technology field
[One]
This application claims priority based on Korean Patent Application No. 10-2020-0185814 filed on December 29, 2020. The present invention relates to a separator for an electrochemical device. More specifically, the electrode adhesive layer is disposed on one or both surfaces of the outermost layer of the separator to improve the stability and durability of the separator and to a separator of an electrochemical device with improved binding force with an electrode. In addition, the present invention relates to an electrochemical device including the separator.
[2]
background art
[3]
Secondary batteries are composed of anode/cathode/separator/electrolyte, and chemical energy and electrical energy are reversibly converted into energy storage devices with a high level of energy that can be charged and discharged. They are widely used in small electronic devices such as mobile phones and laptop computers. Recently, in response to environmental problems, high oil prices, energy efficiency and storage, hybrid electric vehicles (HEVs), plug-in EVs, e-bikes and energy storage systems have been developed. (Energy storage system, ESS) applications are rapidly expanding.
[4]
In the manufacture and use of these secondary batteries, securing their safety is an important challenge. In particular, separators commonly used in electrochemical devices have stability problems such as internal short circuits by exhibiting extreme thermal contraction behavior in situations such as high temperatures due to their material characteristics and manufacturing process characteristics. In order to secure the safety of such a secondary battery, an organic-inorganic composite porous separator in which a porous inorganic coating layer is formed by coating a mixture of inorganic particles and a binder resin on a porous substrate for a secondary battery separator has been proposed (Korean Patent Application No. 10-2004-0070096). Reference). However, when an electrode assembly is formed by stacking electrodes and separators, there is a high risk of electrodes and separators being separated from each other due to insufficient interlayer binding force, and in this case, there is a problem that inorganic particles detached during the separation process may act as local defects in the device. exist.
[5]
In order to solve this problem, Publication No. 10-2006-0116043 discloses a method in which ethanol is added to a solution in which PVDF is dissolved in a good solvent such as acetone, and then applied on a separator and dried to obtain a porous adhesive layer by a phase separation effect. are doing The porous adhesive layer obtained in this way has the advantages of excellent permeability and low resistance during battery operation, but due to swelling after injection during the battery manufacturing process, the bonding force with the separator, that is, the mechanical strength is lowered and exhibits low cycling characteristics Interlayer mixing with the porous inorganic coating layer occurs and pores formed in the porous inorganic coating layer are closed, resulting in deterioration in air permeability and resistance characteristics of the separator.
[6]
Accordingly, there is a demand for the development of a separator in which degradation of resistance characteristics is prevented even when an electrode adhesive layer is disposed.
[7]
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[8]
An object of the present invention is to provide a separator for an electrochemical device having an electrode adhesive layer disposed on a surface thereof. In addition, an object of the present invention is to provide a method for manufacturing a separator having high interfacial resistance between an electrode and a separator, in which air permeability and ion conductivity of the separator are not reduced even when an electrode adhesive layer is disposed. It will be readily apparent that other objects and advantages of the present invention can be realized by means and combinations thereof indicated in the claims.
[9]
means of solving the problem
[10]
A first aspect of the present invention is a method for manufacturing a composite separator having an electrode adhesive layer, the method comprising applying a polymer solution for the adhesive layer to at least one surface of a separator substrate layer and drying the polymer solution, wherein the polymer solution is applied to the electrode adhesive layer. a binder resin and a mixed solvent, wherein the binder resin for the electrode adhesive layer includes a fluorine-based binder resin, the mixed solvent includes first and second solvents, and the first solvent for the polarity of the second solvent The ratio of polarity (polarity of the first solvent / polarity of the second solvent) is 0.360 or more, and the polarity of the first solvent and the second solvent are each independently according to the Dimroth-Reichardt ET30 polarity scale.
[11]
In the second aspect of the present invention, in the first aspect, the polarities of the first and second solvents are E T N values ​​independently calculated through [Equation 1] and [Equation 2] below.
[12]
[13]
[Equation 1]
[14]
E T (A) = 28,592 / λ max
[15]
[16]
[Equation 2]
[17]
E T N = [E T (A) - E T (TMS)] / [E T (H 2 O) - E T (TMS)]
[18]
[19]
In [Formula 1] and [Formula 2], the unit of E T (A) is kcal / mol, and in [Formula 2], E T (H 2 O) is 63.1 kcal / mol, E T ( TMS) is 30.7 kcal/mol.
[20]
[21]
In the third aspect of the present invention, according to any one of the first to second aspects, the first solvent includes one or a mixture of two or more selected from acetone, THF, DMF, and NMP, and the second solvent Is a lower alcohol having 1 to 3 carbon atoms and H 2 O to include one or a mixture of two or more selected from.
[22]
In a fourth aspect of the present invention, in any one of the first to third aspects, the polarity ratio is 0.360 to 0.450.
[23]
In a fifth aspect of the present invention, in any one of the first to fourth aspects, the fluorine-based binder resin is included in an amount of 90 wt% or more compared to 100 wt% of the binder resin for the electrode adhesive layer.
[24]
In the sixth aspect of the present invention, according to any one of the first to fifth aspects, the fluorine-based binder resin is a homopolymer of vinylidene fluoride (polyvinylidene fluoride), a copolymer of vinylidene fluoride and another copolymerizable monomer. It includes a combination or a mixture thereof.
[25]
In the seventh aspect of the present invention, in the sixth aspect, the copolymer of vinylidene fluoride and other copolymerizable monomers is polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene ), polyvinylidene fluoride-co-trichloroethylene, polyvinylidene fluoride-tetrafluoroethylene, and polyvinylidene fluoride-trifluoroethylene.
[26]
In the eighth aspect of the present invention, in the sixth or seventh aspect, the copolymer of the vinylidene fluoride and other copolymerizable monomers has a degree of substitution by the monomers of 5 wt% to 20 wt%.
[27]
A ninth aspect of the present invention relates to a separator for an electrochemical device, wherein the separator includes an electrode adhesive layer, wherein the crystallinity of the fluorine-based binder in the electrode adhesive layer is 40% or more, and the content of beta crystals is 80% or more. And it is prepared by any one of the methods of the first to eighth aspects.
[28]
A tenth aspect of the present invention relates to a lithium ion battery including a separator for an electrochemical device, wherein the electrochemical device includes a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, wherein the separator is It is according to the 9 aspect.
[29]
Effects of the Invention
[30]
When coating the adhesive layer, two types of solvents are used, and the beta crystal phase of the second binder resin is induced by using the polarity ratio. Accordingly, a uniform porous structure is formed to improve the movement path of lithium ions and the resistance of the separator even when the adhesive layer is formed. this does not increase
[31]
Brief description of the drawing
[32]
The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of ​​the present invention together with the contents of the above-described invention, so the present invention is limited to those described in the drawings. It should not be construed as limiting.
[33]
1 shows the distribution of the crystal phase b in the adhesive layer of the separation membranes of Example 1 and Comparative Example 1.
[34]
2a and 2b are SEM images of the surface of the separator obtained in Example 1.
[35]
3 is a SEM image of the surface of the separator obtained in Comparative Example 1.
[36]
4 is a SEM image of the surface of the separator obtained in Comparative Example 3.
[37]
Mode for Carrying Out the Invention
[38]
Hereinafter, one embodiment of the present invention will be described in more detail. In addition, the terms used in this specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventors may properly define the concept of terms in order to explain their invention in the best way. It should be interpreted as a meaning and concept consistent with the technical spirit of the present invention based on the principle that it can be. Therefore, since the configurations shown in the embodiments described herein are only one of the most preferred embodiments of the present invention and do not represent all of the technical spirit of the present invention, various equivalents that can replace them at the time of this application It should be understood that there may be waters and variations.
[39]
[40]
The present invention relates to a method for manufacturing a composite separator for an electrochemical device having an electrode adhesive layer on the outermost layer. In addition, the present invention relates to a composite separator manufactured by the above manufacturing method.
[41]
According to a specific embodiment of the present invention, the composite separator includes a separator substrate layer and an electrode adhesive layer formed on at least one surface of the separator substrate layer. In the present invention, the separator substrate layer refers to a porous ion-conducting barrier used to separate a cathode and an anode in an electrochemical device, and the composite separator has an electrode adhesive layer formed on at least one side of the separator substrate layer It is intended to refer to a separator for an electrochemical device.
[42]
The separator substrate layer constitutes the rest of the composite separator except for the electrode adhesive layer, and performs the function of a conventional separator that passes ions while blocking electrical contact between the cathode and anode. According to a specific embodiment of the present invention, the separator substrate layer may include a porous polymer substrate (A) having a plurality of micropores and/or a porous inorganic coating layer (B) including a plurality of inorganic particles. In one embodiment of the present invention, the separator substrate layer includes both the porous polymer substrate and the porous inorganic coating layer, and has a form in which the porous inorganic coating layer is coated on at least one surface or both surfaces of the porous substrate. can
[43]
[44]
According to a specific embodiment of the present invention, the porous polymer substrate can electrically insulate the negative electrode and the positive electrode to prevent a short circuit and provide a path for lithium ions to move, and if it can be used as a separator material for an electrochemical device, a special Can be used without restrictions. Examples of such a porous substrate include polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, and polyphenyl. There are porous substrates formed of at least one of polymer resins such as lensulfide and polyethylene naphthalene, but are not particularly limited thereto.
[45]
In addition, as the porous polymer substrate, both a film in the form of a sheet formed by melting a polymer resin and a non-woven fabric in which filaments obtained by melting and spinning a polymer resin are integrated can be used. Preferably, it is a porous substrate prepared in the form of a sheet by melting/molding the polymer resin.
[46]
[47]
Specifically, the porous polymer substrate may include any one of the following a) to e).
[48]
a) A porous film formed by melting/extruding a polymer resin
[49]
b) a multilayer film in which two or more layers of the porous film of a) are laminated;
[50]
c) a non-woven fabric web manufactured by integrating filaments obtained by melting/spinning a polymer resin;
[51]
d) a multilayer film in which two or more layers of the nonwoven web of b) are laminated;
[52]
e) A porous composite membrane having a multilayer structure comprising at least two of a) to d).
[53]
[54]
In the present invention, the thickness of the porous polymer substrate may be 5 to 50 ㎛. Although the range of the porous substrate is not particularly limited to the above-mentioned range, if the thickness is excessively thinner than the above-mentioned lower limit, mechanical properties may deteriorate and the separator may be easily damaged during use of the battery. On the other hand, the pore size and porosity present in the porous substrate are also not particularly limited, but may be 0.01 to 50 μm and 10 to 95%, respectively.
[55]
[56]
The porous inorganic coating layer includes a mixture of a plurality of inorganic particles and a binder resin, and since the surface of the porous substrate is coated with the inorganic particles, heat resistance and mechanical properties of the separator substrate layer are further improved.
[57]
The porous inorganic coating layer not only has a microporous structure due to interstitial volume between inorganic particles, but also serves as a kind of spacer capable of maintaining the physical shape of the coating layer. The interstitial volume refers to a space defined by substantially interviewing adjacent inorganic particles. In addition, since the inorganic particles generally have properties that do not change even at a high temperature of 200° C. or higher, the composite separator has excellent heat resistance due to the formed porous inorganic coating layer. In the present invention, the porous inorganic coating layer has a thickness of 1 μm to 50 μm, or 2 μm to 30 μm, or 2 μm to 20 μm.
[58]
The porous inorganic coating layer is prepared by dispersing a binder resin in an appropriate aqueous solvent such as water, injecting inorganic particles into an aqueous product prepared to prepare a uniform slurry, and then coating the slurry on at least one side of the porous substrate. can be manufactured. As the coating method, dip coating, die coating, roll coating, comma coating, or a combination thereof may be used.
[59]
In the porous inorganic coating layer, the content ratio of the inorganic particles and the binder resin is determined in consideration of the thickness, pore size and porosity of the porous inorganic coating layer of the present invention to be finally manufactured, but the inorganic particles are 50 to 99.9 weight based on the weight ratio. % or 70 to 99.5% by weight, and the polymer resin is 0.1 to 50% by weight or 0.5 to 30% by weight. When the content of the inorganic particles is less than 50% by weight, the content of the polymer is excessively high, and the pore size and porosity are reduced due to the reduction of the empty space formed between the inorganic particles, resulting in deterioration in final battery performance. On the other hand, when the content exceeds 99.9% by weight, the mechanical properties of the final porous inorganic coating layer are deteriorated due to the weakening of the adhesion between inorganic materials because the polymer content is too small.
[60]
According to a specific embodiment of the present invention, the inorganic particle size of the porous inorganic coating layer is not limited, but may range from 0.001 to 10 μm as much as possible in order to form a coating layer with a uniform thickness and an appropriate porosity. When the inorganic particle size satisfies this range, dispersibility is maintained, so it is easy to control the physical properties of the composite separator, and mechanical properties can be improved by avoiding an increase in the thickness of the porous inorganic coating layer. Due to the excessively large pore size, the probability of internal short circuit occurring during battery charging and discharging is low.
[61]
The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles are not particularly limited as long as oxidation and/or reduction reactions do not occur in the operating voltage range (eg, 0 to 5V based on Li/Li+) of the electrochemical device to which they are applied. In particular, in the case of using inorganic particles having an ion transport capability, ion conductivity in an electrochemical device may be increased to improve performance. In addition, when inorganic particles having a high permittivity are used as the inorganic particles, the dissociation degree of an electrolyte salt, for example, a lithium salt in the liquid electrolyte may be increased, thereby improving ionic conductivity of the electrolyte solution.
[62]
전술한 이유들로 인해, 상기 무기물 입자는 유전율 상수가 5 이상, 또는 10 이상인 고유전율 무기물 입자, 리튬 이온 전달 능력을 갖는 무기물 입자 또는 이들의 혼합체를 포함할 수 있다. 유전율 상수가 5 이상인 무기물 입자의 비제한적인 예로는 BaTiO 3, Pb(Zr,Ti)O 3 (PZT), Pb 1-xLa xZr 1-yTi yO 3 (PLZT, 여기서, 0 < x < 1, 0 < y < 1임), Pb(Mg 1/3Nb 2/3)O 3-PbTiO 3 (PMN-PT), 하프니아(HfO 2), SrTiO 3, SnO 2, CeO 2, MgO, NiO, CaO, ZnO, ZrO 2, Y 2O 3, Al 2O 3, SiC, TiO 2등을 각각 단독으로 또는 2종 이상을 혼합하여 사용할 수 있다. 또한, 전술한 고유전율 무기물 입자와 리튬 이온 전달 능력을 갖는 무기물 입자들을 혼용할 경우 이들의 상승 효과는 배가될 수 있다.
[63]
[64]
상기 리튬 이온 전달 능력을 갖는 무기물 입자의 비제한적인 예로는 리튬포스페이트(Li 3PO 4), 리튬티타늄포스페이트(Li xTi y(PO 4) 3, 0 < x < 2, 0 < y < 3), 리튬알루미늄티타늄포스페이트(Li xAl yTi z(PO 4) 3, 0 < x < 2, 0 < y < 1, 0 < z < 3), 14Li 2O-9Al 2O 3-38TiO 2-39P 2O 5 등과 같은 (LiAlTiP) xO y 계열 glass (0 < x < 4, 0 < y < 13), 리튬란탄티타네이트(Li xLa yTiO 3, 0 < x < 2, 0 < y < 3), Li 3.25Ge 0.25P 0.75S 4등과 같은 리튬게르마니움티오포스페이트(Li xGe yP zS w, 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), Li 3N 등과 같은 리튬나이트라이드(Li xN y, 0 < x < 4, 0 < y < 2), Li 3PO 4-Li 2S-SiS 2 등과 같은 SiS 2 계열 glass(Li xSi yS z, 0 < x < 3, 0 < y < 2, 0 < z < 4), LiI-Li 2S-P 2S 5등과 같은 P 2S 5 계열 glass(Li xP yS z, 0 < x < 3, 0 < y < 3, 0 < z < 7) 또는 이들의 혼합물 등이 있다.
[65]
상기 다공성 무기 코팅층에 포함되는 바인더 수지는 바람직하게는 유리 전이 온도(glass transition temperature, Tg)가 가능한 낮은 고분자 수지를 사용할 수 있으며, 상기 유리 전이 온도는 바람직하게는 -200℃ 내지 200℃ 범위이다. 이는 복합 분리막의 유연성 및 탄성 등과 같은 기계적 물성을 향상시킬 수 있기 때문이다. 상기 바인더 수지는 무기물 입자간 점착을 안정하게 고정함으로써 최종 제조되는 다공성 무기 코팅층의 기계적 물성 저하 방지에 기여한다. 본 발명에 있어서, 상기 바인더 수지는 이온 전도 능력을 반드시 가질 필요는 없으나, 이온 전도 능력을 갖는 고분자 수지를 사용할 경우 전기 화학 소자의 성능을 더욱 향상시킬 수 있다. 따라서, 바인더 수지는 가능한 유전율 상수가 높은 것이 바람직하다. 이에 따라, 용해도 지수가 15 내지 45 MPa 1/2인 고분자 수지가 바람직하며, 더욱 바람직하게는 15 내지 25 MPa 1/2 및 30 내지 45 MPa 1/2범위이다. 따라서, 폴리올레핀류와 같은 소수성 고분자 수지들 보다는 극성기를 많이 갖는 친수성 고분자 수지들이 바람직하다. 용해도 지수가 15 MPa 1/2 미만 및 45 MPa 1/2를 초과하는 경우 통상적인 전지용 액체 전해액에 의해 함침되기 어렵다.
[66]
Non-limiting examples of the binder resin usable in the present invention include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene , polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer co-vinyl acetate), polyethylene oxide, polyarylate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethyl It may be any one polymer resin selected from the group consisting of cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, or a mixture of two or more of them. However, it is not particularly limited thereto.
[67]
[68]
Meanwhile, the pore size and porosity of the porous inorganic coating layer mainly depend on the size of the inorganic particles. For example, when inorganic particles having a particle size of 1 μm or less are used, formed pores are also 1 μm or less. Such a pore structure is filled with an electrolyte solution to be injected later, and the electrolyte solution filled in this way plays a role in ion transfer. Therefore, the size and porosity of the pores are important factors in controlling the ionic conductivity of the porous inorganic coating layer. The pore size and porosity of the porous inorganic coating layer of the present invention are each in the range of 0.001 to 10 μm, preferably in the range of 5 to 95%.
[69]
[70]
The separator according to the present invention can be obtained by preparing a separator substrate layer as described above and disposing an electrode adhesive layer on the surface thereof. Hereinafter, a method of forming the electrode adhesive layer will be described.
[71]
[72]
First, a polymer solution is prepared by injecting a binder resin for an electrode adhesive layer into a mixed solvent (S1). The mixed solvent includes a first solvent and a second solvent.
[73]
In the present invention, the binder resin for the electrode adhesive layer includes a fluorine-based binder resin. The fluorine-based binder resin may be included in an amount of 90 wt% or more relative to 100 wt% of the binder resin for the electrode adhesive layer. As the fluorine-based binder resin, a homopolymer of vinylidene fluoride (that is, polyvinylidene fluoride), a copolymer of vinylidene fluoride and other copolymerizable monomers, or a mixture thereof may be used.
[74]
In the present invention, preferably, the fluorine-based binder resin includes a copolymer of vinylidene fluoride and other copolymerizable monomers. The copolymer may be included in an amount of 50 wt% or more, 70 wt% or more, preferably 90 wt% or more, based on 100 wt% of the fluorine-based binder resin. On the other hand, in a specific embodiment of the present invention, the copolymer may have a degree of substitution with other copolymerizable monomers of 5 wt% to 20 wt%. In one specific embodiment of the present invention, the degree of substitution can be measured through Solid NMR (Nuclear Magnetic Resonance) analysis.
[75]
The 1 H-NMR may be measured by, for example, Solid NMR analysis. In its measurement, the following conditions can be applied.
[76]
- Agilent DD2 600 MHz SSNMR/ 1.6mm T3 MAS HFXY Solid Probe
[77]
- 19F NMR (one pulse, D1=30, ns=32, aq=0.4)
[78]
- Spinning rate = 35 kHz
[79]
또는 상기 치환도는 1H-NMR 스펙트럼의 상대적 정량 분석을 통해 측정될 수 있으며, 예를 들어 Bruker AC 400과 같은 장치가 상기 1H-NMR 분석에 사용될 수 있으며, 용매로는 중소화된 아세톤 또는 중수소화된 DMF가 사용될 수 있다. 결합상수(coupling constant) 및 화학적 이동(chemical shift)는 각각 헤르츠(Hz) 및 백만 분율(parts per million, ppm) 단위로 주어진다. 1H-NMR에 대한 획득 파리미터는 다음 조건이 적용될 수 있다: 회전 각 90°, 획득시간 4.5s, 펄스 시퀀트 2s, 스캔번호 8.
[80]
[81]
상기 불화비닐리덴과 공중합가능한 모노머로서는, 예를 들면 테트라플루오로에틸렌, 헥사플루오로프로필렌, 트리플루오로에틸렌, 클로로플루오로에틸렌, 1, 2 디플루오로에틸렌, 퍼플루오로(메틸비닐)에테르, 퍼플루오로 (에틸비닐)에테르, 퍼플루오로(프로필비닐)에테르, 더플루오로(1,3 디옥솔), 퍼플루오로(2,2-디메틸-1,3-디옥솔), 트리클로로에틸렌 및 불화비닐 등에서 선택된 1종 또는 2종 이상이 포함될 수 있다. 예를 들어 상기 불소계 바인더 수지는 폴리불화비닐리덴, 폴리불화비닐리덴-헥사플루오로프로필렌 (polyvinylidene fluoride-co-hexafluoropropylene), 폴리비닐리덴플루오라이드-트리클로로에틸렌 (polyvinylidene fluoride-co-trichloroethylene), 폴리불화비닐리덴-테트라플루오로에틸렌, 폴리불화비닐리덴-트리플루오로에틸렌 등을 들 수 있으며, 이들 중 선택된 1종 또는 2종 이상의 혼합물을 포함할 수 있다.
[82]
본 발명의 일 실시양태에 있어서, 상기 혼합 용매는 제1 및 제2 용매의 극성도 비율이 0.360 이상인 것이다. 예를 들어, 상기 극성도 비율은 0.360 내지 0.450 사이의 값을 가질 수 있다. 여기에서 상기 극성도 비율은 제2 용매의 극성도에 대한 제1 용매의 극성도(제1 용매의 극성도/제2 용매의 극성도)를 의미한다.
[83]
한편, 본 발명에 있어서, 극성도 비율의 계산에 있어서, 상기 제2 용매의 극성도가 상기 제1 용매의 극성도에 비해서 상대적으로 큰 것이다. 즉, 두 종류의 용매 중 극성도가 상대적으로 작은 용매를 제1 용매로 하고 나머지 용매를 제2 용매로 하고 상기 극성도 비율을 계산한다.
[84]
상기 용어 극성(Polarity)은 일반적으로 두 개 이상의 원자로 이루어진 분자의 구조적 비대칭성이나 구성 원자간의 전기 음성도 차이에 의하여 전자 구름이 한 방향으로 몰려서 생겨나는 전기 쌍극자 모멘트를 의미하는 것이다.
[85]
본 발명에 있어서, 상기 각 용매의 극성도(E T N)는 Dimroth-Reichardt ET 30 polarity scale에 따른 것이다. 이에 따르면, 기준 물질인 2,6-diphenyl-4-(2,4,6-triphenyl-pyridino) phenoxide를 극성도 측정 대상 용매(A)에 첨가하여 수득된 용액에 대해 흡광도 수치(λ max)를 측정한 후 이를 아래 [식 1] 및 [식 2]에 대입하여 산출하는 방법으로 각 용매의 극성도를 정량화하는 것이다. 상기 흡광도 수치는 UV-vis 측정 장비를 사용하여 측정될 수 있다.
[86]
[87]
[식 1]
[88]
E T (A) = 28,592 / λ max
[89]
[90]
[Equation 2]
[91]
E T N = [E T (A) - E T (TMS)] / [E T (H 2 O) - E T (TMS)]
[92]
[93]
In [Equation 2], E T (H 2 O) is 63.1 as a value calculated by [Equation 1] using water as the solvent of the reference material (λ max is 453 nm), and E T (TMS) is It is 30.7 as calculated by [Equation 1] using Tetramethylsilane (TMS) as a solvent. That is, after setting TMS as the most polar non-polar compound, water as the most polar compound, TMS as 0 and water as 1, the polarity of the solvent (A) to be measured (E T N ) is defined relatively. In other words, the polarity of each solvent may be the relative polarity when water is defined as 1. The unit of E T (A) is kcal/mol.
[94]
The first and second solvents are each independently selected from acetone, tetrahydrofuran (THF), dimethylformamide (DMF), n-methylpyrrolidone (NMP), a lower alcohol having 1 to 3 carbon atoms, and H 2 O. It may be 1 type or a mixture of 2 or more types. In one embodiment of the present invention, the first solvent may be one or a mixture of two or more selected from acetone, THF, DMF, and NMP, and the second solvent may be a lower alcohol having 1 to 3 carbon atoms and H 2 O It may be one selected from among, or a mixture of two or more.
[95]
[96]
In a specific embodiment of the present invention, the mixed solvent may be one selected from a mixture of DMF and EtOH, a mixture of DMF and H 2 O, and a mixture of NMP and H 2 O.
[97]
[98]
In a specific embodiment of the present invention, for the relative polarity, 'https://sites.google.com/site/miller00828/in/solvent-polarity-table', 'K. Refer to Guzow et al./Spectrochemica Acta Part A 61(2005) 1133-1140' and 'Journal of the Korean Society of Military Science and Technology, Vol. 11, No. 3 (June 2008), Theoretical Prediction of Solvent Polarity' can do.
[99]
[100]
In the present invention, when the polarity ratio is in the range of 0.360 to 0.450, the fluorine-based binder of the electrode adhesive layer in the obtained separator has a crystallinity of about 40% or more or 50% or more, of which the beta crystal content is 80% or more. can be induced to
[101]
[102]
In one embodiment of the present invention, the crystallinity can be measured using DSC measurement (differential scanning calorimetry). For example, the crystallinity can be measured by subjecting the heat to a change at a rate of 5°C/min to 15°C/min, and the crystallinity (%) can be calculated through [Equation 3] below.
[103]
[104]
[Equation 3]
[105]
Crystallinity (%) = (ΔHm/ΔH˚m) X 100
[106]
In [Equation 3], ΔH˚m represents the heat of fusion of a polymer having 100% crystallization, and ΔHm represents the heat of fusion of the polymer measured through a differential scanning thermal analyzer.
[107]
[108]
In addition, the beta crystal content can be calculated through the absorbance value measured through FT-IR (Infrared Spectroscopy) and the following [Equation 4].
[109]
[110]
[Equation 4]
[111]

[112]
[113]
- Absorption coefficient
[114]
K(α) = 6.1 x 10 4 cm 2 /mol
[115]
K(β) = 7.7 x 10 4 cm 2 /mol
[116]
[117]
In [Equation 4], F(β) is the content ratio of the B crystal, K(α) is the absorption coefficient of the α crystal, K(β) is the absorption coefficient of the β crystal, A α is the absorption of the α crystal, and A β represents the absorbance of the β crystal.
[118]
본 발명의 구체적인 일 실시양태에 있어서, 상기 FT-IR(Infrared Spectroscopy)를 이용한 흡수도 수치는 ATR 모듈이 구비된 Perkin-Elmer 스펙트럼 1000 분광계에 의해서 측정될 수 있으며, 이때 정밀도는 +/- 2cm -1, 25°의 조건이 적용될 수 있다.
[119]
한편, 주지된 바와 같이, 불화비닐리덴을 포함하는 불소계 중합체는 α, β 및 γ 의 결정 구조를 가질 수 있다. 이 중 α 결정은 분자쇄가 trans-gauche-trans-gauche의 방식으로 연결되어 있는 것이며, β 결정은 분자쇄가 모두 트랜스(all-trans)형태로 되어 있어 분자쇄 자체의 분극도가 가장 큰 동시에 결정격자 내에서도 모든 분자쇄가 동일한 방향으로 배열되어 있다. 상기 전극 접착층에서 불소계 바인더 중 β 결정이 상기 범위를 만족하는 경우 전기음성도가 높은 플루오로 원자의 배열이 일정하게 되어 기공의 크기와 분포가 균일한 접착층이 형성되며 그 결과 리튬 이온의 이동성이 개선되는 효과를 나타낼 수 있다.
[120]
[121]
Next, the polymer solution is applied to at least one surface or both surfaces of the prepared separator substrate layer (S2). The coating may use dip coating, die coating, roll coating, comma coating, or a combination thereof. Then, the coated polymer solution is dried (S3). The drying is not limited to a special method as long as it can remove at least a part or all of the mixed solvent, and an appropriate method among known drying methods can be selected and applied. For example, at least one of natural drying, blowing drying, hot air drying, cold air drying, and vacuum drying may be applied. In one embodiment of the present invention, the drying may be performed by natural drying or blowing drying at room temperature. Alternatively, the drying may be performed by a method of hot air drying at a temperature of more than 30° C. using a convection oven or the like. In one embodiment of the present invention, preferably, the drying may be performed by convection oven drying, wherein the drying temperature is controlled in the range of 50 °C to 100 °C. The drying time may be controlled to an appropriate range for removing the solvent according to the temperature or the presence or absence of ventilation.
[122]
[123]
The separator for a lithium secondary battery prepared in this way can also be used as a separator for an electrochemical device. The electrochemical device includes all devices that undergo an electrochemical reaction, and specific examples include all types of primary and secondary batteries, fuel cells, solar cells, or capacitors. In particular, among the secondary batteries, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery is preferred.
[124]
[125]
In a specific embodiment according to the present invention, the lithium secondary battery may be manufactured according to a conventional method known in the art. According to one embodiment according to the present invention, a secondary battery may be manufactured by preparing an electrode assembly by interposing the above-described separator between a positive electrode and a negative electrode, storing the electrode assembly in a battery case, and then injecting an electrolyte solution.
[126]
[127]
In one embodiment of the present invention, the electrode of the secondary battery may be prepared by attaching an electrode active material to an electrode current collector according to a conventional method known in the art. Non-limiting examples of the cathode active material among the electrode active materials include conventional cathode active materials that can be used for cathodes of conventional electrochemical devices, and in particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or any of these A lithium intercalation material such as a composite oxide formed by combination is preferable. Non-limiting examples of the negative electrode active material include conventional negative electrode active materials that can be used for negative electrodes of conventional electrochemical devices, particularly lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, Lithium adsorbents such as graphite or other carbons are preferred. Non-limiting examples of the anode current collector include a foil made of aluminum, nickel or a combination thereof, and non-limiting examples of the cathode current collector include copper, gold, nickel or a copper alloy or a combination thereof. There are manufactured foils and the like.
[128]
[129]
The electrolyte solution that can be used in the present invention is a salt having a structure such as A + B - , wherein A + includes an alkali metal cation such as Li + , Na + , or K + or an ion composed of a combination thereof, and B - is PF 6 - , BF 4 - , Cl - , Br - , I - , ClO 4 - , AsF 6 - , CH 3 CO 2 - , CF 3 SO 3 - , N(CF 3A salt containing an anion such as SO 2 ) 2 - , C(CF 2 SO 2 ) 3 - or a combination thereof is propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl Carbonate (DMC), Dipropylcarbonate (DPC), Dimethylsulfoxide, Acetonitrile, Dimethoxyethane, Diethoxyethane, Tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), Ethylmethylcarbonate (EMC) , gamma butyrolactone (γ-butyrolactone), or those dissolved or dissociated in organic solvents composed of mixtures thereof, but are not limited thereto.
[130]
[131]
The injection of the electrolyte may be performed at an appropriate stage in the battery manufacturing process according to the manufacturing process and required physical properties of the final product. That is, it may be applied before battery assembly or at the final stage of battery assembly. As a process of applying the electrode assembly of the present invention to a battery, lamination, stack, and folding processes of a separator and an electrode may be performed in addition to winding, which is a general process.
[132]
[133]
이하, 본 발명을 구체적으로 설명하기 위해 실시예를 들어 상세하게 설명하기로 한다. 그러나, 본 발명에 따른 실시예는 여러 가지 다른 형태로 변형될 수 있으며, 본 발명의 범위가 아래에서 상술하는 실시예에 한정되는 것으로 해석되어서는 안 된다. 본 발명의 실시예는 당업계에서 평균적인 지식을 가진 자에게 본 발명을 보다 완전하게 설명하기 위해서 제공되는 것이다.
[134]
[135]
실시예
[136]
실시예 1 및 실시예 2
[137]
A. 분리막 기재층의 준비
[138]
Al 2O 3 분말(입경 500nm)과 PVdF-HFP 바인더 고분자 (Solvay社, Solef 21510, HFP 15wt%)를 바인더 고분자:무기물 입자 = 20:80의 중량비로 NMP에 투입하고 50℃에서 총 1 시간 동안 볼밀법을 이용하여 무기물 입자를 파쇄 및 분산하여 다공성 코팅층 형성용 슬러리를 준비하였다. 이 때 고형분의 비율은 20wt%가 되도록 조절하였다. 다음으로 다공성 고분자 기재로 6 cm x 15 cm 크기의 폴리에틸렌 다공성 고분자 기재 (두께 9 ㎛, 통기도 70sec/100ml, 저항 0.39 Ω)를 준비하였다. 상기 슬러리를 상기 다공성 고분자 기재의 양면에 도포하고 70℃ 조건에서 송풍 건조하여 분리막 기재층을 준비하였다.
[139]
[140]
B. 전극 접착층의 형성
[141]
제1 및 제2 용매를 준비하고 이를 혼합하여 혼합 용매를 준비하였다. 상기 혼합 용매의 조성은 아래 [표 1]과 같다. PVDF-HFP(Solvay社, Solef 21510)를 준비하고 이를 상기 혼합용매에 투입하여 전극 접착층 형성용 고분자 용액을 준비하였다. 상기 고분자 용액을 닥터 블레이드의 방법으로 상기 분리막 기재층의 양면에 도포하고 70℃에서 컨벡션 오븐으로 대류 건조 하여 복합 분리막을 수득하였다.
[142]
[143]
비교예 1 및 비교예 2
[144]
실시예와 동일한 방법으로 분리막 기재층을 수득하였다. 제1 및 제2 용매를 준비하고 이를 혼합하여 혼합 용매를 준비하였다. 상기 혼합 용매의 조성은 아래 [표 1]과 같다. PVDF-HFP(Solvay社, Solef 21510)를 준비하고 이를 상기 혼합용매에 투입하여 전극 접착층 형성용 고분자 용액을 준비하였다. 상기 고분자 용액을 닥터 블레이드의 방법으로 상기 분리막 기재층의 양면에 도포하고 70℃에서 송풍 건조 하여 복합 분리막을 수득하였다.
[145]
[146]
비교예 3
[147]
실시예와 동일한 방법으로 분리막 기재층을 수득하였다. DMF에 PVDF-HFP(Solvay社, Solef 21510)를 투입하여 전극 접착층 형성용 고분자 용액을 준비하였다. 상기 고분자 용액을 닥터 블레이드의 방법으로 상기 분리막 기재층의 양면에 도포하였다. 이후 100℃에서 상대습도 30%로 가습 상분리를 하여 상기 고분자 용액을 고화시켜 분리막을 수득하였다.
[148]
[149]
분리막의 β 결정상 비율 확인
[150]
실시예 1 및 비교예 1의 분리막에 대해서 FT-IR을 통해 흡수도를 측정하였으며, 이를 상기 [식 4] 에 적용하여 β 결정상 비율을 계산하였으며 그 결과를 도 1에 그래프로 나타내었다. 도 1에 따르면 (1 용매)/)(2 용매)의 극성비가 0.360 이상인 실시예 1이 비교예 1에 비해서 β 결정상이 높은 것으로 확인되었다.
[151]
이 때, β 결정상 비율은 FT-IR spectroscopy(Perkin-Elmer)를 사용하여 ATR mode(diamond crystal)로 측정 후 β-phase 결정상 비율을 계산하였다.
[152]
[153]
분리막 표면 관찰
[154]
도 2a 및 도 2b는 실시예 1에서 수득된 분리막 표면에 대한 SEM 이미지이며, 도 3은 비교예 1에서 수득된 분리막 표면에 대한 SEM 이미지이다. 또한, 도 4는 비교예 3에서 수득된 분리막 표면에 대한 SEM 이미지이다. 이를 참조하면 실시예 1에 따른 분리막은 작은 미세 기공들이 많이 생성되며, 저항에 유리하게 작용되는 것을 알 수 있다. 이에 비해 비교예 1 및 비교예 3의 분리막은 비교적 큰 크기의 기공들이 불규칙하게 분포하고 있었다. 또한, 아래 실험에서 확인한 바와 같이 이러한 큰 기공들이 불규칙하게 분포된 경우 저항에 불리하게 작용하는 것이 확인되었다.
[155]
[156]
모노셀의 제조 및 저항 측정
[157]
음극 활물질로 인조흑연, 도전재로 덴카블랙(carbon black), 바인더로 폴리비닐리덴 플루오라이드(PVdF)를 각각 75:5:25의 중량비로 혼합하고, 용매인 N-메틸피롤리돈(NMP)을 첨가하여 음극 슬러리를 제조하였다. 상기 음극 슬러리를 구리 집전체에 코팅 및 건조하여, 음극 활물질층이 형성된 음극을 준비하였다.
[158]
LiNi 0.8 Co 0.1 Mn 0.1 O 2 as a cathode active material, Denka black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are added to N-methylpyrrolidone (NMP) as a solvent in a weight ratio of 85:5:15 Thus, a cathode active material slurry was prepared. The positive electrode active material slurry was coated on a sheet-shaped aluminum current collector and dried to prepare a negative electrode having a positive electrode active material layer.
[159]
An electrode assembly was prepared by interposing the separator obtained in each Example and Comparative Example between the positive electrode and the negative electrode prepared as described above, and an electrolyte solution was injected to prepare a 50mAh monocell. The electrolyte solution was prepared such that ethylene carbonate and ethylmethyl carbonate were mixed in a ratio of 7:3 (volume ratio) and LiPF 6 was included in a concentration of 0.7M. Resistance of the monocell was measured using a Marco charger and discharger. The measurement conditions were 2.5 c-rate pulse at 50% SOC.
[160]
[161]
[Table 1]
Comparative Example 1 Example 1 Example 2 Comparative Example 2
First solvent (polarity degree) THE( 0.207 ) DMF( 0.386 ) NMP (0.404) Acetone (0.355 )
Second solvent (polarity degree) H 2 O( 1 ) H 2 O( 1 ) H 2 O ( 1 ) H 2 O( 1 )
polarity ratio 0.207 0.386 0.404 0.355
Beta crystal of electrode adhesive layer (%) 65% 82% 87% 76%
Thickness of composite separator (um) 15um 15um 15um 15um
Air permeability (sec/100ml) 1,230 163 118 227
Separator resistance (Ω) 1.3 0.8 0.7 0.9
Mono cell resistance (Ω)2.5C, 10 sec, pulse discharge resistance, room temperature - 1.10 1.06 1.24
[162]
[163]
How to measure resistance
[164]
A coin cell was manufactured by interposing the separator obtained in each Example and Comparative Example between SUS. As the electrolyte of the coin cell, ethylene carbonate:ethylmethyl carbonate was mixed in a ratio of 1:2 (volume ratio), and LiPF 6 was added at a concentration of 1M. For each coin cell, resistance was measured using an analysis device (VMP3, Bio logic science instrument) through electrochemical impedance spectroscopy analysis at 25° C. under conditions of an amplitude of 10 mV and a scan range of 0.1 hz to 1 MHz.
[165]
[166]
Air permeability measurement method
[167]
The air permeability is measured by measuring the time for 100 ml of air to pass through the membranes of each Example and Comparative Example. The air permeability was measured by the method of JIS P8117. Air permeability of the porous substrate was also measured accordingly.

We claims:

[Claim 1]
A method for manufacturing a composite separator having an electrode adhesive layer, the method comprising applying a polymer solution for the adhesive layer to at least one surface of a separator substrate layer and drying the polymer solution, wherein the polymer solution is prepared by mixing a binder resin for the electrode adhesive layer and a mixed solvent. wherein the binder resin for the electrode adhesive layer includes a fluorine-based binder resin, the mixed solvent includes first and second solvents, and the ratio of polarity of the first solvent to polarity of the second solvent ( Polarity of one solvent / polarity of second solvent) is 0.360 or more, and the polarity of the first solvent and the second solvent are each independently according to the Dimroth-Reichardt ET30 polarity scale Preparation of a separator for an electrochemical device Way.
[Claim 2]
The method of claim 1, wherein the polarities of the first and second solvents are E T N values ​​independently calculated through [Equation 1] and [Equation 2] below: [Equation 1] E T (A) = 28,592 / λ max [Equation 2] E T N = [E T (A) - E T (TMS)] / [E T (H 2 O) - E T (TMS) ] In the above [Formula 1] and [Formula 2], the unit of E T (A) is kcal / mol, and in [Formula 2], E T (H 2 O) is 63.1 kcal / mol, E T (TMS) is 30.7 kcal/mol.
[Claim 3]
The method of claim 1, wherein the first solvent includes one or a mixture of two or more selected from acetone, tetrahydrofuran (THF), dimethylformamide (DMF), and n-methylpyrrolidone (NMP), wherein the The second solvent is a method for producing a separator for an electrochemical device comprising one or a mixture of two or more selected from a lower alcohol having 1 to 3 carbon atoms and H 2 O.
[Claim 4]
The method of claim 1, wherein the polarity ratio is 0.360 to 0.450.
[Claim 5]
The method of claim 1, wherein the fluorine-based binder resin is contained in an amount of 90 wt% or more relative to 100 wt% of the binder resin for the electrode adhesive layer.
[Claim 6]
The separator for an electrochemical device according to claim 1, wherein the fluorine-based binder resin includes a homopolymer of vinylidene fluoride (polyvinylidene fluoride), a copolymer of vinylidene fluoride and other copolymerizable monomers, or a mixture thereof. manufacturing method.
[Claim 7]
The method of claim 6, wherein the copolymer of vinylidene fluoride and other copolymerizable monomers is polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-trichloro A method for producing a separator for an electrochemical device, which is at least one selected from polyvinylidene fluoride-co-trichloroethylene, polyvinylidene fluoride-tetrafluoroethylene, and polyvinylidene fluoride-trifluoroethylene.
[Claim 8]
The method of claim 6, wherein the copolymer of vinylidene fluoride and other copolymerizable monomers has a degree of substitution by the monomers of 5 wt% to 20 wt%.
[Claim 9]
A separator for an electrochemical device manufactured by the method according to claim 1, wherein the crystallinity of the fluorine-based binder in the electrode adhesive layer is 40% or more, and the beta crystal content is 80% or more.
[Claim 10]
A lithium ion secondary battery comprising a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, wherein the separator according to claim 9.