Separator substrate, method for manufacturing same, and separator comprising same

Abstract

The present invention relates to a separator substrate, a separator, an electrode assembly, and an electrochemical device. According to one embodiment of the present invention, the separator substrate has a surface roughness value (Sa) within a predetermined range. Accordingly, the adhesive strength of a separator using the separator substrate is well maintained, and the resistance characteristics of the separator are improved by reducing the amount of slurry impregnated during the formation of a porous coating layer.

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 adhesive strength and electrical resistance characteristics, an electrode assembly comprising the same, and electrochemical testing.

[0002] This application claims priority to Korean Patent Application No. 2023-0095298, filed with the Korean Intellectual Property Office on July 21, 2023, 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] However, the slurry solution used to form the porous coating layer described above has the problem of increasing resistance due to partial impregnation of the porous polymer substrate. Recently, demand for batteries with fast charging and high output characteristics has been increasing, leading to ongoing research into reducing battery resistance.

[0006] 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.

[0007] Specifically, the present invention aims to provide a separator substrate for lowering the resistance of a separator, which is one of the components of a battery, in order to lower the resistance of an electrochemical device, for example, a lithium secondary battery, a method for manufacturing the same, a separator using the same, and an electrochemical device including the same.

[0008] In particular, the present invention aims to provide a membrane substrate with improved surface properties and a method for manufacturing the same, which can reduce the increase in resistance of a membrane by reducing the degree of impregnation of a slurry for forming a coating layer when forming a porous coating layer on a membrane substrate.

[0009] To solve the above problem,

[0010] According to one aspect of the present invention, a membrane substrate of the following embodiments is provided.

[0011] The membrane substrate according to the first embodiment is

[0012] A porous polymer substrate having a roughness value (Sa) of at least one surface of 30 nm to 80 nm.

[0013] According to the second embodiment, in the first embodiment,

[0014] The surface roughness value (Sa) of both sides of the above porous polymer substrate may be 30 nm to 70 nm.

[0015]

[0016] According to another aspect of the present invention, a separation membrane of the following embodiments is provided.

[0017] The separation membrane according to the third embodiment is

[0018] A membrane substrate according to the first embodiment or the second embodiment, and

[0019] A porous coating layer formed on at least one surface having a surface roughness value (Sa) of 30 nm to 80 nm, and including inorganic particles and a binder polymer;

[0020] According to the fourth embodiment, in the third embodiment,

[0021] The adhesive strength between the above-mentioned separator substrate and the above-mentioned porous coating layer may be 30 gf / 15 mm or more.

[0022] According to the fifth embodiment, in the third embodiment or the fourth embodiment,

[0023] The adhesive strength between the above-mentioned separator substrate and the above-mentioned porous coating layer may be 30 gf / 15 mm to 140 gf / 15 mm.

[0024] According to the sixth embodiment, in any one of the third to fifth embodiments,

[0025] The electrical resistance of the above separator may be 1Ω or less.

[0026] According to the seventh embodiment, in any one of the third to sixth embodiments,

[0027] The electrical resistance of the above separator may be 0.9 Ω or less.

[0028] According to the eighth embodiment, in any one of the third to seventh embodiments,

[0029] The average particle diameter (D) of the above inorganic particles 50 ) can be greater than 100 nm.

[0030]

[0031] According to another aspect of the present invention, electrode assemblies of the following embodiments are provided.

[0032] An electrode assembly according to the ninth embodiment,

[0033] A separation membrane according to any one of the third to eighth embodiments,

[0034] It includes a positive electrode and a negative electrode formed on each side of the above separator.

[0035] According to the tenth embodiment, in the ninth embodiment,

[0036] The resistance of the above electrode assembly may be 1Ω or less.

[0037] According to the eleventh embodiment, in the ninth or tenth embodiment,

[0038] The resistance of the above electrode assembly may be 0.9 Ω or less.

[0039]

[0040] According to another aspect of the present invention, electrochemical devices of the following embodiments are provided.

[0041] The electrochemical device according to the 12th embodiment,

[0042] An electrode assembly according to any one of the 9th to 11th embodiments is housed in a case.

[0043]

[0044] According to another aspect of the present invention, a method for manufacturing a membrane substrate of the following embodiments is provided.

[0045] The method for manufacturing a membrane substrate according to the 13th embodiment is as follows:

[0046] S1) A step of extruding a polymer slurry to obtain a polymer sheet; and

[0047] S2) A method for manufacturing a membrane substrate, comprising a step of opening and fixing the obtained polymer sheet;

[0048] In the above step S2, heat fixation is performed at a temperature of 119°C to 132°C.

[0049] A membrane substrate according to one embodiment of the present invention can have the effect of improving the degree of impregnation of a slurry for forming a porous coating layer on its surface by improving the surface roughness value (Sa).

[0050] Accordingly, a separator using this can exhibit the advantage of improved adhesive strength and resistance characteristics compared to a conventional separator formed with a porous coating layer to provide heat resistance and adhesiveness.

[0051] Due to this, an electrochemical device using the above-mentioned separator can exhibit the advantages of excellent high-output characteristics due to low electrical resistance as well as heat resistance.

[0052] Hereinafter, the present invention will be described in detail.

[0053] 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.

[0054] In this specification, the term “A and / or B” means “A or B, or both.”

[0055] 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.

[0056] According to one aspect of the present invention, a membrane substrate is provided as a porous polymer substrate, wherein at least one surface has a roughness value (Sa) of 30 nm to 160 nm.

[0057]

[0058] Membrane substrate and manufacturing method thereof

[0059] According to one aspect of the present invention, a membrane substrate is provided as a porous polymer substrate, wherein at least one surface has a roughness value (Sa) of 30 nm to 80 nm.

[0060] To explain this, one feature of a method for manufacturing a membrane substrate according to one embodiment of the present invention will first be described.

[0061] A method for manufacturing a membrane substrate according to one aspect of the present invention is as follows:

[0062] S1) A step of extruding a polymer slurry to obtain a polymer sheet; and

[0063] S2) A step of opening and fixing the obtained polymer sheet;

[0064] At this time, according to one aspect of the present invention, the heat fixation in step S2 is characterized in that it is performed at a temperature of 119°C to 132°C.

[0065] In one embodiment of the present invention, the heat fixation may be performed to forcibly hold the polymer sheet and remove residual stress within the sheet, but the purpose of the present invention is not limited thereto.

[0066] Conventionally, when manufacturing a porous polymer substrate as a membrane substrate, a polymer slurry is extruded to obtain a polymer sheet, and the obtained polymer sheet is heat-set at a high temperature. The inventor of the present invention discovered that when the polymer sheet is heat-set, crystallization of the surface of the polymer sheet progresses, and thus the surface characteristics may vary, and by performing the heat-setting temperature within a specific range, a membrane substrate having a surface roughness value (Sa) of 30 nm to 80 nm was obtained depending on the surface crystallization of the membrane substrate.

[0067] In one embodiment of the present invention, the heat setting in step S2 is performed at a temperature of 119°C to 132°C, and specifically, can be performed at a temperature of 120°C to 131°C or 121°C to 130°C. When the heat setting temperature is in the above-described range, the surface roughness value (Sa) can be implemented as 30 nm to 80 nm. In addition, if the temperature is too high, the surface roughness of the separator substrate may increase, which may cause an increase in the resistance of the separator, and if the temperature is too low, the surface roughness of the separator substrate may be low, which may cause a problem of poor adhesive strength between the separator substrate and the porous coating layer, but the present invention is not limited thereto.

[0068] In one embodiment of the present invention, heat may be applied while uniaxially stretching in the MD (machine direction) or TD (transverse direction) direction during the heat fixation, or heat may be applied while biaxially stretching in the MD and TD directions, but is not limited thereto.

[0069] In this specification, the 'machine direction' refers to a direction parallel to the running direction of the [extrusion->molding->stretching...] process in the manufacturing process of the membrane substrate. The machine direction can be confirmed through the fiber orientation direction of the polymer of the membrane substrate, and the direction parallel to the fiber orientation direction is the machine direction. Accordingly, the 'transverse direction' refers to a direction orthogonal to the machine direction. The transverse direction can also be confirmed as a direction orthogonal to the fiber orientation direction of the polymer of the membrane substrate.

[0070] According to one embodiment of the present invention, the method for manufacturing the membrane substrate may further include, after the extrusion in step S1), the step S1-2) of forming the extrudate into a sheet shape, the step S1-3) of stretching the formed sheet, and the step S1-4) of extracting a diluent from the stretched sheet. In this case, step S2) may be performed to heat-fix the sheet from which the diluent has been extracted.

[0071] First, the extrusion of the above step S1 will be described in detail.

[0072] In one embodiment of the present invention, step S1) may be a step of melting and extruding a polymer resin as a raw material for a membrane substrate and processing it to obtain a porous polymer sheet.

[0073] In one embodiment of the present invention, the polymer resin may be used without particular limitation as long as it is used as a raw material for manufacturing a membrane substrate. The polymer resin may include a resin such as polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, or a mixture of two or more thereof as a raw material for manufacturing a membrane substrate. The polyolefin resin is a polymerized olefin, and refers to a resin polymerized using an olefin generally used in a membrane substrate as a monomer. For example, the polyolefin resin may be a homopolymer of a monomer selected from polyethylene; polypropylene; polybutylene; polypentene; polyhexene; polyoctene; ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; A copolymer of two or more of these; or a mixture thereof, but is not limited thereto.

[0074] In one embodiment of the present invention, the porous polymer substrate may be a polyolefin substrate.

[0075] In one embodiment of the present invention, the porous polymer substrate may be a polyethylene substrate.

[0076] In one embodiment of the present invention, a conventional diluent may be used to extrude the polymer resin by feeding it into an extruder. The diluent may be a liquid or solid paraffin oil, wax, soybean oil, or the like, which are commonly used in membrane manufacturing.

[0077] In one embodiment of the present invention, a conventional single-screw extruder or twin-screw extruder may be used for the melting and extrusion, but is not limited thereto. In one embodiment of the present invention, a mixture of the diluent and the polymer resin may be introduced into an extruder, and then mixed while melting the polymer resin at high temperatures to obtain a molten composition.

[0078] Next, S1-2) The molten composition can be formed into a sheet shape.

[0079] In one embodiment of the present invention, the molten composition may be extruded through a die of an extruder, such as a T-die, and then formed into a sheet using a conventional casting or calendaring method using a method such as water cooling or air cooling. In one embodiment of the present invention, the molten composition may be formed into a sheet by compressing the molten composition by the casting rolls in a cooling device equipped with a pair of casting rolls.

[0080] At this time, since the extrusion of the polymer sheet is generally performed at a high temperature, for example, 150°C to 300°C, the polymer sheet extruded through the extrusion section has a surface temperature of a high temperature, for example, 130°C to 200°C, immediately after extrusion, and is cooled while coming into contact with the casting roll while having this surface temperature. Generally, the surface temperature of the casting roll may be 20°C to 45°C, 25°C to 45°C, 35°C to 45°C, or 25°C.

[0081] Next, a step of stretching the sheet formed into the above sheet shape (S1-3) can be performed.

[0082] In one embodiment of the present invention, the stretching may include secondary stretching of the polymer sheets in the same direction or in different directions. For example, the stretching may include independently stretching the polymer sheets in directions parallel to the MD and / or TD.

[0083] In one embodiment of the present invention, the stretching may be performed, for example, by roll method, tenter method sequential method, or simultaneous stretching. In one embodiment of the present invention, the stretching may be performed at a stretching ratio of, for example, 3 times or more, 5 to 12 times, or 6 to 7 times. When the stretching ratio satisfies the above numerical range, there may be advantageous effects in terms of thickness uniformity and physical property balance between longitudinal and transverse directions of the manufactured membrane substrate, but the present invention is not limited thereto.

[0084] In one embodiment of the present invention, S1-4) after the stretching, a diluent can be extracted from the stretched sheet to form pores.

[0085] In one embodiment of the present invention, the extraction of the diluent may be performed using an organic solvent. Suitable organic solvents include, for example, methyl ethyl ketone, methylene chloride, hexane, or a mixture of two or more thereof, which have high extraction efficiency and rapid drying. However, the present invention is not limited thereto. In one embodiment of the present invention, the temperature at which the extraction is performed is not particularly limited, as long as it does not change the surface roughness value of the formed porous substrate.

[0086] In one embodiment of the present invention, the step S2) may be to extract the diluent as described above and heat-fix the porous polymer sheet in which pores are formed. According to one embodiment of the present invention, a membrane substrate having a surface roughness value (Sa) of 30 nm to 70 nm on both sides of the porous polymer substrate may be provided.

[0087] According to one embodiment of the present invention, the surface roughness value (Sa) of at least one surface of the porous polymer substrate may be 35 nm to 70 nm.

[0088] According to one embodiment of the present invention, when the surface roughness value (Sa) of at least one side of the porous polymer substrate is within the above-described range, it can exhibit advantageous effects in terms of reducing the increase in resistance of the separator when forming a porous coating layer and securing appropriate adhesive strength between the separator substrate and the porous coating layer, but the effects of the present invention are not limited thereto.

[0089] Meanwhile, in addition to measuring the Sa value, there are known methods for measuring the surface roughness of a membrane substrate, such as Ra (center line average), Rmax (maximum peak to valley roughness height), Rz (ten point height), and Rg (root mean square, RMS), which represent the two-dimensional roughness of the surface. However, Ra, Rmax, Rz, and Rg measure the two-dimensional (linear) roughness of the surface, and the roughness shape of the surface cannot be confirmed with these values ​​alone. That is, even if at least one of Ra, Rmax, Rz, and Rg is the same for two different surfaces, the three-dimensional roughness shape may be different, which causes a difference in the impregnation amount of the slurry for forming a porous coating layer, and thus, there is a problem in that it is difficult to confirm whether the resistance characteristics are improved. In consideration of this problem, the present invention defines the surface roughness value of a membrane substrate through Sa.

[0090] In one embodiment of the present invention, the surface roughness value (Sa) can be measured by analyzing the surface of a porous polymer substrate using atomic force microscopy (AFM). For example, a sample of a porous polymer substrate to be measured for surface roughness is obtained in a size of 30 ㎛ X 30 ㎛, and then the surface characteristics of each side are measured. At this time, the surface roughness value (Sa) is measured by analyzing the difference in the average height of the surface of the entire area based on the average height surface.

[0091]

[0092] Hereinafter, the composition of the porous polymer substrate will be exemplarily described. However, the porous substrate is not limited to the constituent components described below.

[0093] In one embodiment of the present invention, the porous polymer 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, allowing gas or liquid to pass from one side of the substrate to the other.

[0094] In one embodiment of the present invention, the porous polymer 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 porous polymer substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery.

[0095] 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-described range based on the total thickness of the separator, but may be, for example, 5 to 300 ㎛, specifically 5 to 100 ㎛, 5 to 50 ㎛, 5 to 20 ㎛, 5 to 15 ㎛, or 9 to 12 ㎛.

[0096] 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 membrane configuration. For example, the thickness of the porous polymer substrate can be measured using a known thickness measuring device, and for example, the thickness can be measured using a commercially available thickness measuring device (Mitutoyo, VL-50S-B).

[0097]

[0098] membrane

[0099] According to one 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, the porous polymer substrate comprising inorganic particles and a binder polymer. In this case, the porous coating layer may be formed on at least one surface of the separator substrate having a roughness value (Sa) of 30 nm to 160 nm.

[0100] 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, the porous polymer substrate comprising inorganic particles and a binder polymer. In this case, the porous coating layer is formed on at least one surface of the separator substrate having a roughness value (Sa) of 30 nm to 80 nm.

[0101] The above porous coating layer includes a large amount of inorganic particles and a binder polymer that binds them to improve the safety of the separator. The inorganic particles can improve the heat resistance of the separator, and the binder polymer can provide adhesive strength to the surface of the separator. At this time, if the surface of the separator substrate on which the porous coating layer is formed is flat, there may be a problem of low adhesive strength at the interface between the separator substrate and the porous coating layer. However, if the surface of the separator substrate is too rough, a large amount of slurry for forming a coating layer is impregnated between the pores of the separator substrate, and the inorganic particles and / or the binder polymer are impregnated into the pores of the separator substrate and / or the surface of the separator substrate by the impregnated slurry, which may cause a problem of increasing the resistance of the separator. Accordingly, a separator having a porous coating layer formed on a separator substrate according to one aspect of the present invention can exhibit a characteristic in which the surface roughness is implemented at a certain level to prevent impregnation of inorganic particles and / or binder polymers on the surface, thereby improving the resistance increase phenomenon.

[0102] In one embodiment of the present invention, the separator may be characterized in that the adhesion strength between the surface of the separator substrate having a surface roughness value (Sa) of 30 nm to 80 nm, specifically 30 nm to 70 nm, and the porous coating layer is 30 gf / 15 mm or more. For example, the adhesion strength between the surface of the separator substrate having a surface roughness value (Sa) in the above-described range and the porous coating layer may be 30 gf / 15 mm to 140 gf / 15 mm, 30 gf / 15 mm to 120 gf / 15 mm, 30 gf / 15 mm to 100 gf / 15 mm, 30 gf / 15 mm to 85 gf / 15 mm, or 32 gf / 15 mm to 81 gf / 15 mm. When the adhesive strength between the separator substrate and the porous coating layer of the above-mentioned separator is within the above-mentioned range, it can exhibit advantageous effects in terms of improving the manufacturing process of an electrode assembly using the separator and improving the stability of the separator.

[0103] The adhesive strength of the above separator can be measured, for example, by the following method. The separator to be measured for adhesive strength is sampled to a width of 15 mm and attached to a slide glass using 18 mm wide double-sided tape (3M) so that the side to be measured for adhesive strength is in contact with the glass. Then, the peel strength between the separator substrate and the porous coating layer is measured using a UTM device (Instron) at 180° and 300 mm / min.

[0104] In addition, in one embodiment of the present invention, the separator may be characterized by having an electrical resistance of 1Ω or less. When the surface roughness value (Sa) of the separator substrate is in the above-described range, the degree of impregnation of the slurry for forming a porous coating layer on the separator substrate is improved, thereby reducing the amount of slurry impregnated at the interface between the separator substrate and the porous coating layer, thereby reducing the amount of inorganic particles and / or binder polymers that permeate the separator substrate, thereby exhibiting the advantage of reducing an increase in resistance of the separator.

[0105] According to one embodiment of the present invention, the electrical resistance of the separator may be 0.9 Ω or less. Specifically, the electrical resistance of the separator may be 0.5 Ω to 0.9 Ω, 0.6 Ω to 0.85 Ω, or 0.63 Ω to 0.82 Ω.

[0106] The resistance of the separator can be measured, for example, through electrochemical impedance spectroscopy (EIS). Specifically, the separator to be measured for resistance is punched to 19Φ to prepare a CR2016 type coin cell. At this time, a solution in which an active material (NCMA), a binder polymer (PVDF), and a conductive material (CNT) are dissolved in a solvent (NMP) at a weight ratio of 97:1:2 is applied and dried on aluminum foil as a positive electrode, and one punched to 12Φ can be used. A solution in which an active material (Graphite), a binder polymer (SBR), and a conductive material (Super P) are dissolved in distilled water at a weight ratio of 95:0.5:4.5, and one punched to 12Φ can be used as a negative electrode. After stacking the positive electrode / separator / cathode in that order, the coin cell can be assembled by impregnating it with an electrolyte solution of 1M LiPF6, ethyl carbonate (EC), and ethyl methyl carbonate (EMC) (3 / 7 v / v), and 2 wt% vinylene carbonate (VC).

[0107] For the above EIS measurement, for example, a Solartron analytical EIS device from Solartron Co., Ltd. can be used, and the resistance value can be measured under the condition of a frequency of 100,000 Hz to 10,000 Hz.

[0108] Hereinafter, the composition of the porous coating layer will be exemplarily described. However, the composition of the porous coating layer is not limited thereto.

[0109] In one embodiment of the present invention, the porous coating layer may include inorganic particles and a binder polymer, such that the inorganic particles have all or at least a portion of their surfaces coated with the binder polymer. In this case, the inorganic particles are surface-bonded and / or point-bonded via the binder polymer.

[0110] For example, the inorganic particles and the binder resin in the porous coating layer may be included in a weight ratio of 99:1 to 1:99. Specifically, the inorganic particles and the binder resin in the porous coating layer may be included 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 above porous coating layer has a structure in which a number of micropores are formed inside, and these micropores are interconnected, and has the structural characteristics of a porous layer in which gas or liquid can pass from one side to the other side.

[0111] 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.

[0112] In one embodiment of the present invention, the porous coating layer comprises 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 shape from the binder polymer 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 polymer intersect with each other to form a three-dimensional network structure.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] In one embodiment of the present invention, the binder polymer may include, for example, a polyvinylidene fluoride-based resin (PVdF-based resin) and / or an acrylic binder. 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. The acrylic binder may include, for example, polyacrylic acid (PA), polyacrylonitrile (PAN), polyacrylamide (PAA), or a (meth)acrylic polymer, or a mixture of two or more thereof, but the present invention is not limited thereto. The (meth)acrylic polymer refers to a polymer that includes a (meth)acrylic acid ester as a monomer. Such monomers may include, for example, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-oxyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate or mixtures of two or more thereof, but the present invention is not limited thereto.

[0118] In one embodiment of the present invention, the binder polymer may include, but is not limited to, an oil-based binder, an aqueous binder, or a mixture thereof that can be used in a porous coating layer.

[0119] 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.

[0120]

[0121] electrode assembly

[0122] 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.

[0123] As described above, the separator according to one aspect of the present invention is characterized by improved resistance characteristics and low resistance. Accordingly, an electrode assembly using the separator is characterized by low resistance and, accordingly, high output characteristics.

[0124] In one embodiment of the present invention, the resistance of the electrode assembly may be 1Ω or less.

[0125] In one embodiment of the present invention, the resistance of the electrode assembly may be 0.9Ω or less. Specifically, the resistance of the electrode assembly may be 0.5Ω to 1Ω, 0.5Ω to 0.9Ω, 0.5Ω to 0.8Ω, 0.5Ω to 0.7Ω, or 0.52Ω to 0.62Ω.

[0126] In one embodiment of the present invention, the resistance of the electrode assembly may be measured by the following method.

[0127] A positive electrode and a negative electrode are attached to each side with the above separator in between and pressurized to prepare an electrode assembly with a theoretical capacity of 50 mAh. Next, CC / CV charging is repeated three times under the conditions of 4.2 V, 2.5 mA cut-off and CC discharging is repeated three times at 2.5 V, 50 mA. After that, the fully charged cell is set to SOC 50% and then discharged for 30 seconds with a current of 250 mA, the voltage drop occurring at the SOC50 state is recorded, and the DC resistance value is calculated using R=V / I (Ohm's law). At this time, the composition of the positive electrode, negative electrode, and electrolyte can use the composition described above in the method for measuring the resistance of the separator.

[0128] In one embodiment of the present invention, when a separator using the separator substrate is applied, not only is the adhesion between the positive and negative electrodes excellent, but the resistance of the electrode assembly is reduced, thereby providing an electrochemical device with high output characteristics.

[0129] Hereinafter, the configuration of the above electrode will be described by way of example. However, the present invention is not limited thereto.

[0130] 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.

[0131] In one embodiment of the present invention, the positive electrode active material may include, but is not limited to, 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 lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more thereof. Specifically, the positive electrode active material may include, but is not limited to, 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-xLithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); chemical formula LiMn 2-x M x Lithium 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 Cob 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.

[0132] 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.

[0133]

[0134] electrochemical devices

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139]

[0140] 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.

[0141]

[0142] [Manufacture of membrane substrate]

[0143] A porous polymer substrate was manufactured by the following method.

[0144] After mixing polyethylene polymer with a molecular weight of 600,000 (g / mol) and an antioxidant in an extruder, the mixture was melted at 200℃, extruded through a T-die, and then cooled and formed into a sheet shape on a stainless steel casting roll having a surface temperature of 25℃ to obtain a polymer sheet. The polymer sheet passing through the casting roll was stretched in the MD (stretch ratio 7 times, stretching temperature 115℃) and TD (stretch ratio 6 times, stretching temperature 125℃) using a tenter-type sequential stretching machine placed at the rear end of the casting roll, and the diluent was then extracted using methylene chloride. Thereafter, the obtained polymer sheet was heat-set at the temperatures shown in Table 1 below to obtain a porous polymer substrate. The heat-setting was performed while holding the polymer sheet in the MD and TD directions, and the obtained porous polymer substrate had a thickness of 9 ㎛ and a porosity of 45 vol%.

[0145] Separation column fixing temperature (℃) Comparative example 1117 Example 1121 Example 2125 Example 3130 Comparative example 2134

[0146] [Manufacturing of membranes]

[0147] Using the porous polymer substrates of Comparative Examples 1 and 2 and Examples 1 to 3 manufactured above as a membrane substrate, a porous coating layer was formed on both sides of the membrane substrate by the following method to manufacture a membrane.

[0148] Manufacturing of porous coating layers

[0149] A slurry for inorganic coating was prepared by mixing PVDF-HFP binder (Mw 500,000 g / mol, HFP 15 wt%) and inorganic particles (Al2O3) 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 a dip coating method and dried by a humidification separation method, thereby forming a porous coating layer with a thickness of 3 μm on each of the upper and lower surfaces of the porous substrate prepared above.

[0150] In this way, a separation membrane with a total thickness of 15 ㎛ was manufactured.

[0151]

[0152] [Manufacturing of electrode assembly]

[0153] 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.

[0154] Manufacturing of cathode

[0155] 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.

[0156] 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.

[0157]

[0158] Manufacturing of anodes

[0159] 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.

[0160] 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.

[0161]

[0162] Assembly of the electrode assembly

[0163] Each of the separators prepared above was placed in between, with the positive electrode on one side and the negative electrode on the other side, and then rolled and dried under the conditions of 90°C, 4 MPa, and 1 s to obtain an electrode assembly with a theoretical capacity of 50 mAh.

[0164]

[0165] [Physical property evaluation]

[0166] The properties of the separator substrate, separator, and electrode assembly were evaluated in the manufacturing order above using the following method, and the results are shown in Table 2 below.

[0167] The adhesive strength of the separator in Table 2 below was measured by measuring the adhesive strength between the surface on which the surface roughness value was measured and the porous coating layer.

[0168]

[0169] Measurement of surface roughness value (Sa) of membrane substrate

[0170] A surface analysis of a porous polymer substrate was performed using atomic force microscopy (AFM), a height map of the surface was obtained, and the difference in the average height of the entire surface area based on the average height plane was analyzed to measure the roughness value (Sa).

[0171] Roughness values ​​were measured on both sides of the membrane substrate.

[0172]

[0173] Measurement of the adhesive strength of the separator

[0174] The separator was sampled to a width of 15 mm and attached to a slide glass using 18 mm wide double-sided tape (3M) so that the side 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 UTM device (Instron) at 180° and 300 mm / min.

[0175] The adhesive strength was performed on both sides of the separator.

[0176]

[0177] Measuring the resistance of the separator

[0178] CR2016 coin cells were manufactured using the following method, and the resistance of the separator was measured using the EIS method.

[0179] The separator to be measured was prepared by punching 19Φ. The electrodes manufactured during the manufacture of the above electrode assembly as the positive and negative electrodes were each punched 12Φ, and then stacked in the order of positive electrode / separator / negative electrode in a CR2016 coin cell case, and an electrolyte consisting of 1M LiPF6, ethyl carbonate (EC), and ethyl methyl carbonate (EMC) (3 / 7 v / v), and 2 wt% vinylene carbonate (VC) was injected, and the cap was closed to prepare a coin cell.

[0180] EIS measurements were performed using Solartron analytical EIS equipment from Solartron, Inc., and resistance values ​​were measured under frequency conditions of 100,000 to 10,000 Hz.

[0181]

[0182] Resistance measurement of electrode assembly

[0183] The resistance of the electrode assembly prepared for measuring the resistance of the above separator was measured in the following manner.

[0184] CC / CV charging and 2.5 V, 50 mA CC discharging were repeated three times under the conditions of 4.2 V, 2.5 mA cut-off. After that, the fully charged cell was set to SOC 50% and discharged for 30 seconds with a current of 250 mA, and the voltage drop occurring at SOC50 was recorded, and the DC resistance value was calculated using R=V / I (Ohm's law).

[0185] Separator membrane substrateSeparator electrode assemblySurface roughness value (Sa)Adhesive strength (gf / 15mm)Resistance (Ohm, Ω)Resistance (Ohm, Ω)Comparative example 128.270.450.48Example 136.5320.630.52Example 254.8510.780.56Example 369.1810.820.62Comparative example 290.41972.321.18

[0186] As confirmed in Tables 1 and 2 above, the porous polymer substrate obtained by heat setting at a temperature of 119°C to 132°C as a separator substrate exhibited a surface roughness value (Sa) of 30 nm to 70 nm, thereby confirming that it had low resistance while maintaining an appropriate level of adhesive strength. Furthermore, it was confirmed that the resistance of an electrode assembly using the same could be significantly improved.

[0187] On the other hand, it was confirmed that the porous polymer substrate obtained by heat-setting in a range outside the above temperature as a membrane substrate had a surface roughness value (Sa) exceeding 30 nm to 70 nm. In particular, in the case of Comparative Example 1 where the surface roughness value (Sa) was less than 30 nm, it was confirmed that the adhesive strength was poor even though the resistance of the separator was implemented low, and in the case of Comparative Example 2 where the surface roughness value (Sa) exceeded 70 nm, not only did the adhesive strength appear very high, but also the separator exhibited poor physical properties in terms of resistance, so that the resistance of the electrode assembly using the same was measured to be very high.

Claims

1. A membrane substrate characterized in that the roughness value (Sa) of at least one surface of the porous polymer substrate is 30 nm to 80 nm.

2. In claim 1, A membrane substrate characterized in that the surface roughness value (Sa) of both sides of the porous polymer substrate is 30 nm to 70 nm.

3. A membrane substrate according to claim 1; and A separation membrane characterized by comprising a porous coating layer formed on at least one surface having a surface roughness value (Sa) of 30 nm to 80 nm and containing inorganic particles and a binder polymer.

4. In claim 3, A separator characterized in that the adhesive strength between the separator substrate and the porous coating layer is 30 gf / 15 mm or more.

5. In claim 4, A separator characterized in that the adhesive strength between the separator substrate and the porous coating layer is 30 gf / 15 mm to 140 gf / 15 mm.

6. In claim 3, A separator characterized in that the electrical resistance of the separator is 1Ω or less.

7. In claim 6, A separator characterized in that the electrical resistance of the separator is 0.9 Ω or less.

8. In claim 3, The average particle diameter (D) of the above inorganic particles 50 ) is a separation membrane characterized by a thickness of 100 nm or more.

9. A separator according to any one of claims 3 to 8; An electrode assembly characterized by including a positive electrode and a negative electrode formed on each side of the separator.

10. In claim 9, An electrode assembly characterized in that the resistance of the electrode assembly is 1Ω or less.

11. In claim 10, An electrode assembly characterized in that the resistance of the electrode assembly is 0.9 Ω or less.

12. An electrochemical device characterized in that the electrode assembly according to claim 9 is housed in a case. 13.S1) A step of extruding a polymer slurry to obtain a polymer sheet; and S2) A method for manufacturing a membrane substrate, comprising a step of opening and fixing the obtained polymer sheet; A method for manufacturing a membrane substrate, characterized in that the heat fixation in the above step S2 is performed at a temperature of 119°C to 132°C.