Separator substrate, manufacturing method thereof, and separator including same

Abstract

The present invention relates to a separator substrate, a separator, an electrode assembly, and an electrochemical device, and the separator substrate according to one embodiment of the present invention is characterized in that both surfaces have different surface characteristics, thereby resulting in different adhesive strengths on both surfaces of a separator using the separator, which significantly reduces variations in electrode adhesive strength between a positive electrode and a negative electrode, which have different adhesive strengths.

Description

[Technical Field]

[0001] The present invention relates to a separator substrate, a manufacturing method thereof, and a separator including the same. More specifically, the present invention relates to a separator having improved uniformity in electrode adhesion between both sides, and an electrode assembly and an electrochemical device including the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2023-0097767, filed on July 26, 2023, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings thereof. [Background technology]

[0003] Lithium secondary batteries are manufactured by inserting an electrode assembly, consisting of a positive electrode, a separator, and a negative electrode, into a battery case, injecting an electrolyte, and sealing the battery. Polyolefin-based porous substrates are typically used as separators for lithium secondary batteries. To address the issue of short circuits between the positive and negative electrodes due to the thermal shrinkage of polyolefin-based porous substrates, a separator (hereinafter referred to as a "Safety Reinforced Separator (SRS)") has been developed in which a coating layer made of a mixture of inorganic particles and a binder polymer is formed on the surface of the porous substrate to improve the separator's strength and heat resistance.

[0004] In such an SRS, the inorganic particles in the coating layer act as a spacer that can maintain the physical shape of the separator, preventing the porous substrate from shrinking when exposed to high temperatures and preventing direct contact between the positive and negative electrodes. As a result, an electrode assembly can be manufactured by bonding the positive and negative electrodes with the separator sandwiched between them using an SRS with porous coating layers on both sides.

[0005] However, when silicon (Si)-based active materials are used as negative electrode active materials, the roughness of the material is greater than that of graphite-based active materials, resulting in high adhesive strength between the separator and negative electrode, while the roughness of the material is less in the case of positive electrodes, resulting in low adhesive strength between the separator and positive electrode. If the adhesive strength between the separator and electrode is low, the structure of the electrode assembly may become distorted during cell assembly. Furthermore, if there is a large variation in adhesive strength between the separator and the positive and negative electrodes, the cell may bend. Therefore, efforts are needed to develop technology to improve the adhesive strength between the separator and positive electrode. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, an object of the present invention is to provide a separator that solves the above-mentioned problems, and an electrode assembly and an electrochemical device including the separator.

[0007] Specifically, the present invention aims to provide a separator with improved uniformity in adhesive strength between the negative electrode and the positive electrode, and an electrode assembly and an electrochemical device using the separator with improved safety.

[0008] In particular, from the viewpoint of improving the variation in adhesive strength between the separator and the negative electrode and the positive electrode, an object of the present invention is to provide a separator substrate having different surface characteristics on both sides, and a separator including the same.

[0009] Meanwhile, an object of the present invention is to provide an electrode assembly including Si-based particles as a negative electrode active material, and an electrochemical device including the same. [Means for solving the problem]

[0010] To solve the above problems, According to one aspect of the present invention, there is provided a separator substrate having the following features.

[0011] The separator substrate according to the first aspect comprises: The porous polymer substrate has two surfaces with different surface roughnesses.

[0012] According to the second aspect, in the first aspect, The surface roughness values ​​(Sa) of both surfaces of the porous polymer substrate may be different from each other.

[0013] According to the third aspect, in the first aspect or the second aspect, The porous polymer substrate may have a surface roughness value (Sa) of 50 nm or less on one side and a surface roughness value (Sa) of more than 50 nm on the other side.

[0014] According to another aspect of the present invention, there is provided a separator having the following configuration. The separator according to the fourth aspect comprises: A separator substrate according to any one of the first to third aspects; a porous coating layer formed on each of both surfaces of the separator substrate, the porous coating layer including inorganic particles and a binder polymer; may include:

[0015] According to the fifth aspect, in the fourth aspect, The separator has two surfaces with different adhesive strengths, When the surface having the higher adhesive strength is designated as a first surface and the surface having the lower adhesive strength is designated as a second surface, the ratio of adhesive strengths of the first surface and the second surface according to the following formula 1 may be 150% or more: [Formula 1] Adhesion strength ratio (%) = [(adhesion strength of first surface / adhesion strength of second surface) x 100] In the above formula 1, The adhesive strength indicates the adhesive strength between the separator substrate and the porous coating layer.

[0016] According to the sixth aspect, in the fourth or fifth aspect, The adhesive strength of each of the two surfaces of the separator may be 30 gf / 15 mm or more.

[0017] According to the seventh aspect, in any one of the fourth to sixth aspects, The separator has an adhesive strength of 80 gf / 15 mm or less on one side and an adhesive strength of more than 80 gf / 15 mm on the other side, The adhesive strength may indicate the adhesive strength between the separator substrate and the porous coating layer. According to still another aspect of the present invention, there is provided an electrode assembly having the following configuration.

[0018] An electrode assembly according to an eighth aspect of the present invention comprises: The battery may include a separator according to any one of the fourth to sixth aspects, and a positive electrode and a negative electrode formed on both sides of the separator, respectively.

[0019] According to the ninth aspect, in the eighth aspect, The adhesive strengths of the two surfaces of the separator are different from each other, The positive electrode may face the surface with the higher adhesive strength, and the negative electrode may face the surface with the lower adhesive strength.

[0020] According to the tenth aspect, in the eighth or ninth aspect, The variation in electrode adhesive strength between the separator and each of the positive electrode and the negative electrode, as determined by the following formula 2, may be 10% or less. [Formula 2] Electrode adhesion variation (%) = │{1-F (x) / F (y) )}│×100 In the above formula 2, F (x) is the electrode adhesion strength between the separator and the positive electrode, and F (y) is the electrode adhesion between the separator and the negative electrode, or F (x) is the electrode adhesion strength between the separator and the negative electrode, and F(y) is the electrode adhesion strength between the separator and the positive electrode.

[0021] According to an eleventh aspect, in any one of the eighth to tenth aspects, The negative electrode may contain a Si-based active material as an active material. According to still another aspect of the present invention, there is provided an electrochemical device having the following configuration.

[0022] The electrochemical device according to the twelfth aspect comprises: The electrode assembly according to any one of the eighth to eleventh aspects may be housed in a case.

[0023] According to still another aspect of the present invention, there is provided a method for producing a separator substrate having the following features. A method for producing a separator substrate according to a thirteenth aspect includes the steps of: S1) extruding a polymer slurry to obtain a polymer sheet; S2) placing the obtained polymer sheet on a casting roll and cooling it; A method for producing a separator substrate comprising: In step S2, the polymer sheet may be cooled in a state where there is no touch roll on the surface opposite to the surface facing the casting roll. [Effects of the Invention]

[0024] According to an embodiment of the present invention, the surface characteristics of both sides of the separator substrate are different from each other, which has the effect of making the electrode adhesive strength of both sides of the separator formed using the same different from each other.

[0025] Therefore, even if the properties of the active materials in the electrodes formed on both sides of the separator are different from each other, there is little variation in the adhesive strength between the separator and the electrodes.

[0026] As a result, the bending phenomenon caused by the uneven adhesive strength between the separator and the positive and negative electrodes on both sides of the separator is improved, which has the advantage of improving the safety of the electrochemical device using the separator.

[0027] The separator substrate and separator according to one embodiment of the present invention have the advantage that they can be used in an electrode assembly with improved stability and productivity. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a schematic diagram of a conventional apparatus for manufacturing a separator substrate. [Figure 2] FIG. 1 is a schematic diagram of an apparatus for manufacturing a separator substrate according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will be described in detail below. Throughout this specification, when a part is said to "comprise" a certain component, this does not mean that other components are excluded, but that other components may also be included, unless otherwise specified.

[0030] Throughout this specification, the phrase "A and / or B" means "A or B, or both."

[0031] Certain terminology used in the following detailed description is for ease of explanation only and is not intended to limit the invention. Additionally, directional words such as up, down, left, right, front, rear, inside, outside, etc., refer to directions in the drawings to which reference is made or to directions toward or away from the geometric center of the specified device, system, and components thereof, respectively.

[0032] Separator substrate and manufacturing method thereof According to one aspect of the present invention, there is provided a separator substrate which is a porous polymer substrate and has two surfaces with different surface roughnesses.

[0033] To explain this, first, one feature of the method for producing a separator substrate according to one embodiment of the present invention will be described.

[0034] A method for producing a separator substrate according to one aspect of the present invention includes the steps of: S1) extruding a polymer slurry to obtain a polymer sheet; S2) placing the resulting polymer sheet on a casting roll and cooling it.

[0035] According to one aspect of the present invention, in step S2, the polymer sheet is cooled without a touch roll on the surface opposite to the surface facing the casting roll.

[0036] A schematic diagram of a manufacturing apparatus for manufacturing a conventional separator substrate is shown in Figure 1. Figure 1 shows an extrusion section 1 and a cooling section 2. In this case, the cooling section includes a contact roll 202 arranged to support a polymer sheet extruded through a T-die 200 and placed on a casting roll 201 to cool it.

[0037] Conventionally, when manufacturing a porous polymer substrate as a separator substrate, a polymer slurry is extruded to obtain a polymer sheet, and the obtained polymer sheet is cooled in a state where one side of the polymer sheet is in contact with a casting roll 201 and the other side is in contact with a touch roll 202 to support the other side. As a result, both sides of the polymer sheet are forced to be cooled in a state where they are in contact with the casting roll and the touch roll, respectively, and therefore the surface shapes of both sides of the polymer sheet obtained by cooling are formed to be approximately the same, and the surface roughness of both sides of the separator substrate is formed to be approximately the same.

[0038] Figure 2 shows a schematic diagram of an apparatus for producing a separator substrate according to one aspect of the present invention. Shown in Figure 2 are an extrusion section 1 and a cooling section 2. In this case, the cooling section cools a polymer sheet extruded through a T-die 200 by placing it on a casting roll 201, with one side of the polymer sheet not equipped with a contact roll so that it is cooled in the air.

[0039] According to one aspect of the present invention, when the extruded polymer sheet is cooled, the cooling conditions on both sides are different, thereby forming different surface shapes on both sides of the obtained polymer sheet, and thereby obtaining a polymer sheet with different surface roughness on both sides. To this end, the method for producing a separator substrate of the present invention is characterized in that one side of the polymer sheet obtained in step S1 is cooled in a state in which it is in contact with a casting roll, and the other side is cooled in a state in which it is not provided with a contact roll.

[0040] The separator substrate obtained by the above method may have a relatively smooth surface on the side that is cooled by contact with the casting roll, and a relatively rough surface on the side that is cooled by contact with air without contact with the contact roll, thereby obtaining a porous polymer substrate having different surface roughness on both sides.

[0041] Next, each step of the method for producing a separator substrate according to one aspect of the present invention will be described in detail.

[0042] First, in one embodiment of the present invention, the step S1) of extruding a polymer slurry to obtain a polymer sheet may include melt-extruding a polymer resin as a raw material.

[0043] In one embodiment of the present invention, the polymer resin may be any resin that can be used as a raw material for manufacturing a separator substrate. The polymer resin may include resins such as polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, or a mixture of two or more of these resins. The polyolefin resin refers to a polymer of an olefin, typically used in separator substrates, polymerized using an olefin as a monomer. For example, the polyolefin resin may be, but is not limited to, polyethylene; polypropylene; polybutylene; polypentene; polyhexene; polyoctene; a homopolymer of a monomer selected from ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; a copolymer of two or more of these; or a mixture thereof.

[0044] In one embodiment of the present invention, the porous polymer substrate may be a polyolefin substrate.

[0045] In one embodiment of the present invention, the porous polymer substrate may be a polyethylene substrate.

[0046] In one embodiment of the present invention, a common diluent can be used to extrude the polymer resin into an extruder, such as liquid or solid paraffin oil, wax, soybean oil, or the like, which are commonly used in the manufacture of separators.

[0047] In one embodiment of the present invention, the melting and extrusion may be performed using a conventional single-screw extruder or a twin-screw extruder, but is not limited thereto. In one embodiment of the present invention, the mixture of the diluent and the polymer resin may be fed into an extruder, and then mixed while melting the polymer resin at a high temperature to obtain a molten composition.

[0048] In one embodiment of the present invention, the polymer sheet is extruded at a high temperature, for example, 150° C. to 300° C., so that the polymer sheet extruded through the extrusion section has a high surface temperature, for example, 130° C. to 200° C., immediately after extrusion, and contacts the casting roll while maintaining such a surface temperature. In one embodiment of the present invention, the temperature of the casting roll may be, for example, 20° C. to 45° C., 25° C. to 45° C., 35° C. to 45° C., or 25° C., but the present invention is not limited thereto.

[0049] In one embodiment of the present invention, step S2 may be a step for achieving different surface roughnesses on both sides of the polymer sheet by cooling them under different environments, but the present invention is not limited thereto.

[0050] The method for manufacturing the separator substrate according to one aspect of the present invention may further include, after the step S2) of cooling, the step S3) of stretching and heat-setting the formed polymer sheet using a casting roll.

[0051] In one embodiment of the present invention, the stretching may include secondary stretching of the polymer sheet in the same direction or in different directions, for example, independently stretching the polymer sheet in a direction parallel to the machine direction (MD) and / or the transverse direction (TD).

[0052] In this specification, the "machine direction" refers to the direction parallel to the running direction of the steps [extrusion → molding → stretching...] in the manufacturing process of the separator substrate. The machine direction can be confirmed using the orientation direction of the polymer fibers of the separator substrate, and the direction parallel to the orientation direction of the fibers is the machine direction. Accordingly, the "transverse direction" refers to the direction perpendicular to the machine direction. The transverse direction can also be confirmed by the direction perpendicular to the orientation direction of the polymer fibers of the separator substrate.

[0053] In one embodiment of the present invention, the stretching can be performed by, for example, sequential or simultaneous stretching using a roll system or a tenter system.

[0054] In one embodiment of the present invention, the stretching may be performed at a stretch ratio of, for example, 3 times or more, 5 times to 12 times, or 6 times to 7 times. When the stretch ratio satisfies the above numerical range, advantageous effects are achieved in terms of thickness uniformity of the separator substrate to be manufactured and balance of physical properties between the machine direction and the cross direction, but the present invention is not limited thereto.

[0055] In one embodiment of the present invention, after the stretching, a step of extracting a diluent from the stretched sheet to form pores and then heat-setting the stretched sheet may be included.

[0056] In one embodiment of the present invention, the diluent may be extracted using an organic solvent, such as methyl ethyl ketone, methylene chloride, hexane, or a mixture of two or more thereof, which has high extraction efficiency and quick drying, but the present invention is not limited thereto.

[0057] In one embodiment of the present invention, the temperature at which the extraction is carried out is not particularly limited as long as it is within a range that does not change the surface roughness value of the porous substrate to be formed.

[0058] In one embodiment of the present invention, after the stretching and diluent extraction, the porous sheet may be heat-set to forcibly grip the sheet and remove residual stress within the sheet, although the purpose of the heat-set is not limited thereto.

[0059] In one embodiment of the present invention, the heat setting temperature may vary depending on the type of polymer resin used in manufacturing the separator substrate, and may be, for example, 100°C to 180°C, specifically 110°C to 150°C, more specifically 120°C to 140°C, for example, 130°C, but the present invention is not limited thereto.

[0060] In one embodiment of the present invention, heat may be applied during the heat setting while the film is uniaxially stretched in the MD or TD direction, or while the film is biaxially stretched in both the MD and TD directions, but the present invention is not limited thereto.

[0061] According to one aspect of the present invention, the separator substrate obtained by the above-described manufacturing method is a porous polymer substrate having two surfaces with different surface roughnesses.

[0062] In one embodiment of the present invention, the surface roughness of both surfaces of the separator substrate can be determined, for example, using a surface roughness value (Sa). For example, a porous polymer substrate having different surface roughness values ​​(Sa) on both surfaces may be a porous polymer substrate having different surface roughness values ​​(Sa) on both surfaces.

[0063] In one embodiment of the present invention, the surface roughness value (Sa) can be measured by performing surface analysis of the porous polymer substrate using atomic force microscopy (AFM). For example, a 50 mm x 50 mm sample of the porous polymer substrate to be measured for surface roughness is obtained, and the surface characteristics of both sides of a 30 μm x 30 μm area are repeatedly measured. The surface roughness value (Sa) is then measured by analyzing the average height difference of the surface of the entire area based on the average height plane.

[0064] In one embodiment of the present invention, the porous polymer substrate may have different surface roughness values ​​(Sa) on both sides, for example, the surface roughness value (Sa) on one side may be 50 nm or less and the surface roughness value (Sa) on the other side may be greater than 50 nm.

[0065] In one embodiment of the present invention, when the surface roughness of the porous polymer substrate, i.e., the separator substrate, is different on both sides, the surface characteristics of the separator using the porous polymer substrate are different on both sides, and as a result, the adhesive strength between each side of the separator and the electrode is different. In particular, when the surface roughness value (Sa) of one side of the separator substrate is 50 nm or less, it is advantageous in terms of adhesive strength with the negative electrode, and when the surface roughness value (Sa) of the other side is more than 50 nm, it is advantageous in terms of adhesive strength with the positive electrode.

[0066] In one embodiment of the present invention, the surface roughness value (Sa) of one surface of the separator substrate can be, for example, 30 nm to 45 nm or 35 nm to 40 nm, and the surface roughness value (Sa) of the other surface of the separator substrate can be, for example, 60 nm to 90 nm, 70 nm to 85 nm, or 75 nm to 80 nm.

[0067] The porous polymer substrate will be exemplified below, but is not limited to the components described below.

[0068] In one embodiment of the present invention, the porous polymer substrate refers to a substrate having a plurality of pores formed therein, which act as a porous ion-conducting barrier that allows ions to pass through while blocking electrical contact between the anode and cathode. The pores are interconnected, allowing gas or liquid to pass from one side of the substrate to the other.

[0069] In one embodiment of the present invention, the porous polymer substrate may be a porous polymer film containing a thermoplastic resin, which provides a shutdown function. Here, the shutdown function refers to the function of preventing thermal runaway of the battery by blocking ion migration when the temperature of the battery rises by melting the thermoplastic resin and closing the pores of the porous polymer substrate.

[0070] In one embodiment of the present invention, the thickness of the porous polymer substrate is not particularly limited as long as it satisfies the above-mentioned range based on the overall thickness of the separator, and may be, for example, 5 μm to 300 μm, specifically 5 μm to 100 μm, 5 μm to 50 μm, 5 μm to 20 μm, 5 μm to 15 μm, or 9 μm to 12 μm.

[0071] In one embodiment of the present invention, the "thickness" of the porous polymer substrate can be measured by a known method for measuring the thickness of each component of a separator. For example, the thickness of the porous polymer substrate can be measured using a known thickness measuring device, such as a commercially available thickness measuring device (VL-50S-B, manufactured by Mitutoyo Corporation, Japan).

[0072] Separator According to one aspect of the present invention, the porous polymer substrate described above can itself be provided as a separator.

[0073] According to another aspect of the present invention, a separator may be provided, which includes a porous coating layer formed on each side of the separator substrate using the porous polymer substrate described above as the separator substrate, the porous coating layer including inorganic particles and a binder polymer.

[0074] The porous coating layer includes a large amount of inorganic particles and a binder polymer that binds the particles together to improve the safety of the separator. The binder polymer provides adhesive strength to the surface of the separator. Since the surface roughness of both sides of the separator substrate is different, when a porous coating layer is formed on the surface of the separator substrate, the adhesive strength of both sides of the separator can be different.

[0075] In one embodiment of the present invention, the separator may have a feature that the adhesive strengths of both sides of the separator are different from each other. By having the adhesive strengths of both sides of the separator be different from each other, the separator can exhibit excellent adhesive strength not only to a negative electrode having a relatively high adhesive strength but also to a positive electrode having a relatively low adhesive strength.

[0076] In one embodiment of the present invention, when the side of the separator having a higher adhesive strength is designated as the first side and the side having a lower adhesive strength is designated as the second side, the ratio of the adhesive strengths of the first side and the second side according to the following formula 1 may be, for example, 150% or more. [Formula 1] Adhesion strength ratio (%) = [(adhesion strength of first surface / adhesion strength of second surface) x 100]

[0077] In an embodiment of the present invention, the adhesive strength may indicate the adhesive strength between the separator substrate and the porous coating layer, and may be measured by the following method.

[0078] The adhesive strength of the separator can be measured, for example, by the following method. A 15 mm wide sample of the separator to be measured for adhesive strength is attached to a glass slide using 18 mm wide double-sided tape (manufactured by 3M) so that the surface to be measured for adhesive strength is in contact with the glass. Then, a universal testing machine (manufactured by Instron) is used to measure the peel strength between the separator substrate and the porous coating layer under conditions of 180° and 300 mm / min.

[0079] In one embodiment of the present invention, the adhesive strength ratio according to Equation 1 may be, for example, 150% or more, 160% or more, or 170% or more. For example, the adhesive strength ratio may be 150% to 200%, 160% to 190%, 170% to 180%, or 175% to 180%, but the present invention is not limited thereto. According to the present invention, the separator can be realized with a large difference in adhesive strength between both sides. As a result, even if there is a large variation in adhesive strength between the positive electrode and the negative electrode, the adhesive strength between the separator and the electrode can be maintained at a constant level, thereby improving the problem of electrode bending.

[0080] In one embodiment of the present invention, the adhesive strength of the first surface of the separator, which has a relatively high adhesive strength, may be, for example, greater than 80 gf / 15 mm, and the adhesive strength of the second surface, which has a relatively low adhesive strength, may be, for example, 80 gf / 15 mm or less. Preferably, the adhesive strength of each of the two surfaces of the separator may be 30 gf / 15 mm or more.

[0081] In one embodiment of the present invention, the adhesive strength of the first surface of the separator may be, for example, 85 to 110 gf / 15 mm, 90 to 105 gf / 15 mm, or 95 to 100 gf / 15 mm. The adhesive strength of the second surface of the separator may be, for example, 30 to 70 gf / 15 mm, 40 to 60 gf / 15 mm, or 50 to 60 gf / 15 mm. When the adhesive strengths of both surfaces of the separator are within the above-mentioned ranges, the separator has an advantageous effect in terms of excellent adhesive strength with each of the positive electrode and the negative electrode, but the present invention is not limited thereto.

[0082] In one embodiment of the present invention, since the adhesive strengths of both sides of the separator are different from each other, the sides of the separator that face the positive electrode and / or the negative electrode may be determined in consideration of the adhesive strength of the electrodes depending on the composition of the electrodes, for example, the type of active material and / or the type of binder polymer.

[0083] For example, in one embodiment of the present invention, if the adhesive strength of the positive electrode is relatively low and the adhesive strength of the negative electrode is relatively high, the first surface of the separator having the relatively high adhesive strength may face the positive electrode during the manufacture of the electrode assembly, and the second surface of the separator having the relatively low adhesive strength may face the negative electrode during the manufacture of the electrode assembly.

[0084] For example, in another embodiment of the present invention, if the adhesive strength of the negative electrode is relatively low and the adhesive strength of the positive electrode is relatively high, the first surface of the separator having the relatively high adhesive strength may face the negative electrode during the manufacture of the electrode assembly, and the second surface of the separator having the relatively low adhesive strength may face the positive electrode during the manufacture of the electrode assembly.

[0085] In one embodiment of the present invention, the difference in adhesive strength between the two surfaces of the separator is due to the difference in surface roughness between the two surfaces of the separator substrate. For example, the separator may exhibit a characteristic in which the adhesive strength is relatively high on the surface of the separator substrate with a high surface roughness value and the adhesive strength is relatively low on the surface of the separator substrate with a low surface roughness value. In this case, it may be preferable that the porous coating layers formed on both surfaces of the separator are formed so that the strength of the adhesive strength between the two surfaces of the separator is not reversed with the surface roughness of the separator substrate.

[0086] The structure of the porous coating layer will be described below by way of example, but the structure of the porous coating layer is not limited thereto.

[0087] In one embodiment of the present invention, the porous coating layer may include inorganic particles and a binder polymer, and the inorganic particles may be coated with the binder polymer on all or at least a portion of their surfaces. In this case, the inorganic particles may be bound by the binder polymer at surfaces and / or points.

[0088] For example, the inorganic particles and binder resin in the porous coating layer may be contained in a weight ratio of 99:1 to 1:99. Specifically, the inorganic particles and binder resin in the porous coating layer may be contained in a weight ratio of 95:5 to 5:95, 90:10 to 10:90, 80:20 to 10:90, 70:30 to 10:90, 60:40 to 10:90, 50:50 to 10:90, 40:60 to 15:85, 60:40 to 15:85, 70:30 to 20:80, or 20:80. The porous coating layer has a large number of micropores therein, and these micropores are interconnected, providing a structural feature of a porous layer that allows gas or liquid to pass from one surface to the other.

[0089] In one embodiment of the present invention, the porous coating layer may have a porous structure due to pores formed by the interstitial volume between inorganic particles. The pore size and porosity (pore volume ratio) of the pores can be adjusted depending on the particle size and particle size distribution. This structure enhances resistance to metallic foreign matter present in the electrode and suppresses shrinkage of the porous polyolefin substrate, thereby enhancing the safety of the electrochemical device.

[0090] In one embodiment of the present invention, the porous coating layer includes a plurality of nodes including the inorganic particles and a binder polymer covering at least a portion of the surface of the inorganic particles, and one or more filaments formed in a thread-like shape from the binder polymer at the nodes, the filaments having node connection portions extending from the nodes to connect to other nodes, and the node connection portions may have a structure in which a plurality of filaments derived from the binder polymer cross each other to form a three-dimensional network structure.

[0091] In one embodiment of the present invention, as described above, the porous coating layer may be formed using a manufacturing method for a safety reinforced separator (SRS), a ceramic coated separator (CCS), or other known manufacturing methods, but is not limited thereto.

[0092] In one embodiment of the present invention, the inorganic particles can be used without any particular limitation as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention can be used within the operating voltage range (e.g., Li / Li) of the applied electrochemical device. + There are no particular limitations on the inorganic particles as long as they do not undergo oxidation and / or reduction reactions at a voltage of 0 to 5 V relative to the reference voltage. Non-limiting examples of such 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, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, and TiO2, and one or more of these may be included.

[0093] In one embodiment of the present invention, the binder polymer may include, for example, a polyvinylidene fluoride-based resin (PVdF-based resin). In one embodiment of the present invention, the PVdF-based resin may include at least one of a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer of vinylidene fluoride and a copolymerizable monomer, and a mixture thereof. In one embodiment of the present invention, the monomer may be, for example, a fluorinated monomer and / or a chlorine-based monomer. Non-limiting examples of the fluorinated monomer include vinyl fluoride; trifluoroethylene (TrFE); chlorofluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), and the like, and one or more of these may be included.

[0094] In one embodiment of the present invention, the porous coating layers formed on both sides of the separator may be formed to have the same composition. In another embodiment of the present invention, the porous coating layers may be formed to have different compositions to further improve the adhesive strength of the two sides of the separator. Specifically, it may be preferable for the porous coating layers formed on both sides of the separator to have the same composition in consideration of production efficiency and cost reduction, but the present invention is not limited thereto.

[0095] In one embodiment of the present invention, the thickness of the porous coating layer is not particularly limited as long as it satisfies the above-mentioned ratio range relative to the overall thickness of the separator, and may be, for example, 0.5 μm to 50 μm, specifically 0.5 μm to 10 μm, 0.5 μm to 5 μm, or 1.5 μm to 3 μm.

[0096] In one embodiment of the present invention, the thicknesses of the porous coating layers formed on both sides of the separator may be the same or different from each other. In this case, it may be preferable that the thicknesses of the porous coating layers formed on both sides of the separator be the same so that the surface characteristics of the separator substrate have the same effect on the adhesive strength of the separator due to the porous coating layer, but the present invention is not limited thereto.

[0097] In addition, in one embodiment of the present invention, in terms of the energy density of an electrochemical device to which the separator is applied, it is advantageous for the separator to be thin-walled, and for this reason, it may be preferable for the porous coating layer to be thin, for example, 0.5 μm to 5 μm or 1.5 μm to 3 μm. In this case, it is advantageous for the thicknesses of the porous coating layers formed on both sides of the separator substrate to be the same in terms of thinning the separator, but the present invention is not limited thereto.

[0098] electrode assembly According to yet another aspect of the present invention, there is provided an electrode assembly including the separator described above, and a positive electrode and a negative electrode formed on both sides of the separator, respectively.

[0099] In one embodiment of the present invention, the separator is characterized in that the adhesive strengths of both surfaces are different from each other, as described above.

[0100] In an embodiment of the present invention, when the adhesive strength of the positive electrode is relatively weak, the positive electrode may face the side of the separator having a relatively high adhesive strength, and the negative electrode may face the side of the separator having a relatively low adhesive strength.

[0101] In another embodiment of the present invention, when the adhesive strength of the negative electrode is relatively weak, the negative electrode may face the side of the separator having a relatively high adhesive strength, and the positive electrode may face the side of the separator having a relatively low adhesive strength.

[0102] Thus, one of the features of the electrode assembly of the present invention is that the adhesive strengths of both sides of the separator are different from each other, so that even if the adhesive strengths of the surfaces of the positive electrode and the negative electrode themselves are different from each other, there is little variation in the electrode adhesive strength between the separator and each of the positive electrode and the negative electrode.

[0103] In one embodiment of the present invention, the variation in electrode adhesive strength between the separator and each of the positive electrode and the negative electrode, as determined by the following formula 2, may be 10% or less. [Formula 2] Electrode adhesion variation (%) = │{1-F (x) / F (y) )}│×100 In the above formula 2, F (x) is the electrode adhesion strength between the separator and the positive electrode, and F (y) is the electrode adhesion strength between the separator and the negative electrode, or F (x) is the electrode adhesive strength between the separator and the negative electrode, and F (y) is the electrode adhesion strength between the separator and the positive electrode.

[0104] In one embodiment of the present invention, the electrode adhesive strength may be measured by the following method. First, the electrode and separator to be measured for adhesive strength are sampled to a width of 25 mm, overlapped, and pressed together under conditions of 60°C, 6.5 MPa, and 1 s to prepare a sample. Next, the peel strength between the separator and electrode is measured under conditions of 180° and 300 mm / min using a universal testing machine (manufactured by Instron).

[0105] In one embodiment of the present invention, when a separator using the separator substrate is used, it is possible to reduce variations in electrode adhesive strength between the positive electrode and the negative electrode, thereby alleviating the problem of electrode curvature, and thereby improving the safety and processability of an electrochemical device using the separator.

[0106] In one embodiment of the present invention, the electrode adhesive strength ratio according to the above formula 2 may be, for example, 10% or less, 8% or less, 6% or less, 5% or less, 4.5% or less, 4% or less, 3% or less, 2% or less, 1% or less, or 0% (no variation at all).

[0107] The configuration of the electrodes will be described below by way of example, but the present invention is not limited thereto.

[0108] In one embodiment of the present invention, the positive electrode and the negative electrode may each be formed by coating an electrode active material on a current collector, and the size and shape thereof are not particularly limited.

[0109] In one embodiment of the present invention, the positive electrode active material may include, but is not limited to, lithium transition metal oxides; lithium metal iron phosphate; lithium nickel-manganese-cobalt oxide; an oxide in which a portion of lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more of these. Specifically, the positive electrode active material may include, but is not limited to, layered compounds such as lithium cobalt oxide (LiCoO) and lithium nickel oxide (LiNiO), or compounds substituted with one or more transition metals; 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M x O2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3); 2-x M xO2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 - 0.1) or lithium manganese composite oxide represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); lithium metal phosphate LiMPO4 (where M = Fe, CO, Ni, or Mn); lithium nickel - manganese - cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2 (x = 0 - 0.03, a = 0.3 - 0.95, b = 0.01 - 0.35, c = 0.01 - 0.5, a + b + c = 1); oxide in which part of lithium nickel - manganese - cobalt oxide is substituted with aluminum Li a [Ni b Co c Mn d Al e 1-f M1 f O2 (M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, 0.8 ≤ a ≤ 1.2, 0.5 ≤ b ≤ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≤ e ≤ 0.1, 0 ≤ f ≤ 0.1); oxide in which part of lithium nickel - manganese - cobalt oxide is substituted with other transition metals Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (x = 0 - 0.03, a = 0.3 - 0.95, b = 0.01 - 0.35, c = 0.01 - 0.5, d = 0.001 - 0.03, a + b + c + d = 1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg and Mo), disulfide compounds; Fe2(MoO4)3 etc. are included, but are not limited thereto.

[0110] ​In one embodiment of the present invention, the negative electrode active material may be, for example, lithium metal or a lithium alloy, soft carbon, hard carbon, natural graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, petroleum or coal tar pitch-derived cokes, silicon (Si)-based compounds, or a mixture of two or more thereof, but is not limited thereto.

[0111] In one embodiment of the present invention, the negative electrode may include a Si-based active material as an active material. In one embodiment of the present invention, the negative electrode active material may include a silicon (Si)-based compound, and the silicon-based compound may be silicon-based particles.

[0112] In one embodiment of the present invention, the silicon-based particles may be, for example, (M)-SiOx (M=Li, Mg, Ca, Al, or Ti, 0≦x<2). The (M)-SiOx may include a Si phase, a SiO2 phase, a metal oxide phase, a metal silicate phase, or a mixed phase of two or more of these, but the present invention is not limited thereto.

[0113] In one embodiment of the present invention, the negative electrode active material may be composed only of Si particles.

[0114] Electrochemical elements According to yet another aspect of the present invention, there is provided an electrochemical device in which the above-described electrode assembly is housed in a case.

[0115] In one embodiment of the present invention, the electrochemical device may be a primary battery, a secondary battery, a supercapacitor, an electric double layer capacitor, etc. More specifically, the secondary battery may be a lithium ion secondary battery.

[0116] In one embodiment of the present invention, the case may be a commonly used battery case and is not particularly limited in shape depending on the intended use of the battery. For example, the case may be cylindrical, rectangular, pouch-like, or coin-like using a can.

[0117] Once the electrode assembly is completed, it can be housed in a case and sealed in a conventional manner to manufacture an electrochemical device, which may be, for example, a lithium secondary battery.

[0118] The present invention will be described in more detail below with reference to examples. However, the following examples are merely for the purpose of illustrating the present invention, and the scope of the present invention is not necessarily limited to these examples.

[0119] [Separator substrate manufacturing] The porous polymer substrates, which are separator substrates of Example 1 and Comparative Example 1, were prepared as follows.

[0120] Comparative Example 1 Polyethylene polymer with a molecular weight of 600,000 (g / mol) and an antioxidant were mixed in an extruder, melted at 200°C, extruded through a T-die, and cooled on a stainless steel casting roll with a surface temperature of 25°C. The cooled casting roll was installed on the upper surface of the polymer sheet, and a touch roll was installed at a corresponding position on the lower surface to perform cooling (see Figure 1). The polymer sheet passed through the cooled casting roll and was then stretched in the MD direction (stretch ratio: 7x, stretch temperature: 115°C) and the TD direction (stretch ratio: 6x, stretch temperature: 125°C) using a tenter-type sequential stretching machine installed downstream of the casting roll. The diluent was then extracted using methylene chloride. The resulting polymer sheet was then heat-set at 130°C to obtain a polymer substrate. The resulting porous polymer substrate had a thickness of 9 μm and a porosity of 45 vol%.

[0121] Example 1 A separator substrate was obtained in the same manner as in Comparative Example 1, except that a cooling casting roll was provided on the upper surface of the polymer sheet and no contact roll was provided at the corresponding position on the lower surface (see Figure 2). The resulting porous polymer substrate had a thickness of 9 μm and a porosity of 45 vol%.

[0122] [Separator manufacturing] Separators were manufactured by forming porous coating layers on both sides of the separator substrate using the porous polymer substrates of Comparative Example 1 and Example 1 prepared above as separator substrates, respectively, in the following manner.

[0123] Fabrication of porous coating layer A slurry for inorganic coating was prepared by mixing a PVDF-HFP binder (Mw: 500,000 g / mol, HFP 15 wt%) and inorganic particles in a weight ratio of 80:20 in an appropriate solvent. The slurry for inorganic coating prepared above was applied to the entire surface of the porous substrate by dip coating and dried using a humidified phase separation method to form a porous coating layer with a thickness of 3 μm on each of the upper and lower surfaces of the porous substrate prepared above. This produced a separator with an overall thickness of 15 μm.

[0124] [Manufacturing of electrode assemblies] The separators prepared above were used as separators, and negative and positive electrodes were prepared as follows and attached to one side of the separators, respectively, to manufacture electrode assemblies.

[0125] Anode manufacturing A composition for forming a negative electrode was prepared by mixing distilled water as a solvent with Si particles (Si: 100%) as a negative electrode active material, SBR as a binder polymer, and CNT as a conductive material in a weight ratio of 80:10:10.

[0126] The negative electrode composition was applied to one surface of a copper current collector and dried to prepare a negative electrode. The loading of the negative electrode was 8.5 mAh / cm. 2 It was manufactured to be.

[0127] Cathode manufacturing NMP was used as the solvent and NCMA (Li[Ni 0.86 Co 0.06 Mn 0.07 Al 0.01 ]O2, PVDF as a binder polymer, and CNT as a conductive material were mixed in a weight ratio of 97:1:2 to prepare a composition for forming a positive electrode.

[0128] The positive electrode composition was applied to one surface of an aluminum current collector and dried to prepare a positive electrode. The loading of the positive electrode was 4.5 mAh / cm2 It was manufactured to be.

[0129] Assembling the electrode assembly With the separators prepared as described above still sandwiched between them, the positive electrode was placed on one side and the negative electrode on the other side, and then the electrodes were rolled under conditions of 70°C, 9 MPa, and 1 sec, and dried to obtain an electrode assembly.

[0130] [Evaluation of physical properties] The properties of the separator substrate, separator, and electrode assembly prepared in the above order were evaluated by the following methods, and the results are shown in Table 1 below.

[0131] Table 1 below shows the results of evaluating the physical properties of the separator substrate, with both sides designated as side A and side B. When manufacturing the electrode assembly, the negative electrode was attached to side A and the positive electrode to side B, and the electrode adhesive strength with the separator was also evaluated by attaching the negative electrode to side A and the positive electrode to side B.

[0132] Measurement of the surface roughness value (Sa) of the separator substrate The surface of the porous polymer substrate was analyzed using atomic force microscopy (AFM) to obtain a height map of the surface. The roughness value (Sa) was measured by analyzing the difference in the average height of the surface over the entire area based on the average height plane. The roughness measurements were performed on both sides of the separator substrate.

[0133] Separator adhesive strength measurement The separator was sampled to a width of 15 mm and attached to a glass slide using 18 mm double-sided tape (manufactured by 3M Co.) so that the surface to be measured for adhesive strength was in contact with the glass.Then, the peel strength between the separator substrate and the porous coating layer was measured using a universal testing machine (manufactured by Instron Co.) under conditions of 180° and 300 mm / min. The adhesive strength was measured on both sides of the separator.

[0134] Measurement of electrode adhesive strength between separator and electrode The electrode and separator were sampled to a width of 25 mm, overlapped, and pressed together under conditions of 60°C, 6.5 MPa, and 1 s to prepare a sample. Then, the peel strength between the separator and electrode was measured under conditions of 180° and 300 mm / min using a universal testing machine (manufactured by Instron Corporation). The electrode adhesive strength was measured for both the separator and the positive electrode and the separator and the negative electrode.

[0135] After measuring the physical properties as described above, the ratio of adhesive strength between the two surfaces of the separator and the variation in adhesive strength between the separator and the electrode were calculated using the following formulas, and are shown in Table 1 below. [Formula 1] Adhesion strength ratio (%) = [(adhesion strength of first surface / adhesion strength of second surface) x 100] In this case, the first surface indicates a surface with a relatively high adhesive strength, and the second surface indicates a surface with a relatively low adhesive strength.

[0136] [Formula 2] Electrode adhesion variation (%) = │{1-F (x) / F (y) )}│×100 At this time, F (x) is the electrode adhesive strength between the separator and the negative electrode, and F (y) was substituted for the electrode adhesive strength between the separator and the positive electrode. [Table 1]

[0137] As can be clearly seen from Table 1 above, by using a separator substrate having different surface roughness values ​​on both sides according to one aspect of the present invention, the adhesive strength on both sides of the separator appears to be different from each other, and as a result, it has been confirmed that the variation in adhesive strength between the positive electrode and the negative electrode can be dramatically reduced. [Explanation of symbols]

[0138] 1. Extrusion section 2 Cooling section 200 T-die 201 Casting Roll 202 Touch Roll 203 Guide Roll

Claims

1. The separator substrate is a porous polymer substrate having two surfaces with different surface roughnesses.

2. The separator substrate according to claim 1 , wherein the surface roughness values ​​(Sa) of both surfaces of the porous polymer substrate are different from each other.

3. 2. The separator substrate according to claim 1, wherein the porous polymer substrate has one surface having a surface roughness value (Sa) of 50 nm or less and the other surface having a surface roughness value (Sa) of more than 50 nm.

4. The separator substrate according to claim 1 ; a porous coating layer formed on each of both surfaces of the separator substrate, the porous coating layer including inorganic particles and a binder polymer; Including, separator.

5. The separator has two surfaces with different adhesive strengths, When the surface having the relatively high adhesive strength is defined as a first surface and the surface having the relatively low adhesive strength is defined as a second surface, The separator according to claim 4, wherein the ratio of adhesive strength between the first surface and the second surface according to the following formula 1 is 150% or more: [Formula 1] Adhesion strength ratio (%) = [(adhesion strength of first surface / adhesion strength of second surface) × 100] In the above formula 1, The adhesive strength indicates the adhesive strength between the separator substrate and the porous coating layer.

6. The separator according to claim 4 , wherein the adhesive strength of each of the two surfaces of the separator is 30 gf / 15 mm or more.

7. The separator has an adhesive strength of 80 gf / 15 mm or less on one side and an adhesive strength of more than 80 gf / 15 mm on the other side, The separator according to claim 6 , wherein the adhesive strength indicates the adhesive strength between the separator substrate and the porous coating layer.

8. The separator according to any one of claims 4 to 6; a positive electrode and a negative electrode formed on both sides of the separator, respectively; An electrode assembly comprising:

9. The adhesive strengths of the two surfaces of the separator are different from each other, The electrode assembly according to claim 8 , wherein a positive electrode faces the surface having the relatively high adhesive strength, and a negative electrode faces the surface having the relatively low adhesive strength.

10. 9. The electrode assembly according to claim 8, wherein a variation in electrode adhesive strength between the separator and each of the positive electrode and the negative electrode, as determined by the following formula 2, is 10% or less: [Formula 2] Variation in electrode adhesive strength (%) = |{1-F （ｘ） / F （ｙ） )│×100 In the above formula 2, F （ｘ） is the electrode adhesive strength between the separator and the positive electrode, and F （ｙ） is the electrode adhesion strength between the separator and the negative electrode, or F （ｘ） is the electrode adhesive strength between the separator and the negative electrode, and F （ｙ） is the electrode adhesion strength between the separator and the positive electrode.

11. The electrode assembly according to claim 8 , wherein the negative electrode contains a Si-based active material as an active material.

12. An electrochemical device comprising the electrode assembly according to claim 8 housed in a case.

13. S1) extruding a polymer slurry to obtain a polymer sheet; S2) cooling the obtained polymer sheet on a casting roll; A method for producing a separator substrate, comprising: In the step S2, the polymer sheet is cooled in a state where there is no touch roll on the surface opposite to the surface facing the casting roll.

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