Separator for electrochemical device, method for manufacturing same, and electrochemical device comprising same

Abstract

The present invention relates to a separator for an electrochemical device, a method for manufacturing same, and an electrochemical device comprising same and, specifically, to a separator for an electrochemical device, a method or manufacturing same, and an electrochemical device comprising same, the separator having improved heat resistance and mechanical properties by comprising a photoinitiator in a coating layer, while increasing the porosity of a porous polymer substrate.

Description

Separator for an electrochemical device, method for manufacturing the same, and electrochemical device including the same

[0001] The present invention claims the benefit of the filing dates of Patent Application No. 10-2024-0133068 filed with the Korean Intellectual Property Office on September 30, 2024, and Patent Application No. 10-2025-0141144 filed with the Korean Intellectual Property Office on September 29, 2025, the entire contents of which are incorporated into the present invention.

[0002] The present invention relates to a separator for an electrochemical device, a method for manufacturing the same, and an electrochemical device including the same. Specifically, the invention relates to a separator for an electrochemical device capable of improving heat resistance and mechanical properties by including a photoinitiator in the coating layer while increasing the porosity of a porous polymer substrate, a method for manufacturing the same, and an electrochemical device including the same.

[0003] Electrochemical devices convert chemical energy into electrical energy using electrochemical reactions; recently, lithium-ion batteries, which offer high energy density and voltage, long cycle life, and applicability to various fields, are widely used.

[0004] A lithium secondary battery may comprise an electrode assembly made of a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, and may be manufactured by housing the electrode assembly together with an electrolyte in a case. The separator may comprise a coating layer comprising a polymer binder and inorganic particles on at least one surface of a porous polymer substrate. The inorganic particles may be connected to other inorganic particles by the polymer binder to form an interstitial volume, and lithium ions may move through said interstitial volume. In addition to fixing the inorganic particles, the polymer binder may impart adhesive force to the coating layer, and the coating layer may be adhered to the porous polymer substrate and the electrode, respectively.

[0005] The porous polymer substrate uses a polyolefin (polyethylene, polypropylene, etc.) film. Such a separator can be manufactured using a wet manufacturing method in which pores are formed using a pore-forming agent, or a dry manufacturing method in which a polymer material is melted, manufactured into a membrane form, and then stretched to form pores. Typically, a stretching process is performed during the manufacturing of the separator to increase the mechanical strength of the obtained separator; separators manufactured by the wet manufacturing method mainly undergo a biaxial stretching process, while separators manufactured by the dry manufacturing method undergo a uniaxial stretching process.

[0006] Furthermore, when a biaxial stretching process is applied to a separator manufactured by the above dry manufacturing method, it is difficult to use alone due to weak mechanical properties, and it may break or cause damage during assembly.

[0007] Accordingly, there was a need to develop a separator with improved low resistance and output performance while increasing the porosity of the porous polymer substrate by controlling the separator process.

[0008] The technical problem to be solved by the present invention is to provide a separator for an electrochemical device capable of improving heat resistance and mechanical properties by including a photoinitiator in the coating layer while increasing the porosity of the porous polymer substrate, a method for manufacturing the same, and an electrochemical device including the same.

[0009] However, the problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0010] 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 and comprising a photoinitiator, a polymer binder, and inorganic particles, wherein the puncture strength is 400 gf or more.

[0011] According to one embodiment of the present invention, the porosity of the porous polymer substrate may be 50% or more.

[0012] According to one embodiment of the present invention, the thickness of the porous polymer substrate may be 5 μm or more and 20 μm or less.

[0013] According to one embodiment of the present invention, the porous polymer substrate may be a dry film.

[0014] According to one embodiment of the present invention, the porous polymer substrate may comprise polypropylene (PP).

[0015] According to one embodiment of the present invention, the porous polymer substrate may not contain a pore-forming agent and may be biaxially stretched in the MD direction and the TD direction.

[0016] According to one embodiment of the present invention, the thickness of the coating layer may be 1.5 μm or more and 5 μm or less.

[0017] According to one embodiment of the present invention, the photoinitiator may be an aqueous photoinitiator and may not include a non-aqueous photoinitiator.

[0018] According to one embodiment of the present invention, the photoinitiator may be one selected from the group consisting of Acylphosphine Oxide (APO), Bis-Acylphosphine Oxide (BAPO), Hydroxyalkylphenones, Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), and the same.

[0019] According to one embodiment of the present invention, the photoinitiator may be in an amount of 0.5 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the coating layer.

[0020] One embodiment of the present invention provides a method for manufacturing a separator for an electrochemical device, comprising the steps of: providing a porous polymer substrate manufactured by dry biaxial stretching; and providing a coating layer comprising a photoinitiator, a polymer binder, and inorganic particles on at least one surface of the porous polymer substrate, wherein the puncture strength is 400 gf or more.

[0021] According to one embodiment of the present invention, the coating layer may be manufactured by curing after ultraviolet irradiation.

[0022] 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.

[0023] A separator for an electrochemical device according to one embodiment of the present invention can improve heat resistance and mechanical properties by increasing the porosity of the porous polymer substrate while including a photoinitiator in the coating layer.

[0024] A method for manufacturing a separator for an electrochemical device according to one embodiment of the present invention includes a porous polymer substrate manufactured by dry biaxial stretching and a coating layer that undergoes a UV curing process, which can increase the porosity of the separator while improving heat resistance and mechanical properties.

[0025] An electrochemical device according to one embodiment of the present invention can improve low resistance and output performance by increasing the porosity of the separator while improving heat resistance and mechanical properties.

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

[0027] FIG. 2 is an SEM image showing the porosity of a porous polymer substrate of Example 1 according to one embodiment of the present invention.

[0028] Figure 3 is an SEM image showing the porosity of a porous polymer substrate of Comparative Example 3 according to one embodiment of the present invention.

[0029] Figure 4 is an SEM image showing the porosity of a porous polymer substrate of Comparative Example 4 according to one embodiment of the present invention.

[0030] In this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0031] In this specification, "A and / or B" means "A and B, or A or B".

[0032] In this specification, "about," "approximately," and "substantially" are used to mean a range of numerical values ​​or degrees or approximations thereof, taking into account inherent manufacturing and material tolerances, and are used to prevent an infringer from unfairly exploiting the disclosure in which precise or absolute figures provided to aid in understanding the invention are mentioned.

[0033] In this specification, when a component is described as being "on" one component, this means that, unless specifically stated otherwise, other components may be placed in between, without excluding the placement of other components.

[0034] 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.

[0035] In this specification, the separator has porous characteristics including a plurality of pores and acts as a porous ion-conducting barrier that blocks electrical contact between the cathode and the anode in an electrochemical device while allowing ions to pass through.

[0036] In this specification, "Wet state" may mean a state in which the separator is impregnated with at least a portion of the electrolyte, and "Dry state" may mean a dry state in which the separator is not impregnated by the electrolyte.

[0037] In this specification, "durability" may mean a property in which the binder does not swell or deform when in contact with an electrolyte and exhibits adhesive strength or mechanical strength as its original physical properties.

[0038] 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.

[0039] FIG. 1 is a schematic diagram of a separator for an electrochemical device according to one embodiment of the present invention.

[0040] The present invention will be described in more detail below.

[0041] One embodiment of the present invention comprises a porous polymer substrate (110); and a coating layer (130) provided on at least one surface of the porous polymer substrate and comprising a photoinitiator, a polymer binder, and inorganic particles, and a separator (100) for an electrochemical device having a puncture strength of 400 gf or more.

[0042] A separator for an electrochemical device according to one embodiment of the present invention can improve heat resistance and mechanical properties by increasing the porosity of the porous polymer substrate while including a photoinitiator in the coating layer.

[0043] The above-described separator (100) for an electrochemical device includes a porous polymer substrate (110). As described above, by including the porous polymer substrate (110) for the electrochemical device separator (100), it is possible to block electrical contact while allowing lithium ions to pass through, and to implement a shutdown function at an appropriate temperature.

[0044] 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 polyolefin-based resins include polyethylene, polypropylene, polypentene, etc., and may include one or more of these. A porous membrane, i.e., having a plurality of pores, manufactured using such a polyolefin-based resin as a base resin, can provide a shutdown function at an appropriate temperature.

[0045] According to one embodiment of the present invention, the porous polymer substrate (110) may comprise polypropylene (PP). Specifically, the polypropylene has a higher melting point compared to polyethylene, thus providing high-temperature stability; has less thermal shrinkage, which can improve thermal safety; and has high strength and durability, making it easy to manufacture high-performance separation membranes. As described above, by including polypropylene (PP) in the porous polymer substrate (110), high thermal stability, excellent mechanical strength, and a uniform pore structure can be achieved.

[0046] 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 using a mixture of different types of polyolefin resins or forming a separator 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.

[0047] In the present 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.

[0048] - Column: PL Olexis (Polymer Laboratories)

[0049] - Solvent: TCB (Trichlorobenzene)

[0050] - Flow rate: 1.0 ml / min

[0051] - Sample concentration: 1.0 mg / ml

[0052] - Injection volume: 200 µl

[0053] - Column temperature: 160 ℃

[0054] - Detector: Agilent High Temperature RI detector

[0055] - Standard: Polystyrene (corrected by a cubic function)

[0056] According to one embodiment of the present invention, the thickness of the porous polymer substrate (110) may be 5 μm or more and 20 μm or less. Specifically, the thickness of the porous polymer substrate (110) may be 5 μm or more and 18 μm or less, 5 μm or more and 16 μm or less, 5 μm or more and 15 μm or less, 6 μm or more and 14 μm or less, 7 μm or more and 13 μm or less, 8 μm or more and 12 μm or less, or 9 μm or more and 11 μm or less. If the thickness falls below the above-described range, manufacturing itself may not be easy, and if the thickness exceeds the above-described range, the electrolyte impregnation ability may be reduced due to an excessive increase in thickness and may cause an increase in resistance.

[0057] 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 gauge (Mitutoyo, VL-50S-B).

[0058] 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, 55% or more and 65% or less, 55% or more and 63% or less, or 55% or more and 60% or less. If the above-described range is not met, the ion conductivity may decrease, increasing internal resistance and reducing capacity retention performance. If the above-described range is exceeded, the separator may not be able to sufficiently perform the role of physical isolation between electrodes, which may result in a risk of short circuit in the battery and reduced durability.

[0059] 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.

[0060] According to one embodiment of the present invention, the porous polymer substrate (110) may be a dry film. Specifically, the dry film may refer to a porous polymer substrate manufactured by a dry method. The dry method may refer to a method of melting a polymer resin using an extruder, extruding the molten resin into a sheet form, and then forming pores through stretching. Unlike the wet method, which uses pore-forming agents such as plasticizers, the dry method forms pores by utilizing the crystallinity of a polymer resin such as a polyolefin. Accordingly, the mixing and extraction processes of the diluent used in the wet method are eliminated, making it environmentally friendly and desirable in terms of cost reduction.

[0061] According to one embodiment of the present invention, the porous polymer substrate (110) may not contain a pore-forming agent and may be biaxially stretched in the MD direction and the TD direction. Specifically, the porous polymer substrate (110) may be manufactured by a method of biaxially stretching an extruded sheet in the MD and TD directions. Generally, the porous polymer substrate can be given mechanical strength and become a thin film through a stretching process. When manufactured by uniaxial stretching in either the TD direction or the MD direction, mechanical strength is given in the stretched direction, while mechanical strength in the direction perpendicular to the stretching is very weak. Accordingly, handling of the separator substrate is not easy in the process of assembling an electrode assembly by laminating it with an electrode, and it is easily torn by external impact, which may result in a risk of a direct short circuit between the anode and the cathode. The present invention manufactures a porous polymer substrate by biaxially stretching an unoriented sheet obtained through extrusion in the TD and MD directions. In this case, since both the TD and MD directions are stretched, the mechanical strength in the MD direction and the TD direction of the porous polymer substrate is balanced, thereby resolving the problem of asymmetry in mechanical strength mentioned above.

[0062] 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, by including the coating layer (130) provided on at least one surface of the porous polymer substrate (110) in the electrochemical device separator (100), the heat resistance of the separator is improved, mechanical properties are improved, and the separator shrinks at high temperatures, thereby preventing an electrical short circuit of the electrode.

[0063] According to one embodiment of the present invention, the coating layer (130) comprises a photoinitiator, a polymer binder, and inorganic particles. As described above, by including the photoinitiator, the polymer binder, and inorganic particles, the coating layer (130) improves the heat resistance of the separator, improves mechanical properties, prevents the separator from shrinking at high temperatures and causing an electrical short circuit in the electrode, and can form pores within the coating layer.

[0064] According to one embodiment of the present invention, the coating layer (130) may be formed by inorganic particles being bound by a polymer binder and accumulated within the layer. The pores within the coating layer may originate from interstitial volumes, which are empty spaces between the inorganic particles.

[0065] 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 (130) may be a porous coating layer that includes a plurality of pores inside. As described above, by including a plurality of pores in the coating layer, it is possible to physically block the negative electrode and the positive electrode while allowing lithium ions to pass through and current to flow.

[0066] According to one embodiment of the present invention, the inorganic particles usable in the coating layer (130) are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in one embodiment of the present invention are within the operating voltage range of the electrochemical device to which they are applied (e.g., Li / Li + It is not particularly limited as long as oxidation and / or reduction reactions do not occur at a standard of 0 V to 5 V.

[0067] According to one embodiment of the present invention, non-limiting examples of the inorganic particles include BaTiO3, Pb(Zr,Ti)O3(PZT), and Pb1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 Examples include O3-PbTiO3(PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, 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.

[0068] According to one embodiment of the present invention, the average particle size (D50) of the inorganic particles is not subject to any particular limitation, but it is preferable that it be in the range of 0.1 μm or more and 1 μm or less for the formation of a coating layer (130) of uniform thickness and appropriate porosity. Specifically, the average particle size (D50) of the inorganic particles may be 0.2 μm or more and 0.9 μm or less, 0.3 μm or more and 0.8 μm or less, 0.4 μm or more and 0.7 μm or less, or 0.5 μm or more and 0.6 μm or less. If the above-described range is not met, the dispersibility of the inorganic particles in the slurry prepared for manufacturing the coating layer may be reduced, and as the coating density increases with smaller particle size and the porosity decreases, the ion conductivity may decrease. If the above-described range is exceeded, the thickness of the coating layer formed may increase and the uniformity of the coating layer may be reduced.

[0069] In this specification, "D50 particle size" refers to the particle size at the 50% point of the cumulative distribution of the number of particles according to particle size. The particle size can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) to measure the difference in diffraction patterns according to particle size as the particles pass through a laser beam, thereby calculating the particle size distribution. The D50 particle size can be measured by calculating the particle diameter at the point that is 50% of the cumulative distribution of the number of particles according to particle size in the measuring device.

[0070] According to one embodiment of the present invention, the content of the inorganic particles with respect to 100 parts by weight of the coating layer (130) may be 85 parts by weight or more and 95 parts by weight or less. Specifically, the content of the inorganic particles with respect to 100 parts by weight of the coating layer (130) may be 86 parts by weight or more and 94 parts by weight or less, 87 parts by weight or more and 93 parts by weight or less, 88 parts by weight or more and 92 parts by weight or less, or 89 parts by weight or more and 91 parts by weight or less. By controlling the content of the inorganic particles included in the coating layer (130) within the above-described range, the safety of the battery can be ensured by improving the heat resistance of the separator.

[0071] According to one embodiment of the present invention, the polymer binder may be one selected from the group consisting of polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyacrylamide (PAAM), and the same.

[0072] According to one embodiment of the present invention, the polymer binder may be in an amount of 4.5 parts by weight or more and 14.5 parts by weight or less per 100 parts by weight of the coating layer (130). Specifically, the polymer binder may be in an amount of 5 parts by weight or more and 14 parts by weight or less, 5 parts by weight or more and 12 parts by weight or less, 5 parts by weight or more and 10 parts by weight or less, 5 parts by weight or more and 8 parts by weight or less, or 5 parts by weight or more and 7 parts by weight or less per 100 parts by weight of the coating layer (130). By controlling the content of the polymer binder within the above-described range, the binding strength with inorganic particles and the binding strength between the separator and the electrode can be improved, thereby improving battery performance.

[0073] According to one embodiment of the present invention, the coating layer is based on a water-based system, and accordingly, the photoinitiator may be a water-based photoinitiator and may not include a non-aqueous photoinitiator. This is because non-aqueous photoinitiators require solubility in organic solvents, which entails a separate organic solvent process and entails significant environmental and economic burdens. For example, 2-isopropylthioxanthone (ITX), a representative non-aqueous photoinitiator, is not suitable for water-based processes because it can only be used stably in organic solvent systems.

[0074] Furthermore, benzoyl peroxide (BPO), a representative example of a non-aqueous thermal initiator, can initiate a reaction by generating radicals under high-temperature conditions; however, uniform reaction control within the coating layer is difficult due to reduced stability resulting from the exothermic decomposition reaction and low dispersibility within the aqueous system. Therefore, the present invention does not require the introduction of such non-aqueous photoinitiators or thermal initiators, and by applying an aqueous-based photoinitiator, process stability, heat resistance, and environmental friendliness can be simultaneously secured.

[0075] Accordingly, the separator of the present invention improves the heat resistance and mechanical strength of the coating layer while securing the porosity of the porous substrate, thereby exhibiting the effect of simultaneously improving the low resistance characteristics and output performance of the battery.

[0076] According to one embodiment of the present invention, the photoinitiator may be one selected from the group consisting of Acylphosphine Oxide (APO), Bis-Acylphosphine Oxide (BAPO), Hydroxyalkylphenones, Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), and the same. Preferably, the photoinitiator may be Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP). By selecting the photoinitiator from the above, a coating layer can be formed through UV curing and the heat resistance of the separator can be secured.

[0077] According to one embodiment of the present invention, the photoinitiator may be in an amount of 0.5 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the coating layer. Specifically, the photoinitiator may be in an amount of 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, 1 part by weight or more and 3 parts by weight or less, or 1 part by weight or more and 2 parts by weight or less per 100 parts by weight of the coating layer. By controlling the content of the photoinitiator within the above-described range, a coating layer can be formed through UV curing and the heat resistance of the separation membrane can be secured.

[0078] According to one embodiment of the present invention, the thickness of the coating layer may be 1.5 μm or more and 5 μm or less. Specifically, the thickness of the coating layer may be 1.5 μm or more and 4 μm or less, or 2 μm or more and 4 μm or less, based on one side. If the thickness falls below the above-described range, the heat resistance of the coating layer may be reduced, and if the thickness exceeds the above-described range, an increase in resistance may be caused by an excessive increase in thickness. By controlling the thickness of the coating layer (130) within the above-described range, the heat resistance and resistance performance of the separator can be improved.

[0079] In one embodiment of the present invention, the thickness of the coating layer (130), etc., can be measured by applying a contact-type thickness gauge. For example, the contact-type thickness gauge may use the VL-50S-B from Mitutoyo.

[0080] In one embodiment of the present invention, the separation membrane (100) has a puncture strength of 400 gf or more. Specifically, the puncture strength of the separation membrane may be 400 gf or more and 1,000 gf or less. If the above-described range is not met, it may be difficult to secure the mechanical properties of the separation membrane.

[0081] One embodiment of the present invention comprises a step of providing a porous polymer substrate manufactured by dry biaxial stretching; and a step of providing a coating layer comprising a photoinitiator, a polymer binder, and inorganic particles on at least one surface of the porous polymer substrate; and a method for manufacturing a separator for an electrochemical device having a puncture strength of 400 gf or more.

[0082] A method for manufacturing a separator for an electrochemical device according to one embodiment of the present invention includes a porous polymer substrate manufactured by dry biaxial stretching and a coating layer that undergoes a UV curing process, which can increase the porosity of the separator while improving heat resistance and mechanical properties.

[0083] A method for manufacturing a separator for an electrochemical device according to one embodiment of the present invention can contribute to low resistance and high power performance of the separator by selecting a dry biaxial stretching process when manufacturing a porous polymer substrate, thereby improving the porosity of the porous polymer substrate compared to a dry uniaxial stretching process.

[0084] A method for manufacturing a separator for an electrochemical device according to one embodiment of the present invention can contribute to low resistance and high power performance of the separator by selecting a dry biaxial stretching process when manufacturing a porous polymer substrate, thereby improving the porosity of the porous polymer substrate compared to a wet biaxial stretching process.

[0085] According to one embodiment of the present invention, the coating layer may be manufactured by curing after ultraviolet irradiation. Specifically, during the manufacture of the coating layer, a photoinitiator may be included to promote the curing reaction by irradiating with ultraviolet light, thereby improving the heat resistance and mechanical strength of the coating layer. Accordingly, it is possible to realize a separator without a decrease in strength while improving low resistance and high power performance by increasing the porosity of the porous polymer substrate.

[0086] One embodiment of the present invention comprises an electrochemical element comprising: an anode; a cathode; and one of the aforementioned separators interposed between the anode and the cathode. In the electrochemical element according to one embodiment of the present invention, details that overlap with the description of the separator for the electrochemical element are omitted.

[0087] An electrochemical device according to one embodiment of the present invention can improve low resistance and output performance by increasing the porosity of the separator while improving heat resistance and mechanical properties.

[0088] In one embodiment of the present invention, the electrochemical element is a device that converts chemical energy into electrical energy through an electrochemical reaction, and is a concept that encompasses primary batteries and secondary batteries. In this 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 include a non-aqueous electrolyte secondary battery containing a liquid electrolyte, an all-solid-state battery containing a solid electrolyte, a lithium polymer battery containing a gel polymer electrolyte, and a lithium metal battery using lithium metal as a negative electrode, but are not limited thereto.

[0089] According to one embodiment of the present invention, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer comprising a positive electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. The positive electrode active material is a layered compound such as a lithium manganese complex 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-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; 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 ~ 0.3); chemical formula LiMn1-xM xIt may include a lithium manganese complex oxide represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of the Li of the chemical formula is substituted with alkaline earth metal ions; a disulfide compound; and one or more of Fe2(MoO4)3.

[0090] 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, Group 1, 2, and 3 elements 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.

[0091] According to one embodiment of the present invention, the conductive material may be, for example, any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whiskers, conductive metal oxide, activated carbon, and polyphenylene derivative, or a mixture of two or more of these conductive materials. More specifically, it 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, thermal black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0092] 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.

[0093] According to one embodiment of the present invention, the binder resin may be a polymer commonly used in the industry for electrodes. 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 include acetatepropionate), cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, but are not limited thereto.

[0094] 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).

[0095] According to one embodiment of the present invention, the electrochemical element may further include an electrolyte, and the electrolyte is A + B - As a salt with a structure like that, A + is Li + , Na + , K + It may include alkali metal cations such as or ions composed of a combination thereof. In addition, B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - A salt comprising an anion such as or a combination thereof may be dissolved or dissociated in an organic solvent comprising 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), ethylmethyl carbonate (EMC), gamma butyrolactone, or a mixture thereof, but is not limited thereto.

[0096] According to one embodiment of the present invention, a battery module comprising a battery including the electrochemical element as a unit cell, a battery pack comprising the battery module, and a device comprising 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 moves by receiving power from a battery 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) or an electric scooter (E-scooter); an electric golf cart; and a power storage system.

[0097] 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.

[0098]

[0099] <Example 1>

[0100] Manufacturing of porous polymer substrates

[0101] Polypropylene (weight-average molecular weight: 200,000 g / mol) was fed into an extruder, melted, and extruded in the form of a sheet at 230°C. The extruded unoriented sheet was crystallized by contacting it with a chill roll maintained at 126°C. Subsequently, it was biaxially stretched in the MD direction and the TD direction. Specifically, using a roller, it was stretched at 160°C to achieve a stretching ratio of 400% in the MD direction. Then, at a temperature of 170°C, it was stretched in the TD direction to achieve 400% relative to the initial input width.

[0102] In this way, a polypropylene porous polymer substrate (thickness: 10 μm, porosity: 60%, air permeability: 50 s / 100cc, resistance: 0.5 ohm, MI: 0.8 g / 10min, Tm: 160℃) was prepared.

[0103] Formation of a coating layer

[0104] Al2O3 (AES 11, Sumitomo) with a D50 particle size of 500 nm was prepared as an inorganic particle. Polyacrylic acid (PAA, CK-702, Lubrizol) was prepared as a polymer binder, Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) was prepared as a UV initiator, and a silicone-based surfactant (BYK-348, BYK) was prepared.

[0105] A slurry for a coating layer was prepared by adding the above-prepared inorganic particles, polymer binder, surfactant, and UV initiator to water in a weight ratio of 90:6:2:2 and then dispersing them.

[0106] The slurry for the coating layer was applied to both sides of the porous polymer substrate using a doctor blade in a bar coating manner. A UV lamp was irradiated to promote a curing reaction, and a heat gun was used to dry the coating layer with a temperature of 50°C to form a coating layer with a thickness of 2 μm on each side.

[0107]

[0108] <Example 2>

[0109] In the above Example 1, a separator was manufactured in the same manner as in Example 1, except that the coating layer was formed with a thickness of 4 μm on one side instead of having a thickness of 2 μm on each side.

[0110]

[0111] <Comparative Example 1>

[0112] In the above Example 1, a separator was prepared in the same manner as in Example 1, except that a coating layer was not formed.

[0113]

[0114] <Comparative Example 2>

[0115] Manufacturing of porous polymer substrates

[0116] A porous polymer substrate was prepared in the same manner as in Example 1 above.

[0117] Formation of a coating layer

[0118] Al2O3 (AES 11, Sumitomo) with a D50 particle size of 500 nm was prepared as an inorganic particle. Polyacrylic acid (PAA, CK-702, Lubrizol) was prepared as a polymer binder, and a silicone-based surfactant (BYK-348, BYK) was prepared.

[0119] The above-prepared inorganic particles, polymer binder, and surfactant were added to water in a weight ratio of 90:8:2 and dispersed to prepare a slurry for a coating layer (solid content: 35%).

[0120] The slurry for the coating layer was applied to both sides of the porous polymer substrate using a doctor blade in a bar coating method, and dried with a heat gun at 50°C to form a coating layer with a thickness of 2 μm on each side.

[0121]

[0122] <Comparative Example 3>

[0123] Manufacturing of porous polymer substrates

[0124] Polypropylene (weight-average molecular weight: 200,000 g / mol) was fed into an extruder, melted, and extruded in the form of a sheet at 230°C. The extruded unoriented sheet was crystallized by contacting it with a chill roll maintained at 126°C. Subsequently, it was uniaxially stretched in the MD direction. Specifically, it was stretched using a roller at 160°C to achieve an MD direction stretching ratio of 400%.

[0125] In this way, a polypropylene porous polymer substrate (thickness: 10 μm, porosity: 30%, air permeability: 130 s / 100cc, resistance: 1.0 ohm, MI: 0.8 g / 10min, Tm: 160℃) was prepared.

[0126] Formation of a coating layer

[0127] A coating layer was formed in the same manner as in Example 1 above.

[0128]

[0129] <Comparative Example 4>

[0130] Manufacturing of porous polymer substrates

[0131] A porous polymer substrate (thickness: 10 μm, porosity: 40%, air permeability: 90 s / 100cc, resistance: 0.7 ohm, MI: 0.1 g / 10 min, Tm: 140℃) was prepared by extruding a polyethylene resin (weight-average molecular weight 1 million) and using a wet biaxial stretching process including a pore-forming agent.

[0132] Polyethylene resin (weight-average molecular weight 1 million) was fed into an extruder, melted, and extruded in the form of a sheet at 200°C. The extruded unoriented sheet was crystallized by contacting it with a chill roll maintained at 80°C. Subsequently, it was biaxially stretched in the MD direction and the TD direction. Specifically, using a roller, it was stretched at 100°C to achieve a stretching ratio of 400% in the MD direction. Then, at a temperature of 130°C, it was stretched in the TD direction to achieve 400% relative to the initial input width.

[0133] Formation of a coating layer

[0134] A coating layer was formed in the same manner as in Comparative Example 2 above.

[0135]

[0136] <Comparative Example 5>

[0137] In the above Example 1, a separator was manufactured in the same manner as in Example 1, except that the coating layer thickness was formed with a thickness of 1 μm on each side instead of 2 μm on each side.

[0138]

[0139] <Comparative Example 6>

[0140] In the above Example 1, a separator was manufactured in the same manner as in Example 1, except that the coating layer was formed with a thickness of 6 μm on one side instead of having a thickness of 2 μm on each side.

[0141]

[0142] <Comparative Example 7>

[0143] In the above Example 1, a separation membrane was prepared in the same manner as in Example 1, except that the thickness of the porous polymer substrate was 4 μm.

[0144]

[0145] <Comparative Example 8>

[0146] In the above Example 1, a separation membrane was prepared in the same manner as in Example 1, except that the thickness of the porous polymer substrate was 25 μm.

[0147]

[0148] Manufacture of Electrochemical Devices

[0149] Electrochemical devices were each manufactured using the separator membranes for electrochemical devices of the above examples and comparative examples.

[0150] 1) Manufacture of the anode

[0151] Cathode active material (LiNi 0.8 Mn 0.1 Co 0.1O2), a conductive material (carbon black), a dispersant (N-methylpyrrolidone, ADC-01, LG Chem), 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 an anode active material layer with a concentration of 50 wt% of the components excluding water. Next, the slurry was applied to the surface of an aluminum thin film (thickness 10 μm) and dried to manufacture an anode having an anode active material layer (thickness 120 μm).

[0152] 2) Preparation of the cathode

[0153] Graphite (a blend of natural graphite and artificial graphite), a conductive material (carbon black), a dispersant (Polyvinylpyrrolidone, Junsei, Japan), 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 negative electrode active material layer with a concentration of 50 wt% of the components excluding water. Next, the slurry was applied to the surface of a copper thin film (thickness 10 μm) and dried to manufacture a negative electrode having a negative electrode active material layer (thickness 120 μm).

[0154] 3) Lamination Process

[0155] 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.

[0156]

[0157] <Experimental Example>

[0158] Electrical Resistance (ER) Measurement

[0159] Coin cells were manufactured by interposing the separators of the above examples and comparative examples between SUS layers. An electrolyte containing 1M LiPF6 and mixed with ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:2 was injected into the coin cells. To measure the resistance of the coin cells, the resistance was measured using a VMP3 from BioLogic Science Instrument at 25°C under conditions of Amplitude 10 mV and Scan range 0.1 Hz to 1 MHz, and the results of electrochemical impedance spectroscopic analysis were shown in Table 1 below.

[0160]

[0161] Measurement of puncture strength

[0162] The maximum load value when the individual membranes of the above examples and comparative examples were pierced at a speed of 120 mm / min using a needle with a diameter of 1 mm (0.5 mmR) was measured using ASTM D5748-95 and ASTM D4649. This was performed 5 times for each membrane, and the average value was calculated using an Instron testing machine and is shown in Table 1 below.

[0163]

[0164] Measurement of electrolyte wettability

[0165] 2 μL of propylene carbonate (PC) was dropped onto the surface of the separator membranes of the above examples and comparative examples, and after 5 minutes, the distance (diameter of the droplet) of the propylene carbonate spread out in the MD / TD direction from the droplet interface was measured and is shown in Table 1 below.

[0166]

[0167] Measurement of initial resistance of an electrochemical device

[0168] For the electrochemical elements of the above examples and comparative examples, the resistance was evaluated by the resistance value confirmed when a current was applied for 10 seconds at a rate of 2.5 C-rate at 50 SOC after charging and discharging three times at 25 ℃ and 0.33 C-rate. The measurement results are shown in Table 1 below.

[0169]

[0170] Measurement of discharge capacity retention rate of electrochemical devices

[0171] For the electrochemical elements of the above examples and comparative examples, 100 charge-discharge cycles were performed by charging at 25°C at 1C until the voltage reached 4.2V and discharging at a constant current of 1C until the voltage reached 3.0V. The discharge capacity after 1 cycle and the discharge capacity after 100 cycles were measured to determine the discharge capacity retention rate, which is shown in Table 1 below.

[0172]

[0173] Porosity measurement

[0174] The porosity of the porous polymer substrates of Example 1, Comparative Examples 3 and 4 was measured by SEM to visually confirm the porosity and is shown in FIGS. 2 to 4.

[0175]

[0176] Example 1 Example 2 Substrate Process Dry PP Dry PP Stretch Biaxial Biaxial Porosity (%) 60 60 Thickness (㎛) 10 10 Coating Layer Process UV Curing UV Curing Thickness (㎛) Double-sided / 2 ㎛ Single-sided / 4 ㎛ Separator Physical Properties ER (ohm) 0.7 0.7 Perforation Strength (gf) 500 450 Electrolyte Impregnation (mm) 15 10 Electrochemical Device Physical Properties Initial Resistance (ohm) 1.2 1.3 Discharge Capacity Retention Rate (%) 70 65

[0177]

[0178] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Substrate Process Dry PP Dry PP Dry PP Wet PE Dry PP Dry PP Dry PP Dry PP Stretching 2-axis 2-axis 1-axis 2-axis 2-axis 2-axis 2-axis Porosity (%) 60 60 30 45 60 60 60 60 Thickness (㎛) 10 10 10 10 10 10 4 25 Coating Layer Process - Bar Coating UV Curing Bar Coating UV Curing UV Curing UV Curing UV Curing Thickness (㎛) - Double-sided / 2 ㎛ Double-sided / 2 ㎛ Double-sided / 1 ㎛ Single-sided / 6 ㎛ Double-sided / 2 ㎛ Double-sided / 2 ㎛ Separator Physical Properties ER (ohm) 0.9 1.1 1.3 0.9 0.6 1.3 Fabricated due to insufficient processability Possible 2.5 Perforation Strength (gf) 250 270 500 350 300 500 600 Electrolyte Impregnation (mm) 110 10 137 155 Electrochemical Device Properties Initial Resistance (ohm) 2.0 1.7 2.1 1.5 1.2 2.0 3.0 Discharge Capacity Retention Rate (%) 60 60 40 50 60 50 40

[0179]

[0180] According to Table 1 above, in Examples 1 and 2, the porosity of the porous polymer substrate was increased to contribute to low resistance and high power output, while also ensuring the heat resistance of the coating layer.

[0181] In contrast, according to Table 2 above, Comparative Example 1 does not include a coating layer, so it can be seen that the puncture strength is low due to weakened heat resistance.

[0182] It can be confirmed that Comparative Example 2 above has low puncture strength due to weakened heat resistance because a UV curing process was not used when forming the coating layer.

[0183] Comparative Example 3 above is manufactured by a dry uniaxial stretching process of a porous polymer substrate, and it can be seen that the porosity of the porous polymer substrate is low, and accordingly, the resistance is increased.

[0184] Comparative Example 4 above is manufactured by a wet biaxial stretching process of a porous polymer substrate, and it can be seen that the porosity of the porous polymer substrate is lower compared to the example, and accordingly, the resistance is increased, and it can be seen that the puncture strength is low due to weakened heat resistance because a UV curing process is not used when forming the coating layer.

[0185] Comparative Example 5 above was manufactured with a coating layer thickness of 1 μm on each side, and it can be confirmed that the heat resistance is reduced compared to the example, resulting in lower puncture strength.

[0186] In Comparative Example 6 above, it can be confirmed that the resistance increased due to the increase in thickness when the coating layer thickness is 6 μm in cross-section.

[0187] Comparative Example 7 above could not be produced due to insufficient processability when the thickness of the porous polymer substrate was 4 μm.

[0188] In Comparative Example 8 above, it can be seen that when the thickness of the porous polymer substrate is 25 μm, the electrolyte impregnation is reduced and the resistance increases significantly due to the increase in thickness.

[0189] Figures 2 to 4 show the porosity of the porous polymer substrates of Example 1, Comparative Examples 3 and 4 as seen by SEM for visual confirmation.

[0190] According to Figure 2 above, the porous polymer substrate manufactured by the dry biaxial stretching process of Example 1 can be visually confirmed to have a large porosity.

[0191] In contrast, according to FIGS. 3 and 4 above, it can be visually confirmed that the porous polymer substrates produced by the dry uniaxial stretching process of Comparative Example 3 and the wet biaxial stretching process of Comparative Example 4 have a lower porosity compared to the example.

[0192] Accordingly, a separator for an electrochemical device according to one embodiment of the present invention, a method for manufacturing the same, and an electrochemical device including the same can improve heat resistance and mechanical properties by including a photoinitiator in the coating layer while increasing the porosity of the porous polymer substrate.

[0193] [Explanation of the symbol]

[0194] 100: Separator for electrochemical devices

[0195] 110: Porous polymer substrate

[0196] 130: Coating layer

Claims

1. Porous polymer substrate; and A coating layer provided on at least one surface of the above-mentioned porous polymer substrate and comprising a photoinitiator, a polymer binder, and inorganic particles; A separator for an electrochemical device having a puncture strength of 400 gf or more.

2. In Claim 1, A separator for an electrochemical device, wherein the porosity of the above-mentioned porous polymer substrate is 50% or more.

3. In Claim 1, A separator for an electrochemical device, wherein the thickness of the porous polymer substrate is 5 μm or more and 20 μm or less.

4. In Claim 1, The above porous polymer substrate is a dry film, a separator for an electrochemical device.

5. In Claim 1, The above porous polymer substrate comprises polypropylene (PP), and is a separator for an electrochemical device.

6. In Claim 1, The above porous polymer substrate does not contain a pore-forming agent, and A separator for an electrochemical device that is biaxially stretched in the MD direction and the TD direction.

7. In Claim 1, A separator for an electrochemical device, wherein the thickness of the coating layer is 1.5 μm or more and 5 μm or less.

8. In Claim 1, The above photoinitiator is an aqueous photoinitiator, and A separator for an electrochemical device that does not contain a non-aqueous photoinitiator.

9. In Claim 1, A separator for an electrochemical device, wherein the photoinitiator is one selected from the group consisting of Acylphosphine Oxide (APO), Bis-Acylphosphine Oxide (BAPO), Hydroxyalkylphenones, Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), and the same.

10. In Claim 1, A separator for an electrochemical device, wherein the above photoinitiator is present in an amount of 0.5 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the coating layer.

11. A step of providing a porous polymer substrate manufactured by dry biaxial stretching; and The method comprises the step of providing a coating layer comprising a photoinitiator, a polymer binder, and inorganic particles on at least one surface of the porous polymer substrate. A method for manufacturing a separator for an electrochemical device having a puncture strength of 400 gf or more.

12. In Claim 11, A method for manufacturing a separator for an electrochemical device, wherein the above coating layer is manufactured by curing after UV irradiation.

13. An electrochemical device comprising: an anode; a cathode; and a separator of claim 1 interposed between the anode and the cathode.

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