Separator for electrochemical device and electrochemical device comprising same

Abstract

The present invention relates to a separator for an electrochemical device and an electrochemical device comprising same. Specifically, the present invention relates to a separator for an electrochemical device and an electrochemical device comprising same, wherein the separator contains substituted polyacrylic acid in a coating layer and thus can improve resistance and cycle performance.

Description

Separator for electrochemical devices and electrochemical devices containing the same

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0120095 filed September 4, 2024 and Korean Patent Application No. 10-2025-0123276 filed September 1, 2025, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of this specification.

[0002] The present invention relates to a separator for an electrochemical device and an electrochemical device including the same, and more particularly, to a separator for an electrochemical device capable of improving resistance and cycle performance by including polyacrylic acid substituted in a coating layer, and to an electrochemical device including the same.

[0003] Electrochemical devices convert chemical energy into electrical energy using electrochemical reactions. Recently, lithium secondary batteries have been widely used due to their high energy density and voltage, long cycle life, and wide range of applications.

[0004] Among the components of these electrochemical devices, the separator may include a polymer substrate having a porous structure located between the anode and cathode. The separator isolates the anode and cathode, preventing electrical short-circuiting between the two electrodes while simultaneously allowing electrolyte and ions to pass through. Although the separator itself does not participate in the electrochemical reaction, its physical properties, such as wettability with respect to the electrolyte, porosity, and thermal shrinkage, may affect the performance and safety of the electrochemical device.

[0005] Therefore, to enhance the physical properties of such membranes, various methods have been attempted, such as adding a coating layer to a porous polymer substrate and adding various substances to the coating layer to improve the properties of the coating layer. For example, inorganic substances may be added to the coating layer to enhance the mechanical strength of the membrane, or inorganic substances or hydrates may be added to the coating layer to enhance the flame retardancy and heat resistance of the polymer substrate.

[0006] Within the above coating layer, inorganic particles can be linked to other inorganic particles by a polymer binder to form an interstitial volume, and lithium ions can move through the interstitial volume. That is, the coating layer including the polymer binder and inorganic particles serves to prevent thermal shrinkage of the separator while also assisting the movement of lithium ions through the separator.

[0007] Meanwhile, alkali metals are recognized as impurities in lithium secondary batteries. Higher alkali metal content within the battery can lead to reduced battery life, increased resistance, and reduced cycle performance. Therefore, research and development is needed to minimize the alkali metal content within the separator.

[0008] Furthermore, if the porosity of the porous polymer substrate within the separator is low, resistance may increase and cycle performance may deteriorate. Therefore, the development of separators to improve battery performance is urgently needed.

[0009] The technical problem to be achieved by the present invention is to provide a separator for an electrochemical device capable of improving resistance and cycle performance by including polyacrylic acid substituted in a coating layer, and an electrochemical device including the same.

[0010] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the description below.

[0011] One embodiment of the present invention provides a separator for an electrochemical device, comprising: a porous polymer substrate; and a coating layer provided on at least one surface of the porous polymer substrate, the coating layer including a first polymer binder, a second polymer binder, and inorganic particles; wherein the first polymer binder is a substituted polyacrylic acid.

[0012] According to one embodiment of the present invention, the porous polymer substrate may be a separator for an electrochemical device, wherein the thickness is 8 ㎛ or more and 15 ㎛ or less.

[0013] According to one embodiment of the present invention, the air permeability of the porous polymer substrate may be 30 s / 100cc or more and 100 s / 100cc or less.

[0014] According to one embodiment of the present invention, the porosity of the porous polymer substrate may be 50% or more.

[0015] According to one embodiment of the present invention, the melt index (Melt Index, g / 10 min) of the porous polymer substrate may be less than 0.2.

[0016] According to one embodiment of the present invention, the coating layer may be provided on both sides of the porous polymer substrate.

[0017] According to one embodiment of the present invention, the thickness of the coating layer may be 1 ㎛ or more and less than 3 ㎛.

[0018] According to one embodiment of the present invention, the content ratio of the first polymer binder and the second polymer binder may be 2:1 to 1:2.

[0019] According to one embodiment of the present invention, the first polymer binder may be lithiated polyacrylic acid, and the second polymer binder may be an acrylic binder.

[0020] According to one embodiment of the present invention, the sodium content in the separation membrane may be 3,000 ppm or less.

[0021] According to one embodiment of the present invention, the lithium content in the separator may be 750 ppm or more.

[0022] According to one embodiment of the present invention, the rate of increase in air permeability after compression of the separation membrane may be 35% or less.

[0023] One embodiment of the present invention provides an electrochemical device comprising: an anode; a cathode; and a separator interposed between the anode and the cathode and any one of the aforementioned separators.

[0024] A separator for an electrochemical device according to one embodiment of the present invention can improve resistance and cycle performance by including polyacrylic acid substituted in a coating layer.

[0025] An electrochemical device according to one embodiment of the present invention can improve resistance and electrochemical device performance by including polyacrylic acid substituted in a coating layer within a separator.

[0026] Figure 1 is a schematic diagram of a separator for an electrochemical device according to one embodiment of the present invention.

[0027] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0028] In this specification, “A and / or B” means “A and B, or A or B.”

[0029] In this specification, “about,” “approximately,” and “substantially” are used to mean a range of or approximation to a numerical value or degree, taking into account inherent manufacturing and material tolerances, and are used to prevent infringers from unfairly using the disclosure, which mentions exact or absolute numbers provided to aid understanding of the present invention.

[0030] In this specification, when it is said that a component is “on”, this does not exclude other components being placed therebetween, unless otherwise specifically stated, but rather means that other components may be placed thereon.

[0031] In this specification, the characteristic of having pores means that a gaseous and / or liquid fluid can pass from one side to the other side of the object through a structure in which the object includes a plurality of pores and said pores are interconnected.

[0032] In this specification, the separator has a porous characteristic including a plurality of pores, and acts as a porous ion-conducting barrier that allows ions to pass while blocking electrical contact between the cathode and the anode in an electrochemical device.

[0033] Hereinafter, an embodiment of the present invention will be described in detail with reference to the attached drawings. The drawings may be exaggerated, omitted, or schematically illustrated to explain or emphasize the contents of an embodiment of the present invention.

[0034] Hereinafter, the present invention will be described in more detail.

[0035] Figure 1 is a schematic diagram of a separator for an electrochemical device according to one embodiment of the present invention.

[0036] One embodiment of the present invention includes a separator (100) for an electrochemical device, including a porous polymer substrate (110); and a coating layer (130) provided on at least one surface of the porous polymer substrate (110) and including a first polymer binder, a second polymer binder, and inorganic particles; wherein the first polymer binder is a substituted polyacrylic acid.

[0037] A separator for an electrochemical device according to one embodiment of the present invention can improve resistance and cycle performance by including polyacrylic acid substituted in a coating layer.

[0038] The above electrochemical device separator (100) includes a porous polymer substrate (110). As described above, the electrochemical device separator (100) includes the porous polymer substrate (110), thereby allowing lithium ions to pass through while blocking electrical contact, and can implement a shutdown function at an appropriate temperature.

[0039] According to one embodiment of the present invention, the porous polymer substrate (110) may be manufactured using a polyolefin-based resin as a base resin. Examples of the polyolefin-based resin include polyethylene, polypropylene, polypentene, etc., and the porous polymer substrate may include one or more of these. A porous separation membrane manufactured using such a polyolefin-based resin as a base resin, i.e., having a large number of pores, can provide a shutdown function at an appropriate temperature.

[0040] According to one embodiment of the present invention, the weight average molecular weight of the polyolefin resin may be 500,000 or more and 2,000,000 or less. By controlling the weight average molecular weight of the polyolefin resin within the above-described range, the compression resistance of the separator can be improved. Furthermore, when different types of polyolefin resins are mixed and used or the separator is formed with a multilayer structure made of different types of polyolefin resins, the weight average molecular weight of the polyolefin resin can be calculated by adding the weight average molecular weights according to the content ratio of each polyolefin resin.

[0041] In this specification, the weight average molecular weight (Mw) can be measured by gel permeation chromatography (GPC: gel permeation chromatography, PL GPC220, Agilent Technologies), and the measurement conditions can be set as follows.

[0042] - Column: PL Olexis (Polymer Laboratories)

[0043] - Solvent: TCB (Trichlorobenzene)

[0044] - Flow rate: 1.0 ml / min

[0045] - Sample concentration: 1.0 mg / ml

[0046] - Injection volume: 200 ㎕

[0047] - Column temperature: 160 ℃

[0048] - Detector: Agilent High Temperature RI detector

[0049] - Standard: Polystyrene (corrected with a cubic function)

[0050] According to one embodiment of the present invention, the porous polymer substrate (110) may be manufactured by a method (wet method) in which a polyolefin-based resin is mixed with a plasticizer (diluent) at a high temperature to form a single phase, the polymer material and the plasticizer are separated during the cooling process, the plasticizer is extracted to form pores, and then stretched and heat-set.

[0051] According to one embodiment of the present invention, the average size of the pores and the maximum size of the pores of the porous polymer substrate (110) can be easily manufactured by a person skilled in the art to conform to the scope of the present invention by controlling the mixing ratio of the plasticizer, the stretching ratio, and the heat-setting treatment temperature.

[0052] According to one embodiment of the present invention, the thickness of the porous polymer substrate (110) may be 8 ㎛ or more and 15 ㎛ or less. Specifically, the thickness of the porous polymer substrate (110) may be 8 ㎛ or more and 14 ㎛ or less, 8 ㎛ or more and 13 ㎛ or less, 8 ㎛ or more and 12 ㎛ or less, 8 ㎛ or more and 11 ㎛ or less, or 9 ㎛ or more and 11 ㎛ or less, and preferably about 10 ㎛. By controlling the thickness of the porous polymer substrate within the above-described range, the energy density of the battery can be improved.

[0053] According to one embodiment of the present invention, the thickness of the porous polymer substrate can be measured by a contact measurement method using a thickness measuring device (Mitutoyo, VL-50S-B).

[0054] According to one embodiment of the present invention, the air permeability of the porous polymer substrate (110) may be 30 s / 100cc or more and 100 s / 100cc or less. Specifically, the air permeability of the porous polymer substrate may be 40 s / 100cc or more and 95 s / 100cc or less, 50 s / 100cc or more and 90 s / 100cc or less, 60 s / 100cc or more and 85 s / 100cc or less, 65 s / 100cc or more and 80 s / 100cc or less, and preferably 70 s / 100cc or more and 80 s / 100cc or less. If it is less than the above-mentioned range, the mechanical strength of the separation membrane may be lowered, and if it is more than the above-mentioned range, the ionic conductivity may be lowered, which may cause an increase in resistance. By controlling the air permeability of the porous polymer substrate within the above-described range, ion conductivity and durability can be improved, and further, the resistance and cycle performance of the battery can be improved.

[0055] According to one embodiment of the present invention, the air permeability (Gurley) can be measured by the ASTM D726-94 method. The Gurley used herein is resistance to air flow, which is measured by a Gurley densometer. The air permeability value described herein is the value obtained when 100 cc of air is injected into 1 in of the sample porous support under a pressure of 12.2 in H2O. 2 The time (sec) it takes to pass through the cross section is expressed as the ventilation time.

[0056] According to one embodiment of the present invention, the porosity of the porous polymer substrate (110) may be 50% or more. Specifically, the porosity of the porous polymer substrate (110) may be 50% or more and 70% or less, 50% or more and 65% or less, 50% or more and 63% or less, or 50% or more and 60% or less. If the porosity is less than the above-described range, the ion conductivity may decrease, which may increase the internal resistance and deteriorate the cycle performance, and if the porosity is more than the above-described range, the separator may not be able to sufficiently perform the physical isolation role between electrodes, which may cause a risk of battery short circuit and deteriorate the durability.

[0057] According to one embodiment of the present invention, the porosity refers to the ratio of the volume occupied by pores to the volume of the separation membrane, and the porosity can be measured according to ASTM D-2873.

[0058] According to one embodiment of the present invention, the melt index (g / 10 min) of the porous polymer substrate (110) may be less than 0.2. The melt index is a measure of the fluidity of a polymer material or the ease of flow of a polymer melt, and may refer to the flow rate when a polymer melt is extruded at a specific temperature and pressure. The melt index may be affected by the molecular weight of the polymer, etc., and when the molecular weight of the polymer is high, the melt index of the polymer may be low. Specifically, the melt index of the polymer may be measured at a temperature of 190° C. and a load of 21.6 kg according to ASTM D1238. Specifically, the melt index (Melt Index, g / 10 min) of the porous polymer substrate (110) may be 0.00001 g / 10 min or more and 0.15 g / 10 min or less, 0.0001 g / 10 min or more and 0.10 g / 10 min or less, 0.001 g / 10 min or more and 0.075 g / 10 min or less, 0.005 g / 10 min or more and 0.05 g / 10 min or less, 0.01 g / 10 min or more and 0.05 g / 10 min or less, or 0.02 g / 10 min or more and 0.05 g / 10 min or less. If it is less than the above-mentioned range, the ease of flow may be reduced, and if it is more than the above-mentioned range, the ease of flow may be increased, but the shape of the pores may not be maintained after compression of the membrane, so the rate of increase in air permeability may be high.

[0059] According to one embodiment of the present invention, the coating layer (130) is provided on at least one surface of the porous polymer substrate (110). As described above, the electrochemical device separator (100) includes the coating layer (130) provided on at least one surface of the porous polymer substrate (110), thereby improving the heat resistance of the separator, improving the mechanical properties, and preventing the separator from shrinking at high temperatures and causing an electrical short circuit in the electrode.

[0060] According to one embodiment of the present invention, the coating layer (130) includes a first polymer binder, a second polymer binder, and inorganic particles. As described above, the coating layer (130) includes the first polymer binder, the second polymer binder, and the inorganic particles, thereby improving the heat resistance of the separator, improving the mechanical properties, preventing the separator from shrinking at high temperatures and causing an electrical short circuit of the electrode, and forming pores within the coating layer.

[0061] According to one embodiment of the present invention, the coating layer (130) may be formed by inorganic particles being bound by a first polymer binder and a second polymer binder and accumulated within the coating layer. The pores within the coating layer may originate from the interstitial volume, which is the empty space between the inorganic particles.

[0062] According to one embodiment of the present invention, the coating layer (130) may include a plurality of pores. Specifically, the coating layer may be a porous coating layer. More specifically, the coating layer may be a porous coating layer including a plurality of pores therein. As described above, by including a plurality of pores, the coating layer can physically block the negative electrode and the positive electrode while allowing lithium ions to pass through and current to flow.

[0063] According to one embodiment of the present invention, the inorganic particles that can be used in the coating layer (130) are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in one embodiment of the present invention are those that can be used in the operating voltage range of the applied electrochemical device (e.g., Li / Li). + There are no particular limitations as long as no oxidation and / or reduction reaction occurs at a voltage of 0 V to 5 V (as a reference).

[0064] According to one embodiment of the present invention, non-limiting examples of the inorganic particles 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, SiC, boehmite, Al(OH)3, TiO2, aluminum peroxide, zinc tin hydroxide (ZnSn(OH)6), tin-zinc oxide (Zn2SnO4, ZnSnO3), antimony trioxide (Sb2O3), antimony tetroxide (Sb2O4), antimony pentoxide (Sb2O5), etc., and may include one or more of these.

[0065] According to one embodiment of the present invention, the average particle diameter (D50) of the inorganic particles is not particularly limited, but is preferably in the range of 0.1 ㎛ to 1 ㎛ in order to form a coating layer (130) with a uniform thickness and an appropriate porosity. Specifically, the average particle diameter (D50) of the inorganic particles may be 0.2 ㎛ to 0.9 ㎛, 0.3 ㎛ to 0.8 ㎛, 0.4 ㎛ to 0.7 ㎛, or 0.5 ㎛ to 0.6 ㎛. If it is less than the above-mentioned range, the dispersibility of the inorganic particles in the slurry prepared for manufacturing the coating layer may be reduced, and the coating density may increase according to the small particle size, which may result in a decrease in the porosity, thereby lowering the ionic conductivity, and if it is more than the above-mentioned range, the thickness of the formed coating layer may increase, and the uniformity of the coating layer may be reduced.

[0066] In this specification, "D50 particle size" means the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size. The particle size can be measured using a laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and when the particles pass through the laser beam, the difference in the diffraction pattern according to the particle size is measured to calculate the particle size distribution. By calculating the particle diameter at the point where it becomes 50% of the cumulative distribution of particle numbers according to particle size in the measuring device, the D50 particle size can be measured.

[0067] According to one embodiment of the present invention, the content of the inorganic particles may be 90 parts by weight or more and less than 100 parts by weight with respect to 100 parts by weight of the coating layer (130). Specifically, the content of the inorganic particles may be 92 parts by weight or more and 99 parts by weight or less, 93 parts by weight or more and 98 parts by weight or less, 94 parts by weight or more and 97 parts by weight or less, or 95 parts by weight or more and 96 parts by weight or less with respect to 100 parts by weight of the coating layer (130). By controlling the content of the inorganic particles included in the coating layer (130) within the above-described range, the heat resistance of the separator can be improved, thereby ensuring the safety of the battery.

[0068] According to one embodiment of the present invention, the first polymer binder is a substituted polyacrylic acid. As described above, by selecting a substituted polyacrylic acid as the first polymer binder, the content of alkali metals corresponding to impurities in the battery can be minimized.

[0069] According to one embodiment of the present invention, the substituted polyacrylic acid may be lithiated poly(acrylic acid). Specifically, the lithiated polyacrylic acid may be a lithium-exchangeable polymer in which hydrogen of the polyacrylic acid is neutralized with LiOH and substituted with Li. At this time, the purity of the applied LiOH has a great influence on the sodium (Na) content, and the higher the purity of the LiOH, the lower the sodium (Na) content in the LiOH, so that the sodium (Na) content in the separator can be reduced due to the produced lithium-exchangeable polymer. As described above, by selecting lithiated polyacrylic acid as the substituted polyacrylic acid, a lithium source can be sufficiently supplied into the battery, thereby improving battery storage and cycle performance, and further, the sodium content corresponding to an impurity in the battery can be minimized.

[0070] According to one embodiment of the present invention, the second polymer binder may be an acrylic binder. Specifically, the acrylic binder may be a polymer containing a carboxylic acid ester as a repeating unit, and may preferably be a (meth)acrylic acid ester or an acrylic-styrene copolymer.

[0071] According to one embodiment of the present invention, the (meth)acrylic acid ester is methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, n-amyl (meth)acrylate, i-amyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, ethylene glycol (meth)acrylate, di(meth)acrylate, propylene glycol (meth)acrylate, Examples thereof include trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, and ethylene di(meth)acrylate, and the like may be at least one selected from these. Among these, at least one selected from methyl (meth)acrylate, ethyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate is preferable, and methyl (meth)acrylate is particularly preferable.

[0072] According to one embodiment of the present invention, the acrylic-styrene copolymer may include an acrylic binder, and the acrylic binder may be a polyacrylate. For example, the binder may be at least one selected from the group consisting of styrene-butyl acrylate, styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and acrylate polymers, and more specifically, may be a copolymer including acrylate.

[0073] According to one embodiment of the present invention, the average particle diameter (D50) of the second polymer binder is not particularly limited, but is preferably in the range of 0.1 ㎛ to 1 ㎛ in order to form a coating layer (130) with a uniform thickness and an appropriate porosity. Specifically, the average particle diameter (D50) of the second polymer binder may be 0.1 ㎛ to 0.8 ㎛, 0.1 ㎛ to 0.6 ㎛, 0.1 ㎛ to 0.4 ㎛, or 0.1 ㎛ to 0.2 ㎛. By controlling the average particle diameter (D50) of the second polymer binder within the above-described range, the dispersibility in the slurry prepared for manufacturing the coating layer can be improved, and the thickness of the formed coating layer can be reduced.

[0074] According to one embodiment of the present invention, the content of the first polymer binder may be 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the coating layer (130). Specifically, the content of the first polymer binder may be 1 part by weight or more and 9 parts by weight or less, 1 part by weight or more and 8 parts by weight or less, 1 part by weight or more and 7 parts by weight or less, 1 part by weight or more and 6 parts by weight or less, 1 part by weight or more and 5 parts by weight or less, 1 part by weight or more and 4 parts by weight or less, or 2 parts by weight or more and 3 parts by weight or less with respect to 100 parts by weight of the coating layer (130). By controlling the content of the first polymer binder within the above-described range, it is possible to sufficiently supply a lithium source within the battery, thereby improving battery storage and cycle performance, and further minimizing the sodium content corresponding to an impurity within the battery.

[0075] According to one embodiment of the present invention, the content of the second polymer binder may be 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the coating layer (130). Specifically, the content of the second polymer binder may be 1 part by weight or more and 9 parts by weight or less, 1 part by weight or more and 8 parts by weight or less, 1 part by weight or more and 7 parts by weight or less, 1 part by weight or more and 6 parts by weight or less, 1 part by weight or more and 5 parts by weight or less, 1 part by weight or more and 4 parts by weight or less, or 2 parts by weight or more and 3 parts by weight or less with respect to 100 parts by weight of the coating layer (130). By controlling the content of the second polymer binder within the above-described range, the adhesion with an inorganic material and the adhesion between a separator and an electrode can be improved, thereby improving battery performance.

[0076] According to one embodiment of the present invention, the content ratio of the first polymer binder and the second polymer binder may be 2:1 to 1:2. Specifically, the content ratio of the first polymer binder and the second polymer binder may be 1:1. As described above, by controlling the content of the first polymer binder and the second polymer binder, a lithium source can be sufficiently supplied within the battery, thereby improving battery storage and cycle performance, and further, the sodium content corresponding to impurities within the battery can be minimized, and the adhesion with inorganic substances and the adhesion between the separator and the electrode can be improved, thereby improving battery performance.

[0077] According to one embodiment of the present invention, the first polymer binder may be lithiated polyacrylic acid, and the second polymer binder may be an acrylic binder. As described above, by selecting the first polymer binder as lithiated polyacrylic acid and the second polymer binder as an acrylic binder, a lithium source can be sufficiently supplied into the battery, thereby improving battery storage and cycle performance, and further, the sodium content corresponding to impurities in the battery can be minimized, and the adhesion with inorganic substances and the adhesion between the separator and the electrode can be improved, thereby improving battery performance.

[0078] According to one embodiment of the present invention, the coating layer (130) may be provided on both sides of the porous polymer substrate (110). As described above, since the electrochemical device separator (100) includes the coating layer (130) provided on both sides of the porous polymer substrate (110), the heat resistance of the separator can be improved and the mechanical properties can be improved. On the other hand, if the coating layer (130) is provided on a cross section of the porous polymer substrate (110), the heat resistance characteristics may be inferior compared to double-sided coating.

[0079] According to one embodiment of the present invention, the thickness of the coating layer (130) may be 1 ㎛ or more and less than 3 ㎛. Specifically, the thickness of the coating layer (130) may be 1 ㎛ or more and 2 ㎛ or less. If it is less than the above-mentioned range, the heat resistance characteristics of the separator may be deteriorated, and if it is more than the above-mentioned range, the air permeability may increase after compression of the separator, and further, the resistance and cycle performance may be deteriorated. By controlling the thickness of the coating layer (130) within the above-mentioned range, the heat resistance and resistance performance of the separator can be improved.

[0080] In one embodiment of the present invention, the thickness of the coating layer (130) or the like can be measured using a contact thickness measuring device. The contact thickness measuring device can be, for example, VL-50S-B from Mitutoyo.

[0081] According to one embodiment of the present invention, the sodium content in the separator may be 3,000 ppm or less. Specifically, the sodium content in the separator may be more than 0 ppm and less than 3,000 ppm, more than 0 ppm and less than 2,995 ppm, more than 0 ppm and less than 2,990 ppm, or more than 0 ppm and less than 2,985 ppm. If the sodium content in the separator is high, the mobility of lithium ions may be reduced and battery performance may be deteriorated.

[0082] According to one embodiment of the present invention, the lithium content within the separator may be 750 ppm or more. Specifically, the lithium content within the separator may be 750 ppm or more and 1,000 ppm or less. If the lithium content falls below the above-described range, it may be due to an increase in the sodium content within the separator. By controlling the sodium content within the separator to a certain level or less, the mobility of lithium ions can be increased and battery performance can be improved.

[0083] According to one embodiment of the present invention, the rate of increase in air permeability (%) of the separator after compression may be 35% or less. If it exceeds the above-mentioned range, the shape of the pores of the separator after compression may not be maintained. In addition, if the melt index of the porous polymer substrate increases, the rate of increase in air permeability of the separator after compression may also increase, and if the thickness of the coating layer increases, the rate of increase in air permeability of the separator after compression may also increase.

[0084] One embodiment of the present invention includes an electrochemical device comprising: an anode; a cathode; and a separator interposed between the anode and the cathode, and any one of the above-described membranes. In the electrochemical device according to one embodiment of the present invention, any description overlapping with the description of the separator for the electrochemical device will be omitted.

[0085] An electrochemical device according to one embodiment of the present invention can improve resistance and electrochemical device performance by including polyacrylic acid substituted in a coating layer within a separator.

[0086] In one embodiment of the present invention, the electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, and is a concept encompassing a primary battery and a secondary battery. In the present specification, the secondary battery is capable of charging and discharging, and refers to a lithium secondary battery, a nickel-cadmium battery, a nickel-hydrogen battery, etc. The lithium secondary battery uses lithium ions as an ion conductor, and examples thereof include, but are not limited to, a non-aqueous electrolyte secondary battery including a liquid electrolyte, an all-solid-state battery including a solid electrolyte, a lithium polymer battery including a gel polymer electrolyte, and a lithium metal battery using lithium metal as an anode.

[0087] According to one embodiment of the present invention, the positive electrode has a positive electrode current collector and a positive electrode active material layer including a positive electrode active material, a conductive material, and a binder resin on at least one surface of the positive electrode current collector. The positive electrode active material is a layered compound such as lithium manganese oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-xLithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); chemical formula LiMn1-xM x A lithium manganese composite oxide represented by O2 (wherein, M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (wherein, M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which a portion of Li in the chemical formula is replaced by an alkaline earth metal ion; a disulfide compound; or a mixture of two or more of Fe2(MoO4)3.

[0088] According to one embodiment of the present invention, the cathode comprises a cathode current collector and a cathode active material layer comprising a cathode active material, a conductive material, and a binder resin on at least one surface of the current collector. The cathode comprises, as the cathode active material, carbon such as lithium metal oxide, non-graphitizable carbon, or graphite-based carbon; LixFe2O3 (0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, 및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료; 티타늄 산화물 중 선택된 1종 또는 2종 이상의 혼합물을 포함할 수 있다.

[0089] According to one embodiment of the present invention, the conductive material may be, for example, one selected from the group consisting of graphite, carbon black, carbon fibers or metal fibers, metal powders, conductive whiskers, conductive metal oxides, activated carbon, and polyphenylene derivatives, or a mixture of two or more conductive materials among these. More specifically, the conductive material may be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more conductive materials among these.

[0090] According to one embodiment of the present invention, the current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used.

[0091] According to one embodiment of the present invention, the binder resin may be a polymer commonly used in electrodes in the art. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples thereof include, but are not limited to, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose.

[0092] According to one embodiment of the present invention, the anode slurry for manufacturing the anode active material layer may include a dispersant, and the dispersant may be a pyrrolidone-based compound. Specifically, it may be N-methylpyrrolidone (N-methylpyrrolidone, ADC-01, LG Chem).

[0093] According to one embodiment of the present invention, the electrochemical device may further include an electrolyte, and the electrolyte is A + B - As a salt with the same structure, A + is Li + , Na + , K + It may include an ion composed of an alkali metal cation such as B or a combination thereof. In addition, B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - The salt containing an anion such as or a combination thereof may be dissolved or dissociated in an organic solvent consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone or a mixture thereof, but is not limited thereto.

[0094] According to one embodiment of the present invention, a battery module including a battery including the electrochemical element as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source may be provided. Specific examples of the device include, but are not limited to, a power tool that is powered by an electric motor; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc.; an electric two-wheeled vehicle including an electric bicycle (E-bike) and an electric scooter (E-scooter); an electric golf cart; and a power storage system.

[0095] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention is not to be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain the present invention to those with average knowledge in the art.

[0096]

[0097] <Example 1>

[0098] Manufacturing of porous polymer substrates

[0099] Polyethylene resin (weight-average molecular weight 1.5 million) was extruded, and a porous polymer substrate (total thickness about 10 μm, porosity 50%, air permeability 75 s / 100cc, melt index 0.02 g / 10min) was prepared by a wet method.

[0100] Coating layer formation

[0101] Al2O3 (AES 11, Sumitomo Corporation) with a D50 particle size of 500 nm was prepared as an inorganic particle. Lithium polyacrylate (Li-PAA, LA136D, Chengdu Indigo) was prepared as the first polymer binder, and an acrylic copolymer (CSB-140, Toyo Corporation) with a D50 particle size of 150 nm and a silicone surfactant (BYK-348, BYK Corporation) were prepared as the second polymer binder.

[0102] The above-prepared inorganic particles, first polymer binder, second polymer binder, and surfactant were added to water at a weight ratio of 95.4:2:2:0.6, and dispersed to prepare a slurry for a coating layer (solid content: 35%).

[0103] The slurry for the coating layer was applied to both sides of the porous polymer substrate using a doctor blade by bar coating, and dried with air at 50°C using a heat gun to form a coating layer each having a thickness of 1.5 μm.

[0104]

[0105] <Example 2>

[0106] In the above Example 1, a separator was manufactured in the same manner as in the above Example 1, except that the thickness of each coating layer was 1.0 μm.

[0107]

[0108] <Example 3>

[0109] In the above Example 1, a separator was manufactured in the same manner as in the above Example 1, except that the thickness of each coating layer was 2.0 μm.

[0110]

[0111] <Example 4>

[0112] In the above Example 1, a separation membrane was prepared in the same manner as in Example 1, except that the porosity of the porous polymer substrate was 60%.

[0113]

[0114] <Example 5>

[0115] In the above Example 1, a separation membrane was manufactured in the same manner as in the above Example 1, except that the melting index of the porous polymer substrate was 0.05 g / 10 min.

[0116]

[0117] <Comparative Example 1>

[0118] In the above Example 1, a separation membrane was manufactured in the same manner as in the above Example 1, except that polyacrylic acid (PAA, CK-702, Miwon Corporation) was used as the first polymer binder.

[0119]

[0120] <Comparative Example 2>

[0121] In the above Comparative Example 1, a separation membrane was manufactured in the same manner as in the above Comparative Example 1, except that the porosity of the porous polymer substrate was 45%.

[0122]

[0123] <Comparative Example 3>

[0124] In the above Comparative Example 2, a separation membrane was manufactured in the same manner as in the above Comparative Example 2, except that the melting index of the porous polymer substrate was 0.2 g / 10 min.

[0125]

[0126] <Comparative Example 4>

[0127] In the above Example 1, a separation membrane was prepared in the same manner as in Example 1, except that carboxymethylcellulose (CMC, SG-L02, GL Chem) was used as the first polymer binder.

[0128]

[0129] Comparative Example 5

[0130] In Comparative Example 4 above, a separation membrane was prepared in the same manner as in Comparative Example 4, except that the porosity of the porous polymer substrate was 45%.

[0131]

[0132] Comparative Example 6

[0133] In Comparative Example 5, a separation membrane was manufactured in the same manner as in Comparative Example 5, except that the melting index of the porous polymer substrate was 0.2 g / 10 min.

[0134]

[0135] Comparative Example 7

[0136] In the above Example 1, a separator was prepared in the same manner as in Example 1, except that the thickness of each coating layer was 3.0 μm.

[0137]

[0138] Comparative Example 8

[0139] In the above Example 1, a separator was manufactured in the same manner as in the above Example 1, except that the thickness of the coating layer was 1.5 μm and it was a single-sided coating.

[0140]

[0141] <Manufacturing of electrochemical devices>

[0142] Electrochemical devices were manufactured using the electrochemical device separators of the above examples and comparative examples.

[0143] 1) Manufacturing of the anode

[0144] Cathode active material (LiNi) 0.8 Mn 0.1 Co 0.1 O2), a conductive agent (carbon black), a dispersant (N-methylpyrrolidone, ADC-01, LG Chemical), and a binder resin (a mixture of PVDF-HFP and PVDF) were mixed with water in a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for a positive electrode active material layer with a concentration of 50 wt% of the remaining components excluding water. Next, the slurry was applied to the surface of an aluminum thin film (thickness 10 μm) and dried to manufacture a positive electrode having a positive electrode active material layer (thickness 120 μm).

[0145] 2) Manufacturing of cathode

[0146] Graphite (natural graphite and artificial graphite blend), conductive agent (carbon black), dispersant (polyvinylpyrrolidone, Junsei, Japan), and binder resin (PVDF-HFP and PVDF blend) were mixed with water in a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for an anode active material layer with a concentration of 50 wt% of the remaining components excluding water. Next, the slurry was applied to the surface of a copper thin film (thickness 10 μm) and dried to manufacture an anode having an anode active material layer (thickness 120 μm).

[0147] 3) Lamination process

[0148] An electrochemical device was obtained by interposing the separator of the above example and comparative example between the above-manufactured cathode and anode, stacking them, and performing a lamination process. The lamination process was performed using a hot press at 70°C and 4 MPa for 60 seconds.

[0149]

[0150] <Experimental Example>

[0151] Measurement of the rate of increase in ventilation after compression

[0152] Clear PET (35㎛) specimens (50 mm X 50 mm) and A4 paper (100 mm X 70 mm) were laminated on both sides of the membrane specimens (50 mm X 50 mm) manufactured in the above examples and comparative examples, and compressed using a hot press at 70°C and 4 MPa for 60 seconds, and then the air permeability thereof was measured.

[0153] Afterwards, the rate of increase in air permeability (%) of each membrane was measured using Equation 1 below and shown in Tables 1 and 2.

[0154] [Formula 1]

[0155] [(Air permeability after compression - Air permeability before compression) / Air permeability before compression] X 100

[0156]

[0157] Membrane 150℃ heat shrinkage measurement

[0158] The membrane specimens (50 mm X 50 mm) manufactured in the above examples and comparative examples were prepared, left for 30 minutes under temperature conditions of 150°C, and then the shrinkage rate of the membrane was measured.

[0159] The above shrinkage rate is the result of marking two arbitrary points in the MD direction and TD direction of the membrane, respectively, and calculating the increase / decrease rate of the distance between them (the point distance) according to the following (Formula 1).

[0160] (Formula 1) Shrinkage rate (%) = {(BA) / A} X 100

[0161] In the above equation, A is the gauge distance in the initial state before high-temperature storage, and B is the gauge distance in the final state after high-temperature storage. The measurement results are shown in Tables 1 and 2 below.

[0162]

[0163] Measurement of Na and Li content in the membrane

[0164] The Na and Li contents of the membranes manufactured in the above examples and comparative examples were measured through ICP-OES analysis. Approximately 0.04 g of the sample was aliquoted into a conical tube, weighed, and then 3 mL of nitric acid and 0.5 mL of hydrogen peroxide were added to the sample, shaken to mix, and heated to dissolve. Once the sample was dissolved, 100 μL of 1000 mg / kg Internal STD (Sc) was added, and the mixture was diluted to 10 mL with ultrapure water. The measurement results are shown in Tables 1 and 2 below.

[0165]

[0166] Measurement of initial battery resistance

[0167] For the electrochemical elements of the above examples and comparative examples, a current of 2.5C was applied at 25°C until the SOC reached 50%. When each electrochemical element reached 50% SOC, the resistance value according to Equation 1 below was calculated and shown in Tables 1 and 2 below.

[0168] [Formula 1]

[0169] Initial resistance = (V0-V1) / I (V0 = voltage before pulse, V1 = voltage 10 seconds after pulse, I = applied current)

[0170]

[0171] Capacity loss rate measurement after 500 cycles

[0172] For the electrochemical devices of the above examples and comparative examples, the capacity loss rate (%) of the monocell was measured as the charge-discharge efficiency after 500 charge-discharge cycles under conditions of 0.33C / 0.33C at 25°C and is shown in Tables 1 and 2 below.

[0173]

[0174] Example 1 Example 2 Example 3 Example 4 Example 5 First Polymer Binder Li-PAALi-PAALi-PAALi-PAALi-PAA Second Polymer Binder Acrylic Acrylic Acrylic Acrylic Acrylic Separator Thickness (㎛) 13.0 12.0 14.0 13.0 13.0 Air Permeability (s / 100cc) 75 70 80 70 76 Porosity (%) 50 50 50 60 50 Melting Index (g / 10min) 0.0 20.0 20.0 20.0 20.0 Air Permeability Increase Rate After Compression (%) 24 26 22 28 35 150 Thermal Shrinkage (%, MD / TD) 1 / 1 2 / 20 0 2 / 2 1 / 1 Na in Separator Content (ppm) 2,970 2,750 2,985 2,775 2,960 Li content in separator (ppm) 750 750 755 750 750 Initial battery capacity (mAh) 40.1 40.2 40.0 40.3 40.1 Initial battery resistance (mohm) 1.21 1.20 1.22 1.20 1.21 500 Capacity loss rate after cycle (%) 2.7 2.2 3.4 2.0 2.8

[0175]

[0176] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 First polymer binder PAAPAAPAACMCCMCCMCLi-PAALi-PAA Second polymer binder Acrylic Acrylic Acrylic Acrylic Acrylic Acrylic Acrylic Acrylic Acrylic Acrylic Membrane thickness (㎛) 12.9 12.9 13.0 12.9 13.1 12.8 16.0 11.5 (cross-section coating) Air permeability (s / 100cc) 76 110 111 85 120 124 110 75 Porosity (%) 50 45 45 50 45 45 50 50 Melt index (g / 10min) 0.0 20.0 20.0 20.2 0.0 20.0 20.0 20.0 2 Air permeability after compression Growth Rate (%) 25 24 4 8 23 24 50 90 15 150 Thermal Shrinkage (%, MD / TD) 1 / 10 / 0 1 / 12 / 2 1 / 11 / 10 / 0 60 60 Na Content in Separator (ppm) 3,100 3,150 3,120 3,778 3,800 3,750 4,200 3,020 Li Content in Separator (ppm) 430 420 420 450 440 445 800 750 Initial Battery Capacity (mAh) 39.8 39.2 39.1 39.5 39.0 39.0 38.5 40.2 Initial Battery Resistance (mohm) 1.25 1.30 1.30 1.26 1.31 1.32 1.45 1.20 500 Capacity After Cycle Loss Rate (%) 4.3 7.0 7.0 5.0 7.8 8.2 15.2 2.5

[0177]

[0178] According to Table 1 above, the separator and electrochemical device according to Examples 1 to 5 introduced lithium polyacrylate (Li-PAA) to control the sodium content contained in the separator to 3,000 ppm or less, the lithium content in the separator to 750 ppm, and the porosity and melting index of the porous polymer substrate were controlled to control the rate of increase in air permeability after compression to 35% or less, and it was confirmed that the low resistance and cycle performance of the electrochemical device were improved.

[0179] According to Table 2 above, Comparative Examples 1 to 6 did not include lithium polyacrylate (Li-PAA), so the sodium content included in the separator increased compared to the examples, and as a result, the resistance and cycle performance also deteriorated.

[0180] According to Table 2 above, Comparative Examples 2 and 5 have lower resistance and cycle performance than Comparative Examples 1 and 5 due to lower porosity of the porous polymer substrate.

[0181] According to Table 2 above, Comparative Examples 3 and 6 showed an increased rate of increase in air permeability after membrane compression due to the high melting index of the porous polymer substrate.

[0182] According to Table 2 above, it can be seen that in Comparative Example 7, the thickness of the coating layer increased, the rate of increase in air permeability after membrane compression increased, the sodium content contained in the membrane also increased, and furthermore, the resistance and cycle performance decreased.

[0183] According to Table 2 above, it can be confirmed that Comparative Example 8 has poor heat resistance compared to double-sided coating due to single-sided coating, and thus the heat shrinkage rate increases.

[0184] Therefore, the electrochemical device separator according to one embodiment of the present invention and the electrochemical device including the same can improve resistance and cycle performance by including polyacrylic acid substituted in the coating layer.

[0185] [Explanation of symbols]

[0186] 100: Separator for electrochemical devices

[0187] 110: Porous polymer substrate

[0188] 130: Coating layer

Claims

1. Porous polymer substrate; and A coating layer provided on at least one surface of the porous polymer substrate, comprising a first polymer binder, a second polymer binder, and inorganic particles; A separator for an electrochemical device, wherein the first polymer binder is a substituted polyacrylic acid.

2. In claim 1, A separator for an electrochemical device, wherein the thickness of the porous polymer substrate is 8 ㎛ or more and 15 ㎛ or less.

3. In claim 1, A separator for an electrochemical device, wherein the porous polymer substrate has an air permeability of 30 s / 100cc or more and 100 s / 100cc or less.

4. In claim 1, A separator for an electrochemical device, wherein the porosity of the porous polymer substrate is 50% or more.

5. In claim 1, A separator for an electrochemical device, wherein the melt index (g / 10 min) of the porous polymer substrate is less than 0.

2.

6. In claim 1, A separator for an electrochemical device, wherein the coating layer is provided on both sides of the porous polymer substrate.

7. In claim 1, A separator for an electrochemical device, wherein the thickness of the coating layer is 1 ㎛ or more and less than 3 ㎛.

8. In claim 1, A separator for an electrochemical device, wherein the content ratio of the first polymer binder and the second polymer binder is 2:1 to 1:

2.

9. In claim 1, The above first polymer binder is lithiated polyacrylic acid, A separator for an electrochemical device, wherein the second polymer binder is an acrylic binder.

10. In claim 1, A separator for an electrochemical device, wherein the sodium content in the separator is 3,000 ppm or less.

11. In claim 1, A separator for an electrochemical device, wherein the lithium content in the separator is 750 ppm or more.

12. In claim 1, A separator for an electrochemical device, wherein the rate of increase in air permeability after compression of the above separator is 35% or less.

13. An electrochemical device comprising: a positive electrode; a negative electrode; and a separator interposed between the positive electrode and the negative electrode, the separator of claim 1.

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