KR102515029B1 - A separator with an adhesive layer and an electrochemical device comprising the same - Google Patents

Abstract

One aspect of the present invention, a porous substrate; a heat resistance layer including a plurality of inorganic particles located on at least one surface of the porous substrate and bound by a binder; and an adhesive layer including a plurality of organic particles located on a surface of the heat-resistant layer and bound by a binder, wherein the number of organic particles included in the adhesive layer per unit area is 100,000,000 to 150,000,000/mm ² , and It provides an electrochemical device comprising

Description

Separator having an electrode adhesive layer and an electrochemical device including the same {A SEPARATOR WITH AN ADHESIVE LAYER AND AN ELECTROCHEMICAL DEVICE COMPRISING THE SAME}

The present invention relates to a separator having an electrode adhesive layer and an electrochemical device including the same.

Lithium secondary batteries are widely used as a power source for various electric products that require miniaturization and light weight, such as smartphones, laptops, and tablet PCs. Development of a lithium secondary battery having a large, long lifespan and high stability is required.

As a means to achieve the above object, a separator having micropores that separates the positive electrode and the negative electrode to prevent internal short circuits and facilitates the movement of lithium ions during charging and discharging, especially thermally induced phase separation Research and development on microporous membranes using polyolefins such as polyethylene, which are advantageous for pore formation by thermally induced phase separation, are economical, and are easy to satisfy the physical properties required for separation membranes.

However, a separator using polyethylene having a melting point as low as 135° C. may undergo shrinkage and deformation at a high temperature above the melting point due to heat generation of the battery. When a short circuit occurs due to such deformation, a thermal runaway phenomenon of the battery may cause safety problems such as ignition.

On the other hand, conventionally widely used polyolefin-based separators are weak in heat resistance and mechanical strength, so when exposed to a temperature of 150 ° C for about 1 hour, the heat shrinkage rate occurs at 50 to 90%, and the function of the separator is lost. , there is a problem in which an internal short circuit is likely to occur in the event of an external impact. In order to compensate for this problem, a technique of coating a heat-resistant layer containing CERAIP particles on the surface of the separator has been proposed.

However, these heat-resistant layers leave significant technical challenges in relation to air permeability and conductivity (resistance), which are factors that have a very important effect on the performance of the separator. That is, when a heat-resistant layer containing ceramic particles is formed on the surface of a porous substrate, the heat resistance of the separator is improved, but the ceramic particles included in the heat-resistant layer close pores formed in the porous substrate, thereby reducing air permeability of the separator. Accordingly, the ion movement path between the positive electrode and the negative electrode is greatly reduced, and as a result, there is a problem in that the charging and discharging performance of the secondary battery is greatly deteriorated.

In addition, as the heat-resistant layer is continuously exposed to the electrolyte inside the battery, the ceramic particles may be partially and continuously detached from the porous substrate, and in this case, the heat resistance of the separator may gradually decrease.

On the other hand, an attempt is made to improve the adhesion to the electrode and thus the lifespan characteristics of the secondary battery by additionally forming an adhesive layer containing a PVDF-HFP copolymer, etc. in order to express the adhesion with the electrode on the conventional polyolefin-based separator or heat-resistant layer. has also been made (Korean Patent Application No. 10-2012-0117249, etc.). However, since these PVDF-based binders are also lipophilic materials and generally use volatile organic materials as solvents, they adversely affect the health of workers during coating and drying processes, and increase the cost of treating these volatile organic materials.

In contrast, an aqueous coating solution in which PVDF-based polymer particles are dispersed in water has been developed and applied, but since the PVDF-based polymer particles exist in particulate form even after the coating solution is dried, PVDF-based polymer particles included in the adhesive layer as in the heat-resistant layer By closing the pores formed in the porous substrate and/or the heat-resistant layer, the air permeability of the separator is reduced, and thus the ion movement passage between the positive electrode and the negative electrode is greatly reduced, resulting in a problem in that the charging and discharging performance of the secondary battery is greatly reduced. .

The present invention is to solve the problems of the prior art described above, and an object of the present invention is to provide a separator capable of implementing heat resistance, adhesiveness, air permeability, and conductivity in a balanced manner.

One aspect of the present invention, a base film comprising a porous substrate, and a heat-resistant layer including a plurality of inorganic particles located on at least one surface of the porous substrate and bound by a binder; and an adhesive layer including a plurality of organic particles located on a surface of the heat-resistant layer and bound by a binder, wherein the number of organic particles per unit area of the adhesive layer is 100,000,000 to 150,000,000/mm ² .

In one embodiment, the porous substrate may include one selected from the group consisting of polyethylene, polypropylene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof.

In one embodiment, the content of the inorganic particles in the heat-resistant layer may be 60 to 99% by weight.

In one embodiment, the content of the organic particles in the adhesive layer may be 50 to 99% by weight.

In one embodiment, the heat resistance layer may have a thickness of 0.1 μm to 5 μm, and the thickness of the adhesive layer may be 0.5 μm to 1.5 μm.

In one embodiment, the ratio of the thickness of the adhesive layer to the thickness of the heat resistance layer may be 0.15 to 0.5.

In one embodiment, the average particle diameter of the organic particles may be 50 ~ 300nm.

In one embodiment, the organic particles may include a fluorine-based polymer.

In one embodiment, the separator may satisfy one or more of the following conditions (i) to (vi).

(i) air permeability 190-350 seconds/100ml; (ii) Rs ≤ 100 mΩ (Rs is the resistance of the separator); (iii) 1.0% or less in longitudinal heat shrinkage at 150°C; (iv) 1.0% or less of transverse heat shrinkage at 150°C; (v) 0 mΩ < Rs - Ra ≤ 20 mΩ, where Ra is the resistance of the porous substrate; (vi) 0 mΩ < Rb - Rs ≤ 10 mΩ (Rb is the resistance of the base film).

Another aspect of the present invention provides an electrochemical device including the separator, preferably a secondary battery, more preferably a lithium secondary battery or a lithium ion battery.

The separator according to one aspect of the present invention includes a porous substrate, a heat resistance layer, and an adhesive layer, but the area density of organic particles included in the adhesive layer is based on the number (number) observable through a microscope, not the weight of the organic particles. By specifying it, heat resistance, adhesiveness, air permeability, and conductivity can be implemented in a balanced way.

The effects of the present invention are not limited to the above effects, and should be understood to include all effects that can be inferred from the detailed description of the present invention or the configuration of the invention described in the claims.

1 is a SEM image of a plane of a separator according to an embodiment of the present invention.
2 is a SEM image of a cross section of a separator according to an embodiment of the present invention.
Figure 3 shows a method for measuring and calculating the number of organic particles per unit area of the adhesive layer according to an embodiment of the present invention.

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and, therefore, is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is said to be "connected" to another part, this includes not only the case where it is "directly connected" but also the case where it is "indirectly connected" with another member interposed therebetween. . In addition, when a part "includes" a certain component, it means that it may further include other components without excluding other components unless otherwise stated.

One aspect of the present invention, a base film comprising a porous substrate, and a heat-resistant layer including a plurality of inorganic particles located on at least one surface of the porous substrate and bound by a binder; and an adhesive layer including a plurality of organic particles located on a surface of the heat-resistant layer and bound by a binder, wherein the number of organic particles per unit area of the adhesive layer is 100,000,000 to 150,000,000/mm ² .

The porous substrate may include a plurality of pores having a substantially uniform average size, and such pores may contribute to improving resistance characteristics and ionic conductivity of the separator. In addition, the separator can be thinned to a required thickness because of its high porosity and high mechanical strength.

The porosity of the porous substrate may be 30 to 90 vol%, preferably 40 to 80 vol%, and more preferably 40 to 70 vol%. As used herein, the term "porosity" means the ratio of the volume occupied by pores to the total volume in any porous article. If the porosity of the porous substrate is less than 30% by volume, air permeability and ion conductivity may be reduced, and if it exceeds 90% by volume, mechanical properties such as tensile strength and puncture strength may be reduced.

The average size of pores included in the porous substrate may be 10 to 100 nm, preferably 20 to 80 nm, and more preferably 30 to 60 nm. If the average size of the pores is less than 10 nm, air permeability and ionic conductivity may decrease, and if the average size of the pores exceeds 100 nm, mechanical properties such as tensile strength and puncture strength may decrease.

The thickness of the porous substrate may be 5 to 20 μm, preferably 5 to 15 μm, more preferably 5 to 12 μm, in terms of thinning and high energy density of the electrochemical device. If the thickness of the porous substrate is less than 5 μm, mechanical properties may be deteriorated, and if the thickness is greater than 20 μm, air permeability and ionic conductivity may be decreased.

The porous substrate may include a polymer resin having electrical insulation properties, and the polymer resin may include a thermoplastic resin in consideration of shutdown characteristics. As used herein, the term "shutdown characteristics" means that when a battery is overheated and its temperature is high, the polymer resin melts and closes the pores of the porous substrate, thereby blocking the movement of ions. From this point of view, the melting point of the polymer resin or the thermoplastic resin may be 200 ℃ or less.

The thermoplastic resin, for example, may include one selected from the group consisting of polyethylene, polypropylene, polypentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof. It may preferably include at least one of polyethylene and polypropylene, and more preferably may include polyethylene.

The polyethylene is ultra high molecular weight polyethylene (UHMWPE, Mw: 1,000,000 ~ 7,000,000 g / mol), high molecular weight polyethylene (HMWPE, Mw: 100,000 ~ 1,000,000 g / mol), high density polyethylene (HDPE, Mw: 100,000 ~ 1,000,000 g / mol), It may be one selected from the group consisting of low-density polyethylene (LDPE, Mw: 10,000-100,000 g/mol), homogeneous linear and linear low-density polyethylene (LLDPE), and combinations of two or more thereof.

For example, the polyethylene may be high-density polyethylene having a weight average molecular weight (M _w ) of 250,000 to 450,000. If the weight average molecular weight of the polyethylene is greater than 450,000, the viscosity may increase and processability may be deteriorated. If the weight average molecular weight of the polyethylene is less than 250,000, the viscosity is excessively low, resulting in extremely low dispersibility with pore formers and antioxidants used in manufacturing a porous substrate. In some cases, phase separation or layer separation may occur.

The porous substrate is subjected to a hydrophilization treatment to sufficiently secure wettability of the slurry when coating the slurry to form the heat-resistant layer, thereby improving bonding strength between the porous substrate and the heat-resistant layer. The contact angle for water (H ₂ O) of the hydrophilized porous substrate may be 15˚ or less, and the absolute value of the zeta potential measured as a negative value (-) on the surface of the porous substrate is 10 mV or more, preferably , 15 mV or more, more preferably, may be 20 mV or more.

Since the hydrophilized support has a hydrophilic functional group, for example, -SO ₃ group generated on its surface and the surface of the internal pores, it has a high affinity with the essentially hydrophilic slurry. It can be easily combined with the heat-resistant layer, and its bonding strength can be strengthened, so that the durability of the separator can be remarkably improved. Conductivity and heat resistance can be improved.

The separation membrane may include a heat-resistant layer including a plurality of inorganic particles located on at least one surface of the porous substrate and bound by a binder. The heat-resistant layer may also include a plurality of pores through which fluid is permeable.

The content of the inorganic particles in the heat-resistant layer may be 60 to 99% by weight. If the content of the inorganic particles is less than 60% by weight, the required level of heat resistance cannot be imparted, and if it exceeds 99% by weight, the breathability, ion conductivity, and resistance characteristics of the separator may be reduced, and the dispersibility of the inorganic particles may be reduced or slurry Workability and processability may deteriorate during coating.

The average particle diameter of the inorganic particles may be greater than the average size of pores included in the porous substrate. If the average particle diameter of the inorganic particles is less than or equal to the average size of the pores included in the porous substrate, the inorganic particles penetrate into the pores of the porous substrate to close the pores, thereby significantly reducing air permeability and ionic conductivity of the separator. . The average particle diameter of the inorganic particles may be 100 to 1,000 nm, preferably 200 to 800 nm, more preferably 400 to 800 nm, but is not limited thereto.

The heat resistance layer may have a thickness of 0.1 μm to 5 μm. If the thickness of the heat-resistant layer is less than 0.1 μm, heat resistance of a required level cannot be imparted, and if the thickness exceeds 5 μm, the separation membrane becomes thick, which may hinder miniaturization and integration of electrochemical devices.

The inorganic particles may be, for example, SiO ₂ , AlOOH, Mg(OH) ₂ , Al(OH) ₃ , TiO ₂ , BaTiO ₃ , Li ₂ O, LiF, LiOH, Li ₃ N, BaO, Na ₂ O, Li ₂ CO ₃ , CaCO ₃ , LiAlO ₂ , Al ₂ O ₃ , SiO, SnO, SnO ₂ , PbO ₂ , ZnO, P ₂ O ₅ , CuO, MoO, V ₂ O ₅ , B ₂ O ₃ , Si ₃ N ₄ , CeO ₂ , Mn ₃ O ₄ , Sn ₂ P ₂ O ₇ , Sn ₂ B ₂ O ₅ , Sn ₂ BPO ₆ , and may be one selected from the group consisting of combinations of two or more of these, but is not limited thereto.

The separation membrane may include an adhesive layer including a plurality of organic particles located on a surface of the heat-resistant layer and bound by a binder, and the number of organic particles per unit area of the adhesive layer may be 100,000,000 to 150,000,000/mm ² . there is. The heat-resistant layer may also include a plurality of pores through which fluid is permeable.

As used herein, the term "organic particle" may refer to microparticles containing a high molecular material, preferably, a fluorine-based polymer. The fluorine-based polymer may be a homopolymer containing a vinylidene fluoride (VDF) unit, a copolymer, or a mixture thereof. For example, the fluorine-based polymer may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-trichloroethylene (PVDF-TCE), etc. , but is not limited thereto.

The organic particles including the fluorine-based polymer may be bound to each other by the binder to form a predetermined electric conduction path, and this electric conduction path may restore resistance characteristics of the separator deteriorated by the heat-resistant layer. For example, when the resistances of the porous substrate, the base membrane, and the separator are Ra, Rb, and Rs, respectively, a relationship of Ra < Rb and Rs < Rb may be satisfied.

The content of the organic particles in the adhesive layer may be 50 to 99% by weight. If the content of the organic particles is less than 50% by weight, the required level of adhesion cannot be imparted, and if it exceeds 99% by weight, air permeability and ionic conductivity of the separator may be reduced, and the dispersibility of the organic particles may be reduced or when slurry coating Workability and workability may deteriorate.

An average particle diameter of the organic particles may be smaller than an average particle diameter of the inorganic particles included in the heat-resistant layer. When the average particle diameter of the organic particles is greater than or equal to the average particle diameter of the inorganic particles, the average pore size of the adhesive layer may be larger than the average particle diameter of the inorganic particles. In this case, as the heat-resistant layer is continuously exposed to the electrolyte solution in the battery, Since the inorganic particles are partially and continuously desorbed from the porous substrate, the heat resistance of the separator may gradually decrease.

An average particle diameter of the organic particles may be 50 to 300 nm. If the average particle diameter of the organic particles is less than 50 nm, air permeability and ionic conductivity of the separator may be reduced, and if it is more than 300 nm, the surface area of the adhesive layer may be reduced to decrease adhesiveness and resistance characteristics, and the inorganic particles included in the heat-resistant layer may be reduced. Particles cannot be effectively prevented from being exposed to the electrolyte solution.

The adhesive layer may have a thickness of 0.5 to 1.5 μm. When the thickness of the adhesive layer is less than 0.5 μm, adhesiveness may be deteriorated, and exposure of the inorganic particles included in the heat-resistant layer to the electrolyte cannot be effectively prevented. Conversely, if the thickness of the adhesive layer exceeds 1.5 μm, air permeability, ionic conductivity, and resistance characteristics may be deteriorated, and the separator may be thick, which may hinder miniaturization and integration of the electrochemical device.

If necessary, in order to enhance heat resistance of the separator, the adhesive layer may further include inorganic particles such as the heat resistance layer. The weight ratio of the organic particles and the inorganic particles may be 1:50 to 80, respectively. If the content of the inorganic particles is excessively low, a required level of heat resistance cannot be imparted, and if the content is excessively high, the dispersibility of the inorganic particles may deteriorate or workability and processability may deteriorate during slurry coating.

The binder refers to a material that binds the inorganic particles to each other in the heat-resistant layer and binds the organic particles to each other in the adhesive layer. The binder may be independently included in each composition for forming the heat resistant layer and the adhesive layer, and each binder included in the heat resistant layer and the adhesive layer may be the same or different.

The binder, for example, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate Propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, hydroxyethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, It may be one selected from the group consisting of acrylonitrile-acrylic acid copolymer, ethylene-acrylic acid copolymer, styrene-butadiene copolymer, alkyl acrylate-acrylonitrile copolymer, polyethylene glycol, acrylic rubber, and a combination of two or more thereof. , but is not limited thereto.

Preferably, in consideration of dispersibility in the water-based coating composition and affinity for inorganic particles or organic particles, the binder included in the heat-resistant layer may be an acrylonitrile-based copolymer and included in the adhesive layer. The binder may be polyvinyl alcohol, but is not limited thereto.

A ratio of the thickness of the adhesive layer to the thickness of the heat-resistant layer may be 0.15 to 0.5. If the ratio of the thickness of the adhesive layer to the thickness of the heat-resistant layer is out of the above range, it is difficult to achieve a well-balanced heat resistance, adhesiveness, air permeability, ionic conductivity, and resistance characteristics of the separator. Specifically, when the ratio of the thickness of the adhesive layer to the thickness of the heat-resistant layer is less than 0.15, air permeability and resistance characteristics may be improved, but heat resistance and adhesiveness may be deteriorated. On the other hand, when the thickness ratio exceeds 0.5, air permeability and resistance characteristics may be reduced, and heat resistance and adhesiveness may be improved.

In general, when the thickness and/or areal density (weight/unit area) of the heat-resistant layer and/or the adhesive layer coated on the surface of the porous substrate is increased, heat resistance and adhesiveness are improved, while air permeability and resistance properties tend to deteriorate. there is. That is, "heat resistance and adhesiveness" and "air permeability and resistance characteristics" are in a so-called trade-off relationship that are difficult to coexist with each other.

In contrast, the separator according to the present invention specifies the areal density of the organic particles included in the adhesive layer based on the number (number) observable through a microscope, rather than the weight of the organic particles as in the prior art, so that heat resistance, adhesiveness, It can realize breathability and conductivity in a balanced way. Specifically, the separation membrane specifies the area density of the organic particles included in the adhesive layer based on the number (number) observable through a microscope, so that the trade- The trade-off can be significantly mitigated. The number of organic particles per unit area of the adhesive layer may be 100,000,000 to 150,000,000/mm ² . If the number of organic particles per unit area of the adhesive layer is less than 100,000,000 / mm ² , the heat resistance and adhesiveness of the separator may be deteriorated, and if it exceeds 150,000,000 / mm ² , air permeability, ionic conductivity and resistance characteristics of the separator may be deteriorated. .

The separation membrane may satisfy at least one of the following conditions (i) to (vi), preferably all of the conditions (i) to (vi). (i) air permeability 190-350 seconds/100ml; (ii) Rs ≤ 100 mΩ (Rs is the resistance of the separator); (iii) 1.0% or less in longitudinal heat shrinkage at 150°C; (iv) 1.0% or less of transverse heat shrinkage at 150°C; (v) 0 mΩ < Rs - Ra ≤ 20 mΩ, where Ra is the resistance of the porous substrate; (vi) 0 mΩ < Rb - Rs ≤ 10 mΩ (Rb is the resistance of the base film).

Hereinafter, embodiments of the present invention will be described in detail.

Example 1

Solids containing 93% by weight of boehmite (AlOOH) having an average particle diameter of 500 nm and 7% by weight of an acrylonitrile copolymer and distilled water were mixed in a weight ratio of 23:77, respectively, and uniformly dispersed to prepare a first coating slurry. .

A solid content containing 95% by weight of a PVdF-HFP copolymer (containing 5% by weight of HPF) and 5% by weight of polyvinyl alcohol with an average particle diameter of 150 nm and distilled water were mixed in a weight ratio of 5:95, respectively, and uniformly dispersed in the second A coating slurry was prepared.

The first coating slurry was roll-to-roll coated to a thickness of 3 μm on one side of a polyethylene porous substrate (air permeability: 110 seconds/100 ml) with a thickness of 9 μm, and then dried to form a base film including a heat-resistant layer. got

The second coating slurry was roll-to-roll coated on the heat-resistant layer to a thickness of 0.5 μm, and then dried to obtain a separator sequentially including a porous substrate/heat-resistant layer/adhesive layer.

Example 2

Except for roll-to-roll coating the second coating slurry on the heat-resistant layer to a thickness of 0.7 μm, a separator comprising a porous substrate/heat-resistant layer/adhesive layer in sequence was prepared in the same manner as in Example 1. got it

Example 3

Except for roll-to-roll coating the second coating slurry on the heat-resistant layer to a thickness of 0.8 μm, a separator comprising a porous substrate/heat-resistant layer/adhesive layer in sequence was prepared in the same manner as in Example 1. got it

Example 4

Except for roll-to-roll coating the second coating slurry on the heat-resistant layer to a thickness of 1.0 μm, a separator comprising a porous substrate/heat-resistant layer/adhesive layer in sequence was prepared in the same manner as in Example 1. got it

Example 5

Except for roll-to-roll coating the second coating slurry on the heat-resistant layer to a thickness of 1.1 μm, a separator comprising a porous substrate/heat-resistant layer/adhesive layer in sequence was prepared in the same manner as in Example 1. got it

Example 6

Except for roll-to-roll coating the second coating slurry on the heat-resistant layer to a thickness of 1.3 μm, a separator comprising a porous substrate/heat-resistant layer/adhesive layer in sequence was prepared in the same manner as in Example 1. got it

Example 7

Except for roll-to-roll coating the second coating slurry on the heat-resistant layer to a thickness of 1.4 μm, a separator comprising a porous substrate/heat-resistant layer/adhesive layer in sequence was prepared in the same manner as in Example 1. got it

Example 8

Except for roll-to-roll coating the second coating slurry on the heat-resistant layer to a thickness of 1.5 μm, a separator comprising a porous substrate/heat-resistant layer/adhesive layer in sequence was prepared in the same manner as in Example 1. got it

Comparative Example 1

Except for roll-to-roll coating the second coating slurry on the heat-resistant layer to a thickness of 0.4 μm, a separator comprising a porous substrate/heat-resistant layer/adhesive layer in sequence was prepared in the same manner as in Example 1. got it

Comparative Example 2

Except for roll-to-roll coating the second coating slurry on the heat-resistant layer to a thickness of 1.6 μm, a separator comprising a porous substrate/heat-resistant layer/adhesive layer in sequence was prepared in the same manner as in Example 1. got it

Comparative Example 3

A solid content containing 95 wt% of a PVdF-HFP copolymer (containing 5 wt% of HPF) and 5 wt% of polyvinyl alcohol with an average particle diameter of 400 nm and distilled water were mixed at a weight ratio of 5:95, respectively, and uniformly dispersed in the second Except that the coating slurry was prepared and used to form the adhesive layer, a separator sequentially including a porous substrate/heat-resistant layer/adhesive layer was obtained in the same manner as in Example 1 above.

Experimental example

Test methods for each of the physical properties measured in the present invention are as follows. If there is no separate mention about the temperature, it was measured at room temperature (25 ℃).

The plane and cross section of the separator prepared according to the above Examples and Comparative Examples were photographed by SEM and shown in FIGS. 1 and 2, respectively, and the physical properties of the separator prepared according to the Examples and Comparative Examples were measured and the results are presented Tables 1 to 3 show.

-Thickness (㎛): A fine thickness meter was used.

-Number of PVdF-HFP copolymer particles (pcs/mm ² ): The number of PVdF-HFP copolymer particles included in a 1 μm ² area according to the method shown in FIG. 3 in the SEM image of the plane of the separator as shown in FIG. 1 The unit area was converted into mm ² by multiplying the measured value by 10 ⁶ .

-Air permeability (Gurley, sec/100ml): Using Asahi Seiko's Gurley Densometer EGO2-5 model, the time for 100ml of air to pass through a membrane specimen having a diameter of 29.8mm was measured at a measuring pressure of 0.025MPa.

-Electrode adhesion (gf/25mm): After bonding the adhesive layer of the separator (MD direction 180mm*TD direction 25mm) so that the electrode faces each other, insert it into an aluminum pouch and press the aluminum pouch under conditions of 80℃ and 5MPa to separate the separator and electrode was compressed. Thereafter, the adhesive force was measured while removing the separator from the electrode using Shimadzu's UTM.

-Heat shrinkage rate (%): After leaving a separator specimen with a size of 200 × 200 mm between A4 papers for 1 hour in an oven at 150 ° C, it is cooled to room temperature and the width (TD) and longitudinal direction (MD) of the specimen are The shrinkage length was measured and the heat shrinkage rate was calculated using the following formula.

(In the above formula, l ₃ is the length in the transverse or longitudinal direction of the specimen before shrinkage, and l ₄ is the length in the transverse or longitudinal direction of the specimen after contraction.)

Properties unit porous substrate basement membrane ventilation sec/100ml 153.6 181.1 resistance mΩ 83.6 99.5 MD heat shrinkage rate % 20 5 TD heat shrinkage rate % 20 5

Properties unit Example 1 Example 2 Example 3 Example 4 number of organic particles pcs/mm ² 100,000,000 110,500,000 110,700,000 120,900,000 ventilation sec/100ml 190.7 205.1 208.8 215.4 adhesion gf/25mm 14.9 21.7 25.8 30.1 resistance mΩ 90.7 91.8 92.1 93.1 MD heat shrinkage rate % One 0.9 0.7 0.5 TD heat shrinkage rate % 0.8 0.8 0.6 0.5

Properties unit Example 5 Example 6 Example 7 Example 8 number of organic particles pcs/mm ² 130,500,000 140,200,000 140,500,000 140,800,000 ventilation sec/100ml 240.6 276.8 299.4 332.1 adhesion gf/25mm 32.2 32.9 33.5 34.1 resistance mΩ 94.6 96.2 97.5 99.2 MD heat shrinkage rate % 0.4 0.5 0.5 0.5 TD heat shrinkage rate % 0.5 0.5 0.4 0.4

Properties unit Comparative Example 1 Comparative Example 2 Comparative Example 3 number of organic particles pcs/mm ² 90,000,000 160,000,000 50,000,000 ventilation sec/100ml 188.2 390.7 185.4 adhesion gf/25mm 13.8 35.2 9.5 resistance mΩ 90.4 103.9 87.6 MD heat shrinkage rate % 3.1 0.5 4.3 TD heat shrinkage rate % 3.2 0.5 4.8

The above description of the present invention is for illustrative purposes, and those skilled in the art can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims (10)

a base film comprising a porous substrate and a heat-resistant layer including a plurality of inorganic particles located on at least one surface of the porous substrate and bound by a binder; and
In the separation membrane comprising an adhesive layer including a plurality of organic particles located on the surface of the heat-resistant layer and bound by a binder to form an electrical conduction path,
The ratio of the thickness of the adhesive layer to the thickness of the heat-resistant layer is 0.15 to 0.5,
A separator that satisfies the condition of Rs < Rb (Rb is the resistance of the base film and Rs is the resistance of the separator). According to claim 1,
The porous substrate includes one selected from the group consisting of polyethylene, polypropylene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more of them. According to claim 1,
The content of the inorganic particles in the heat-resistant layer is 60 to 99% by weight, the separator. According to claim 1,
The content of the organic particles in the adhesive layer is 50 to 99% by weight, the separator. According to claim 1,
The thickness of the heat-resistant layer is 0.1 to 5 μm,
The thickness of the adhesive layer is 0.5 ~ 1.5㎛, the separator. According to claim 5,
The number of organic particles per unit area of the adhesive layer is 100,000,000 to 150,000,000 / mm ² , Separator. According to claim 1,
The average particle diameter of the organic particles is 50 ~ 300nm, the separator. According to claim 1,
Wherein the organic particles include a fluorine-based polymer. According to claim 1,
A separator that satisfies at least one of the following conditions (i) to (vi):
(i) air permeability 190-350 seconds/100ml;
(ii) Rs ≤ 100 mΩ (Rs is the resistance of the separator);
(iii) 1.0% or less in longitudinal heat shrinkage at 150°C;
(iv) 1.0% or less of transverse heat shrinkage at 150°C;
(v) 0 mΩ < Rs - Ra ≤ 20 mΩ, where Ra is the resistance of the porous substrate;
(vi) Rb - Rs ≤ 10 mΩ (Rb is the resistance of the base film). An electrochemical device comprising the separator according to any one of claims 1 to 9.

Images