2C / 4.25V and a cutoff voltage of 0.05C. After resting for 10 minutes, each battery was discharged at a constant current of 0.33C and a cutoff voltage of 2.80V and rested for 10 minutes. After one charge / discharge cycle in the same manner as above, the DC internal resistance (DC-IR) was measured by measuring the voltage drop (V) that occurred while a 1C current was applied for 10 seconds at SOC50 (the state of being charged 50% relative to 100% (fully charged) battery capacity, or equivalently, discharged 50%).

[0203] The DC-IR change rate is the ratio of the DC-IR after 200 cycles to the initial DC-IR, expressed as a percentage.

[0204] Table 2:

[0205] Table 3:

[0206] As shown in Table 2 above, the first copolymer in the preparation examples exhibits low film resistance, which can improve battery capacity, safety, and lifespan. Additionally, the first copolymer has high adhesion to electrodes such as the positive electrode, thus improving reliability.

[0207] As shown in Table 3 above, polymers other than the first copolymer in the preparation example cannot achieve the effect of the first copolymer.

[0208] 2. Verification of the diaphragm Example 1 (1) Preparation of the first and third solutions Each of the first and third solutions was prepared by mixing the copolymer of Preparation Example 1 with dimethylacetamide as a solvent.

[0209] (2) Preparation of the second solution The second solution is prepared by mixing polyimide (PI) and dimethylacetamide as a solvent.

[0210] (3) Electrospinning and diaphragm manufacturing An electrospinning apparatus equipped with a first nozzle, a second nozzle, and a third nozzle positioned sequentially along the direction of movement of the substrate is prepared. A first solution, a second solution, and a third solution are injected into the first nozzle, the second nozzle, and the third nozzle, respectively.

[0211] While moving the substrate, the first solution, the second solution, and the third solution are electrospun sequentially from the first nozzle, the second nozzle, and the third nozzle and pressed, and then the substrate is removed, thereby producing a diaphragm.

[0212] The electrospinning process is performed as follows: An electrospinning solution is added to the tip of a nozzle assembly with a needle size of 25G, positioned 16 cm away from a collecting roller. Electrospinning is carried out at an internal space temperature of 22°C under a voltage of 40 kV to 75 kV. The collecting roller speed is set to 1 m / min to 3 m / min. Electrospinning is then performed under an airflow with an air pressure of 0.275 MPa. After electrospinning, the product is dried with hot air at 90°C.

[0213] Example 2 (1) Preparation of the first and third solutions Each of the first and third solutions was prepared by mixing 40 parts by weight of the copolymer of Preparation Example 1 and 60 parts by weight of polyimide with dimethylacetamide as a solvent.

[0214] (2) Preparation of the second solution The second solution is prepared by mixing polyimide and dimethylacetamide as a solvent.

[0215] (3) Electrospinning and diaphragm manufacturing The diaphragm is manufactured according to the method described in Example 1.

[0216] Example 3 (1) Preparation of the first and third solutions A solution for the core was prepared by mixing the copolymer of Preparation Example 1 with dimethylacetamide as a solvent. A solution for the shell was prepared by mixing polyimide with dimethylacetamide as a solvent.

[0217] (2) Preparation of the second solution The second solution is prepared by mixing polyimide and dimethylacetamide as a solvent.

[0218] (3) Electrospinning and diaphragm manufacturing The diaphragm is manufactured according to the method described in Example 1.

[0219] Example 4 (1) Preparation of the first and third solutions Each of the first and third solutions is prepared by mixing polyimide and dimethylacetamide as a solvent.

[0220] (2) Preparation of the second solution A solution for the core was prepared by mixing the copolymer of Preparation Example 1 with dimethylacetamide as a solvent. A solution for the shell was prepared by mixing polyimide with dimethylacetamide as a solvent.

[0221] (3) Electrospinning and diaphragm manufacturing The diaphragm is manufactured according to the method described in Example 1.

[0222] Example 5 (1) Preparation of the first and third solutions Each of the first and third solutions is prepared by mixing polyvinylidene fluoride and dimethylacetamide as a solvent.

[0223] (2) Preparation of the second solution The second solution was prepared by mixing the copolymer of Preparation Example 1 and the polyimide with dimethylacetamide as a solvent.

[0224] (3) Electrospinning and diaphragm manufacturing The diaphragm is manufactured according to the method described in Example 1.

[0225] Example 6 (1) Preparation of the first and third solutions Each of the first and third solutions is prepared by mixing polyvinylidene fluoride and dimethylacetamide as a solvent.

[0226] (2) Preparation of the second solution A solution for the core was prepared by mixing the copolymer of Preparation Example 1 with dimethylacetamide as a solvent. A solution for the shell was prepared by mixing polyimide with dimethylacetamide as a solvent.

[0227] (3) Electrospinning and diaphragm manufacturing The diaphragm is manufactured according to the method described in Example 1.

[0228] Comparison Example 1 A solution for electrospinning is prepared by mixing polyimide and dimethylacetamide as a solvent, and a diaphragm is manufactured by means of a fiber layer consisting only of a network of polyimide nanofibers, as described in Example 1.

[0229] Comparison Example 2 The membrane was manufactured in the same manner as in Example 2, except that the copolymer of Comparative Preparation Example 1 was used instead of the copolymer of Preparation Example 1.

[0230] Compare Example 3 The membrane was manufactured in the same manner as in Example 3, except that the copolymer of Comparative Preparation Example 1 was used instead of the copolymer of Preparation Example 1.

[0231] Compare Example 4 Except that polyethylene is used instead of polyimide, the diaphragm is manufactured in the same manner as in Example 1.

[0232] Compare Example 5 Except that a polyimide was used instead of the copolymer and polyimide mixture used in Example 1, the membrane was manufactured in the same manner as in Example 5.

[0233] The physical properties of the diaphragms manufactured in the example and comparative examples are evaluated below.

[0234] Thermal shrinkage rate in electrolytes (unit: %) The separators of the lithium secondary batteries used for the examples and comparative examples were cut into 8cm × 8cm dimensions to prepare samples. A 5cm × 5cm square was drawn on the surface of each sample.

[0235] A positive electrode slurry was prepared by mixing 97 wt% LiCoNiAl as the active material of the positive electrode, 1.5 wt% carbon nanotubes as the conductive material, and 1.5 wt% polyvinyl fluoride, and then adding water. The positive electrode was then manufactured by coating the prepared positive electrode slurry onto aluminum foil, drying, and rolling it.

[0236] A negative electrode active material slurry was prepared by mixing 97.4 wt% of a negative electrode active material, 1.0 wt% of carboxymethyl cellulose, 1.5 wt% of styrene-butadiene rubber, and 0.1 wt% of carbon nanotubes as a conductive material. A silicon-based negative electrode active material was used. The negative electrode was manufactured by coating the prepared negative electrode slurry onto copper foil and then drying and rolling it.

[0237] A sample was placed between the positive and negative electrodes to create three positive electrode-sample-negative electrode laminates, which were then placed in a bag. The laminates were completely filled with electrolyte by injecting 2g of electrolyte (containing 1.5M LiPF6 dissolved in ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate (volume ratio 30:50:20)), sealed, and then placed at 25°C for 12 hours. After placing the sample in an oven at 150°C for 1 hour, the sample was removed, and the dimensions of the sides of the stretched square were measured to calculate the shrinkage rate in each of the mechanical direction (MD) and transverse direction (TD). The shrinkage rate was calculated according to Equation 1 below.

[0238] Equation 1: Shrinkage rate = (L0-L1) / L0×100.

[0239] L0: Initial length of the diaphragm; L1: Length of the diaphragm after being placed at 150°C for 1 hour.

[0240] DC-IR (unit: mΩ) Each of the 75mAh batteries manufactured using the separators from the example and comparative examples was charged at 25°C and 45°C with a constant current / constant voltage of 0.2C / 4.25V and a cutoff voltage of 0.05C. After resting for 10 minutes, each battery was discharged with a constant current of 0.33C and a cutoff voltage of 2.80V and rested for 10 minutes. After one charge / discharge cycle in the same manner as above, the DC internal resistance (DC-IR) was measured by measuring the voltage drop (V) that occurred while a 1C current was applied for 10 seconds at SOC50 (the state of being charged 50% relative to 100% (fully charged) battery capacity, or equivalently, discharged 50%).

[0241] Table 4:

[0242]

[0243] As shown in Table 4 above, the example membrane does not have a porous substrate and can provide desired or improved heat resistance, low membrane resistance and high adhesion.

[0244] Although exemplary embodiments of the present disclosure have been described above, the present disclosure is not limited thereto, and various modifications may be made within the scope of the claims, the detailed description and the drawings, and these modifications are obviously also within the scope of the present disclosure.

Claims

1. A separator for a rechargeable lithium battery, the separator comprising: One or more fiber layers, Wherein, at least one of the one or more fiber layers comprises a fiber network of fibers, the fibers comprising a first copolymer, or At least one of the one or more fiber layers comprises a network of core-shell fibers, the core-shell fibers comprising a first copolymer. The first copolymer comprises a copolymer of monomer mixtures, the copolymer comprising: a first structural unit comprising a unit derived from an aromatic unsaturated monomer; a second structural unit derived from a (meth)acrylic acid monomer, wherein the (meth)acrylic acid monomer includes an alkyl group having four or more carbon atoms in the main chain in the ester moiety; and a third structural unit derived from a monomer containing a sulfonic acid group, and Relative to 100 mol% of the copolymer, the first structural unit, the second structural unit, and the third structural unit are included in the ranges of 5 mol% to 80 mol%, 10 mol% to 60 mol%, and 5 mol% to 80 mol%, respectively.

2. The diaphragm according to claim 1, wherein, The first copolymer includes a binder.

3. The diaphragm according to claim 1, wherein, The first copolymer has a glass transition temperature in the range of 60°C to 80°C.

4. The diaphragm according to claim 1, wherein, The total content of the first structural unit, the second structural unit, and the third structural unit in the copolymer is 95 mol% or greater.

5. The diaphragm according to claim 1, wherein, The unit derived from the aromatic unsaturated monomer is represented by chemical formula 1. Chemical Formula 1: ； In chemical formula 1, R 1 and R 2 Each independently comprises hydrogen or substituted or unsubstituted C1 to C5 alkyl groups, and Ar includes substituted or unsubstituted monocyclic or polycyclic C6 to C20 aryl groups. The second structural unit is represented by chemical formula 4. Chemical formula 4: ； In chemical formula 4, R 7 and R 8 Each independently includes either hydrogen or methyl. L 2 Including substituted or unsubstituted straight-chain or branched C4 to C30 alkyl groups, and The third structural unit is represented by any one of chemical formulas 5, 6, and 7: Chemical formula 5: ； Chemical Formula 6: ； Chemical Formula 7: ； In chemical formulas 5 to 7 R 9 R 10 R 11 R 12 R 13 and R 14 Each independently includes hydrogen or C1 to C3 alkyl groups. L 3 L 5 and L 7 Each independently includes -C(=O)-, -C(=O)O-, -OC(=O)-, -O-, or -C(=O)NH-. L 4 L 6 and L 8 Each independently 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 all independent integers in the range of 0 to 2, and In chemical formula 6, M includes alkali metals.

6. The diaphragm according to claim 1, wherein, The first structural unit also includes a unit derived from a (meth)acrylic acid monomer, wherein the (meth)acrylic acid monomer contains an alkyl group having one to three carbon atoms in the main chain in the ester portion.

7. The diaphragm according to claim 6, wherein, The unit derived from the (meth)acrylic acid monomer is a unit represented by chemical formula 3: Chemical formula 3: ； In chemical formula 3, R 5 and R 6 Each independently includes either hydrogen or methyl. L 1 Includes substituted or unsubstituted straight-chain or branched C1 to C3 alkyl groups.

8. The diaphragm according to claim 1, wherein, The diaphragm includes a multilayer diaphragm comprising one or more fiber layers.

9. The diaphragm according to claim 8, wherein, The multilayer membrane includes one or more fiber layers, or two or more fiber layers, wherein the fiber layers include a fiber network comprising fibers of the first copolymer.

10. The diaphragm according to claim 9, wherein, The multilayer membrane further includes one or more fiber layers, or two or more fiber layers, wherein the fiber layers comprise a fiber network containing fibers of one or more types of second copolymers.

11. The diaphragm according to claim 8, wherein, The multilayer membrane comprises one or more fiber layers, or two or more fiber layers, the fiber layers containing a network of core-shell fibers, and the first copolymer is included in the core or shell of the core-shell fibers.

12. The diaphragm according to claim 11, wherein, The core-shell fiber also includes a second copolymer.

13. The diaphragm according to claim 11, wherein, The multilayer membrane further includes one or more of the following types: a fiber layer comprising a network of fibers containing the first copolymer; and a fiber layer comprising a network of fibers containing one or more types of a second copolymer.

14. The diaphragm according to claim 8, wherein, The multilayer membrane comprises one or more fiber layers, or two or more fiber layers, wherein the fiber layers comprise a network of fibers containing a mixture of the first copolymer and the second copolymer.

15. The diaphragm according to claim 14, wherein, The multilayer membrane further includes one or more of the following types: a fiber layer comprising a network of fibers containing the first copolymer; and a fiber layer comprising a network of fibers containing one or more types of a second copolymer.

16. The diaphragm according to claim 10, wherein, The second copolymer includes any one or more of polyacrylonitrile, polyaniline, polypyrrole, polyrhodanine, melamine, polyurea, polyvinyl chloride, polyvinyl alcohol, polyethylene oxide, polymethyl methacrylate, polyacrylic acid, polylactic acid, polyimide, polyamide-imide, polyarylamide, polybenzylimazole, polypropylene, resorcinol-formaldehyde resin, melamine-formaldehyde resin, asphalt, sucrose, glucose, cellulose, and polyvinylidene fluoride.

17. The diaphragm according to claim 1, wherein, The diaphragm does not have a porous substrate.

18. The diaphragm according to claim 1, wherein, The diaphragm has a thickness of 8 μm or less.

19. A rechargeable lithium battery, said rechargeable lithium battery comprising: Positive electrode; negative electrode; as well as The diaphragm according to claim 1 is located between the positive electrode and the negative electrode.

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