阅读说明：本技术 包括具有不同玻璃化转变温度的粘合剂的隔板及其制造方法 (Separator including binders having different glass transition temperatures and method of manufacturing the same ) 是由 金明洙 尹秀珍 于 2018-12-18 设计创作，主要内容包括：本文披露了一种用于二次电池的隔板,所述隔板包括：由聚合物树脂制成的具有多孔结构的隔板基板；涂覆在隔板基板上的第一涂层,第一涂层包括第一无机材料和第一粘合剂；以及涂覆在第一涂层上的第二涂层,第二涂层包括第二无机材料和第二粘合剂,其中第一涂层进一步包括玻璃化转变温度(Tg)低于30℃的第三粘合剂,并且第二涂层进一步包括玻璃化转变温度(Tg)为30℃或更高的第四粘合剂。(Disclosed herein is a separator for a secondary battery, the separator including: a separator substrate having a porous structure made of a polymer resin; a first coating layer coated on the separator substrate, the first coating layer including a first inorganic material and a first binder; and a second coating layer coated on the first coating layer, the second coating layer including a second inorganic material and a second binder, wherein the first coating layer further includes a third binder having a glass transition temperature (Tg) of less than 30 ℃, and the second coating layer further includes a fourth binder having a glass transition temperature (Tg) of 30 ℃ or higher.)

1. A separator for a secondary battery, the separator comprising:

A separator substrate having a porous structure made of a polymer resin;

A first coating layer coated on the separator substrate, the first coating layer including a first inorganic material and a first binder; and

A second coating layer coated on the first coating layer, the second coating layer comprising a second inorganic material and a second binder, wherein

The first coating further comprises a third binder having a glass transition temperature (Tg) of less than 30 ℃, and

The second coating further includes a fourth binder having a glass transition temperature (Tg) of 30 ℃ or greater.

2. The separator of claim 1, wherein

the first inorganic material is a main component of the first coating layer, and

The second binder is a main component of the second coating layer.

3. The separator of claim 1, wherein the first inorganic material and the second inorganic material are the same material.

4. The separator of claim 1, wherein

The first inorganic material and the second inorganic material are the same as or different from each other, and

each of the first inorganic material and the second inorganic material is at least one selected from the group consisting of: (a) inorganic particles having a dielectric constant of 5 or more; (b) inorganic particles having piezoelectricity (piezoelectricity); and (c) inorganic particles having lithium ion transport ability.

5. the separator of claim 4, wherein

The inorganic particles (a) having a dielectric constant of 5 or more are SrTiO₃、SnO₂、CeO₂、MgO、NiO、CaO、ZnO、ZrO₂、Y₂O₃、Al₂O₃、TiO₂Or a mixture of SiC and a metal oxide or a metal oxide,

The inorganic particles (b) having piezoelectricity form a potential difference due to positive and negative charges generated between opposite surfaces of the particles when a predetermined pressure is applied thereto, and are at least one selected from the group consisting of: BaTiO 2₃、Pb(Zr,Ti)O₃(PZT)、Pb_1-xLa_xZr_1-yTi_yO₃(PLZT)、Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃(PMN-PT), hafnium oxide (hafnia, HfO)₂)、SrTiO₃、SnO₂、CeO₂、MgO、NiO、CaO、ZnO、ZrO₂、Y₂O₃、Al₂O₃、TiO₂SiC, and mixtures thereof, and

The inorganic particle (c) having lithium ion transport ability comprises a lithium elementAnd transporting lithium ions without storing lithium, and is at least one selected from the group consisting of: lithium phosphate (Li)₃PO₄) (ii) a Lithium titanium phosphate (Li)_xTi_y(PO₄)₃,0<x<2,0<y<3) (ii) a Lithium aluminum titanium phosphate (Li)_xAl_yTi_z(PO₄)₃,0<x<2,0<y<1,0<z<3)；(LiAlTiP)_xO_yBase glass (0)<x<4,0<y<13) Such as 14Li₂O-9Al₂O₃-38TiO₂-39P₂O₅(ii) a Lithium lanthanum titanate (Li)_xLa_yTiO₃,0<x<2,0<y<3) (ii) a Lithium germanium thiophosphate (Li)_xGe_yP_zS_w,0<x<4,0<y<1,0<z<1,0<w<5) Such as Li_3.25Ge_0.25P_0.75S₄(ii) a Lithium nitride (Li)_xN_y,0<x<4,0<y<2) Such as Li₃N；SiS₂-base glass (Li)_xSi_yS_z,0<x<3,0<y<2,0<z<4) Such as Li₃PO₄-Li₂S-SiS₂；P₂S₅-base glass (Li)_xP_yS_z,0<x<3,0<y<3,0<z<7) such as LiI-Li₂S-P₂S₅And mixtures thereof.

6. The separator of claim 1, wherein the first binder and the second binder are the same material.

7. The separator of claim 1, wherein

The first adhesive and the second adhesive are the same as or different from each other, and

Each of the first adhesive and the second adhesive is at least one selected from the group consisting of: polyvinylidene fluoride-co-hexafluoropropylene (polyvinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride-trichloroethylene (polyvinylidene fluoride-co-trichloroethylene), polymethyl methacrylate (polymethyl methacrylate), polyacrylonitrile (polyacrylonitrile), polyvinylpyrrolidone (polyvinylpyrrolidone), polyvinyl acetate (polyvinyl acetate), polyethylene-co-vinyl acetate (polyethylene-co-vinyl acetate), polyimide (polyimide), polyethylene oxide (polyethylene oxide), cellulose acetate (cellulose acetate), cellulose acetate butyrate (cellulose acetate), cellulose acetate propionate (cellulose acetate), cyanoethyl pullulan (cyanoethyl cellulose), cellulose acetate (cellulose acetate, cellulose acetate, cellulose acetate, cellulose acetate.

8. The separator according to claim 2, wherein the first inorganic material as a main component of the first coating layer is included to account for 50 to 99 wt% of the total solid mass of the first coating layer.

9. The separator according to claim 2, wherein the second binder as a main component of the second coating layer is included to account for 50 to 100 wt% of the total solid mass of the second coating layer.

10. The separator of claim 1, wherein said separator base plate is made of at least one selected from the group consisting of high density polyethylene, low density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, and polypropylene.

11. A secondary battery comprising the separator according to any one of claims 1 to 10.

12. A method of manufacturing a separator plate according to any one of claims 1 to 10, the method comprising:

(a) Preparing a separator substrate having a porous structure made of a polymer resin;

(b) Forming a first coating layer on the separator substrate;

(c) Drying the first coating;

(d) Forming a second coating layer on the first coating layer; and

(e) Drying the second coating.

Technical Field

The present invention relates to a separator including binders having different glass transition temperatures, and more particularly, to a separator for a secondary battery configured such that a first coating layer and a second coating layer coated on a separator substrate include different kinds of binders, wherein the first coating layer includes a binder having a glass transition temperature of less than 30 ℃, and the second coating layer includes a binder having a glass transition temperature of 30 ℃ or more.

Background

In recent years, with the increasing development of portable devices such as portable computers, mobile phones, and cameras, and the increasing demand for such portable devices, the demand for secondary batteries has also sharply increased as an energy source for such portable devices. Among these secondary batteries, a lithium secondary battery having a high energy density, a high operating potential, a long life span, and a low self-discharge rate has been much studied, and is now commercialized and widely used.

With increasing concern for environmental issues, much research has been conducted on electric vehicles and hybrid electric vehicles that can replace vehicles using fossil fuels, such as gasoline vehicles and diesel vehicles, as one of the main causes of air pollution. Lithium secondary batteries are used as power sources for these electric vehicles and hybrid electric vehicles.

accordingly, efforts are being made to improve the safety of lithium secondary batteries having high energy density.

In general, a separator includes a separator substrate and a coating layer coated on the separator substrate, and physical properties of the separator may be determined according to the composition of the coating layer.

Specifically, a coating layer having a single-layer structure may be formed on the separator substrate, or a coating layer having a multi-layer structure may be formed on the separator substrate. In the case where the coating layer having a multilayer structure is formed on the separator substrate, the layer adjacent to the separator substrate is configured to increase the peel strength of the coating layer from the separator, and the layer facing the electrode is configured to increase the adhesion to the electrode mixture layer.

in the case where the adhesion between the electrodes and the separator is low, short circuits may occur between the electrodes due to the separator and the electrodes being pushed during the charge and discharge of the battery. At this time, the battery may catch fire or explode due to heat generated by an overcurrent locally flowing through the battery. In the case where the adhesion between the electrodes and the separator is low, the interfacial resistance may increase due to the looseness between the electrodes, and thus the electrodes may be bent, thereby causing a safety-related problem of the battery.

Patent document 1 discloses a separator for a power storage device, which is configured such that a porous layer including a first resin binder having a glass transition temperature Tg of 30 ℃ or higher and a second resin binder having a glass transition temperature Tg of less than 30 ℃ is formed on a porous substrate layer.

However, since the separator of patent document 1 has a structure in which a single porous layer is formed on a separator substrate, the separator of patent document 1 exhibits a higher thermal shrinkage rate and a lower adhesive force than a separator having a structure in which a plurality of coating layers are formed on a separator substrate.

Patent document 2 discloses a technique for adjusting the contents of inorganic particles and a binder polymer as active layer components formed on the surface of a polyolefin-based separator substrate and/or in some pores of the separator substrate to increase adhesion.

Although patent document 2 discloses effects related to thermal shrinkage and short-circuit stability of the separator, patent document 2 does not disclose a technique for improving peel strength and adhesion of the separator.

As described above, an effective technical solution capable of improving the peel strength between the coating layer of the separator and the separator substrate to prevent the coating layer from being separated from the separator substrate and capable of increasing the bonding force between the coating layer of the separator and the electrode to prevent the occurrence of short circuit between the electrodes due to pushing or loosening of the separator has not been proposed yet.

(related art documents)

(patent document 1) Japanese patent application laid-open No. 2016-072117

(patent document 2) Korean patent application laid-open No. 2006-

Disclosure of Invention

Technical problem

The present invention has been made in view of the above-mentioned problems and other technical problems that have yet to be resolved, and an object of the present invention is to provide a separator for a secondary battery configured such that a plurality of coating layers are coated on a separator substrate, wherein a first coating layer includes a binder having a glass transition temperature of less than 30 ℃, and a second coating layer includes a binder having a glass transition temperature of 30 ℃ or more, thereby increasing peel strength with the separator substrate and increasing adhesion to an electrode mixture layer.

Technical scheme

In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a separator for a secondary battery comprising: a separator substrate made of a polymer resin having a porous structure; a first coating layer coated on the separator substrate, the first coating layer including a first inorganic material and a first binder; and a second coating layer coated on the first coating layer, the second coating layer including a second inorganic material and a second binder, wherein the first coating layer further includes a third binder having a glass transition temperature (Tg) of less than 30 ℃, and the second coating layer further includes a fourth binder having a glass transition temperature (Tg) of 30 ℃ or higher.

the separator for a secondary battery according to the present invention includes a coating layer composed of a first coating layer and a second coating layer. The separator for a secondary battery according to the present invention has advantages of low thermal shrinkage and high adhesion between the separator and an electrode, as compared to a separator configured to form a single coating layer on a separator substrate.

The first coating layer is a layer coated on the separator substrate and has an effect on the peel strength of the separator, and the second coating layer is a layer coated on the first coating layer and has an effect on the adhesion of the electrode.

The first coating includes a third binder having a glass transition temperature of less than 30 ℃. The glass transition temperature of the third binder may preferably be 10 ℃ or less, more preferably-5 ℃ or less.

as described above, since the first coating layer includes the third binder having a glass transition temperature of less than 30 ℃, the binder particles may not be maintained in a circular form, the form of the binder particles may be uncertain, and the binder particles may move even at a low temperature, whereby a film-forming phenomenon may occur. Accordingly, the bonding force between the first coating layer and the raw material of the separator may be increased, and thus the peel strength may be increased.

The second coating includes a fourth binder having a glass transition temperature of 30 ℃ or greater. The glass transition temperature of the fourth adhesive may preferably be 45 ℃ or higher, more preferably 60 ℃ or higher.

As described above, since the second coating layer includes the fourth binder having a glass transition temperature of 30 ℃ or more, a film-forming phenomenon does not easily occur. Therefore, in the case where the fourth adhesive is used in the second coating layer, the conventional problem that the pores in the separator substrate are clogged to cause an increase in the resistance of the separator can be solved.

In a specific example, the first inorganic material may be a main component of the first coating layer, and the second binder may be a main component of the second coating layer.

That is, the first coating layer includes an inorganic material instead of a binder as its main component. Interstitial volumes may be formed between the inorganic particles, thus forming micropores, and also serve as a kind of spacer (spacer) capable of maintaining the physical shape of the first coating layer. In addition, the physical properties of the inorganic particles are not generally changed even at a high temperature of 200 ℃ or more, and thus the organic/inorganic composite porous film formed exhibits high heat resistance.

The inorganic particles are not particularly limited as long as the inorganic particles are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as the inorganic particles are within the operating voltage range of the battery to which the inorganic particles are applied (e.g., based on Li/Li)⁺0 to 5V) is not oxidized and/or reduced. In particular, in the case of using inorganic particles having ion transport ability, ion conductivity in the electrochemical device may be increased, and thus performance of the electrochemical device may be improved. Therefore, it is preferable that the ion transport ability of the inorganic particles is as high as possible. In addition, in the case where the inorganic particles have a high density, it may be difficult to disperse the inorganic particles upon coating, and the weight of the battery may increase upon manufacturing the battery. For these reasons, it is preferable that the density of the inorganic particles is as low as possible. In addition, the method can be used for producing a composite materialIn the case where the inorganic particles have a high dielectric constant, the degree of dissociation of an electrolyte salt (such as a lithium salt) in the liquid electrolyte may be increased, whereby the ionic conductivity of the electrolyte solution may be improved.

The first inorganic material and the second inorganic material may be the same as or different from each other, and each of the first inorganic material and the second inorganic material may be at least one selected from the group consisting of: (a) inorganic particles having a dielectric constant of 5 or more; (b) inorganic particles having piezoelectricity (piezoelectricity); and (c) inorganic particles having lithium ion transport ability.

Each of the first inorganic material and the second inorganic material may be a high dielectric constant inorganic particle having a dielectric constant of 5 or more, preferably 10 or more, such as SrTiO₃、SnO₂、CeO₂、MgO、NiO、CaO、ZnO、ZrO₂、Y₂O₃、Al₂O₃、TiO₂Or SiC.

Inorganic particles having piezoelectricity (piezoelectric) are materials that are non-conductive at normal pressure, but exhibit conductivity due to a change in their internal structure when a predetermined pressure is applied thereto. The inorganic particles exhibit high dielectric characteristics with a dielectric constant of 100 or more. In addition, when the inorganic particles are tensioned or compressed at a predetermined pressure, electric charges are generated. One face is positively charged and the other is negatively charged, thereby creating a potential difference between the two faces.

The inorganic particles having piezoelectricity may form a potential difference due to positive and negative charges generated between opposite surfaces of the particles when a predetermined pressure is applied thereto, and may be at least one selected from the group consisting of: BaTiO 2₃、Pb(Zr,Ti)O₃(PZT)、Pb_1-xLa_xZr_1-yTi_yO₃(PLZT)、Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃(PMN-PT), hafnium oxide (hafnia, HfO)₂)、SrTiO₃、SnO₂、CeO₂、MgO、NiO、CaO、ZnO、ZrO₂、Y₂O₃、Al₂O₃、TiO₂SiC, and mixtures thereof.

The inorganic particles having lithium ion transport ability are inorganic particles that contain lithium element and transport lithium ions without storing lithium. The inorganic particles having lithium ion transport ability can transport and transport lithium ions due to one kind of defect (defect) existing in the particle structure. Therefore, the lithium ion conductivity of the battery can be improved, and thus the battery performance can be improved.

The inorganic particles having lithium ion transport ability may contain lithium element and may transport lithium ions without storing lithium, and may be at least one selected from the group consisting of: lithium phosphate (Li)₃PO₄) (ii) a Lithium titanium phosphate (Li)_xTi_y(PO₄)₃,0<x<2,0<y<3) (ii) a Lithium aluminum titanium phosphate (Li)_xAl_yTi_z(PO₄)₃,0<x<2,0<y<1,0<z<3)；(LiAlTiP)_xO_yBase glass (0)<x<4,0<y<13) Such as 14Li₂O-9Al₂O₃-38TiO₂-39P₂O₅(ii) a Lithium lanthanum titanate (Li)_xLa_yTiO₃,0<x<2,0<y<3) (ii) a Lithium germanium thiophosphate (Li)_xGe_yP_zS_w,0<x<4,0<y<1,0<z<1,0<w<5) such as Li_3.25Ge_0.25P_0.75S₄(ii) a Lithium nitride (Li)_xN_y,0<x<4,0<y<2) Such as Li₃N；SiS₂-base glass (Li)_xSi_yS_z,0<x<3,0<y<2,0<z<4) such as Li₃PO₄-Li₂S-SiS₂；P₂S₅-base glass (Li)_xP_yS_z,0<x<3,0<y<3,0<z<7) Such as LiI-Li₂S-P₂S₅And mixtures thereof.

the first adhesive and the second adhesive may be the same as or different from each other, and for example, each of the first adhesive and the second adhesive may be at least one selected from the group consisting of: polyvinylidene fluoride-co-hexafluoropropylene (polyvinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride-trichloroethylene (polyvinylidene fluoride-co-trichloroethylene), polymethyl methacrylate (polymethyl methacrylate), polyacrylonitrile (polyacrylonitrile), polyvinylpyrrolidone (polyvinylpyrrolidone), polyvinyl acetate (polyvinyl acetate), polyethylene-co-vinyl acetate (polyethylene-co-vinyl acetate), polyimide (polyimide), polyethylene oxide (polyethylene oxide), cellulose acetate (cellulose acetate), cellulose acetate butyrate (cellulose acetate), cellulose acetate propionate (cellulose acetate), cyanoethyl pullulan (cyanoethyl cellulose), cellulose acetate (cellulose acetate, cellulose acetate, cellulose acetate, cellulose acetate.

The first inorganic material, which is a main component of the first coating layer, may be included to be 50 to 99 wt%, preferably 60 to 95 wt%, based on the total solid mass of the first coating layer.

In the case where the content of the first inorganic material is less than 50% by weight of the total solid mass of the first coating layer, it is difficult to maintain the physical shape of the first coating layer, and the heat resistance of the first coating layer may be lowered, which is undesirable. In the case where the content of the first inorganic material is more than 99 wt% of the total solid mass of the first coating layer, since the content of the binder is too small, the bonding force between the inorganic materials and the separator substrate may be reduced, which is also undesirable.

The second binder, which is a main component of the second coating layer, may be included to account for 50 to 100 wt%, preferably 60 to 95 wt%, of the total solid mass of the second coating layer.

In the case where the content of the second binder is less than 50% by weight of the total solid mass of the second coating layer, the adhesion between the second coating layer and the electrode may be undesirably reduced.

The separator substrate may be a composite porous separator substrate having a uniformly formed porous structure. Therefore, it is possible to provide a separator configured to allow lithium ions to smoothly move through pores and having a high impregnation rate of an electrolyte solution.

The material for the separator substrate is not particularly limited. For example, the separator substrate may be made of at least one selected from the group consisting of high density polyethylene, low density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, and polypropylene.

According to another aspect of the present invention, there is provided a method of manufacturing a separator for a secondary battery.

in a specific example, the separator for a secondary battery may be manufactured using a method including:

(a) Preparing a separator substrate having a porous structure made of a polymer resin;

(b) forming a first coating layer on the separator substrate;

(c) Drying the first coating;

(d) Forming a second coating layer on the first coating layer; and

(e) The second coating is dried.

In the separator manufactured through the steps of forming the first coating layer on the separator substrate, drying the first coating layer, forming the second coating layer on the first coating layer, and drying the second coating layer as described above, a boundary is formed between the first coating layer and the second coating layer, thereby forming a coating layer having a multilayer structure. Accordingly, physical properties of each of the first coating layer and the second coating layer can be exhibited to the maximum, whereby a separator having high peel strength and adhesion can be manufactured.

According to other aspects of the present invention, there are provided a secondary battery including the separator for a secondary battery, and a battery pack including the secondary battery as a unit cell.

Specifically, the battery pack may be used as a power source for devices that require the ability to withstand high temperatures, long life, high rate characteristics, and the like. Specific examples of the apparatus may include: a mobile electronic device (mobile device); wearable electronic devices (wearable devices); a power tool driven by a battery powered motor; electric vehicles such as Electric Vehicles (EVs), Hybrid Electric Vehicles (HEVs), or Plug-in Hybrid Electric vehicles (PHEVs); an electric two-wheeled vehicle such as an electric bicycle (E-bike) or an electric scooter (E-scooter); electric golf cart (electric golf cart); and an Energy Storage System. However, the present invention is not limited thereto.

The structure and manufacturing method of the device are well known in the art to which the present invention pertains, and thus a detailed description thereof will be omitted.

Detailed Description

Hereinafter, the present invention will be described with reference to the following examples; however, this example should not be construed as limiting the scope of the invention.

< example 1>

5g of an acrylic-based polymer binder (binder having a Tg of-5 ℃ C.) and 95g of Al as an inorganic material₂O₃Dispersed in water to prepare a first coating slurry.

100g of an acrylic-based polymer binder (binder having a Tg of 60 ℃) was dispersed in water to prepare a second coating slurry.

The first coating slurry was coated on a separator substrate made of a porous polypropylene material, and then dried at 25 ℃ for 1 hour to form a first coating layer. Subsequently, the second coating slurry was coated on the first coating layer, and then dried at 25 ℃ for 1 hour to form a second coating layer.

< comparative example 1>

5g of an acrylic-based polymer binder (binder having a Tg of-5 ℃ C.) and 95g of Al as an inorganic material₂O₃dispersed in water to prepare a first coating slurry.

100g of an acrylic-based polymer binder (binder having a Tg of-5 ℃) was dispersed in water to prepare a second coating slurry.

The first coating slurry was coated on a separator substrate made of a porous polypropylene material, and then dried at 25 ℃ for 1 hour to form a first coating layer. Subsequently, the second coating slurry was coated on the first coating layer, and then dried at 25 ℃ for 1 hour to form a second coating layer.

< comparative example 2>

5g of an acrylic-based polymer binder (binder having a Tg of 60 ℃ C.) and 95g of Al as an inorganic material₂O₃Dispersed in water to prepare a first coating slurry.

100g of an acrylic-based polymer binder (binder having a Tg of 60 ℃) was dispersed in water to prepare a second coating slurry.

The first coating slurry was coated on a separator substrate made of a porous polypropylene material, and then dried at 25 ℃ for 1 hour to form a first coating layer. Subsequently, the second coating slurry was coated on the first coating layer, and then dried at 25 ℃ for 1 hour to form a second coating layer.

< comparative example 3>

5g of an acrylic-based polymer binder (binder having a Tg of 60 ℃ C.) and 95g of Al as an inorganic material₂O₃Dispersed in water to prepare a first coating slurry.

100g of an acrylic-based polymer binder (binder having a Tg of-5 ℃) was dispersed in water to prepare a second coating slurry.

The first coating slurry was coated on a separator substrate made of a porous polypropylene material, and then dried at 25 ℃ for 1 hour to form a first coating layer. Subsequently, the second coating slurry was coated on the first coating layer, and then dried at 25 ℃ for 1 hour to form a second coating layer.

< comparative example 4>

First and second coating pastes were prepared in the same manner as in example 1.

The first coating slurry was coated on a separator substrate made of a porous polypropylene material, the second coating slurry was coated on the first coating slurry, and the first coating slurry and the second coating slurry were dried at 25 ℃ for 1 hour to form a separator.

Measurement of peel Strength

In order to measure the peel strength of each separator manufactured according to example 1 and comparative examples 1 to 4, the following method was used: the double-sided tape and each of the manufactured spacers were sequentially attached to a slide glass, and one end of the spacer was pulled to 180 ° in a state where the slide glass was fixed, to measure the force of the spacer.

The measured peel strengths are shown in table 1 below.

Measurement of electrode adhesion

In order to measure the electrode adhesion of each of the separators manufactured according to example 1 and comparative examples 1 to 4, a load of 8.5MPa was applied to the negative electrode and each separator at 90 ℃ using a flat press to manufacture an electrode adhesion measurement sample. The following methods were used: the double-sided tape and the electrode adhesion force measurement sample were sequentially attached to a slide glass and one end of the separator was pulled to 180 ° to measure the electrode adhesion force of the separator.

The measured electrode adhesion is shown in table 1 below.

[ Table 1]

referring to table 1 above, each of example 1 and comparative example 1 using an adhesive having Tg of-5 ℃ in the first coating layer had high strength of peeling from the raw material. The peel strength of each of comparative examples 2 and 3 using an adhesive having a Tg of 60 ℃ in the first coating layer was much lower than that of example 1 and comparative example 1. In addition, example 1 using a binder having Tg of 60 ℃ in the second coating layer had higher electrode adhesion than comparative example 1 using a binder having Tg of-5 ℃ in the second coating layer, while the electrode adhesion measured was also lower in comparative examples 2 and 3 due to the low peel strength of comparative examples 2 and 3. The electrode adhesion of comparative example 4 in which the slurry was simultaneously applied to form a single layer was slightly increased, but the peel strength of comparative example 4 was measured to be very low.

therefore, it can be seen that in the case of using an adhesive having Tg lower than 30 ℃ in the first coating layer and an adhesive having Tg of 30 ℃ or higher in the second coating layer, both the effects of increasing the peel strength and the electrode adhesion can be obtained.

Those skilled in the art to which the invention pertains will appreciate that various applications and modifications can be made based on the above description without departing from the scope of the invention.

Industrial applicability

As is apparent from the above description, a separator for a secondary battery according to the present invention is configured such that a first coating layer and a second coating layer are formed on a separator substrate, wherein the first coating layer includes a binder having a glass transition temperature Tg of less than 30 ℃, and the second coating layer includes a binder having a glass transition temperature Tg of 30 ℃ or more. Since the separator for a secondary battery including the multi-layer coating layer is used as described above, a coating layer having increased strength of peeling from the separator substrate can be provided, whereby separation or looseness of the coating layer can be prevented.

In addition, the adhesion between the separator and the electrode is increased. Therefore, it is possible to effectively prevent the occurrence of a short circuit between the electrodes due to the charge and discharge of the battery cell, thereby further improving the safety of the battery cell.