Separator for electrochemical devices and method of manufacturing the separator

Abstract

The present disclosure relates to a separator for an electrochemical device, the separator including a porous polymer substrate and an inorganic coating layer formed on at least one surface of the porous polymer substrate, wherein the inorganic coating layer includes inorganic particles and a binder resin, the binder resin includes a polyvinylidene fluoride (PVdF)-based polymer, and the PVdF-based polymer has a main chain and at least one hydrogen atom in the main chain is substituted with a functional group derived from an acrylic compound.

Description

TECHNICAL FIELD

[0001] This application claims priority to Korean Patent Application No. 10-2018-0130072 filed in Korea on October 29, 2018. The present disclosure relates to a separator for an electrochemical device, wherein the electrochemical device can be a primary battery or a secondary battery, and the secondary battery includes a lithium ion secondary battery. BACKGROUND

[0002] Non-aqueous secondary batteries, represented by lithium ion secondary batteries, have been widely used as power sources for portable electronic appliances such as notebook computers, mobile phones, digital cameras, camcorders, etc. In addition, recently, since such batteries have the characteristics of high energy density, research on their application to vehicles has been conducted.

[0003] As portable electronic appliances are miniaturized and lightened, the housing of non-aqueous secondary batteries is simplified. In the initial stage, a battery can made of stainless steel was used as the housing. However, since a housing made of aluminum was developed, a soft-pack housing made of aluminum laminate packaging has been developed recently. In the case of the soft-pack housing made of aluminum laminate packaging, they are flexible, so that a gap can be formed between the electrode and the separator during the charging / discharging process, thereby causing a technical problem of a decrease in cycle life. In order to solve the above problem, the adhesion technology between the electrode and the separator is important, and many suggestions have been made for the technology.

[0004] In addition, when a curved battery is manufactured, the electrode assembly including the separator bonded to the electrode is subjected to deformation such as bending. When the bonding force between the electrode and the separator is low, they can be separated from each other under such deformation. As a result, an electrochemical reaction does not occur between the electrode and the separator, or a dead space with low efficiency can be generated, thereby causing a problem of a decrease in battery quality.

[0005] Generally, a polyvinylidene fluoride (PVdF)-based resin is used as an adhesive resin for an electrode adhesive layer. In addition, the adhesive resin is migrated to the surface of a separator by a wet phase separation process, so that an adhesive top layer portion having a high adhesive resin content can be formed near the surface of an inorganic coating layer. However, the PVdF-based resin itself does not have high adhesion, so it is difficult to secure a high level of binding force. In order to improve the adhesion, the content or coating amount of the adhesive resin can be increased. However, in this case, the resulting adhesive layer has an increased thickness, resulting in a decrease in energy density and an increase in resistance, which is undesirable. Even if the thickness of the separator is thin, the adhesive layer of the separator is required to achieve high adhesion and high ionic conductivity. In addition, in order to use the battery stably for a long period of time, the separator should be a chemically and electrochemically stable material. In addition, the process for manufacturing the separator should provide high productivity to allow mass production at a low cost. Under these circumstances, there is a need to develop a separator for a secondary battery satisfying the above requirements. SUMMARY

[0006] Technical problem

[0007] The present disclosure aims to provide a separator having a small thickness and including an inorganic coating layer having improved adhesion to an electrode. The present disclosure also aims to provide a method for manufacturing a separator having the above characteristics. It will be readily understood that the objects and advantages of the present disclosure can be achieved by means shown in the attached claims, alone or in combination.

[0008] Technical scheme

[0009] In one aspect of the present disclosure, a separator for an electrochemical device is provided. According to a first embodiment of the present disclosure, a separator for an electrochemical device is provided, the separator including a porous polymer substrate and an inorganic coating layer formed on at least one surface of the porous polymer substrate, wherein the inorganic coating layer includes inorganic particles and an adhesive resin including a polyvinylidene fluoride (PVdF)-based polymer, and the PVdF-based polymer has a main chain and at least one hydrogen atom in the main chain is substituted with a functional group derived from an acrylic compound.

[0010] According to a second embodiment of the present disclosure, the separator for an electrochemical device as defined in the first embodiment is provided, wherein the polyvinylidene fluoride (PVdF)-based polymer includes a polymer represented by the following [Chemical Formula 1], wherein R1 and R2 each independently represent H or a group represented by the following [Chemical Formula 2], wherein R3, R4, and R5 each independently represent H or a C10 or lower alkyl group.

[0011] [Chemical Formula 1]

[0012]

[0013] [Chemical Formula 2]

[0014]

[0015] According to a third embodiment of the present disclosure, there is provided a separator for an electrochemical device as defined in the second embodiment, wherein at least one hydrogen bonded to each carbon atom of R3, R4, and R5 is each independently replaced with an element or a functional group other than H, and the functional group is at least one selected from the group consisting of an ester, a ketone, a hydroxyl, an ether, a carboxyl, and a carbonyl.

[0016] According to a fourth embodiment of the present disclosure, there is provided a separator for an electrochemical device as defined in any one of the first to third embodiments, wherein the PVdF-based polymer has a main chain including a copolymer of vinylidene fluoride and a monomer copolymerizable with the vinylidene fluoride, the monomer being at least one selected from the group consisting of trifluoroethylene (TrFE); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ether such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), or perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxolane); and perfluoro(2,2-dimethyl-1,3-dioxolane) (PDD), and a substitution rate of the monomer is 1-20 wt%.

[0017] According to a fifth embodiment of the present disclosure, there is provided a separator for an electrochemical device as defined in any one of the first to fourth embodiments, wherein the acrylic compound-derived functional group is derived from at least one selected from the group consisting of (meth)acrylic acid, (meth)acrylate, (meth)acrylonitrile, and dimethyl 2-methylenepentanedionate.

[0018] According to a sixth embodiment of the present disclosure, there is provided a separator for an electrochemical device as defined in any one of the first to fifth embodiments, wherein the PVdF-based polymer includes an acrylic compound-derived functional group introduced thereto at a ratio of 0.1-5 wt% based on 100 wt% of the PVdF-based polymer.

[0019] According to a seventh embodiment of the present disclosure, there is provided a separator for an electrochemical device as defined in any one of the first to sixth embodiments, wherein the PVdF-based polymer has a weight average molecular weight of 100,000 to 600,000.

[0020] According to an eighth embodiment of the present disclosure, there is provided a separator for an electrochemical device as defined in any one of the first to seventh embodiments, wherein the inorganic coating includes inorganic particles in an amount of 50% by weight or more, based on the total weight of the inorganic particles and the binder resin of 100% by weight.

[0021] According to a ninth embodiment of the present disclosure, there is provided a separator for an electrochemical device as defined in any one of the first to eighth embodiments, wherein the separator has a binder top layer portion having a high content of the binder resin and disposed on the surface of the inorganic coating.

[0022] According to a tenth embodiment of the present disclosure, there is provided a separator for an electrochemical device as defined in any one of the first to ninth embodiments, wherein the inorganic particles in the inorganic coating are held together with each other by the binder resin, the inorganic coating has a plurality of micropores derived from the volume of gaps formed between the inorganic particles, the inorganic coating has a binder top layer portion having a high content of the binder resin and formed on the surface of the inorganic coating, and the inorganic coating and the binder top layer portion are integrally and inseparably combined with each other.

[0023] According to an eleventh embodiment of the present disclosure, there is provided a separator for an electrochemical device as defined in any one of the first to tenth embodiments, wherein the binder top layer portion is obtained from a phase separation process of the binder resin when the separator is dried under a humidified condition.

[0024] According to a twelfth embodiment of the present disclosure, there is provided a separator for an electrochemical device as defined in the eleventh embodiment, wherein the humidified condition includes a relative humidity of 40 to 80%.

[0025] According to a thirteenth embodiment of the present disclosure, there is provided an electrochemical device including a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, wherein the separator is defined in any one of the first to twelfth embodiments.

[0026] Beneficial effects

[0027] The separator and the electrochemical device including the same according to the present disclosure show excellent adhesion to an electrode by using a binder into which an acrylic monomer is introduced. By using the achieved high adhesion, different changes can be applied in the assembly process of the electrochemical device without the problem of adhesion force reduction. In addition, since the introduction of the binder resin, the peeling strength between the inorganic coating and the separator substrate can be improved, and thus improved heat resistance and stability, such as reduction in shrinkage of the separator, can be provided. In addition, thinning of the separator can be completed, and thus the energy density of the battery can be effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings illustrate preferred embodiments of the present disclosure and together with the foregoing disclosure, provide further understanding of the technical features of the present disclosure, and therefore, the present disclosure is not to be interpreted as being limited to the accompanying drawings. In addition, the shape, size, ratio, or ratio of some constituent elements in the drawings can be exaggerated for the purpose of clearer description.

[0029] Figure 1 is a schematic view illustrating a cross-sectional structure of a separator according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0030] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Before the description, it is to be understood that the term used in the specification and the appended claims should not be construed as being limited to general and dictionary meanings and should be construed as having meanings and concepts meeting the technical aspects of the present disclosure based on the principle that the inventor is allowed to define appropriate terms in order to best explain the technical idea. Therefore, the description proposed herein is just a preferred example for the purpose of illustrations only and should not be construed as limiting the scope of the disclosure and, therefore, should be understood that other equally effective alternatives and modifications could be made without departing from the scope of the present disclosure.

[0031] Throughout the specification, the expression "a component 'includes' an element" does not exclude the presence of additional elements, but means that the component can further include other elements.

[0032] As used herein, the terms "about", "substantially" and the like are used as terms of approximation and are presented, when proposing acceptable manufacturing and material errors inherent in the meaning of the numerical value, and are used to prevent dishonest infringers from improperly using the disclosure including accurate numbers or absolute numbers provided to help understand the present disclosure.

[0033] As used herein, the expression "A and / or B" means "A, B, or both".

[0034] The specific terms used in the following description are used for illustrative purposes and are not limiting. Terms such as "right," "left," "top surface," and "bottom surface" show the directions to which they refer in the drawings. Terms such as "inward" and "outward" mean the direction toward the geometric center of the respective device, system, and its components, and the direction away from the center, respectively. "Front," "rear," "top," and "bottom," and related words and expressions show the positions and points to which they refer in the drawings, and should not be limiting. Such terms include the words listed above, their derivatives, and words with similar meanings.

[0035] Unless otherwise stated, the ratios described herein refer to weight ratios.

[0036] The present disclosure relates to a separator for an electrochemical device and an electrochemical device including the same. As used herein, the term "electrochemical device" refers to a device that converts chemical energy into electrical energy by an electrochemical reaction, and its concept encompasses primary batteries and secondary batteries, wherein the secondary batteries are rechargeable and its concept encompasses lithium ion batteries, nickel-cadmium batteries, nickel-hydrogen batteries, or the like.

[0037] 1. Separator

[0038] 1) Structure of the separator

[0039] The separator 100 according to the present disclosure includes a porous polymer substrate 110 and an inorganic coating layer 120 formed on at least one surface of the porous polymer substrate. The inorganic coating layer includes inorganic particles and a binder resin. The binder resin includes a polyvinylidene fluoride (PVdF)-based polymer, and the PVdF-based polymer has a main chain and at least one hydrogen atom in the main chain is substituted with a functional group derived from an acrylic compound. In other words, the PVdF copolymer is characterized in that it is modified with an acrylic monomer. Further, according to embodiments of the present disclosure, the inorganic coating layer has a top layer portion with a high content of the binder resin, thus showing high adhesion between the separator and the electrode.

[0040] According to embodiments of the present disclosure, the separator can have a thickness of 5-30 μm, and the thickness can be appropriately adjusted within the above range. For example, the thickness can be 15-25 μm. Further, the separator can have a magnetic permeability of about 50 sec / 100 cc to 3000 sec / 100 cc.

[0041] As used herein, the term "permeability" refers to the time required for 100 cc of air to pass through an object (such as a separator or a porous polymer substrate) whose permeability is to be tested, expressed in seconds / 100 cc, and is used interchangeably with "transmission rate", and is generally indicated by a Gurley value or the like. According to embodiments of the present disclosure, permeability can be determined according to JIS P8117. Further, according to the mathematical formula P2 = (P1 x 20) / T1, air permeability P1 determined for an object having a thickness of T1 can be converted to air permeability P2 for an object having a thickness of 20 μm.

[0042] Further, according to the present disclosure, porosity and pore diameter can be determined by a BELSORP (BET apparatus) available from BEL JAPAN Co. using an adsorbing gas such as nitrogen, or via a method such as mercury intrusion porosimetry or capillary flow porosimetry. According to embodiments of the present disclosure, the thickness and weight of the resulting coating can be measured to calculate porosity from the theoretical density of the coating.

[0043] 2) Porous polymer substrate

[0044] The porous polymer substrate refers to a porous ion-conducting barrier that allows ions to pass through while interrupting electrical contact between the negative electrode and the positive electrode, and has a plurality of pores formed therein. These pores are connected to each other so that a gas or a liquid can reach from one surface of the substrate to the other surface of the substrate.

[0045] The material forming the porous polymer substrate can be any organic material or inorganic material having an electrically insulating property. Specifically, a thermoplastic resin is preferably used as the material forming the substrate in view of imparting a shutdown function. Herein, the term "shutdown function" refers to a function of preventing thermal runaway of a battery by causing a thermoplastic resin to melt so that the pores of the porous substrate can be closed and ion conduction can be interrupted when the battery temperature rises. As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200°C is suitable, and a polyolefin is particularly preferred.

[0046] In addition to the polyolefin, the thermoplastic resin can further include at least one polymeric resin selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene ether, polyphenylene sulfide, and polyethylene naphthalate. The porous polymer substrate can include a nonwoven web, a porous polymer film, or a laminate of two or more layers thereof, but is not limited thereto.

[0047] In particular, the porous polymer substrate is any one of a) to e) below:

[0048] a) a porous film formed by melting / extruding a polymer resin;

[0049] b) a multi-layer film formed by stacking two or more layers of the porous film of a);

[0050] c) a non-woven web formed by integrating filaments obtained by melting / spinning a polymer resin;

[0051] d) a multi-layer film formed by stacking two or more layers of the non-woven web of c); and

[0052] e) a porous composite film having a multi-layer structure including two or more of a) to d).

[0053] According to the present disclosure, the porous polymer substrate preferably has a thickness of 3-12 μm or 5-12 μm. When the thickness is less than the above range, a sufficient conductive barrier function cannot be obtained. On the other hand, when the thickness is too large to be greater than the above range (i.e., the porous polymer substrate is too thick), the separator can show an excessively increased resistance.

[0054] According to an embodiment of the present disclosure, the polyolefin preferably has a weight average molecular weight of 100,000-5,000,000. When the weight average molecular weight is less than 100,000, it is difficult to secure sufficient dynamic physical properties. In addition, when the weight average molecular weight is greater than 5,000,000, the shutdown characteristics can become poor or it can be difficult to mold.

[0055] As used herein, the term "molecular weight" refers to a weight average molecular weight (Mw) of a polymer. w For example, the molecular weight can be measured by using a gel permeation chromatography (GPC: PL GPC220, Agilent Technologies).

[0056] In addition, in terms of improving productivity, the porous polymer substrate can have a puncture strength of 300 gf or more. The puncture strength of the porous substrate refers to the maximum puncture load (gf) measured by using a Katotech KES-G5 hand-held compression tester under the conditions that the needle tip curvature radius is 0.5 mm and the puncture rate is 2 mm / sec.

[0057] According to embodiments of the present disclosure, the porous polymer substrate can be any porous polymer substrate as long as it is a planar porous polymer substrate for an electrochemical device. For example, an insulating film exhibiting high ion permeability and mechanical strength and generally having a pore diameter of 10-100 nm and a thickness of 5-12 μm can be used.

[0058] 3) Inorganic coating layer

[0059] According to the present disclosure, the separator includes an inorganic coating layer formed on at least one surface of the porous polymer substrate. The inorganic coating layer includes a mixture containing a binder resin and inorganic particles. In the inorganic coating layer, the inorganic particles are attached to each other (i.e., the binder resin connects and fixes the inorganic particles to each other), so that the inorganic particles can maintain their combined state. According to embodiments of the present disclosure, the inorganic particles are closely packed in the inorganic coating layer, and the inorganic coating layer can have a plurality of micropores derived from the volume of gaps formed between the inorganic particles. The micropores are connected to each other to provide a porous structure allowing a gas or a liquid to reach from one surface to the other surface. According to embodiments of the present disclosure, the inorganic particles are entirely or partially surface-coated with the binder resin and are combined with each other in a face-to-face or point-to-point manner by means of the binder resin. According to embodiments of the present disclosure, the inorganic particles can be present in an amount of 50% by weight or more, preferably 60% by weight or more, 70% by weight or more, or 80% by weight or more, based on the total weight of the binder resin and the inorganic particles of 100% by weight. Within the above range, the inorganic particles can also be present in an amount of 95% by weight or less, or 90% by weight or less, based on the total weight of the binder resin and the inorganic particles of 100% by weight.

[0060] The thickness of the inorganic coating layer on one surface of the porous substrate is preferably 1-5 μm. Preferably, the thickness can be 3 μm or more. Within the above range, excellent adhesion of the electrode can be provided, thereby providing increased cell strength. At the same time, in terms of the cycle characteristics and resistance characteristics of the battery, it is recommended that the thickness of the inorganic coating layer be 4 μm or less.

[0061] Further, according to the present disclosure, due to the features of the method for manufacturing the separator described hereinafter, the inorganic coating layer is provided with an electrode-adhesion portion 121 having a high binder resin content at a top portion thereof. Figure 1 is a schematic diagram showing a cross-sectional structure of a separator 100 according to embodiments of the present disclosure. Referring to Figure 1The separator according to the present disclosure includes an inorganic coating layer 120 formed on the surface of the porous polymer substrate 110, in which the binder resin is distributed at a higher concentration at the top layer portion of the inorganic coating layer compared to other portions. For ease of description, the top layer portion in which the binder resin is distributed at a higher concentration will be referred to as an "electrode adhesion portion 121" hereinafter. According to embodiments of the present disclosure, the electrode adhesion portion is a result of migration of the binder resin toward the top layer portion by a process such as wet phase separation. Thus, the electrode adhesion portion is not a structure physically separated from the inorganic coating layer, but is integrally and inseparably combined on the surface of the inorganic coating layer as a part of the inorganic coating layer. In addition, the thickness of the electrode adhesion portion can be non-uniform. According to embodiments of the present disclosure, the electrode adhesion portion can be defined as a portion in which the content of the binder resin is 70% by weight or more, preferably 85% by weight or more, from the topmost portion in the thickness direction of the inorganic coating layer.

[0062] B. Materials for the inorganic coating layer

[0063] B1. Binder resin

[0064] According to embodiments of the present disclosure, the inorganic coating layer includes a polyvinylidene fluoride (PVdF)-based polymer as the binder resin. The PVdF-based polymer has a main chain and at least one hydrogen atom in the main chain is substituted with a functional group derived from an acrylic compound. The PVdF-based polymer has higher adhesion compared to a binder resin not containing a functional group derived from an acrylic compound, and thus is able to ensure adhesion to a level that cannot be achieved by other PVdF-based binder polymers having the same molecular weight and / or the same substitution rate with another monomer such as hexafluoropropylene (HFP). In addition, the binder polymer provides an effect of improving adhesion in a wet state after injection of an electrolyte, i.e., in a state in which the separator is impregnated with an electrolyte.

[0065] According to the present disclosure, the PVdF-based polymer includes a copolymer of vinylidene fluoride (VDF) and a monomer copolyable with the vinylidene fluoride as its main chain. According to embodiments of the present disclosure, specific examples of the monomer can include at least one of trifluoroethylene (TrFE); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ether such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), or perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxolane); and perfluoro(2,2-dimethyl-1,3-dioxolane) (PDD). According to embodiments of the present disclosure, the PVdF-based polymer can include at least one selected from polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polyvinylidene fluoride-trifluorochloroethylene (PVdF-TrFE), polyvinylidene fluoride-tetrafluoroethylene (PVdF-TFE), or the like.

[0066] According to embodiments of the present disclosure, the substitution rate of the monomer of the PVdF-based polymer is 1-20% by weight, preferably 2-15% by weight. When the substitution rate is lower than the above range, the melting point (T m ) of the adhesive resin increases, thereby causing a decrease in adhesion. According to embodiments of the present disclosure, the substitution rate of the monomer can be determined based on the integration of characteristic peaks of the monomer determined in H NMR (Nuclear Magnetic Resonance) spectroscopy. For analysis of the substitution rate, refer to Journal of Materials Chemistry, 2012, Vol. 22, p. 341 or AMT-3412-Ok. The determination can be made by NMR spectroscopy using a suitable instrument such as Bruker Avance III HD 700MHz NMR or Varian 500MHz NMR. 1

[0067] According to embodiments of the present disclosure, the adhesive resin can include a polyvinylidene fluoride (PVdF)-based polymer into which a functional group derived from an acrylic compound is introduced. For example, the PVdF-based polymer can be represented by the following [Chemical Formula 1]. In [Chemical Formula 1], at least one hydrogen atom in the main chain of PVdF-HFP is substituted with a functional group derived from an acrylic compound.

[0068] [Chemical Formula 1]

[0069] ​

[0070] In [Chemical Formula 1], R1and R2each independently represent H or a group represented by the following [Chemical Formula 2], and x, y, and z each are an integer of 1 or more.

[0071] [Chemical Formula 2]

[0072]

[0073] In [Chemical Formula 2], R3, R4, and R5may each independently represent H or an alkyl group of C10or less. In addition, each hydrogen atom bonded to each carbon atom of R3, R4, and R5may be independently substituted with an element or a functional group other than H. The functional group can include at least one of an ester, a ketone, a hydroxyl group, an ether, a carboxyl group, and a carbonyl group.

[0074] According to embodiments of the present disclosure, the functional group derived from an acrylic compound can be derived from at least one selected from the group consisting of (meth)acrylic acid, (meth)acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, (meth)acrylonitrile, (meth)acrylic acid butyl ester, (meth)acrylic acid 2-ethylhexyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid methyl ester, (meth)acrylic acid n-propyl ester, (meth)acrylic acid isopropyl ester, (meth)acrylic acid tert-butyl ester, (meth)acrylic acid pentyl ester, (meth)acrylic acid n-octyl ester, (meth)acrylic acid isooctyl ester, (meth)acrylic acid isononyl ester, (meth)acrylic acid lauryl ester, (meth)acrylic acid myristyl ester, dimethyl 2-methylenepentanedionate, hydroxypropyl methacrylate, or the like.

[0075] According to embodiments of the present disclosure, the PVdF-based polymer can include at least one compound represented by [Chemical Formula 2].

[0076] According to the present disclosure, the acrylic compound-derived functional group can be introduced into the PVdF-based polymer in an amount of 0.1-5% by weight, preferably 0.1-3% by weight. When the content of the acrylic compound-derived functional group is too high, the formation of the adhesive portion can be interrupted. When the content of the acrylic compound-derived functional group is lower than the above range, even if the adhesive portion is formed, it is not possible to achieve the desired level of adhesion.

[0077] According to embodiments of the present disclosure, the content of the acrylic compound-derived functional group introduced into the PVdF-based polymer can be determined based on the integration of characteristic peaks of monomers determined in H NMR (Nuclear Magnetic Resonance) spectroscopy. 1 The content of the acrylic compound-derived functional group introduced into the PVdF-based polymer can be determined based on the integration of characteristic peaks of monomers determined in H NMR (Nuclear Magnetic Resonance) spectroscopy. For analysis of the substitution rate, refer to Journal of Materials Chemistry, 2012, Vol. 22, p. 341 or AMT-3412-Ok. The determination can be made by NMR spectroscopy using a suitable instrument such as a Bruker Avance III HD 700MHz NMR or a Varian 500MHz NMR.

[0078] According to embodiments of the present disclosure, the PVdF-based polymer can have a weight average molecular weight of 100,000-800,000, preferably 100,000-600,000. For example, the PVdF-based polymer can have a weight average molecular weight of 300,000-500,000. When the weight average molecular weight is too large, the formation of the adhesive portion on the surface of the inorganic coating layer is delayed as described below, and thus it is difficult to achieve adhesion. When the weight average molecular weight is too small, the adhesive portion can be formed rapidly. However, in this case, the content of the binder resin in the inorganic coating layer is low, and thus the adhesion between the inorganic particles or the peel strength between the inorganic particles and the substrate can be reduced.

[0079] As used herein, the term "molecular weight" refers to a weight average molecular weight (Mw) and can be expressed in g / mol. Further, the molecular weight can be determined, for example, by using gel permeation chromatography (GPC: PL GPC220, Agilent Technologies).

[0080] According to embodiments of the present disclosure, the method of preparing the PVdF-based polymer into which the acrylic compound-derived functional group is introduced is not particularly limited as long as it can provide a polymer having the above-described properties. For example, the method disclosed in Korean Patent Publication No. 10-1298507 can be used.

[0081] According to embodiments of the present disclosure, a PVdF-based polymer into which a functional group derived from an acrylic compound is introduced can be obtained by a method of polymerizing monomers in an aqueous medium using a surfactant. For example, polymerization can be performed by introducing water, at least one non-fluorinated surfactant, at least one monomer, at least one acrylic compound, and a polymerization initiator into a reactor and initiating polymerization. As for vinylidene fluoride (VDF) and monomers copolymerizable with vinylidene fluoride, see the above description. Preferably, the monomers can include vinylidene fluoride and hexafluoropropylene (HFP). Further, as for the acrylic compound, see the above description. The non-fluorinated surfactant can include at least one selected from the group consisting of polyacrylic acid, polyvinylsulfonic acid, and polyvinylphosphonic acid. The polymerization initiator is a chemical capable of providing a radical source, and a persulfate or an organic peroxide compound can be used as the polymerization initiator.

[0082] The polymerization can be performed at a temperature of about 35-130°C, optionally at a pressure of about 2,000-11,000 KPa. Further, the polymerization is preferably performed with stirring. The polymer obtained by the above method can have a latex shape.

[0083] Further, according to embodiments of the present disclosure, a PVdF-based polymer into which a functional group derived from an acrylic compound is introduced can be obtained by subjecting a PVdF-based polymer into which no functional group derived from an acrylic compound is introduced and an acrylic compound to light irradiation or electron beam irradiation. For example, an acrylic compound can be introduced into a PVdF-HFP chain using the following method: preparing a particulate or powdery mixture including PVdF-HFP and an acrylic compound, and irradiating photons or electrons to the mixture under an oxygen-free condition.

[0084] According to embodiments of the present disclosure, if necessary, the inorganic coating layer can further include a second binder resin in addition to the PVdF-based copolymer. Specific examples of the second binder resin can include, but are not limited to, polymethylmethacrylate, polybutyl acrylate, polybutylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinylalchol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxy methyl cellulose, or the like. The content of the second binder resin can be appropriately adjusted in consideration of adhesion. For example, the second binder resin can be used in an amount of 10% by weight or less, based on 100% by weight of the binder resin.

[0085] According to embodiments of the present disclosure, the inorganic coating can further include an additive, such as a dispersant and / or a thickening agent, in an amount of 1-3% by weight, based on 100% by weight of the inorganic coating. According to embodiments of the present disclosure, the additive can be suitably selected from at least one of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), ethylhydroxyethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose, and cyanoethyl polyvinyl alcohol.

[0086] B2. Inorganic particles

[0087] According to specific embodiments of the present disclosure, the inorganic particles are not particularly limited as long as they are electrochemically stable. In other words, the inorganic particles usable herein are not particularly limited as long as they do not cause oxidation and / or reduction within the working voltage range of an applicable electrochemical device (e.g., 0-5V based on Li / Li+). Specifically, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolyte can be improved by increasing the degree of dissociation of an electrolyte salt, such as a lithium salt, in the liquid electrolyte.

[0088] For the above reasons, the inorganic particles can be high-dielectric-constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more can include BaTiO3, Pb(Zr,Ti)O3(PZT, where 0 1-x La x Zr 1-y Ti y O3(PLZT, where 0 1 / 3 Nb 2 / 3 )O3PbTiO3(PMN-PT), hafnium dioxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, and TiO2, or a mixture thereof.

[0089] Further, as the inorganic particles, inorganic particles having lithium ion transportability, i.e., inorganic particles containing lithium element and not storing lithium but transporting lithium ions, can be used. Non-limiting examples of the inorganic particles having lithium ion transportability include: lithium phosphate (Li3PO4); lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3); lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3); (LiAlTiP) x O y based glass (0 < x < 4, 0 < y < 13), such as 14Li2O-9Al2O3-38TiO2-39P2O5; lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3); lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), such as Li 3.25 Ge 0.25 P 0.75 S4; lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), such as Li3N; SiS2-based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), such as Li3PO4-Li2S-SiS2; and P2S5-based glass (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), such as LiI-Li2S-P2S5, or a mixture of two or more thereof.

[0090] Further, the average particle diameter of the inorganic particles is not particularly limited. However, from the viewpoint of forming a coating layer having a uniform thickness and a suitable porosity, the average particle diameter of the inorganic particles is preferably 0.1-1.5 μm. When the average particle diameter is less than 0.1 μm, dispersibility can be deteriorated. When the average particle diameter is greater than 1.5 μm, the resulting coating layer can have an increased thickness.

[0091] 2. A method for forming an inorganic coating layer

[0092] The manufacturing method of the separator according to the embodiments of the present disclosure includes: preparing a slurry for an inorganic coating layer including inorganic particles, a binder resin, and a solvent; and,

[0093] The slurry is coated on at least one surface of a separator substrate, and then dried. Further, the drying step can be performed under a humidified condition. In one modification, the drying step can be performed by immersing the porous substrate coated with the slurry in a non-solvent for the binder resin, such as water or alcohol, to solidify the binder resin.

[0094] First, the binder resin is dissolved in a solvent to prepare a polymer binder solution. Next, the polymer binder solution is introduced into and mixed with a mixture including inorganic particles and a solvent to prepare a slurry for forming an inorganic coating layer. The inorganic particles can be added after being previously pulverized to a predetermined average particle diameter. In one modification, the inorganic particles can be introduced and then dispersed, while being controlled and pulverized to a predetermined average particle diameter by a ball milling process or the like. If necessary, an auxiliary agent such as a dispersant can be further introduced into the mixture and / or the slurry.

[0095] Then, the slurry is applied to a porous polymer substrate, and allowed to stand for a predetermined time under a humidified condition to solidify (dry) the binder resin.

[0096] When the binder resin is solidified under a humidified condition, phase separation of the binder resin occurs in the slurry. According to the embodiments of the present disclosure, the humidified condition can include a relative humidity of about 40-80%. During the phase separation, the solvent migrates toward the surface portion of the inorganic coating layer, and as the solvent migrates, the binder resin migrates toward the surface portion of the inorganic coating layer, thereby forming an electrode-adhering portion having a high binder resin content in the top portion. As a result, according to the present disclosure, the electrode-adhering portion having a high binder content is effectively formed in the top portion by the PVdF-based polymer, and a sufficient amount of the functional group derived from the acrylic compound is present in the binder resin distributed in the electrode-adhering portion, so that high adhesion between the electrode and the separator can be achieved.

[0097] The solvent can be a component capable of dissolving the binder resin. Preferably, a ketone solvent can be used. According to the embodiments of the present disclosure, the solvent can be appropriately selected from acetone, methyl ethyl ketone, N-methylpyrrolidone, and polar amide solvents such as dimethylacetamide, dimethylformamide, and diethylformamide, but is not limited thereto.

[0098] The slurry can be applied by a conventional coating process, such as a Mayer rod coating, a die coating method, a reverse roll coating method, or a gravure coating. When the inorganic coating layer is formed on both surfaces of the porous substrate, the coating solution can be applied to each surface, and then the wet phase separation and drying can be performed. However, in terms of productivity, it is preferable that the coating solution is simultaneously coated on both surfaces of the porous substrate, and then the wet phase separation and drying are performed.

[0099] 3. Electrode assembly including separator

[0100] Further, the present disclosure provides a secondary battery including the separator. The battery includes a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, wherein the separator is a low-resistance separator having the above-described characteristics.

[0101] According to the present disclosure, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the current collector and containing a positive electrode active material, a conductive material, and a binder resin. The positive electrode active material can include any one selected from the group consisting of a layered compound such as lithium manganese composite oxides (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), and lithium nickel oxide (LiNiO2), or those compounds substituted with one or more transition metals; those represented by the chemical formula Li 1+x Mn 2-x O4 (wherein x is 0-0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, or Cu2V2O7; Ni-site type lithium nickel oxides represented by the chemical formula Li 1-x M x NiO2 (wherein M is Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x is 0.01-0.3); lithium manganese composite oxides represented by the chemical formula Li a Ni x Co y Mn z O2 (0 2- x M x O2 (wherein M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01-0.1) or Li2Mn3MO8 (wherein M = Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which Li is partially substituted with an alkaline earth metal ion; a disulfide compound; and Fe2(MoO4)3; or a mixture of two or more thereof.

[0102] According to the present disclosure, a negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the current collector and containing a negative electrode active material, a conductive material, and a binder resin. The negative electrode can include any one selected from the group consisting of lithium metal oxides; carbon such as non-graphitized carbon or graphite-based carbon; metal composite oxides such as Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, elements of Group 1, 2, or 3 of the periodic table, halogen; 0 < x < 1; 1 < y < 3; 1 < z < 8); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxide such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymer such as polyacetylene; Li-Co-Ni type material; and titanium oxide; or a mixture of two or more of them.

[0103] According to embodiments of the present disclosure, the conductive material can be any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon, and polyaniline derivative, or a mixture of two or more of these conductive materials. More specifically, the conductive material can be any one selected from the group consisting of natural graphite, artificial graphite, Super-P, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium dioxide, or a mixture of two or more of such conductive materials.

[0104] The current collector is not particularly limited as long as it does not cause chemical changes within the corresponding battery and has high conductivity. Specific examples of the current collector can include stainless steel, copper, aluminum, nickel, titanium, calcined carbon, aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver, or the like.

[0105] The binder resin can be a polymer currently used in the art for electrodes. Non-limiting examples of binder resins include, but are not limited to: polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinylalchol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxy methyl cellulose.

[0106] The electrode assembly prepared as described above can be introduced into a suitable housing, and an electrolyte can be injected thereto to obtain a battery.

[0107] According to the present disclosure, the electrolyte is a salt having a structure of A + B - wherein A + comprises an alkali metal cation such as Li + , Na + , K + or a combination thereof, and B - comprises an anion such as PF6 - , BF4 - , Cl - , Br - , I- , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - or a combination thereof, the salt being dissolved or dissociated in an organic solvent selected from propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone (γ-butyrolactone), an ester compound, or a mixture thereof. However, the present disclosure is not limited thereto.

[0108] Further, according to an embodiment of the present disclosure, the organic solvent includes an ester compound. Preferably, the ester compound is used in an amount of 30% by weight or more, 50% by weight or more, 60% by weight or more, or 65% by weight or more, based on 100% by weight of the organic solvent.

[0109] According to an embodiment of the present disclosure, the ester compound includes any one selected from the group consisting of isobutyl propionate, isoamyl propionate, isobutyl butyrate, isopropyl propionate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

[0110] Further, the present disclosure provides a battery module including a battery including the electrode assembly as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include, but are not limited to, a power tool driven by an electric motor, an electric vehicle including an Electric Vehicle (EV), a Hybrid Electric Vehicle (HEV), a Plug-in Hybrid Electric Vehicle (PHEV), or the like, an electric two-wheeler including an E-bike and an E-scooter, an electric golf cart, a power storage system, or the like.

[0111] Embodiments will be described more fully below to enable a readily understandable understanding of this disclosure. However, the following embodiments may be embodied in many different forms and should not be construed as limiting to the exemplary implementations set forth herein. Rather, these exemplary implementations are provided so that this disclosure will be comprehensive and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0112] (1) Manufacturing of partitions

[0113] Example 1

[0114] First, Al2O3, PVdF-HFP (Arkema), and a dispersant (cyanoethyl polyvinyl alcohol) were introduced into acetone in a weight ratio of 90:9:1 to obtain a slurry for forming an inorganic coating. PVdF-HFP had an HFP substitution rate of 8% by weight and included a functional group derived from an acrylic compound (dimethyl 2-methylenepentanedioate) introduced in an amount of 1% by weight. Furthermore, the molecular weight (M) of PVdF-HFP used as an adhesive resin was... w The concentration was 450,000 g / mol. The slurry was prepared at a concentration of 15 g / m² based on the partition area. 2 The load was applied to the separator (polyethylene, 45% porosity, 9μm thickness) and dried under humidified conditions at a relative humidity of 55%. The dried product was then cut into 60mm (length) × 25mm (width) dimensions to obtain the separator.

[0115] Example 2

[0116] First, Al2O3, PVdF-HFP (Arkema), and a dispersant (cyanoethyl polyvinyl alcohol) were introduced into acetone in a weight ratio of 84:15:1 to obtain a slurry for forming an inorganic coating. PVdF-HFP had an HFP substitution rate of 8% by weight and included a functional group derived from an acrylic compound (dimethyl 2-methylenepentanedioate) introduced in an amount of 1% by weight. Furthermore, the molecular weight (M) of PVdF-HFP used as an adhesive resin was... w The concentration was 450,000 g / mol. The slurry was prepared at a concentration of 15 g / m² based on the partition area. 2 The load was applied to the separator (polyethylene, 45% porosity, 9μm thickness) and dried under humidified conditions at a relative humidity of 55%. The dried product was then cut into 60mm (length) × 25mm (width) dimensions to obtain the separator.

[0117] Example 3

[0118] First, Al203, PVdF-HFP (Arkema) and a dispersant (cyanoethyl polyvinyl alcohol) were introduced into acetone at a weight ratio of 78:20:2 to obtain a slurry for forming an inorganic coating layer. The PVdF-HFP had an HFP substitution rate of 8 wt%, and included a functional group derived from an acrylic compound (dimethyl 2-methylenepentanedioate) introduced in an amount of 1 wt%. In addition, the molecular weight (Mw) of the PVdF-HFP used as a binder resin was 450,000 g / mol. The slurry was applied to a separator (polyethylene, porosity 45%, thickness 9 μm) at a loading of 15 g / m2based on the area of the separator, and dried under humidification conditions at a relative humidity of 55%. Then, the dried product was cut to a size of 60 mm (length) x 25 mm (width), thereby obtaining a separator. w 2

[0119] Example 4

[0120] First, Al203, PVdF-HFP (Arkema) and a dispersant (cyanoethyl polyvinyl alcohol) were introduced into acetone at a weight ratio of 90:9:1 to obtain a slurry for forming an inorganic coating layer. The PVdF-HFP had an HFP substitution rate of 8 wt%, and included a functional group derived from an acrylic compound (dimethyl 2-methylenepentanedioate) introduced in an amount of 3 wt%. In addition, the molecular weight (Mw) of the PVdF-HFP used as a binder resin was 380,000 g / mol. The slurry was applied to a separator (polyethylene, porosity 45%, thickness 9 μm) at a loading of 15 g / m2based on the area of the separator, and dried under humidification conditions at a relative humidity of 55%. Then, the dried product was cut to a size of 60 mm (length) x 25 mm (width), thereby obtaining a separator. w 2

[0121] Example 5

[0122] ​​​​First, Al2O3, PVdF-HFP (Arkema), and a dispersant (cyanoethyl polyvinyl alcohol) were introduced into acetone in a weight ratio of 90:9:1 to obtain a slurry for forming an inorganic coating. PVdF-HFP had an HFP substitution rate of 15% by weight and included a functional group derived from an acrylic compound (dimethyl 2-methylenepentanedioate) introduced in an amount of 1% by weight. Furthermore, the molecular weight (M) of PVdF-HFP used as an adhesive resin was... w The concentration is 500,000 g / mol. The slurry is prepared at a concentration of 15 g / m² based on the partition area. 2 The load was applied to the separator (polyethylene, 45% porosity, 9μm thickness) and dried under humidified conditions at a relative humidity of 55%. The dried product was then cut into 60mm (length) × 25mm (width) dimensions to obtain the separator.

[0123] Comparative Example 1

[0124] First, Al2O3, PVdF-HFP (Arkema), and a dispersant (cyanoethyl polyvinyl alcohol) were introduced into acetone in a weight ratio of 90:9:1 to obtain a slurry for forming an inorganic coating. PVdF-HFP had an HFP substitution rate of 15% by weight. Furthermore, unlike Examples 1-5, PVdF-HFP did not include the introduced acrylic compound-derived functional groups. Additionally, the molecular weight (M) of PVdF-HFP used as an adhesive resin was... w The concentration was 450,000 g / mol. The slurry was prepared at a concentration of 15 g / m² based on the partition area. 2 The load was applied to the separator (polyethylene, 45% porosity, 9μm thickness) and dried under humidified conditions at a relative humidity of 55%. The dried product was then cut into 60mm (length) × 25mm (width) dimensions to obtain the separator.

[0125] Comparative Example 2

[0126] First, Al2O3, PVdF-HFP (Arkema), and a dispersant (cyanoethyl polyvinyl alcohol) were introduced into acetone in a weight ratio of 90:9:1 to obtain a slurry for forming an inorganic coating. PVdF-HFP had an HFP substitution rate of 8% by weight. Furthermore, unlike Examples 1-5, PVdF-HFP did not include the introduced acrylic compound-derived functional groups. Additionally, the molecular weight (M) of PVdF-HFP used as an adhesive resin was... w The concentration was 380,000 g / mol. The slurry was prepared at a concentration of 15 g / m² based on the partition area. 2The binder solution was applied to a separator (polyethylene, porosity 45%, thickness 9 μm) at a loading amount of 15 g / m

[0127] Comparative Example 3

[0128] First, Al2O3, PVdF-HFP (Arkema), and a dispersant (cyanoethyl polyvinyl alcohol) were introduced into acetone at a weight ratio of 90:9:1 to obtain a slurry for forming an inorganic coating layer. The PVdF-HFP had a HFP substitution rate of 22 wt%. In addition, the molecular weight (M w ) of the PVdF-HFP used as a binder resin was 400,000 g / mol. The slurry was applied to a separator (polyethylene, porosity 45%, thickness 9 μm) at a loading amount of 15 g / m 2

[0129] (2) Manufacture of an electrode

[0130] Natural graphite, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) (weight ratio of 90:9:1) were introduced into water to obtain a negative electrode slurry. The negative electrode slurry was applied to a copper film (thickness 10 μm) at a loading amount of 125 mg / cm 2

[0131] (3) Analysis of results

[0132] 1) Evaluation of the adhesion of the binder to the electrode

[0133] The binder resin used in each of Examples 1-5 and Comparative Examples 1-3 was introduced into dimethyl carbonate (DMC) to obtain a binder solution. The binder solution was applied to a separator (polyethylene, porosity 45%, thickness 9 μm) at a loading amount of 15 g / m 2 ​​The load amount of the above-mentioned was applied to a glass plate (thickness 200 μm), and then dried. Next, the resulting product was cut into a size of 60 mm (length) x 25 mm (width) to obtain an adhesive film. The adhesive film was disposed on the surface of the negative electrode prepared by the preparation example, and lamination was performed at a temperature of 90°C under a pressure of 8.5 MPa to prepare a sample. The sample was cut into a size of 70 mm (length) x 15 mm (width), and the sample was attached to a glass plate to which a double-sided tape was applied, so that the electrode surface can be attached to the glass plate. Each sample was fixed to an adhesive strength tester (LLOYD Instrument, LF plus), and the upper separator sample was peeled at an angle of 180° at a rate of 15 mm / min at 25°C, and the strength was measured.

[0134] 2) Adhesion to the electrode ((-)-adhesion)

[0135] 2-1) Dry adhesion

[0136] The separator according to each of Examples 1-5 and Comparative Examples 1-3 was cut into a size of 70 mm (length) x 25 mm (width), and the separator was laminated with the negative electrode prepared as described above using a press at 70°C, 4 MPa to obtain a sample. The sample was attached and fixed to a glass plate using a double-sided tape so that the negative electrode can face the glass plate. The separator portion of the sample was peeled at an angle of 180° at a rate of 15 mm / min at 25°C, and the strength was measured.

[0137] 2-2) Wet adhesion

[0138] The separator according to each of Examples 1-5 and Comparative Examples 1-3 was cut into a size of 70 mm (length) x 25 mm (width), and the separator was laminated with the negative electrode prepared as described above using a press at 70°C, 4 MPa to obtain a sample. The sample was introduced into a battery case together with an electrolyte, and left therein for 4 hours so that the sample can be impregnated with the electrolyte. The electrolyte included 1M LiPF6dissolved in ethylene carbonate and propionate mixed at a volume ratio of 7:3. Then, the sample was taken out of the case, and then attached and fixed to a glass plate using a double-sided tape so that the negative electrode can face the glass plate. The separator portion of the sample was peeled at an angle of 180° at a rate of 15 mm / min at 25°C, and the strength was measured.

[0139] 3) Measurement of thermal shrinkage

[0140] 3-1) Measurement of dry thermal shrinkage

[0141] The separator according to each of Examples 1-5 and Comparative Examples 1-3 was cut into a size of 70 mm (length) x 25 mm (width), and was laminated with the negative electrode prepared as described above using a press at 70°C, 4 MPa to obtain a sample. Each sample was left in an oven at 150°C for 30 minutes, and the shrinkage in the longitudinal and transverse directions was measured. Here, the shrinkage was calculated by the following [Mathematical Formula 1].

[0142] [Mathematical Formula 1]

[0143] Thermal shrinkage (%) = [(length before thermal shrinkage - length after thermal shrinkage) / length before thermal shrinkage] x 100

[0144] 3-2) Measurement of wet thermal shrinkage

[0145] The separator according to each of Examples 1-5 and Comparative Examples 1-3 was cut into a size of 70 mm (length) x 25 mm (width), and was laminated with the negative electrode prepared as described above using a press at 70°C, 4 MPa to obtain a sample. The sample was introduced into a battery case together with an electrolyte, and was left therein for 4 hours so that the sample can be impregnated with the electrolyte. The electrolyte included 1M LiPF6dissolved in ethylene carbonate and propionate mixed at a volume ratio of 7:3. Then, the sample was taken out of the case, and then the sample was left in an oven at 150°C for 30 minutes, and the shrinkage thereof in the longitudinal and transverse directions was measured. Here, the shrinkage was calculated by [Mathematical Formula 1].

[0146] Table 1 below shows the results of the measurement of the adhesion force and the thermal shrinkage.

[0147] As can be seen from Table 1, the separators according to Examples 1-5 showed higher peel strength and adhesion to the electrode compared to the separators according to Comparative Examples 1-3. In particular, it can be seen that the separators according to the Comparative Examples did not achieve adhesion to the electrode in the wet state. Further, it can be seen that in the case of thermal shrinkage, the separators according to Examples 1-5 showed a decrease in thermal shrinkage in both the dry state and the wet state.

[0148] The separators having higher adhesion between the separator substrate and the inorganic coating layer showed lower thermal shrinkage when the same thickness and the same load amount were used. The separator substrate based on a polymer material exhibits a characteristic (shrinkage characteristic) of returning to its state before orientation once heated. In the case of the separator having the inorganic coating layer formed on the surface of the separator substrate, as the binding force between the separator substrate and the inorganic coating layer increases, the separator substrate is better attached to the inorganic coating layer. Thus, the inorganic coating layer functions to fix the separator substrate. Therefore, shrinkage of the separator substrate can be prevented even when heat is applied to the separator, and thus the separator can maintain its original shape without shrinking. It can be seen that each of the separators according to Embodiments 1-5 of the present disclosure showed excellent binding force between the separator substrate and the inorganic coating layer in both the dry state and the wet state, thus providing lower thermal shrinkage in both states.

[0149] [Table 1]

[0150]

[0151]

Claims

1. A separator for an electrochemical device, the separator comprising a porous polymer substrate and an inorganic coating layer formed on at least one surface of the porous polymer substrate, wherein the inorganic coating layer comprises inorganic particles and a binder resin, the binder resin is polyvinylidene hexafluoropropylene, and the polyvinylidene hexafluoropropylene has a main chain and at least one hydrogen atom in the main chain is substituted with a functional group derived from an acrylic compound, wherein the separator has a high binder resin content and a binder top layer portion provided on a surface of the inorganic coating layer, the binder top layer portion is obtained from a phase separation process of the binder resin when the separator is dried under a humidified condition, and The polyvinylidene fluoride-hexafluoropropylene includes: the functional group derived from the acrylic compound is introduced into the polyvinylidene hexafluoropropylene at a ratio of 0.1-5% by weight based on 100% by weight of the polyvinylidene hexafluoropropylene, and the polyvinylidene hexafluoropropylene has a weight average molecular weight of 100,000-600,000, and a substitution rate of the hexafluoropropylene is 8-20% by weight.

2. The separator for an electrochemical device according to claim 1, wherein the functional group derived from the acrylic compound is derived from at least one selected from the group consisting of (meth)acrylic acid, (meth)acrylate, (meth)acrylonitrile, and dimethyl 2-methylenepentanedionate.

3. The separator for an electrochemical device according to claim 1, wherein the inorganic coating layer comprises the inorganic particles in an amount of 50% by weight or more based on the total weight of the inorganic particles and the binder resin of 100% by weight.

4. The separator for an electrochemical device according to claim 1, wherein the inorganic particles in the inorganic coating layer are held together with each other by the binder resin, the inorganic coating layer has a plurality of micropores derived from interstitial volumes formed between the inorganic particles, the inorganic coating layer has a high binder resin content and a binder top layer portion formed on a surface of the inorganic coating layer, and the inorganic coating layer and the binder top layer portion are integrally and inseparably combined with each other.

5. The separator for an electrochemical device according to claim 1, wherein the humidified condition includes a relative humidity of 40-80%.

6. An electrochemical device comprising a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, wherein the separator is defined in any one of claims 1 to 5.

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