Separator and electrochemical element including the same

Abstract

The invention relates to a separator and an electrochemical element comprising the same. According to one aspect of the present disclosure, provided is a separator comprising: a porous substrate; and an inorganic particle layer which is formed on at least one surface of the porous substrate, contains a binder and inorganic particles, has a peak value in the range of 1082.5 cm-1 to 1086.5 cm-1 in the spectrum of Fourier transform infrared spectroscopy, and has a saturated moisture content of 350 ppm to 1000 ppm as measured by the Karl Fischer method. The separator according to the present invention can have excellent heat resistance and adhesiveness even with a thin thickness.

Description

Technical Field

[0001] The present disclosure relates to a separator and an electrochemical element including the separator. Background Art

[0002] With the recent increase in demand for environmentally friendly energy, research on electrochemical devices is being conducted in various fields, including electronic devices such as mobile phones and personal computers (PCs), as well as electric vehicles.

[0003] To achieve high capacity and high output characteristics in electrochemical devices, research is being conducted to reduce the thickness of the insulating separator between the positive and negative electrodes. However, reducing the thickness of the separator can reduce mechanical strength and / or heat resistance. Reduced mechanical strength and / or heat resistance increase the likelihood of safety issues during battery manufacturing and use. For example, damage or deformation of the separator caused by increased internal battery temperature can cause a short circuit between the electrodes, increasing the risk of battery overheating or fire.

[0004] Therefore, it is necessary to develop a thin separator with improved mechanical strength and heat resistance. In addition, to increase capacity and output, it is necessary to develop a separator with high transmittance.

[0005]

Prior art literature

[0006] [Patent Literature]

[0007] (Patent Document 1): Korean Patent Publication No. 2016-0109669 (September 21, 2016) Summary of the Invention

[0008] Technical issues

[0009] According to one aspect of the present disclosure, a separator having excellent heat resistance and adhesiveness even in a thin thickness and an electrochemical element including the separator can be provided.

[0010] According to another aspect of the present disclosure, a separator having improved mechanical strength and permeability even in a thin thickness and an electrochemical element including the separator may be provided.

[0011] According to yet another aspect of the present disclosure, an electrochemical element having excellent resistance characteristics and thermal safety may be provided.

[0012] The separator disclosed herein can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-based solar and wind power generation. Furthermore, the separator disclosed herein can be used in eco-friendly electric vehicles and hybrid vehicles, which suppress air pollution and greenhouse gas emissions to prevent climate change.

[0013] Technical Solution

[0014] The separator according to the present disclosure includes: a porous substrate; and an inorganic particle layer formed on at least one side of the porous substrate, comprising a binder and inorganic particles, wherein the inorganic particle layer has a peak at 1082.5 cm in the spectrum of Fourier transform infrared spectroscopy (FT-IR). -1 to 1086.5cm -1 The saturated moisture content determined by the Karl Fischer method was 350 ppm to 1000 ppm.

[0015] In one implementation example, the saturated moisture content may be 450 ppm to 1000 ppm.

[0016] In one implementation example, the average thickness of the porous substrate may be 5 μm to 15 μm, and the ratio of the average thickness of the porous substrate to the average thickness of the separator may be greater than 0.7.

[0017] In one implementation example, the total thickness of the inorganic particle layer formed on the porous substrate may be 3.2 μm or less.

[0018] In one implementation example, the adhesive may include polyacrylamide resin.

[0019] In one implementation example, the polyacrylamide resin may be a copolymer including units derived from (meth)acrylamide monomers and units derived from comonomers.

[0020] In one implementation example, the polyacrylamide resin may include a structural unit derived from a (meth)acrylamide monomer and a structural unit derived from a (meth)acrylic acid monomer containing a hydroxyl group.

[0021] In one implementation example, the weight average molecular weight of the polyacrylamide resin may be 100,000 g / mol to 2,000,000 g / mol.

[0022] In one implementation example, the adhesive may further include any one or more additional adhesives selected from the group consisting of polyvinyl alcohol, polyvinylidene fluoride, carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, polyethylene glycol, polyacrylonitrile, polyvinyl pyrrolidone and copolymers thereof.

[0023] In one implementation example, the content of the additional binder may be 0.1 wt % to 30 wt % of the total weight of the binder.

[0024] In one embodiment, the BET specific surface area of ​​the inorganic particles can be 3 m 2 / g to 7m 2 / g.

[0025] In one implementation example, the average particle size (D50) of the inorganic particles may be 0.5 μm to 1.5 μm.

[0026] In one implementation example, the inorganic particles may include any one or more selected from the group consisting of metal hydroxides, metal oxides, metal nitrides, and metal carbides.

[0027] In one implementation example, the longitudinal and transverse thermal shrinkage rates of the separator measured after being placed at 130° C. for 60 minutes may be 5% or less.

[0028] In one implementation example, the weight ratio of the inorganic particles to the binder in the inorganic particle layer may be 50:50 to 99.9:0.1.

[0029] In one embodiment, the inorganic particle layer may be formed to have a particle size of 0.5 g / m 2 Up to 10g / m 2 .

[0030] Furthermore, the present disclosure provides an electrochemical element including the separator as described above.

[0031] Effects of the Invention

[0032] The separator according to the present disclosure may also have excellent heat resistance and adhesiveness at a thin thickness.

[0033] Furthermore, the separator according to the present disclosure may have excellent mechanical strength and permeability even at a thin thickness.

[0034] Also, the present disclosure may provide an electrochemical element having excellent resistance characteristics and thermal safety due to including the separator according to one implementation example. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is an FT-IR spectrum measured for the diaphragm according to Example 1;

[0036] Figure 2 is an FT-IR spectrum measured for the diaphragm according to Comparative Example 2;

[0037] Figure 3 is an FT-IR spectrum measured for the diaphragm according to Comparative Example 3;

[0038] Figure 4 is an FT-IR spectrum measured for the diaphragm according to Comparative Example 4;

[0039] Figure 5 It is an enlarged view of a part of the FT-IR spectrum measured for the membranes according to Example 1 and Comparative Examples 2 to 4. DETAILED DESCRIPTION

[0040] The present disclosure is described in detail below, but this is merely exemplary, and the present disclosure is not limited to the specific embodiments described in the exemplary embodiments.

[0041] Furthermore, singular forms used in the specification and the appended claims may be intended to include the plural forms as well, unless the context otherwise indicates.

[0042] Furthermore, the numerical ranges used in this specification include the lower limit, the upper limit, and all values ​​within the range, increments logically derived from the form and magnitude of the defined range, all values ​​that are doubly defined, and all possible combinations of upper and lower limits of numerical ranges defined in different forms. Unless otherwise specified in this specification, values ​​outside the numerical range that may occur due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0043] Furthermore, throughout the specification, unless otherwise stated, “comprising” a certain component does not exclude other components, but rather indicates that other components may also be included.

[0044] In this specification, when it is described that a layer, film, region, plate or the like is “on” or “over” another part, this includes not only the case where it is “directly above” another part, but also the case where there are other parts in between.

[0045] In this specification, "average particle size" refers to "D50," which is the particle size at which 50% of the inorganic particles are present on a cumulative volume basis. The average particle size can be derived from the particle size distribution of the inorganic particles to be measured, obtained by collecting a sample according to ISO 13320-1 and analyzing it using a Microtrac S3500. Furthermore, "D90" refers to the particle size at which 90% of the inorganic particles are present on a cumulative volume basis, and "D10" refers to the particle size at which 10% of the inorganic particles are present on a cumulative volume basis. D90 and D10 can be derived in the same manner as D50.

[0046] The present disclosure provides a separator, comprising: a porous substrate; and an inorganic particle layer formed on at least one side of the porous substrate, comprising a binder and inorganic particles, wherein the inorganic particle layer has a peak at 1082.5 cm in a Fourier transform infrared spectroscopy (FT-IR) spectrum. -1 to 1086.5cm -1 A peak (hereinafter referred to as the first peak) appeared in the range of , and the saturated moisture content measured by the Karl Fischer method was 350 ppm to 1000 ppm.

[0047] According to one embodiment, in the FT-IR spectrum at 1082.5 cm -1 to 1086.5cm -1 A separator having a peak in the range of 350 ppm to 1000 ppm and a saturated moisture content of 350 ppm to 1000 ppm can provide a separator having excellent heat resistance and adhesion even in a thin thickness and excellent transmittance.

[0048] Furthermore, an electrochemical device according to one embodiment includes a separator that simultaneously satisfies a specific range of first peaks appearing in an FT-IR spectrum and a specific range of saturated moisture content, thereby exhibiting excellent resistance characteristics and thermal safety. Specifically, the electrochemical device according to one embodiment can exhibit significantly low discharge resistance after 600 cycles, thereby exhibiting improved charge and discharge performance.

[0049] On the other hand, if the rate of increase of the moisture content of the diaphragm is large, the moisture content remaining in the battery will become high even after the battery is assembled. This increase in moisture content may cause a decrease in battery capacity by inducing electrolyte decomposition, etc. In the past, in order to reduce the moisture content in the battery, expensive packaging materials such as aluminum had to be used. However, the diaphragm according to the present disclosure satisfies both the first peak in a specific range that appears in the FT-IR spectrum and the saturated moisture content in a specific range, thereby having the advantage of a low rate of increase in moisture content with storage. Therefore, the present disclosure can provide a battery with excellent performance even if a polyethylene packaging material is used instead of an aluminum material due to the low residual moisture content in the battery. That is, according to the present disclosure, there is the advantage of being able to reduce the price of the battery while improving battery performance.

[0050] As an implementation example, the separator can have the following excellent mechanical, electrical, and thermal properties despite having a porous substrate with an average thickness of 15 μm or less and a very thin inorganic particle layer having a thickness of at least 0.7 times the total thickness of the separator. The separator having the above-mentioned properties can be manufactured by adjusting any one or more of the thickness of each layer selected from the separator, the size of the inorganic particles, the type of binder, the type of binder further used, the surface properties of the porous substrate, the surface area of ​​the inorganic particles, and the saturated moisture content of the separator, but the method is not particularly limited as long as it can be achieved.

[0051] As an implementation example, a membrane having a first peak in a specific range and a saturated moisture content in a specific range in the FT-IR spectrum can be manufactured using inorganic particles having a specific specific surface area. For example, the BET specific surface area of ​​the inorganic particles included in the membrane according to one implementation example can be 3 m 2 / g or more, 4m 2 / g or more, 7m 2 / g or less, 6m 2 / g or below or between the above values, specifically 3m 2 / g to 7m 2 / g or 4m 2 / g to 6m 2 / g.

[0052] As an implementation example, the separator described above can be manufactured by adjusting the thickness ratio of the porous substrate and the separator to a specific value. For example, the ratio of the average thickness of the porous substrate to the average thickness of the separator can be 0.7 or greater, 0.75 or greater, 0.77 or greater, 0.99 or less, 0.9 or less, 0.85 or less, or a value in between these values. Specifically, it can be 0.7 to 0.99, 0.75 to 0.9, or 0.77 to 0.85.

[0053] As an implementation example, the separator described above can be manufactured by using a specific resin as the binder contained therein. For example, the binder may include a polyacrylamide resin, preferably a polyacrylamide resin including structural units derived from (meth)acrylamide monomers and structural units derived from (meth)acrylic acid monomers containing hydroxyl groups.

[0054] According to an implementation example, the diaphragm described above can be manufactured by simultaneously using the above-mentioned polyacrylamide resin and a specific additional binder as a binder. For example, the specific additional binder can be any one or more selected from the group consisting of polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), and copolymers thereof.

[0055] According to another embodiment, the diaphragm described above can be manufactured by using a polyacrylamide resin as a binder and a porous substrate including polar functional groups on the surface. As non-limiting examples of the polar functional groups, carboxyl groups, aldehyde groups, hydroxyl groups, etc. can be listed, but are not particularly limited. Regarding the polar functional groups, according to one example, they can be introduced by hydrophilic surface treatment, and about the hydrophilic surface treatment, according to one example, it can include one or more of corona discharge treatment and plasma discharge treatment.

[0056] The separator having a first peak within a specific range and a saturated moisture content within a specific range as described above in the FT-IR spectrum can be obtained by adjusting any one or a combination of two or more selected from the thickness and thickness ratio of each layer of the separator, the size of the inorganic particles, the type of binder, the type of binder used, the surface properties of the porous substrate, and the surface area of ​​the inorganic particles. However, as long as the separator can meet the requirements of the first peak appearing in the FT-IR spectrum and the saturated moisture content within a specific range, it is included in the scope of the present disclosure, and as long as these requirements are met, the method of use is not particularly limited.

[0057] The separator will be described in more detail below.

[0058] In one implementation example, the first peak is at 1082.5 cm -1 to 1086.5cm -1 The peak with the maximum intensity in the range of -1 to 1086.5cm -1 Range or 1083.5cm -1 to 1086cm -1 The range has the peak with maximum intensity.

[0059] In one embodiment, the membrane may also have a wavelength of 1140 cm -1 to 1160cm -1 The second peak is a peak with the maximum intensity in the above range, specifically, at 1145 cm -1 to 1155cm -1 The range has the peak with maximum intensity.

[0060] In one embodiment, the membrane may have a wavelength of 2910 cm-1 on the FT-IR spectrum. -1 to 2930cm -1 The third peak is a peak with the maximum intensity in the above range, specifically, at 2915 cm -1 to 2925cm -1 Range or 2915cm -1 to 2920cm -1 The range has the peak with maximum intensity.

[0061] In one embodiment, the membrane may also have a wavelength of 3090 cm-1 on the FT-IR spectrum. -1 to 3100cm -1 The fourth peak is a peak with the maximum intensity in the above range, specifically, at 3092 cm -1 to 3098cm -1 The range has the peak with maximum intensity.

[0062] In one embodiment, the membrane may also have a wavelength of 3270 cm-1 in the FT-IR spectrum. -1 to 3295cm -1 The fifth peak is a peak with the maximum intensity in the above range, specifically, at 3275 cm -1 to 3290cm -1 Range or 3275cm -1 to 3285cm -1 The range has the peak with maximum intensity.

[0063] In one embodiment, the FT-IR spectrum of the membrane can be measured using an FT-IR device equipped with an MCT (mercury cadmium telluride) detector. Specifically, the FT-IR spectrum can be measured at 4000 cm -1 Up to 675cm -1 The range is 4cm -1 The resolution was measured by scanning 5 to 200 times in transmission mode.

[0064] In one embodiment, the Gurley permeability of the separator may be 250 sec / 100cc or less, 230 sec / 100cc or less, 200 sec / 100cc or less, 180 sec / 100cc or less, 10 sec / 100cc or more, 50 sec / 100cc or more, 90 sec / 100cc or more, 100 sec / 100cc or more, or a value between the above values. Specifically, the Gurley permeability may be 10 sec / 100cc to 250 sec / 100cc, 50 sec / 100cc to 200 sec / 100cc, 90 sec / 100cc to 230 sec / 100cc, or 100 sec / 100cc to 180 sec / 100cc. With the Gurley permeability meeting the above range, excellent ionic conductivity can be achieved, thereby improving the charge and discharge characteristics of the electrochemical element due to the low internal resistance of the electrochemical element.

[0065] In one implementation example, the puncture strength of the diaphragm may be greater than 0.3 N / μm, greater than 0.32 N / μm, greater than 0.35 N / μm, less than 1.0 N / μm, less than 0.8 N / μm, less than 0.5 N / μm, or a value in between. Specifically, the puncture strength may be 0.3 N / μm to 1.0 N / μm, 0.32 N / μm to 0.8 N / μm, or 0.35 N / μm to 0.5 N / μm.

[0066] In one embodiment, the tensile strength of the diaphragm in the machine direction (MD) can be 1500 kgf / cm 2 Up to 2500kgf / cm 2 or 1500kgf / cm 2 Up to 2000kgf / cm 2 .

[0067] In one embodiment, the tensile strength of the diaphragm in the transverse direction (TD) can be 1500 kgf / cm 2 Above, 1600kgf / cm2 Above, 1700kgf / cm 2 Above, 2500kgf / cm 2 Below, 2000kgf / cm 2 Specifically, the transverse tensile strength can be 1500 kgf / cm 2 Up to 2500kgf / cm 2 、1600kgf / cm 2 Up to 2000kgf / cm 2 or 1700kgf / cm 2 Up to 2000kgf / cm 2 .

[0068] With the puncture strength and tensile strength satisfying the above ranges, the electrochemical device has excellent resistance to external stress generated during the manufacture of the electrochemical device and dendrites generated during charge and discharge of the electrochemical device, thereby ensuring the safety of the electrochemical device.

[0069] In one implementation, the saturated moisture content is measured after being placed in a constant temperature and humidity chamber set at 40°C and 90% relative humidity for 24 hours, and can be 350 ppm or more, 450 ppm or more, 500 ppm or more, 550 ppm or more, 600 ppm or more, 1000 ppm or less, 900 ppm or less, 800 ppm or less, 750 ppm or less, or a value in between. Specifically, the saturated moisture content can be 350 ppm to 1000 ppm, 450 ppm to 1000 ppm, 500 ppm to 900 ppm, 550 ppm to 800 ppm, or 600 ppm to 750 ppm.

[0070] In one embodiment, the average thickness (t1) of the porous substrate can be 5 μm to 15 μm, and the ratio (t1 / t2) of the average thickness of the porous substrate to the average thickness of the separator (t2) can be 0.7 or greater. The separator according to one embodiment can also simultaneously achieve the above-mentioned ranges of Gurley permeability, puncture strength, tensile strength, and saturated moisture content under the conditions of thickness within the above-mentioned ranges. This allows for thin-filming of secondary battery separators, making them suitable for use in high-capacity / high-output batteries.

[0071] In one embodiment, the average thickness of the porous substrate is not necessarily limited thereto, and can be 5 μm or more, 8 μm or more, 15 μm or less, 12 μm or less, or a value in between. Specifically, the average thickness of the porous substrate can be 5 μm to 15 μm or 8 μm to 12 μm.

[0072] In one embodiment, the ratio of the average thickness of the porous substrate to the average thickness of the separator can be 0.7 or greater, 0.75 or greater, 0.77 or greater, 0.99 or less, 0.9 or less, 0.85 or less, or a value in between. Specifically, the ratio of the average thickness of the porous substrate to the average thickness of the separator can be 0.7 to 0.99, 0.75 to 0.9, or 0.77 to 0.85.

[0073] In one embodiment, the average thickness of the separator is not necessarily limited thereto, and can be 7 μm or more, 10 μm or more, 12 μm or more, 20 μm or less, 15 μm or less, or a value in between. Specifically, the average thickness of the separator can be 7 μm to 20 μm, 10 μm to 15 μm, or 12 μm to 15 μm.

[0074] In one embodiment, the inorganic particle layer may be coated on one or both sides of the porous substrate. When the inorganic particle layer is coated on both sides of the porous substrate, the thickness of the inorganic particle layer coated on one side and the other side may be the same or different.

[0075] In one implementation example, the total thickness of the inorganic particle layer formed on the porous substrate is not necessarily limited thereto, and may be 4 μm or less, 3.5 μm or less, 1 μm or more, 1.5 μm or more, or a value between the above values. Preferably, the total thickness of the inorganic particle layer may be 3.2 μm or less. Specifically, the total thickness of the inorganic particle layer may be 1 μm to 4 μm, 1.5 μm to 3.5 μm, 1 μm to 3.2 μm, or 1.5 μm to 3.2 μm.

[0076] In one implementation example, the adhesive may include polyacrylamide resin.

[0077] In one embodiment, the polyacrylamide resin may be polyacrylamide or a copolymer thereof. In one embodiment, the copolymer may be a block copolymer or a random copolymer, but the copolymer described in one embodiment of the present disclosure refers to a random copolymer formed by mixing and polymerizing two or more monomers.

[0078] In one embodiment, the polyacrylamide resin may be a copolymer comprising units derived from (meth)acrylamide monomers and units derived from comonomers. Preferably, the polyacrylamide resin may comprise structural units derived from (meth)acrylamide monomers and structural units derived from (meth)acrylic acid monomers containing hydroxyl groups.

[0079] According to one embodiment, a separator comprising the copolymer rather than a homopolymer derived from an acrylamide-based monomer can further enhance mechanical strength, gas permeability, heat resistance, and adhesion. Furthermore, the inclusion of the separator can provide an electrochemical device with superior electrical resistance and thermal safety.

[0080] The unit derived from the (meth)acrylamide monomer of the polyacrylamide resin can be represented by the following Chemical Formula 1:

[0081] Chemical formula 1

[0082]

[0083] In the Chemical Formula 1, R1 may be hydrogen or a C1 to C6 alkyl group.

[0084] The unit derived from the (meth)acrylic acid monomer containing a hydroxyl group of the polyacrylamide resin can be represented as shown in the following Chemical Formula 2:

[0085] Chemical formula 2

[0086]

[0087] In the chemical formula 2, R2 is hydrogen or a C1 to C6 alkyl group. Also, L1 may be a C1 to C6 linear or branched alkylene group, specifically a C1 to C3 alkylene group, more specifically ethylene.

[0088] In a polyacrylamide resin according to one embodiment, 65 to 98 mol%, 70 to 97 mol%, or 75 to 95 mol% of a (meth)acrylamide monomer may be included. A hydroxyl-containing (meth)acrylic monomer may be included in an amount of 2 to 35 mol%, 3 to 30 mol%, or 5 to 25 mol%. When preparing a polyacrylamide resin within these content ranges, sufficient adhesive strength can be achieved, and a more significant effect can be achieved in terms of high-temperature shrinkage.

[0089] In one implementation example, the polyethylene glycol-converted weight average molecular weight of the polyacrylamide resin measured using gel permeation chromatography may be 100,000 g / mol or more, 200,000 g / mol or more, 2,000,000 g / mol or less, 1,000,000 g / mol or less, 500,000 g / mol or less, or a value between the above values. Specifically, the weight average molecular weight of the polyacrylamide resin may be 100,000 g / mol to 2,000,000 g / mol, 200,000 g / mol to 1,000,000 g / mol, or 200,000 g / mol to 500,000 g / mol. According to one implementation example, when the weight average molecular weight of the polyacrylamide resin meets the above range, heat resistance and adhesion can be further improved.

[0090] In one implementation example, the adhesive may further include any one or more additional adhesives selected from the group consisting of polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP) and copolymers thereof.

[0091] According to one embodiment, the separator uses the aforementioned additional binder together with the polyacrylamide resin as a binder, thereby further improving mechanical strength, gas permeability, heat resistance, and adhesion. Furthermore, these improvements in physical properties can be achieved without pre-treatment of the porous substrate, such as corona discharge treatment, thereby reducing process time and material costs.

[0092] In one implementation, the content of the additional binder can be 0.1% by weight or more, 1% by weight or more, 5% by weight or more, 30% by weight or less, 20% by weight or less, 15% by weight or less, or a value in between, based on the total weight of the binder. Specifically, the content of the additional binder can be 0.1% by weight to 30% by weight, 1% by weight to 20% by weight, or 5% by weight to 15% by weight, but is not necessarily limited thereto.

[0093] In an implementation example, when the additional binder is polyvinyl alcohol, the saponification degree of the additional binder may be 80 mol % to 95 mol %, specifically 85 mol % to 90 mol %, but is not particularly limited thereto.

[0094] In an implementation example, the weight average molecular weight of the additional binder may be 10,000 g / mol to 100,000 g / mol, specifically, 30,000 g / mol to 70,000 g / mol, but is not particularly limited thereto.

[0095] According to one embodiment, the separator can have excellent heat resistance even at a thin thickness. In one embodiment, the longitudinal and transverse thermal shrinkage of the separator measured after 60 minutes at 130°C can be 5% or less, preferably 4% or less, and more preferably 3% or less, 2% or less, or 1.5% or less.

[0096] In one embodiment, the porous substrate can be a polyolefin-based porous substrate such as polyethylene, polypropylene, and copolymers thereof, but is not limited thereto. Any porous substrate known as a porous substrate for a separator of an electrochemical device can be used. In one embodiment, the porous substrate can be manufactured into a film or sheet, but is not particularly limited thereto.

[0097] In an implementation example, the porosity of the porous substrate may be 20% to 60%, specifically 30% to 60%, but is not limited thereto.

[0098] In one embodiment, the inorganic particle layer may include a binder and inorganic particles, and may be a porous inorganic particle layer in which the inorganic particles are connected and fixed by the binder to form pores. In one embodiment, the inorganic particle layer is provided on at least one side of the porous substrate, and may occupy an area fraction of greater than 60%, greater than 70%, greater than 80%, or greater than 90% of the entire surface of the porous substrate. Preferably, the inorganic particle layer may be formed on 100% of the area of ​​the porous substrate.

[0099] In one implementation example, the inorganic particles are not limited as long as they are inorganic particles used in this technical field. As a non-limiting example, the inorganic particles may include any one or more selected from the group consisting of metal hydroxides, metal oxides, metal nitrides and metal carbides. For example, the inorganic particles may include any one or more selected from the group consisting of magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), aluminum oxide (Al2O3), boehmite (γ-AlO(OH)), aluminum hydroxide (Al(OH)3), silicon dioxide (SiO2), silicon carbide (SiC), calcium oxide (CaO), titanium dioxide (TiO2), strontium titanate (SrTiO3), zinc oxide (ZnO), yttrium oxide (Y2O3), zirconium oxide (ZrO2), tin oxide (SnO2) and cerium oxide (CeO2). From the perspective of battery stability, the inorganic particles may preferably be particles of any one or two or more metal hydroxides selected from the group consisting of bohemite, aluminum hydroxide (Al(OH) 3 ) and magnesium hydroxide (Mg(OH) 2 ).

[0100] In one implementation example, the shape of the inorganic particles is not limited and can be spherical, elliptical, needle-shaped, etc.

[0101] In one embodiment, the BET specific surface area of ​​the inorganic particles can be 3 m 2 / g or more, 4m 2 / g or more, 7m 2 / g or less, 6m 2 / g or a value between the above values. Specifically, the BET specific surface area of ​​the inorganic particles can be 3m 2 / g to 7m 2 / g or 4m 2 / g to 6m 2 / g. The present disclosure can provide a separator that simultaneously satisfies the physical properties to be achieved by the present disclosure when the specific surface area satisfies the above range. In this case, the BET specific surface area of ​​the inorganic particles can be measured by the ASTM C1069 method.

[0102] In one embodiment, the average particle size (D50) of the inorganic particles can be 0.5 μm or more, 0.6 μm or more, 1.5 μm or less, 1.0 μm or less, or a value in between. Specifically, the D50 of the inorganic particles can be 0.5 μm to 1.5 μm or 0.6 μm to 1.0 μm, but this can be changed without departing from the scope of the present disclosure.

[0103] In one implementation example, the weight ratio of the inorganic particles to the binder in the inorganic particle layer may be 50:50 to 99.9:0.1, 60:40 to 98:2, or 80:20 to 98:2, but is not particularly limited thereto.

[0104] In one embodiment, the inorganic particle layer can be formed to have a particle size of 0.5 g / m 2 Up to 10g / m 2 , specifically it can be formed into 1g / m 2 Up to 5g / m 2 , more specifically it can be formed into 2.5g / m 2 Up to 4g / m 2 , but is not particularly limited thereto.

[0105] The following describes a method for producing the separator of the present disclosure.

[0106] A method for manufacturing a separator that satisfies the above properties may include: a first step of preparing a coating slurry containing a binder and inorganic particles; and a second step of coating the coating slurry on at least one side of a porous substrate to form an inorganic particle layer.

[0107] The descriptions of the porous substrate, inorganic particle layer, inorganic particles, and binder are the same as those described above, and thus detailed descriptions are omitted.

[0108] The method for preparing the coating slurry in the first step can adopt all conventional methods known in the technical field without restriction. Although not particularly limited, according to non-limiting examples, the slurry can be prepared by stirring and dispersing inorganic particles, or a ball mill can be used to disperse agglomerated inorganic particles.

[0109] The coating slurry may include inorganic particles, a binder, and a solvent. The solvent may be water, ethanol, methanol, lower alcohols such as propanol, dimethylformamide, acetone, tetrahydrofuran, diethyl ether, methylene chloride, DMF, N-methyl-2-pyrrolidone, hexane, cyclohexane, or a mixture thereof, but is not necessarily limited thereto.

[0110] In one embodiment, the solid content of the coating slurry is not particularly limited, and may be, for example, 1 wt % to 50 wt %, 5 wt % to 30 wt %, or 10 wt % to 30 wt %, but is not limited thereto.

[0111] In one implementation example, based on the total weight of the solid components, the coating slurry may contain 50 wt% to 99.9 wt% of inorganic particles and 0.1 wt% to 50 wt% of a binder. Specifically, it may contain 60 wt% to 98 wt% of inorganic particles and 2 wt% to 40 wt% of a binder. More specifically, it may contain 80 wt% to 98 wt% of inorganic particles and 2 wt% to 20 wt% of a binder, but is not limited thereto.

[0112] The method for applying the coating slurry in the second step can be any conventional method known in the art without limitation. According to non-limiting examples, roller coating, spin coating, dip coating, rod coating, die coating, slit coating, inkjet printing, and combinations thereof can be used. The applied slurry can be dried to form an inorganic particle layer. The drying process for forming the inorganic particle layer is not particularly limited, but can be performed at a temperature below 100°C or between 30°C and 60°C.

[0113] In a specific implementation example, after the drying for forming the inorganic particle layer is completed, the process of aging the porous substrate on which the inorganic particle layer is formed may not be further included. The aging can be performed at 50°C to 150°C or 60°C to 120°C, and the aging time can be performed for 2 hours to 24 hours or 10 to 20 hours. More specifically, it can be performed in a temperature range of 70°C to 120°C for 10 to 15 hours. According to an implementation example, even without performing the aging process, a diaphragm that meets the above-mentioned physical properties can be manufactured, and therefore has the advantage of reducing time and material costs at the process level.

[0114] The present disclosure can provide an electrochemical device including a separator according to one of the above-mentioned embodiments. The electrochemical device includes the separator, thereby reducing resistance, thereby having significantly excellent lifespan characteristics, and having excellent thermal stability at high temperatures.

[0115] The electrochemical element can be any known energy storage device and is not particularly limited. However, a non-limiting example thereof includes a lithium secondary battery. The lithium secondary battery is well known and its structure is also known, so it is not described in detail in this disclosure.

[0116] According to one embodiment, a lithium secondary battery may include the separator described above between a positive electrode and a negative electrode. In this case, any of the separators commonly used in lithium secondary batteries may be used as the positive electrode and the negative electrode without limitation.

[0117] According to an implementation example, the separator is usually manufactured by assembling a negative electrode, a separator, and a positive electrode and injecting an electrolyte when used in a battery, so it will not be described in detail here.

[0118] The embodiments of the present disclosure are further described below in conjunction with specific experimental examples. The embodiments and comparative examples included in the experimental examples are merely illustrative of the present disclosure and are not intended to limit the scope of the appended claims. Various changes and modifications can be made to the embodiments within the scope of the present disclosure and the scope of the technical concept, which is obvious to those skilled in the art, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0119] First, the method for measuring the physical properties of the separator and the method for evaluating the characteristics of the secondary battery will be described.

[0120] [Measurement of FT-IR spectrum]

[0121] The separator was cut into a size of 1 cm×1 cm to prepare a measurement sample, and measurement was performed under the following conditions using an FT-IR instrument (Nicolet iN10 Infrared Microscope, Thermo Scientific) equipped with an MCT (mercury cadmium telluride) detector.

[0122] -Resolution: 4cm -1

[0123] - Scans: 16

[0124] -Range: 4000cm -1 ~675cm -1

[0125] - Measurement points per sample: 15 points (10 μm interval) * 15 points (10 μm interval) mapped to 3 positions (mapping 3 positions)

[0126] [Average thickness of separator and porous substrate (μm)]

[0127] After stacking the diaphragms into 10 layers, the thickness was measured at 5 random points in the width direction using a thickness gauge from Mitutoyo. The sum was then divided by 5 to derive the average thickness of the 10 layers of diaphragms, which was then divided by 10 to obtain the overall average thickness of the single diaphragm.

[0128] The average thickness of the porous substrate is determined by laminating the porous substrate into 10 layers. The thickness is then measured at 5 random points along the width of the porous substrate using a Mitutoyo thickness gauge. The sum is then divided by 5 to derive the average thickness of the 10 layers, and then divided by 10 to obtain the average thickness of the porous substrate. If an inorganic particle layer has already been formed, the inorganic particle layer is removed and thoroughly dried, and then the average thickness of the porous substrate from which the inorganic particle layer has been removed is determined in the same manner as described above.

[0129] [Gurley air permeability (sec / 100cc)]

[0130] The measurements were performed using a Toyoseiki Densometer according to ASTM D726. The time required for 100 cc of air to pass through a 1 square inch area of ​​the membrane was recorded in seconds and compared.

[0131] [Puncture strength (N / μm)]

[0132] The puncture strength was measured by attaching a pin tip with a diameter of 1.0 mm and a radius of curvature of 0.5 mm to an INSTRON Universal Test Machine (UTM) 3345 and pressing against the diaphragm at a speed of 120 mm / min. The puncture strength was calculated by dividing the load (N) at rupture by the diaphragm thickness (μm).

[0133] [Tensile strength (kgf / cm 2 )]

[0134] The tensile strength was measured at room temperature (25° C.) according to ASTM D882. The separator was pulled in both the transverse and longitudinal directions at a speed of 100 mm / min using an Instron Universal Test Machine (UTM) 3345 to measure the strength at break.

[0135] [Heat shrinkage (%)]

[0136] Cut the separator into a 10cm square and mark the transverse direction (TD) and machine direction (MD). Place the sample in the center, place five pieces of paper above and below the sample, and wrap the four edges of the paper with tape. Place the paper-wrapped sample in a hot air drying oven at 130°C for 60 minutes. Then remove the sample and measure the separator using a camera. Calculate the heat shrinkage in the machine direction (MD) and transverse direction (TD) using the following formula.

[0137] MD heat shrinkage (%) = [(MD length before heating - MD length after heating) / MD length before heating] × 100

[0138] TD heat shrinkage (%) = [(TD length before heating - TD length after heating) / TD length before heating] × 100

[0139] [Saturated moisture content (ppm)]

[0140] The saturated moisture content of the separator was measured using the Karl Fischer method. A Karl Fischer titrator from Metrohm was used. The measurement conditions were: a separator sample weight of 0.3 g, an oven temperature of 150° C., and a measurement time of 600 seconds.

[0141] Specifically, the manufactured separator was placed in a constant temperature and humidity chamber set at 40° C. and 90% relative humidity for 24 hours, and then the saturated moisture content was measured under the above-mentioned conditions.

[0142] [Adhesion]

[0143] The diaphragm was cut into a size of 50 mm wide × 50 mm long and arranged so that the inorganic particle layer was on the upper part. Black drawing paper (20 mm wide × 150 mm long × 0.25 mm thick) with a dynamic friction coefficient of 0.15 was placed on top and a certain pressure (200 g / cm 2 ), then forcibly pull out the black drawing paper to the side and confirm the degree of inorganic adhesion on the surface. According to the degree of adhesion, refer to the following grades to judge A / B / C / D / E / F.

[0144] A: Not attached

[0145] B: A small amount of inorganic matter is attached

[0146] C to F are the levels at which both the adhesive and the inorganic matter are attached, and the closer to F, the more severe the condition.

[0147] [Battery resistance characteristics]

[0148] The batteries manufactured according to the examples and comparative examples were charged and discharged using a charge / discharge cycler at 4.2V CC-CV (constant current-constant voltage). Specifically, each battery was charged at 25°C at a constant current rate of 0.5C until the voltage reached 4.2V, and then charged at a constant voltage rate of 4.2V until the current reached 0.01C. The cycle was then repeated 600 times, with a constant current of 0.5C until the voltage reached 3.0V. When the remaining capacity (state of charge (SoC)) at the 600th charge and discharge cycle was 60%, the resistance value was derived by measuring the DC-IR (Direct Current Internal Resistance) during discharge using the J-Pulse method.

[0149] In this case, based on the resistance value of Example 1, if the resistance increase of each battery manufactured according to the example and the comparative example was less than 5%, it was marked as "low", if it was 5% or more, it was marked as "medium", and if it was 10% or more, it was marked as "high".

[0150] <Example 1>

[0151] Preparation of coating slurry

[0152] Based on the total weight of the solid content, boehmite (D10: 0.45 μm, D50: 0.71 μm, D90: 1.57 μm, BET specific surface area: 5 m 2 A coating slurry having a solid content concentration of 28 wt% was prepared by adding 96.5 wt% of polyacrylamide (Mw = 300,000 g / mol), 3.0 wt% of a polyacrylamide resin (Mw = 300,000 g / mol, acrylamide and 2-hydroxyethyl methacrylate in a ratio of 90 mol%:10 mol%) as a binder, and 0.5 wt% of polyvinyl alcohol (degree of saponification: 88 mol%, Mw: 50,000 g / mol) to water and stirring.

[0153] Manufacturing diaphragms

[0154] A polyethylene porous film with an average thickness of 10 μm (porosity: 42%, Gurley air permeability: 128 sec / 100 cc, MD tensile strength: 2317 kgf / cm 2 , TD tensile strength: 2514kgf / cm 2) as a porous substrate. The above-prepared coating slurry was applied to both sides of the porous substrate and then dried to produce a separator having an inorganic particle layer with an average thickness of 1.35 μm formed on both sides of the porous substrate. The physical properties of the separator are shown in Table 1 below, and the FT-IR spectrum measurement results of the separator are shown in Table 3. Figure 1 and Figure 5 .

[0155] Manufacturing secondary batteries

[0156] 94 wt% of LiCoO2 as the positive electrode active material, 2.5 wt% of polyvinylidene fluoride as the flux, and 3.5 wt% of carbon black as the conductive agent were added to N-methyl-2-pyrrolidone (NMP) as the solvent and stirred to prepare a uniform positive electrode slurry. The prepared slurry was coated on a 30 μm thick aluminum foil, dried and pressed to produce a positive electrode with a total thickness of 150 μm. 95 wt% of artificial graphite as the negative electrode active material, 3 wt% of acrylic latex with a Tg of -52°C as the flux, and 2 wt% of carboxymethylcellulose (CMC) as the thickener were added to water as the solvent and stirred to prepare a uniform negative electrode slurry. The prepared slurry was coated on a copper foil with a thickness of 20 μm and dried and pressed to produce a negative electrode with a total thickness of 150 μm. After assembling the pouch-type battery by stacking the above-mentioned separator between the positive electrode and the negative electrode, the assembled battery was heat-welded at 80°C and 1 MPa using a hot press to weld the positive electrode, negative electrode and separator to each other. Thereafter, an electrolyte containing 1M lithium hexafluorophosphate (LiPF6) dissolved in a solution containing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 30:50:20 was injected and sealed to produce a secondary battery with a capacity of 2 Ah. The resistance characteristics of the secondary battery are included in the following Table 1.

[0157] <Example 2>

[0158] The same procedure as in Example 1 was followed except that 3.5% by weight of a polyacrylamide resin was used as the binder instead of polyvinyl alcohol, and a porous substrate pretreated as follows was used. The pretreated porous substrate was a polyethylene porous film having an average thickness of 10 μm (porosity: 42%, Gurley air permeability: 128 sec / 100 cc, MD tensile strength: 2317 kgf / cm 2, TD tensile strength: 2514kgf / cm 2 ) are produced by performing corona discharge treatment on both sides. In this case, the power density of the corona discharge treatment is 2W / mm and the speed is 3mpm to 20mpm (meters per minute).

[0159] The properties of the manufactured separator and secondary battery are shown in Tables 1 and 3 below.

[0160] <Example 3>

[0161] In addition to the inorganic particles used in Example 1 when preparing the coating slurry, boehmite (D10: 0.56 μm, D50: 0.85 μm, D90: 1.93 μm, BET specific surface area: 4 m 2 A separator and a secondary battery were manufactured in the same manner as in Example 1, except that the separator and the secondary battery had the same properties as in Example 1. The properties of the separator and the secondary battery are shown in Tables 1 and 3 below.

[0162] <Example 4>

[0163] In addition, in Example 1, when the coating slurry was prepared, the inorganic particles used were boehmite (D10: 0.38 μm, D50: 0.67 μm, D90: 1.52 μm, BET specific surface area: 6 m 2 A separator and a secondary battery were manufactured in the same manner as in Example 1, except that the separator and the secondary battery had the same properties as in Example 1. The properties of the separator and the secondary battery are shown in Tables 1 and 3 below.

[0164] <Example 5>

[0165] A separator and a secondary battery were manufactured in the same manner as in Example 1, except that polyacrylamide with a weight average molecular weight of 200,000 g / mol was used instead of the polyacrylamide resin in Example 1. The properties of the separator and the secondary battery are summarized in Tables 1 and 3 below.

[0166] Comparative Example 1

[0167] In addition to the polyethylene porous film with an average thickness of 9 μm (porosity: 40%, Gurley air permeability: 152 sec / 100 cc, MD tensile strength: 2242 kgf / cm) used in the manufacture of the separator in Example 2, 2 , TD tensile strength: 1864kgf / cm 2 ) were formed on both sides of the membrane with an average thickness of 2 μm, and a separator and a secondary battery were manufactured in the same manner as in Example 2. The characteristics of the separator and the secondary battery are summarized in Tables 2 and 3 below.

[0168] Comparative Example 2

[0169] In addition, in Example 2, when the coating slurry was prepared, the inorganic particles were boehmite (D10: 0.16 μm, D50: 0.31 μm, D90: 0.75 μm, BET specific surface area: 20 m 2 / g), a separator and a secondary battery were manufactured in the same manner as in Example 2. The characteristics of the separator and the secondary battery are summarized in Tables 2, 3, Figure 2 and Figure 5 .

[0170] Comparative Example 3

[0171] In Example 2, the inorganic particles used were boehmite (D10: 0.79 μm, D50: 1.64 μm, D90: 2.85 μm, BET specific surface area: 2.5 m 2 / g), a separator and a secondary battery were manufactured in the same manner as in Example 2. The characteristics of the separator and the secondary battery are summarized in Tables 2, 3, Figure 3 and Figure 5 .

[0172] Comparative Example 4

[0173] In addition, in Example 2, when the coating slurry was prepared, the inorganic particles were boehmite (D10: 0.31 μm, D50: 0.58 μm, D90: 1.28 μm, BET specific surface area: 8 m 2 / g), a separator and a secondary battery were manufactured in the same manner as in Example 2. The characteristics of the separator and the secondary battery are summarized in Tables 2, 3, Figure 4 and Figure 5 .

[0174]

Table 1

[0175]

[0176]

Table 2

[0177]

[0178]

Table 3

[0179]

[0180] Tables 1 and 2 above confirm that, compared to the comparative example, the separators of Examples 1 to 5 exhibited thermal shrinkage rates of less than 5% even at thin thicknesses, demonstrating excellent heat resistance. Adhesion tests showed no adhesion, demonstrating excellent adhesion. Furthermore, batteries using these separators demonstrated low discharge resistance after 600 cycles.

[0181] Specifically, referring to Table 3 above, it can be seen that in the FT-IR spectrum at 1082.5 cm -1 to 1086.5cm -1 The separator of the embodiment in which a peak appears in the range of and a saturated moisture content satisfies 350ppm to 1000ppm is different from Comparative Examples 2 to Comparative Examples 4 which do not have a peak and a saturated moisture content in the above range or Comparative Example 1 which does not have a saturated moisture content in the above range, and is excellent in heat resistance, adhesion and battery resistance characteristics.

[0182] In particular, it was confirmed that the polyacrylamide resins prepared in Examples 1 to 4 using a hydroxyl-containing (meth)acrylate monomer in addition to a (meth)acrylamide monomer as a binder had better heat resistance than Example 5 using a (meth)acrylamide monomer alone.

[0183] Furthermore, it was confirmed that in Example 1, since the binder further contained polyvinyl alcohol, the heat resistance was superior to that of Example 2 even though the porous substrate was not pretreated.

[0184] On the contrary, it was confirmed that the t1 / t2 value of the separator of Comparative Example 1 was less than 0.75, and therefore could not meet the range of saturated moisture content to be achieved in the present disclosure. Therefore, the discharge resistance of the battery using this separator after 600 cycles was significantly higher than that of the embodiment.

[0185] Furthermore, it was confirmed that the separator of Comparative Example 2 had a BET specific surface area of ​​20 m 2 / g of inorganic particles, thus failing to meet the specific range of peaks appearing in the FT-IR spectrum and the specific range of saturated moisture content to be achieved in the present disclosure. Therefore, the discharge resistance of the battery using this separator after 600 cycles is higher than that of the embodiment.

[0186] Furthermore, it was confirmed that the separator of Comparative Example 3 used a BET specific surface area of ​​2.5 m 2 / g of inorganic particles, thus failing to meet the specific range of peaks appearing in the FT-IR spectrum and the specific range of saturated moisture content to be achieved in the present disclosure. Consequently, heat resistance and adhesive strength were significantly reduced at thin thicknesses. Furthermore, it was confirmed that the discharge resistance of batteries using this separator after 600 cycles was significantly higher than that of the examples.

[0187] Furthermore, it was confirmed that the separator of Comparative Example 4 used a BET specific surface area of ​​8 m 2 / g of inorganic particles, thus failing to meet the specific range of peaks appearing in the FT-IR spectrum and the specific range of saturated moisture content to be achieved in the present disclosure. Therefore, the discharge resistance of the battery using this separator after 600 cycles is higher than that of the embodiment.

[0188] The above description is merely an example of applying the principles of the present disclosure, and other configurations may be included without departing from the scope of the present disclosure.

Claims

1. A diaphragm, comprising: Porous substrate; as well as an inorganic particle layer, which is formed on at least one side of the porous substrate and comprises a binder and inorganic particles, In the Fourier transform infrared spectroscopy spectrum, at 1082.5 cm -1 Up to 1086.5cm -1 The peak value appears in the range of , and the saturated moisture content determined by the Karl Fischer method is 350ppm to 1000ppm. 2 . The separator according to claim 1 , wherein the saturated moisture content is 450 ppm to 1000 ppm. 3 . The separator according to claim 1 , wherein the average thickness of the porous substrate is 5 μm to 15 μm, and the ratio of the average thickness of the porous substrate to the average thickness of the separator is 0.7 or more. 4 . The separator according to claim 1 , wherein the total thickness of the inorganic particle layer formed on the porous substrate is 3.2 μm or less. The separator according to claim 1 , wherein the binder comprises a polyacrylamide-based resin. The separator according to claim 5 , wherein the polyacrylamide-based resin is a copolymer including a unit derived from a (meth)acrylamide-based monomer and a unit derived from a comonomer. 7 . The separator according to claim 6 , wherein the polyacrylamide-based resin comprises a structural unit derived from a (meth)acrylamide-based monomer and a structural unit derived from a (meth)acrylic acid-based monomer containing a hydroxyl group. The separator according to claim 5 , wherein the weight average molecular weight of the polyacrylamide-based resin is 100,000 g / mol to 2,000,000 g / mol. 9 . The separator according to claim 5 , wherein the binder further comprises any one or more additional binders selected from the group consisting of polyvinyl alcohol, polyvinylidene fluoride, carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, polyethylene glycol, polyacrylonitrile, polyvinyl pyrrolidone and copolymers thereof. 10 . The separator according to claim 9 , wherein the content of the additional binder is 0.1 wt % to 30 wt % based on the total weight of the binder.

11. The diaphragm according to claim 1, wherein the inorganic particles have a BET specific surface area of ​​3 m 2 / g to 7m 2 / g. 12 . The separator according to claim 1 , wherein an average particle size D50 of the inorganic particles is 0.5 μm to 1.5 μm. 13 . The separator according to claim 1 , wherein the inorganic particles include any one or two or more selected from the group consisting of metal hydroxides, metal oxides, metal nitrides, and metal carbides. The separator according to claim 1 , wherein the heat shrinkage rate in the longitudinal direction and the transverse direction of the separator measured after being left to stand at 130° C. for 60 minutes is 5% or less. 15 . The separator according to claim 1 , wherein a weight ratio of the inorganic particles to the binder in the inorganic particle layer is 50:50 to 99.9:0.

1.

16. The separator according to claim 1, wherein the inorganic particle layer is formed to have a particle size of 0.5 g / m 2 Up to 10g / m 2 .

17. An electrochemical element comprising the separator according to any one of claims 1 to 16.

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