Separator for electrochemical device and electrochemical device including the same

Abstract

The present invention relates to a separator for an electrochemical device, the separator comprising an inorganic hybrid porous layer located on at least one surface of a polymeric porous support and comprising an inorganic filler and a binder polymer, the binder polymer comprising a first binder polymer, the first binder polymer being poly(vinylidene fluoride-co-hexafluoropropylene) having a tan δ peak at −18° C. to −5° C. as measured by dynamic mechanical analysis, and an electrochemical device comprising the separator. The separator for an electrochemical device according to one embodiment of the present invention has excellent adhesion to an electrode and can improve safety at high temperatures.

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to a separator for an electrochemical device and an electrochemical device including the same.

[0002] This application claims priority based on Korean Patent Applications Nos. 2021-0095122, 2021-0095123, and 2021-0095124, filed on July 20, 2021, and the entire contents disclosed in the specifications and drawings of those applications are incorporated herein by reference. [Background technology]

[0003] In recent years, interest in energy storage technology has been growing. As its applications expand to include mobile phones, camcorders, notebook PCs, and even electric vehicles, there is a growing demand for higher energy density batteries used to power these electronic devices. Lithium secondary batteries are the electrochemical device that best meets these demands, and research into them is currently in full swing.

[0004] In the manufacture and use of such lithium secondary batteries, ensuring the safety of the lithium secondary battery is an important issue to be resolved. In particular, separators commonly used in lithium secondary batteries exhibit severe thermal shrinkage at high temperatures due to their material properties and manufacturing process characteristics, resulting in safety issues such as internal short circuits.

[0005] To address these safety concerns, a separator has been proposed in which a mixture of inorganic filler and binder polymer is coated on a porous polymer support. However, because the melting temperature (Tm) of the binder polymer used here is around 120°C, the separator still exhibits thermal shrinkage at high temperatures such as 150°C. Furthermore, when an electrode and separator are stacked to form an electrode assembly, the interlayer adhesion is insufficient, causing the electrode and separator to separate from each other, and the inorganic filler that is detached during this process can act as local defects within the electrochemical device. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a separator for an electrochemical device that has excellent adhesion to an electrode and improved safety at high temperatures, and an electrochemical device including the separator. [Means for solving the problem]

[0007] To achieve the above object, according to one aspect of the present invention, there is provided a separator for an electrochemical device according to the following embodiment.

[0008] The first embodiment is a polymeric porous support; an inorganic composite porous layer located on at least one surface of the polymeric porous support and including an inorganic filler and a binder polymer; the binder polymer comprises a first binder polymer; The first binder polymer is poly(vinylidene fluoride-co-hexafluoropropylene) having a tan δ peak at −18° C. to −5° C. when measured by dynamic mechanical analysis.

[0009] The second embodiment is the first embodiment, The content of the hexafluoropropylene repeating unit in the first binder polymer may be 4 wt % to 22 wt % based on 100 wt % which is the sum of the content of the vinylidene fluoride repeating unit and the content of the hexafluoropropylene repeating unit.

[0010] The third embodiment is the first or second embodiment, the binder polymer further comprises a second binder polymer; The second binder polymer may be poly(vinylidene fluoride-co-chlorotrifluoroethylene) having a tan δ peak at −11° C. to 0° C. when measured by dynamic mechanical analysis.

[0011] The fourth embodiment is the third embodiment, The second binder polymer may have a melting temperature of 155°C or higher.

[0012] The fifth embodiment is the third or fourth embodiment, The content of the chlorotrifluoroethylene repeating unit of the second binder polymer may be 10 wt % to 30 wt % based on 100 wt % of the total content of the vinylidene fluoride repeating unit and the chlorotrifluoroethylene repeating unit.

[0013] The sixth embodiment is any one of the third to fifth embodiments, The weight ratio of the first binder polymer to the second binder polymer may be 50:50 to 95:5.

[0014] The seventh embodiment is any one of the first to sixth embodiments, The inorganic composite porous layer may have a thickness of 10 μm or less.

[0015] The eighth embodiment is any one of the first to seventh embodiments, The separator for an electrochemical device may have a thermal shrinkage of 25% or less in both a machine direction (MD) and a transverse direction (TD) after being left at 130° C. for 1 hour.

[0016] The ninth embodiment is any one of the first to eighth embodiments, The separator for an electrochemical device may have a heat shrinkage of 55% or less in both a machine direction (MD) and a transverse direction (TD) after being left at 150° C. for 30 minutes.

[0017] A tenth embodiment is any one of the first to ninth embodiments, The separator for an electrochemical device may have an electrode adhesive strength of 40 gf / 25 mm or more.

[0018] An eleventh embodiment is any one of the first to tenth embodiments, The first binder polymer may be poly(vinylidene fluoride-hexafluoropropylene) having a γ-type crystal form.

[0019] A twelfth embodiment is any one of the first to eleventh embodiments, The first binder polymer may have a melting temperature of 155° C. or higher.

[0020] The thirteenth embodiment is The electrochemical device includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, The separator for an electrochemical device is the separator for an electrochemical device according to any one of the first to twelfth embodiments. [Effects of the Invention]

[0021] A separator for an electrochemical device according to one embodiment of the present invention includes poly(vinylidene fluoride-hexafluoropropylene) having a tan δ peak at −18°C to −5°C when measured by dynamic mechanical analysis, thereby providing excellent adhesion to electrodes and improving thermal shrinkage at high temperatures.

[0022] A separator for an electrochemical device according to one embodiment of the present invention includes poly(vinylidene fluoride-hexafluoropropylene) having a tan δ peak at -18°C to -5°C when measured by dynamic mechanical analysis, and poly(vinylidene fluoride-chlorotrifluoroethylene) having a tan δ peak at -11°C to 0°C when measured by dynamic mechanical analysis, thereby providing excellent adhesion to electrodes and improving thermal shrinkage at high temperatures.

[0023] In a separator for an electrochemical device according to one embodiment of the present invention, the first binder polymer provides adhesive strength to the electrode, and the second binder polymer provides adhesive strength between the polymer porous support and the inorganic composite porous layer, thereby providing excellent adhesive strength to the electrode.

[0024] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical concept of the present invention, so the present invention should not be interpreted as being limited to the matters described in the drawings. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a graph showing the relationship between temperature and tan δ of the first binder polymer used in Examples 1 to 3 and Comparative Example 1, measured by dynamic mechanical analysis (DMA). [Figure 2] 1 is a graph showing the relationship between temperature and tan δ of the second binder polymer used in Example 1, measured by dynamic mechanical analysis (DMA). [Figure 3] FIG. 2 is a diagram showing the crystalline structure of the first binder polymer used in Example 1 measured by wide-angle X-ray diffraction (WAXS). [Figure 4] FIG. 2 is a diagram showing the crystal structure of the first binder polymer used in Example 2 measured by wide-angle X-ray diffraction. [Figure 5]FIG. 2 is a diagram showing the crystal structure of the first binder polymer used in Example 3, measured by wide-angle X-ray diffraction. [Figure 6] FIG. 2 is a diagram showing the crystal structure of the first binder polymer used in Comparative Example 1, measured by wide-angle X-ray diffraction. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in the specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as having meanings and concepts corresponding to the technical ideas of the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best explain the invention.

[0027] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiment of the present invention and do not represent the entire technical idea of the present invention, and that there may be various equivalents and modifications that can be substituted for them at the time of this application.

[0028] The terms "first," "second," etc. are used to distinguish one component from another, and do not limit each component to the terms.

[0029] The separator for an electrochemical device according to one aspect of the present invention comprises: a polymeric porous support; an inorganic composite porous layer located on at least one surface of the polymeric porous support and including an inorganic filler and a binder polymer; the binder polymer comprises a first binder polymer; The first binder polymer is characterized in that it is poly(vinylidene fluoride-co-hexafluoropropylene) which has a tan δ peak at -18°C to -5°C when measured by dynamic mechanical analysis.

[0030] A separator for an electrochemical device according to one embodiment of the present invention includes a polymeric porous support.

[0031] The polymeric porous support may be any material commonly used as a separator for electrochemical devices. Such a polymeric porous support is a thin film containing a polymer material. Non-limiting examples of the polymer material include olefin polymers, ethylene terephthalate polymers, butylene terephthalate polymers, acetal polymers, amide polymers, carbonate polymers, imide polymers, ether ether ketone polymers, ether sulfone polymers, phenylene oxide polymers, phenylene sulfide polymers, and ethylene naphthalene polymers. The polymeric porous support may be a nonwoven fabric or porous polymer film made from the above-mentioned polymeric materials, or a laminate of two or more of these. Specifically, the polymeric porous support may be any one of a) to e) below.

[0032] a) Porous film formed by melting and extruding a polymer material b) A porous membrane in which two or more layers of the porous film of a) are laminated. c) A nonwoven web produced by accumulating filaments obtained by melting / radiating a polymer material d) A multilayer film in which two or more layers of the nonwoven fabric web of c) are laminated. e) A porous membrane with a multilayer structure comprising two or more of the above a) to d).

[0033] The polymeric porous support may be prepared by forming pores from the above-mentioned materials by a method known in the art, for example, a wet method using a solvent, diluent, or pore-forming agent, or a dry method using a stretching method, in order to ensure excellent breathability and porosity.

[0034] In one embodiment of the present invention, the thickness of the porous polymer support is not particularly limited, and may be 1 μm to 100 μm, or 1 μm to 30 μm. When the thickness of the porous polymer support is within the above range, it is possible to prevent the separator from being easily damaged during use of the battery and ensure energy density.

[0035] In this specification, the thickness of the polymeric porous support can be measured, for example, using a thickness meter (Mitutoyo, VL-50S-B).

[0036] Meanwhile, the average pore size and porosity of the polymer porous support are not particularly limited as long as they are suitable for use in electrochemical devices, and the average pore size may be 0.01 μm to 50 μm, or 0.1 μm to 20 μm, and the porosity may be 5% to 95%. When the pore size and porosity are within the above-mentioned ranges, the polymer porous support can be easily prevented from acting as a resistor, and the mechanical properties of the polymer porous support can be easily maintained.

[0037] The average pore size and porosity of the polymeric porous support can be measured by a BET 6-point method using a scanning electron microscope (SEM) image, a mercury porosimeter, a capillary flow porometer, or a porosimetry analyzer (Bell Japan Inc., Belsorp-II mini) in a flow-through nitrogen gas adsorption method.

[0038] Alternatively, the porosity of the polymeric porous support can be measured by calculating the net density of the porous support from the density (apparent density) of the porous support, the composition ratio of the materials contained in the porous support, and the density of each component, and then calculating the porosity of the porous support from the difference between the apparent density and the net density. For example, the porosity can be calculated using the following Equation 1:

[0039] [Formula 1] Porosity (volume%) = {1 - (apparent density / true density)} x 100

[0040] The apparent density in the above formula 1 can be calculated from the following formula 2.

[0041] [Formula 2] Apparent density (g / cm 3 ) = (weight of porous support (g)) / {(thickness of porous support (cm)) × (area of porous support (cm 2 ))}

[0042] A separator for an electrochemical device according to one embodiment of the present invention includes an inorganic composite porous layer formed on at least one surface of the porous polymer support. The inorganic composite porous layer may be formed on one or both surfaces of the porous polymer support.

[0043] The inorganic composite porous layer includes an inorganic filler and a binder polymer that bonds the inorganic fillers together (i.e., the binder polymer connects and fixes the inorganic fillers together) so that the inorganic fillers can be maintained in a bonded state, and the binder polymer can maintain the bonded state between the inorganic filler and the polymeric porous support.

[0044] The inorganic filler is not particularly limited as long as it is electrochemically stable. That is, the inorganic filler that can be used in the present invention is selected from those that are within the operating voltage range (e.g., Li / Li) of the applied electrochemical device. +There are no particular limitations on the dielectric constant as long as oxidation and / or reduction reactions do not occur at a potential of 0 to 5 V relative to the reference potential. In particular, when an inorganic filler with a high dielectric constant is used as the inorganic filler, it can contribute to an increase in the degree of dissociation of the electrolyte salt, for example, lithium salt, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte solution.

[0045] For the reasons described above, in one embodiment of the present invention, the inorganic filler may include a high dielectric constant inorganic filler having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic fillers having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1、0<y<1)、Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, AlOOH, Al(OH)3, SiC, TiO2 or mixtures thereof.

[0046] In another embodiment of the present invention, the inorganic filler may be an inorganic filler having lithium ion transport ability, i.e., an inorganic filler that contains lithium element but does not store lithium but has the function of transporting lithium ions. Non-limiting examples of inorganic fillers having lithium ion transport ability include lithium phosphate (LiPO), lithium titanium phosphate (Li x Ti y (PO4)3,0 <x<2、0<y<3)、リチウムアルミニウムチタンホスフェート(Li x Al y Ti z (PO4)3,0 <x<2、0<y<1、0<z<3)、14Li2O-9Al2O3-38TiO2-39P2O5などのような(LiAlTiP) x O ySystem glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 S4 such as lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride such as Li3N (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass such as LiI-Li2S-P2S5 (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), or mixtures thereof, etc.

[0047] In one embodiment of the present invention, the average particle size of the inorganic filler can be 0.01 μm to 1.5 μm. When the average particle size of the inorganic filler satisfies the above-mentioned range, it is easy to form an inorganic hybrid void layer having a uniform thickness and appropriate porosity, the dispersibility of the inorganic filler is good, and a desired energy density can be provided.

[0048] At this time, the average particle size of the inorganic filler is D 50 meaning particle size, "D 50The term "particle size" refers to the particle size at the 50% point of the cumulative particle number distribution according to particle size. The particle size can be measured using a laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in diffraction pattern according to particle size when the particles pass through a laser beam. The D50 particle size can be measured by calculating the particle diameter at the 50% point of the cumulative particle number distribution according to particle size measured by the analyzer.

[0049] In general, in the case of poly(vinylidene fluoride-hexafluoropropylene), as the content of hexafluoropropylene repeating units increases, the adhesive strength increases but the heat resistance decreases, which is a problem.

[0050] The inventors of the present invention discovered that when poly(vinylidene fluoride-hexafluoropropylene) has a tanδ peak in a specific temperature range, it exhibits excellent adhesive strength and heat resistance regardless of the content of hexafluoropropylene repeating units, and thus completed the present invention.

[0051] Herein, the content of the poly(vinylidene fluoride-hexafluoropropylene) repeating unit can be determined, for example, by measuring the content of HFP (hexafluoropropylene) functional groups in the inorganic hybrid porous layer, for example, by confirming the HFP content of the inorganic hybrid porous layer using fluorine atomic nuclear magnetic resonance spectroscopy.

[0052] In one embodiment of the present invention, the fluorine nuclear magnetic resonance spectroscopy can be measured using, for example, a 19F NMR (Bruker, DRX-300) analyzer and CFCl3 as a reference material. For example, the sample to be measured is first dissolved in deuterated acetone at 8 wt%. The weight-average molecular weight is determined by gel permeation chromatography (GPC, high temperature PL 220, Waters) equipped with a refractive index detector and two PLgel-10 μm Mixed-B columns (Polymer Laboratory). The mobile phase solvent is dimethylformamide supplemented with 0.1 M LiBr, and the measurement is performed at 80°C and a flow rate of 1.0 mL / min. The standard sample can be polystyrene with an average molecular weight ranging from 2,000 g / mol to 2,000,000 g / mol.

[0053] In another embodiment of the present invention, the fluorine nuclear magnetic resonance spectroscopy may be performed using a Unity 400 spectrophotometer at 376.3 MHz. For example, spectra may be obtained in deuterated dimethylformamide at 50°C with an 8.0 microsecond excitation pulse width and a 10-second recycle delay, or in deuterated dimethylsulfoxide at 50°C with a 6.0 microsecond excitation pulse width and a 5-second recycle delay, or in deuterated acetone at 50°C with an 8.0 microsecond excitation pulse width and a 20-second recycle delay.

[0054] The binder polymer includes poly(vinylidene fluoride-co-hexafluoropropylene) as a first binder polymer, which has a tan δ peak at −18° C. to −5° C. when measured by dynamic mechanical analysis.

[0055] As used herein, tan δ refers to the ratio of the loss modulus (E″) to the storage modulus (E′), and the magnitude of the tan δ peak refers to the amount of amorphous regions present in a sample.

[0056] The "tan δ peak" refers to the inflection point where the gradient of a tangent to a graph changes from positive (+) to negative (-) in a graph showing the relationship between temperature on the x-axis and tan δ on the y-axis. Alternatively, it refers to the point where the gradient of a tangent to the graph becomes 0. In this case, the tan δ peak may refer to the second peak among multiple tan δ peaks.

[0057] The first binder polymer has a tan δ peak in the aforementioned temperature range, thereby exhibiting excellent adhesive strength and excellent heat resistance at high temperatures. For example, the first binder polymer may exhibit excellent heat resistance regardless of the content of hexafluoropropylene repeating units. The first binder polymer may exhibit excellent heat resistance even when the content of hexafluoropropylene repeating units is increased.

[0058] As a result, the separator for an electrochemical device according to one embodiment of the present invention, which includes the first binder polymer, can have improved safety at high temperatures. For example, the separator may have a thermal shrinkage of 25% or less, 20% or less, 15% or less, 10% or less, or 5% or less in the machine direction (MD) and transverse direction (TD) after being left at 130°C for 1 hour.

[0059] Furthermore, the heat shrinkage rate of the separator after being left at 150°C for 30 minutes may be 55% or less, or 50% or less, or 45% or less, or 40% or less, or 35% or less, or 30% or less, or 25% or less, or 20% or less, or 15% or less, or 10% or less, or 5% or less in the machine direction (MD) and transverse direction (TD).

[0060] Here, the term "machine direction" refers to the direction in which a separation membrane advances during continuous production or the direction in which a manufactured separation membrane is wound up, i.e., the longitudinal direction of the separation membrane. The term "transverse direction" refers to the direction across the machine direction, i.e., the direction perpendicular to the direction in which a separation membrane advances during continuous production or the direction in which a manufactured separation membrane is wound up, i.e., the direction perpendicular to the longitudinal direction of the separation membrane.

[0061] If the first binder polymer does not have a tan δ peak in the above-mentioned temperature range, for example, if it has a tan δ peak at 17°C to 28°C, the adhesive strength increases as the content of hexafluoropropylene repeating units increases, but the heat resistance decreases.

[0062] In one embodiment of the present invention, the first binder polymer may have a tan δ peak at -15°C or higher, or -13°C or higher, or -12.12°C or higher, or -12°C or higher, or -10°C or higher, or -9.68°C or higher, or -9°C or higher, or -8.74°C, and at -6°C or lower, or -7°C or lower, or -8°C or lower, or -8.74°C or lower, or -9°C or lower, or -9.68°C or lower, or -12°C or lower, or -12.12°C or lower, as measured by dynamic mechanical analysis.

[0063] The dynamic mechanical analysis is an analytical method in which a polymer specimen is subjected to an oscillating force or deformation to measure the modulus and damping depending on temperature and frequency.

[0064] In one embodiment of the present invention, a first binder polymer is pressed at 190°C to prepare a binder specimen having a thickness of 0.5 mm. The binder specimen is then subjected to dynamic mechanical analysis by maintaining the binder specimen at -80°C for 10 minutes, and then heating the binder specimen to 140°C at a rate of 5°C / min, thereby measuring the ratio of the storage modulus E' to the loss modulus E'' and measuring the tan δ value.

[0065] In one embodiment of the present invention, the dynamic mechanical analysis can be measured using a TA Instruments DMA Q800.

[0066] In one embodiment of the present invention, the melting temperature of the first binder polymer may be 155°C or higher, or 160°C or higher, or 165°C or higher, or 165.36°C or higher, or 166°C or higher, or 166.31°C or higher, or 166.37°C or higher. The melting temperature of the first binder polymer may be 200°C or lower, or 190°C or lower, or 180°C or lower, or 170°C or lower, or 166.37°C or lower, or 166.31°C or lower, or 166°C or lower, or 165.36°C or lower. The first binder polymer may have a tan δ peak at -18°C to -5°C when measured by dynamic mechanical analysis, and have a melting temperature within the aforementioned range. When the melting temperature of the first binder polymer satisfies the aforementioned range, the separator for an electrochemical device according to one embodiment of the present invention, including the first binder polymer, exhibits improved heat resistance at high temperatures. For example, it may have better heat shrinkage at higher temperatures.

[0067] Throughout this specification, the melting temperature of the binder polymer may be measured using a differential scanning calorimeter (DSC), a thermal analysis instrument that measures the difference in heat required to raise the temperature of a sample and a reference material as a function of temperature.

[0068] In one embodiment of the present invention, the melting temperature of the binder polymer can be calculated from the peak temperature of the curve measured by a differential scanning calorimeter in the range of 155°C to 180°C when the binder polymer is heated from 25°C to 200°C at 10°C / min, left at 200°C for 10 minutes, cooled to 25°C at 10°C / min, left at 25°C for 10 minutes, and then further heated to 200°C at 10°C / min.

[0069] In one embodiment of the present invention, the content of the hexafluoropropylene repeat unit of the first binder polymer may be 4 wt% or more, 7 wt% or more, 9 wt% or more, 10 wt% or more, 11 wt% or more, 13 wt% or more, 15 wt% or more, 17 wt% or more, 18 wt% or more, 18.1 wt% or more, or 18.5 wt% or more, based on 100 wt% of the total content of the vinylidene fluoride repeat unit and the hexafluoropropylene repeat unit. It may be 22 wt% or less, 20 wt% or less, 19 wt% or less, 18.5 wt% or less, 18.1 wt% or less, 18 wt% or less, 17 wt% or less, 15 wt% or less, 13 wt% or less, 11 wt% or less, or 10 wt% or less. When the first binder polymer contains the above-mentioned amount of hexafluoropropylene repeating units, it may be more advantageous to ensure adhesion to the electrode.

[0070] In one embodiment of the present invention, the first binder polymer may have a γ-crystal form.

[0071] In this specification, a γ-type crystal structure refers to a crystal structure having a trans-trans-trans-gauche structure. When the first binder polymer has a γ-type crystal structure, the first binder polymer has a trans-trans-trans-gauche structure, which makes it easy for the first binder polymer to have superior heat resistance. That is, the first binder polymer may have a tan δ peak at -18°C to -5°C when measured by dynamic mechanical analysis, and may have a γ-type crystal structure.

[0072] Whether the first binder polymer has a γ-type crystal structure can be confirmed by wide-angle X-ray diffraction (WAXS). When the first binder polymer has a γ-type crystal structure, a diffraction peak is observed at a 2θ position of approximately 20.73°, which is relatively broad compared to, for example, α-type or β-type crystal structures, and a shoulder peak is observed at a 2θ position of approximately 20.73°. Furthermore, the relative proportions of the diffraction peaks at 2θ positions of 17.7°, 18.44°, 20.04°, 20.73°, 26.72°, and 27.70° are 46, 62, 100, 52, 15, and 8, respectively. The relative proportions of the diffraction peaks indicate the degree of crystallization of the first binder polymer.

[0073] In one embodiment of the present invention, the binder polymer may further include a second binder polymer in addition to the first binder polymer.

[0074] The second binder polymer may be poly(vinylidene fluoride-co-chlorotrifluoroethylene) having a tan δ peak at -11°C or higher, -9°C or higher, -7°C or higher, or -6.26°C or higher, and 0°C or lower, -2°C or lower, -4°C or lower, -6°C or lower, or -6.26°C or lower, as measured by dynamic mechanical analysis. In this case, the tan δ peak may be the second peak among a plurality of tan δ peaks. Because the second binder polymer has a tan δ peak in the above temperature range, excellent heat resistance at high temperatures may be achieved.

[0075] Therefore, when both the first binder polymer and the second binder polymer are included, the safety of the separator for an electrochemical device according to an embodiment of the present invention at high temperatures can be more easily improved.

[0076] In addition, in one embodiment of the present invention, when the first binder polymer and the second binder polymer are both included, the first binder polymer migrates to the interface between the separator and the electrode to ensure adhesion between the separator for electrochemical devices and the electrode, and the second binder polymer can ensure adhesion between the polymer porous support and the inorganic composite porous layer.

[0077] Due to the different phase separation rates of poly(vinylidene fluoride-hexafluoropropylene) and poly(vinylidene fluoride-chlorotrifluoroethylene), the first binder polymer migrates to the interface between the separator and the electrode to ensure adhesion between the separator for electrochemical devices and the electrode, and the second binder polymer can ensure adhesion between the polymer porous support and the inorganic composite porous layer.

[0078] After fabricating a separator containing a binder polymer in an inorganic composite porous layer, the binder polymer in the inorganic composite porous layer may be dissolved by the electrolyte during application to a battery. This dissolution of the binder polymer due to the electrolyte may be exacerbated by elevated temperatures within the battery. Typically, after battery fabrication, aging is performed at temperatures above 60°C. During this aging process, the binder polymer in the inorganic composite porous layer may be dissolved by the electrolyte, reducing the adhesive strength of the inorganic composite porous layer. This can lead to peeling of the inorganic composite porous layer from the porous polymer support or detachment of the inorganic filler from the inorganic composite porous layer.

[0079] The separator for an electrochemical device according to an embodiment of the present invention may include the second binder polymer, thereby reducing the leaching of the binder polymer and easily preventing the detachment of the inorganic filler.

[0080] In one embodiment of the present invention, the melting temperature of the second binder polymer may be 155°C or higher, or 160°C or higher, or 165°C or higher, or 166°C or higher, or 166.6°C or higher. The melting temperature of the second binder polymer may be 200°C or lower, 190°C or lower, 180°C or lower, 170°C or lower, or 166.6°C or lower. The second binder polymer may have a tan δ peak between -11°C and 0°C when measured by dynamic mechanical analysis, and may have a melting temperature within the aforementioned range. When the melting temperature of the second binder polymer is within the aforementioned range, the separator for an electrochemical device according to one embodiment of the present invention, including the second binder polymer, may have better heat resistance at high temperatures. For example, it may have a better heat shrinkage rate at high temperatures.

[0081] In one embodiment of the present invention, the content of chlorotrifluoroethylene repeating units in the second binder polymer may be 10 wt% or more, or 15 wt% or more, or 17 wt% or more, or 20 wt% or more, and 30 wt% or less, or 25 wt% or less, or 22 wt% or less, or 20 wt% or less, based on 100 wt% of the total content of vinylidene fluoride repeating units and chlorotrifluoroethylene repeating units. The second binder polymer may include poly(vinylidene fluoride-chlorotrifluoroethylene) having a tan δ peak between -11°C and 0°C when measured by dynamic mechanical analysis and having the above-mentioned content of chlorotrifluoroethylene repeating units. When the second binder polymer contains the above-mentioned content of repeating units, adhesion to the electrode can be more effectively ensured.

[0082] In one embodiment of the present invention, the weight ratio of the first binder polymer to the second binder polymer may be 50:50 to 95:5, or 86:14 to 80:20, or 84:16 to 80:20, or 82:18 to 80:20. When the weight ratio of the first binder polymer to the second binder polymer satisfies the above range, adhesion to the electrode is ensured, and binder elution at high temperatures during immersion in an electrolyte solution can be more easily suppressed. This also helps reduce microvoids.

[0083] In one embodiment of the present invention, the weight ratio of the inorganic filler to the binder polymer is determined taking into consideration the thickness, pore size, and porosity of the inorganic composite porous layer, and may be 50:50 to 99.9:0.1, 50:50 to 80:20, 80:20 to 99.9:0.1, or 95:5 to 99.9:0.1. When the weight ratio of the inorganic filler to the binder polymer is within the above range, sufficient space is formed between the inorganic fillers, making it easier to ensure the pore size and porosity of the inorganic composite porous layer. In addition, the adhesive strength between the inorganic fillers and between the inorganic filler and the polymeric porous support can be easily ensured.

[0084] In one embodiment of the present invention, the inorganic composite porous layer may further include additives such as a dispersant and / or a thickener, such as citric acid, hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), ethyl hydroxyethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose, cyanoethylene polyvinyl alcohol, or two or more thereof.

[0085] In one embodiment of the present invention, the inorganic composite porous layer may have a structure in which the inorganic fillers are filled and bound together by the binder polymer while in contact with each other, thereby forming interstitial volumes between the inorganic fillers, and the interstitial volumes between the inorganic fillers become spaces to form pores.

[0086] A slurry for forming the inorganic composite porous layer may be prepared, including an inorganic filler, a first binder polymer, and a solvent for the first binder polymer, and the slurry may be coated on at least one surface of the polymeric porous support and dried to form the inorganic composite porous layer.

[0087] The solvent for the first binder polymer may also function as a solvent for the second binder polymer when the second binder polymer is further included.

[0088] In one embodiment of the present invention, the solvent for the first binder polymer may include N-methyl-2-pyrrolidone, acetone, methyl ethyl ketone, dimethylformamide, dimethylacetamide, or two or more thereof.

[0089] The slurry for forming the inorganic composite porous layer may be prepared by dissolving or dispersing the first binder polymer, or the first binder polymer and the second binder polymer, in a solvent for the first binder polymer, and then adding and dispersing an inorganic filler, but the method for preparing the slurry is not limited thereto.

[0090] In one embodiment of the present invention, after the slurry for forming the inorganic composite porous layer is coated on at least one surface of a polymeric porous support, the method may further include a step of phase-separating the slurry using a non-solvent for the first binder polymer by a method known in the art. The phase-separation step may be performed to form a pore structure in the inorganic composite porous layer. The phase-separation may be performed by a humid phase-separation method or a immersion phase-separation method.

[0091] Among the phase separations, humidification phase separation will be described below.

[0092] First, the humidification phase separation can be performed at a temperature of 15°C to 70°C or 20°C to 50°C and a relative humidity of 15% to 80% or 30% to 50%. The slurry for forming the inorganic composite porous layer can have phase transition characteristics due to a vapor-induced phase separation phenomenon known in the art during the drying process.

[0093] For the humidification phase separation, a non-solvent for the first binder polymer may be introduced in a gaseous state. The non-solvent for the first binder polymer is not particularly limited as long as it does not dissolve the first binder polymer and is partially compatible with the solvent for the first binder polymer. For example, a non-solvent in which the solubility of the first binder polymer at 25°C is less than 5 wt % may be used.

[0094] The non-solvent for the first binder polymer may also be a non-solvent for the second binder polymer, i.e., a solvent that does not dissolve the second binder polymer, e.g., a solvent that has a solubility of the second binder polymer of less than 5 wt % at 25°C, may be used.

[0095] For example, the non-solvent for the first binder polymer may be water, methanol, ethanol, isopropanol, butanol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol, or two or more thereof.

[0096] Among the phase separation methods, immersion phase separation will be described below.

[0097] The inorganic composite porous layer-forming slurry is coated onto at least one surface of the polymeric porous support, which is then immersed in a coagulation solution containing a non-solvent for the first binder polymer for a predetermined period of time. This induces phase separation in the coated inorganic composite porous layer slurry, solidifying the first binder polymer. This process forms a porous inorganic composite porous layer. The coagulation solution is then removed by rinsing with water, and the support is then dried. The drying may be performed using a method known in the art, either batchwise or continuously, using an oven or heated chamber at a temperature range that takes into account the vapor pressure of the solvent for the first binder polymer used. The drying process is intended to remove most of the solvent for the first binder polymer present in the slurry. It is desirable for this process to be as fast as possible, taking productivity into consideration, such as within 1 minute or 30 seconds.

[0098] The solidification liquid may be a non-solvent for the first binder polymer alone, or a mixed solvent of a non-solvent for the first binder polymer and a solvent for the first binder polymer. When a mixed solvent of a non-solvent for the first binder polymer and a solvent for the first binder polymer is used, the content of the non-solvent for the first binder polymer may be 50 wt % or more relative to 100 wt % of the solidification liquid in order to form a good porous structure and improve productivity.

[0099] In one embodiment of the present invention, the average pore size of the inorganic composite porous layer may be 0.001 μm to 10 μm. The average pore size of the inorganic composite porous layer may be measured by capillary flow porometry. Capillary flow porometry is a method for measuring the diameter of the smallest pore in the thickness direction. Therefore, in order to measure the average pore size of the inorganic composite porous layer alone by capillary flow porometry, the inorganic composite porous layer must be separated from the polymeric porous support and surrounded by a nonwoven fabric capable of supporting the separated inorganic composite porous layer. In this case, the pore size of the nonwoven fabric must be much larger than the pore size of the inorganic composite porous layer.

[0100] In one embodiment of the present invention, the porosity of the inorganic composite porous layer may be 5% to 95%, or 10% to 95%, or 20% to 90%, or 30% to 80%. The porosity is calculated by subtracting the volume calculated from the weight and density of each component of the inorganic composite porous layer from the volume calculated using the thickness, width, and length of the inorganic composite porous layer.

[0101] The porosity of the inorganic composite porous layer can be measured by a BET 6-point method using a scanning electron microscope (SEM) image, a mercury porosimeter, a capillary flow porometer, or a porosimetry analyzer (Bell Japan Inc., Belsorp-II mini) in a flow-through nitrogen gas adsorption method.

[0102] In one embodiment of the present invention, the thickness of the inorganic composite porous layer may be 10 μm or less, or 8 μm or less, or 6 μm or less, or 5 μm or less, or 4 μm or less, and 3 μm or more, or 4 μm or more. Here, the thickness of the inorganic composite porous layer refers to the combined thickness of the inorganic composite porous layer on both sides of the polymeric porous support. When the thickness of the inorganic composite porous layer is within the above range, excellent adhesion to the electrode and increased cell strength of the battery can be achieved.

[0103] A separator for an electrochemical device according to one embodiment of the present invention includes a first binder polymer having a tan δ peak at -18°C to -8°C when measured by dynamic mechanical analysis, thereby improving safety at high temperatures and providing excellent adhesion to electrodes.

[0104] In one embodiment of the present invention, the separator for an electrochemical device may have a heat shrinkage of 25% or less or 20% or less in the machine direction (MD) and transverse direction (TD) after being left at 130°C for 1 hour.

[0105] Furthermore, the heat shrinkage rate after being left at 150°C for 30 minutes may be 55% or less, or 50% or less in both the machine direction (MD) and the transverse direction (TD).

[0106] In one embodiment of the present invention, the separator for an electrochemical device may have an electrode adhesive strength of 40 gf / 25 mm or more, or 50 gf / 25 mm or more, or 60 gf / 25 mm or more, and 70 gf / 25 mm or less.

[0107] In one embodiment of the present invention, the electrode adhesive strength can be measured by sandwiching a separator and an electrode between 100 μm PET films, pressing them together using a horizontal laminator at a temperature of 60° C. and a pressure of 1,000 kgf for 1 second, and then applying a force in a 180° direction to the bonded separator at a measurement speed of 300 mm / min, and measuring the force required to separate the separator.

[0108] For example, after stacking one separator and one electrode facing each other, they are sandwiched between 100 μm PET films and then heated to 1,000 kgf / cm in a horizontal laminator at 60°C. 2 The electrode and separator were bonded to each other by passing them through a pressure of 1000 kJ / s for 1 second while being heated, and the bonded electrode and separator were attached to a glass with double-sided tape attached so that the electrode surface could be attached. The end of the separator was then attached to a UTM device (LLOYD Instrument LF Plus), and a force was applied in a 180° direction at a measurement speed of 300 mm / min, and the electrode adhesive strength of the separator was measured from the force required to separate the bonded separator.

[0109] The separator for an electrochemical device may be interposed between a positive electrode and a negative electrode to manufacture the electrochemical device.

[0110] The electrochemical device of the present invention includes all devices that perform electrochemical reactions, and specific examples include all types of primary and secondary batteries, fuel cells, solar cells, and capacitors such as supercapacitors.

[0111] In particular, the electrochemical device may be a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0112] The electrode to be used together with the separator for the electrochemical device of the present invention is not particularly limited, and may be prepared by a conventional method known in the art in the form of an electrode active material layer including an electrode active material, a conductive material, and a binder, bound to a current collector.

[0113] Non-limiting examples of the positive electrode active material include layered compounds such as lithium cobalt complex oxide (LiCoO2) and lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals; 1+x Mn 2-xO4 (where x = 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O5, LiV3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3) 2-x M x Examples of such compounds include, but are not limited to, lithium manganese composite oxides represented by the formula LiMnO2 (where M=Co, Ni, Fe, Cr, Zn, or Ta, and x=0.01 to 0.1) or Li2Mn3MO5 (where M=Fe, Co, Ni, Cu, or Zn); LiMn2O4, in which part of the Li is replaced with an alkaline earth metal ion; disulfide compounds; and Fe2(MoO4)3.

[0114] Non-limiting examples of the negative electrode active material include conventional negative electrode active materials that have been used in negative electrodes of electrochemical devices, and in particular, lithium metal or lithium alloys, and lithium adsorbent materials such as carbon, petroleum coke, activated carbon, graphite, or other carbons.

[0115] Non-limiting examples of positive electrode current collectors include foils made of aluminum, nickel, or a combination thereof, and non-limiting examples of negative electrode current collectors include foils made of copper, gold, nickel, or a copper alloy, or a combination thereof.

[0116] In one embodiment of the present invention, the conductive material used in the negative electrode and positive electrode may typically be added in an amount of 1 wt % to 30 wt % based on the total weight of each active material layer. There are no particular limitations on the conductive material, as long as it does not induce chemical changes in the battery and is conductive. Examples of conductive materials that may be used include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0117] In one embodiment of the present invention, the binder used in the negative and positive electrodes is a component that aids in binding the active material and conductive material, etc., and binding to the current collector, and is typically added in an amount of 1 wt% to 30 wt% based on the total weight of each active material layer. Examples of such binders include polyvinylidene fluoride (PVdF), polyacrylic acid (PAA), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0118] In one embodiment of the present invention, the electrochemical device includes an electrolyte solution, which may include an organic solvent and a lithium salt. The electrolyte solution may be an organic solid electrolyte or an inorganic solid electrolyte.

[0119] Examples of the organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-oxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0120] The lithium salt is a substance that is easily dissolved in the organic solvent, such as LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylates, lithium 4-phenylborate, imides, and the like may be used.

[0121] In addition, to the electrolyte solution, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added to improve charge / discharge characteristics, flame retardancy, etc. In some cases, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be further added to impart non-flammability, and carbon dioxide may be further added to improve high-temperature storage properties.

[0122] Examples of the organic solid electrolyte that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociative groups.

[0123] Examples of the inorganic solid electrolyte that can be used include nitrides, halides, and sulfates of Li, such as LiN, LiI, LiNI, LiN-LiI-LiOH, LiSiO, LiSiO-LiI-LiOH, LiSiS, LiSiO, LiSiO-LiI-LiOH, and LiPO-LiS-SiS.

[0124] The electrolyte injection may be performed at an appropriate stage in the battery manufacturing process depending on the manufacturing process and desired properties of the final product, i.e., before battery assembly or at the final stage of battery assembly.

[0125] In one embodiment of the present invention, the process of applying the separator for an electrochemical device to a battery may include lamination (stack) and folding of the separator and electrodes in addition to the conventional winding process.

[0126] In one embodiment of the present invention, the separator for an electrochemical device may be interposed between a positive electrode and a negative electrode of an electrochemical device, or may be interposed between adjacent cells or electrodes when a plurality of cells or electrodes are assembled to form an electrode assembly. The electrode assembly may have various structures, such as a simple stack type, a jelly roll type, a stack-folding type, or a lamination-stack type.

[0127] The present invention will be described in detail below with reference to examples to aid in understanding the present invention. However, the examples according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the following examples. The examples of the present invention are provided to more completely explain the present invention to those with average knowledge in the field to which the present invention pertains.

[0128] In the following examples and comparative examples, the HFP content was measured using a Unity 400 spectrophotometer at 376.3 MHz, and the spectrum was obtained using deuterated dimethylformamide at 50°C with an excitation pulse width of 8.0 microseconds and a recycle delay of 10 seconds.

[0129] Example 1 As a porous polymer support, a porous ethylene polymer film having a thickness of 9 μm was prepared.

[0130] Al2O3 (D50: 300 nm) as an inorganic filler, poly(vinylidene fluoride-hexafluoropropylene) (Kynar 3121-50, Tm measured by DSC: 166.31°C, HFP content: 10 wt%) as a first binder polymer, and poly(vinylidene fluoride-chlorotrifluoroethylene) (Solvay, solef 32008, Tm measured by DSC: 166.6°C, CTFE content: 20 wt%) as a second binder polymer were added to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 80:16:4, and the inorganic filler was crushed and dispersed using a ball mill to prepare a slurry for forming an inorganic composite porous layer.

[0131] The inorganic composite porous layer-forming slurry was coated on at least both sides of the polymeric porous support, and then immersed in a coagulation solution containing water and NMP at a weight ratio of 6:4 to perform immersion phase separation. The support was then washed with water multiple times and dried to produce a separation membrane.

[0132] Example 2 A separator was prepared in the same manner as in Example 1, except that poly(vinylidene fluoride-hexafluoropropylene) (Kynar 3031-10, Tm measured by DSC: 166.37°C, HFP content: 18.5 wt%) was used as the first binder polymer instead of poly(vinylidene fluoride-hexafluoropropylene) (Kynar 3121-50).

[0133] Example 3 A separator was prepared in the same manner as in Example 1, except that poly(vinylidene fluoride-hexafluoropropylene) (Kynar 3031-50, Tm measured by DSC: 165.36°C, HFP content: 18.1 wt%) was used as the first binder polymer instead of poly(vinylidene fluoride-hexafluoropropylene) (Kynar 3121-50).

[0134] Comparative Example 1 A separator was prepared in the same manner as in Example 1, except that poly(vinylidene fluoride-hexafluoropropylene) (Solef 20808, Tm measured by DSC: 151.53°C, HFP content: 8 wt%) was used instead of poly(vinylidene fluoride-hexafluoropropylene) (Kynar 3121-50) as the first binder polymer.

[0135] Evaluation example 1: Tan δ peak temperature analysis of binder polymer The relationship between the temperature and tan δ of the first binder polymer used in Examples 1 to 3 and Comparative Example 1 is shown in FIG.

[0136] The first binder polymer used in Examples 1 to 3 and Comparative Example 1 was pressed at 190°C to prepare a binder specimen having a thickness of 0.5 mm. The binder specimen was then held at -80°C for 10 minutes using a TA Instruments DMA Q800, and then heated to room temperature at 140°C at a rate of 5°C / min to measure the ratio of storage modulus E' and loss modulus E'', thereby measuring the tan δ value.

[0137] The relationship between the temperature and tan δ of the second binder polymer used in Example 1 is shown in FIG.

[0138] The second binder polymer used in Example 1 was pressed at 190°C to prepare a binder specimen with a thickness of 0.5 mm. The binder specimen was then held at -80°C for 10 minutes using a TA Instruments DMA Q800, and then heated to room temperature at 140°C at a rate of 5°C / min to measure the ratio of storage modulus E' and loss modulus E'', thereby measuring the tan δ value.

[0139] As can be seen from FIG. 1, the first binder polymer used in Example 1 was confirmed to have a second tan δ peak at -12.12°C. In addition, the first binder polymer used in Example 2 was confirmed to have a second tan δ peak at -9.68°C. The first binder polymer used in Example 3 was confirmed to have a second tan δ peak at -8.74°C.

[0140] On the other hand, it was confirmed that the first binder polymer used in Comparative Example 1 had a second tan δ peak at about 20°C.

[0141] In addition, as can be seen from FIG. 2, the second binder polymer used in Example 1 was confirmed to have a second tan δ peak at -6.26°C.

[0142] Evaluation example 2: Crystal structure analysis of the first binder polymer The crystal structures of the first binder polymers used in Examples 1 to 3 and Comparative Example 1 were measured using wide angle X-ray diffraction (WAXS), and are shown in FIGS. 3 to 6, respectively.

[0143] 3 to 5, when measured by wide-angle X-ray diffraction (WAXS), the first binder polymer used in Examples 1 to 3 had relative diffraction peak intensities of 46, 62, 100, 52, 15, and 8 at 2θ positions of 17.7°, 18.44°, 20.04°, 20.73°, 26.72°, and 27.70°, respectively. In addition, it was confirmed that a relatively broad diffraction peak was observed near the 2θ position of 20.73°, and a shoulder peak was observed near 20.73°.

[0144] From this, it was possible to confirm that the first binder polymer used in Examples 1 to 3 had a γ-type crystal structure.

[0145] On the other hand, in Figure 6, when measured by wide-angle X-ray diffraction, the relative ratios of the diffraction peak intensities at 2θ positions of 17.65°, 18.43°, 19.93°, 21.29°, 26.75°, and 32.05° were 52, 64, 100, 17, 70, and 41, respectively. In addition, a relatively narrow diffraction peak was observed around the 2θ position of 20.73°, and it was confirmed that a shoulder peak was not observed around 20.73°.

[0146] From this, it was possible to confirm that the first binder polymer used in Comparative Example 1 did not have a γ-type crystal structure.

Claims

1. a polymeric porous support; an inorganic composite porous layer located on at least one surface of the polymeric porous support and including an inorganic filler and a binder polymer; the binder polymer includes a first binder polymer and a second binder polymer; the first binder polymer is poly(vinylidene fluoride-hexafluoropropylene) having a tan δ peak at −18° C. to −5° C. when measured by dynamic mechanical analysis; The content of the hexafluoropropylene repeating unit of the first binder polymer is 10 wt% to 22 wt% based on the total of the content of the vinylidene fluoride repeating unit and the content of the hexafluoropropylene repeating unit (100 wt%); The separator for an electrochemical device, wherein the second binder polymer is poly(vinylidene fluoride-chlorotrifluoroethylene) having a tan δ peak at −11° C. to 0° C. when measured by dynamic mechanical analysis.

2. 2. The separator for an electrochemical device according to claim 1, wherein the second binder polymer has a melting temperature of 155[deg.] C. or higher.

3. 10. The separator for an electrochemical device according to claim 1, wherein the second binder polymer has a chlorotrifluoroethylene repeating unit content of 10 to 30 wt %, based on a total of 100 wt % of the vinylidene fluoride repeating unit and the chlorotrifluoroethylene repeating unit.

4. 2. The separator for an electrochemical device according to claim 1, wherein a weight ratio of the first binder polymer to the second binder polymer is 50:50 to 95:

5.

5. 2. The separator for an electrochemical device according to claim 1, wherein the inorganic composite porous layer has a thickness of 10 [mu]m or less.

6. 2. The separator for an electrochemical device according to claim 1, wherein the separator for an electrochemical device has a thermal shrinkage of 25% or less in both a machine direction (MD) and a transverse direction (TD) after being left at 130°C for 1 hour.

7. 2. The separator for an electrochemical device according to claim 1, wherein the separator for an electrochemical device has a thermal shrinkage of 55% or less in both a machine direction (MD) and a transverse direction (TD) after being left at 150°C for 30 minutes.

8. 2. The separator for an electrochemical device according to claim 1, wherein the separator for an electrochemical device has an electrode adhesive strength of 40 gf / 25 mm or more.

9. 2. The separator for an electrochemical device according to claim 1, wherein the first binder polymer is poly(vinylidene fluoride-hexafluoropropylene) having a γ-type crystal structure.

10. 2. The separator for an electrochemical device according to claim 1, wherein the first binder polymer has a melting temperature of 155[deg.] C. or higher.

11. The electrochemical device includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, An electrochemical device, wherein the separator for an electrochemical device is the separator for an electrochemical device according to claim 1 .

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