Composite separator and secondary battery using the same

Abstract

The present disclosure relates to a composite separator having an adhesive layer and a secondary battery including the same. In the composite separator according to the present invention, the adhesive layers contain a particulate organic binder having a glass transition temperature of 60-80 DEG C, the adhesive layers do not adhere to each other when the adhesive layers are brought into contact with each other, pressurized at a pressure of 1.7 MPa at 50 DEG C for 2 hours and then peeled off at a speed of 300 mm / min for 180 degrees, and the adhesive force to a positive electrode is 5 gf / cm or more. According to the composite diaphragm disclosed by the invention, the electrode adhesion force is excellent, and the adhesion phenomenon occurring during winding can be improved.

Description

Technical Field

[0001] The present disclosure relates to a composite separator and a secondary battery including the composite separator. Background Art

[0002] In the case of a separator made of an existing porous substrate or a highly heat-resistant separator having a porous ceramic layer (or an inorganic particle layer) on one or both surfaces of the porous substrate, since the adhesiveness to the electrode is insufficient, the separator and the electrode are separated during the cell assembly process, resulting in frequent twisting, deformation, etc. of the electrode assembly. In particular, when the adhesiveness of the separator having the porous ceramic layer to the electrode is insufficient, a misalignment problem occurs between the electrode and the separator inside the jelly roll during cell stacking.

[0003] When driving a stack cell battery with misalignment as described above, local resistance occurs due to the misalignment, or a short circuit occurs between the electrodes due to physical damage caused by continuous use, resulting in safety problems such as fire.

[0004] Moreover, in recent years, in order to be applied to electric vehicles, etc., the secondary battery has been made high-capacity and large-sized. Therefore, a separator having a porous ceramic layer (or an inorganic particle layer) formed on one or both surfaces of the porous substrate (Ceramic Coated Separator, CCS) is used as an automotive battery for thick, high-capacity, and high-heat-resistant batteries. Therefore, it is particularly important to solve the above problems.

[0005] One method for improving the adhesiveness between the separator and the electrode is to provide a separator having an adhesive layer formed on the upper part of the separator by coating a solution composed of an adhesive organic substance on the separator surface and drying it. However, due to the adhesive organic substance layer, the gas permeability deteriorates and it is difficult to thin-filmize, and the electrode adhesiveness is still poor.

[0006] Therefore, when winding the separator, there is still an urgent problem to be solved, that is, the adhesion phenomenon in which the adhesive organic substance layer frequently transfers to the opposite side and detaches, and various problems including this problem lead to a decrease in the ion conductivity of the separator or / and a thickness deviation when aligning the electrode assembly, hindering the battery performance, etc.

[0007]

Prior Art Documents

[0008]

Patent Documents

[0009] (Patent Document 1): Japanese Patent Gazette No. 4414165 (Publication Date: Mar. 03, 2005) Summary of the Invention

[0010] Technical Problem

[0011] According to one aspect of the present disclosure, there is provided a composite separator having a bonding layer containing a particulate organic binder with specific physical properties formed on one or both sides of a porous separator, thereby providing a composite separator having excellent electrode adhesiveness and improved adhesion phenomenon occurring during winding of the separator. The porous separator may be a porous separator composed of a porous substrate or a porous separator having a porous substrate and a porous ceramic layer formed on one or both sides of the porous substrate.

[0012] Moreover, it is an object to provide a composite separator whose adhesive force does not decrease when the wound composite separator is unwound and reused as a separator, can maintain the initial adhesive force, and does not cause adhesion, and has excellent heat resistance.

[0013] Moreover, it is an object to provide a composite separator that does not cause adhesion between the bonding layers of the wound rollers, between the bonding layer and the ceramic layer, or between the bonding layer and the porous substrate not only at room temperature of about 25°C but also during storage at a high temperature of 50 to 70°C during the transfer and storage of the wound separator, and has excellent anti-adhesion properties.

[0014] Moreover, it is known that the separator of the present disclosure can solve the above-mentioned existing problems when the bonding layers are joined to each other, pressed at a pressure of 1.7 MPa at 50°C for 2 hours, and then peeled at a speed of 300 mm / min (mm / min) by 180 degrees without adhesion, and thus it is an object to provide a separator that satisfies this.

[0015] Moreover, it is an object to provide a composite separator having uniform lithium ion conductivity over the entire area of the separator.

[0016] The composite separator of the present disclosure and a secondary battery including the same can be widely applied to electric vehicles, battery charging stations, and other green technology fields such as solar power generation and wind power generation that use batteries.

[0017] Moreover, the composite separator of the present disclosure and a secondary battery including the same can be used for eco-friendly electric vehicles (EVs), hybrid vehicles, etc. that prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0018] Technical Solution

[0019] The inventors of the present disclosure have conducted research to provide a separator that has excellent adhesion to the counter electrode, does not adhere during storage and transfer after being wound around a roller, and can maintain good alignment during battery assembly. As a result, it has been found that all of the above objects can be achieved by including a particulate organic binder and having an adhesive force to the positive electrode within a specific range, and not adhering under specific conditions when evaluating the adhesive force between the adhesive layers.

[0020] One aspect of the present disclosure provides a composite separator, which is a composite separator including an adhesive layer on the outermost layer of at least one side of a porous separator. The adhesive layer includes a particulate organic binder, and when the adhesive layers are brought into contact with each other and pressed at a pressure of 1.7 MPa at 50 °C for 2 hours and then peeled 180 degrees at a speed of 300 mm / min, no adhesion occurs between the adhesive layers, and the adhesive force to the positive electrode is 5 gf / cm or more.

[0021] As one aspect, the content of the particulate organic binder in the adhesive layer may be 0.1 to 0.5 g / m 2 , but is not limited thereto.

[0022] As one aspect, the average particle diameter of the particulate organic binder may be 400 to 600 nm, but is not limited thereto.

[0023] As one aspect, the porous separator may be a porous substrate, or the porous separator may have a porous ceramic layer containing inorganic particles formed on one or both sides of the porous substrate, but is not limited thereto.

[0024] As one aspect, the particulate organic binder may be a core-shell particulate organic binder. In the core-shell particulate organic binder, the glass transition temperature of the entire core-shell particle measured with respect to the entire core-shell particle may be higher than the glass transition temperature of the core.

[0025] As one aspect, the glass transition temperature of the core of the core-shell particulate organic binder may be 50 to 75 °C, and the glass transition temperature of the entire particle of the core-shell particulate organic binder may be 60 to 80 °C, and the glass transition temperature of the entire core-shell particle is higher than the glass transition temperature of the core.

[0026] As one aspect, the core-shell particulate organic binder is an acrylic organic particle, and the shell may include a structure derived from an aromatic vinyl monomer.

[0027] As one aspect, the composite separator may be obtained by cutting the electrodes into a width of 4 cm and a length of 6 cm, cross-stacking (Stacking) 4 cut positive electrodes and 4 cut negative electrodes on the surface of the composite separator, and then at a temperature of 80 °C in an atmosphere of 10 kgf / cm 2A composite separator in which the electrodes do not detach when unfolded 30 seconds after bonding.

[0028] As one aspect, the average particle size of the inorganic particles in the porous ceramic layer can be 50 nm to 2 µm, but is not limited thereto.

[0029] As one aspect, the inorganic particles in the porous ceramic layer may include: first inorganic particles having an average particle size of 50 to 500 nm; and second inorganic particles having an average particle size of 500 nm to 2000 nm, but are not limited thereto.

[0030] As one aspect, in the porous ceramic layer, the inorganic particles may be connected by an adhesive, and air holes are formed between the inorganic particles.

[0031] As one aspect, the porous substrate may be a polyolefin-based porous film, but is not limited thereto.

[0032] As one aspect, the longitudinal and transverse thermal shrinkage rates of the composite separator at 150 °C may both be 3% or less.

[0033] Another aspect of the present disclosure provides a lithium secondary battery including the composite separator of the above aspect.

[0034] As one aspect, when performing a cycle evaluation of measuring the discharge capacity after charging and discharging the lithium secondary battery 300 times at a discharge rate of 1C to measure the degree of reduction compared to the initial capacity, the discharge capacity ratio calculated by the following formula may be 90% or more.

[0035] Discharge capacity ratio = (measured capacity of the battery after 300 cycles) / initial battery capacity.

[0036] Another aspect of the present disclosure provides a composite separator which is a composite separator including an adhesive layer on the outermost layer of at least one side of a porous separator, wherein:

[0037] The adhesive layer contains a particulate organic adhesive,

[0038] The content of the particulate organic adhesive in the adhesive layer is 0.1 g / m 2 to 0.5 g / m 2 ,

[0039] The average particle size of the particulate organic adhesive is 400 to 600 nm,

[0040] The particulate organic adhesive contains a core-shell particulate organic adhesive,

[0041] The glass transition temperature of the entire core-shell particle of the core-shell particulate organic adhesive is higher than the glass transition temperature of the core.

[0042] Effect of the Invention

[0043] The composite separator according to an invention of the present disclosure has excellent adhesion to the electrode, and can improve the adhesion phenomenon occurring during winding.

[0044] Another aspect of the present disclosure can provide a composite separator that does not exhibit peeling of the coating due to adhesion even when exposed to high temperatures during the storage and transfer of the wound separator.

[0045] Specifically, a composite separator excellent in anti-adhesion can be provided, which does not adhere between the adhesive layers of the wound rollers, between the adhesive layer and the ceramic layer, or between the adhesive layer and the porous substrate even when stored at a high temperature of 50 to 70 °C, not only at room temperature of about 25 °C, during the transfer and storage of the wound separator.

[0046] Moreover, a composite separator that does not adhere when the adhesive layers of the separator of the present disclosure are brought into contact with each other and pressed at a pressure of 1.7 MPa at 50 °C for 2 hours and then peeled 180 degrees at a speed of 300 mm / min can be provided.

[0047] Moreover, a composite separator with less heat shrinkage and excellent battery safety can be provided.

[0048] Moreover, a composite separator can be provided that has little change in adhesion when rewound and used after winding, and thus has excellent adhesion to the battery.

[0049] Moreover, a battery can be provided that is well aligned between the electrode and the separator during cell stacking, can suppress misalignment during the process, and has uniform thickness deviation.

[0050] Moreover, a battery can be provided that can provide uniform lithium ion conductivity over the entire area of the separator, and the capacity retention rate after 300 cycles is maintained at 90% or more or 95% or more compared to the initial capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a cross-sectional view of a composite separator according to one aspect of the present disclosure;

[0052] Figure 2 is a cross-sectional view of a composite separator according to one aspect of the present disclosure;

[0053] Figure 3 is an SEM photograph that is "passed" in the adhesion evaluation of the present disclosure;

[0054] Figure 4 is an SEM photograph that is "failed" in the adhesion evaluation of the present disclosure.

[0055] Description of Reference Numerals

[0056] 100: Composite separator

[0057] 110: Porous separator

[0058] 120: Adhesive layer Detailed Description of the Invention

[0059] Hereinafter, the present disclosure will be described in detail. However, this is only an example, and the present disclosure is not limited to the specific embodiments of the exemplary description.

[0060] Moreover, unless otherwise defined, the meanings of all technical terms and scientific terms are the same as those generally understood by those of ordinary skill in the technical field to which the present disclosure pertains. The terms used in the description of the present disclosure are only for effectively describing specific examples, and are not intended to limit the present disclosure.

[0061] Moreover, the singular forms used in the specification and the appended claims are also intended to include the plural forms, unless the context specifically indicates otherwise.

[0062] Moreover, when it is described that a certain part "includes" a certain component, this does not mean excluding other components, but may also include other components, unless there is a particularly contrary statement.

[0063] Moreover, unless otherwise defined, when it is described that a certain layer or component is "on" another layer or component, this includes not only the case where a certain layer or component is in contact with another layer or component, but also the case where there are other layers or components between the two layers or two components.

[0064] Moreover, when referring to manufacturing and material allowable tolerances inherent in the meaning described, terms such as "about" and "substantially" are used to represent a value that is close to or equal to that value, in order to prevent malicious infringers from misusing the disclosure of precise or absolute values described to assist in understanding the present disclosure.

[0065] In the present disclosure, "average particle size" refers to "D50", and "D50" is the cumulative fraction based on volume, which refers to the particle size equivalent to 50% of the inorganic particles and particulate organic binders. The average particle size can be derived from the particle size distribution results obtained by collecting samples of the inorganic particles and / or particulate organic binders to be measured according to the ISO 13320-1 standard and using the S3500 of MICROTRAC company for analysis.

[0066] In the present disclosure, the "glass-transition temperature (Tg)" refers to the temperature range at which the glass transition occurs, and is a value measured using a dilatometer or a differential scanning calorimeter (DSC).

[0067] In the present disclosure, the "composite separator" refers to a form having an adhesive layer formed on one or both sides of a porous separator. The "porous separator" may be in the form of a porous substrate itself, or may be a porous ceramic layer (a porous inorganic particle layer may also be used in the same meaning) formed on one or both sides of a porous substrate. The porous ceramic layer may be a layer in which inorganic particles are connected and fixed by an adhesive to form pores between the inorganic particles.

[0068] In the present disclosure, "adhesion" is measured by bringing the adhesive layers of two composite separators into contact with each other. Herein, the meaning of "no adhesion" includes the case where the coating does not peel off when randomly selected 5 regions of 50×50 μm are observed using a scanning electron microscope (SEM) and the case where the peeling occurs less than 2% of the coating area. That is, when the adhesive layer is formed only on one side of the composite separator, two composite separators are prepared, and after laminating them such that the adhesive layers of the composite separators face each other, they are pressed at 1.7 MPa for 2 hours at 50°C and then peeled 180 degrees at a speed of 300 mm / min to evaluate the adhesion. Moreover, when the adhesive layer is formed on both sides of the composite separator, two composite separators are prepared, and after selecting any one of the two sides and laminating them such that the adhesive layers face each other, they are pressed at 1.7 MPa for 2 hours at 50°C and then peeled 180 degrees at a speed of 300 mm / min to evaluate the adhesion. Herein, the compositions of the adhesive layers formed on the two sides may be the same.

[0069] Hereinafter, one aspect of the present disclosure will be described.

[0070] One aspect of the present disclosure is as Figure 1 and Figure 2As shown, a composite separator 100 can be provided, which includes an adhesive layer 120 formed on one or both sides of a porous separator 110. The porous separator 110 includes a porous substrate or a porous ceramic layer formed on one or both sides of the porous substrate (a porous inorganic particle layer can also be used with the same meaning). In the porous ceramic layer, inorganic particles are connected and fixed by an adhesive, and pores are formed between the inorganic particles. The adhesive layer contains a particulate organic adhesive. When the adhesive layers are brought into contact with each other and pressed at a pressure of 1.7 MPa at 50°C for 2 hours and then peeled at a speed of 300 mm / min by 180 degrees, no adhesion occurs between the adhesive layers.

[0071] Moreover, the composite separator can provide a composite separator in which the adhesive force of the adhesive layer to the positive electrode is 5 gf / cm or more.

[0072] One aspect of the present disclosure can provide a composite separator, which is a composite separator including an adhesive layer on the outermost layer of at least one side of a porous separator. The adhesive layer contains a particulate organic adhesive. When the adhesive layers are brought into contact with each other and pressed at a pressure of 1.7 MPa at 50°C for 2 hours and then peeled at 300 mm / min by 180 degrees, no adhesion occurs between the adhesive layers. The adhesive force of the adhesive layer to the positive electrode is 5 gf / cm or more. By simultaneously satisfying the physical properties, it is possible to prevent adhesion from occurring during the process of winding the composite separator around a roller for storage and transfer. Moreover, the effects of well maintaining alignment during the assembly of a secondary battery and improving the capacity retention rate of the battery can be achieved simultaneously.

[0073] As one aspect, the adhesive layer can be an adhesive layer having only the particulate organic adhesive.

[0074] As one aspect, the adhesive layer can be laminated opposite to the negative electrode and the positive electrode of a lithium secondary battery. That is, it can be an adhesive layer that exhibits adhesiveness when laminated on the negative electrode or the positive electrode during the assembly of a lithium secondary battery.

[0075] As one aspect, the areas of the porous substrate, the porous ceramic layer, and the adhesive layer can be substantially the same or different. For example, the porous ceramic layer can be formed on the entire surface of the porous substrate with the same area, or can be formed on the porous substrate with an area smaller than that of the porous substrate. Moreover, the adhesive layer can be formed on the entire surface with the same area as the porous substrate or the porous ceramic layer, or can be formed with an area smaller than that of the porous substrate or the porous ceramic layer.

[0076] For example, regarding the formation area of the adhesive layer, it can be formed to an area of 10% to 100% of the total area of the porous ceramic layer or the porous substrate, and can have an area of 99% or less, 95% or less, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or more, 20% or more, 50% or more, or an area between the above values. For example, it can be formed to an area of 10 to 90% or 20 to 80%, but there is no limitation as long as the object of the present disclosure can be achieved. Preferably, it can be formed in an area of 80% to 100%.

[0077] As one aspect, the porous ceramic layer can be formed to a thickness of 1 to 50%, 1 to 45%, 1 to 40%, 1 to 35% relative to the thickness of the entire composite separator. As an example, the thickness can be 5 µm or less, 4 µm or less, 3 µm or less, 2 µm or less, 1 µm or less, or 1 to 5 µm, or can be any range between the above values, and is not limited thereto.

[0078] As one aspect, the coating amount of the adhesive layer can be 0.05 to 1.0 g / m 2 、0.1 to 0.8 g / m 2 、0.1 to 0.5 g / m 2 or 0.1 to 0.3 g / m 2 , or can be any range between the above values, and is not limited thereto.

[0079] As one aspect, the composite separator of the present disclosure is a composite separator in which the adhesive layers are connected to each other and after being pressed at a pressure of 1.7 MPa at 50 °C for 2 hours and then peeled 180 degrees at a speed of 300 mm / min, no adhesion occurs between the adhesive layers. In view of the discovery that when evaluating whether adhesion occurs between the adhesive layers by the above method and no adhesion occurs, adhesion can be prevented even under severe conditions during the storage and transfer after winding the composite separator, the invention of the present disclosure has been completed. For example, it can be confirmed that no adhesion occurs even when the wound roll is stored at 50 to 70 °C for seven days. Whether the above adhesion can be evaluated by the method described in the measurement method described below.

[0080] As one aspect, the adhesive layer can be an adhesive layer having an adhesive force to the positive electrode of 5 gf / cm or more, 6 gf / cm or more, 7 gf / cm or more, 8 gf / cm or more, 9 gf / cm or more, 10 gf / cm or more, 20 gf / cm or less, or any range between the above values. For example, it can be an adhesive layer of 5 to 20 gf / cm, 5 to 15 gf / cm, 5 to 12 gf / cm, or 5.2 to 10.2 gf / cm. Although the higher the adhesive force, the better, in terms of the angle that is easy to align during battery assembly while preventing adhesion after winding, it can be an adhesive layer having an adhesive force to the positive electrode of 5 to 15 gf / cm. When the above range is satisfied, it is more beneficial to provide an effect of not causing adhesion not only at room temperature but also at 50 to 70 °C.

[0081] The positive electrode is not limited, but can be formed from the following positive electrode paste, that is, the positive electrode paste is prepared by adding lithium cobalt composite oxide (LiCoO2), carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent.

[0082] As one aspect, the adhesive layer can be an adhesive layer having an adhesive force to the negative electrode of 2 gf / cm or more, 3 gf / cm or more, 4 gf / cm or more, 5 gf / cm or more, 6 gf / cm or more, 7 gf / cm or more, 15 gf / cm or less, or any range between the above values, and is not limited thereto.

[0083] The negative electrode is not limited, but can be formed from the following negative electrode paste, that is, the negative electrode paste is prepared by adding artificial graphite, acrylic latex as a binder, and carboxymethyl cellulose as a thickener to water as a solvent.

[0084] The composite separator according to one aspect of the present disclosure can be a composite separator having a thermal shrinkage rate of 3% or less, 2% or less, 1.5% or less, 1% or less, or 0.5% or less after being placed at 150 °C for 1 hour. With the above low thermal shrinkage rate, it is possible to prevent ignition or rupture caused by abnormal phenomena such as a sharp temperature rise in the lithium secondary battery.

[0085] Moreover, a lithium secondary battery including a composite separator according to an aspect of the present disclosure can provide a battery having a discharge capacity ratio of 90% or more, 95% or more, or 97% or more when a cycle evaluation is performed, where the cycle evaluation is based on an initial cell capacity of 1800 mAh, and after charging and discharging the lithium secondary battery 300 times at a discharge rate of 1C, the discharge capacity is measured to determine the degree of reduction compared to the initial capacity. For example, a battery with a ratio of 90 to 99% or 92 to 97% can be provided.

[0086] Discharge capacity ratio = (measured capacity of the battery after 300 cycles) / initial battery capacity

[0087] Moreover, a composite separator according to an aspect of the present disclosure can provide a composite separator in which the electrodes are cut into a width of 4 cm and a length of 6 cm, 4 cut positive electrodes and 4 cut negative electrodes are cross-stacked on the surface of the composite separator, and then, when vertically lifted after heating and pressing at 80 °C in a temperature atmosphere of 10 kgf / cm 2 for 30 seconds, the number of electrodes that do not substantially fall off.

[0088] Moreover, the present disclosure can provide a composite separator in which the composite separator having the porous separator and the adhesive layer is wound for more than 1000 m and then stored in an oven at 50 °C and 70 °C for 12 hours respectively, and then when the wound composite separator is unwound, there is no surface adhesion between the facing adhesive layers and the ceramic layer does not peel off.

[0089] Exemplary descriptions of the respective components of the composite separator according to an aspect of the present disclosure are given below.

[0090] [Porous separator]

[0091] As an aspect of the present disclosure, the porous separator may be composed of a porous substrate, or a porous ceramic layer containing inorganic particles is formed on one or both sides of the porous substrate.

[0092] The porous substrate may be a film, sheet, etc. composed of a polyolefin-based resin, and as long as it is a microporous membrane used in the technical field, it can be used without limitation. In addition, as long as it is a non-woven fabric, paper, and their microporous membranes having pores inside or on the surface including inorganic particles and other porous membranes applicable to batteries, there is no particular limitation.

[0093] The polyolefin-based resin may be a single polyolefin-based resin or a mixture of polyolefin-based resins. For example, it may be any one or a mixture of two or more selected from polyethylene, polypropylene, and their copolymers. Moreover, the porous substrate may be made of the polyolefin-based resin alone, or may be made mainly of the polyolefin-based resin and further contain inorganic particles or organic particles. Moreover, the porous substrate may be used in a laminated form. For example, it may be composed of multiple layers of polyolefin-based resin. When the porous substrate is composed of multiple layers, inorganic particles and organic particles may be included in the polyolefin-based resin in any one layer or all layers.

[0094] The thickness of the porous substrate is not particularly limited, but may be 5 to 30 µm. The porous substrate may be a porous substrate mainly made by stretching, but is not limited thereto.

[0095] The porous ceramic layer may be such that inorganic particles are connected by an adhesive to form pores between the inorganic particles.

[0096] Based on 100 parts by weight of the inorganic particles, 0.1 to 20 parts by weight, 0.1 to 10 parts by weight, or 1 to 5 parts by weight of the adhesive may be included. As long as it is an adhesive commonly used in the art, it can be used without limitation. As described above, compared with the inorganic particles, a significantly small amount of the adhesive is used, so that as a structure in which the inorganic particles are connected to each other, pores are formed by the surface contact of the inorganic particles, and thus porosity can be ensured.

[0097] Examples of the adhesive that can be used include various water-soluble and water-insoluble resins and their mixtures such as polymethyl methacrylate and its copolymers or acrylic resins such as polyacrylamide, ester resins, polyamides, polyimides, fluorine-based resins, polyacrylonitrile, polyethylene oxide, cellulose-based resins, polyvinyl alcohol-based resins, polyvinylpyrrolidone, ethylene-vinyl acetate copolymers, and cyanoethyl pullulan. It can be dissolved in a solvent or used in particulate form, so there is no limitation thereto.

[0098] Regarding the inorganic particles of the porous ceramic layer, any inorganic particles commonly used in the art can be used without limitation. For example, it can be any one or more than two inorganic particles selected from alumina, boehmite, aluminum hydroxide, titanium oxide, barium titanium oxide, magnesium oxide, magnesium hydroxide, silica, clay, glass powder, etc., but is not limited thereto.

[0099] Based on 100% by weight of the total weight of the porous ceramic layer, the inorganic particles may be contained in an amount of 70% by weight or more and 99.5% by weight or less. For example, it may be contained in an amount of 70% by weight or more and 99% by weight or less, 70% by weight or more and 98% by weight or less, 80% by weight or more and 98% by weight or less, 85% by weight or more and 98% by weight or less, or 90% by weight or more and 98% by weight or less, but is not limited thereto. When the porous ceramic layer contains the above-mentioned content of the binder and inorganic particles, the pores of the porous ceramic layer can be ensured, and the adhesiveness between the porous substrate and the porous ceramic layer or between the inorganic particles can be ensured.

[0100] The average particle size (D50) of the inorganic particles is not limited. For example, it can be 50 nm to 2 µm or 50 to 1000 nm.

[0101] As an aspect, two or more inorganic particles with different average particle sizes can be mixed and used as the inorganic particles. For example, when taking the above two inorganic particles with different average particle sizes as an example for illustration, the first inorganic particle can be 50 to 500 nm or 100 to 400 nm, and the second inorganic particle can be 500 nm to 2000 nm, or can be 600 to 1000 nm.

[0102] As an aspect, the porous ceramic layer can have a thickness of 5 µm or less, 4 µm or less, 3 µm or less, 2 µm or less, 1 µm or less, or 1 to 5 µm, or can be any range between the above values, and is not limited thereto.

[0103] [Adhesive layer]

[0104] The adhesive layer of the present disclosure can be formed on the outermost layer of at least one side of the porous separator.

[0105] When the adhesive layer of the present disclosure contains a particulate organic binder and satisfies the conditions that the adhesive layers are joined to each other, no adhesion occurs between the adhesive layers when peeled at a speed of 300 mm / min at 180 degrees under a pressure of 1.7 MPa for 2 hours at 50 °C, and the adhesive force of the adhesive layer to the positive electrode is 5 gf / cm or more, the object of the present disclosure can be more easily achieved. The non-occurrence of adhesion means non-occurrence of adhesion in the evaluation method described in the <Adhesion Evaluation Method> in the following physical property evaluation method.

[0106] The composite separator having an adhesive layer according to the present disclosure can achieve the effect that no adhesion occurs between the adhesive layers even at high temperatures, no misalignment occurs during battery assembly, and at the same time, it can endow the battery with very excellent characteristics of capacity retention rate.

[0107] The reason for the particulate organic binder to exhibit adhesion characteristics is not limited, and the particulate organic binder can be used without limitation as long as it satisfies the adhesive force and adhesion characteristics. For example, it can be a core-shell particulate organic binder, and the glass transition temperature of the entire core-shell particle can be higher than that of the core part. Moreover, the size or particle distribution of the core-shell particles, the degree of crosslinking, the type or content of comonomers, etc. can affect the above physical properties, and as long as the above adhesion characteristics are exhibited under the above conditions, there is no particular limitation.

[0108] The core-shell particulate organic binder refers to a binder composed of a particulate core and a shell surrounding its surface.

[0109] As an example, the glass transition temperature measured for the entire core-shell particle of the core-shell particulate organic binder can be 60 °C or higher, 80 °C or lower, or any value between the above values. For example, the glass transition temperature can be 60 to 80 °C, 65 to 80 °C, 69 to 78 °C, or 70 to 78 °C. The core-shell particles can also be acrylic particles, or can be particulate binders prepared by adjusting the degree of crosslinking to a specific range with the above glass transition temperature, or can be particulate acrylic organic binders prepared by modifying the surface of organic binder particles with a specific modifier, etc., but there is no limitation as long as it is an organic particulate binder that satisfies the physical properties of the present disclosure.

[0110] As an example, the glass transition temperature of the core of the core-shell particulate organic binder may be 50 °C or higher, 75 °C or lower, or any value between the above values. For example, it may be 50 to 75 °C, 55 to 70 °C, 60 to 70 °C, 62 to 70 °C, 65 to 70 °C, and the glass transition temperature of the entire core-shell particulate organic binder is 60 to 80 °C. It may be an acrylic particulate organic binder with a higher glass transition temperature range compared to the core. As described above, by making the glass transition temperature of the entire particle including the core-shell higher than that of the core, an effect can be provided that can exhibit the desired anti-blocking property and adhesiveness and has an excellent battery capacity retention rate.

[0111] As one aspect, the content of the core and the shell of the core-shell particulate organic binder may be 60 to 99:40 to 1% by weight, 60 to 90:40 to 10% by weight. Although not limited thereto, in the case of the above range, an effect of more excellent electrode adhesion and anti-blocking property can be provided.

[0112] As one aspect, the core-shell particulate organic binder is a polymer particle that can be prepared by emulsion polymerization or suspension polymerization, and may be a non-crosslinked or crosslinked particle.

[0113] The core-shell particulate organic binder may be an acrylic organic particle, and the shell may include a structure derived from an aromatic vinyl monomer.

[0114] The acrylic organic particle may be composed of an acrylic polymer. As examples of the acrylic polymer, it may be selected from (meth)acrylic C1-C10 alkyl esters; (meth)acrylates; (meth)acrylonitriles such as acrylonitrile and methacrylonitrile; and aromatic vinyl monomers such as styrene, α-methylstyrene, styrenesulfonic acid, butoxystyrene, and vinylnaphthalene; maleimide derivatives such as maleimide and phenylmaleimide; etc. Any one or more of the monomers are polymerized to form a polymer. Not limited thereto, it may be prepared by mixing a variety of monomers to have a glass transition temperature of 60 to 80 °C.

[0115] For example, in the case of core-shell particulate organic binders, the core may be an acrylic copolymer obtained by copolymerizing C1-C10 alkyl (meth)acrylates, (meth)acrylates, and (meth)acrylonitrile, and the glass transition temperature can be lowered by adjusting the content of C1-C10 alkyl (meth)acrylates. The (meth)acrylate means acrylate or methacrylate. Specifically, for example, it may be methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, etc., without being limited thereto. The shell may be an acrylic copolymer obtained by copolymerizing a monomer mixture including aromatic vinyl monomers such as styrene and (meth)acrylates, and the glass transition temperature can be increased by adjusting the content of aromatic vinyl monomers. The (meth)acrylate refers to acrylate or methacrylate.

[0116] As one aspect, when the particulate organic binder is immersed in the electrolyte, the swelling ratio based on the following formula 1 is 300 to 500%, 320 to 490%. Since it is beneficial to achieve the object pursued by the present disclosure within the above range, it is more preferred, but not limited thereto.

[0117] [Formula 1]

[0118] Swelling ratio = W2 / W1 × 100

[0119] The W2 is the weight measured after immersion in the electrolyte, and W1 is the weight measured before immersion in the electrolyte.

[0120] Here, the swelling ratio can be measured according to the measurement method of the following examples. The electrolyte may be a mixture of ethylene carbonate:ethyl methyl carbonate:dimethyl carbonate in a volume ratio of 3:5:2.

[0121] The adhesive layer may be coated with the particulate organic binder at a content of 0.05 to 1.0 g / m 2 , 0.1 to 0.8 g / m 2 , 0.1 to 0.5 g / m 2 , 0.1 to 0.4 g / m 2 or 0.1 to 0.3 g / m 2 , but not limited thereto.

[0122] Regarding the size of the particulate organic binder, the average particle diameter of D50 may be 300 nm or more, 700 nm or less, or a value between the above values. For example, it may be 300 to 700 nm, 400 to 600 nm, 450 to 550 nm, or 450 to 520 nm, and may be a value between the above values. However, when within the above range, clogging of the pores of the porous separator can be prevented, and the electrode adhesion can be more easily exhibited, so it is preferred.

[0123] Although the particulate organic binder has been exemplified, as long as it satisfies the glass transition temperature and does not adhere when evaluated by the method described in the above-mentioned evaluation method of the present disclosure, its type is not limited. For example, in addition to acrylic polymers, fluoropolymers or their copolymers can also be used, so no limitation is made thereto.

[0124] [Method for manufacturing a composite separator]

[0125] Hereinafter, a method for manufacturing the composite separator of the present disclosure will be described.

[0126] The method for manufacturing a composite separator for a secondary battery according to one aspect of the present disclosure includes: a step of coating an aqueous dispersion containing a particulate organic binder on one or both surfaces of a porous separator and drying to form a bonding layer.

[0127] Moreover, the method for manufacturing a composite separator for a secondary battery according to one aspect of the present disclosure includes: a) a step of coating a slurry containing inorganic particles and a binder on one or both surfaces of a porous substrate and drying to form a porous ceramic layer; and b) a step of coating an aqueous dispersion containing a particulate organic binder on one or both surfaces of the ceramic-coated separator having the porous ceramic layer formed thereon and drying to form a bonding layer.

[0128] Each of the above structures is the same as those described above.

[0129] The slurry for forming the porous ceramic layer may be an aqueous slurry using water as a dispersion medium.

[0130] The dispersion for forming the bonding layer may use water as a dispersion medium. The particulate organic binder may be provided in the form of particles dispersed in water by emulsion or suspension polymerization.

[0131] The coating method may employ a conventional method known in the art without limitation. As a non-limiting example, roll coating, spin coating, dip coating, bar coating, die coating, slot coating, inkjet printing, and combinations of these methods may be used.

[0132] The drying step is not particularly limited, but the drying temperature can be 100 °C or lower, for example, it can be 30 to 100 °C or 40 to 100 °C. When drying at the above temperature, the coating can be uniformly dried without affecting the physical properties of the porous substrate to prevent coating defects.

[0133] Moreover, after the drying, a step of winding and storing on a roller and transporting may be included.

[0134] [Lithium secondary battery]

[0135] One aspect of the present disclosure provides a lithium secondary battery including the above-mentioned composite separator for secondary battery. The lithium secondary battery may be made by including the composite separator for secondary battery, a positive electrode, a negative electrode, and a non-aqueous electrolyte according to one aspect of the present invention.

[0136] As one aspect, the lithium secondary battery is made by using a conventional manufacturing method in which a negative electrode, a composite separator, and a positive electrode are assembled and an electrolyte is injected, so no specific description will be given here.

[0137] Here, regarding the positive electrode, the negative electrode, and the non-aqueous electrolyte, those commonly used in lithium secondary batteries can be used without limitation.

[0138] As one aspect, the positive electrode and the negative electrode can be prepared by mixing a solvent in a positive electrode active material and a negative electrode active material, mixing a binder, a conductive material, a dispersing material, etc. as needed, and stirring to prepare a composition, and then coating it on a current collector of a metal material, drying, and rolling.

[0139] Regarding the positive electrode active material, any active material commonly used in the positive electrode of a secondary battery can be used. For example, lithium metal oxide particles containing one or more metals selected from the group consisting of Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B, and combinations thereof can be used.

[0140] Regarding the negative electrode active material, any active material commonly used in the negative electrode of a secondary battery can be used. Preferably, the negative electrode active material of the lithium secondary battery is a material capable of intercalating lithium. As a non-limiting example, the negative electrode active material can be selected from lithium (metallic lithium), soft carbon, hard carbon, graphite, silicon, Sn alloy, Si alloy, Sn oxide, Si oxide, Ti oxide, Ni oxide, Fe oxide (FeO), and lithium titanate oxide (LiTiO2, Li4Ti5O 12 ) and the like, and one or more substances from the group of negative electrode active materials.

[0141] As the conductive material, a normal conductive carbon material can be used without particular limitation.

[0142] The non-aqueous electrolyte contains a lithium salt as an electrolyte and an organic solvent. Any lithium salt that is commonly used in electrolytes for lithium secondary batteries can be used without limitation and can be represented as Li + X - .

[0143] The negative ion of the lithium salt is not particularly limited, and F - , Cl - , Br - , I - , NO 3- , N(CN) 2- , BF 4- , ClO 4- , PF 6- , (CF3)2PF 4- , (CF3)3PF 3- , (CF3)4PF 2- , (CF3)5PF - , (CF3)6P - , CF3SO 3- , CF3CF2SO 3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO 3- , CF3CO 2- , CH3CO 2- , SCN - and any one or more of (CF3CF2SO2)2N - etc.

[0144] As the organic solvent, any one or more mixtures selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, and tetrahydrofuran can be used.

[0145] The non-aqueous electrolyte can be injected into an electrode structure composed of a positive electrode, a negative electrode, and a composite separator interposed between the positive electrode and the negative electrode.

[0146] The external shape of the lithium secondary battery is not particularly limited, but may be selected from a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0147] Although the embodiments of the present invention have been described in detail above, those of ordinary skill in the art to which the present invention pertains can implement the present invention in various ways without departing from the spirit and scope of the present invention defined by the appended claims. Therefore, any changes to the embodiments of the present invention hereafter will not depart from the technology of the present invention.

[0148] The embodiments of the present disclosure will be further described below with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the scope of the appended claims. Various changes and modifications can be made to the examples within the scope and technical concept of the present invention, which will be obvious to those of ordinary skill in the art, and these deformations and modifications naturally also fall within the scope of the appended claims.

[0149] 1. Adhesion to the positive electrode

[0150] After the adhesive layer of the composite separator is laminated facing the surface of the following positive electrode, it is bonded by using a hot press at 80 °C and 20 MPa for 30 seconds. The electrode adhesion is measured by peeling 180° using a UTM device (product name: Instron 3365) of Instron Corporation according to ASTM D 903. When the adhesion of the adhesive layer of the composite separator is too low to be peeled off by the UTM device, it is rated as "unmeasurable".

[0151] Manufacture of the positive electrode: 94% by weight of lithium cobalt composite oxide (LiCoO2) as the positive electrode active material, 3.5% by weight of carbon black as the conductive material, and 2.5% by weight of polyvinylidene fluoride (PVdF) as the binder are added to N-methyl-2-pyrrolidone (NMP) as the solvent to prepare a positive electrode slurry. The prepared slurry is coated on a 30 µm thick aluminum (Al) film and dried at a temperature of 120 °C, and then roll-pressed to manufacture a positive electrode with a thickness of 150 µm.

[0152] 2. Evaluation of electrode adhesiveness

[0153] The electrode is cut into 4 cm wide and 6 cm long, and 4 cut positive electrodes and 4 cut negative electrodes are cross-laminated on the surface of the composite separator, and then bonded at 10 kgf / cm in a temperature atmosphere of 80 °C 2 After bonding for 30 seconds, it is unfolded to evaluate the number of electrodes adhered.

[0154] A: 8 sheets, B: 6 - 7 sheets, C: 4 - 5 sheets, D: less than 4 sheets

[0155] The positive and negative electrodes for evaluation were manufactured in the following manner.

[0156] Manufacture of the positive electrode: 94 wt% of lithium cobalt composite oxide (LiCoO₂) as the positive electrode active material, 3.5 wt% of carbon black as the conductive material, and 2.5 wt% of polyvinylidene fluoride (PVdF) as the binder were added to N-methyl-2-pyrrolidone (NMP) as the solvent to prepare a positive electrode slurry. The prepared slurry was coated on a 30 µm thick aluminum (Al) film and dried at a temperature of 120 °C and then roll-pressed to manufacture a positive electrode with a thickness of 150 µm.

[0157] Manufacture of the negative electrode: 95 wt%, 3 wt%, and 2 wt% of artificial graphite, a binder (acrylic latex with a Tg of -52 °C), and a thickener (CMC carboxymethyl cellulose) were added to water as the solvent to prepare a negative electrode mixture slurry. The prepared slurry was coated on a 20 µm thick copper (Cu) film and dried at 120 °C and roll-pressed to manufacture a negative electrode with a thickness of 150 µm.

[0158] 3. Evaluation of adhesion

[0159] Two specimens were prepared, and it was evaluated whether coating detachment occurred between the adhesive layers when the adhesive layers were joined to each other and pressed at a pressure of 1.7 MPa at 50 °C for 2 hours and then peeled 180 degrees at a speed of 300 mm / min. It was evaluated whether coating detachment occurred in the 50×50 µm area by visual observation and confirmation by SEM.

[0160] Pass: When visually observing and randomly checking 5 areas of 50×50 µm in the entire area of the SEM specimen, there was no coating detachment at all.

[0161] OK: When visually observing, no coating detachment was confirmed. When randomly checking 5 areas of 50×50 µm in the entire area of the SEM specimen, less than 2% coating detachment was confirmed.

[0162] Fail: When visually observing, coating detachment was also observed, or when randomly checking 5 areas of 50×50 µm in the entire area of the SEM specimen, more than 2% coating detachment was confirmed.

[0163] 4. Thermal shrinkage rate

[0164] After placing a 10 cm × 10 cm composite separator at 150 °C for 1 hour, the area reduction rate was measured, and the thermal shrinkage rate was calculated by the following formula.

[0165] Thermal shrinkage rate (%) = ((length before heating - length after heating) / length before heating) × 100

[0166] 5. Discharge capacity ratio relative to the initial battery life

[0167] The pouch cells were assembled in a stacking manner in the same way as the evaluation of the electrode adhesiveness. Before injecting the electrolyte into each of the assembled cells, thermal crimping was performed at 80 °C and 10 kgf / cm 2 for 30 seconds, and an electrolyte solution of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) = 3:5:2 (volume ratio) dissolved with 1 M lithium hexafluorophosphate (LiPF6) was injected to fabricate lithium secondary batteries.

[0168] A cycle evaluation was performed to measure the degree of reduction compared to the initial capacity by measuring the discharge capacity after charging and discharging each of the fabricated cells 300 times at a discharge rate of 1C.

[0169] Discharge capacity ratio = (measured capacity of the battery after 300 cycles) / initial battery capacity (1.8 Ah)

[0170] 6. Method for measuring the average particle size

[0171] The average particle size D50 was measured using a S3500 particle size analyzer from Microtrac according to the ISO 13320-1 standard.

[0172] 7. Method for measuring the glass transition temperature

[0173] Analysis was performed using a differential scanning calorimeter (Differential Scanning Calorimeter, DSC, Mettler Toledo, DSC-822E). The analysis conditions were as follows: a 5 mg sample of the solvent-removed and solidified sample was heated from -50 °C to 200 °C at a scanning rate of 10 °C / min under nitrogen conditions until the sample was completely melted, then cooled at 10 °C / min to solidify it, and then reheated from -50 °C to 200 °C at 10 °C / min to measure the glass transition temperature. The glass transition temperature of the particulate organic binder was measured as follows. For example, the glass transition temperature of the core-shell particulate organic binder was measured as follows. First, the core polymer was synthesized and the glass transition temperature (Tg) of the core was measured. Then, the core-shell particles were prepared and the Tg of the entire particle was measured.

[0174] 8. Weight change rate (swelling ratio) during electrolyte impregnation

[0175] Aqueous dispersion containing organic particles for forming a bonding layer was placed in a Teflon Petri dish and evaporated for one day at 60 °C to form a film. Then, 1 g of the film was impregnated in an electrolyte in which ethylene carbonate:ethyl methyl carbonate:dimethyl carbonate (DMC) were mixed at a volume ratio of 3:5:2, and left at 50 °C for 48 hours. Then, the electrolyte was poured out and the weight of the film was measured to calculate the weight change rate.

[0176] Swelling ratio = W2 / W1 × 100

[0177] W2 is the weight measured after impregnation in the electrolyte, and W1 is the weight measured before impregnation in the electrolyte. The unit is %.

[0178] 9. Average thickness (µm)

[0179] The average thickness of the separator was obtained as follows. After stacking 10 layers of the separator, the thickness was measured at five arbitrary points in the width direction using a thickness gauge from Mitutoyo Corporation, and the sum was obtained. Then, the sum was divided by 5 to obtain the average thickness of the 10 - layer separator, and then divided by 10 to obtain the overall average thickness of a single separator.

[0180] Regarding the average thickness of the porous substrate, only stack 10 layers of the porous substrate, measure the thickness at five arbitrary points in the width direction using a thickness gauge from Mitutoyo Corporation, sum them up, and then divide by 5 to obtain the average thickness of the 10 - layer porous substrate, and then divide by 10 to obtain the average thickness of the porous substrate. If an inorganic particle layer has been formed, remove the inorganic particle layer, dry it thoroughly, and then obtain the average thickness of the porous substrate without the inorganic particle layer in the above manner.

[0181] 10. Gurley air permeability (sec / 100cc)

[0182] Measurement was carried out according to ASTM D726 standard using a densometer from Toyoseiki Co., Ltd. The time required for 100 cc of air to pass through a separator with an area of 1 square inch was recorded in seconds and compared.

[0183] [Example 1]

[0184] 1) Manufacture of a ceramic - coated separator

[0185] On both sides of a polyethylene porous substrate (SKinnovation, ENPASS) with Gurley air permeability of 126 sec / 100cc and a thickness of 9 µm, the following slurry for the inorganic particle layer was bar-coated at a speed of 5 m / min to form a coating, and dried sufficiently at 40 °C to form a porous ceramic layer. After drying, the coating thickness of the porous ceramic layer on both sides was 1.5 µm, respectively.

[0186] Regarding the slurry for the inorganic particle layer, 29.1 wt% of boehmite particles with an average particle size (D 50 ) of 300 nm, 67.9 wt% of boehmite particles with an average particle size (D 50 ) of 700 nm, and 3 wt% of polyacrylamide resin were mixed as inorganic particles, and water as a solvent was added and stirred to prepare a composition with a solid content concentration of 25 wt%.

[0187] 2) Manufacturing a composite separator

[0188] On both sides of the manufactured ceramic-coated separator, the following coating liquid for the adhesive layer was bar-coated at a speed of 5 m / min to form an adhesive layer, and after sufficient drying at 40 °C, it was wound into a roll form. The thickness of the adhesive coatings on both sides was 0.5 µm, respectively, and the coating amounts were 0.2 g / m 2 .

[0189] The coating liquid for the adhesive layer used a polymer particle aqueous dispersion (D50 0.5 µm, Tg 77.4 °C, acrylic particles with a core-shell structure prepared from butyl methacrylate, methyl methacrylate, acrylonitrile, and styrene monomers).

[0190] The physical properties of the manufactured composite separator were evaluated and shown in Table 2 below.

[0191] [Examples 2 to 5]

[0192] As shown in Table 1 below, except for changing the physical properties of the core-shell particles, it was manufactured in the same manner as in Example 1.

[0193] The physical properties of the manufactured composite separator were evaluated and shown in Table 2 below.

[0194] [Comparative Examples 1 to 3]

[0195] Except for changing the physical properties of the core-shell particles by adjusting the monomer content as shown in Table 1 below, it was manufactured in the same manner as in Example 1.

[0196] The physical properties of the manufactured composite separator were evaluated and shown in Table 2 below.

[0197]

Table 1

[0198]

[0199] (Coating amount: the weight of the coating per unit area of the separator)

[0200]

Table 2

[0201]

[0202] As shown in Table 1 and Table 2 above, it can be seen that in the case of the embodiments of the present disclosure using an organic particle binder that satisfies the glass transition temperature and the swelling ratio, the electrode adhesion is excellent, no adhesion occurs in the adhesion evaluation, and there is no detachment of the electrode in the electrode adhesion evaluation. The capacity retention rate after 300 cycles is more than 90% and more than 92%, showing very excellent characteristics. Moreover, it is confirmed that a composite separator with excellent anti-adhesion can be provided. When the composite separator is wound and stored after manufacturing, not only at room temperature, but also when stored at a high temperature of 50 to 70 °C, no adhesion occurs between the adhesive layers of the wound rollers, between the adhesive layer and the ceramic layer, or between the adhesive layer and the porous substrate.

[0203] As shown in Comparative Examples 1 and 2, when an organic particle type binder that does not satisfy the glass transition temperature of the present invention is used, the electrode adhesion is low and electrode detachment occurs in the electrode adhesion evaluation, and adhesion is also confirmed in the adhesion evaluation.

[0204] Moreover, it can be seen that as shown in Comparative Example 3, when the glass transition temperature of the whole particle is lower than that of the core, although the electrode adhesion is satisfied, the adhesion is serious in the adhesion evaluation. Moreover, it can be seen that the capacity retention rate is very low.

[0205] Therefore, the existing method of predicting electrode adhesion or adhesion characteristics only through electrode adhesion cannot be fully and accurately predicted. However, as shown in the present disclosure, it is confirmed that when using an organic particle type binder and satisfying the glass transition temperature characteristics of the organic particle type binder while satisfying the adhesion characteristics, the adhesion characteristics, electrode adhesion, and capacity retention rate can be satisfied simultaneously. Moreover, it is confirmed that when the glass transition temperature characteristics are not satisfied, even if the electrode adhesion is satisfied, the adhesion characteristics and capacitance cannot be satisfied. From this, it can be seen that whether adhesion occurs cannot be predicted only through the existing electrode adhesion evaluation, and thus the effects of the present invention can be well demonstrated.

[0206] The content described above is only an illustration of applying the principle of the present disclosure, and other configurations may also be included within the scope of the present invention without departing from the scope of the present invention.

[0207] As described above, in the present disclosure, specific matters and defined embodiments have been described, but these are only provided to help a more comprehensive understanding of the present disclosure. The present disclosure is not limited to the above embodiments, and those of ordinary skill in the art to which the present disclosure pertains can make various modifications and variations based on the above description.

[0208] Therefore, the idea of the present disclosure is not limited to the described embodiments, and those within the scope of the appended claims and equivalent or equivalent variations thereof fall within the scope of the idea of the present disclosure.

Claims

1. A composite membrane, comprising a bonding layer on the outermost layer of at least one side of a porous membrane, wherein: The bonding layer contains a granular organic binder. When the bonding layers are bonded to each other and pressurized at 50°C at a pressure of 1.7 MPa for 2 hours and then peeled 180 degrees at a speed of 300 mm / min, no adhesion occurs between the bonding layers, and the bonding force to the positive electrode is greater than 5 gf / cm.

2. The composite diaphragm according to claim 1, wherein: The content of the granular organic binder in the bonding layer is 0.1 g / m 2 Up to 0.5g / m 2 .

3. The composite diaphragm according to claim 1, wherein: The average particle size of the particulate organic binder is 400 to 600 nm.

4. The composite diaphragm according to claim 1, wherein: The porous separator is a porous substrate, or the porous separator is a porous substrate on one or both sides of which a porous ceramic layer containing inorganic particles is formed.

5. The composite diaphragm according to claim 1, wherein: The particle-type organic binder is a core-shell particle-type organic binder.

6. The composite diaphragm according to claim 5, wherein: The glass transition temperature of the entire core-shell particle of the core-shell particle type organic binder is higher than the glass transition temperature of the core.

7. The composite diaphragm according to claim 5, wherein: The core of the core-shell particle type organic binder has a glass transition temperature of 50 to 75°C.

8. The composite diaphragm according to claim 5, wherein: The core-shell particle type organic binder has a glass transition temperature of the entire particle of 60 to 80°C.

9. The composite diaphragm according to claim 5, wherein: The core-shell particle type organic binder is an acrylic organic particle, and the shell includes a structure derived from an aromatic vinyl monomer.

10. The composite diaphragm according to claim 1, wherein: The composite separator is prepared by cutting the electrode into 4 cm wide and 6 cm long pieces and stacking the cut 4 positive electrodes and 4 negative electrodes cross-layered on the surface of the composite separator, and then heating the composite separator at 80°C in an atmosphere with a pressure of 10 kgf / cm 2 The composite separator has no electrodes separated when it is unfolded after bonding for 30 seconds.

11. The composite diaphragm according to claim 4, wherein: The average particle size of the inorganic particles of the porous ceramic layer is 50nm to 2µm.

12. The composite diaphragm according to claim 11, wherein: The inorganic particles of the porous ceramic layer include: first inorganic particles having an average particle size of 50 to 500 nm; and The second inorganic particles have an average particle diameter of 500 nm to 2000 nm.

13. The composite diaphragm according to claim 4, wherein: In the porous ceramic layer, inorganic particles are connected by a binder, and pores are formed between the inorganic particles.

14. The composite diaphragm according to claim 4, wherein: The porous substrate is a polyolefin-based porous film.

15. The composite diaphragm according to claim 1, wherein: The longitudinal heat shrinkage rate and the transverse heat shrinkage rate of the composite diaphragm at 150° C. are both less than 3%. 16 . A lithium secondary battery comprising the composite separator according to claim 1 .

17. The lithium secondary battery according to claim 16, wherein: In a cycle evaluation in which the lithium secondary battery is charged and discharged 300 times at a discharge rate of 1 C and then the discharge capacity is measured to measure the degree of reduction compared to the initial capacity, the discharge capacity ratio calculated by the following formula is 90% or more, Discharge capacity ratio = (battery measurement capacity after 300 cycles) / initial battery capacity.

18. A composite membrane, comprising a membrane having an adhesive layer as the outermost layer on at least one side of a porous membrane, wherein: The bonding layer comprises a particle-type organic binder, The content of the particulate organic binder in the bonding layer is 0.1 to 0.5 g / m 2 , The average particle size of the granular organic binder is 400 to 600 nm. The particle-type organic binder comprises a core-shell particle-type organic binder, The glass transition temperature of the entire core-shell particle of the core-shell particle type organic binder is higher than the glass transition temperature of the core.

19. The composite diaphragm according to claim 18, wherein: The core of the core-shell particle type organic binder has a glass transition temperature of 50 to 75°C, and the glass transition temperature of the entire core-shell particle is 60 to 80°C.

20. A lithium secondary battery comprising the composite separator according to claim 18.

Images