Separator for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

Examples of the present disclosure relate to a separator for a rechargeable lithium battery and a rechargeable lithium battery including the same. The separator includes a separator for a rechargeable lithium battery, the separator including a porous substrate and a coating layer on at least one surface of the porous substrate. The coating layer includes a composition including a filler and a crosslinking product of a binder and a crosslinking agent, the binder including a (meth) acryloyl-based binder, and the (meth) acryloyl-based binder including a first structural unit derived from (meth) acrylamide and a second structural unit including a heterocyclic ketone group. The crosslinking agent includes an aziridine-based crosslinking agent, and the filler has a particle diameter D100 of about 1.0 [mu] m or less.

Description

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0169415, filed with the Korean Intellectual Property Office on November 29, 2023, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] The present disclosure relates to a separator for a rechargeable lithium battery and a rechargeable lithium battery including the separator. Background Art

[0003] As the use of electronic devices using batteries (such as mobile phones, laptop computers, electric vehicles, etc.) increases, the demand for secondary batteries with high energy density and high capacity is increasing. Therefore, it may be advantageous to improve the performance of rechargeable lithium batteries.

[0004] A rechargeable lithium battery generally includes a positive electrode and a negative electrode, includes active materials capable of intercalating and deintercalating lithium ions, and generates electrical energy through oxidation and reduction reactions when lithium ions intercalate into and deintercalate from the positive electrode and the negative electrode.

[0005] A rechargeable lithium battery may include a separator between the positive electrode and the negative electrode. The separator is impregnated with an electrolyte. When the separator does not undergo thermal shrinkage in the electrolyte and maintains its initial form, the safety of the battery can be improved. Summary of the Invention

[0006] Example embodiments include a separator for a rechargeable lithium battery having a low dry shrinkage rate and a low shrinkage rate in an electrolyte, thereby improving the safety of the battery.

[0007] Another example embodiment includes a rechargeable lithium battery including a separator for a rechargeable lithium battery.

[0008] According to an aspect of the present disclosure, a separator for a rechargeable lithium battery includes a porous substrate and a coating layer disposed on at least one surface of the porous substrate, wherein the coating layer includes a crosslinked product of a binder and a crosslinking agent and a filler. The binder includes a (meth)acryloyl binder, the (meth)acryloyl binder includes a first structural unit derived from (meth)acrylamide and a second structural unit including a heterocyclic ketone group, the crosslinking agent includes an aziridine crosslinking agent, and the filler has a particle size D100 of about 1.0 μm or less.

[0009] Another example embodiment includes a rechargeable lithium battery including a separator for a rechargeable lithium battery, a positive electrode, and a negative electrode. Brief Description of the Drawings

[0010] Figure 1 is a cross-sectional view showing a separator for a rechargeable lithium battery according to an exemplary embodiment.

[0011] Figures 2 to 5 is a cross-sectional view schematically showing a rechargeable lithium battery according to an exemplary embodiment. Detailed Description

[0012] Hereinafter, exemplary embodiments of the present disclosure are described in detail. However, the embodiments are presented as examples, and the present disclosure is not limited thereto, and the present disclosure is only defined by the scope of the appended claims.

[0013] Unless otherwise stated herein, when a component such as a layer, film, region, plate, etc. is described as being "on" another component, it includes not only the case where the component is "directly on" the other component, but also the case where there are other components therebetween.

[0014] 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".

[0015] In this specification, "a combination thereof" may refer to a mixture, stack, composite, copolymer, alloy, blend, or reaction product of components.

[0016] Unless otherwise defined herein, "particle size D100" may refer to the diameter of particles having a cumulative volume of 100 volume% in a particle size distribution. The particle size distribution can be measured by methods known to those skilled in the art. For example, a particle size analyzer, transmission electron microscope photograph, or scanning electron microscope photograph can be used to measure the particle size distribution. As another method, the particle size distribution can be measured by using a measuring device utilizing dynamic light scattering to measure the particle size, performing data analysis to count the number of particles in each particle size range to obtain the particle size distribution, and then calculating the particle size D100 therefrom. Alternatively, the particle size distribution can be measured using the laser diffraction method. When measuring the particle size distribution by the laser diffraction method, for example, the particles to be measured can be dispersed in a dispersion medium, and then the dispersion medium can be introduced into a commercially available laser diffraction particle size measuring device (e.g., MT 3000 of Microtrac), and ultrasonic waves of about 28 kHz can be irradiated at an output of 60 W to calculate the particle size D100 based on the 100% particle size distribution in the measuring device.

[0017] Unless otherwise defined herein, "particle size D50" may refer to the diameter of particles having a cumulative volume of 50 volume% in a particle size distribution. The particle size distribution can be obtained by the methods described for particle size D100.

[0018] In this specification, “(meth)acryloyl” means acryloyl and / or methacryloyl.

[0019] Hereinafter, unless otherwise defined, “substituted” means that a hydrogen in a compound is substituted with a substituent such as or including C1-C30 alkyl, C2-C30 alkenyl, C2-C30 alkynyl, C6-C30 aryl, C7-C30 alkylaryl, C1-C30 alkoxy, C1-C30 heteroalkyl, C3-C30 heteroalkylaryl, C3-C30 cycloalkyl, C3-C15 cycloalkenyl, C6-C30 cycloalkynyl, C2-C30 heterocycloalkyl, halogen (F, Cl, Br or I), hydroxy (-OH), nitro (-NO 2 ), cyano (-CN), amino (-NRR’) (wherein R and R’ are each independently hydrogen or C1-C6 alkyl), sulfobetaine group (-RR’N + (CH2) n SO 3 - , n is a natural number from 1 to 10), carboxybetaine group (-RR’N + (CH 2 ) n COO - , n is a natural number from 1 to 10) (wherein R and R’ are each independently C1-C20 alkyl), azide (-N 3 ), amidino (-C(=NH)NH 2 ), hydrazino (-NHNH 2 ), hydrazone group (=N(NH 2 )), carbamoyl (-C(O)NH 2 ), mercapto (-SH), acyl (-C(=O)R, where R represents hydrogen, C1-C6 alkyl, C1-C6 alkoxy or C6-C12 aryl), carboxyl (-COOH) or its salt (-C(=O)OM, where M represents an organic or inorganic cation), sulfonic acid group (-SO 3 H) or its salt (-SO 3 M, where M represents an organic or inorganic cation), phosphoric acid group (-PO 3 H 2 ) or its salt (-PO 3 MH or -PO 3 M 2 , where M represents an organic or inorganic cation) and at least one of their combinations.

[0020] Hereinafter, the C1-C3 alkyl group may be or include at least one of methyl, ethyl, and propyl. The C1-C10 alkylene group may be or include, for example, at least one of C1-C6 alkylene group, C1-C5 alkylene group, and C1-C3 alkylene group and may be or include, for example, at least one of methylene, ethylene, and propylene. The C3-C20 cycloalkylene group may be or include, for example, at least one of C3-C10 cycloalkylene group and C5-C10 alkylene group, for example, cyclohexylene. The C6-C20 arylene group may be or include, for example, C6-C10 arylene group, for example, phenylene. The C3-C20 heterocyclic group may be or include, for example, C3-C10 heterocyclic group, for example, pyridyl.

[0021] Hereinafter, "hetero" means including one or more heteroatoms, such as or including at least one of N, O, S, Si, and P.

[0022] In addition, in the chemical formula, the symbol * refers to the part connected to the same or different atoms, groups, or structural units.

[0023] Hereinafter, "alkali metal" refers to an element 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.

[0024] In this specification, when describing a numerical range, "X to Y" means "X or greater and Y or less (greater than or equal to X and less than or equal to Y)".

[0025] When the terms "about" or "substantially" are used in combination with a numerical value in this specification, it is intended that the relevant numerical value includes a tolerance of ±10% around the stated numerical value. When specifying a range, the range includes all values therebetween, such as an increment of 0.1%.

[0026] The separator for a rechargeable lithium battery according to an exemplary embodiment includes a porous matrix (or referred to as a porous substrate) and a coating layer located on at least one surface of the porous matrix. The coating layer includes a crosslinked product of a binder and a crosslinking agent and a filler. The binder includes a (meth)acryloyl binder containing a first structural unit derived from (meth)acrylamide and a second structural unit containing a heterocyclic ketone group. The crosslinking agent includes an aziridine crosslinking agent, and the particle size D100 of the filler is about 1.0 μm or less.

[0027] Since the coating layer includes a crosslinked product of a (meth)acryloyl binder and an aziridine crosslinking agent and a filler, the separator for a rechargeable lithium battery may have a significantly low dry shrinkage rate and a shrinkage rate in the electrolyte.

[0028] According to an exemplary embodiment, the dry shrinkage rate of the separator for a rechargeable lithium battery may be about 5% or less, and the shrinkage rate in the electrolyte may be about 15% or less, for example, 10% or less, or for example, 5% or less.

[0029] According to an exemplary embodiment, the separator for a rechargeable lithium battery exhibits a significantly low shrinkage rate in the electrolyte. The shrinkage rate in the electrolyte is obtained considering the application position of the separator in the rechargeable lithium battery. The electrolyte can be used to impregnate the separator. The separator having a low shrinkage rate in the electrolyte can improve the battery stability by maintaining heat resistance without weakening the mechanical properties of the (meth)acryloyl binder when the electrolyte impregnates the separator.

[0030] A separator formed of or including a composition containing a (meth)acryloyl binder but not including an aziridine crosslinker as a crosslinker or including a crosslinker other than an aziridine crosslinker may not satisfy the above shrinkage rate range in the electrolyte. According to an exemplary embodiment, the content of the aziridine crosslinker may be 95 wt% or more of the total crosslinkers in the composition, for example, in the range of 98 wt% to 100 wt%, or for example, 100 wt%.

[0031] A separator formed of or including a composition containing a (meth)acryloyl binder but not including a filler having a particle size D100 of about 1.0 μm or less or including a filler having a particle size D100 greater than about 1.0 μm may not satisfy the above shrinkage rate range in the electrolyte.

[0032] A separator formed of or including a composition containing an aziridine crosslinker and a filler but not including a (meth)acryloyl binder or including a binder other than a (meth)acryloyl binder may not satisfy the above dry shrinkage rate and shrinkage rate range in the electrolyte. According to an exemplary embodiment, the content of the (meth)acryloyl binder may be about 95 wt% or more of the total binders in the composition, for example, in the range of 98 wt% to 100 wt%, or for example, 100 wt%.

[0033] According to an exemplary embodiment, the coating layer may include a composition containing a crosslinked product of a (meth)acryloyl binder and an aziridine crosslinker and a filler having a particle size D100 of about 1.0 μm or less.

[0034] According to an exemplary embodiment, the crosslinked product may be or include a thermally crosslinked product.

[0035] According to an exemplary embodiment, the coating layer may be formed of a composition including a (meth)acryloyl binder, an aziridine crosslinker, and a filler having a particle size D100 of about 1.0 μm or less.

[0036] Coating layer

[0037] The coating layer may be or include a heat-resistant layer.

[0038] The binder includes a (meth)acryloyl binder including a first structural unit derived from (meth)acrylamide and a second structural unit including a heterocyclic ketone group. According to an exemplary embodiment, in the total structural units of the binder, the total amount of the first structural unit derived from (meth)acrylamide and the second structural unit including a heterocyclic ketone group in the binder may be equal to about 95 mol% or more, for example, in the range of 99 mol% to 100 mol%, or for example, 100 mol%. Within the above range, the effects of the separator according to the above exemplary embodiment can be easily achieved.

[0039] (The (meth)acryloyl binder is an aqueous heat-resistant binder and can fix the filler to the porous substrate, providing a bonding strength such that the coating layer binds to the porous substrate and the electrode, and contributing to improving the heat resistance, air permeability, and oxidation resistance of the separator.

[0040] The first structural unit derived from (meth)acrylamide has an amide functional group (-(C=O)-NH 2 ). -(C=O)-NH 2 The functional group can improve the binding characteristics with the porous substrate and the electrode by forming hydrogen bonds with the -OH functional group of the filler and more firmly fix the inorganic particles in the coating layer, thereby enhancing the heat resistance of the separator.

[0041] The heterocyclic ketone group included in the second structural unit can be configured to fix the filler to the porous substrate, provide a bonding strength such that the coating layer binds to the porous substrate and the electrode, and contribute to improving the heat resistance and air permeability of the separator.

[0042] With respect to 100 mol% of the (meth)acryloyl binder, the content of the first structural unit can be in the range of about 55 mol% to about 95 mol%, for example, 55 mol%, 56 mol%, 57 mol%, 58 mol%, 59 mol%, 60 mol%, 61 mol%, 62 mol%, 63 mol%, 64 mol%, 65 mol%, 66 mol%, 67 mol%, 68 mol%, 69 mol%, 70 mol%, 71 mol%, 72 mol%, 73 mol%, 74 mol%, 75 mol%, 76 mol%, 77 mol%, 78 mol%, 79 mol%, 80 mol%, 81 mol%, 82 mol%, 83 mol%, 84 mol%, 85 mol%, 86 mol%, 87 mol%, 88 mol%, 89 mol%, 90 mol%, 91 mol%, 92 mol%, 93 mol%, 94 mol%, 95 mol%, and with respect to 100 mol% of the (meth)acryloyl binder, the content of the second structural unit can be in the range of about 5 mol% to about 45 mol%, for example, 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%.

[0043] In an exemplary embodiment, with respect to 100 mol% of the (meth)acryloyl binder, the content of the first structural unit can be in the range of about 75 mol% to about 95 mol%, for example, in the range of 80 mol% to 95 mol%. With respect to 100 mol% of the (meth)acryloyl binder, the content of the second structural unit can be in the range of about 5 mol% to about 25 mol%, for example, in the range of 5 mol% to 20 mol%.

[0044] When the content of each structural unit is within the above range, the heat resistance and bonding strength of the separator can be further improved.

[0045] In an exemplary embodiment, among 100 mol% of the (meth)acryloyl binder, the total amount of the first structural unit and the second structural unit may be about 95 mol% or more, for example, in the range of 99 mol% to 100 mol%, or for example, 100 mol%.

[0046] The first structural unit derived from (meth)acrylamide may be represented by the following Chemical Formula 1:

[0047] Chemical Formula 1:

[0048]

[0049] In Chemical Formula 1, each of R 1 and R 11 is independently hydrogen or methyl, or includes hydrogen or methyl.

[0050] According to an exemplary embodiment, R 1 may be hydrogen or include hydrogen, and R 11 may be hydrogen or methyl.

[0051] The structural unit containing a heterocyclic ketone group may be represented, for example, by the following Chemical Formula 2:

[0052] Chemical Formula 2:

[0053]

[0054] In Chemical Formula 2, each of R 2 to R 6 is independently hydrogen, deuterium, a halogen group, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 heteroalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C1 to C20 heteroaryl group, and m is an integer in the range of 1 to 10, and n is equal to 0 or 1.

[0055] In Chemical Formula 2, each of R 2 , R 3 and R 4 is independently hydrogen or methyl, and R 5 is hydrogen or a substituted or unsubstituted C1 to C10 alkyl group.

[0056] The structural unit containing a heterocyclic ketone group may be represented, for example, by the following Chemical Formula 3:

[0057] Chemical Formula 3:

[0058]

[0059] In Chemical Formula 3, R 2 , R 3 and R4 Each independently is or comprises hydrogen or methyl, and n is 0 or 1.

[0060] The structural unit containing a heterocyclic ketone group may be derived from one or more of vinylpyrrolidone and (meth)acryloylpyrrolidone.

[0061] In addition to the above units, the (meth)acryloyl binder may further include other units. For example, the (meth)acryloyl binder may contain units derived from an alkyl (meth)acrylate, units derived from a diene binder, units derived from a styrene binder, units containing an ester group, units containing a carbonate group, and at least one of their combinations.

[0062] The (meth)acryloyl binder may be in various forms, such as an alternating polymer in which the units are alternately distributed, a random polymer in which the units are randomly distributed, or a graft polymer in which some structural units are grafted.

[0063] The weight-average molecular weight of the (meth)acryloyl binder may be in the range of about 350,000 g / mol to 970,000 g / mol. For example, it may be in the range of 450,000 g / mol to 970,000 g / mol or 450,000 g / mol to 700,000 g / mol. When the weight-average molecular weight of the (meth)acryloyl binder satisfies the above range, the (meth)acryloyl binder and the separator including the (meth)acryloyl binder may exhibit desired or improved bonding strength, heat resistance, and air permeability. In this specification, the "weight-average molecular weight" may indicate the polystyrene-converted average molecular weight measured by gel permeation chromatography.

[0064] The (meth)acryloyl binder may be manufactured by various known methods such as, for example, emulsion polymerization, suspension polymerization, bulk polymerization, or solution polymerization. For example, the (meth)acryloyl binder may be prepared by solution polymerization.

[0065] According to an exemplary embodiment, the (meth)acryloyl binder may be included in the coating layer of the separator in the form of a film.

[0066] The crosslinking agent includes aziridine crosslinking agents. The aziridine crosslinking agents may crosslink the (meth)acryloyl binder and also enable the separator to easily meet the above dry shrinkage rate range and shrinkage rate range in the electrolyte.

[0067] The aziridine crosslinking agents may be or include bifunctional or higher-functional aziridine crosslinking agents. Here, the term "bifunctional or higher-functional" means that there are two or more aziridine groups in the molecule. According to an exemplary embodiment, the aziridine crosslinking agents may be or include bifunctional or trifunctional aziridine crosslinking agents.

[0068] For example, the aziridine crosslinking agent may include one or more of N,N'-toluene-2,4-bis(1-aziridinecarboxamide), N,N'-(methylenedi-p-phenylene) bis(aziridine-1-carboxamide), triethylenetrlamine, 1,1-isophthaloyl bis(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).

[0069] The crosslinking agent (e.g., aziridine crosslinking agent) may be included in a desired amount relative to the binder (e.g., (meth)acrylic binder). According to an exemplary embodiment, the content of the aziridine crosslinking agent may be in the range of about 5 wt% to about 50 wt% relative to the content of the (meth)acrylic binder, for example, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, for example, in the range of 10 wt% to 40 wt%, or for example in the range of 10 wt% to 20 wt%. When within the above range, the shrinkage rate of the separator in the electrolyte can be reduced.

[0070] The filler has a particle size D100 of about 1.0 μm or less. Within the above particle size range, when the (meth)acrylic binder is combined with the aziridine crosslinking agent, the separator can easily meet the dry shrinkage rate range and the shrinkage rate range in the electrolyte. For example, the particle size D100 of the filler may be 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1.0 μm, 0.8 μm or less, 0.7 μm or less, 0.5 μm to 1.0 μm, 0.5 μm to 0.8 μm, or 0.5 μm to 0.7 μm.

[0071] According to an exemplary embodiment, the filler may have a particle size D50 of about 0.5 μm or less, for example, 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, for example, 0.4 μm or less, for example, in the range of 0.1 μm to 0.4 μm or 0.2 μm to 0.35 μm. When within the above range, the shrinkage rate in the electrolyte can be reduced.

[0072] The filler may be or include at least one of, for example, an inorganic filler, an organic filler, an organic-inorganic composite filler, and combinations thereof. The inorganic filler may be or include a ceramic material that can improve heat resistance. The inorganic filler may include at least one of, for example, metal oxides, metalloid oxides, metal fluorides, metal hydroxides, and combinations thereof. The inorganic filler may include, for example, Al 2 O 3 、SiO 2 、TiO 2 、SnO 2 、CeO 2 、MgO, NiO, CaO, GaO, ZnO, ZrO 2 、Y 2 O 3 、SrTiO 3 、BaTiO 3 、Mg(OH) 2 、boehmite, and combinations thereof, but is not limited thereto. The organic filler may include at least one of acrylic compounds, imide compounds, amide compounds, and combinations thereof, but is not limited thereto. The organic filler may have a core-shell structure, but is not limited thereto.

[0073] The filler may be substantially spherical, substantially plate-shaped, substantially cubic, or amorphous. For example, the filler may be or include plate-shaped filler.

[0074] The filler may be included in a desired amount relative to a binder (e.g., a (meth)acryloyl binder). According to an exemplary embodiment, the (meth)acryloyl binder and the filler may be included in a mass ratio ( (meth)acryloyl binder: filler) in the range of about 1:10 to about 1:50. For example, the mass ratio ( (meth)acryloyl binder: filler) may be 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23, 1:24, 1:25, 1:26, 1:27, 1:28, 1:29, 1:30, 1:31, 1:32, 1:33, 1:34, 1:35, 1:36, 1:37, 1:38, 1:39, 1:40, 1:41, 1:42, 1:43, 1:44, 1:45, 1:46, 1:47, 1:48, 1:49, 1:50. For example, the mass ratio ( (meth)acryloyl binder: filler) may be included in the range of 1:20 to 1:30. Within the above range, the bonding strength between the separator and the porous substrate can be increased.

[0075] The content of the filler can be in the range of about 50 wt% to about 99 wt% of the total amount of the coating layer, for example, 70 wt% to 99 wt%, for example, 75 wt% to 99 wt%, for example, 80 wt% to 99 wt%, for example, 85 wt% to 99 wt%, for example, 90 wt% to 99 wt%, or for example 95 wt% to 99 wt%. When the content of the filler is within the above range, the separator can exhibit desired or improved heat resistance, durability, oxidation resistance, and stability.

[0076] The coating layer can have a thickness in the range of about 0.01 μm to about 20 μm, and within the above range, it can have a thickness in the range of 1 μm to 10 μm, 1 μm to 5 μm, or 1 μm to 3 μm.

[0077] The ratio of the thickness of the coating layer to the thickness of the porous substrate can be in the range of about 0.05 to about 0.5, for example, 0.05 to 0.4, 0.05 to 0.3, or 0.1 to 0.2. Within the above range, the separator can exhibit desired or improved gas permeability, heat resistance, and bonding strength. Here, the term "thickness of the coating layer" refers to the thickness of one coating layer when the coating layer is formed only on one surface of the porous substrate, and the thickness of two coating layers when the coating layer is formed on both surfaces of the porous substrate.

[0078] Porous substrate

[0079] The porous substrate can be or include a substrate that has a plurality of pores and is generally included in an electrochemical device. The porous substrate can be or include a polymer membrane, and the polymer membrane is formed of or includes any one polymer, such as or including at least one of the following: polyolefins, such as polyethylene or polypropylene; polyesters, such as polyethylene terephthalate or polybutylene terephthalate; polyacetals; polyamides; polyimides; polycarbonates; polyether ether ketones; polyaryl ether ketones; polyetherimides; polyamideimides; polybenzimidazoles; polyethersulfones; polyphenylene ethers; cycloolefin copolymers; polyphenylene sulfides; polyethylene naphthalate; glass fibers; Teflon (polytetrafluoroethylene); and copolymers or mixtures of two or more types thereof.

[0080] The porous substrate can be or include, for example, a polyolefin-based substrate containing polyolefins, and the polyolefin-based substrate can have a desired or improved shut-off function, thus contributing to improving the safety of the battery. The polyolefin-based substrate can be or include, for example, at least one of a polyethylene single film, a polypropylene single film, a polyethylene / polypropylene double film, a polypropylene / polyethylene / polypropylene triple film, and a polyethylene / polypropylene / polyethylene triple film. In an example, the polyolefin-based resin can include a non-olefin resin in addition to the olefin resin or a copolymer including olefin and non-olefin monomers.

[0081] The porous substrate can have a thickness in the range of about 1 μm to about 40 μm, for example, a thickness in the range of 1 μm to 30 μm, 1 μm to 20 μm, or 5 μm to 15 μm.

[0082] The separator for a rechargeable lithium battery according to an exemplary embodiment can have a desired or improved bonding strength. For example, the bonding strength of the separator for a rechargeable lithium battery can be about 0.05 gf / mm or greater, for example, in the range of about 0.05 gf / mm to about 0.1 gf / mm, for example, in the range of 0.05 gf / mm to 0.2 gf / mm. The bonding strength can be measured by the method described below.

[0083] The separator for a rechargeable lithium battery is located between the positive electrode and the negative electrode, and the separator is bonded to the positive electrode and the negative electrode by passing between rollers having a pressure of 250 kgf at a speed of 150 mm / sec in an 80°C chamber. A sample is made by cutting the separator bonded to the positive electrode and the negative electrode into a width of 25 mm and a length of 50 mm. As a bonding strength measuring device, a UTM 90° peel test device (universal testing machine) of Tinius Olsen company is used. In the above sample, the separator is separated from the negative electrode plate by about 10 mm to 20 mm, then the separator is fixed to the upper clamp, and the negative electrode plate is fixed to the lower clamp so that the gap between the clamps is 20 mm, and then peeled by pulling in the 180° direction. After starting to peel at a peeling speed of 20 mm / minute, the average value is obtained by measuring the force required to peel 40 mm three times. The average value is calculated as the average of the measured values.

[0084] The separator for a rechargeable lithium battery according to an exemplary embodiment can exhibit a desired or improved air permeability, and has an air permeability value of, for example, less than about 200 sec / 100 cc, for example, an air permeability value of 190 sec / 100 cc or less or 180 sec / 100 cc or less. That is, the separator can have an air permeability value of less than about 40 sec / 100 cc·1 μm per unit thickness, for example, 30 sec / 100 cc·1 μm or less or 25 sec / 100 cc·1 μm or less. Here, the air permeability refers to the time (seconds) taken for 100 cc of air to pass through a separator of unit thickness. The air permeability per unit thickness can be obtained by measuring the air permeability of the separator of the total thickness and dividing the air permeability by the thickness. The air permeability can be obtained by measuring the time taken for 100 cc of air to pass through the separator using an air permeability measuring device (EG01-55-1MR, Asahi Seiko Co., Ltd.).

[0085] The separator for a secondary battery according to an exemplary embodiment can be formed by applying a composition for forming a coating layer on one or both surfaces of a porous substrate, drying the coating layer, and then curing the coating layer. The curing can be performed using conventional methods known to those skilled in the art.

[0086] Figure 1 is a cross-sectional view showing a separator for a rechargeable lithium battery according to an exemplary embodiment. Referring to Figure 1 , the separator for a rechargeable lithium battery includes a porous substrate 1 and coating layers 2 located on both surfaces of the porous substrate 1. The coating layer 2 includes a filler 3 and a crosslinked product 4 such as a (meth)acryloyl-based binder and a crosslinking agent.

[0087] Rechargeable lithium battery

[0088] According to an exemplary embodiment, a rechargeable lithium battery includes a separator for a rechargeable lithium battery, a positive electrode, and a negative electrode.

[0089] The separator for a rechargeable lithium battery can correspond to the above description. The separator for a rechargeable lithium battery can be located between the positive electrode and the negative electrode.

[0090] Positive electrode

[0091] The positive electrode for a rechargeable lithium battery can include a current collector and a positive electrode active material layer on the current collector. The positive electrode active material layer can include a positive electrode active material and can also include a binder and / or a conductive material. For example, the positive electrode can also include an additive that can constitute a sacrificial positive electrode.

[0092] Positive electrode active material

[0093] The positive electrode active material can include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). For example, at least one of a composite oxide of lithium and at least one metal such as or including cobalt, manganese, nickel, and combinations thereof can be used.

[0094] The composite oxide can be or include a lithium transition metal composite oxide. Examples of the composite oxide can include at least one of lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free lithium nickel manganese-based oxides, and combinations thereof.

[0095] 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 O 2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0 ≤ e ≤ 0.1); Li a NiG b O 2 (0.90 ≤ a ≤ 1.8, and 0.001 ≤ b ≤ 0.1); Li a CoG b O 2 (0.90 ≤ a ≤ 1.8, and 0.001 ≤ b ≤ 0.1); Li a Mn 1-b G b O 2 (0.90 ≤ a ≤ 1.8, and 0.001 ≤ b ≤ 0.1); Li a Mn 2 G b O 4 (0.90 ≤ a ≤ 1.8, and 0.001 ≤ b ≤ 0.1); Li a Mn 1-g G g PO 4 (0.90 ≤ a ≤ 1.8, and 0 ≤ g ≤ 0.5); Li (3-f) Fe 2 (PO 4 ) 3 (0 ≤ f ≤ 2); and Lia FePO 4 (0.90 ≤ a ≤ 1.8).

[0096] In the above chemical formula, 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 is or includes at least one of Mn, Al, and combinations thereof.

[0097] The positive electrode active material can be or include, for example, a high-nickel type positive electrode active material. Based on 100 mol% of the metals other than lithium in the lithium transition metal composite oxide, the nickel content of the high-nickel type 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%. The high-nickel type positive electrode active material can achieve a high capacity and can be applied to high-capacity, high-density rechargeable lithium batteries.

[0098] Based on 100 wt% of the positive electrode active material layer, the amount of the positive electrode active material can be in the range of about 90 wt% to about 99.5 wt%. Based on 100 wt% of the positive electrode active material layer, the amounts of the binder and the conductive material can be in the range of about 0.5 wt% to about 5 wt% respectively.

[0099] The binder is configured to attach the positive electrode active material particles to each other and also attach the positive electrode active material to the current collector. As non-limiting examples, examples of the binder can include at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0100] A conductive material can be configured to impart electrical conductivity (e.g., electroconductivity) to an electrode. Any material that does not cause a chemical change (e.g., does not cause an undesirable chemical change in a rechargeable lithium battery) and conducts electrons can be included in the battery. Examples of conductive materials can include: carbonaceous materials, such as or including at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metallic materials, including at least one of copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0101] Al can be included as a current collector, but is not limited thereto.

[0102] Negative electrode

[0103] The negative electrode for a rechargeable lithium battery can include a current collector and a negative electrode active material layer on the current collector. The negative electrode active material layer can include a negative electrode active material, and can also include a binder and / or a conductive material (e.g., an electroconductive material).

[0104] For example, the negative electrode active material layer can include about 90 wt% to about 99 wt% of the negative electrode active material, about 0.5 wt% to about 5 wt% of the binder, and about 0 wt% to about 5 wt% of the conductive material.

[0105] Negative electrode active material

[0106] The negative electrode active material can include at least one of a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / de-doping lithium, and a transition metal oxide.

[0107] The material that reversibly intercalates / deintercalates lithium ions can include carbonaceous negative electrode active materials, such as crystalline carbon, amorphous carbon, or a combination thereof as an example. Crystalline carbon can be graphite, such as natural graphite or artificial graphite that is non-shaped, substantially flaky, substantially lamellar, substantially spherical, or substantially fibrous. Amorphous carbon can be or include at least one of soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke, etc.

[0108] 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.

[0109] The material capable of doping / de-doping lithium can be or include at least one of Si-based negative electrode active materials and Sn-based negative electrode active materials. The Si-based negative electrode active material can include silicon, a silicon-carbon composite, SiO x(0 < x < 2), at least one of Si-Q alloys (where Q is or includes at least one of 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). The Sn-based negative electrode active material may include Sn, SnO 2 , at least one of Sn-based alloys and combinations thereof.

[0110] The silicon-carbon composite may be or include a composite of silicon and amorphous carbon. According to an exemplary embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite may include secondary particles (cores) in which primary silicon particles are aggregated and an amorphous carbon coating layer (shell) on the surface of the secondary particles. The amorphous carbon may also be between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0111] The silicon-carbon composite may also include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer on the surface of the core.

[0112] The Si-based negative electrode active material or the Sn-based negative electrode active material may be combined with a carbon-based negative electrode active material.

[0113] The binder may be configured to attach the negative electrode active material particles to each other and attach the negative electrode active material to the current collector. The binder may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0114] The non-aqueous binder may 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 combinations thereof.

[0115] The aqueous binder 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, epichlorohydrin rubber, 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.

[0116] When an aqueous binder is included as a negative electrode binder, a cellulose-based compound capable of imparting adhesiveness may also be included. The cellulose-based 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.

[0117] The dry binder may be or include a polymeric material capable of being fibrous. For example, the dry binder may be or include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, and combinations thereof.

[0118] The conductive material may be configured to impart conductivity (e.g., electrical conductivity) to the electrode. Any material that does not cause a chemical change (e.g., does not cause an undesirable chemical change in a rechargeable lithium battery) and conducts electrons may be included in the battery. Non-limiting examples of the conductive material may include: carbon-based materials, such as or including at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials, including at least one of copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0119] The negative electrode current collector may include at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0120] The rechargeable lithium battery may also include an electrolyte.

[0121] Electrolyte

[0122] The electrolyte for the rechargeable lithium battery may include a non-aqueous organic solvent and a lithium salt.

[0123] The non-aqueous organic solvent may constitute a medium for transporting ions participating in the electrochemical reaction of the battery.

[0124] The non-aqueous organic solvent may be or include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, and combinations thereof.

[0125] The 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), butylene carbonate (BC), etc.

[0126] The ester solvents may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc.

[0127] The ether solvents may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Additionally, the ketone solvents may include cyclohexanone, etc. The alcohol solvents may include at least one of ethanol, isopropanol, etc., and the 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-chain or cyclic hydrocarbon group and includes double bonds, aromatic rings or ether bonds, etc.); amides, such as dimethylformamide; dioxolanes, such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane, etc.

[0128] The non-aqueous organic solvents may be included alone or in combination of two or more solvents.

[0129] Additionally, in the case of using carbonate solvents, cyclic carbonates and chain carbonates may be used in combination, and the cyclic carbonates and chain carbonates may be mixed in a volume ratio of about 1:1 to about 1:9.

[0130] The lithium salt dissolved in the organic solvent is configured to supply lithium ions in the battery to enable the rechargeable lithium battery to perform basic operations and improve the transport of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt include LiPF 6 、LiBF 4 、LiSbF 6 、LiAsF 6 、LiClO 4 、LiAlO 2 、LiAlCl 4 、LiPO 2 F 2 、LiCl、LiI、LiN(SO 3 C 2 F 5 ) 2 、Li(FSO 2 ) 2 N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC 4 F 9 SO 3 、LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2)(wherein, x and y are integers from 1 to 20), and at least one of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), lithium difluorobis(oxalato)borate (LiDFBOB), and lithium bis(oxalato)borate (LiBOB).

[0131] Rechargeable lithium batteries can be classified into cylindrical, prismatic, pouch-type, coin-type batteries, etc. according to their shapes.

[0132] Figures 2 to 5 is a schematic diagram showing a rechargeable lithium battery according to an exemplary embodiment. Figure 2 shows a cylindrical battery, Figure 3 shows a prismatic battery, and Figure 4 and Figure 5 shows a pouch-type battery. Referring to Figures 2 to 5 , the rechargeable lithium battery 100 may include an electrode assembly 40 and a housing 50. The electrode assembly 40 includes a separator 30 between a positive electrode 10 and a negative electrode 20, and the electrode assembly 40 is included in the housing 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). As Figure 2 shown, the rechargeable lithium battery 100 may include a sealing member 60 for sealing the housing 50. In Figure 3 , the rechargeable lithium 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 Figure 4 and Figure 5 shown, the rechargeable lithium battery 100 may include Figure 5 the electrode tab 70 shown in Figure 4 , or may include, for example, Figure 4 the positive electrode tab 71 and the negative electrode tab 72 shown in Figure 4 . The electrode tabs 70, 71, 72 form a circuit path for inducing the current formed in the electrode assembly 40 to the outside of the battery 100.

[0133] As a non-limiting example, the rechargeable lithium battery according to the exemplary embodiment may be applied to automobiles, mobile phones, and / or various types of electrical devices.

[0134] The following examples and comparative examples are provided to emphasize one or more characteristics of the exemplary embodiments, but it is understood that the examples and comparative examples will not be construed as limiting the scope of the exemplary embodiments, and the comparative examples will not be construed as being outside the scope of the exemplary embodiments. In addition, it is understood that the exemplary embodiments are not limited to the specific details described in the examples and comparative examples.

[0135] Preparation Example 1

[0136] In a 10 L four-necked flask equipped with a stirrer, a thermometer, and a cooling tube, the following steps were repeated three times: Distilled water, acrylamide, potassium persulfate, N-vinylpyrrolidone, and a 5N aqueous lithium hydroxide solution (1.05 equivalents relative to the total amount of acrylamide) were added, and then the internal pressure was reduced to 10 mmHg using a diaphragm pump and restored to atmospheric pressure using nitrogen.

[0137] The reaction was carried out for 12 hours while controlling the temperature of the reaction solution to be stable between 65 °C and 70 °C. After cooling to room temperature, the pH of the reaction solution was adjusted to 7 to 8 using a 25% aqueous ammonia solution.

[0138] In this way, lithium poly(acrylamide-co-(N-vinylpyrrolidone)) was prepared. The molar ratio of acrylamide to N-vinylpyrrolidone was 90:10. The non-volatile components in about 10 mL of the reaction solution (reaction product) were measured, and the measurement result was 9.5 wt% (theoretical value: 10%).

[0139] Preparation Example 2

[0140] An acrylate binder containing only acrylamide was prepared in the same manner as in Preparation Example 1, except that acrylamide was used and N-vinylpyrrolidone was not used. The non-volatile components of the reaction solution were 9.0 wt% (theoretical value: 10%).

[0141] Preparation Example 3

[0142] An acrylate binder containing only N-vinylpyrrolidone was prepared in the same manner as in Preparation Example 1, except that N-vinylpyrrolidone was used and acrylamide was not used. The non-volatile components of the reaction solution were 9.0 wt% (theoretical value: 10%).

[0143] Example 1

[0144] A dispersion was prepared by mixing the acrylate binder (10 wt% in distilled water) prepared in Preparation Example 1 and boehmite as a filler (particle size D100: 0.5 μm, particle size D50: 0.2 μm, plate-like) at a mass ratio of acrylate binder: filler = 1 part by weight: 30 parts by weight based on the solid content, adding the mixture to an aqueous solvent, and then grinding it for 30 minutes at 25 °C using a bead mill and dispersing it.

[0145] A composition for forming a coating layer was prepared by adding tris(2-methyl-1-aziridinepropionate) (a trifunctional aziridine crosslinking agent) as an aziridine crosslinking agent in an amount of 0.1 part by weight based on the solid content (10 wt% content of the acrylate binder) to the dispersion and adding water so that the total solid content became 20 wt%.

[0146] The composition for forming a coating layer was applied by die coating on both sides of a polyethylene film (thickness: 8 μm, SK Corporation, air permeability: 120 sec / 100 cc, puncture strength: 480 kgf) as a porous substrate to a thickness of 1.5 μm. A separator for a lithium secondary battery was manufactured by drying and aging at 80 °C for 16 hours in an oven.

[0147] Examples 2 to 7

[0148] A separator for a rechargeable lithium battery was manufactured in the same manner as in Example 1, except that, as shown in Table 1 below, boehmite was used as a filler, but the D50 and D100 were changed, the mass ratio of acrylate binder: filler was changed, or the content of aziridine crosslinker was changed.

[0149] Comparative Examples 1 to 6

[0150] A separator for a rechargeable lithium battery was manufactured in the same method as in Example 1, except that, as shown in Table 1 below, the D50 and D100 of the filler, the type of crosslinker, the content of the crosslinker, the mass ratio of (meth)acrylate binder: filler, or the type of the combined binder, etc. were changed. PVA is a homopolymer of vinyl alcohol. The epoxy crosslinker is ethylene glycol diglycidyl ether.

[0151] The following physical properties of the separators of the manufactured examples and comparative examples were evaluated and shown in Table 1.

[0152] Dry shrinkage rate (unit: %)

[0153] Samples were prepared by cutting the separators for rechargeable lithium batteries of the examples and comparative examples into a size of 8 cm × 8 cm. By drawing a square with a size of 5 cm × 5 cm on the surface of the sample, then placing it between pieces of paper or alumina powder, placing it in an oven at 150 °C for 1 hour, taking out the sample, and then measuring the side dimensions of the drawn square, the shrinkage rate in each of the longitudinal direction (MD) and the transverse direction (TD) was calculated. The shrinkage rate was calculated according to Equation 1 below.

[0154] Equation 1:

[0155] Shrinkage rate (%) = (L0 - L1) / L0 × 100

[0156] L0 represents the initial length of the separator, and L1 represents the length of the separator after being placed at 150 °C for 1 hour.

[0157] Shrinkage rate in electrolyte (unit: %)

[0158] Samples were fabricated by cutting diaphragms for rechargeable lithium batteries of the example and comparative example into a size of 8 cm × 8 cm. A square with a size of 5 cm × 5 cm was drawn on the surface of the sample.

[0159] A positive electrode paste was prepared by mixing 97 wt% of LiCoNiAl as a positive electrode active material, 1.5 wt% of carbon nanotubes, and 1.5 wt% of polyvinyl fluoride as a conductive material, and adding water thereto.

[0160] A positive electrode was fabricated by coating the prepared positive electrode paste onto an aluminum foil and drying and rolling it.

[0161] A negative electrode active material paste was prepared by mixing 97.4 wt% of a negative electrode active material (artificial graphite), 1.0 wt% of carboxymethyl cellulose, 1.5 wt% of styrene-butadiene rubber, and 0.1 wt% of carbon nanotubes as a conductive agent. The same negative electrode active material as that used in the evaluation of the binder was used. A positive electrode was fabricated by coating the prepared negative electrode paste onto a copper foil and drying and rolling it.

[0162] One sample was positioned between the positive electrode and the negative electrode to form three sets of positive electrode-sample-negative electrode laminates, which were then placed in a bag. 2 g of an electrolyte (in which 1.5 M of LiPF 6 ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 30:50:20)) was injected to fully impregnate the laminate with the electrolyte, sealed, and left at 25 °C for 12 hours. Then, the laminate was placed in an oven at 150 °C for 1 hour, and then the sample was taken out, and the side dimensions of the drawn square were measured to calculate the shrinkage rate in each of the machine direction (MD) and the transverse direction (TD). The shrinkage rate was calculated according to Equation 1.

[0163] Presence or absence of crosslinking

[0164] Samples were fabricated by cutting diaphragms for rechargeable lithium batteries of the example and comparative example into a size of 8 cm × 8 cm. When the sample was fully immersed in deionized water at 25 °C and left for 25 hours, visual inspection was carried out to check whether the filler detached from the coating layer. In the case where the filler did not detach, it indicated that crosslinking occurred in the coating layer composition, and in the case where the filler detached, it indicated that crosslinking did not occur in the coating layer composition.

[0165] Table 1:

[0166]

[0167] As shown in Table 1 above, the diaphragms of the example had a low dry shrinkage rate and a low shrinkage rate in the electrolyte, thus improving the stability of the battery.

[0168] The separator for a rechargeable lithium battery according to the exemplary embodiment may have a significantly low dry shrinkage rate and shrinkage rate in the electrolyte, thereby improving the stability of the battery.

[0169] Although the exemplary embodiments of the present disclosure have been described above, the present disclosure is not limited thereto, and may be modified in any form within the scope of the claims, the detailed description of the present disclosure, and the drawings, and the modifications also fall within the scope of the present disclosure.

Claims

1. A separator for a rechargeable lithium battery, the separator comprising: Porous matrix; as well as a coating layer disposed on at least one surface of the porous substrate, Wherein, the coating layer comprises a cross-linked product of a binder and a cross-linking agent and a filler, The binder includes a (meth)acryl-based binder, wherein the (meth)acryl-based binder includes a first structural unit derived from (meth)acrylamide and a second structural unit including a heterocyclic ketone group, The cross-linking agent includes an aziridine cross-linking agent, and The filler has a particle size D100 of 1.0 μm or less.

2. The diaphragm according to claim 1, wherein The coating layer is formed of a composition including the (meth)acryl-based binder, the aziridine-based cross-linking agent, and the filler having a particle size D100 of 1.0 μm or less.

3. The diaphragm according to claim 1, wherein The aziridine crosslinking agent includes one or more of N,N'-toluene-2,4-bis(1-aziridinecarboxamide), N,N'-(methylenediphenylene)bis(aziridine-1-carboxamide), triethylene melamine, 1,1-isophthaloylbis(2-methylaziridine), tris(1-aziridine)phosphine oxide, N,N-hexamethylene-bis(aziridinecarboxamide), trimethylolpropane tris(2-methyl-1-aziridine propionate), trimethylolpropane tris(β-N-aziridine) propionate and pentaerythritol tris(3-(1-aziridine) propionate).

4. The diaphragm according to claim 1, wherein The content of the aziridine-based crosslinking agent is in a range of 5 wt % to 50 wt % relative to the content of the (meth)acryl-based binder.

5. The diaphragm according to claim 1, wherein The mass ratio of the (meth)acryl-based binder to the filler is in the range of 1:10 to 1:

50.

6. The diaphragm according to claim 1, wherein The filler has a particle size D50 of 0.5 μm or less.

7. The diaphragm according to claim 1, wherein The filler includes a substantially plate-shaped inorganic filler.

8. The diaphragm according to claim 1, wherein The first structural unit derived from (meth)acrylamide is represented by Chemical Formula 1: Chemical formula 1: In Chemical Formula 1, R 1 and R 11 Each of independently comprises hydrogen or methyl, and The second structural unit comprising a heterocyclic ketone group is represented by Chemical Formula 2: Chemical formula 2: In chemical formula 2, R 2 To R 6 Each of the above independently includes hydrogen, deuterium, a halogen group, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 heteroalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C1 to C20 heteroaryl group, and m is an integer in the range of 1 to 10, and n is equal to 0 or 1.

9. The diaphragm according to claim 1, wherein: The second structural unit comprising a heterocyclic ketone group is represented by Chemical Formula 3: Chemical formula 3: In chemical formula 3, R 2 , R 3 and R 4 Each of wherein independently comprises hydrogen or methyl, and n is equal to 0 or 1.

10. The diaphragm according to claim 1, wherein The content of the first structural unit is in the range of 55 mol % to 95 mol %, and the content of the second structural unit is in the range of 5 mol % to 45 mol % with respect to 100 mol % of the (meth)acryl-based binder.

11. The diaphragm according to claim 1, wherein The total amount of the first structural unit derived from (meth)acrylamide and the second structural unit containing a heterocyclic ketone group in the binder is equal to 95 mol% or more in the total structural units of the binder.

12. The diaphragm according to claim 2, wherein: The content of the aziridine-based crosslinking agent is 95 wt % or more of the total crosslinking agents in the composition.

13. The diaphragm according to claim 2, wherein: The (meth)acryl-based binder is present in an amount of 95 wt % or more of the total binder in the composition.

14. The diaphragm according to claim 1, wherein The coating layer has a thickness in the range of 1 μm to 3 μm.

15. A rechargeable lithium battery, the rechargeable lithium battery include ： The separator for a rechargeable lithium battery according to claim 1; a positive electrode; and Negative electrode.

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