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 one embodiment of the present invention is characterized in that the two surfaces have different surface characteristics. Accordingly, the adhesive strength of the two surfaces of a separator using the separator substrate are different, and the deviation in electrode adhesiveness with a positive electrode and a negative electrode that differ in adhesive strength is remarkably improved.

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 having improved variation in electrode adhesion on both sides, an electrode assembly comprising the same, and electrochemical testing.

[0002] This application claims priority to Korean Patent Application No. 2023-0097767, filed with the Korean Intellectual Property Office on July 26, 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, which consists of a cathode / separator / cathode as a single unit, into a battery case, and then injecting and sealing the electrode assembly. A polyolefin-based porous substrate is typically used as a separator for lithium secondary batteries. In order to solve the problem of short circuits between the cathode and anode due to the thermal shrinkage behavior of the polyolefin-based porous substrate, a separator (hereinafter referred to as a 'Safety Reinforced Separator' (SRS)) was developed by forming a coating layer made of a mixture of inorganic particles and binder polymers on the surface of the porous substrate to improve the strength and heat resistance of the separator.

[0004] These SRSs 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. Therefore, electrode assemblies are manufactured by bonding the anode and cathode with a separator between them using SRSs with porous coating layers on both sides.

[0005] However, when using a silicon (Si)-based active material as an anode active material, the roughness of the material is greater than when using a graphite-based active material, so the adhesion between the separator and the anode is high, but in the case of the cathode, the roughness of the material is small, so the adhesion between the separator and the anode is low. If the adhesion between the separator and the electrode is low, there is a concern that the structure of the electrode assembly may be distorted during cell assembly, and if the difference in adhesion between the separator and the anode and cathode is large, there may be a bending problem of the cell, so it is necessary to develop technology to improve the adhesion between the anode and the separator.

[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 having improved adhesion between a cathode and an anode, and an electrode assembly and electrochemical device having improved safety using the same.

[0008] In particular, the present invention aims to provide a separator substrate having different surface properties on both sides and a separator including the same, in terms of improving the difference in adhesive strength between the cathode and anode of the separator.

[0009] Meanwhile, the present invention aims to provide an electrode assembly including Si particles as a negative electrode active material and an electrochemical device including the same.

[0010] To solve the above problem,

[0011] According to one aspect of the present invention, a membrane substrate of the following embodiments is provided.

[0012] The membrane substrate according to the first embodiment is

[0013] It is assumed to be a porous polymer substrate having different surface roughnesses on both sides.

[0014] According to the second embodiment, in the first embodiment,

[0015] The surface roughness values ​​(Sa) on both sides of the above porous polymer substrate may be different from each other.

[0016] According to the third embodiment, in the first embodiment or the second embodiment,

[0017] The surface roughness value (Sa) of one side of the above porous polymer substrate may be 50 nm or less, and the surface roughness value (Sa) of the other side may be greater than 50 nm.

[0018]

[0019] According to another aspect of the present invention, a separation membrane of the following embodiments is provided.

[0020] The separation membrane according to the fourth embodiment is

[0021] A membrane substrate according to any one of the first to third embodiments; and

[0022] It may include a porous coating layer formed on each of both sides of the above-mentioned separation membrane substrate and including inorganic particles and a binder polymer.

[0023] According to the fifth embodiment, in the fourth embodiment,

[0024] The above separator has different adhesive strengths on both sides, and when the side with the higher adhesive strength is referred to as the first side and the side with the lower adhesive strength is referred to as the second side, the ratio of the adhesive strengths of the first side and the second side according to the following equation 1 may be 150% or more.

[0025] According to the sixth embodiment, in the fourth embodiment or the fifth embodiment,

[0026] The adhesive strength of both sides of the above separator may be 30 gf / 15 mm or more.

[0027] According to the seventh embodiment, in any one of the fourth to sixth embodiments,

[0028] The adhesive strength of one side of the separator may be 80 gf / 15 mm or less, and the adhesive strength of the other side may be greater than 80 gf / 15 mm. In this case, the adhesive strength may represent the adhesive strength between the separator substrate and the porous coating layer.

[0029]

[0030] According to another aspect of the present invention, electrode assemblies of the following embodiments are provided.

[0031] The electrode assembly according to the eighth embodiment is:

[0032] A separator according to any one of the fourth to sixth embodiments, which may include an anode and a cathode formed on each of both sides of the separator.

[0033] According to the ninth embodiment, in the eighth embodiment,

[0034] The adhesive strengths of the two sides of the above separator may be different from each other, and the positive electrode may face the side with the high adhesive strength, and the negative electrode may face the side with the low adhesive strength.

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

[0036] The deviation of the electrode adhesion between the separator and each of the positive and negative electrodes according to the following Equation 2 may be 10% or less.

[0037] [Formula 2]

[0038] Deviation of electrode adhesion (%) = │{1-F (x) / F (y) )}│ X 100

[0039] In the above equation 2,

[0040] F (x) is the electrode adhesion between the separator and the anode, and F (y) is the electrode adhesion between the separator and the cathode, or

[0041] F (x)is the electrode adhesion between the separator and the cathode, and F (y) is the electrode adhesion between the separator and the anode.

[0042] According to the eleventh embodiment, in any one of the eighth to tenth embodiments,

[0043] The above negative electrode may include a Si-based active material as an active material.

[0044]

[0045] According to another aspect of the present invention, electrochemical devices of the following embodiments are provided.

[0046] The electrochemical device according to the 12th embodiment,

[0047] An electrode assembly according to any one of the eighth to eleventh embodiments may be housed in a case.

[0048]

[0049] According to another aspect of the present invention, a method for manufacturing a membrane substrate of the following embodiments is provided.

[0050] The method for manufacturing a membrane substrate according to the 13th embodiment is as follows:

[0051] S1) A step of extruding a polymer slurry to obtain a high-spray sheet; and

[0052] S2) A method for manufacturing a membrane substrate, comprising the step of positioning the obtained polymer sheet on a casting roll and cooling it;

[0053] In the above step S2, the polymer sheet may be cooled without a touch roll on the opposite side of the side facing the casting roll.

[0054] By providing different surface properties on both sides of a separator substrate according to one embodiment of the present invention, it is possible to have the effect of exhibiting different electrode adhesive strengths on both sides of a separator formed using the same.

[0055] Accordingly, both sides of the separator can exhibit the advantage of having a small deviation in adhesive strength between the separator and the electrode even if the characteristics of the active material in the electrode formed on both sides of the separator are different.

[0056] Due to this, the bending phenomenon that occurs due to the difference in adhesive strength between the separator and the positive and negative electrodes on both sides of the separator can be improved, which can have the advantage of improving the safety of the electrochemical device using it.

[0057] The separator substrate and separator according to one embodiment of the present invention have the advantage of being usable in an electrode assembly with improved stability and productivity.

[0058] Figure 1 is a schematic diagram of a device for manufacturing a conventional separation membrane substrate.

[0059] Figure 2 is a schematic diagram of an apparatus for manufacturing a membrane substrate according to one embodiment of the present invention.

[0060] Hereinafter, the present invention will be described in detail.

[0061] 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.

[0062] In this specification, the term “A and / or B” means “A or B, or both.”

[0063] 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.

[0064]

[0065] Membrane substrate and manufacturing method thereof

[0066] According to one aspect of the present invention, a porous polymer substrate is provided, wherein the surface roughness of both sides of the membrane substrate is different from each other.

[0067] 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.

[0068] A method for manufacturing a membrane substrate according to one aspect of the present invention is as follows:

[0069] S1) A step of extruding a polymer slurry to obtain a high-spray sheet; and

[0070] S2) A step of positioning the obtained polymer sheet on a casting roll and cooling it.

[0071] At this time, according to one aspect of the present invention, in the step S2, the polymer sheet is cooled without a touch roll on the opposite side of the side facing the casting roll.

[0072] Fig. 1 is a schematic diagram of a manufacturing device for manufacturing a conventional membrane substrate. Fig. 1 shows an extrusion section (1) and a cooling section (2). The cooling section cools a polymer sheet extruded through a T-die (200) on a casting roll (201), and a contact roll (202) is provided to support the polymer sheet.

[0073] When manufacturing a porous polymer substrate as a conventional membrane substrate, a polymer slurry is extruded to obtain a polymer sheet, and the obtained polymer sheet is cooled while one side is in contact with a casting roll (201) and the other side is in contact with a touch roll (202) for support of the other side. Accordingly, since both sides of the polymer sheet are cooled while in contact with the casting roll and the touch roll, respectively, the shapes of the surfaces of both sides of the polymer sheet obtained through cooling are formed similarly, and the surface roughness of both sides of the membrane substrate is formed similarly.

[0074] Fig. 2 is a schematic diagram of an apparatus for manufacturing a membrane substrate according to one aspect of the present invention. Fig. 2 shows an extrusion section (1) and a cooling section (2), wherein the cooling section cools a polymer sheet extruded through a T-die (200) on a casting roll (201), and one side of the polymer sheet does not have a contact roll for cooling in the air.

[0075] According to one aspect of the present invention, when cooling a polymer sheet obtained by extrusion, the cooling conditions on both sides are performed differently from each other, thereby forming different surface morphologies on both sides of the obtained polymer sheet, thereby obtaining a polymer sheet having different surface roughnesses on both sides. To this end, the method for manufacturing a membrane substrate of the present invention is characterized in that cooling is performed while one side of the polymer sheet obtained through step S1 is in contact with a casting roll, and while the other side is not provided with a contact roll.

[0076] The membrane substrate obtained by the above method can have a relatively smooth surface on the side cooled by contact with the casting roll, and a relatively rough surface on the side cooled by contact with air without contact with the contact roll. As a result, a porous polymer substrate having different surface roughnesses on both sides can be obtained.

[0077] Next, a method for manufacturing a membrane substrate according to one aspect of the present invention will be described in detail for each step.

[0078] First, in one embodiment of the present invention, the step of extruding the polymer slurry S1) to obtain a polymer sheet may include melt-extruding a polymer resin as a raw material.

[0079] 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.

[0080] In one embodiment of the present invention, the porous polymer substrate may be a polyolefin substrate.

[0081] In one embodiment of the present invention, the porous polymer substrate may be a polyethylene substrate.

[0082] 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.

[0083] 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.

[0084] In one embodiment of the present invention, since the extrusion of the polymer sheet is performed at a high temperature, for example, 150°C to 300°C, the polymer sheet extruded through the extrusion unit has a surface temperature of a high temperature, for example, 130°C to 200°C, immediately after extrusion, and comes into contact with the casting roll while having this surface temperature. In one embodiment of the present invention, the temperature of the casting roll may be, for example, 20°C to 45°C, 25°C to 45°C, 35°C to 45°C, or 25°C, but the present invention is not limited thereto.

[0085] In one embodiment of the present invention, the step S2 may be a step for implementing different surface roughness on both sides by cooling both sides of the polymer sheet in different environments, but the present invention is not limited thereto.

[0086] Next, the method for manufacturing a membrane substrate according to one aspect of the present invention may further include a step of stretching and heat-setting a polymer sheet formed through a casting roll S3) after the cooling step S2).

[0087] 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 a direction parallel to the machine direction (MD) and / or the transverse direction (TD).

[0088] 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.

[0089] In one embodiment of the present invention, the stretching can be performed, for example, by roll stretching, tenter stretching, or simultaneous stretching.

[0090] 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.

[0091] In one embodiment of the present invention, a step of extracting a diluent from the stretched sheet after the stretching to form pores and then heat-setting may be included.

[0092] 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.

[0093] 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.

[0094] In one embodiment of the present invention, after the stretching and extraction of the diluent, heat setting may be performed to forcibly hold the porous sheet and remove residual stress within the sheet. However, the purpose of the heat setting is not limited thereto.

[0095] In one embodiment of the present invention, the heat setting temperature may vary depending on the type of polymer resin used in the manufacture of the membrane substrate. The heat setting temperature may be, for example, 100°C to 180°C, specifically 110°C to 150°C, more specifically 120°C to 140°C, for example, 130°C, but the present invention is not limited thereto.

[0096] In one embodiment of the present invention, heat may be applied while uniaxially stretching in the MD or TD direction during the heat fixation, or heat may be applied while biaxially stretching in the MD and TD directions, but is not limited thereto.

[0097] According to one aspect of the present invention, the membrane substrate obtained by the above-described manufacturing method is a porous polymer substrate having different surface roughnesses on both sides.

[0098] In one embodiment of the present invention, the surface roughness of both sides of the membrane substrate can be determined, for example, through the surface roughness value (Sa). For example, a porous polymer substrate having different surface roughnesses on both sides can represent a porous polymer substrate having different surface roughness values ​​(Sa) on both sides.

[0099] 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 50 mm X 50 mm, and then the surface characteristics of each side are repeatedly measured for an area of ​​30 ㎛ X 30 ㎛. 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 plane of the height.

[0100] In one embodiment of the present invention, the porous polymer substrate may have different surface roughness values ​​(Sa) on both sides, for example, the surface roughness value (Sa) of one side may be 50 nm or less, and the surface roughness value (Sa) of the other side may be greater than 50 nm.

[0101] In one embodiment of the present invention, when the surface roughness of both sides of the porous polymer substrate, i.e., the membrane substrate, is different from each other, the surface characteristics of both sides of the membrane using the same are different, and accordingly, the adhesive strength between each side of the membrane and the electrode is different. In particular, when the surface roughness value (Sa) of one side of the membrane substrate is 50 nm or less, it is advantageous in terms of adhesive strength with the negative electrode, and when the surface roughness value (Sa) of the other side is greater than 50 nm, it can exhibit an advantageous effect in terms of adhesive strength with the positive electrode.

[0102] In one embodiment of the present invention, the surface roughness value (Sa) of one side of the membrane substrate may be, for example, 30 nm to 45 nm or 35 nm to 40 nm. In addition, the surface roughness value (Sa) of the other side of the membrane substrate may be, for example, 60 nm to 90 nm, 70 nm to 85 nm or 75 nm to 80 nm.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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 μm, specifically 5 to 100 μm, 5 to 50 μm, 5 to 20 μm, 5 to 15 μm, or 9 to 12 μm.

[0107] 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).

[0108]

[0109] membrane

[0110] According to one aspect of the present invention, the porous polymer substrate itself described above can be provided as a separator.

[0111] According to another aspect of the present invention, a separator can be provided that uses the above-described porous polymer substrate as a separator substrate and includes a porous coating layer formed on each of both sides of the separator substrate and including inorganic particles and a binder polymer.

[0112] 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 binder polymer can provide adhesive strength to the surface of the separator, and since the surface roughness of both sides of the separator substrate is different, when a porous coating layer is formed on the surface of the separator substrate, the adhesive strengths of the two sides of the separator can exhibit different characteristics.

[0113] In one embodiment of the present invention, the separator may be characterized by having different adhesive strengths on both sides. By having different adhesive strengths on both sides of the separator, the separator can exhibit excellent adhesive strength not only with a negative electrode having relatively high adhesive strength, but also with a positive electrode having relatively low adhesive strength.

[0114] In one embodiment of the present invention, when the side with higher adhesive strength of the separator is referred to as the first side and the side with lower adhesive strength is referred to as the second side, the ratio of adhesive strengths of the first side and the second side according to the following Equation 1 may be, for example, 150% or more.

[0115] [Formula 1]

[0116] Adhesive strength ratio (%) = [(Adhesive strength of the first side / Adhesive strength of the second side) X 100]

[0117] In one embodiment of the present invention, the adhesive strength may represent the adhesive strength between the separator substrate and the porous coating layer, and may be measured by the following method.

[0118] 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.

[0119] In one embodiment of the present invention, the ratio of the adhesive strength according to the above formula 1 may be, for example, 150% or more, 160% or more, or 170% or more. For example, the ratio of the adhesive strength may be 150 to 200%, 160 to 190%, 170 to 180%, or 175 to 180%, but the present invention is not limited thereto. According to the present invention, the separator can realize a large difference in the adhesive strength of both sides, and thus, even if the difference in adhesive strength between the positive and negative electrodes is large, the adhesive strength between the separator and the electrode is maintained at a certain level, thereby improving the bending problem of the electrode.

[0120] In one embodiment of the present invention, the adhesive strength of the first side of the separator having a higher adhesive strength may be, for example, greater than 80 gf / 15 mm, and the adhesive strength of the second side having a lower adhesive strength may be, for example, 80 gf / 15 mm or less. Preferably, the adhesive strengths of each of the two sides of the separator may be, for example, 30 gf / 15 mm or more.

[0121] In one embodiment of the present invention, the adhesive strength of the first side of the separator may be, for example, 85 to 110 gf / 15 mm, 90 to 105 gf / 15 mm, or 95 to 100 gf / 15 mm. In addition, the adhesive strength of the second side of the separator may be, for example, 30 to 70 gf / 15 mm, 40 to 60 gf / 15 mm, or 50 to 60 gf / 15 mm. When the adhesive strengths of both sides of the separator are each in the above-described range, the separator may exhibit an advantageous effect in terms of having excellent adhesive strength with each of the positive and negative electrodes, but the present invention is not limited thereto.

[0122] In one embodiment of the present invention, since the adhesive strengths of the two sides of the separator are different from each other, the surface facing the positive electrode and / or negative electrode on each side of the separator can be determined by considering the adhesive strength of the electrode according to the composition of the electrode, for example, the type of active material and / or the type of binder polymer.

[0123] For example, in one embodiment of the present invention, when the adhesive strength of the positive electrode is lower and the adhesive strength of the negative electrode is higher, the first side of the separator with high adhesive strength can face the positive electrode during manufacture of the electrode assembly, and the second side of the separator with low adhesive strength can face the negative electrode during manufacture of the electrode assembly.

[0124] For example, in another embodiment of the present invention, when the adhesive strength of the negative electrode is lower and the adhesive strength of the positive electrode is higher, the first side of the separator with high adhesive strength can face the negative electrode during manufacture of the electrode assembly, and the second side of the separator with low adhesive strength can face the positive electrode during manufacture of the electrode assembly.

[0125] In one embodiment of the present invention, the difference in adhesive strength on both sides of the separator is due to the difference in surface roughness on both sides of the separator substrate. For example, the separator may exhibit a characteristic in which the adhesive strength is higher on the side of the separator substrate with a high surface roughness value, and lower on the side of the separator substrate with a low surface roughness value. In this case, it may be preferable that the porous coating layer formed on each side of the separator be formed so that the strength / weakness of the adhesive strength on both sides of the separator is not reversed from the high / low characteristics of the surface roughness value of the separator substrate.

[0126] Hereinafter, the composition of the porous coating layer will be exemplarily described. However, the composition of the porous coating layer is not limited thereto.

[0127] 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.

[0128] 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.

[0129] 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 size and size distribution of the particles. Through this structure, the resistance to metallic foreign substances present in the electrode is increased, and at the same time, shrinkage of the porous polyolefin substrate is suppressed, thereby enhancing the safety of the electrochemical device.

[0130] In one embodiment of the present invention, the porous coating layer includes a plurality of nodes including the inorganic particles and a binder polymer covering at least a portion of the surface of the inorganic particles, and one or more filaments formed in a thread 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.

[0131] 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.

[0132] 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.

[0133] In one embodiment of the present invention, the binder polymer may include, for example, a polyvinylidene fluoride-based resin (PVdF-based resin). In one embodiment of the present invention, the PVdF-based resin may include at least one of a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer of 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.

[0134] In one embodiment of the present invention, the porous coating layers formed on both sides of the separator may be formed with the same composition. Furthermore, in another embodiment of the present invention, the porous coating layers may be formed with different compositions to further improve the adhesive strength of the two sides of the separator. Specifically, it may be preferable to form the porous coating layers formed on both sides of the separator with the same composition for reasons such as production efficiency and cost reduction, but the present invention is not limited thereto.

[0135] 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.

[0136] In one embodiment of the present invention, the thicknesses of the porous coating layers formed on both sides of the separator may be the same or different. In this case, it may be preferable that the thicknesses of the porous coating layers formed on both sides of the separator be the same so that the surface properties of the separator substrate can have the same effect on the adhesive strength of the separator due to the porous coating layers, but the present invention is not limited thereto.

[0137] In addition, in one embodiment of the present invention, it is advantageous for the separator to be implemented thinly in terms of the energy density of the electrochemical device to which the separator is applied, and for this purpose, it may be preferable for the porous coating layer to be implemented thinly, for example, with a thickness of 0.5 to 5 ㎛ or 1.5 to 3 ㎛. In this case, the porous coating layer formed on both sides of the separator substrate having the same thickness may have an advantageous effect in terms of thinning the separator, but the present invention is not limited thereto.

[0138]

[0139] electrode assembly

[0140] 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.

[0141] In one embodiment of the present invention, the separator is characterized in that the adhesive strengths on both sides are different from each other as described above.

[0142] In one embodiment of the present invention, when the adhesive strength of the positive electrode is lower among the positive electrode and the negative electrode, the positive electrode may face the side of the separator with high adhesive strength, and the negative electrode may face the side of the separator with low adhesive strength.

[0143] In another embodiment of the present invention, when the adhesive strength of the negative electrode is lower among the positive electrode and the negative electrode, the negative electrode may face the side of the separator with high adhesive strength, and the positive electrode may face the side of the separator with low adhesive strength.

[0144] Through this, the electrode assembly of the present invention is characterized in that the adhesive strengths of both sides of the separator are provided differently, so that even if the adhesive strengths of the surfaces of the positive and negative electrodes themselves are different, the deviation in the electrode adhesive strength between the separator and the positive and negative electrodes is small.

[0145] In one embodiment of the present invention, the deviation of the electrode adhesion between the separator and each of the anode and cathode according to the following Equation 2 may be 10% or less.

[0146] [Formula 2]

[0147] Deviation of electrode adhesion (%) = │{1-F (x) / F (y) )}│ X 100

[0148] In the above equation 2,

[0149] F (x) is the electrode adhesion between the separator and the anode, and F (y) is the electrode adhesion between the separator and the cathode, or

[0150] F (x) is the electrode adhesion between the separator and the cathode, and F (y) is the electrode adhesion between the separator and the anode.

[0151] In one embodiment of the present invention, the electrode adhesion may be measured by the following method. First, the electrode and separator to be measured for adhesion are sampled with a width of 25 mm, overlapped, and then pressurized under the conditions of 60°C, 6.5 MPa, and 1 s to produce a sample. Next, the peel strength between the separator and the electrode is measured using a UTM device (Instron) under the conditions of 180° and 300 mm / min.

[0152] In one embodiment of the present invention, when a separator using the separator substrate is applied, the deviation in electrode adhesion between the positive and negative electrodes is reduced, thereby improving the bending problem of the electrode, and the safety and processability of the electrochemical device using the same can be improved.

[0153] In one embodiment of the present invention, the ratio of electrode adhesion according to the above formula 2 may be, for example, 10% or less, 8% or less, 6% or less, 5% or less, 4.5% or less, 4% or less, 3% or less, 2% or less, 1% or less, or 0% (no deviation at all).

[0154] Hereinafter, the configuration of the electrode is exemplarily described. However, the present invention is not limited thereto.

[0155] 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.

[0156] 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-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 xNi-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 Co b Mn c M d ) 1-xO2(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.

[0157] In one embodiment of the present invention, the negative electrode active material may be, but is not limited to, 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, or mixtures of two or more thereof.

[0158] In one embodiment of the present invention, the negative electrode may include a Si-based active material as the active material.

[0159] In one embodiment of the present invention, the negative active material may include a silicon (Si)-based compound, and the silicon-based compound may be silicon-based particles.

[0160] In one embodiment of the present invention, the silicon-based particles may be, for example, (M)-SiOx (M=Li, Mg, Ca, Al, or Ti, 0≤x<2). The (M)-SiOx may include a Si phase, a SiO2 phase, a metal oxide phase, a metal silicate phase, or a mixed phase of two or more thereof, but the present invention is not limited thereto.

[0161] In one embodiment of the present invention, the negative active material may be composed only of Si particles.

[0162]

[0163] electrochemical devices

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168]

[0169] 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.

[0170]

[0171] [Manufacture of membrane substrate]

[0172] A porous polymer substrate was manufactured as a membrane substrate of Example 1 and Comparative Example 1 as follows.

[0173] Comparative Example 1

[0174] After mixing polyethylene polymer with a molecular weight of 600,000 (g / mol) and an antioxidant in an extruder, it was melted at a temperature of 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 cooling casting roll was provided on the upper surface of the polymer sheet, and a touch roll was provided at a corresponding position on the lower surface, while cooling was performed (see Fig. 1). Afterwards, the polymer sheet that passed through the cooling casting roll was subjected to MD stretching (stretch ratio 7 times, stretching temperature 115℃) and TD stretching (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. Afterwards, the obtained polymer sheet was heat-set at a temperature of 130℃ to obtain a polymer substrate. The obtained porous polymer substrate had a thickness of 9 μm and a porosity of 45 vol%.

[0175]

[0176] Example 1

[0177] A membrane substrate was obtained in the same manner as in Comparative Example 1, except that cooling was performed in a state where a cooling casting roll was provided on the upper surface of the polymer sheet and no contact roll was provided at the corresponding position on the lower surface (see Fig. 2). The obtained porous polymer substrate had a thickness of 9 μm and a porosity of 45 vol%.

[0178]

[0179] [Manufacturing of membranes]

[0180] Using the porous polymer substrates of Comparative Example 1 and Example 1 manufactured above as a membrane substrate, a porous coating layer was formed on both sides of the membrane substrate using the following method to manufacture a membrane.

[0181] Manufacturing of porous coating layers

[0182] A slurry for inorganic coating was prepared by mixing PVDF-HFP binder (Mw 500,000 g / mol, HFP 15 wt%) and inorganic particles in a weight ratio of 80:20 in an appropriate solvent. The slurry for inorganic coating prepared above was applied to the entire surface of the porous substrate by 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.

[0183] In this way, a separation membrane with a total thickness of 15 ㎛ was manufactured.

[0184]

[0185] [Manufacturing of electrode assembly]

[0186] 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.

[0187] Manufacturing of cathode

[0188] A composition for forming a negative electrode was prepared by mixing Si particles (100% Si) as a negative electrode active material, SBR as a binder polymer, and CNT as a conductive material in a weight ratio of 80:10:10 in distilled water as a solvent.

[0189] 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 8.5 mAh / cm 2 It was manufactured to be.

[0190]

[0191] Manufacturing of anodes

[0192] NCMA(Li[Ni) as a cathode active material in NMP as a solvent 0.86 Co 0.06 Mn 0.07 Al 0.01 ]O2), PVDF as a binder polymer, and CNT as a conductive material were mixed in a weight ratio of 97:1:2 to prepare a composition for forming an anode.

[0193] 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 4.5 mAh / cm 2 It was manufactured to be.

[0194]

[0195] Assembly of the electrode assembly

[0196] An electrode assembly was obtained by placing the positive electrode on one side and the negative electrode on the other side with each of the separators prepared above interposed therebetween, and then rolling and drying under the conditions of 70°C, 9 MPa, and 1 sec.

[0197]

[0198] [Physical property evaluation]

[0199] 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 1 below.

[0200] Table 1 below shows the results of the property evaluation based on the two sides of the separator substrate, designated as side A and side B, respectively. When manufacturing the electrode assembly, the negative electrode was attached to side A and the positive electrode was attached to side B, and the separator-electrode adhesion was also evaluated by attaching the negative electrode to side A and the positive electrode to side B.

[0201]

[0202] Measurement of surface roughness value (Sa) of membrane substrate

[0203] 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).

[0204] Roughness values ​​were measured on both sides of the membrane substrate.

[0205]

[0206] Measurement of the adhesive strength of the separator

[0207] 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.

[0208] The adhesive strength was performed on both sides of the separator.

[0209]

[0210] Measurement of electrode adhesion between the separator and the electrode

[0211] The electrode and separator were overlapped by sampling with a width of 25 mm, and then pressurized under the conditions of 60°C, 6.5 MPa, and 1 s to produce a sample. Thereafter, the peel strength between the separator and the electrode was measured using a UTM device (Instron) under the conditions of 180° and 300 mm / min.

[0212] Electrode adhesion was performed on both the separator and the anode and the separator and the cathode.

[0213]

[0214] After measuring the physical properties as described above, the ratio of the adhesive strength on both sides of the separator and the deviation of the membrane-electrode adhesive strength were calculated according to the following equation and are shown together in Table 1 below.

[0215] [Formula 1]

[0216] Adhesive strength ratio (%) = [(Adhesive strength of the first side / Adhesive strength of the second side) X 100]

[0217] At this time, the first side represents the side with high adhesive strength, and the second side represents the side with low adhesive strength.

[0218] [Formula 2]

[0219] Deviation of electrode adhesion (%) = │{1-F (x) / F (y) )}│ X 100

[0220] At this time, F (x) is the electrode adhesion between the separator and the cathode, F (y) The electrode adhesion between the silver separator and the anode was input.

[0221]

[0222] Example 1 Comparative Example 1 Membrane substrate Surface roughness value (Sa) 37.1 nm 34.2 nm Surface roughness value (Sa) 78.4 nm 36.5 nm Membrane Adhesive strength (gf / 15 mm) 5552 Adhesive strength (gf / 15 mm) 9854 Ratio of adhesive strength 178.1% 103.8% Electrode assembly Adhesive strength of side A - negative electrode (gf / 25 mm) 8178 Adhesive strength of side B - positive electrode (gf / 25 mm) 8541 Deviation of electrode adhesive strength 4.7% 90.2%

[0223] As confirmed in Table 1 above, according to one aspect of the present invention, by using a separator substrate having different surface roughness values ​​on both sides, it was confirmed that the adhesive strengths on both sides of the separator are different from each other, and through this, the difference in adhesive strength between the positive and negative electrodes can be drastically reduced.

[0224] [Explanation of symbols]

[0225] 1 - Extrusion section

[0226] 2 - Cooling section

[0227] 200 - T-die

[0228] 201 - Casting Roll

[0229] 202 - Touch Roll

[0230] 203 - Guide Roll

Claims

1. A membrane substrate characterized by being a porous polymer substrate having different surface roughnesses on both sides.

2. In claim 1, A membrane substrate characterized in that the surface roughness values ​​(Sa) on both sides of the porous polymer substrate are different from each other.

3. In claim 1, A membrane substrate characterized in that the surface roughness value (Sa) of one side of the porous polymer substrate is 50 nm or less, and the surface roughness value (Sa) of the other side is greater than 50 nm.

4. A membrane substrate according to claim 1; and A separator characterized by comprising a porous coating layer formed on each of both sides of the separator substrate and containing inorganic particles and a binder polymer.

5. In claim 4, The above separator has different adhesive strengths on both sides, When the side with the higher adhesive strength is called the first side, and the side with the lower adhesive strength is called the second side, A separator characterized in that the ratio of the adhesive strength of the first side and the second side according to the following formula 1 is 150% or more: [Formula 1] Adhesive strength ratio (%) = [(Adhesive strength of the first side / Adhesive strength of the second side) X 100] In the above equation 1, The above adhesive strength represents the adhesive strength between the separator substrate and the porous coating layer.

6. In claim 4, A separator characterized in that the adhesive strength of both sides of the separator is 30 gf / 15 mm or more.

7. In claim 6, The adhesive strength of one side of the above separator is 80 gf / 15 mm or less, and the adhesive strength of the other side is more than 80 gf / 15 mm, A separator, wherein the above adhesive strength represents the adhesive strength between the separator substrate and the porous coating layer.

8. A separator according to any one of claims 4 to 6, An electrode assembly characterized by including a positive electrode and a negative electrode formed on each side of the separator.

9. In claim 8, The adhesive strengths of both sides of the above separator are different from each other, An electrode assembly characterized in that the positive electrode faces the surface having high adhesive strength and the negative electrode faces the surface having low adhesive strength.

10. In claim 8, An electrode assembly characterized in that the deviation of the electrode adhesion between the separator and each of the anode and cathode according to the following formula 2 is 10% or less: [Formula 2] Deviation of electrode adhesion (%) = │{1-F (x) / F (y) )}│ X 100 In the above equation 2, F (x) is the electrode adhesion between the separator and the anode, and F (y) is the electrode adhesion between the separator and the cathode, or F (x) is the electrode adhesion between the separator and the cathode, and F (y) is the electrode adhesion between the separator and the anode.

11. In claim 8, An electrode assembly characterized in that the above negative electrode includes a Si-based active material as an active material.

12. An electrochemical device characterized in that the electrode assembly according to claim 8 is housed in a case. 13.S1) A step of extruding a polymer slurry to obtain a high-spray sheet; and S2) A method for manufacturing a membrane substrate, comprising the step of positioning the obtained polymer sheet on a casting roll and cooling it; A method for manufacturing a membrane substrate, characterized in that in the above step S2, the polymer sheet is cooled in a state in which there is no touch roll on the opposite side of the side facing the casting roll.

Images