Lithium secondary battery separator and lithium secondary battery containing the same

Abstract

To provide a separator for lithium secondary batteries that embodies excellent safety when exposed to heat. [Solution] The present invention relates to a separator for lithium secondary batteries and a lithium secondary battery containing the same, wherein the separator for lithium secondary batteries comprises a porous substrate, a coating layer located on at least one surface of the porous substrate, and an adhesive layer located on one surface of the coating layer, the coating layer comprises a binder, a crosslinking agent, a crosslinking product of carboxyalkylcellulose or a salt thereof, and a filler, the binder comprises a (meth)acrylic binder comprising a first structural unit derived from (meth)acrylamide and a second structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof, the crosslinking agent comprises an aziridine crosslinking agent, and the adhesive layer comprises a (meth)acrylic adhesive binder.

Description

[Technical Field]

[0001] This invention relates to a separator for lithium secondary batteries and a lithium secondary battery containing the same. [Background technology]

[0002] This application claims priority and interest in Korean Patent Application No. 10-2024-0125491, filed with the Korean Intellectual Property Office on 13 September 2024, all of which are incorporated herein by reference.

[0003] In recent years, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries has been rapidly increasing. As a result, research and development to improve the performance of lithium-ion rechargeable batteries is being actively pursued.

[0004] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material capable of intercalation and deintercalation of lithium ions, and an electrolyte. It produces electrical energy through oxidation and reduction reactions that occur when lithium ions intercalate / deintercalate in the positive and negative electrodes.

[0005] Lithium secondary batteries may include a separator between the positive and negative electrodes. The separator is impregnated in the electrolyte. It is preferable for the separator to maintain its original shape without thermal shrinkage in the electrolyte to ensure the safety of the battery. [Overview of the project] [Problems that the invention aims to solve]

[0006] One example is providing a separator for lithium secondary batteries that embodies a battery with excellent safety when exposed to heat.

[0007] Another embodiment is to provide a lithium secondary battery including the aforementioned lithium secondary battery separator.

[0008] According to one example, a separator for lithium secondary batteries is provided.

[0009] The lithium secondary battery separator comprises a porous substrate, a coating layer located on at least one surface of the porous substrate, and an adhesive layer located on one surface of the coating layer. The coating layer comprises a binder, a crosslinking agent, a crosslinking product of carboxyalkylcellulose or a salt thereof, and a filler. The binder comprises a (meth)acrylic binder comprising a first structural unit derived from (meth)acrylamide and a second structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof. The crosslinking agent comprises an aziridine crosslinking agent. The adhesive layer comprises a (meth)acrylic adhesive binder.

[0010] In another embodiment, a lithium secondary battery is provided.

[0011] The lithium secondary battery includes a positive electrode, a negative electrode, and a lithium secondary battery separator located between the positive electrode and the negative electrode.

[0012] A lithium secondary battery separator based on one embodiment can enhance battery reliability by realizing a battery with superior safety in terms of thermal exposure. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view showing a lithium secondary battery separator based on one actual example. [Figure 2] This is a conceptual diagram of an electrode assembly consisting of an anode, cathode, and separator according to one embodiment. [Figure 3] This is a schematic cross-sectional view showing a lithium secondary battery as an example. [Figure 4] This is a schematic cross-sectional view showing a lithium secondary battery as an example. [Figure 5]This is a schematic cross-sectional view showing a lithium secondary battery as an example. [Figure 6] This is a schematic cross-sectional view showing a lithium secondary battery as an example. [Figure 7] This is a conceptual diagram of the cross-section of a jelly roll used for dry bending strength measurement. [Figure 8] This is a conceptual diagram of a three-point bending test used for measuring dry bending strength. [Figure 9] This is a conceptual diagram of the heated tip test. [Modes for carrying out the invention]

[0014] The following describes in detail some examples of the present invention. However, these are presented as examples only and do not limit the present invention; the present invention is defined solely by the scope of the claims described below.

[0015] Unless otherwise specified in this specification, when a part such as a layer, film, region, or plate is said to be "on top of" another part, this includes not only the case where it is "directly on top of" the other part, but also the case where there are other parts in between them.

[0016] Unless otherwise specified in this specification, singular nouns may also include plural nouns. Furthermore, unless otherwise specified, "A or B" may mean "including A, including B, or including both A and B."

[0017] In this specification, “combinations thereof” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0018] As used herein, "particle size D100" means the particle size representing the diameter of particles with a cumulative volume of 100% in the particle size distribution. The particle size distribution may be measured by methods widely known to those skilled in the art. For example, the particle size distribution may be measured using a particle size distribution meter or by measuring a transmission electron microscope photograph or a scanning electron microscope photograph. As another method, it may be measured using a measuring device employing the dynamic light scattering method, followed by data analysis to count the number of particles for each particle size range, and then calculating to obtain the D100 value. Alternatively, it may be measured using the laser diffraction method. When measuring by the laser diffraction method, more specifically, after dispersing the particles to be measured in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., MT 3000 of Microtrac), irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then the average particle size D100 at the 100% standard of the particle size distribution in the measuring device may be calculated.

[0019] As used herein, "particle size D50" means the particle size representing the diameter of particles with a cumulative volume of 50% in the particle size distribution. The particle size distribution is measured by the method described for "particle size D100".

[0020] As used herein, "(meth)acryl" means acrylic and / or methacrylic.

[0021] Hereinafter, unless otherwise defined, "substituted" means that hydrogen in a compound is a C1-C 30 alkyl group, C2-C 30 alkenyl group, C2-C 30 alkynyl group, C6-C 30 aryl group, C7-C 30 alkylaryl group, C1-C 30 alkoxy group, C1-C 30 heteroalkyl group, C3-C 30 heteroalkylallyl group, C3-C 30 cycloalkyl group, C3-C 15 cycloalkenyl group, C6-C 30 cycloalkynyl group, C2-C 30Heterocycloalkyl groups, halogens (F, Cl, Br, or I), hydroxyl groups (-OH), nitro groups (-NO2), cyano groups (-CN), amino groups (-NRR') (where R and R' are independently hydrogen or C1-C6 alkyl groups), sulfobetaine groups (-RR'N+(CH2)) n SO3 - (where n is a natural number from 1 to 10), carboxybetaine group (-RR'N + (CH2) n COO - (where n is a natural number from 1 to 10) (where R and R' are independently C1-C20 alkyl groups), azide group (-N3), amidino group (-C(=NH)NH2), hydrazino group (-NHNH2), hydrazono group (=N(NH2)), carbamoyl group (-C(O)NH2), thiol group (-SH), acyl group (-C(=O)R, where R is hydrogen, a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C 12 This means that the molecule is substituted with substituents selected from an aryl group, a carboxyl group (-COOH) or its salt (-C(=O)OM, where M is an organic or inorganic cation), a sulfonic acid group (-SO3H) or its salt (-SO3M, where M is an organic or inorganic cation), a phosphonic acid group (-PO3H2) or its salt (-PO3MH or -PO3M2, where M is an organic or inorganic cation), and combinations thereof.

[0022] Hereinafter, C1-C3 alkyl groups refer to methyl, ethyl, or propyl groups. 10 The alkylene group may be, for example, a C1-C6 alkylene group, a C1-C5 alkylene group, or a C1-C3 alkylene group, or it may be a methylene group, an ethylene group, or a propylene group. 20 Cycloalkylene groups are, for example, C3-C 10 Cycloalkylene group, or C5~C 10 It may be an alkylene group, for example, a cyclohexylene group. C6~C 20 The allylene group is, for example, C6~C 10It may be an allylene group, for example, a phenylene group. C3~C 20 A heterocyclic group is, for example, C3~C 10 It may be a heterocyclic group, for example, a pyridine group.

[0023] Hereinafter, "hetero" means containing at least one heteroatom selected from N, O, S, Si, and P.

[0024] Furthermore, in chemical formulas, * represents a portion linked to the same or different atoms, groups, or structural units. In the chemical formulas described herein, unless otherwise specified, hydrogen can be considered to be bonded in the structure of the chemical formula.

[0025] Hereinafter, "alkali metals" refers to elements belonging to Group 1 of the periodic table, such as lithium, sodium, potassium, rubidium, cesium, or francium, and may exist in a cationic or neutral state.

[0026] In this specification, when numerical ranges are described, "X to Y" means "X or greater and Y or less (X ≤ and ≤ Y)."

[0027] A separator for a lithium secondary battery according to one embodiment includes a porous substrate, a coating layer located on at least one surface of the porous substrate, and an adhesive layer located on one surface of the coating layer. The coating layer includes a binder, a crosslinking agent, a crosslinking product of carboxyalkylcellulose or a salt thereof, and a filler. The binder includes a (meth)acrylic binder comprising a first structural unit derived from (meth)acrylamide and a second structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof. The crosslinking agent includes an aziridine crosslinking agent. The adhesive layer includes a (meth)acrylic adhesive binder.

[0028] According to one example, the coating layer may be formed from a coating layer composition comprising a (meth)acrylic binder, an aziridine crosslinking agent, carboxyalkyl cellulose or a salt thereof, and a filler.

[0029] According to one example, the crosslinking product may be a thermal crosslinking product.

[0030] The separator, by including a coating layer and an adhesive layer sequentially arranged on a porous substrate, can provide excellent safety in the event of thermal exposure of the battery. In this regard, the separator can provide excellent safety in the event of thermal exposure of the battery by providing a low dry shrinkage rate, a low electrolyte shrinkage rate, high bonding strength between the porous substrate and the coating layer, and high dry bending strength to the electrode plate. The excellent safety of the battery in the event of thermal exposure can be confirmed by the electrolyte shrinkage rate and a heated tip test.

[0031] According to one example, the dry shrinkage rate of the separator is 5% or less in both the MD (longitudinal direction) and TD (transverse direction), and the shrinkage rate in the electrolyte may be 15% or less in both the MD and TD directions, for example, 10% or less and 5% or less. Here, "MD" and "TD" are the same directions as the MD and TD of the porous substrate, respectively.

[0032] According to one example, the bonding strength of the coating layer to the porous substrate of the separator may be 1.8 N or more.

[0033] According to one example, the separator may have a dry bending strength of 95N or more relative to the electrode plate. This dry bending strength may be advantageous for the stacked electrode assembly described below.

[0034] Separators having only a coating layer on a porous substrate without an adhesive layer may not provide excellent safety in the event of thermal exposure of the battery. Separators in which the coating layer and adhesive layer are not formed sequentially on the porous substrate, and where the adhesive binder is contained within the coating layer, may also not provide excellent safety in the event of thermal exposure of the battery.

[0035] Separators having a coating layer formed from a coating layer composition that contains a (meth)acrylic binder but does not contain an aziridine crosslinking agent, or contains a crosslinking agent other than an aziridine crosslinking agent, may have difficulty providing excellent safety in the case of thermal exposure of the battery as described above.

[0036] According to one example, the aziridine crosslinking agent may be present in an amount of 95% by weight or more of the total crosslinking agent in the coating layer composition, for example, 98-100% by weight or 100% by weight.

[0037] A separator having a coating layer formed from a coating layer composition containing an aziridine crosslinking agent and a filler, but not containing a (meth)acrylic binder, or containing a binder other than a (meth)acrylic binder, may not be able to reach the range of dry shrinkage and electrolyte shrinkage. In one example, the (meth)acrylic binder may be included in the coating layer composition in an amount of 95% by weight or more of the total binder, for example, 98-100% by weight or 100% by weight.

[0038] Separators having a coating layer formed from a coating layer composition that does not contain carboxyalkylcellulose or its salts may have difficulty providing excellent safety in the event of thermal exposure of the battery.

[0039] coating layer The coating layer is a heat-resistant layer, and the binder contains a (meth)acrylic binder comprising a first structural unit derived from (meth)acrylamide and a second structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0040] According to one example, the total amount of the first and second structural units may be 95 mol% or more, for example, 95-100 mol% or 100 mol%, per 100 mol% of the (meth)acrylic binder.

[0041] The (meth)acrylic binder may further contain a third structural unit derived from (meth)acrylic acid or (meth)acrylate.

[0042] According to one example, the total amount of the first structural unit, the second structural unit, and the third structural unit may be 95 mol% or more, for example, 95-100 mol% or 100 mol%, per 100 mol% of the (meth)acrylic binder.

[0043] (Meth)acrylic binders are water-based heat-resistant binders that can fix fillers onto porous substrates and provide adhesive strength so that the coating layer adheres well to the porous substrate and electrodes, thereby contributing to improved heat resistance, breathability, and oxidation resistance of separators.

[0044] The first structural unit derived from (meth)acrylamide has an amide functional group (-(C=O)-NH2) within the structural unit. The (-(C=O)-NH2) functional group can improve adhesion properties with porous substrates and electrodes, and by forming hydrogen bonds with the -OH functional group of the filler, inorganic particles can be more firmly fixed within the coating layer, thereby enhancing the heat resistance of the separator.

[0045] The second structural unit, derived from (meth)acrylamide sulfonic acid or a salt thereof, can enhance the heat resistance of the separator by reducing the mobility of the binder containing it through the presence of bulky functional groups.

[0046] The third structural unit derived from (meth)acrylic acid or (meth)acrylate plays a role in fixing the filler onto the porous substrate and can provide adhesive strength so that the coating layer adheres well to the porous substrate and electrodes, thereby contributing to improved heat resistance and air permeability of the separator. Furthermore, the structural unit derived from (meth)acrylic acid or (meth)acrylate may contribute to improved dispersibility of the coating layer composition by containing a carboxyl functional group (-C(=O)O-) within the structural unit.

[0047] The first structural unit is present in an amount of 55 mol% to 95 mol% per 100 mol% of the (meth)acrylic binder, and may be present in amounts such as 70 mol% to 95 mol%, 75 mol% to 95 mol%, 80 mol% to 95 mol%, or 80 mol% to 90 mol%.

[0048] The total amount of the second and third structural units may be 5 mol% to 45 mol%, for example, 5 mol% to 30 mol%, 5 mol% to 25 mol%, 5 mol% to 20 mol%, or 10 to 20 mol%, relative to 100 mol% of the (meth)acrylic binder.

[0049] The second structural unit may be present in an amount of 0.1 to 45 mol%, for example, 5 to 45 mol%, 0.1 to 30 mol%, 0.1 to 20 mol%, for example, 0.1 to 10 mol%, or 1 to 10 mol%, relative to 100 mol% of the (meth)acrylic binder.

[0050] The third structural unit may be present in amounts of 0 to 30 mol%, 1 to 30 mol%, for example, 1 to 20 mol%, 1 to 10 mol%, 5 to 15 mol%, or 5 to 20 mol%, relative to 100 mol% of the (meth)acrylic binder.

[0051] When the content of each structural unit is within the aforementioned range, the heat resistance and adhesive strength of the separator can be further improved.

[0052] The first structural unit derived from (meth)acrylamide is represented by chemical formula 1.

[0053] [ka]

[0054] (In the formula, R 1 , R 2 These are, independently, hydrogen or a methyl group.

[0055] The second structural unit derived from (meth)acrylamidesulfonic acid or a salt thereof may be a structural unit derived from (meth)acrylamidesulfonic acid or (meth)acrylamidesulfonate, where (meth)acrylamidesulfonate may be a conjugate base of (meth)acrylamidesulfonic acid, a (meth)acrylamidesulfonate salt, or a derivative thereof. The structural unit derived from (meth)acrylamidesulfonic acid or (meth)acrylamidesulfonate may be represented, for example, by any of chemical formulas 2, 3, 4, or combinations thereof.

[0056] [ka]

[0057] During the ceremony, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 These are, independently, hydrogen or methyl group, L 1 , L 2 , and L 3 These are C1-C, each independently of substitution or non-substitution. 10 Alkylene group, substituted or unsubstituted C3-C 20 Cycloalkylene group, substituted or unsubstituted C6-C 20 Allylene group, or substituted or unsubstituted C3-C 20 It is a heterocyclic group, a, b, and c are each independent integers between 0 and 2. M is an alkali metal, and the alkali metal may be, for example, lithium, sodium, potassium, rubidium, or cesium.

[0058] As an example, in chemical formulas 2-4, L 1 , L 2 , and L 3 These are C1-C, each independently of substitution or non-substitution. 10 It is an alkylene group, and a, b, and c may each be 1.

[0059] The structural units derived from (meth)acrylamide sulfonic acid or its salts may include, respectively, the structural units represented by chemical formula 2, the structural units represented by chemical formula 3, and the structural units represented by chemical formula 4, or may include all two or more of them. For example, it may include the structural unit represented by chemical formula 2, or, as another example, it may include both the structural unit represented by chemical formula 2 and the structural units represented by chemical formula 3.

[0060] When both structural units represented by chemical formula 2 and structural units represented by chemical formula 3 are included, the structural units represented by chemical formula 2 and structural units represented by chemical formula 3 may be included in a molar ratio of 10:1 to 1:2, preferably 5:1 to 1:1, and more preferably 3:1 to 1:1.

[0061] The sulfonate group in the structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof may be a functional group derived from, for example, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, anethole sulfonic acid, acrylamide alkane sulfonic acid, sulfoalkyl (meth)acrylate, or a salt thereof. Here, the alkane is C1-C 20 Alkane, C1~C 10 It may be an alkane, or a C1-C6 alkane, and the alkyl is C1-C 20 Alkyl, C1-C 10The molecule may be alkyl or C1-C6 alkyl. "Salt" refers to a salt composed of the aforementioned sulfonic acid and an appropriate ion. The ion may be, for example, an alkali metal ion; in this case, the salt may be an alkali metal salt of the sulfonic acid.

[0062] The acrylamide alkanesulfonic acid may also be, for example, 2-acrylamido-2-methylpropanesulfonic acid.

[0063] The third structural unit derived from (meth)acrylic acid or (meth)acrylate is represented by one of the following chemical formulas: 5, 6, 7, or any combination thereof.

[0064] [ka]

[0065] During the ceremony, R 3 , R 4 , R 6 , R 7 , R 8 and R 9 These are, independently, hydrogen or methyl group, R 5 C1-C are either substituted or non-substituted. 20 It is an alkyl group, M is an alkali metal.

[0066] The structural units derived from the (meth)acrylate may be derived from alkyl (meth)acrylates, perfluoroalkyl (meth)acrylates, and (meth)acrylates having functional groups in their side chains, for example, from alkyl (meth)acrylates. Furthermore, the number of carbon atoms in the alkyl group or perfluoroalkyl group bonded to the non-carbonyl oxygen atom of the alkyl (meth)acrylate or perfluoroalkyl (meth)acrylate may be specifically 1 to 20, more specifically 1 to 10, for example, 1 to 5.

[0067] Specific examples of alkyl (meth)acrylate esters in which the alkyl group or perfluoroalkyl group bonded to a non-carbonyl oxygen atom has 1 to 5 carbon atoms include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate and t-butyl acrylate; 2-(perfluoroalkyl)ethyl acrylate such as 2-(perfluorobutyl)ethyl acrylate and 2-(perfluoropentyl)ethyl acrylate; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate and t-butyl methacrylate; and 2-(perfluoroalkyl)ethyl methacrylate such as 2-(perfluorobutyl)ethyl methacrylate, 2-(perfluoropentyl)ethyl methacrylate and 2-(perfluoroalkyl)ethyl methacrylate.

[0068] Other alkyl (meth)acrylates include: Alkyl acrylates having 6 to 18 carbon atoms in the alkyl group bonded to the non-carbonyl oxygen atom, such as n-hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate, cyclohexyl acrylate, and isobonyl acrylate; Alkyl methacrylates having 6 to 18 carbon atoms in the alkyl group bonded to a non-carbonyl oxygen atom, such as n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate, and cyclohexyl methacrylate; 2-(perfluoroalkyl)ethyl acrylates, such as 2-(perfluorohexyl)ethyl acrylate, 2-(perfluorooctyl)ethyl acrylate, 2-(perfluorononyl)ethyl acrylate, 2-(perfluorodecyl)ethyl acrylate, 2-(perfluorododecyl)ethyl acrylate, 2-(perfluorotetradecyl)ethyl acrylate, and 2-(perfluorohexadecyl)ethyl acrylate, in which the perfluoroalkyl group bonded to the non-carbonyl oxygen atom has 6 to 18 carbon atoms; 2-(perfluoroalkyl)ethyl methacrylate, such as 2-(perfluorohexyl)ethyl methacrylate, 2-(perfluorooctyl)ethyl methacrylate, 2-(perfluorononyl)ethyl methacrylate, 2-(perfluorodecyl)ethyl methacrylate, 2-(perfluorododecyl)ethyl methacrylate, 2-(perfluorotetradecyl)ethyl methacrylate, and 2-(perfluorohexadecyl)ethyl methacrylate, which have 6 to 18 carbon atoms in the perfluoroalkyl group bonded to the non-carbonyl oxygen atom. These are some examples.

[0069] The structural units derived from (meth)acrylic acid or (meth)acrylate or its salts may include, respectively, the structural units represented by chemical formula 5, the structural units represented by chemical formula 6, and the structural units represented by chemical formula 7, or all of them. If all of them are included, the total molar ratio of the structural units represented by chemical formula 5 to the structural units represented by chemical formula 6 and chemical formula 7 may be 10:1 to 1:1, preferably 6:1 to 1:1, and more preferably 3:1 to 1:1.

[0070] (Meth)acrylic binders are represented, for example, by chemical formula 8.

[0071] [ka]

[0072] During the ceremony, R 1 , R2 , R 12 , R 13 , R 16 , R 17 are each independently hydrogen or a methyl group, R 18 is OR or O - M + where R is hydrogen or a C1-C6 alkyl group, and M is an alkali metal, L 2 is a substituted or unsubstituted C1-C 10 alkylene group, a substituted or unsubstituted C3-C 20 cycloalkylene group, a substituted or unsubstituted C6-C 20 arylene group, or a substituted or unsubstituted C3-C 20 heterocyclic group, b is an integer from 0 to 2, M is an alkali metal, l, m, and n represent the molar ratios of each unit.

[0073] The alkali metal may be lithium, sodium, potassium, rubidium, cesium, etc.

[0074] As an example, in Chemical Formula 8, l + m + n may be 1. Also, as an example, 0.05 ≤ (l + n) ≤ 0.45 and 0.55 ≤ m ≤ 0.95 may be satisfied. Specifically, 0 < l ≤ 0.4 and 0 < n ≤ 0.1 may also be satisfied. For example, 0.8 ≤ m ≤ 0.9, 0 < l ≤ 0.1, and 0 < n ≤ 0.1, or for example, 0.8 ≤ m ≤ 0.9, 0.01 ≤ l ≤ 0.1, and 0.01 ≤ n ≤ 0.1 may be satisfied.

[0075] As an example, in Chemical Formula 8, L 2 is a substituted or unsubstituted C1-C 10 alkylene group, and b may be 1.

[0076] In the (meth)acrylic binder, the alkali metal (M +The structural units substituted with (meth)acrylamidesulfonic acid may be present in amounts of 50 to 100 mol%, for example, 60 to 90 mol%, or 70 to 90 mol%, relative to 100 mol% of the total amount of (meth)acrylamidesulfonic acid structural units. When the above range is met, the (meth)acrylic binder and the separator containing it can exhibit excellent adhesive strength, heat resistance, and oxidation resistance.

[0077] (Meth)acrylic binders may further contain other units in addition to those described above. For example, (meth)acrylic binders may further contain units derived from alkyl (meth)acrylates, units derived from dienes, units derived from styrenes, ester group-containing units, carbonate group-containing units, or combinations thereof.

[0078] The (meth)acrylic binder may take various forms, such as an alternating polymer in which the aforementioned structural units are distributed alternately, a random polymer in which they are distributed arbitrarily, or a graft polymer in which some structural units are grafted.

[0079] The weight-average molecular weight of the (meth)acrylic binder may be between 350,000 and 970,000, for example, between 450,000 and 970,000, or between 450,000 and 700,000. When the weight-average molecular weight of the (meth)acrylic binder satisfies the above range, the (meth)acrylic binder and the separator containing it may exhibit excellent adhesion, heat resistance, and air permeability. The "weight-average molecular weight" may also be the average molecular weight on a polystyrene basis, measured using gel permeation chromatography.

[0080] (Meth)acrylic binders may be produced by a variety of known methods, such as emulsion polymerization, suspension polymerization, bulk polymerization, solution polymerization, or bulk polymerization.

[0081] (Meth)acrylic binders may be manufactured by solution polymerization.

[0082] According to one example, the (meth)acrylic binder may be included in the coating layer of the separator in film form.

[0083] The (meth)acrylic binder is 30 to 70% by weight of the total of the (meth)acrylic binder, crosslinking agent, and carboxyalkylcellulose or its salt (e.g., 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%) It may be included in amounts of 1%, 47% by weight, 48% by weight, 49% by weight, 50% by weight, 51% by weight, 52% by weight, 53% by weight, 54% by weight, 55% by weight, 56% by weight, 57% by weight, 58% by weight, 59% by weight, 60% by weight, 61% by weight, 62% by weight, 63% by weight, 64% by weight, 65% by weight, 66% by weight, 67% by weight, 68% by weight, 69% by weight, 70% by weight), 30-60% by weight, and 40-60% by weight. Within the above ranges, an effect of improving the heat resistance properties of the electrolyte may be observed.

[0084] The crosslinking agent includes aziridine-based crosslinking agents.

[0085] Aziridine-based crosslinking agents can crosslink (meth)acrylic binders and facilitate the separator reaching its dry shrinkage rate and shrinkage rate range within the electrolyte.

[0086] The aziridine crosslinking agent may be a bifunctional or trifunctional aziridine crosslinking agent. Here, "bifunctional or trifunctional" means that there are two or more aziridine groups in the molecule. For example, the aziridine crosslinking agent may be a bifunctional or trifunctional aziridine crosslinking agent.

[0087] For example, the aziridine crosslinking agent may contain one or more of the following: N,N'-toluene-2,4-bis(1-aziridinecarboxamide), N,N'-(methylenedi-p-phenylene)bis(aziridine-1-carboxamide), triethylenemelamine, 1,1-isophthaloylbis(2-methylaziridine), tris(1-aziridinyl)phosphine oxide, N,N-hexamethylene-bis(aziridinecarboxamide), trimethylolpropane tris(2-methyl-1-aziridinepropionate), trimethylolpropane tris(β-N-aziridinyl)propionate, and pentaerythritol tris(3-(1-aziridinyl)propionate.

[0088] The crosslinking agent, for example, an aziridine crosslinking agent, must be present in an appropriate amount relative to the binder, for example, a (meth)acrylic binder and carboxyalkylcellulose or a salt thereof.

[0089] According to one example, the crosslinking agent may be present in amounts of 5 to 30% by weight (for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%), 10 to 30%, or 10 to 20% by weight of the total of the (meth)acrylic binder, the crosslinking agent, and carboxyalkylcellulose or its salts. Within this range, an effect of improving the heat resistance in the electrolyte may be observed.

[0090] The crosslinking agent, for example, an aziridine-based crosslinking agent, must be included in an appropriate amount per 100 parts by weight of the binder, for example, a (meth)acrylic binder. For example, the crosslinking agent should be 5 to 50 parts by weight (for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27) per 100 parts by weight of the (meth)acrylic binder. It may also be included in amounts of parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 37 parts by weight, 38 parts by weight, 39 parts by weight, 40 parts by weight, 41 parts by weight, 42 parts by weight, 43 parts by weight, 44 parts by weight, 45 parts by weight, 46 parts by weight, 47 parts by weight, 48 parts by weight, 49 parts by weight, 50 parts by weight), 10 to 50 parts by weight, or 10 to 40 parts by weight. The heat resistance effect may be improved within the above ranges.

[0091] Carboxyalkylcellulose or its salts have a cyclic structure within the molecule and contain carboxyl groups. The carboxyl groups can react with crosslinking agents, which readily increase the modulus of the coating layer and further reduce dry shrinkage and shrinkage in the electrolyte.

[0092] Carboxyalkylcellulose may also be, for example, carboxymethylcellulose.

[0093] A salt of carboxyalkylcellulose is a salt of carboxyalkylcellulose, and may be, for example, a monovalent metal salt of carboxyalkylcellulose, such as a sodium carboxyalkylcellulose salt.

[0094] Carboxyalkylcellulose or its salts must be present in an appropriate amount relative to the binder, such as a (meth)acrylic binder or crosslinking agent.

[0095] According to one example, carboxyalkylcellulose or its salts make up 20-70% by weight (for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%) of the total amount of the (meth)acrylic binder, crosslinking agent, and carboxyalkylcellulose or its salts. It may be included in amounts of 43% by weight, 44% by weight, 45% by weight, 46% by weight, 47% by weight, 48% by weight, 49% by weight, 50% by weight, 51% by weight, 52% by weight, 53% by weight, 54% by weight, 55% by weight, 56% by weight, 57% by weight, 58% by weight, 59% by weight, 60% by weight, 61% by weight, 62% by weight, 63% by weight, 64% by weight, 65% by weight, 66% by weight, 67% by weight, 68% by weight, 69% by weight, 70% by weight), 20-65% by weight, 20-60% by weight, 30-70% by weight, 30-60% by weight, and 40-60% by weight. Within the above ranges, there may be an effect of improving the heat resistance properties in the electrolyte.

[0096] The filler may include fillers with a particle size D100 of 0.7 μm or less. Within this range, when combined with a (meth)acrylic binder, a crosslinking agent, and carboxyalkylcellulose or a salt thereof, it is easier to achieve the dry shrinkage rate and the shrinkage rate in the electrolyte. For example, the filler may have a particle size D100 of 0.01 μm, 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.1 to 0.7 μm, or 0.5 to 0.7 μm.

[0097] According to one example, the filler may have a particle size D50 of 0.4 μm or less, for example, 0.35 μm or less, 0.3 μm or less, or 0.1 to 0.3 μm. Within this range, an improvement in heat resistance properties may be achieved.

[0098] According to one example, fillers with a particle size D100 of 0.7 μm or less may be present in the coating layer at a concentration of 95% by weight or more of the total fillers, for example, 95-100% by weight, 98-100% by weight, or 100% by weight. Within this range, the effects of the separator in this case can be easily realized.

[0099] According to one example, the filler does not undergo surface modification.

[0100] The filler may be, for example, an inorganic filler, an organic filler, an organic / inorganic composite filler, or a combination thereof. The inorganic filler may be a ceramic material that can improve heat resistance. The inorganic filler may include, for example, metal oxides, metalloid oxides, metal fluorides, metal hydroxides, or a combination thereof. The inorganic filler may include, but is not limited to, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof. The organic filler may include, but is not limited to, an acrylic compound, an imide compound, an amide compound, or a combination thereof. The organic filler may have, but is not limited to, a core-shell structure. For example, the filler is preferably boehmite.

[0101] The filler may be spherical, plate-shaped, cubic, or amorphous. Preferably, the filler may be cubic, as the cubic shape significantly reduces the shrinkage rate mentioned above.

[0102] The filler must be present in an appropriate amount relative to the binder, such as a (meth)acrylic binder. In one example, the mass ratio of (meth)acrylic binder to filler may be 1:10 to 1:50, for example, 1:20 to 1:30. Within this range, an improvement in the heat resistance properties of the electrolyte may be achieved.

[0103] The filler may be included in an amount of 50% to 99% by weight of the total amount of the coating layer, for example, 70% to 99% by weight, for example, 75% to 99% by weight, for example, 80% to 99% by weight, for example, 85% to 99% by weight, for example, 90% to 99% by weight, for example, 95% to 99% by weight. When the filler is included in the above range, excellent heat resistance, durability, oxidation resistance, and stability can be observed.

[0104] Each coating layer may have a thickness of 0.01 μm to 20 μm, and within that range, it may have a thickness of 1 μm to 10 μm, 1 μm to 5 μm, or 1 μm to 3 μm.

[0105] The ratio of the thickness of the coating layer to the thickness of the porous substrate may be 0.05 to 0.5, for example, 0.05 to 0.4, 0.05 to 0.3, or 0.1 to 0.2. Within this range, the separator can exhibit excellent breathability, heat resistance, and adhesive strength. Here, "thickness of the coating layer" means the thickness of one coating layer if the coating layer is formed on only one surface of the porous substrate, or the total thickness of two coating layers if the coating layers are formed on both surfaces of the porous substrate.

[0106] adhesive layer The adhesive layer contains a crosslinked (meth)acrylic adhesive binder. The crosslinked (meth)acrylic adhesive binder can further reduce the shrinkage rate of the separator by lowering the moisture content, which can provide superior safety in the event of thermal exposure of the battery.

[0107] Crosslinked (meth)acrylic adhesive binders, through high crosslinking, can improve heat resistance and suppress shrinkage of porous substrates at high temperatures. In one example, the adhesive binder may include acrylate compounds or their derivatives, diallyl phthalate compounds or their derivatives, polyimide compounds or their derivatives, polyurethane compounds or their derivatives.

[0108] For example, the crosslinked (meth)acrylic adhesive binder may be crosslinked polymethyl methacrylate particles. The crosslinked (meth)acrylic adhesive binder may be manufactured by conventional methods known to those skilled in the art. The crosslinked polymer filler may be manufactured by adding a crosslinking agent during the polymerization of monomers.

[0109] The crosslinked (meth)acrylic adhesive binder may have a particle size D50 of 0.7 μm or less, for example, 0.5 μm or less, or 0.2 to 0.7 μm. Within this range, a uniform thickness adhesive layer can be formed, reducing the thickness of the separator and providing excellent safety in the event of thermal exposure of the battery.

[0110] The adhesive binder is applied at a rate of 0.01 to 0.5 g / m² relative to the negative electrode surface, for example, the surface of the coating layer. 2 For example, 0.06~0.25 g / m 2 For example, 0.07~0.21 g / m 2 The coating may be applied with a loading amount. Within the range, it is easy to increase the dry bending strength of the separator.

[0111] porous substrate Porous substrates have numerous pores and may be substrates commonly used in electrochemical devices. Porous substrates may be polymer films formed from any polymer selected from the group consisting of polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or copolymers or mixtures of two or more of these polymers.

[0112] The porous substrate may be, for example, a polyolefin-based substrate containing polyolefin, and the polyolefin-based substrate has excellent shutdown function and can contribute to improving battery safety. The polyolefin-based substrate may be selected from, for example, a polyethylene single layer film, a polypropylene single layer film, a polyethylene / polypropylene double layer film, a polypropylene / polyethylene / polypropylene triple layer film, and a polyethylene / polypropylene / polyethylene triple layer film. Furthermore, the polyolefin resin may contain a non-olefin resin in addition to the olefin resin, or a copolymer of olefin and non-olefin monomer.

[0113] The porous substrate may have a thickness of 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, or 5 μm to 15 μm.

[0114] A lithium secondary battery separator based on one example can exhibit excellent air permeability, for example, 200 seconds / 100 cm. 3 Less than, for example, 190 seconds / 100cm 3 Below, or 180 seconds / 100cm 3 The following air permeability values ​​may be used: namely, 40 seconds / 100 cm per unit thickness. 3 • Less than 1 μm, e.g., 30 seconds / 100 cm 3 • Less than 1 μm, or 25 seconds / 100 cm 3 It may have an air permeability value of 1 μm or less. Here, air permeability is defined as 100 cm 3 This refers to the time (in seconds) it takes for air to pass through a unit thickness of the separator. The air permeability per unit thickness can be determined by measuring the air permeability for the entire thickness of the separator and then dividing by the thickness. The air permeability is measured using an air permeability measuring device (Asahi Seiko Co., Ltd., EG01-55-1MR) at 100 cm². 3 It is possible to measure the time (in seconds) it takes for air to pass through.

[0115] A separator for a secondary battery according to one embodiment may be formed by applying a coating layer-forming composition to one or both sides of a porous substrate, drying it, and then curing it. Curing may be carried out using a conventional method known to those skilled in the art.

[0116] Figure 1 is a cross-sectional view showing a separator for a lithium secondary battery according to one embodiment. Referring to Figure 1, the separator for a lithium secondary battery includes a porous substrate 1 and a laminate 2 of a coating layer 5 and an adhesive layer 7 located on both sides of the porous substrate 1. The laminate 2 may include a filler 3, a coating layer (carboxyalkylcellulose not shown) 5 containing a (meth)acrylic binder and a crosslinking product 4 of a crosslinking agent, and an adhesive layer 7 located on the heat-resistant layer 5 and containing an adhesive binder 6.

[0117] Lithium-ion battery Another embodiment provides a lithium secondary battery including a separator, a positive electrode, and a negative electrode according to one embodiment. The separator for the lithium secondary battery is as described above. The separator for the lithium secondary battery may be located between the positive electrode and the negative electrode.

[0118] A positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material and further include a binder and / or a conductive material. As an example, the positive electrode may further include an additive that can act as a sacrificial positive electrode.

[0119] As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithified intercalation compound) may be used. Specifically, one or more composite oxides of lithium and metals selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0120] The composite oxide may be a lithium transition metal composite oxide. Specific examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0121] As an example, a compound represented by any of the following chemical formulas may be used. Li a A 1-b X b O 2-c D c [[ID=]](0.90≦a≦1.8,0≦b≦0.5,0≦c≦0.05);Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8,0≦b≦0.5,0≦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≦0.5,0<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≦0.5,0<α<2);Li a Ni b Co c L<​​​​​​​​​​​​​​​​​​​​​O4(0.90≦a≦1.8,0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8,0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4 (0.90 ≤ a ≤ 1.8).

[0122] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 This is Mn, Al, or a combination thereof.

[0123] As an example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium is 80 mol% to 99 mol%, 85 mol% to 99 mol%, 90 mol% to 99 mol%, 91 mol% to 99 mol%, or 94 mol% to 99 mol%. High-nickel positive electrode active materials can achieve high capacity and may be applied to high-capacity, high-density lithium secondary batteries.

[0124] The content of the positive electrode active material is 90% to 99.5% by weight, based on 100% by weight of the positive electrode active material layer, and the content of the binder and conductive material may be 0.5% to 5% by weight, each based on 100% by weight of the positive electrode active material layer.

[0125] The binder plays a role in ensuring that the positive electrode active material particles adhere well to each other, and further, that the positive electrode active material adheres well to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0126] Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not undergo chemical changes in the battery that makes up the battery can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0127] Al can be used as the current collector, but it is not limited to this.

[0128] The negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0129] For example, the negative electrode active material layer may contain 90% to 99% by weight of negative electrode active material, 0.5% to 5% by weight of binder, and 0% to 5% by weight of conductive material.

[0130] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0131] As the material capable of reversibly intercalating / deintercalating lithium ions, for example, a carbon-based negative electrode active material such as crystalline carbon, amorphous carbon, or a combination thereof may be included. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0132] As the alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn may be used.

[0133] As the material capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiO x (0 < x < 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0134] A silicon-carbon composite may be a composite of silicon and amorphous carbon. In one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coating on the surface of the silicon particles. For example, it may include secondary particles (core) formed by aggregates of primary silicon particles, and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles; for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0135] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of this core.

[0136] Si-based or Sn-based anode active materials may be used in combination with carbon-based anode active materials.

[0137] The binder plays a role in ensuring that the negative electrode active material particles adhere well to each other, and further, that the negative electrode active material adheres well to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0138] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0139] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, 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.

[0140] When using an aqueous binder as the negative electrode binder, it may further contain a cellulosic compound that can impart viscosity. This cellulosic compound may be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or their alkali metal salts. As the alkali metal, Na, K, or Li may be used.

[0141] The dry binder is a fibrous polymeric substance, which may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0142] Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not undergo chemical changes in the battery that makes up the battery can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0143] As the negative electrode current collector, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with a conductive metal, and combinations thereof may be used.

[0144] Lithium secondary batteries may also contain an electrolyte.

[0145] The electrolyte for lithium secondary batteries may also contain a non-aqueous organic solvent and a lithium salt.

[0146] Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reactions of batteries can move.

[0147] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0148] Examples of carbonate-based solvents that may be used include 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 butylene carbonate (BC).

[0149] Examples of ester solvents include methyl acetate, ethyl acetate, and n-propyl acetate. Dimethyl acetate Methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. may be used.

[0150] As ether-based solvents, dibutyl ether, tetraglyceride, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran may be used. As ketone-based solvents, cyclohexanone may be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol may be used. As aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double bond, aromatic ring, or ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes may be used.

[0151] Non-aqueous organic solvents may be used individually or in combination of two or more.

[0152] Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates may be mixed together, and the cyclic carbonates and linear carbonates may be mixed in a volume ratio of 1:1 to 1:9.

[0153] Lithium salts dissolve in organic solvents and act as a source of lithium ions within batteries, enabling the operation of basic lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical 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+1SO2) (where x and y are integers from 1 to 20), may contain one or more selected from lithium trifluoromethanesulfonate, lithium tetrafluoroethersulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB). According to one embodiment, a positive electrode, a negative electrode, and a separator can form a stacked electrode assembly. The stacked electrode assembly includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes, the separator having a continuous sheet-like structure, and the separator can be bent in a first direction to enclose the positive electrode and bent in a second direction opposite to the first direction to enclose the negative electrode. Figure 2 is a conceptual diagram of a stacked electrode assembly according to one embodiment. Referring to Figure 2, the stacked electrode assembly includes a positive electrode 110 having a positive terminal 111, a negative electrode 120 having a negative terminal 121, and a separator 130 located between the positive electrode 110 and the negative electrode 120. Referring to Figure 2, the separator 130 has a continuous sheet-like structure and is alternately folded in a first direction and a second direction opposite to it. Therefore, the vertical cross-section of the separator 130 in the stacked electrode assembly can have a zigzag shape.

[0154] Lithium secondary batteries may be classified into cylindrical, rectangular, pouch-shaped, coin-shaped, etc., depending on their form. Figures 3 to 6 are schematic diagrams showing a lithium secondary battery according to one embodiment, and Figure 3 may be cylindrical, Figure 4 rectangular, and Figures 5 and 6 pouch-shaped. Referring to Figures 3 to 6, the lithium secondary battery 100 may include an electrode assembly 40 with a separator 30 between the positive electrode 10 and the negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in Figure 3. Also, in Figure 4, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in Figures 5 and 6, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which function as electrical pathways for guiding the current formed in the electrode assembly 40 to the outside.

[0155] A lithium secondary battery according to one embodiment of the present invention may be applied to automobiles, mobile phones, and / or various forms of electrical devices, but the present invention is not limited thereto.

[0156] Examples and comparative examples of the present invention are described below. However, the following examples are merely one embodiment of the present invention, and the present invention is not limited to these examples.

[0157] Manufacturing Example 1 In a 10 L four-necked flask equipped with a stirrer, thermometer, and condenser, distilled water (6361 g), acrylic acid (72.06 g, 1.0 mol), acrylamide (604.1 g, 8.5 mol), potassium persulfate (2.7 g, 0.01 mol), 2-acrylamido-2-methylpropanesulfonic acid (103.6 g, 0.5 mol), and 5N lithium hydroxide aqueous solution (1.05 equivalents relative to the total amount of 2-acrylamido-2-methylpropanesulfonic acid) were added. Then, the internal pressure was reduced to 10 mmHg using a diaphragm pump, and the internal pressure was returned to atmospheric pressure with nitrogen. This process was repeated three times.

[0158] The reaction was carried out for 12 hours while controlling the temperature of the reaction mixture to remain stable between 65°C and 70°C. After cooling to room temperature, the pH of the reaction mixture was adjusted to 7-8 using a 25% aqueous ammonia solution.

[0159] Poly(acrylic acid-co-lithium acrylate-co-acrylamide-co-2-acrylamide-2-methylpropanesulfonate lithium salt) was produced using this method. The molar ratio of acrylic acid + lithium acrylate, acrylamide, and 2-acrylamide-2-methylpropanesulfonate lithium salt was 10:85:5. Approximately 10 mL of the reaction solution (reaction product) was taken and the non-volatile components were measured, which was found to be 9.5% (theoretical value: 10%).

[0160] Manufacturing Example 2 An acrylic binder was prepared using the same method as in Production Example 1, except that acrylamide and 2-acrylamide-2-methylpropanesulfonic acid were used, and acrylic acid was not used. The molar ratio of acrylamide to acrylamide-2-methylpropanesulfonic acid was 74:26. ​​The non-volatile component of the reaction solution was 9.0% by weight (theoretical value: 10%).

[0161] Example 1 The acrylic binder (10% by weight in distilled water) produced in Production Example 1 and boehmite (particle size D100: 0.5 μm, particle size D50: 0.2 μm, cubic shape) as filler were mixed in a mass ratio of acrylic binder:filler = 1:20 based on solid content. After adding the mixture to an aqueous solvent, the mixture was milled using a bead mill at 25°C for 30 minutes to disperse and produce a dispersion.

[0162] Trimethylolpropanetris (2-methyl-1-aziridinepropionate) (a trifunctional aziridine crosslinking agent) and carboxymethylcellulose (CMC) were added to the dispersion, and water was added to make a coating layer composition so that the total solids content was 20% by weight. At this time, the acrylic binder, carboxymethylcellulose, and aziridine crosslinking agent were present in a ratio of 45 parts by weight, 45 parts by weight, and 10 parts by weight out of a total of 100 parts by weight.

[0163] A porous substrate, a polyethylene film (thickness: 8 μm, manufactured by SK Corporation, air permeability: 120 sec / 100 cc, puncture strength: 480 kgf), was used as a substrate. Both sides were coated with the aforementioned coating layer-forming composition to a thickness of 1.5 μm using a die-coating method, and then dried and aged in an oven at 80°C for 16 hours to form the coating layer.

[0164] A cross-linked polymethyl methacrylate polymer (cross-linked PMMA, particle size D50: 0.5 μm), diluted to 2% by weight of solids, is coated to both sides of the coating layer in a 0.5 μm layer thickness. After drying at 50°C for 10 minutes, an adhesive layer with a total thickness of 1.0 μm is formed (loading amount per unit area on the electrode plate: 0.21 g / m²). 2 A separator for lithium secondary batteries was manufactured by forming ( ).

[0165] Examples 2 to 5 As shown in Table 1, the separator was manufactured in the same manner as in Example 1, except that the coating layer composition and the loading amount of the adhesive layer were changed.

[0166] Example 6 The separator was manufactured in the same manner as in Example 1, except that the binder from Manufacturing Example 2 was used instead of the acrylic binder from Manufacturing Example 1.

[0167] Comparative Examples 1 to 3 As shown in Table 1, the separator was manufactured in the same manner as in Example 1, except that the coating layer composition and the loading amount of the adhesive layer were changed.

[0168] Comparative Example 4 As shown in Table 1, the separator was manufactured in the same manner as in Example 1, except that the coating layer composition was changed and no adhesive layer was formed.

[0169] Comparative Example 5 In Production Example 1, an acrylic binder (10% by weight in distilled water) and boehmite (particle size D100: 0.5 μm, particle size D50: 0.2 μm, cubic shape) were mixed in a mass ratio of acrylic binder:filler = 1:20 based on solid content. The mixture was then added to an aqueous solvent and pulverized using a bead mill at 25°C for 30 minutes to produce a dispersion. Trimethylolpropanetris (2-methyl-1-aziridinepropionate) and carboxymethylcellulose (CMC) were added to the dispersion as aziridine crosslinking agents. Water was added to bring the total solid content to 20% by weight, and a crosslinked polymethyl methacrylate polymer (crosslinked PMMA, particle size D50: 0.5 μm) was added as an adhesive binder to produce a coating layer composition. At this time, the acrylic binder, carboxymethylcellulose, and aziridine crosslinking agent were included in a total of 45 parts by weight, 45 parts by weight, and 10 parts by weight out of a total of 100 parts by weight. At this time, the crosslinked polymethyl methacrylate polymer in the coating layer composition was 0.05 g / m² relative to the electrode plate surface. 2 It was included.

[0170] Polyethylene film as a porous substrate (thickness: 8 μm, SK Corporation, air permeability: 120 seconds / 100 cm) 3 A separator was manufactured by applying a coating layer-forming composition to both sides of a material with a puncture strength of 480 kgf using a die coating method, to a thickness of 1.5 μm, and then drying and aging it in an oven at 80°C for 16 hours to form the coating layer.

[0171] Dry shrinkage rate (in %) Prepare samples by cutting out lithium secondary battery separators of the examples and comparative examples to a size of 8 cm x 8 cm. After drawing a 5 cm x 5 cm rectangle on the surface of the sample, place it between sheets of paper or alumina powder and leave it in an oven at 150°C for 1 hour. Then, remove the sample and measure the dimensions of the sides of the drawn rectangle, and calculate the shrinkage rates in the mechanical direction (MD) and perpendicular direction (TD). The shrinkage rate is calculated using the following formula 1: Contraction rate = (L0 - L1) / L0 × 100 (Equation 1) (In the formula, L0 is the initial length of the separator, and L1 is the length of the separator after being left at 150°C for 1 hour.) It is calculated by [this method].

[0172] Contraction rate in electrolyte solution (unit: %) Prepare samples by cutting out lithium secondary battery separators from the examples and comparative examples to a size of 8 cm x 8 cm. Draw a rectangle measuring 5 cm x 5 cm on the surface of the sample.

[0173] A cathode slurry was prepared by mixing 97% by weight of LiCoNiAl as the cathode active material, 1.5% by weight of carbon nanotubes and 1.5% by weight of polyvinyl fluoride as conductive materials, and adding water. The prepared cathode slurry was applied to aluminum foil, dried, and rolled to produce a cathode.

[0174] A negative electrode active material slurry was prepared by mixing 97.4% by weight of negative electrode active material, 1.0% by weight of carboxymethylcellulose, 1.5% by weight of styrene-butadiene rubber, and 0.1% by weight of carbon nanotubes as a conductive agent. A silicon-based negative electrode active material was used as the negative electrode active material. The prepared negative electrode slurry was coated onto copper foil, dried, and rolled to produce a negative electrode.

[0175] One sample was placed between the positive and negative electrodes, and three sets of positive-sample-negative electrode laminates were prepared and placed in pouches. 2 g of electrolyte (ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (30:50:20 volume ratio) in which 1.5 M LiPF6 was dissolved) was injected to completely hydrate the laminates with the electrolyte, and after sealing, they were left at 25°C for 12 hours. Next, after leaving them in an oven at 150°C for 1 hour, the samples were removed, the dimensions of the sides of the drawn rectangles were measured, and the shrinkage rates in the longitudinal (MD) and transverse (TD) directions were calculated. The shrinkage rates were calculated using Equation 1.

[0176] Dry bending strength (unit: N) As shown in Figure 7, a jelly roll (D) was fabricated by layering the positive electrode (B), separator (A), negative electrode (C), and separation membrane (A) in a zigzag pattern. As shown in Figure 8, the layered jelly roll (D) was placed between an upper jig (E) and a lower jig (F), which had been preheated to 75°C using a heat press device, and then pressed for 90 seconds. After the heat press was completed, the jelly roll was linked to the Nexygen Plus program using a Lloyd UTM device, and a three-point bending test was performed. As shown in Figure 8, the jelly roll (D) was placed on the lower jig (F) located at the left and right ends, and then the upper jig (E) located in the middle was lowered at a specific speed to apply force, and the force (N) at which the jelly roll (D) broke was calculated.

[0177] Substrate bonding strength (unit: N) The tests were conducted according to Korean Industrial Standard KS-A-01107 (Test Method for Adhesive Tapes and Adhesive Sheets). Separators manufactured in the examples and comparative examples were cut to a width of 3 cm and a length of 8 cm, and tape (nitto 31B) was applied to both sides of each to prepare test specimens. The specimens were then compressed using a 2 kg load compression roller at a speed of 300 mm / min for one back-and-forth pass. After 30 minutes, the specimens were flipped over 180° and approximately 25 mm was peeled off. The separator and the tape applied to one side of the separator were then fixed to the upper clip of a tensile strength tester (Instron Series 1X / s Automated materials Tester-3343, Instron). After fixing the tape applied to the other side of the separator to the lower clip, the pressure at which the adhesive layer and coating layer of the separator peeled off from the porous substrate was measured by pulling at a tensile speed of 60 mm / min.

[0178] Hot-tip test (unit: mm) As shown in Figure 9, the separators of the examples and comparative examples were cut to a size of 5 × 5 cm to prepare sample G, and the top of sample G was fixed with a magnet H and placed on a jig I. A rod (J) formed with a tip of diameter (φ) 2 mm was heated to 400°C, then passed through the center of the surface of sample (G), and the length (mm) of the diameter of the resulting hole was measured.

[0179] [Table 1]

[0180] As shown in Table 1, the lithium secondary battery separators of the examples exhibited remarkably low shrinkage in the electrolyte, high dry bending strength, and high substrate bonding strength. In addition, the separators of the examples had remarkably low perforation diameter length when tested in the heated tip test, providing excellent safety when the battery is exposed to heat. However, the separators of the comparative examples did not provide superior results compared to the examples described above.

[0181] While preferred embodiments of the present invention have been described above, the present invention is not limited thereto. It can be modified and implemented in various ways within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and these modifications naturally also fall within the scope of the present invention. [Explanation of Symbols]

[0182] 1 Separator 2 Porous base material 3 Filler 4. Crosslinking products of (meth)acrylic binders and crosslinking agents 100 Lithium-ion rechargeable batteries 10 positive electrode 11 Positive lead tab 12 Positive terminal 20 negative electrode 21 Negative lead tab 22 Negative terminal 30 Separators 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode Tabs 71 Positive Tab 72 Negative Electrode Tabs

Claims

1. The material comprises a porous substrate, a coating layer located on at least one surface of the porous substrate, and an adhesive layer located on one surface of the coating layer. The coating layer comprises a binder, a crosslinking agent, a crosslinking product of carboxyalkylcellulose or a salt thereof, and a filler. The binder comprises a (meth)acrylic binder containing a first structural unit derived from (meth)acrylamide and a second structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof. The aforementioned crosslinking agent includes an aziridine-based crosslinking agent. The adhesive layer comprises a (meth)acrylic adhesive binder. Separator for lithium secondary batteries.

2. The lithium secondary battery separator according to claim 1, wherein the coating layer is formed from a composition comprising the (meth)acrylic binder, the crosslinking agent, the carboxyalkyl cellulose or a salt thereof, and the filler.

3. The separator for lithium secondary batteries according to claim 1, wherein the carboxyalkylcellulose or a salt thereof comprises carboxymethylcellulose or a salt thereof.

4. The separator for lithium secondary batteries according to claim 1, wherein the carboxyalkylcellulose or a salt thereof is included in an amount of 20 to 70% by weight of the total of the (meth)acrylic binder, the crosslinking agent, and the carboxyalkylcellulose or salt thereof.

5. The lithium secondary battery separator according to claim 1, wherein the aziridine crosslinking agent comprises one or more of the following: N,N'-toluene-2,4-bis(1-aziridinecarboxamide), N,N'-(methylenedi-p-phenylene)bis(aziridine-1-carboxamide), triethylenemelamine, 1,1-isophthaloylbis(2-methylaziridine), tris(1-aziridinyl)phosphine oxide, N,N-hexamethylene-bis(aziridinecarboxamide), trimethylolpropane tris(2-methyl-1-aziridinepropionate), trimethylolpropane tris(β-N-aziridinyl)propionate, and pentaerythritol tris(3-(1-aziridinyl)propionate.

6. The separator for lithium secondary batteries according to claim 1, wherein the filler includes a filler with a particle size D100 of 1.0 μm or less.

7. The separator for a lithium secondary battery according to claim 1, wherein the filler is spherical, plate-shaped, cubic, or amorphous.

8. The separator for a lithium secondary battery according to claim 1, wherein the mass ratio of the (meth)acrylic binder to the filler is 1:10 to 1:

50.

9. A separator for a lithium secondary battery according to claim 1, wherein, of the total of the (meth)acrylic binder, the crosslinking agent, and the carboxyalkylcellulose or a salt thereof, the (meth)acrylic binder is present in an amount of 30 to 70% by weight, the crosslinking agent is present in an amount of 5 to 30% by weight, and the carboxyalkylcellulose or a salt thereof is present in an amount of 20 to 65% by weight.

10. The first structural unit is chemical formula 1: 【Chemistry 1】 (In the formula, R 1 , R 2 (Each of these is either a hydrogen atom or a methyl group.) It is represented as, The aforementioned second structural unit is represented by chemical formulas 2, 3, and 4: 【Chemistry 2】 (In the formula, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 These are, independently, a hydrogen atom or a methyl group. L 1 、 L 2 、 and L 3 are each independently a substituted or unsubstituted C 1 -C 10 alkylene group, a substituted or unsubstituted C 3 -C 20 cycloalkylene group, a substituted or unsubstituted C 6 -C 20 arylene group, or a substituted or unsubstituted C 3 -C 20 heterocyclic group, a, b, and c are each independent integers between 0 and 2. M is an alkali metal. A separator for a lithium secondary battery according to claim 1, which is represented by any combination thereof.

11. The lithium secondary battery separator according to claim 1, wherein the (meth)acrylic binder further comprises a third structural unit derived from (meth)acrylic acid or (meth)acrylate.

12. The third structural unit is represented by chemical formulas 5, 6, and 7: 【Transformation 3】 (In the formula, R 3 , R 4 , R 6 , R 7 , R 8 and R 9 These are, independently, a hydrogen atom or a methyl group. R 5 C is either substituted or non-substituted. 1 ~C 20 It is an alkyl group, M is an alkali metal. A separator for a lithium secondary battery according to claim 11, which is represented by any combination thereof.

13. The adhesive binder is applied at a concentration of 0.01 to 0.5 g / m² relative to the surface of the coating layer. 2 A separator for a lithium secondary battery according to claim 1, which is included in the loading amount.

14. The separator for lithium secondary batteries according to claim 1, wherein the adhesive binder is crosslinked polymethyl methacrylate particles with a particle size D50 of 0.7 μm or less.

15. A lithium secondary battery comprising a positive electrode, a negative electrode, and a lithium secondary battery separator according to any one of claims 1 to 14, positioned between the positive electrode and the negative electrode.

16. The lithium secondary battery according to claim 15, wherein the separator has a continuous sheet shape, the separator is bent in a first direction to surround the positive electrode, and is bent in a second direction opposite to the first direction to surround the negative electrode.

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