Separator substrate, preparation method thereof, and separator including same

Abstract

The present invention relates to a separator substrate, a separator, an electrode assembly, and an electrochemical device. The separator substrate, according to an embodiment of the present invention, comprises a polyolefin-based porous substrate which has regions with different porosities, wherein a silicone rubber is coated on the region with lower porosity.

Description

Membrane substrate, manufacturing method thereof, and membrane comprising the same

[0001] The present invention relates to a separator substrate, a method for manufacturing the same, and a separator comprising the same. Specifically, the present invention relates to a separator with improved wear and impact resistance, an electrode assembly comprising the same, and an electrochemical device.

[0002] This application claims priority to Korean Patent Application No. 2024-0004387, filed with the Korean Intellectual Property Office on January 10, 2024, the entire disclosure of which is incorporated herein by reference.

[0003] Lithium secondary batteries are manufactured through a process of inserting an electrode assembly consisting of a cathode / separator / cathode as a single unit into a battery case, then injecting and sealing the electrode assembly. Polyolefin-based porous substrates are typically used as separators for lithium secondary batteries. To address the problem of short circuits between the cathode and anode due to the thermal shrinkage behavior of the polyolefin-based porous substrate, separators have been developed that enhance the strength and heat resistance of the separator by forming a coating layer made of a mixture of inorganic particles and binder polymers on the surface of the porous substrate. Examples include the Safety Reinforced Separator (SRS) and the Ceramic Coated Separator (CCS).

[0004] These SRS or CCS particles act as spacers, allowing the inorganic particles within the coating layer to maintain the physical form of the separator. This prevents the porous substrate from shrinking when exposed to high temperatures, thereby preventing direct contact between the anode and cathode. This allows for the manufacture of electrode assemblies by bonding the anode and cathode with a separator having porous coating layers on both sides.

[0005] Meanwhile, known types of secondary battery unit cells include cylindrical, square, and pouch-shaped. In the case of a cylindrical secondary battery cell, an insulator separator is interposed between the positive and negative electrodes, and this is wound to form a jelly-roll-shaped electrode assembly, which is then inserted into a battery can to form the battery.

[0006] At this time, due to the volume expansion of the cathode caused by repeated charging and discharging of the battery, the porous coating layer of the separator is continuously scratched, ultimately damaging the separator and causing an internal short circuit, or impingement. This internal short circuit can cause the cylindrical battery cell to catch fire.

[0007] In addition, if the porous coating layer of the separator is scratched, the inorganic particles and / or binder polymers that make up the porous coating layer may drift as foreign substances within the battery, which may cause a phenomenon in which a voltage drop behavior exceeding the self-discharge rate of the battery is exhibited.

[0008] This requires the development of a separator that has improved heat resistance by providing a porous coating layer, while also having excellent friction resistance and effectively improving internal short-circuit problems.

[0009] Accordingly, the problem to be solved by the present invention is to provide a separator that solves the above-described problem and an electrode assembly and electrochemical device including the same.

[0010] Specifically, the present invention aims to provide a separator having a porous coating layer and excellent durability against friction, and an electrochemical device, such as a lithium secondary battery, having improved voltage drop behavior by applying the same.

[0011] In particular, the present invention seeks to improve damage to the coating layer of the separator due to pressure and friction applied to the separator at the center of the core when the volume of a jelly-roll-shaped electrode assembly expands due to charge and discharge when applied to a cylindrical electrochemical device.

[0012] In addition, it is intended to improve damage to the separator due to pressure applied to the separator at the center of the core of the electrode assembly due to electrode burrs that may occur during cutting of the electrode used in the jelly roll-shaped electrode assembly for manufacturing the cylindrical electrochemical device of the present invention.

[0013] Thus, according to one aspect of the present invention, it is intended to provide a membrane substrate having surface properties with improved wear resistance and impact resistance against friction and pressure, a membrane using the same, and a method for manufacturing the same.

[0014] To solve the above problem,

[0015] According to one aspect of the present invention, a membrane substrate of the following embodiments is provided.

[0016] The membrane substrate according to the first embodiment is

[0017] A membrane substrate comprising a polyolefin-based porous substrate and silicone rubber coated on at least a portion of a surface of the polyolefin-based porous substrate, wherein the porosity of one end of the polyolefin-based porous substrate is lower than that of the other end, and the silicone rubber is coated on the one end of the polyolefin-based porous substrate having lower porosity.

[0018] According to the second embodiment, in the first embodiment,

[0019] The above silicone rubber may include polydimethylsiloxane (PDMS).

[0020] According to the third embodiment, in the first embodiment or the second embodiment,

[0021] The porosity of one end portion with low porosity of the above polyolefin-based porous substrate may be 40% by volume or less.

[0022] According to the fourth embodiment, in any one of the first to third embodiments,

[0023] One end of the polyolefin-based porous substrate having low porosity may have a length of less than 15% of the total length.

[0024]

[0025] According to another aspect of the present invention, a separation membrane of the following embodiments is provided.

[0026] The separation membrane according to the fifth embodiment is

[0027] A membrane substrate according to any one of the first to fourth embodiments, and

[0028] It includes a porous coating layer formed on at least one surface of the above separation membrane substrate.

[0029] At this time, the porous coating layer includes inorganic particles and a binder.

[0030] According to the sixth embodiment, in the fifth embodiment,

[0031] The coefficient of friction of one end of the above separator may be 0.25 or more.

[0032] At this time, the above friction coefficient is assumed to be the friction coefficient of the surface on which the porous coating layer is formed.

[0033] According to the seventh embodiment, in the fifth embodiment or the sixth embodiment,

[0034] The coefficient of friction of one end of the above membrane may be 0.80 to 1.50.

[0035] According to the eighth embodiment, in any one of the fifth to seventh embodiments,

[0036] The puncture strength of one end of the above membrane may be 450 gf or more.

[0037] At this time, the above-mentioned perforation strength is assumed to be the perforation strength of the surface on which the porous coating layer is formed.

[0038] According to the ninth embodiment, in any one of the fifth to eighth embodiments,

[0039] The puncture strength of the above membrane may be 550 gf to 750 gf.

[0040]

[0041] According to another aspect of the present invention, electrode assemblies of the following embodiments are provided.

[0042] An electrode assembly according to the 10th embodiment,

[0043] A separator according to any one of the fifth to ninth embodiments, and a positive electrode and a negative electrode formed on each of both sides of the separator.

[0044] According to the 11th embodiment, in the 10th embodiment,

[0045] The above electrode assembly may have a jelly roll shape wound around a winding axis.

[0046]

[0047] According to another aspect of the present invention, electrochemical devices of the following embodiments are provided.

[0048] The electrochemical device according to the 12th embodiment,

[0049] The electrode assembly according to the 10th or 11th embodiment is housed in a case.

[0050] According to the 13th embodiment, in the 12th embodiment,

[0051] The above case may be a cylindrical case.

[0052]

[0053] According to another aspect of the present invention, a method for manufacturing a membrane substrate of the following embodiments is provided.

[0054] The method for manufacturing a membrane substrate according to the 14th embodiment is as follows:

[0055] S1) A step of obtaining a polymer sheet from a slurry containing a polyolefin resin,

[0056] S2) A step of rolling one end of the polymer sheet, and

[0057] S3) A step of coating silicone rubber on one rolled end of the polymer sheet is included.

[0058] A membrane substrate according to one embodiment of the present invention can exhibit the effect of enhancing the durability of a membrane by improving the mechanical strength of a region vulnerable to damage when applied to an electrochemical device, and thus exhibiting different mechanical strengths for each region of the membrane in consideration of the influence of external impact when applied to an electrochemical device.

[0059] In particular, due to the surface properties of the above-mentioned membrane substrate, it can exhibit the effect of improving the wear resistance against friction of the porous coating layer in the membrane and improving mechanical properties such as puncture strength.

[0060] In addition, an electrochemical device to which a separator having the above-described characteristics is applied can exhibit an effect of preventing and / or improving destruction of the separator caused by volume expansion of an electrode, for example, a cathode, and burrs of an anode due to repeated charge and discharge, and a short circuit phenomenon of the anode and cathode resulting therefrom.

[0061] In addition, by using a separator having a porous coating layer, not only can the heat resistance of the electrochemical device be improved, but also the wear resistance of the separator can be improved, thereby preventing and / or reducing the formation of foreign substances inside the electrochemical device during charging and discharging, thereby improving the voltage drop phenomenon of the electrochemical device.

[0062] Figure 1 is a schematic diagram of a membrane substrate (1) according to one embodiment of the present invention.

[0063] Figure 2 is a schematic diagram of a membrane substrate (1) according to one embodiment of the present invention.

[0064] Figure 3 is a schematic diagram of a separation membrane (5) according to one embodiment of the present invention.

[0065] Figure 4 is a schematic diagram of a laminated structure of an electrode assembly (10) according to one embodiment of the present invention.

[0066] FIG. 5 is a schematic diagram of a laminated structure of an electrode assembly (10) according to one embodiment of the present invention, in which the position where the winding axis is formed is indicated by a dotted box.

[0067] Hereinafter, the present invention will be described in detail.

[0068] In this specification, when a part is said to "include" a certain component, this does not mean that other components are excluded, but rather that other components may be included, unless otherwise specifically stated.

[0069] In this specification, the term “A and / or B” means “A or B, or both.”

[0070] Certain terminology used in the following detailed description of the invention is for convenience only and is not intended to limit the invention. Furthermore, directional words such as "up," "down," "left," "right," "front," "back," "inside," and "outside" indicate directions within the drawings to which reference is made, or indicate directions toward or away from the geometric center of the designated device, system, or its components, respectively.

[0071]

[0072] Membrane substrate and manufacturing method thereof

[0073] According to one aspect of the present invention, a membrane substrate is provided, which comprises a polyolefin-based porous substrate and silicone rubber coated on at least a portion of a surface of the polyolefin-based porous substrate.

[0074] Specifically, according to one aspect of the present invention, the polyolefin-based porous substrate is provided with a porosity different at one end and the other end.

[0075] At this time, the separation membrane according to one aspect of the present invention has a configuration in which the silicone rubber is coated on one end portion with low porosity of the polyolefin-based porous substrate.

[0076] Referring to Fig. 1, a membrane substrate (1) according to one embodiment of the present invention includes a silicone rubber (120) formed on one end of a polyolefin-based porous substrate (120) having a low porosity formed on one end. The silicone rubber may be formed on one surface of the polyolefin-based porous substrate.

[0077] In addition, referring to FIG. 2, a membrane substrate (1) according to one embodiment of the present invention may be formed with silicone rubber (120) on both surfaces of a polyolefin-based porous substrate (120) formed with low porosity on one end.

[0078] As described below, when forming silicone rubber on one end of the polyolefin-based porous substrate, when the silicone rubber slurry is applied to one surface of the porous substrate and dried, the silicone rubber slurry can be impregnated into the interior through the pores of the porous substrate, so even if the silicone rubber is applied to one surface of the porous substrate, the silicone rubber can also be present on the other surface of the porous substrate. In the present invention, the shape of the silicone rubber coated on one end of the polyolefin-based porous substrate is not particularly limited.

[0079] In one embodiment of the present invention, one end of the separator substrate having low porosity, specifically one end coated with silicone rubber, may include a winding start point of a jelly roll-shaped electrode assembly used in a cylindrical battery, as described below.

[0080] According to one aspect of the present invention, when one end of the separator substrate is coated with silicone rubber, and the start point of winding of a jelly-roll-type electrode assembly is included in the area coated with silicone rubber, the area coated with silicone rubber can be positioned at the center of the core of the electrode assembly. Accordingly, an excellent effect of preventing or alleviating damage to the separator can be exhibited despite pressure applied to the center of the core of the electrode assembly during charging / discharging of an electrochemical device and / or cutting of the electrode.

[0081] In one embodiment of the present invention, the low porosity end may refer to a region having a length of 15% or less of the total length of the membrane substrate. For example, the low porosity end may refer to a region having a length of 10% or less of the total length of the membrane substrate. That is, when one end point of the membrane substrate is defined as a 0% length point of the total length and the other end is defined as a 100% length point, the one end may refer to a region of 0% to 15%, or 0% to 10%. However, depending on the shape of the electrochemical device to which the membrane substrate is applied, the size of the one end may not be limited thereto.

[0082] According to one aspect of the present invention, by filling one end of the membrane substrate with silicone rubber, which has low porosity, the overall thickness uniformity of the membrane substrate can be maintained, which can have a beneficial effect. This can have the effect of improving the mechanical strength of one end while maintaining the overall thickness of the membrane substrate constant.

[0083] In addition, when silicone rubber is filled in one end portion of the membrane substrate having low porosity, the number of pores in the one end portion having low porosity is small, so the amount of pores filled with silicone rubber is reduced, and a shape in which silicone rubber is coated on the surface portion of the membrane substrate can be provided, which may have an advantageous effect.

[0084] In one embodiment of the present invention, a polyolefin-based porous substrate having a porosity of one end lower than that of the other end as described above may be implemented by rolling one end as described below.

[0085] Specifically, the thickness of the one end portion may be reduced by rolling, and accordingly, the porosity of the one end portion of the polyolefin-based porous substrate may be lowered.

[0086] In one embodiment of the present invention, the porosity of the membrane substrate may be measured, for example, by the following method. The width, length, and thickness of the membrane substrate are each measured to obtain the volume, and the weight is measured. The porosity is measured as a ratio of the weight when the volume occupies 100% of the membrane substrate. As another example, the porosity may be measured by measuring the diameter of pores filled by mercury at a constant pressure according to the ASTM D 4284-92 standard, and then measuring the porosity from the cumulative measurement results of the diameter of pores filled by mercury while continuously applying pressure. For the measurement using mercury, the Autopore IV9500 equipment of Micrometrics Co. may be used, but the present invention is not limited thereto.

[0087] As described above, the porosity of the membrane substrate of the present invention may be measured for each of one end and the other end.

[0088] In one embodiment of the present invention, the membrane substrate having a thinner thickness and thus a lower porosity, and thus coated with silicone rubber on at least one surface of the end, may still have a thickness of the one end thinner than the thickness of the other end, but preferably, the membrane substrate may have a uniform thickness between the one end and the other end by coating the silicone rubber on at least one surface of the end having a lower porosity. This may be to alleviate the problem of short circuiting due to breakage of the membrane substrate by maintaining the thickness of the membrane substrate constant, but the present invention is not limited thereto.

[0089] In one embodiment of the present invention, the thickness of the membrane substrate may be measured using a known method for measuring the thickness of the membrane substrate. For example, the thickness may be measured using a radiation thickness gauge such as the ASC-190 from Eurotherm Gauging System Inc. Alternatively, the thickness may be measured using a known thickness gauge, for example, a commercially available thickness gauge (Mitutoyo, VL-50S-B), but the present invention is not limited thereto.

[0090] In one embodiment of the present invention, the porosity of the other end of the polyolefin-based porous substrate with high porosity may be 40 vol% to 70 vol%, taking into account the ion permeability of the separation membrane using the same. In one embodiment of the present invention, as long as the one end of the polyolefin-based porous substrate with low porosity is lower than the porosity of the other end, the specific numerical range of the porosity is not limited.

[0091] However, considering that the porosity of the other end of the membrane substrate with high porosity is 40 vol% or more, the porosity of one end of the membrane substrate may be 40 vol% or less, specifically 35 vol% or less. In addition, considering the ion permeability of the membrane using the membrane substrate, the porosity of one end of the membrane substrate may be, for example, 25 vol% to 40 vol% or 30 vol% to 35 vol%, but the present invention is not limited thereto.

[0092] In one embodiment of the present invention, the thickness of the other end of the polyolefin-based porous substrate on which the silicone rubber is not coated may be, for example, 5 to 300 μm, specifically 5 to 100 μm, 5 to 50 μm, 5 to 20 μm, 5 to 15 μm, or 9 to 12 μm. Before the silicone rubber is coated, the thickness of the one end of the polyolefin-based porous substrate with low porosity may be provided to be smaller than the thickness of the other end as described above.

[0093] In one embodiment of the present invention, the silicone rubber collectively refers to a compound having a structure represented by the following chemical formula 1 as a repeating unit.

[0094] [Chemical Formula 1]

[0095] -[Si-O-Si]n- (n ≥ 1)

[0096] In one embodiment of the present invention, the silicone rubber may include an organo silicone compound represented by the following chemical formula 2.

[0097] [Chemical Formula 2]

[0098] R 1 3Si-[O-SiR 2 2]m-OSiR 3 3(m ≥ 0)

[0099] In chemical formula 2, the R 1 Inland R3 may be independently selected from a hydrogen group, a hydroxyl group, an aliphatic saturated hydrocarbon group having 1 to 20 carbon atoms, an aliphatic unsaturated hydrocarbon group having 1 to 20 carbon atoms, or an aromatic unsaturated hydrocarbon group having 5 to 10 carbon atoms. Specifically, the aliphatic saturated hydrocarbon group may be an alkyl group having 1 to 10 carbon atoms, and may be, for example, a methyl group, an ethyl group, a propyl group, a hexyl group, an octyl group, a decyl group, etc. The aliphatic unsaturated hydrocarbon group may be an alkenyl group having 2 to 10 carbon atoms, and may be, for example, a vinyl group, a butenyl group, etc. The aromatic unsaturated hydrocarbon group may be an aryl group having 6 to 10 carbon atoms, and may be, for example, a phenyl group, a methylphenyl group, an ethylphenyl group, etc.

[0100] In one embodiment of the present invention, the silicone rubber may include polydimethylsiloxane having a structure represented by the following chemical formula 3.

[0101] [Chemical Formula 3]

[0102] (CH3)3Si-[O-Si(CH3)2]pO-Si(CH3)3(p ≥ 0)

[0103] In one embodiment of the present invention, the silicone rubber may have excellent impact resistance as an elastomer.

[0104] In one embodiment of the present invention, the separator substrate comprises silicone rubber coated on one end of a polyolefin-based porous substrate, thereby providing a separator substrate having silicone rubber coated on the winding center of a jelly roll-type electrode assembly using the same. As a result, the durability of a cylindrical battery using the same can be improved despite repeated charge / discharge cycles and / or pressure applied due to electrode burrs.

[0105] In one embodiment of the present invention, the silicone rubber coated on at least a portion of the surface of the polyolefin-based porous substrate may have a weight average molecular weight (Mw) of, for example, 50,000 g / mol to 300,000 g / mol, 100,000 g / mol to 200,000 g / mol, or 100,000 g / mol to 150,000 g / mol.

[0106] In one embodiment of the present invention, the silicone rubber may have a weight average molecular weight of 110,000 g / mol.

[0107] In this specification, the weight average molecular weight (Mw) of the silicone rubber may be a value measured according to a known method for measuring the molecular weight of a polymer. For example, the weight average molecular weight of the silicone rubber may be a value measured using gel permeation chromatography (GPC).

[0108] The method for measuring the weight average molecular weight of silicone rubber using the above GPC method may be, for example, a known gel permeation chromatography, for example, PL GPC220 (Agilent Technologies Co.), and measured under the following conditions, but the present invention is not limited thereto.

[0109] - Column: PL Olexis (Polymer Laboratories)

[0110] - Solvent: TCB (Trichlorobenzene)

[0111] - Flow rate: 1.0 ml / min

[0112] - Sample concentration: 1.0 mg / ml

[0113] - Injection volume: 200 ㎕

[0114] - Column temperature: 160℃

[0115] - Detector: Agilent High Temperature RI detector

[0116] - Standard: Polystyrene (corrected with a cubic function)

[0117] In one embodiment of the present invention, the silicone rubber is coated on at least a portion of the surface of a polyolefin-based porous substrate, and at least a portion of the silicone rubber can be impregnated in the thickness direction of the polyolefin-based porous substrate through a plurality of pores formed on the surface of the polyolefin-based porous substrate. When the weight average molecular weight of the silicone rubber is in the above-described range, the mechanical strength of the membrane substrate can be improved by controlling the amount of the silicone rubber coated on the surface of the polyolefin-based substrate and the amount of the silicone rubber impregnated through the pores of the polyolefin-based substrate, but the present invention is not limited thereto.

[0118] In one embodiment of the present invention, the polyolefin-based porous substrate refers to a substrate having a plurality of pores formed therein as a porous ion-conducting barrier that allows ions to pass while blocking electrical contact between the cathode and the anode. The pores are structured to be interconnected to allow gas or liquid to pass from one side of the substrate to the other.

[0119] In one embodiment of the present invention, the polyolefin-based porous substrate may be a porous polymer film containing a thermoplastic resin, from the perspective of imparting a shutdown function. Here, the shutdown function refers to a function in which, when the battery temperature rises, the thermoplastic resin melts and closes the pores of the polyolefin-based porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery.

[0120] In one embodiment of the present invention, the polyolefin-based porous substrate represents a porous polyolefin-based sheet having a plurality of pores. The type of polyolefin constituting the polyolefin-based porous substrate is not particularly limited as long as it can be used as a membrane substrate.

[0121] In one embodiment of the present invention, the porous polymer substrate may be a polyethylene substrate.

[0122]

[0123] According to another aspect of the present invention, a method for manufacturing the above-described membrane substrate is provided.

[0124] The method for manufacturing the above membrane substrate is as follows:

[0125] S1) A step of obtaining a polymer sheet from a slurry containing a polyolefin resin,

[0126] S2) A step of rolling one end of the polymer sheet, and

[0127] S3) A step of coating silicone rubber on one rolled end of the polymer sheet is included.

[0128]

[0129] In one embodiment of the present invention, the step S1) may include, for example, the following detailed processes.

[0130] S1-1) Step of mixing polyolefin resin and diluent, extruding, and cooling;

[0131] S1-2) Step of stretching the cooled extrudate,

[0132] S1-3) Step of removing the diluent to obtain a porous polyolefin sheet having multiple pores.

[0133] In the above S1-1), the polyolefin resin refers to the above-described type of polyolefin porous resin.

[0134] The above diluent is a polymeric material that can be used to form pores in a porous polyolefin-based substrate, and refers to a material that can form pores by causing phase separation and removal upon cooling after being mixed with a polyolefin-based resin to form an extrudate. The diluent is not particularly limited as long as it satisfies this function. Non-limiting examples include, but are not limited to, aliphatic hydrocarbon solvents such as paraffin oil; vegetable oils such as soybean oil; or plasticizers such as dialkyl phthalate. Among these, liquid paraffin oil having excellent compatibility with the polyolefin-based resin, for example, paraffin oil having a kinematic viscosity of 20 to 200 cSt at 40°C, can be suitably used. The diluent can be used alone or in the form of a mixture of two or more. The content of the diluent is not particularly limited, and may range from 15.0 to 95.0 wt% or from 20.0 to 90.0 wt%, based on a total of 100 wt% of the polyethylene resin and the diluent.

[0135] Next, the composition is extruded, and the die and extrusion conditions can be selected according to those commonly used in the art. For example, the extruder can be a twin-screw extruder, and the temperature of the extrusion process can be approximately 160 to 240°C.

[0136] Next, the extrudate may be cooled to form an extruded sheet. At this time, the difference between the melting temperature and the cooling temperature of the extrudate may be 60°C or less, and the cooling may be performed slowly at a cooling rate of about 100 to about 250°C / min. The cooling rate may be a value obtained by dividing the difference between the melting temperature of the extrudate and the cooling roll temperature by the time it takes to pass through the air gap, as shown in the following equation.

[0137] Cooling rate = (melt temperature of extrudate - cooling roll temperature) / (air gap passage time)

[0138] In the above formula, the air gap represents the area (section) through which the molten sheet passes between the die lip and the cooling roll.

[0139] Next, S1-2) the extruded material is stretched.

[0140] The extruded sheet obtained above can be biaxially stretched in the machine direction (MD) and the transverse direction (TD), which correspond to the running direction of the manufacturing process. For example, the machine direction stretching temperature can be 120 to 135°C, and the transverse direction stretching temperature can be 105 to 125°C. In the step of stretching the extruded sheet, a conventional biaxial stretching method can be used.

[0141] For example, after stretching the extruded sheet about 3 to about 9 times in the machine direction, it may be stretched about 3 to about 9 times in the transverse machine direction (TD) using a sequential stretching method, such as a tenter method, for reasons such as increased equipment costs.

[0142] Next, S1-3) the diluent is removed to obtain a porous polyolefin sheet having multiple pores.

[0143] In the present invention, the solvent that can be used to remove the diluent is not particularly limited, and any solvent that can extract the diluent used in the extrusion can be used, but preferably, methyl ethyl ketone, methylene chloride, hexane, etc., which have high extraction efficiency and fast drying, are suitable. As the extraction method, all general solvent extraction methods such as immersion method, solvent spray method, and ultrasonic method can be used individually or in combination. The amount of diluent remaining during extraction should be 1 wt% or less. If the remaining diluent exceeds 1 wt%, the physical properties deteriorate and the permeability of the membrane decreases. Preferably, the solvent may be methylene chloride.

[0144]

[0145] Next, a step of rolling one end of the polymer sheet obtained above is performed (S2).

[0146] In one embodiment of the present invention, the rolled region may be a region coated with silicone rubber, for example, a region having a length within 15% of one end of the entire length of the polymer sheet. For example, rolling may be performed to a region having a length within 10% of one end of the entire length of the polymer sheet.

[0147] In one embodiment of the present invention, the rolling may be performed without particular limitation using any rolling method applicable to the electrode manufacturing process. For example, the rolling may be performed using a pair of rolling rolls or a plate press.

[0148] In one embodiment of the present invention, the rolling may be performed at, for example, a temperature of 20°C to 30°C or 23°C to 25°C to prevent heat-induced damage to the polymer sheet.

[0149] In one embodiment of the present invention, the porosity of one end of the polymer sheet can be reduced through the rolling.

[0150] In one embodiment of the present invention, the rolling may be performed with a compression ratio of 20% to 40%.

[0151] The above compression ratio represents the ratio of the porosity of the polymer sheet before and after rolling and can be measured as follows.

[0152] Compression ratio (%) = [1-(porosity after rolling / porosity before rolling)] X 100

[0153] In one embodiment of the present invention, rolling can be performed so that the porosity of one end of the polymer sheet is 45 vol% before rolling and 34 vol% after rolling, and at this time, the compression ratio according to the above formula is 24%.

[0154]

[0155] Next, silicone rubber is coated on one end of the polymer sheet whose porosity has been reduced through the above rolling.

[0156] In one embodiment of the present invention, before coating the silicone rubber, a step S4) of preparing a silicone rubber coating liquid may be further included.

[0157] In one embodiment of the present invention, the step of preparing the silicone rubber coating liquid may include a step of dispersing the silicone rubber in a dispersion medium, and non-limiting examples of the dispersion medium include one or a mixture of two or more selected from the group consisting of chloroform, carbon tetrachloride, benzene, o-dichlorobenzene, toluene, xylene, pentane, mesitylene, cyclohexane, hexane, heptane diethyl ether, tetrachloroethylene acetonitrile, dimethyl sulfoxide, dimethylformamide, and trichloroethylene. As described above, the silicone rubber may be an organosilicone compound, and in this case, taking into account the swelling of the organosilicone compound, it may be preferable to use n-hexane having a low boiling point as the dispersion medium.

[0158] The step of preparing the above silicone rubber coating liquid may be performed before the step of obtaining the polymer sheet S1), or before the step of rolling one end of the polymer sheet S2), or before the step of coating S3), and the order is not particularly limited as long as it is performed before the step of coating S3).

[0159] In one embodiment of the present invention, the method for coating the silicone rubber is not particularly limited and can be used as long as it is a coating method used in the art. Non-limiting examples include one or a combination of two or more methods selected from the group consisting of spray coating, dip coating, slot coating, die coating, roll coating, gravure coating, and comma coating. A coating can be applied to one end of a porous polyolefin-based substrate having low porosity by being rolled using a conventional method used in the art.

[0160]

[0161] According to one embodiment of the present invention, after coating the silicone rubber, a heat fixing step S5) may be further included.

[0162] The above heat-setting step is a post-processing step of the obtained membrane substrate. It is a step of applying heat to the polyolefin substrate to prevent shrinkage of the polyolefin substrate and then forcibly fixing it so that it does not shrink, thereby removing any residual stress. This can be performed using a method commonly performed in the art, but it may be preferable to perform this under conditions where the silicone rubber coated on one end of the polyolefin substrate is not lost.

[0163]

[0164] membrane

[0165] According to another aspect of the present invention, a separator is provided, which comprises a porous polymer substrate as a separator substrate and a porous coating layer formed on at least one surface of the separator substrate, and which includes inorganic particles and a binder.

[0166] At this time, when the porous coating layer is formed on only one side of the membrane substrate, it may be preferable to form the porous coating layer on the side coated with silicone rubber. If silicone rubber is coated on both sides of the membrane substrate, the side on which the porous coating layer is formed is not particularly limited.

[0167] Referring to FIG. 3, a separator (5) according to one embodiment of the present invention may include a porous coating layer (520) on each side of a separator substrate (510) in which silicone rubber is coated on both sides of one end of a polyolefin-based porous substrate formed with low porosity. However, the side on which the porous coating layer of the separator of the present invention is formed is not particularly limited.

[0168] The porous coating layer comprises a large amount of inorganic particles and a binder to bind them, to enhance the safety of the separator. The inorganic particles can enhance the heat resistance of the separator, and the binder can provide adhesiveness to the surface of the separator.

[0169] In one embodiment of the present invention, the separator may include a porous coating layer on one end portion coated with the silicone rubber, and at this time, the one end portion of the separator may be characterized in that the friction coefficient of 0.25 or more is. In the present specification, the 'friction coefficient' refers to the coefficient of friction when the porous coating layer is detached due to destruction or damage caused by the frictional force applied to the separator, thereby exposing the separator substrate to the surface. When the silicone rubber is coated on one end portion of the separator substrate and the porous coating layer is formed on the surface, the one end portion of the separator substrate becomes harder due to the coating of the silicone rubber. Accordingly, the force required for detaching the separator substrate and the porous coating layer due to friction increases, which may exhibit the advantage of increasing the friction coefficient.

[0170] In one embodiment of the present invention, the friction coefficient of the separator on the other end where the silicone rubber is not coated may be less than 0.25, while the friction coefficient of the separator on the one end where the silicone rubber is coated may be greater than 0.25.

[0171] According to one embodiment of the present invention, the friction coefficient of one end of the separator may be 0.25 or greater. Specifically, the friction coefficient of one end of the separator may be 0.5 to 1.5, 0.50 to 1.50, 0.50 to 1.0, or 0.80 to 1.50.

[0172] The friction coefficient of the above-mentioned separator can be measured, for example, using a known friction and wear test device. Specifically, the friction coefficient of the above-mentioned separator can be measured, for example, by measuring the friction coefficient when the porous coating layer is detached when applying repeated friction 5 times with a 5g / dia tip using Heidon's friction and wear device.

[0173] In addition, in one embodiment of the present invention, the separator may exhibit impact resistance characteristics due to the silicone rubber at one end coated with the silicone rubber. Accordingly, the pressure at which the one end coated with the silicone rubber begins to break due to external pressure may be greater than the pressure at which the other end not coated with the silicone rubber begins to break due to external pressure. For example, the puncture strength of the other end of the separator may exhibit less than 450 gf, while the puncture strength of one end of the separator may exhibit 450 gf or more.

[0174] In one embodiment of the present invention, the separator may be characterized in that one end portion coated with silicone rubber has a puncture strength of 450 gf or more. In the present specification, the 'puncture strength' refers to the magnitude of the resistance of the separator to the vertical force when the vertical force is applied to the separator.

[0175] According to one embodiment of the present invention, the puncture strength of one end of the separation membrane may be 450 gf or more. Specifically, it may be 450 gf to 750 gf, 450 gf to 700 gf, 450 gf to 650 gf, 500 gf to 750 gf, 500 gf to 650 gf, 500 gf to 600 gf, 550 gf to 750 gf, 550 gf to 700 gf, 600 gf to 700 gf, or 600 gf to 650 gf.

[0176] The puncture strength of the above-mentioned separator can be measured, for example, by a known method for measuring puncture strength. Specifically, the puncture strength of the above-mentioned separator can be measured, for example, by measuring the force required to penetrate the separator when a force is applied under the conditions of a 1 mm tip and 120 mm / min using Instron's UTM equipment.

[0177] Hereinafter, the composition of the porous coating layer will be exemplarily described. However, the composition of the porous coating layer is not limited thereto.

[0178] In one embodiment of the present invention, the porous coating layer may include inorganic particles and a binder, such that the inorganic particles have all or at least a portion of their surfaces coated with a binder polymer. In this case, the inorganic particles are surface-bonded and / or point-bonded via the binder polymer.

[0179] For example, the inorganic particles and binder in the porous coating layer may be included in a weight ratio of 95:5 to 50:50. The porous coating layer has a plurality of micropores therein, and these micropores are interconnected, and has the structural characteristics of a porous layer that allows gas or liquid to pass from one side to the other.

[0180] In one embodiment of the present invention, the porous coating layer may have a porous structure derived from pores formed by the interstitial volume between inorganic particles. The pore size and porosity (pore volume ratio) can be controlled depending on the particle size and size distribution. Through this structure, the resistance to metallic foreign substances present in the electrode is increased, and at the same time, the shrinkage of the porous polymer substrate is suppressed, thereby enhancing the safety of the electrochemical device.

[0181] In one embodiment of the present invention, the porous coating layer includes a plurality of nodes including the inorganic particles and a binder covering at least a portion of the surface of the inorganic particles; and one or more filaments formed in a thread shape from the binder of the nodes, the filaments having a node connecting portion extending from the nodes and connecting other nodes; and the node connecting portion may have a structure in which a plurality of filaments derived from the binder intersect with each other to form a three-dimensional network structure.

[0182] In one embodiment of the present invention, as described above, the porous coating layer may be formed through a safety reinforced separator (SRS) manufacturing method, a ceramic coated separator (CCS) manufacturing method, or another known manufacturing method, but is not limited thereto.

[0183] In one embodiment of the present invention, the porous coating layer may be formed by a CCS (Ceramic Coated Separator) manufacturing method.

[0184] In one embodiment of the present invention, the inorganic particles can be used without particular limitation as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li / Li+). 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.

[0185] In one embodiment of the present invention, the average particle diameter (D) of the inorganic particles 50 ) may be, for example, 100 nm or more. Specifically, the average particle diameter (D) of the inorganic particles 50 ) may be 100 nm to 1 μm, or 100 nm to 500 nm. When the average particle diameter of the inorganic particles is within the above-described range, it may exhibit a beneficial effect in terms of suppressing an increase in resistance of the separation membrane, but the present invention is not limited thereto.

[0186] The particle size of the above inorganic particles can be measured by a known particle size measuring method, for example, using a particle size analyzer (PSA, Particle Size Analyzer) from Melbourne Co. In addition, the average particle size (D 50 ) refers to the particle size at the 50% point of the cumulative distribution of the number of particles according to particle size, and may be measured using a known laser diffraction method. At this time, the laser diffraction particle size measuring device may be, for example, Microtrac S3500 from Microtrac Corporation.

[0187] In one embodiment of the present invention, the binder 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 a monomer copolymerizable with vinylidene fluoride, and a mixture thereof. In one embodiment of the present invention, the monomer may include, for example, a fluorinated monomer and / or a chlorinated monomer. Non-limiting examples of the fluorinated monomer include vinyl fluoride; trifluoroethylene (TrFE); chlorofluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); Perfluoro(alkylvinyl) ethers such as perfluoro(methylvinyl) ether (PMVE), perfluoro(ethylvinyl) ether (PEVE), and perfluoro(propylvinyl) ether (PPVE); perfluoro(1,3-dioxole); and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), and more than one of these may be included.

[0188] 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-described ratio range relative to the total thickness of the separator, but may be, for example, 0.5 to 50 μm, specifically 0.5 to 10 μm, 0.5 to 5 μm, or 1.5 to 3 μm.

[0189]

[0190] electrode assembly

[0191] According to another aspect of the present invention, an electrode assembly is provided, which includes the above-described separator and an anode and a cathode formed on each side of the separator.

[0192] As described above, the separator according to one aspect of the present invention has improved heat resistance by including a porous coating layer, excellent wear resistance of the porous coating layer, and improved impact resistance due to the superior mechanical properties of the separator substrate. An electrode assembly using the same is characterized in that the voltage drop phenomenon is prevented or delayed, thereby effectively improving the low voltage problem caused by the destruction of the separator.

[0193] Referring to FIG. 4, an electrode assembly (10) according to one embodiment of the present invention may include a structure in which a cathode (1010) / separator (5) / anode (1020) / separator (5) / cathode (1010) are stacked in that order.

[0194] Referring to Fig. 5, when the electrode assembly (10) is wound around a winding axis and is provided in a jelly roll shape, it is preferable to wind the electrode assembly with the location of the area where the silicone rubber is coated in the separator substrate in the sequentially laminated body as the winding axis (indicated by a red dotted box).

[0195] In one embodiment of the present invention, the electrode assembly may exhibit a characteristic in that no voltage drop phenomenon occurs or the degree of the voltage drop is very small even after 200 cycles of charge and discharge repetition.

[0196] In one embodiment of the present invention, when a separator using the above-described separator substrate is applied, the wear resistance of the separator is excellent, and thus an electrochemical device having excellent battery safety and lifespan characteristics can be provided.

[0197] Hereinafter, the configuration of the electrode is exemplarily described. However, the present invention is not limited thereto.

[0198] In one embodiment of the present invention, the positive electrode and the negative electrode may each be a current collector coated with an electrode active material, and their size and shape are not particularly limited.

[0199] In one embodiment of the present invention, the positive electrode active material may include, for example, a lithium transition metal oxide; a lithium metal iron phosphate; a lithium nickel-manganese-cobalt oxide; an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more thereof, but is not limited thereto. Specifically, the positive electrode active material may include, for example, a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a compound having the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); chemical formula LiMn 2-x M xLithium manganese composite oxides represented by O2 (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (wherein M = Fe, Co, Ni, Cu or Zn); lithium metal phosphate LiMPO4 (wherein 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); Lithium nickel-manganese-cobalt oxide partially substituted with aluminum a [Ni b Co c Mn d Al e ] 1-f M1 f O2 (M1 is at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and 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); 리튬 니켈-망간-코발트 산화물에 일부가 다른 전이금속으로 치환된 산화물 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., but are not limited thereto.

[0200] 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, meso-carbon microbeads, mesophase pitches, petroleum or coal tar pitch derived cokes, silicon (Si)-based compounds (M-SiOx (M=Li, Mg, Ca, Al or Ti, 0≤x<2)) or a mixture of two or more thereof, but is not limited thereto.

[0201] In one embodiment of the present invention, the electrode assembly may be a jelly roll type electrode assembly having a structure in which a first electrode plate and a second electrode plate having a sheet shape and a separator interposed therebetween are wound in one direction. In this case, the separator is the separator described above, and the first electrode plate and the second electrode plate may be a positive electrode plate and a negative electrode plate, respectively.

[0202] As described above, the winding starting point is included in the area of ​​one end of the silicone rubber coated separator substrate.

[0203]

[0204] electrochemical devices

[0205] According to another aspect of the present invention, an electrochemical device can be provided in which the above-described electrode assembly is housed in a case.

[0206] In one embodiment of the present invention, the electrochemical device may be, for example, a primary battery, a secondary battery, a supercapacitor, an electric double layer capacitor, etc. The secondary battery may be, more specifically, a lithium ion secondary battery.

[0207] In one embodiment of the present invention, the case may adopt a conventional battery case, and there are no particular limitations on the external shape depending on the intended use of the battery. For example, the case may be cylindrical, square, pouch-shaped, or coin-shaped, such as using a can.

[0208] In one embodiment of the present invention, the case may be a cylindrical case, and the electrochemical device may be a cylindrical battery.

[0209] In one embodiment of the present invention, the cylindrical battery comprises: a jelly-roll type electrode assembly having a structure in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive and negative electrode plates are wound in one direction; a battery can in which the electrode assembly is accommodated; and a sealing body for sealing an open end of the battery can, wherein the separator is the separator described above.

[0210] In one embodiment of the present invention, the cylindrical battery may be a large cylindrical battery cell having a form factor ratio (defined as the ratio of the diameter (Φ) to the height (H) of the cylindrical battery divided by the height) of 0.4 or more.

[0211] In one embodiment of the present invention, the cylindrical battery may be, for example, a 46110 cell (diameter 46 mm, height 110 mm, form factor ratio 0.418), a 48750 cell (diameter 48 mm, height 75 mm, form factor ratio 0.640), a 48110 cell (diameter 48 mm, height 110 mm, form factor ratio 0.418), a 48800 cell (diameter 48 mm, height 80 mm, form factor ratio 0.600), or a 46800 cell (diameter 46 mm, height 80 mm, form factor ratio 0.575). In the numerical value representing the form factor, the first two numbers represent the diameter of the cell, the next two numbers represent the height of the cell, and the last number O represents that the cross-section of the cell is circular.

[0212] Once the electrode assembly as described above is completed, it can be housed and sealed in a case in a conventional manner to manufacture an electrochemical device. At this time, the electrochemical device can be, for example, a lithium secondary battery.

[0213]

[0214] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0215]

[0216] [Manufacture of membrane substrate]

[0217] A porous polymer substrate was manufactured by the following method.

[0218]

[0219] Comparative Example 1

[0220] Polyethylene polymer with a molecular weight of 600,000 (g / mol) and an antioxidant were mixed in an extruder and extruded at a temperature of 200°C. After forming into a sheet shape through a T-die and a cooling casting roll, a porous polymer substrate was obtained by biaxially stretching in a tender-type sequential stretching machine with machine direction (MD) and transverse direction stretching.

[0221] The thickness of the obtained porous polymer substrate was 10 μm and the porosity was 45 vol%. It was cut into a size of 210 mm X 297 mm.

[0222]

[0223] Example 1

[0224] First, poly(dimethylsiloxane) (Sigma-aldrich, MW 110,000 g / mol) was dissolved in n-hexane to prepare a 3 wt% polydimethylsiloxane dispersion.

[0225] Next, a 20 mm long region from one end of the machine direction (MD) of the porous polymer substrate of Comparative Example 1 prepared above was rolled using a rolling roller. The porosity of the rolled region was rolled to be 34 vol% (compression ratio 24%).

[0226] Thereafter, the polydimethylsiloxane dispersion prepared above was applied to the rolled area and dried to obtain a membrane substrate having polydimethylsiloxane coated on both ends of the porous polymer substrate.

[0227] The polydimethylsiloxane was coated so that the thickness of the above membrane substrate was constant from one end to the other end.

[0228]

[0229] [Manufacturing of membranes]

[0230] Using Comparative Example 1 and Example 1 manufactured above as a membrane substrate, a membrane was manufactured by forming a porous coating layer on both sides of the membrane substrate using the following method.

[0231]

[0232] Manufacturing of porous coating layers

[0233] A coating slurry was prepared by mixing PAA (MW 350,000 g / mol) binder and inorganic particles in a weight ratio of 5:95 in an aqueous solvent. The inorganic coating slurry prepared above was applied to the entire surface of the porous substrate by a bar coating method and dried to form a porous coating layer with a thickness of 1.5 μm on each of the upper and lower surfaces of the porous substrate prepared above.

[0234] In this way, a separation membrane with a total thickness of 13 ㎛ was manufactured.

[0235]

[0236] [Manufacturing of electrode assembly]

[0237] Each of the above-prepared separators was used as a separator, and a cathode and an anode were prepared as follows and attached to one side of the separator to manufacture an electrode assembly.

[0238]

[0239] Manufacturing of cathode

[0240] A composition for forming a negative electrode was prepared by mixing an active material (Graphite), a binder polymer (SBR), and a conductive material (Super P) in distilled water at a weight ratio of 95:0.5:4.5.

[0241] The negative electrode was prepared by applying and drying the above negative electrode forming composition on one side of a copper current collector. The loading amount of the negative electrode was 5.3 mAh / cm 2 It was manufactured to be.

[0242]

[0243] Manufacturing of anodes

[0244] A composition for forming a positive electrode was prepared by mixing an active material (NCMA), a binder polymer (PVDF), and a conductive material (CNT) in a solvent (NMP) at a weight ratio of 97:1:2.

[0245] The anode was prepared by applying and drying the composition for forming the anode on one side of an aluminum current collector. The loading amount of the anode was 4.949 mAh / cm 2 It was manufactured to be.

[0246]

[0247] Assembly of the electrode assembly

[0248] After the positive electrode / separator / cathode / separator prepared above were laminated in that order, they were wound around the core to manufacture a jelly roll-shaped electrode assembly.

[0249]

[0250] [Physical property evaluation]

[0251] The properties of the membrane manufactured above were evaluated using the following method, and the results are shown in Table 1 below.

[0252]

[0253] Measurement of friction coefficient of separator

[0254] Using Heidon's friction and wear equipment, friction was applied to the above membrane 5 times with a 5g / Dia tip, and the coefficient of friction was measured when the porous coating layer was detached.

[0255] At this time, the area where the coefficient of friction was measured was within the area coated with polydimethylsiloxane in Example 1 and the area corresponding to the area in Comparative Example 1 (i.e., an area 20 mm long from one end based on the machine direction).

[0256]

[0257] Measurement of puncture strength of membrane

[0258] The force required to penetrate the membrane was measured using Instron's UTM equipment when a force was applied under the conditions of a 1 mm tip and 120 mm / min.

[0259] At this time, the area where the puncture strength was measured was within the area coated with polydimethylsiloxane in Example 1 and the area corresponding to the area in Comparative Example 1 (i.e., an area 20 mm long from one end based on the machine direction).

[0260]

[0261] Friction coefficient puncture strength (gf) Comparative example 10.22413 Example 10.81631

[0262] As confirmed in Table 1 above, it was confirmed that the separator according to one embodiment of the present invention has excellent adhesive strength between the coating layer and the separator substrate, and not only does the friction resistance of the coating layer improve, but also the impact resistance is improved.

[0263] Through this, it was confirmed that a cylindrical battery using a separator substrate and an electrode assembly wound with the PDMS-coated region of the separator as the winding axis according to one embodiment of the present invention can alleviate damage to the separator due to burr generation at the upper end of the positive electrode where cutting occurs, and can drastically reduce the possibility of an internal short circuit occurring.

[0264] [Explanation of symbols]

[0265] 1: Membrane substrate

[0266] 110: Polyolefin porous substrate

[0267] 120: Silicone rubber

[0268] 5: Membrane

[0269] 510: Membrane substrate

[0270] 520: Porous coating layer

[0271] 10: Electrode assembly

[0272] 1010: Cathode

[0273] 1020: Bipolar

Claims

1. A membrane substrate comprising a polyolefin-based porous substrate and silicone rubber coated on at least a portion of the surface of the polyolefin-based porous substrate, The porosity of one end of the above polyolefin-based porous substrate is lower than the porosity of the other end. A membrane substrate, wherein the above silicone rubber is coated on one end having low porosity of the above polyolefin-based porous substrate.

2. In claim 1, The above silicone rubber is a membrane substrate including polydimethylsiloxane (PDMS).

3. In claim 1, A membrane substrate, wherein the porosity of one end of the polyolefin-based porous substrate with low porosity is 40% by volume or less.

4. In claim 1, A membrane substrate, wherein one end of the polyolefin-based porous substrate having a low porosity has a length of less than 15% of the total length.

5. A membrane substrate according to any one of claims 1 to 4, and Comprising a porous coating layer formed on at least one surface of the above membrane substrate, A separator, wherein the porous coating layer comprises inorganic particles and a binder.

6. In claim 5, The friction coefficient of one end of the above membrane is 0.25 or more, The above friction coefficient is the friction coefficient of the surface on which the porous coating layer is formed.

7. In claim 6, A separator having a friction coefficient of one end of the separator of 0.80 to 1.

50.

8. In claim 5, The puncture strength of one end of the above membrane is 450 gf or more, The above puncture strength is the puncture strength of the surface on which the porous coating layer is formed, a separator.

9. In claim 8, A membrane having a puncture strength of 550 gf to 750 gf.

10. A separation membrane according to claim 5, and An electrode assembly including a positive electrode and a negative electrode formed on each side of the separator.

11. In claim 10, The above electrode assembly is an electrode assembly having a jelly roll shape wound around a winding axis.

12. An electrochemical device, wherein the electrode assembly according to claim 10 is housed in a case.

13. In claim 12, The above case is an electrochemical device having a cylindrical case. 14.S1) A step of obtaining a polymer sheet from a slurry containing a polyolefin resin, S2) a step of rolling one end of the polymer sheet, and S3) A method for manufacturing a membrane substrate, comprising the step of coating silicone rubber on one rolled end of the polymer sheet.

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