One]This application claims the benefit of priority based on Korean Patent Application No. 2019-0112581 dated September 11, 2019, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification. [2] The present invention relates to a separator for a secondary battery having excellent electrolyte impregnation property, and relates to a separator having improved electrolyte impregnation property by including a minimum amount of key factors negatively affecting the electrolyte impregnation property of the separator and maximizing the porosity of the separator coating layer. background [3] Among the separators of lithium secondary batteries, safety reinforced separators with improved safety are widely used. The SRS separator is a polyolefin-based substrate in which a coating layer including an inorganic material and a binder is formed. Since the coating layer is formed on a heat-sensitive polyolefin-based substrate to supplement it, the SRS separator has high high-temperature stability. [4] The coating layer of the SRS separator has a pore structure made of an inorganic material and a binder. The pore structure increases the amount of space for liquid electrolyte to enter, thereby improving lithium ion conductivity and electrolyte impregnation rate. [5] The electrolyte impregnation rate is a very important factor affecting the lifespan and capacity of the battery, and the higher the electrolyte impregnation rate, the more advantageous. [6] Patent Document 1 relates to a separator for a non-aqueous secondary battery that improves output characteristics by reducing battery internal resistance. The separation membrane includes a fluorine-containing nonionic surfactant having a hydrophilic structural unit and a hydrophobic structural unit including a fluorine atom. The content of the fluorine-containing nonionic surfactant is 0.001% by weight or more and 1 g/m 2 or less. [7] Patent Document 2 relates to a separator having a relatively thin thickness and strong peeling force and electrode adhesion. By using a polyvinylidene fluoride homopolymer having a weight average molecular weight of 1 million g/mol or more and inorganic particles having an average particle diameter of 1 nm to 700 nm as a coating agent component, the density of the separator is adjusted to 1.2 g/m 3 to 2 g/m 3 did. [8] Patent Document 3 discloses a separator having excellent dispersibility, in which an inorganic material mixture including inorganic particles, a dispersing agent, and a binder is applied on a porous substrate. The dispersant is a copolymer comprising a main chain of ionic properties and a side chain of nonionic surfactant. [9] The above patent documents do not disclose specific details for improving the impregnability of the separator while minimizing the addition of surfactant. [10] (Prior art literature) [11] (Patent Document 1) Republic of Korea Patent Publication No. 2017-10022977 (2017.03.02) [12] (Patent Document 2) Republic of Korea Patent Publication No. 1488918 (2015.02.03) [13] (Patent Document 3) Republic of Korea Patent Publication No. 1820459 (2018.01.15) DETAILED DESCRIPTION OF THE INVENTION technical challenge [14] The present invention is to solve the above problems, and to provide a separator for secondary batteries that contains only a very small amount of surfactant included in the slurry forming the coating layer of the separator, and has improved electrolyte impregnation by using a certain amount of binder. do it with means of solving the problem [15] The present invention for achieving the above object provides a separator for a secondary battery in which a coating layer is formed on a separator substrate. The coating layer may be formed on at least one surface of the separator substrate, and the coating layer may include an acrylate-based binder and an additive, and the additive may be a fluorine-based nonionic surfactant. [16] The content of the acrylate-based binder may be 10% by weight or less based on the total weight of the solid content excluding the additive in the coating layer. [17] Preferably, the content of the acrylate-based binder may be 5 wt% or less based on the total weight of the solid content excluding the additive in the coating layer. [18] The content of the fluorine-based nonionic surfactant may be 0.001 wt% or less based on the sum of the inorganic material and the acrylate-based binder in the coating layer. [19] Alternatively, the density of the coating layer may be 2 g/m 3 or less. [20] The separation membrane may be an aqueous separation membrane. [21] In the separation membrane, the difference in diffusion distance of the electrolyte along the MD and TD directions may be within 1.5 times when 2 μl of the electrolyte is dropped. [22] The average diffusion distance of the separator may be 2.0 mm/2 μl to 7.0 mm/2 μl. [23] The coating layer may further include an inorganic material. [24] The present invention also provides a battery cell including an electrode assembly in which the separator for secondary charge is interposed between a positive electrode and a negative electrode. [25] When the battery cell is charged and discharged 150 times, the capacity retention rate may be 80% or more. [26] The present invention provides a battery pack including the battery cell, and provides a device using the battery pack as an energy source. [27] Specific examples of the device are not particularly limited, and those commonly used in the art may be included therein. Brief description of the drawing [28] 1 is a photograph showing the impregnation difference according to the coating density. [29] FIG. 2 is a graph showing the diffusion distance according to the coating density of the separator of FIG. 1 . [30] 3 is a photograph showing the impregnation difference according to the content of the fluorine-based nonionic surfactant. [31] 4 is a graph showing the diffusion distance according to the content of the fluorine-based nonionic surfactant in the separation membrane of FIG. 3 . [32] 5 is a graph showing electrolyte impregnation according to the binder content in the case of using a fluorine-based nonionic surfactant and electrolyte impregnation according to the binder content in the case of using a hydrocarbon-based surfactant. [33] 6 is a photograph comparing the difference in impregnation properties of the separators of Example 2 and Comparative Example 6. [34] 7 is a result of measuring the cycle characteristics of the battery cells. Modes for carrying out the invention [35] Hereinafter, embodiments in which those skilled in the art can easily practice the present invention will be described in detail with reference to the accompanying drawings. However, in the detailed description of the operating principle of the preferred embodiment of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. [36] In addition, the same reference numerals are used throughout the drawings for parts having similar functions and functions. Throughout the specification, when it is said that a part is connected to another part, it includes not only a case in which it is directly connected, but also a case in which it is indirectly connected with another element interposed therebetween. In addition, the inclusion of a certain component does not exclude other components unless otherwise stated, but means that other components may be further included. [37] In addition, limitations or additions to certain embodiments in the present specification may be applied to specific embodiments as well as equally applicable to other embodiments. [38] The separator for a secondary battery according to the present invention has a structure in which a coating layer is formed on at least one surface of a separator substrate, and the coating layer includes an acrylate-based binder and a fluorine-based nonionic surfactant as additives. [39] The separator substrate may be a polyolefin-based separator commonly used in the art, for example, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, polyethylene terephthalate (polyethyleneterephthalate), polybutylene tere. Polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, It may be made of at least one selected from the group consisting of polyphenyleneoxide, polyphenylenesulfidro, polyethylenenaphthalene, and mixtures thereof. [40] The binder may constitute a coating layer of the separator together with the inorganic material, and the binder may maintain bonding between inorganic particles and improve adhesion between the electrode and the separator. [41] The type of such a binder is not particularly limited as long as it does not chemically change the separator coating layer, and for example, polyolefin such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; fluorine-containing rubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymers and hydrides thereof; (meth)acrylic acid ester copolymers, such as a methacrylic acid ester copolymer, an acrylonitrile acrylic acid ester copolymer, and a styrene acrylic acid ester copolymer; rubbers such as ethylene propylene rubber; polyvinyl acetate; The melting point of polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamide, polyimide, polyamideimide, polyetheramide, polyester, aromatic polyester and polyether ether ketone, etc. a resin having a glass transition temperature of 180°C or higher; polycarbonate; polyacetal; and water-soluble resins such as carboxyalkyl cellulose, alkyl cellulose, hydroxyalkyl cellulose, starch, polyvinyl alcohol, sodium alginate, polyethylene glycol, cellulose ester, polyacrylic acid, polyacrylamide and polymethacrylic acid, or two of these It may be a polymer containing more than one. [42] In one specific example, the binder may be an acrylate-based binder, and in general, the acrylate-based binder comprises a soft monomer having a low glass transition temperature (Tg) and a hard monomer having a high glass transition temperature. It can be used by copolymerization in a certain ratio. [43] The acrylate-based binder is a component essentially included in the coating layer, and may be included in an amount of 10% by weight or less based on the total weight of solids excluding additives, and specifically, may be included in an amount of 1% to 5% by weight or less. [44] If the acrylate-based binder is not included, the bonding force with the electrode may be weakened, and if it is greater than 10 wt %, asymmetry in which the electrolyte impregnation property varies depending on the direction may occur, which is not preferable. [45] The separator for a secondary battery according to the present invention includes an additive in the coating layer, and the additive may be a fluorine-based nonionic surfactant. [46] Various surfactants have been conventionally known, for example, among nonionic surfactants having an alkyl group as a hydrophobic structural unit, and fluorine-based surfactants having a fluorine atom as a hydrophobic structural unit, a fluorine-based anionic surfactant containing a sulfonate as a hydrophobic structural unit. , but there are anionic surfactants such as quaternary ammonium salts, but these do not have the effect of lowering the internal resistance of the battery, but rather have a problem of having a property of increasing the internal resistance of the battery. [47] The fluorine-based nonionic surfactant is, for example, a fluoroalkylethylene oxide adduct, a fluoroalkenylethyleneoxide adduct, a fluoroalkylpropyleneoxide adduct, a fluoroalkenylpropyleneoxide adduct, and a perfluoroalkylethyleneoxide adduct. adducts, perfluoroalkenylethylene oxide adducts, and the like. [48] The separator for a secondary battery according to the present invention contains a fluorine-based nonionic surfactant in an amount of 0.001% by weight or less based on the sum of the inorganic material and the acrylate-based binder in the coating layer, and the fluorine-based nonionic surfactant is 0.001% by weight When it contains more, since electrolyte solution impregnation rate falls rapidly, it is unpreferable. [49] In the separator for secondary batteries according to the present invention, the density of the coating layer is 2 g/m3 or less, and when the density of the coating layer is greater than 2 g/m3, the electrolyte impregnation rate is rapidly reduced, which is not preferable. [50] The separator coating layer may further include an inorganic material, wherein the inorganic material is BaTiO 3 , Pb(Zr,Ti)O 3 (PZT), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT) (0 [78] In order to prepare the coating agent for the separator coating layer, Al 2 O 3 97% by weight as an inorganic material, 3% by weight of GL Chem's SG-L02 as an acrylate-based binder, and 100% by weight of the inorganic material and the acrylate-based binder At this time, 0.001 wt% of FC4430 from 3M as a fluorine-based nonionic surfactant was added to water as a solvent and stirred to prepare a coating agent. [79] The coating agent was coated on both sides of a membrane substrate made of a polyethylene porous material having a thickness of 9 μm so that the density of the coating layer was 1.5 g/m 3 , and then dried to prepare a separation membrane. [80] [81] A separator was prepared in the same manner as in Example 1, except that in Example 1, the coating layer density was 1.8 g/m 3 instead of 1.5 g/m 3 . [82] [83] A separator was prepared in the same manner as in Example 1, except that in Example 1, the coating layer density was 1.9 g/m 3 instead of 1.5 g/m 3 . [84] [85] A separator was prepared in the same manner as in Example 1, except that in Example 1, the coating layer density was 2.3 g/m 3 instead of 1.5 g/m 3 . [86] [87] A separator was prepared in the same manner as in Example 1, except that in Example 1, the coating layer density was 3.0 g/m 3 instead of 1.5 g/m 3 . [88] [89] A separation membrane was prepared in the same manner as in Example 3, except that in Example 3, 0.001 wt% to 0.002 wt% of the fluorine-based nonionic surfactant was used. [90] [91] A separation membrane was prepared in the same manner as in Example 3, except that in Example 3, 0.001 wt% to 0.005 wt% of the fluorine-based nonionic surfactant was used. [92] [93] A separation membrane was prepared in the same manner as in Example 3, except that in Example 3, 0.001 wt% to 0.01 wt% of the fluorine-based nonionic surfactant was used. [94] [95] A separator was prepared in the same manner as in Example 3, except that in Example 3, the binder content was used at 1.5 wt% instead of 3 wt%. [96] [97] A separator was prepared in the same manner as in Example 3, except that in Example 3, the binder content was 5 wt% instead of 3 wt%. [98] [99] A separator was manufactured in the same manner as in Example 3, except that in Example 3, the binder content was used at 10 wt% instead of 3 wt%. [100] [101] A separator was manufactured in the same manner as in Example 3, except that in Example 3, the binder content was 15 wt% instead of 3 wt%. [102] [103] A separation membrane was prepared in the same manner as in Example 4, except that in Example 4, a hydrocarbon-based surfactant was used instead of a fluorine-based nonionic surfactant. [104] [105] A separation membrane was prepared in the same manner as in Example 3, except that in Example 3, a hydrocarbon-based surfactant was used instead of a fluorine-based nonionic surfactant. [106] [107] Rimak was prepared in the same manner as in Example 5, except that in Example 5, a hydrocarbon-based surfactant was used instead of a fluorine-based nonionic surfactant. [108] [109] A separation membrane was prepared in the same manner as in Example 6, except that in Example 6, a hydrocarbon-based surfactant was used instead of a fluorine-based nonionic surfactant. [110] [111] A separation membrane was prepared in the same manner as in Comparative Example 6, except that a hydrocarbon-based surfactant was used instead of a fluorine-based nonionic surfactant in Comparative Example 6. [112] [113] In Example 3, using the same method as in Example 3, except that the binder weight was used from 3 wt% to 15 wt%, and the coating layer density was 2.9 g/m 3 instead of 1.9 g/m 3 , the separation membrane was used. prepared. [114] Electrolyte impregnation property [115] Prepare a digital optical microscope (AD7013MZT(R4) of AnMo electronics corporation) and a steel ruler, and focus while adjusting the height of the digital optical microscope so that the measured values ​​of the digital optical microscope's scale bar and the steel ruler match. [116] The separators prepared in the Examples and Comparative Examples are cut to 50 mm in width and 50 mm in length, placed on a slide glass, and an adhesive tape is attached to each vertex to fix the separator to the slide glass. [117] Fill a 10 μl micro syringe with 2 μl of propylene carbonate, make water droplets, and drop it on the separation membrane. [118] Immediately after dripping, press the Capture button to check the shape of the water droplet, and capture additionally after 5 minutes. [119] The diffusion distance of the water droplet falling on the separation membrane was measured in the MD and TD directions. [120] The contents of each component in the Examples and Comparative Examples are summarized in Table 1 below. [121] [122] [123] 1 is a photograph of measuring the electrolyte diffusion distance for the separators of Examples 1 to 3, Comparative Examples 1 and 2 in order to show the impregnation difference according to the coating density of the separator coating layer, and FIG. 1 is a graph showing the diffusion distance according to the coating density of the separator. [124] 1 and 2, the diffusion distance of Example 1 having the lowest coating layer density was the longest, and Comparative Example 2 having the largest coating layer density was measured to have the shortest diffusion distance. [125] In particular, Examples 1 to 3, in which the coating layer density is less than 2 g/m 3 , exhibited a diffusion distance of 1.5 mm/2 μl or more, and it can be seen that the impregnation property is improved as the coating density is lowered. [126] In order to confirm the electrolyte impregnation property according to the content of the surfactant, the diffusion distance was measured using the separators prepared in Example 2 and Comparative Examples 3 to 5, and the photograph is shown in FIG. 3 , and the fluorine-based nonionic interface A graph showing the diffusion distance according to the content of the active agent is shown in FIG. 4 . [127] 3 and 4, in the case of Example 2 using 0.001 wt% of a fluorine-based nonionic surfactant, a diffusion distance of 6.1 mm is shown, whereas the content of a fluorine-based nonionic surfactant is greater than 0.002 g/m 2 The separation membranes of Examples 3 to 5 showed results of less than 50% of the diffusion distance of the separation membrane of Example 2. [128] Therefore, it can be seen that when the fluorine-based nonionic surfactant is included in an amount of 0.001 wt % or less, the electrolyte impregnation property is remarkably improved. [129] 5 is a graph showing electrolyte impregnation according to the binder content in the case of using a fluorine-based nonionic surfactant and electrolyte impregnation according to the binder content in the case of using a hydrocarbon-based surfactant. [130] Referring to FIG. 5 , when a hydrocarbon-based surfactant is used, all of them show a diffusion distance of a size smaller than 2 mm/2 μl regardless of the binder content, whereas when a fluorine-based nonionic surfactant is used, the binder content is When it is less than 10.0 wt%, a diffusion distance of 2 mm/2 μl or more is shown. [131] However, even when a fluorine-based nonionic surfactant is used, a diffusion distance of 1.4 mm/2 μl is shown when 15.0 wt % of the binder is included. [132] Therefore, it can be seen that even when a fluorine-based nonionic surfactant is used, a large diffusion distance is exhibited only when the binder is included in less than 10% by weight. [133] In addition, a photograph comparing the difference in impregnation properties of the separators of Example 2 and Comparative Example 6 is shown in FIG. 6 . [134] Example 2 of FIG. 6 is the same photograph as Example 2 of FIG. 3 , and FIG. 3 shows the average value of the diffusion distance in the MD direction and the diffusion distance in the TD direction of FIG. 6 . [135] 6, the diffusion distance in the MD direction of Example 2 is 6.6 mm and the diffusion distance in the TD direction is 5.5 mm. It can be seen that the diffusion distance appears in a symmetrical form. [136] On the other hand, the diffusion distance in the MD direction of Comparative Example 6 is 2.0 mm, and the diffusion distance in the TD direction is 0.8 mm, and the difference between them is 2.5 times the difference. It can be seen that the distance appears in an asymmetric form. [137] On the other hand, in order to prepare a battery cell including the separator of Example 3 and Comparative Example 12, a positive electrode containing a nickel-cobalt-manganese-based positive electrode active material and a negative electrode containing graphite as a negative electrode active material were prepared, the positive electrode and An electrode assembly was prepared by interposing the separators between the anodes. [138] After the electrode assembly was accommodated in the battery case, an electrolyte was injected to impregnate the electrode assembly in the electrolyte, and the battery case was sealed to prepare a battery cell. [139] Cycle characteristics of the battery cells were measured, and the results are shown in FIG. 7 . [140] The cycle characteristic measurement test shows the result of measuring about 180 times of constant current/constant voltage charging at 0.8C and high-rate discharging at 0.5C. [141] Referring to FIG. 7 , when the separator of Example 3 is included, the capacity retention rate is about 85% when 150 charging and discharging is performed, but when the separator of Comparative Example 12 is included, the capacity is about 72 at the same time. It shows the retention rate. [142] Accordingly, it can be seen that, when the separator for a secondary battery according to the present invention is included, a significantly improved capacity retention rate can be secured. [143] Those of ordinary skill in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents. Industrial Applicability [144] As described above, in the separator for a secondary battery according to the present invention, the generation of bubbles in the slurry for forming the coating layer is suppressed to improve the wettability of the separator substrate, and thus the electrolyte impregnation property can be significantly improved. [145] By controlling the content of the acrylate-based binder included in the separator coating layer, it is possible to prevent the electrolyte diffusion distance from appearing asymmetrically. [146] In addition, by lowering the density of the separator coating layer, the resistance of the separator is reduced, and adhesion can be ensured. WE CLAIMS A separator for secondary batteries in which a coating layer is formed on a separator substrate, wherein the coating layer is formed on at least one surface of the separator substrate, the coating layer includes an acrylate-based binder and an additive, wherein the additive is a fluorine-based nonionic surfactant. . [Claim 2] The separator for a secondary battery according to claim 1, wherein the content of the acrylate-based binder is 10% by weight or less based on the total weight of the solid content excluding the additive in the coating layer. [Claim 3] The separator for secondary batteries according to claim 2, wherein the content of the acrylate-based binder is 5 wt% or less based on the total weight of the solid content excluding the additive in the coating layer. [Claim 4] The separator for a secondary battery according to claim 1, wherein the content of the fluorine-based nonionic surfactant is 0.001% by weight or less based on the sum of the inorganic material and the acrylate-based binder in the coating layer. [Claim 5] The separator for a secondary battery according to claim 1, wherein the coating layer has a density of 2 g/m 3 or less. [Claim 6] The separator for a secondary battery according to claim 1, wherein the separator is an aqueous separator. [Claim 7] The separator for a secondary battery according to claim 1, wherein the difference in diffusion distance of the electrolyte along the MD and TD directions in the separator is within 1.5 times when 2 μl of the electrolyte is added dropwise. [Claim 8] The separator for secondary batteries according to claim 7, wherein the average diffusion distance of the separator is 2.0 mm/2 μl to 7.0 mm/2 μl. [Claim 9] The separator for a secondary battery according to claim 1, wherein the coating layer further comprises an inorganic material. [Claim 10] A battery cell comprising an electrode assembly in which the secondary battery separator according to any one of claims 1 to 9 is interposed between a positive electrode and a negative electrode. [Claim 11] The battery cell according to claim 10, wherein the capacity retention rate when charging and discharging the battery cell is performed 150 times is 80% or more. [Claim 12] A battery pack comprising the battery cell according to claim 10 or 11.

Documents

Application Documents

#	Name	Date
1	202117058364.pdf	2021-12-15
2	202117058364-TRANSLATIOIN OF PRIOIRTY DOCUMENTS ETC. [15-12-2021(online)].pdf	2021-12-15
3	202117058364-STATEMENT OF UNDERTAKING (FORM 3) [15-12-2021(online)].pdf	2021-12-15
4	202117058364-PROOF OF RIGHT [15-12-2021(online)].pdf	2021-12-15
5	202117058364-PRIORITY DOCUMENTS [15-12-2021(online)].pdf	2021-12-15
6	202117058364-POWER OF AUTHORITY [15-12-2021(online)].pdf	2021-12-15
7	202117058364-FORM 1 [15-12-2021(online)].pdf	2021-12-15
8	202117058364-DRAWINGS [15-12-2021(online)].pdf	2021-12-15
9	202117058364-DECLARATION OF INVENTORSHIP (FORM 5) [15-12-2021(online)].pdf	2021-12-15
10	202117058364-COMPLETE SPECIFICATION [15-12-2021(online)].pdf	2021-12-15
11	202117058364-FORM 3 [17-03-2022(online)].pdf	2022-03-17
12	202117058364-FORM 3 [18-08-2022(online)].pdf	2022-08-18
13	202117058364-FORM 3 [19-01-2023(online)].pdf	2023-01-19
14	202117058364-FORM 18 [01-06-2023(online)].pdf	2023-06-01
15	202117058364-FORM 3 [23-06-2023(online)].pdf	2023-06-23
16	202117058364-FER.pdf	2023-07-21
17	202117058364-Information under section 8(2) [02-01-2024(online)].pdf	2024-01-02
18	202117058364-FORM 3 [02-01-2024(online)].pdf	2024-01-02
19	202117058364-OTHERS [17-01-2024(online)].pdf	2024-01-17
20	202117058364-FER_SER_REPLY [17-01-2024(online)].pdf	2024-01-17
21	202117058364-DRAWING [17-01-2024(online)].pdf	2024-01-17
22	202117058364-CLAIMS [17-01-2024(online)].pdf	2024-01-17
23	202117058364-US(14)-HearingNotice-(HearingDate-18-04-2024).pdf	2024-03-27
24	202117058364-FORM-26 [15-04-2024(online)].pdf	2024-04-15
25	202117058364-Correspondence to notify the Controller [15-04-2024(online)].pdf	2024-04-15
26	202117058364-FORM-26 [18-04-2024(online)].pdf	2024-04-18
27	202117058364-Correspondence to notify the Controller [18-04-2024(online)].pdf	2024-04-18
28	202117058364-Written submissions and relevant documents [03-05-2024(online)].pdf	2024-05-03

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1	SEARCHstrategyE_21-07-2023.pdf